# GAS LAWS EXERCISE

CHEM 1311

GAS LAWS EXERCISE

Instruction: Answer all questions. Show your detailed work (NO WORK-NO CREDIT), put units on all numbers, carry correct significant digits for full-credit.

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1. Question 1a. On a rainy day, a barometer reads 745 mmHg. Convert this value to atmospheres. (1 atm = 760. mm Hg)

The gas laws describe the behavior of gases under specific conditions of temperature, pressure, and volume. Three gas laws show the relationship between two variables when all others are held constant: Boyle’s law (pressure and volume are inversely proportional), Charles’s law (volume and temperature are directly proportional), and Gay-Lussac’s law (temperature and pressure are directly proportional).

The three laws can be combined into one law, called the combined gas law.

Question 1b: A sample of krypton gas has a volume of 5.78 L and a pressure of 2.92 atm, under a constant temperature of 300 K. What is the new volume, if the pressure is decreased to 1.75 atm?

The gas laws describe the behavior of gases under specific conditions of temperature, pressure, and volume. Three gas laws show the relationship between two variables when all others are held constant.

Question 2a : Which statement best describes Charles’s Law?

1. Temperature and volume are directly proportional to one another.
2. Pressure and volume are directly proportional to one another.
3. Pressure and volume are inversely proportional to one another.
4. Temperature and volume are inversely proportional to one another.

Question 2b:

A gas, behaving ideally, has a pressure P1 and at a volume V1. The pressure of the gas is changed to P2. Using Avogadro’s, Charles’, or Boyle’s law, develop an expression that would solve for the new volume V2.

Several properties of gases can be experimentally measured: temperature, pressure, volume, and the amount of the gas (i.e., the number of moles). The ideal gas law states that the relationship between these properties, or variables, in a mathematical formula.

The ideal gas law is PV = nRT.

P is the pressure in atmospheres (atm), V is the volume in liters (L), n is the number of moles, R is the gas constant (0.08206 L∙atm/(mol∙K)), and T is the temperature in Kelvins (K).

Question 3: Using the ideal gas law, determine the temperature of a 2.63 mole sample of xenon gas, with a volume of 1.60 × 104 mL and under a pressure of 2.20 atm.

Gases are typically a mixture of several different gases, and each of these gases exerts its own pressure on the walls of the container. The partial pressure of a gas in a mixture is proportional to the mole fraction of the gas in a mixture multiplied by the total pressure.

P1 = X1Pt

Where X1 is the mole fraction of gas 1 and it is = n1/nt (n1 number of moles of gas 1; nt total number of moles of gases in the mixture). {The mole fraction, X, is a dimensionless number that expresses the ratio of the number of moles of a component in a mixture to the total number of moles in the mixture}

Pt = total pressure

Question 4: A mixture of gases contains 4.25 grams of CO2 and 2.25 grams of CH4 and has a total pressure of 0.900 atm. What is the partial pressure of CH4?