Heat of Decomposition of Hydrogen Peroxide Essay

Heat of Decomposition of Hydrogen Peroxide Essay.

Abstract

Our main purpose is to familiarise ourselves with a method to find the heat of decomposition of a compound (hydrogen peroxide). Firstly, we will be looking at information about calorimeter and what it meant by heat of decomposition. Also, we will try to understand why we have to subtract the heat absorbed by the calorimeter to find the heat of decomposition of hydrogen peroxide. Therefore, we found the heat capacity of calorimeter. After that, the enthalpy of decomposition of hydrogen peroxide was calculated by finding the amount of heat lost by solution and the heat absorbed by the calorimeter.

Then, the heat absorbed by the calorimeter was subtracted from the heat lost by the solution to determine the amount of heat absorbed by hydrogen peroxide. The enthalpy of decomposition of hydrogen peroxide obtained is -57.9kJ/mol. Finally, we would look at how the results differ from the literature value and understand reasons to why the difference in the values occurs and find methods to prevent this.

Introduction

* Calorimeter

1A calorimeter is a device that helps to measure the heat of reaction. There are two types of calorimeters which are usually used. The sophisticated and expensive one, while the other can be easily made and available cheap. The one used for this experiment is the simple and cheap one which is basically a Styrofoam cup because its container walls are well insulated to prevent or reduce the heat change to environment.

2However, the calorimeter would also absorb heat as it is a simple calorimeter and thus it is a necessity to take it into the consideration while doing the calculations to find the heat of decomposition of hydrogen peroxide. Also, the reactants are inside the calorimeter with a lid on top before the reaction has been initiated to prevent heat from escaping or it would cause the results to turn inaccurate. Besides this, a thermometer will be placed inside to constantly monitor the temperature as time progresses. It assists in finding the temperature difference before and after the reaction has completed.

* Heat of decomposition

Heat of decomposition is defined as the breaking down of a single compound (Hydrogen peroxide) into 2 simpler compounds or elements upon the application of heat. Enthalpy of decomposition is thus defined as the amount of heat required to chemically break down a compound. In this experiment we will be trying to find the heat of decomposition of hydrogen peroxide. 4Hydrogen peroxide is an unstable compound. Under normal room conditions, it would break down to water and oxygen. However, the process is very slow to be completed in a normal laboratory period. As a solution, catalyst [Iron (III) nitrate] was introduced. It helps to speed up the process without being consumed itself.

Procedure

There are basically 2 parts to this experiment, thus 2 procedures.

* Heat capacity of calorimeter (Part 1)

A simple calorimeter was firstly made using a thermometer, Styrofoam cup and cover. 30ml of tap water next was poured into the simple calorimeter cup and covered back with the cover and the thermometer. It was left at the room temperature for about 5-10 minutes before recording the temperature to the nearest 0.5oC.

Another 30ml of water was poured into a 250ml beaker and heated using a hot plate until the temperature was about 20oC more than the room temperature which would means about 44-50 oC. Then, the heated water was allowed to stand for 1 minute and its temperature was recorded immediately to the nearest 0.5oC and poured completely into the calorimeter. The cover was covered over it with the thermometer along. The cup was next swirled once. The temperature was observed for 3 minutes and was recorded every 15 seconds.

* Enthalpy of decomposition of hydrogen peroxide solution (Part 2) After the first part of the experiment was completed, the calorimeter and the thermometer were dried completely. 50ml of 1.0M hydrogen peroxide (H2O2) was then cautiously measured and poured into the calorimeter. The cover was then replaced along with the thermometer. The solution was swirled once and temperature was recorded every single minute for 4 minutes. At the 5-minute mark, the cover and the thermometer were removed. 10ml of 0.50M Iron (III) nitrate [Fe(NO3)3] was measured and added into the calorimeter containing the hydrogen peroxide.

Temperature was next measured at 5.5 minute mark and for every succeeding minute till a total of 20 minutes. A temperature vs. time curve was then constructed with the data obtained from the experiment to determine change in temperature. Next, enthalpy of the decomposition of hydrogen peroxide was calculated. A starting temperature can be found by extrapolating the 5 points prior to adding the catalyst to the point of mixing. The final temperature can also be found by extrapolating the linear portion of the graph to the point of mixing.

* Discussion

As the literature value stated in the data sheet, the heat of decomposition of the hydrogen peroxide is -94.6kJ/mol. However the value obtained was only -57.9kJ/mol. This was because the heat has been lost to the surroundings around outside the calorimeter. The calorimeter is not perfect and simple and thus its cover is not proper and does not fully cover the top of the Styrofoam cup, leaving a small opening. The heat could have escaped from the calorimeter through here. Besides this, the experiment was done for a long period of 20 minutes. The longer the period, there is more time for the heat to escape from the imperfect calorimeter. This leads to a lower temperature than expected to be recorded as time progresses. This leads to lower temperature difference leading to a lower heat of decomposition of hydrogen peroxide to be obtained from the reaction.

