Rucete ✏ AP Chemistry In a Nutshell
6. Gases — Practice Questions 3
This chapter introduces the relationships between pressure, volume, temperature, and moles of gas, and explains the ideal gas law, gas laws, and real gas behavior.
(Multiple Choice — Click to Reveal Answer)
1. Which law best describes this behavior: pressure?
(A) Boyle’s Law
(B) Charles’s Law
(C) Gay-Lussac’s Law
(D) Avogadro’s Law
Answer
(A) — This is consistent with Boyle’s Law, which shows inverse relationship between P and V.
2. What is the unit of temperature in the ideal gas law when using R = 0.0821?
(A) Celsius
(B) Fahrenheit
(C) Kelvin
(D) Rankine
Answer
(C) — Temperature must be in Kelvin for gas law calculations using this R value.
3. A balloon is placed in a freezer. What happens and why?
(A) It expands due to lower temperature
(B) It contracts because gas particles slow down
(C) It remains unchanged
(D) It bursts
Answer
(B) — Lower temperature reduces kinetic energy, causing the gas volume to decrease.
4. Which law best describes this behavior: volume?
(A) Boyle’s Law
(B) Charles’s Law
(C) Gay-Lussac’s Law
(D) Avogadro’s Law
Answer
(B) — Charles’s Law states that volume is directly proportional to temperature at constant pressure.
5. When temperature is held constant, which of the following changes results in a decrease in volume?
(A) Decrease in pressure
(B) Increase in pressure
(C) Increase in volume
(D) Decrease in number of moles
Answer
(B) — Boyle’s Law: pressure and volume are inversely related when temperature is constant.
6. Which law best describes this behavior: amount of substance?
(A) Boyle’s Law
(B) Charles’s Law
(C) Gay-Lussac’s Law
(D) Avogadro’s Law
Answer
(D) — Avogadro’s Law relates volume to the number of moles of gas.
7. What is the unit of pressure in the ideal gas law when using R = 0.0821?
(A) atm
(B) mmHg
(C) Pa
(D) Torr
Answer
(A) — R = 0.0821 uses atm for pressure.
8. A balloon is placed in hot water. What happens and why?
(A) It contracts due to increased collisions
(B) It expands because gas particles gain energy
(C) It stays the same size
(D) It collapses
Answer
(B) — Increased temperature increases particle motion, expanding the balloon.
9. When volume is held constant, which of the following changes results in increased pressure?
(A) Increase in temperature
(B) Decrease in moles
(C) Decrease in temperature
(D) Increase in volume
Answer
(A) — Gay-Lussac’s Law shows pressure increases with temperature at constant volume.
10. What is the unit of volume in the ideal gas law when using R = 0.0821?
(A) Liters
(B) Milliliters
(C) Cubic meters
(D) Gallons
Answer
(A) — Volume must be in liters for consistent units in the ideal gas law.
11. Which law best describes this behavior: temperature?
(A) Boyle’s Law
(B) Charles’s Law
(C) Gay-Lussac’s Law
(D) Avogadro’s Law
Answer
(C) — Gay-Lussac’s Law relates pressure and temperature directly at constant volume.
12. What is the unit of R in the ideal gas law when pressure is in atm and volume is in liters?
(A) 0.0821 L·atm/mol·K
(B) 8.314 J/mol·K
(C) 62.36 L·Torr/mol·K
(D) 1.00 L·Pa/mol·K
Answer
(A) — That value and unit match the gas constant in common calculations.
13. Which of the following conditions will cause a gas to deviate most from ideal behavior?
(A) Low pressure and high temperature
(B) High pressure and low temperature
(C) Moderate pressure and temperature
(D) STP
Answer
(B) — High pressure and low temperature increase intermolecular forces and particle volume effects.
14. A sample of gas at constant temperature is compressed. What happens to pressure?
(A) It increases
(B) It decreases
(C) It remains the same
(D) It fluctuates randomly
Answer
(A) — Boyle’s Law explains that pressure increases when volume decreases at constant temperature.
