MCAT General Chemistry Question 209: Answer and Explanation

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Question: 209

1. A sample of nitrogen gas is heated in a sealed, rigid container. The pressure inside the container increases because the added energy causes:

  • A. some of the nitrogen molecules to split, so more particles contribute to increase the pressure.
  • B. the molecules of gas to move faster, increasing the frequency of intermolecular collisions.
  • C. the molecules of gas to move faster, increasing the frequency of collisions with the container.
  • D. the molecules of gas to stick together in clusters that have a greater momentum.

Correct Answer: C

Explanation:

C According to kinetic molecular theory, pressure is defined by the frequency of collisions between gas particles and the walls of their container. While increasing the temperature of the gas will cause more collisions between particles as well, these collisions do not define pressure (eliminate choice B). In addition, collisions between particles are elastic, so unless the particles are highly polar and have a strong attraction for each other (the gas is behaving non-ideally), they will not stick together. Since N2 is non-polar it should behave ideally, so choice D can be eliminated. Finally, nitrogen is a very stable diatomic element, and heating a sample of nitrogen is not likely to break the strong triple bond between nitrogen atoms, eliminating choice A.

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