Another possibility of losing heat occurred during the addition of the Iron (III) nitrate as catalyst inside. Once it was added, the reaction was increased rapidly producing a lot of heat. However, the lid was not covered on time and was slow which led to a significant amount of heat to be lost to the surroundings. Also, the temperature shown was not accurate due to the poor calibration of the thermometer. Often estimation to the nearest 0.1oC has to be done when recording the results. Due to the usage of an imperfect calorimeter, the results obtained were inaccurate. Thus we can improve this experiment by using a perfect calorimeter which will help to reduce heat from escaping from the calorimeter drastically and also reduce the heat from being absorbed by the calorimeter itself. 3One perfect example would be the usage of the adiabatic calorimeter.

The calorimeter’s vessel is basically surrounded by a jacket containing water. Therefore, the temperature of which will automatically be same as the temperature inside the vessel. Since the temperature of the reacting system and the surroundings is the same, there is no heat passed in either direction. This would lead to much more accurate results. Besides this, we can also try to reduce the time taken to 15 minutes. I would recommend this because the longer the time taken for the experiment, the higher the possibilities for the calorimeter to lose heat to the surroundings. Hence, by reducing the time, the possibilities of losing heat is minimised. Apart from this, we can also use a thermometer with a finer calibration to note the slightest difference in the temperature which could lead to the significant changes in the results obtained.

Conclusion

From the results obtained, I can conclude that the usage of the simple calorimeter is not an ideal choice due to possibilities of losing heat to the surroundings. A sophisticated and better calorimeter has to be used. 5Styrofoam cup calorimeter isn’t recommended for this decomposition reaction as it involves production of a gas, Oxygen which can escape from the cup easily.

Besides this, we were better familiarised with a method to find the heat of decomposition of compounds with the use of calorimeter. It can also be concluded that hydrogen peroxide is not a stable compound and breaks down slowly in room temperature and pressure and can be speed up by the usage of catalyst. In overall, the values obtained from the experiment are not useful because of the severe errors which occurred during the experiment mainly due to the apparatus used.

References
1CaCT, Calorimetry: Measuring heats of reaction. http://www.science.uwaterloo.ca/~cchieh/cact/c120/calorimetry.html [Accessed 19 July 2012] 2Solomon, S., Rutkowsky, S and Boritz, C (2009) Everyday investigations for General Chemistry John Wiley & Sons 4Cool sciences. Heat of decomposition of hydrogen peroxide. http://www.coolscience.org/CoolScience/KidScientists/h2o2.htm [Accessed 22 July 2012] 5About Chemistry. Measurement of Heat flow and Enthalpy Change; Calorimetry – Coffee Cup Calorimetry and Bomb Calorimetry. http://chemistry.about.com/od/thermodynamics/a/coffee-cup-bomb-calorimetry.htm [Accessed 25 July 2012] 3Silcocks, C.G. Physical Chemistry: Thermochemistry and thermodynamics,3rd Ed,: Macdonald & Evans Ltd, 1982.

Heat of Decomposition of Hydrogen Peroxide Essay

Discussion of Joel Essay

Discussion of Joel Essay.

1.The mechanisms of heat loss contributing to Joel’s feelings of coldness are conduction, due to the loss of his hat somewhere on the trail and also his wet clothes; convention, which is happening because of the cold wind blowing; and lastly evaporation which is occurring as he breathes in the cold air and exhales it as warm moist air. 2.To help Joel maintain a normal body temperature, his body will begin to send signals to conserve and generate heat. This can be done through vasoconstriction which keeps sweat glands inactive and conserves heat, and also by shivering which generate heat through muscle contractions.

3.Thermoregulation, a homeostatic process, is responsible for initiating and controlling the physiological responses helping to keep Joel warm. His body temperature is being monitored by his hypothalamus which has triggered his sympathetic vasomotor center to initiate vasoconstriction of the dermal blood vessels in his extremities. The nervous system is also alerted by the hypothalamus to induce muscle contraction in order to generate internal heat and keep his core near normal temperatures.

4.Joel feels little blood flowing to his hands and feet due to the vasoconstriction occurring. During this process the blood going to his extremities is being rerouting away from the dermal surface to a network of deep veins wrapped around deep arteries. When this occurs diffusion known as countercurrent exchange begins which traps heat closer to the body core and limits heat loss to the environment by reducing the temperature gradient between the arterial blood and the cold whether Joel is in.

5.Joel’s body was more than likely in the beginning stages of the hypothermia. His body began shivering strongly to generate more heat to try to maintain normal temperatures. The vigorous shivering will increase the rate of heat generated and warm the deep vessels by as much as 400 percent. It was caused by stimulation of his thyroid which leads to the release of epinephrine, a hormone that stimulates muscles metabolism and can increase the force of contractions.

6.Had Joel not been rescued he would have been at rise of developing frostbite and hypothermia. Joel was now wearing wet clothes after stumbling into that waist deep creek and his lower body must have been feeling the effects of the cold wind blowing into him, causing numbness and inhibiting his ability to walk, signs of frostbite. His body temperature would have continued to drop below normal and his body would find it harder and harder to maintain homeostasis through thermoregulation alone. His incoherency, violent shivering, and confusion indicate the onset of hypothermia.

Discussion of Joel Essay

Types of Thermometers Essay

Types of Thermometers Essay.

