The Gas Laws: Quiz

The Gas Laws: Quiz

7 questions

1. Question 1EasyAt constant temperature, the volume of a gas is halved. What happens to its pressure?

   AIt halvesBIt doublesCIt stays the sameDIt increases by a factor of four
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   Answer: It doubles

   Boyle's law: P × V stays constant, so halving V doubles P.

2. Question 2MediumA gas at constant pressure is heated from 100 °C to 200 °C. By what factor does its volume change?

   A2.00B1.27C0.50D1.00
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   Answer: 1.27

   Use kelvin: 100 °C = 373 K and 200 °C = 473 K. V₂/V₁ = 473 K ÷ 373 K = 1.27 (the units cancel). Doubling the Celsius number does not double the temperature.

3. Question 3EasyWhich temperature must be used in gas law calculations?

   ADegrees CelsiusBDegrees FahrenheitCKelvinDAny unit, as long as both temperatures match
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   Answer: Kelvin

   Gas laws need an absolute scale that starts at zero. Even if both temperatures are in °C, the ratio is wrong.

4. Question 4MediumA sealed can contains gas at 1.00 atm and 27 °C. It is heated to 327 °C. What is the new pressure?

   A12.1 atmB2.00 atmC1.09 atmD0.50 atm
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   Answer: 2.00 atm

   Gay-Lussac: T₁ = 27 °C + 273 = 300 K and T₂ = 327 °C + 273 = 600 K. P₂ = 1.00 atm × (600 K ÷ 300 K) = 2.00 atm. (Using °C would give 12.1 atm, which is wrong.)

5. Question 5MediumWhat is the pressure of 0.200 mol of gas in a 10.0 L container at 27 °C? (R = 8.314 L·kPa/(mol·K))

   A4.49 kPaB49.9 kPaC499 kPaD0.499 kPa
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   Answer: 49.9 kPa

   T = 27 °C + 273.15 = 300.15 K. P = nRT/V = (0.200 mol × 8.314 L·kPa/(mol·K) × 300.15 K) ÷ 10.0 L = 49.9 kPa. The units of mol, K and L cancel, leaving kPa.

6. Question 6MediumAt the same temperature and pressure, 2 mol of nitrogen and 2 mol of helium occupy…

   Athe same volumeBdifferent volumes, because N₂ molecules are heavierCdifferent volumes, because helium atoms are smallerDno volume, because gases have no fixed volume
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   Answer: the same volume

   Avogadro's law: equal moles of ideal gases at the same T and P occupy equal volumes, whatever the gas.

7. Question 7HardUnder which conditions does a real gas behave most like an ideal gas?

   AHigh pressure and low temperatureBLow pressure and high temperatureCHigh pressure and high temperatureDLow pressure and low temperature
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   Answer: Low pressure and high temperature

   Then the particles are far apart and fast, so their own volume and the attractions between them matter least.