Worksheet: Kinetic Molecular Theory

In this worksheet, we will practice describing kinetic molecular theory and relating temperatures of gases to the energies of randomly moving molecules.

Q1:

Which of the following is not a postulate of kinetic molecular theory?

  • AGas molecules exert no attractive or repulsive forces on each other or the container walls; therefore, their collisions are elastic (they do not involve a loss of energy).
  • BGas molecules join together very briefly when they collide, acting as a single molecule.
  • CGases are composed of molecules that are in continuous motion, traveling in straight lines and changing direction only when they collide with other molecules or with the walls of a container.
  • DThe pressure exerted by a gas in a container results from collisions between the gas molecules and the container walls.
  • EThe molecules composing a gas are negligibly small compared to the distances between them.

Q2:

Under which of the following conditions does a real gas behave most like an ideal gas?

  • ALow temperature and high pressure
  • BSmall volume and low temperature
  • CLarge volume and low temperature
  • DHigh temperature and low pressure
  • EHigh pressure and small volume

Q3:

All gases can condense into a liquid or solid below a critical temperature 𝑇C. Which of the following statements is true?

  • ABelow 𝑇C, the kinetic energy of the molecules is zero.
  • BAbove 𝑇C, the potential energy of the intermolecular interactions is zero.
  • CBelow 𝑇C, the potential energy of the intermolecular interactions is greater in magnitude than the kinetic energy.
  • DThe value of 𝑇C does not depend on the gas pressure.
  • EMaking the potential energy of intermolecular interactions more negative causes 𝑇C to decrease.

Q4:

The velocities, 𝑣, of molecules in a gas vary over a wide range but are strongly affected by their mass. At a particular temperature, heavier molecules move more slowly on average. Shown in the figure are the velocities displayed by different noble gas molecules at room temperature.

If a sample of argon at room temperature is cooled, how and why does the distribution of velocities change?

  • AThe gas molecules gain potential energy, so the distribution changes to resemble neon at room temperature.
  • BThe gas molecules lose kinetic energy, so the distribution changes to resemble krypton at room temperature.
  • CThe gas molecules interact more strongly, so the distribution changes to resemble krypton at room temperature.
  • DThe mass of the molecules is unaffected by cooling, so the distribution does not change.
  • EThe gas molecules occupy a smaller volume, so the distribution changes to resemble neon at room temperature.

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