Thermometers

A thermometer is a device or instrument used for measuring temperature. There are many different types of thermometers; however each one is based on a physical property of a thermometric (temperature measuring) substance that differs in a measurable way with temperature. Some of the physical properties that vary with temperature are volume, resistance and color. A physical property that increases or decreases with temperature can be used to measure temperature. This is called a thermometric property.

Liquid-In-Glass Thermometers

There are two types of liquid-in-glass thermometers: 1) Mercury-In-Glass Thermometers 2) Alcohol-In-Glass Thermometers.

A liquid in glass thermometer uses mercury or alcohol as its thermometric substance. Its thermometric property is volume and it is used to measure the temperature by allowing the mercury or alcohol to expand or contract in the capillary tube as temperature rises or decreases. I.e. an increase in temperature equals an increase in volume while a decrease in temperature equals a decrease in volume. A mercury-in-glass thermometer has a range of -39oC to 360oC while an alcohol-in-glass thermometer has a range of -112o C to 78o C.

Noah Borel

Here are some advantages and disadvantages of mercury-in-glass thermometers:

Advantages| Disadvantages|

* It doesn’t cling to the sides of the tube.| * It’s expensive.| * It expands uniformly.| * Its freezing point is high at -39oC| * It has a visible surface that makes it easily seen in fine capillary tubes.| * It’s poisonous.| * It is a good conductor of heat, which makes it reach the exact temperature faster.| * It cannot expand a great deal.| * Its boiling point is high at 375o C.| |

Here are some advantages and disadvantages of alcohol-in-glass thermometers:

Advantages| Disadvantages|

* Its expansion is uniform.| * It sticks to the tube.| * It can expand a great deal.| * It reaction to changes in temperature is slow.| * It’s cheap.| * It needs to be dyed as it is transparent.| * It’s a safe liquid.| * It’s boiling point is low at 78oC| * Its freezing point is low at -115oC.| |

Liquid-in-glass thermometers can be used as laboratory thermometers for use in schools and labs and as clinical thermometers for use in the measuring of body temperature.

Noah Borel

Thermocouple Thermometers

A thermocouple thermometer consists of two wires made of different metals such as iron and copper. As shown above, the ends of the wires are joined together to form two junctions. These two different metals, maintained at different temperatures, cause a net voltage (e.m.f.) to be generated across the junctions. This voltage generated (once not large) is directly proportional to the difference in temperature between the junctions and so, when measured, can be used to find out an unknown temperature. The most commonly used pair of metals is platinum (Pt) and Rhodium (Rh), which is an alloy of platinum. The voltage is measured with a galvanometer for less accurate readings or a potentiometer for very accurate readings. Due to the junction being made of metal thermocouples can be used to measure high temperatures.

Noah Borel

Its thermometric substances are two different metals and its thermometric property is electrical conductivity. Its range is -183oC to 1127oC.

Some advantages of thermocouple thermometers are:

* The wire junctions may be very small therefore it’ll need little heat to warm up and respond quickly to temperature changes. * The output of this thermometer is an electrical signal that can be used to operate equipment capable of giving warnings of sudden temperature changes or of keeping records of temperature. * By choosing particular pairs of metals A and B, temperatures up to about 1500oC can be measured.

A disadvantage of thermocouple thermometers is:

* It is less accurate than constant gas and platinum resistance thermometers.

Constant Gas Thermometers

Noah Borel

In a constant gas thermometer the bulb contains a fixed amount of hydrogen, helium or nitrogen gas. When the temperature of the gas increases the pressure of it increases as well. A larger height h difference is needed to keep the gas at its fixed volume. The pressure of the gas is equal to ρgh plus atmospheric pressure. Its thermometric substance is the gas and its thermometric property is the pressure on a fixed mass. Its range is -270oC to 1477oC.

Advantages of a constant gas thermometer are:
* It has a wide range.
* It is accurate and sensitive.
* It is used as a standard

Disadvantage of a constant gas thermometer are:
* The reading taken does not come directly from the thermometric substance.
* Its response is slow.
* It is fragile.

Platinum Resistance Thermometers

Noah Borel

A platinum resistance thermometer works by having a platinum coil that has an increase in resistance as the temperatures raises and a decrease in resistance as the temperature decreases. The resistance of the coil is measured accurately with a circuit that makes use of balanced PDs. The platinum resistance thermometer’s thermometric substance is platinum and is thermometric property is resistance. Its range is from -248oC to 1477oC.

Types of Thermometers Essay

Density Lab Write Up Essay

Density Lab Write Up Essay.

Abstract

The purpose of this experiment was to identify whether density is an extensive or intensive physical property. By using water displacement, the volumes of the paper clip samples were measured and the masses were obtained by using an electronic balance. Each mass and volume was unique to their sample so by using their values, density was used to identify substances in the lab. After conducting the experiment, the results showed that there was a positive slope between the different paper clip samples’ masses and their volumes.

It was concluded from this pattern that density is an extensive property.

Introduction

In science, there are two physical properties that are used to classify certain substances; extensive and intensive. Extensive physical properties are properties whose values vary directly with mass. (“Thermodynamic Properties” 2012) Therefore, they rely on the sample’s mass.