15. What is the molar volume of an ideal gas at STP?
(A) 22.4 L
(B) 1.00 L
(C) 273 L
(D) 0.0821 L
Answer
(A) — One mole of ideal gas occupies 22.4 L at STP (0°C and 1 atm).
16. Which gas law shows a direct relationship between volume and moles?
(A) Boyle’s Law
(B) Charles’s Law
(C) Avogadro’s Law
(D) Dalton’s Law
Answer
(C) — Avogadro’s Law: V ∝ n at constant T and P.
17. Which variable must remain constant when applying Boyle’s Law?
(A) Volume
(B) Pressure
(C) Temperature
(D) Moles
Answer
(C) — Boyle’s Law assumes temperature is constant while examining pressure and volume.
18. Which law would be used to calculate the final pressure of a gas when volume is halved?
(A) Boyle’s Law
(B) Charles’s Law
(C) Dalton’s Law
(D) Graham’s Law
Answer
(A) — Boyle’s Law: P₁V₁ = P₂V₂, holding temperature constant.
19. Which pair of variables is held constant in Charles’s Law?
(A) Volume and temperature
(B) Pressure and volume
(C) Pressure and temperature
(D) Pressure and moles
Answer
(D) — Charles’s Law: V ∝ T, with constant pressure and moles.
20. When pressure is held constant, and temperature increases, volume will:
(A) Increase
(B) Decrease
(C) Stay the same
(D) Become zero
Answer
(A) — Charles’s Law shows direct proportionality between temperature and volume.
21. What happens to the pressure of a gas if temperature decreases while volume stays constant?
(A) It increases
(B) It decreases
(C) It remains constant
(D) It becomes zero
Answer
(B) — According to Gay-Lussac’s Law, pressure decreases with decreasing temperature at constant volume.
22. When pressure is increased and temperature remains constant, what happens to volume?
(A) It increases
(B) It decreases
(C) It stays the same
(D) It doubles
Answer
(B) — Boyle’s Law: pressure and volume are inversely related at constant temperature.
23. Which of the following variables must be in Kelvin for ideal gas calculations?
(A) Pressure
(B) Volume
(C) Temperature
(D) Moles
Answer
(C) — Temperature must always be in Kelvin to avoid division by zero or negative values.
24. A sample of gas doubles in temperature (in Kelvin) while pressure is constant. What happens to volume?
(A) It halves
(B) It doubles
(C) It remains the same
(D) It quadruples
Answer
(B) — Charles’s Law shows volume is directly proportional to absolute temperature.
25. Which factor is directly proportional to the number of collisions in a sealed gas container?
(A) Temperature
(B) Molar mass
(C) Volume
(D) Density
Answer
(A) — Higher temperature means faster-moving particles and more collisions.
26. Under which conditions does the ideal gas law break down most significantly and why?
(A) Low pressure and high temperature — particles behave ideally
(B) Moderate pressure and temperature — particles deviate
(C) High pressure and low temperature — real gas effects dominate
(D) STP — all gases deviate
Answer
(C) — At high pressure and low temperature, intermolecular forces and particle volume become significant.
27. In the van der Waals equation, what does the term 'b' account for?
(A) Intermolecular forces
(B) Temperature correction
(C) Volume occupied by gas particles
(D) Ideal gas behavior
Answer
(C) — The 'b' term corrects for the finite volume of gas molecules.
28. Why must temperature always be in Kelvin when using the ideal gas law?
(A) Celsius is incompatible with pressure
(B) Kelvin ensures positive values and proper proportionality
(C) Kelvin matches pressure units
(D) It's a scientific tradition
Answer
(B) — Only the Kelvin scale ensures proportionality with kinetic energy and avoids negative values.
29. Explain the role of molecular collisions in gas pressure as defined by kinetic molecular theory.
(A) Collisions cause gas particles to slow down
(B) Collisions with container walls create pressure
(C) Collisions form chemical bonds
(D) Collisions increase particle size
Answer
(B) — Pressure arises from the force of gas particles colliding with the container walls.
30. Compare the diffusion rates of two gases using Graham’s law. Which diffuses faster?
(A) Heavier gas
(B) Lighter gas
(C) They diffuse at the same rate
(D) Depends on pressure only
Answer
(B) — Graham’s law: lighter gases diffuse faster than heavier gases.
