Chemistry Practice Test: Gas Laws
- Gas Laws
- 10 questions
- 15 minutes
This test covers how the pressure, volume, temperature and amount of a gas are related. Use R = 0.0821 L·atm/(mol·K). Tip: always convert temperatures to kelvins (K = °C + 273) before using a gas law.
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Question 1
A gas occupies 6.0 L at 1.0 atm. At constant temperature, the pressure is raised to 2.0 atm. What is the new volume?
Correct answer: A
Boyle's law: P1V1 = P2V2, so V2 = 1.0 × 6.0 ÷ 2.0 = 3.0 L. Doubling the pressure halves the volume; 12 L treats the relationship as direct.
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Question 2
A balloon holds 2.0 L of gas at 27 °C. At constant pressure it is heated to 327 °C. What is the new volume?
Correct answer: C
In kelvins the temperature goes from 300 K to 600 K, so the volume doubles to 4.0 L (Charles's law). Using Celsius gives 2.0 × 327 ÷ 27 ≈ 24 L, which is wrong.
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Question 3
A sealed container of gas is at 200 kPa and 27 °C. It is heated to 57 °C at constant volume. What is the new pressure?
Correct answer: B
Gay-Lussac's law with kelvins: P2 = 200 × 330 ÷ 300 = 220 kPa. Using Celsius temperatures gives about 422 kPa, a common mistake.
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Question 4
A gas sample has a volume of 4.0 L at 1.0 atm and 273 K. The pressure is changed to 2.0 atm and the temperature to 546 K. What is the new volume?
Correct answer: D
Combined gas law: V2 = 4.0 × (1.0 ÷ 2.0) × (546 ÷ 273) = 4.0 L. Doubling the pressure halves the volume and doubling the kelvin temperature doubles it, so the effects cancel.
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Question 5
A gas sample fills 24.6 L at 1.00 atm and 300 K. About how many moles of gas are in the sample?
Correct answer: C
From PV = nRT, n = PV ÷ RT = (1.00 × 24.6) ÷ (0.0821 × 300) ≈ 1.00 mol. The value 0.0821 is the gas constant, not the number of moles.
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Question 6
A container holds nitrogen, oxygen and argon at a total pressure of 760 mmHg. The partial pressure of nitrogen is 600 mmHg and that of oxygen is 120 mmHg. What is the partial pressure of argon?
Correct answer: D
By Dalton's law the partial pressures add up to the total: 760 − 600 − 120 = 40 mmHg. 720 mmHg is the sum of nitrogen and oxygen, not what is left for argon.
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Question 7
Which statement is an assumption of the kinetic molecular theory of gases?
Correct answer: A
The model assumes tiny particles in constant random motion with no attractions and no loss of energy in collisions. Particles in a real sample have a range of speeds, not one speed.
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Question 8
What happens to the average kinetic energy of gas particles when the kelvin temperature is doubled?
Correct answer: B
Average kinetic energy is directly proportional to kelvin temperature. Quadrupling would be the change in KE if the particles' speed doubled, not the temperature.
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Question 9
Under which conditions does a real gas behave least like an ideal gas?
Correct answer: A
At high pressure the particles' own volume matters, and at low temperature their attractions matter, both of which the ideal model ignores. Low pressure and high temperature is where gases behave most ideally.
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Question 10
Two balloons at the same temperature and pressure each hold 2.0 L of gas: one contains hydrogen (H2), the other carbon dioxide (CO2). Which statement is true?
Correct answer: C
Avogadro's law says equal volumes of gases at the same temperature and pressure contain equal numbers of molecules. The masses differ because a CO2 molecule is 22 times heavier than an H2 molecule.
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