Intensive physical properties are properties that are independent of the amount of mass. (“Thermodynamic Properties” 2012) Therefore, they do not depend on the sample’s mass. One physical property that was investigated during an experiment was density.

Density is a physical property of matter that can be measured by dividing the matter’s mass by its volume. The purpose of the experiment was to answer the following question: Is density an extensive or intensive physical property? To answer this question, the densities of paper clip samples were calculated using their masses and measured volumes obtained from a water displacement technique. If the experiment showed that the sizes of the samples affected the calculated densities, then density would be an extensive property since it would be relying on the samples’ masses.

Hypothesis

If density is an extensive property, then the masses of the different number of paper clips will affect the calculated densities because density depends on the mass of the paper clip samples.

Materials and Methods

During the experiment, an electronic balance, graduated cylinder, paper clips and weighing paper were used. The mass of five paper clips was measured with the electronic balance and was recorded. 30.0 mL of water were poured into a graduated cylinder and were recorded as the starting water volume. The paper clips were then placed into the graduated cylinder and the ending water volume was recorded. To calculate the volume of this sample, the starting water volume was subtracted from the ending water volume. The density of the five paper clips was finally calculated using the formula, d= massvolume. This procedure was repeated for each paper clip sample.

The mass of five paper clips is 4.9 grams, the mass of 9 paper clips is 8.9 grams and the mass of 13 paper clips is 12 grams. Each paper clip sample started out with the same water volume; 30 milliliters. After using water displacement to measure the volume of each sample, the results were that the volume of 5 paper clips is 1.0 milliliters, the volume of 9 paper clips is 1.5 milliliters and the volume of 13 paper clips is 2.0 milliliters. Using this data, the calculated densities were 4.9 g/mL for 5 paper clips, 5.9 g/mL for 9 paper clips and 6.0 g/mL for 13 paper clips.

Discussion

Density is a physical property that can be used to identify substances in a lab. The formula for calculating density involves finding out the mass of a substance as well as the volume. The results of the experiment showed that each paper clip sample started out with the same volume of water; however their different masses led to different volumes when the water displacement technique was used to measure them. Therefore, each paper clip sample had a unique density. This showed that densities can be used to identify substances in a lab.

Water displacement is a technique used to measure the volume of substances by seeing how much water the substances displace or push aside when they are placed into a graduated cylinder. During the experiment, this technique was used to measure the volumes of the paper clip samples.

The density of pure water at room temperature is 0.9907047 g/cm³. The measured density of pure water was concluded to be 0.99 g/mL from the results of a separate experiment.

Conclusion

After the experiment was conducted, the results showed that density is an extensive physical property. The differences between the masses of the samples affected the calculated densities because although the ending volumes were different, each sample started out with the same volume of water. This was because each sample had a different mass. This was what led to the conclusion that density is an extensive physical property.

The conclusion does support the hypothesis however one source of error that may have affected the experiment’s results was the durability of the paper clips. The material they were made out of may have eroded away when water displacement was used to measure the volume of the paper clip samples. This would have affected the size of the samples. An improvement that could be made to this experiment based on this error is using a different sample. Instead of paper clips, pennies could have been used because pennies are made out of copper, which is a heavier metal than the mild steel paper clips are made out of. This would’ve eliminated the problem of mass loss during the experiment.

Density Lab Write Up Essay

Separating the Components of “Panacetin” Essay

Separating the Components of “Panacetin” Essay.

Introduction:

The purpose of this experiment is to investigate the composition of compounds in Panacetin. Generally, it is made up of sucrose, aspirin and an unknown component, either acetanilide or phenacetin. SinceBy using different techniques, such as filtration, extraction, and evaporation, those three components have been isolated out, which is based on varies solubility and acid-based properties. The percentage of composition of Panacetin are also found, which is based on the mass of three dried components.

The process:

“panacetin” + Dichloromethane Solid sucrose + aspirin + unknown component (By Filtration) Aspirin + unknown components + NaOH aqueous layer + organic layer Aqueous layer + HCl aspirin (By filtration)

Organic layer Unknown (By Evaporation)

Procedure and Observation:

0.30093 g of panacetin was weighed and mixed well with 50 ml of dichloromethane. After stirring the solution thoroughly, some solid is formed (solid sucrose) and liquid. With using a preweighed filter paper to filter the mixture, and after the sucrose had dried, it was weighed out to 0.7756g. For the aqueous layer, adding 10ml of 6M HCl(pH 2) and filtered using vacuum filtration and after cooled in the ice bath.

Leaving behind is the solid aspirin which was weighed out as 1.2469g. Lastly, to measure the weight of the unknown solid component of panacetin, putting the organic layer in a warm water bath to evaporate the solvent and the remain is the solid residue.

Extract the unknown solid component of panacetin, which was weighed to be 0.8946g. After measure the unknown component, transferring the sample into the beaker with the hot water to dissolve the sample completely and then letting it cool by putting the beaker into the ice. After that, collect the solid by vacuum filtration and the filtered product was weighed 1.1759g In order to measure the melting point, put the sample into the test tube and put the tube into the machine to heat it up. This helps to melt the sample by putting the heat energy into the system. From the result, the sample starts melt at 72°C and completely melt at 84°C.

