MCAT General Chemistry Question 210: Answer and Explanation
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Question: 210
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
Correct Answer: A
Explanation:
A Since both balloons contain the same number of moles of gas under identical pressure and temperature conditions (STP), they should have the same volume (in this case 5.6 L since 1 mol = 22.4 L). Eliminate choice B. An identical amount of each gas is added to each balloon, so they should also contain the same number of gas particles (0.25 mol × 6.02 × 1023 particles/mol), eliminating choice C. Since the gases are at the same temperature they will have the same average kinetic energy, so by process of elimination, A must be the correct answer. Density is mass/volume. Since the two gases have the same volume, oxygen, with a larger molar mass (O2 = 32 g/mol vs. Ne = 20 g/mol), will have the greater density.