MCAT General Chemistry Practice Questions with Correct Answers 2023

STP Correct Answer 0°C and 1 atm Ideal Gas Law Correct Answer PV = nRT At STP, 1 mol of gas will occupy ... Correct Answer 22.4 L Characteristics of an Ideal Gas Correct Answer 1. Gas molecules have zero volume 2. Gas molecules exert no forces other than repulsive forces due to collisions 3. Gas molecules make completely elastic collisions 4. The avg. kinetic energy of gas molecules is directly proportional to the temperature of the gas Partial pressure of a gas (equation) Correct Answer Partial pressure equals the mole fraction of the gas (number of moles of gas "i" divided by total number of moles of gas in sample) times the total pressure. Average Kinetic Energy (of gas) Correct Answer KEavg = (3/2)RT (R = .08206 L atm K⁻¹ mol⁻¹ or 8.314 J K⁻¹ mol⁻¹) Average kinetic energy applies to ALL gases, regardless of mass. Diffusion Correct Answer Spreading of one gas into another gas or into empty space. Approximated by Graham's Law. Graham's law (diffusion) Correct Answer Effusion Correct Answer Spreading of a gas from high pressure to very low pressure through a "pinhole." Graham's law (effusion) Correct Answer Where rates are effusion rates, and Ms are the molar masses of the gases. When do "real" gases deviate from ideal gas behavior? Correct Answer When molecules are close together: - volume becomes significant - electrostatic forces become significant - high pressure pushes molecules together - low temperatures cause gas molecules to settle close together How does Volume compare for real and ideal gases? Correct Answer V(real) > V(ideal)