Result:

The theatrical mass percentage: sucrose 10%, aspirin 40%, unknown 50%. The theoretical melting point of acetanilide is 90 ̊C and the theoretical melting point of phenacetin is 110 ̊C The actual mass percentage:

Sucrose mass percentage: (2.1409-1.3663) / 3.0093*100% = 25.74% Aspirin mass percentage: (1.2469/3.0093)*100% = 41.43%
Unknown mass percentage: (1.1759/3.0093)*100% = 39.07%
Actual melting point: The melting point of the sample is 84 ̊C, so it is acetanilide.

Discussion

The sum up of the actual mass of sucrose, aspirin and unknown mass sample is 3.1974g. The reason why the total mass is greater than the mass of the original mass, 3.0093g because the extra mass was gaining from the process of adding hot water to dissolve the product. It could also mean that my lab partner and I did not give sufficient time for the sample to recrystallize. There is difference melting point of acetanilide compared to its theoretical melting point. The reason is that the sample has a small melting point range. In my opinion, even though we have used mercury laboratory thermometer, since the sample has a small melting point range, in order to reduce the error made from reading the temperature, we should use more sensitive and accurate thermometer to find out the more “accurate” melting point of the sample. I would conclude that the melting point that our group found is 84 ̊C, which is close enough to the theoretical melting point.

Conclusion:

It can be concluded that in 3.0093g of Panacetin, its composition is distributed as 25.74% of surcrose, 41.4% of Aspirin and 39.07% of acetanilide. The melting point of acetanilide is 84 ̊C, which is close enough to the theatrical melting point, 90 ̊C because acetanilide has a small melting point range.

Separating the Components of “Panacetin” Essay

Pre-Lab Report Density of Liquids and Solids Essay

Pre-Lab Report Density of Liquids and Solids Essay.

Purpose of the experiment:

The purpose of this lab is to help understand how to resolve the density of liquids and solids. Also, the lab is supposed to teach us how to record lab data and how to measure volume and mass the correct way. Lastly, it’s designed to help us understand significant values and its relationship to measurements and data recording.

Lab Techniques:

One technique that will be used during this lab is comparing the accuracy (absolute & percent errors) of your calculated densities to accepted literature values.

Also, learn how to determine the precision for each of your measurements and compare results. We will find out the density of water, hexane, zinc, lead, copper and know which is the densest compared to the others.

Lab Procedures:

1. Obtain the mass of your 100-mL graduated cylinder. Make sure it is dry before you weigh it out.

2. Add 20-25 mL of distilled water to the graduated cylinder. Measure the volume of the water very carefully.

After: Measure the combined mass using an electronic balance.

3. Add another 20-25 mL of distilled water to the graduated cylinder. Measure it carefully.

4. Repeat step 3 to obtain a third set of mass and volume measurements.

5. Use a thermometer to record the temperature of the water in your graduated cylinder.

Analysis: Subtract the mass of the empty cylinder from each combined mass measurement to obtain three mass measurements of water. Take the average of these three density values and look up the TRUE density of water at the temperature used. Evaluate the accuracy of your average density by calculating your percent error.

Pre-Lab Report Density of Liquids and Solids Essay

Determination of Heat of Solution Essay

Determination of Heat of Solution Essay.

ABSTRACT

Thermodynamic values can be determined using the Vant Hoff isochore method. This method entails the use of equilibrium systems to determine the change in enthalpy of the solution, which can b related to the change in internal energy of the solution. The van’t Hoff isochore relates the equilibrium constant of a chemical reaction at one temperature to the equilibrium constant of the same reaction at a different temperature, allowing it to be worked out for all temperatures if it is known for one.

The experiment used the solution of toluene and naphthalene to determine the change in enthalpy. The mole fractions and the tempterature of recrylstallizations were graphed and the slope was determined. From the slope the change in enthalpy was determined to be 3.45J. This implies that energy is absorbed by the system.

INTRODUCTION

Solutions are very common in nature and in the chemistry lab. They provide the environment in which many chemical reactions occur. Thus, in the chemistry classroom and lab, we are immensely interested in solutions, especially liquid solutions.

Solutions are defined as homogeneous mixtures of pure substances in which no precipitation or settling occurs. We often think of solutions as liquids, but we can have solutions of solids (alloys), gases (air is a solution of nitrogen, oxygen, carbon dioxide, and a number of other gases), and a combination of states such as liquid and solid metals (amalgams) and liquids and gases (nitrogen in the blood, carbonated beverages). The ease of dissolution is dependent on two factors: (1) the change in disorder or randomness (entropy) of the system and (2) the change in the energy of the process (heat of solution). The process is generally favored when the degree of randomness increases and the energy of the system decreases (exothermic). When dissolution occur the entropy of the system increases. For example, the ions in crystals are highly ordered. Once dissolved, these same ions in solution are relatively disordered.

