Question

Experiment 8 – Air and the Ideal Gas Laws

This experiment will follow the procedure outlined in Experiment 8 in the lab manual. You may find it useful to review the Gas Laws in the lecture text before lab along with the lab manual Introduction, Theory and Procedure.

1. Define an ideal gas and how this definition is related to the Kinetic Molecular Theory of Gasses. Provide at least one citation for this question.

2. Define a real gas and how this definition is related to the Kinetic Molecular Theory of Gasses. Provide at least one citation for this question.

3. Discuss under what set of conditions a real gas is most likely to deviate from ideal behavior and why.

4. Using Equations 8.4 and 8.6, calculate the volume of 0.523 moles of water vapor at 300 K and 0.986 atm – you must show all work, including necessary unit conversions. Compare the value obtained from both equations and explain how your results compare to the theory discussed in the lab manual.

Answer 1

1. Ideal gas is a hypothetical gas whose molecules occupy negligible space and have no interactions, and which consequently obeys the gas laws exactly.

To better understand the molecular origins of the ideal gas law,

the basics of the Kinetic Molecular Theory of Gases (KMT) should be understood. This model is used to describe the behavior of gases. More specifically, it is used to explain macroscopic properties of a gas, such as pressure and temperature, in terms of its microscopic components, such as atoms. Like the ideal gas law, this theory was developed in reference to ideal gases, although it can be applied reasonably well to real gases.

In order to apply the kinetic model of gases, five assumptions are made:

1. Gases are made up of particles with no defined volume but with a defined mass. In other words their volume is miniscule compared to the distance between themselves and other molecules.
2. Gas particles undergo no intermolecular attractions or repulsions. This assumption implies that the particles possess no potential energy and thus their total energy is simply equal to their kinetic energies.
3. Gas particles are in continuous, random motion.
4. Collisions between gas particles are completely elastic. In other words, there is no net loss or gain of kinetic energy when particles collide.
5. The average kinetic energy is the same for all gases at a given temperature, regardless of the identity of the gas. Furthermore, this kinetic energy is proportional to the absolute temperature of the gas.

References:

• Oxtoby, Gillis and Campion. Principles of Modern Chemistry. 6th Edition. California: Thomson Brooks/Cole. 2008.
• Chang, Raymond. Physical Chemistry for the Biosciences. California: University Science Books. 2005.

2. & 3. Kinetic theory assumes that all gases behave ideally; however, we know that this is not the case. Obviously real gas particles do occupy space and attract each other. These properties become apparent at low temperatures or high pressures. Usually the particles have enough kinetic energy that they whiz by each other without being affected by the push or pull of neighboring molecules. However, at low temperatures the molecules have very little kinetic energy and move around much slower, so there is time for static forces to take hold. At very high pressures, the molecules of a gas become so tightly packed that their volume is significant compared to the overall volume. Also note that before a gas ever reaches absolute zero, it will condense to a liquid.

4. Please provide eq. 8.4 and 8.6 to solve the question.