MCAT General Chemistry Freestanding Practice Questions: Gases

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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.

2. Two identical balloons are filled with different gases at STP. Balloon A contains 0.25 moles of neon, and balloon B contains 0.25 moles of oxygen. Which of the following properties would be greater for balloon B?

  • A. Density
  • B. Volume
  • C. Number of particles
  • D. Average kinetic energy

3. The figure below depicts the relative sizes and mole fractions of two monatomic gases in a closed container.

Which of the following is true about the gas mixture after a small hole is punched in the container and the gases are allowed to completely effuse?

  • A. The partial pressure of Gas X will never equal the partial pressure of Gas Y.
  • B. The partial pressure of Gas Y will decrease faster than the partial pressure of Gas X.
  • C. The partial pressure of Gas Y will increase because the mole fraction of Gas Y will increase.
  • D. The partial pressures of each gas will remain unchanged.

4. There are an unknown number of moles of argon in a steel container. A chemist injects two moles of nitrogen into the container. The temperature and volume do not change, but the pressure increases by ten percent. Originally the container held:

  • A. 16 moles of Ar.
  • B. 18 moles of Ar.
  • C. 20 moles of Ar.
  • D. 22 moles of Ar.

5. Which of the following compounds can best approximate ideal gas behavior?

  • A. CH4(g)
  • B. NH3(g)
  • C. H2O(g)
  • D. HF(g)

6. Which of the following is true for a closed flask containing both 1 mole of ideal Gas X and 1 mole of real Gas Y?

  • A. The total energy of X is equal to the total energy of Y.
  • B. The average kinetic energy of X is equal to the average kinetic energy of Y.
  • C. The total volume available to the gases is the same as the total volume of the flask.
  • D. Gases X and Y are at different temperatures.

7. Given the following combustion reaction, calculate the mole fraction of hydrocarbon in the reactant solution before combustion. Assume neither starting material is limiting.

ZCxHy(g) + 8 O2(g) → 5 CO2(g) + 6 H2O(l)

  • A. 1/8
  • B. 1/9
  • C. 2/9
  • D. 1/3