When a polymer is dissolved in a solvent, the heat measured is a sum of a polymer-solvent interaction term and a term related to the structure that existed in the solid polymer relative to its amorphous liquid state. This latter contribution, termed the “residual” heat, can have an endothermic contribution due to the fusion of crystalline regions and an exothermic contribution due to the disruption of structure in noncrystalline amorphous regions. Toluene, formerly known as toluol, is a clear, water-insoluble liquid with the typical smell of paint thinners. Chemically it is a mono-substituted benzene derivative, i.e. one in which a single hydrogen atom from the benzene molecule has been replaced by a univalent group, in this case CH3. It is an aromatic hydrocarbon that is widely used as an industrial feedstock and as a solvent. Like other solvents, toluene is sometimes also used as an inhalant drug for its intoxicating properties; however, this can potentially cause severe neurological harm.

Figure 1: Structure of Toluene

Naphthalene, also known as naphthalin, bicyclo[4.4.0]deca-1,3,5,7,9-pentene or antimite is a crystalline, aromatic, white, solid hydrocarbon with formula C10H8 and the structure of two fused benzene rings. It is best known as the traditional, primary ingredient of mothballs. It is volatile, forming a flammable vapor, and readily sublimes at room temperature, producing a characteristic odor that is detectable at concentrations as low as 0.08 ppm by mass.

Figure 2: Structure of Naphthalene

EXPERIMENTAL
A. Compounds tested
Naphthalene, Toluene

B. Procedures

An accurate quantity of 15 g of naphthalene was weighed and placed into a test tube. An accurately measured volume of 5mL of toluene was also added. The stopper, thermometer, and stirrer were fitted in the set-up. The test tube was warmed in a water bath until all the solute was dissolved. The solution was allowed to cool in air, and was stirred continuously until an appearance of a solid was observed. The temperature at which the solid was observed was also recorded. Warming the mixture until the entire solid was re-dissolved and allowing the solution to be cooled in air also did a second determination. Another 1mL of toluene was added and steps 3 to 5 were repeated. Another four more 1mL portions of toluene were also added. The mole fractions were determined and graphed with the temperature of recrystallization. From the graph, the slope was determined and from the value of the slope, the enthalpy change of the solution.

RESULTS AND DISCUSSIONS

The mole fraction of the naphthalene to the toluene was determined and the temperature at which is recrystallized is tabulated below:

Table 1: Mole Fraction and temperature of recrystallization

Mole fraction| Temp.|
0.45| 67|
0.41| 60|
0.37| 59|
0.34| 56|
0.31| 56|
0.29| 54|

Besides calorimetric method of analysis, using the equilibrium system may also be utilized to determine thermodynamic values. This is dependent to the enthalpy change. The mole fraction also interferes with the equilibrium system. Changes in the mole fraction will cause the equilibrium system to shift from one form to another. The process is in isochore, denoting no change in volume. The volume of the naphthalene is not diminished in the process of the experiment. The change in enthalpy is determined by determining the slope of the graph between the inverse of the emperature and the mole fraction.

Figure3: Graph of Mole fraction versus the inverse of the recrystallization temperature

From the grpah above, there is an inverse relationship between the recrystallization temperature and the mole fraction of naphthalene. As the mole fraction of the naphthalene is decreased, the inverse of the temperature of crystallization is increased. From the slope of the graph, we are able to determine the enthalpy change of the solution. Using the formula: Figure 4: Equation for enthalpy change

From the equation above the determined enthalpy change is 3.45 J. Since the enthalpy change is a positive value the transfer of energy is towards the system.

REFERENCES
[1] Rossotti and H. Rossotti, The Determination of Stability Constants, McGraw-Hill, 1961

[2] Atkins, Peter; De Paula, Julio (2006-03-10). Physical Chemistry (8th ed.). W.H. Freeman and Company. p. 212.

[3] NonLinear vant hoff solubility. http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T7W-479CM6F-3M&_user=10&_coverDate=01%2F31%2F1984&_rdoc=1&_fmt=high&_orig=search&_origin=search&_sort=d&_docanchor=&view=c&_searchStrId=1474224563&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=bc9cac9220a53d018a21b381170d2732&searchtype=a. taken September 28, 2010

[4] Vant Hoff Isochore. http://www.scenta.co.uk/tcaep/nonxml/science/equations/details/van’t%20Hoff%20isochore.htm taken September 28, 2010.

Determination of Heat of Solution Essay

Heat Transfer Essay

Heat Transfer Essay.

Heat transfer, also known as heat flow, heat exchange, or simply heat, is the transfer of thermal energy from one region of matter or a physical system to another. When an object is at a different temperature from its surroundings, heat transfer occurs so that the body and the surroundings reach the same temperature at thermal equilibrium. Such spontaneous heat transfer always occurs from a region of high temperature to another region of lower temperature, as required by the second law of thermodynamics.

In engineering, energy transfer by heat between objects is classified as occurring by heat conduction, also called diffusion, of two objects in contact; fluid convection, which is the mixing of hot and cold fluid regions; or thermal radiation, the transmission of electromagnetic radiation described by black body theory. Engineers also consider the transfer of mass of differing chemical species, either cold or hot, to achieve heat transfer.

II.THREE MODES OF HEAT TRANSFER

1.Conduction In heat transfer, conduction (or heat conduction) is the transfer of thermal energy between neighboring molecules in a substance due to a temperature gradient.