31. Which factor increases the deviation of real gases from ideal behavior?
(A) Low pressure
(B) High temperature
(C) Low temperature
(D) Small volume
Answer
(C) — Low temperatures reduce kinetic energy, increasing the effect of intermolecular forces, causing deviation.
32. What does the van der Waals constant 'a' correct for?
(A) Pressure due to molecular attraction
(B) Volume of gas particles
(C) Temperature of gas
(D) Mass of molecules
Answer
(A) — The 'a' constant corrects for intermolecular attractions between gas particles.
33. According to kinetic molecular theory, what happens to particle motion as temperature increases?
(A) Motion decreases
(B) Particles condense
(C) Motion increases
(D) Volume remains constant
Answer
(C) — Higher temperature increases kinetic energy, leading to faster particle motion.
34. What gas law explains why a balloon expands as it rises in altitude?
(A) Boyle’s Law
(B) Charles’s Law
(C) Avogadro’s Law
(D) Dalton’s Law
Answer
(A) — Boyle’s Law: lower external pressure at high altitudes allows gas volume to expand.
35. What does STP stand for in gas law calculations?
(A) Standard test pressure
(B) Standard temperature and pressure
(C) Specific thermal property
(D) Standard time protocol
Answer
(B) — STP refers to 0°C (273 K) and 1 atm pressure, standard for gas law calculations.
36. Explain how kinetic molecular theory supports Boyle’s law.
Answer
Answer: As volume decreases, gas particles collide more frequently with the container walls, increasing pressure. This supports Boyle’s Law: P ∝ 1/V at constant temperature.
37. State the five postulates of kinetic molecular theory.
Answer
Answer: 1) Gases consist of tiny particles in constant, random motion. 2) Gas particles are far apart. 3) Collisions are elastic. 4) No intermolecular forces. 5) Temperature relates to average kinetic energy.
38. Derive the density equation from the ideal gas law.
Answer
Answer: Use PV = nRT and substitute n = mass/M. Rearranged, density (ρ) = PM/RT.
39. Explain how Dalton’s law applies when collecting gas over water.
Answer
Answer: Total pressure is the sum of the gas pressure and water vapor pressure. Subtract water vapor pressure to find the dry gas pressure.
40. Describe one assumption of ideal gases that does not apply to real gases.
Answer
Answer: Ideal gases assume no intermolecular forces, but real gases do have attractions and repulsions.
41. How does molar mass affect gas diffusion rate?
Answer
Answer: According to Graham’s Law, gases with lower molar mass diffuse faster than those with higher molar mass.
42. How can you use the ideal gas law to calculate the molar mass of a gas?
Answer
Answer: Use PV = nRT and n = mass/molar mass. Rearranged, molar mass = (mass × R × T) / (P × V).
43. What does it mean when gas particles have “elastic collisions”?
Answer
Answer: No kinetic energy is lost during collisions between gas particles or with container walls.
44. Why do gases exert pressure?
Answer
Answer: Gas particles constantly collide with container walls, exerting force over an area (pressure).
45. Explain why real gases do not behave ideally at low temperatures.
Answer
Answer: At low temperatures, intermolecular attractions become significant, causing deviations from ideal behavior.
46. What happens to the volume of a gas if its absolute temperature is tripled and pressure remains constant?
Answer
Answer: According to Charles’s Law, volume triples since it is directly proportional to temperature in Kelvin.
47. Describe how pressure and temperature are related in Gay-Lussac’s Law.
Answer
Answer: Pressure is directly proportional to temperature when volume is held constant.
48. What conditions must be true to apply Graham’s law?
Answer
Answer: The gases must be at the same temperature and pressure for the diffusion rates to follow the square root relationship.
49. How does increasing the number of moles affect pressure in a rigid container?
Answer
Answer: More particles cause more frequent collisions, increasing pressure (P ∝ n).
50. Why is it important to subtract water vapor pressure when measuring collected gas?
Answer
Answer: Because total pressure includes both the collected gas and water vapor; subtracting gives the pressure of the dry gas alone.