Heat transfer always goes from a region of higher temperature to a region of lower temperature, and acts to equalize the temperature differences. Conduction takes place in all forms of matter, viz. solids, liquids, gases and plasmas, but does not require any bulk motion of matter. In solids, it is due to the combination of vibrations of the molecules in a lattice or phonons with the energy transported by free electrons. In gases and liquids, conduction is due to the collisions and diffusion of the molecules during their random motion.

Steady state conduction is a form of conduction that happens when the temperature difference driving the conduction is constant, so that after an equilibration time, the spatial distribution of temperatures in the conducting object does not change any further. In steady state conduction, the amount of heat entering a section is equal to amount of heat coming out. Transient conduction occurs when the temperature within an object changes as a function of time. Analysis of transient systems is more complex and often calls for the application of approximation theories or numerical analysis by computer.

2.Convection

Convective heat transfer, or convection, is the transfer of heat from one place to another by the movement of fluids. (In physics, the term fluid means any substance that deforms under shear stress; it includes liquids, gases, plasmas, and some plastic solids.) Bulk motion of the fluid enhances the heat transfer between the solid surface and the fluid. Convection is usually the dominant form of heat transfer in liquids and gases. Although often discussed as a third method of heat transfer, convection actually describes the combined effects of conduction and fluid flow.

Free, or natural, convection occurs when the fluid motion is caused by buoyancy forces that result from density variations due to variations of temperature in the fluid. Forced convection is when the fluid is forced to flow over the surface by external means—such as fans, stirrers, and pumps—creating an artificially induced convection current. Convection is described by Newton’s law of cooling: “The rate of heat loss of a body is proportional to the difference in temperatures between the body and its surroundings.”

3.Radiation Form of heat transfer that takes place between two bodies that aren’t in physical contact. Describes a process in which energetic particles or waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing. The word radiation is commonly used in reference to ionizing radiation only (i.e., having sufficient energy to ionize an atom), but it may also refer to non-ionizing radiation (e.g., radio waves or visible light). The energy radiates (i.e., travels outward in straight lines in all directions) from its source.

This geometry naturally leads to a system of measurements and physical units that are equally applicable to all types of radiation. Both ionizing and non-ionizing radiation can be harmful to organisms and can result in changes to the natural environmentThermal radiation is the transfer of heat energy through empty space by means of electromagnetic waves. All objects with a temperature above absolute zero radiate energy. No medium is necessary for radiation to occur, for it is transferred by electromagnetic waves; radiation takes place even in, and through, a perfect vacuum. For instance, the energy from the Sun travels through the vacuum of space before warming the Earth. Radiation is the only form of heat transfer that can occur in the absence of any form of medium (i.e., through a vacuum).

Heat Transfer Essay

The disappearing cross Essay

The disappearing cross Essay.

In this experiment, we shall be adding sodium thiosulphate to hydrochloric acid together and placing a drawn cross underneath and seeing how long the rate of reaction lasts until you cannot see this cross. Before the reaction starts, the liquids are both clear. When added they turn cloudy and milky with a yellow tinge to it, due to the sulphur released. Na2S203 (aq) + 2HCL –> 2Nacl (aq) + H20 (l) + SO2 (g) + S(s) Sodium thiosulphate + hydrochloric acid –> sodium chloride + water + sulphur dioxide + Sulphur The aim of this experiment is to see how each factor affects the rate of reaction.

The factors we are concentrating on are: Concentration  Surface area/Particle size  Temperature  Catalyst Collision Theory: In order to understand rates of reactions, we use this model 1) All chemicals are made from particles (atoms/Molecules) 2) The particles have energy and can move 3) Chemical reactions only happen when particles collide 4) Some collisions are not successful. Thy must have enough energy to react Particle size.

6 surfaces therefore a slow reaction because of a smaller surface area Small chips therefore a faster reaction because of a larger surface area.

The collision theory model explains why smaller particles have a faster reaction Temperature Lower energy therefore particles move slowly so a slow reaction More energy therefore particles move faster so more collisions, so faster reaction The collision theory explains that increasing temperature makes reactions faster. Concentration Concentration measures how many moles per 1000cm3 KEY 1mole=6 x 1023 particles 1 Litre= 1dm–>1000cm3 1dm x 1dm x 1dm= 1cm3 Diluted –> ( 1 mole/litre) (1 mole/dm3) More concentrated so 2 moles/dm3–>.

So there are two times as many particles in the same place, therefore more collisions, so a faster reaction. If we double the concentration, there are twice as many particles in the same space, so therefore twice as many collisions so faster reactions. Catalysts Catalysts provide an alternative path to reaction with lower activation energy. Prediction In this experiment my prediction is that the cross will disappear faster as the temperature gets warmer. This is because as it gets warmer, the atoms vibrate more and move around quicker.

This means that when it mixed with the sodium atoms, they hit each other atoms faster and harder which in result is forcing the reaction to happen quicker. When the temperature is lowered the opposite occurs because the atoms have less energy and would hit less hard and fast so it would take a longer period of time to get the same result. My prediction of how the graph would look like is this: The graph begins to go down because at certain temperatures as the atoms get more energy and hit more making the cross seem to disappear faster.

A theory, which links into this experiment, is the collision theory. This is because the collision theory deals with atoms vibrating as they receive more energy and they then hit more often. Apparatus o 1 thermometer o 1 beaker o 2 measuring cylinders o 1 conical flask o 1 tripod o 1 gauze o 1 heatproof mat o 1 stopwatch o 1 Bunsen burner o X board o 1 pair of tongs o 1 pair of goggles Method o Measure 10ml of hydrochloric acid into conical flask o Heat over Bunsen burner until desired heat o Remove immediately and place on top of hand-drawn flask.

o Add 25ml of Sodium thiosulphate o Time to see how long the cross takes to disappear completely o Repeat 3 times o Rinse and repeat to the heat 5 i?? over the last temperature. Safety A pair of goggles will be worn during the heating part of the experiment in order to protect the eyes. When handling hot beakers and measuring cylinders a pair of tongs will be used. A gauze and heatproof mat will be used while heating to avoid any damage to the equipment. Recording o 3 times o In a table Fair Test In order for my results to be valid the experiment must be a fair one.

I will use the same judgement each time for trying to see when the X has disappeared. I will make sure that the measuring cylinders for the HCl and thiosulphate will not be mixed up. The amount of HCl will be the same each time, and the amount of thiosulphate will be fixed at 15 cm3. During the heating stage of the experiment, a blue flame will be used throughout. Also the same Bunsen burner and gas tap will be used to maintain continuity. All of these precautions will make my final results more reliable and keep anomalies at a minimum so thus make the entire investigation more successful.

The only change that will happen will be that the temperature of the Hydrochloric acid will go up 5 i?? every three times ANALYSIS Results Temp (i?? c) Time (s) 1 2(s) 3(s) Average(s) From my results I can conclude that as the temperature of the hydrochloric acid rises, the rate for reaction also gets higher. This is in line with the collision theory, which defines that as the acid get hotter, the atoms get more energy and vibrate more.

When the two liquids hit, the atoms are pushed together and because they are vibrating more they hit faster and harder therefore causing the reaction to speed up and the solution to turn a yellow colour quicker so the cross seems to disappear quicker. The graph proves that the theory works for this experiment, as it is a curved line. The sketch graph I drew in my prediction matched the real graph showing that the science I used to explain my prediction was correct. Evaluation Looking at my results I can say that they were quite reliable and accurate. I had one anomalous result even after an average over three measurements.

This was at 30i?? and I think may have been because the water we rinsed the beaker out in may have stayed in and caused the reaction to slow down. I can say that looking at my results when I repeated results they were quite close together. I think that I did the experiment quite well although I found it hard to spot where the exact moment when the cross disappeared. This is why we did an average over 3 measurements. To improve the experiment I would need to have a very accurate stopwatch to time exactly how long the cross took to dissappear so I could be really precise in my results.

Ways in which I could extend this experiment are to use a different size of cross so that it doesn’t disappear at such a low temperature this way I could carry on to see whether the collision theory is still right at higher temperatures. ?? ?? ?? ?? Chemistry Sharna Sutherland Show preview only The above preview is unformatted text This student written piece of work is one of many that can be found in our GCSE Patterns of Behaviour section.

The disappearing cross Essay

Experiment Report Essay

Experiment Report Essay.

Objective
In order to demonstrate the isentropic expansion process.

Introduction

see more:chemistry matriculation

Isentropic means no change in entropy. Entropy is a thermodynamic property that is the measure of a system’s thermal energy per unit temperature that is unavailable for doing useful work. In simple terms, the measure of the level of disorder in a closed but changing system, a system in which energy can only be transferred in one direction from an ordered state to a disordered state.

Higher the entropy, higher the disorder and lower the availability of the system’s energy to do useful work.

The expansion process which assumes there is no heat transfer between the system and its surroundings. No heat transfer is called “adiabatic. A isentropic process is for purposes of engineering analysis and calculation, one may assume that the process takes place from initiation to completion without an increase or decrease in the entropy of the system. An isentropic process is an idealisation Since the isentropic process is adiabatic which no heat transfer, therefore the isentropic process is S1 = S2.

In mathematically, the equation for isentropic perfect gas is derived as following: T2T1 = ( P2P1 )k-1k

Where,
P1 and T1 is initial absolute Temperature and absolute Pressure P2 and T2 is Temperature and Pressure after the expansion.
Materials and Apparatus:
Perfect gas expansion unit
Procedure

1. General start up procedure is performed as stated in appendix A. All valve are fully closed 2. The hose is connected from compressive pump to pressurized chamber 3. The compressive pump is switched on and the pressure inside chamber is allowed to increase up to 160kPa.The pump is switched off and the hose is removed from the chamber 4. The pressure reading inside the chamber is monitored until stabilized. The pressure reading P1 and temperature T1 is recorded. 5. Valve V01 is slightly opened and the air is allowed to flow out slowly until it reaches atmospheric pressure. 6. The pressure reading and temperature reading is recorded after the expansion process. 7. The isentropic expansion process is discussed.

Look more: polytropic process essay

Experiment Report Essay