IB · IB Physics
IB Physics: Gas laws — Practice Questions & Answers
308 practice questions available for this topic — here are 10 with full answers and explanations.
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Practice questions with answers
1
Multiple choice · Medium
A fixed mass of gas at constant temperature has its volume halved. What happens to its pressure?
- It doubles
- It halves
- It is unchanged
- It quadruples
Tap an answer to check it.
WhyBy Boyle's law $pV=\text{constant}$, so halving the volume doubles the pressure.
2
Multiple choice · Easy
For a fixed mass of gas at constant pressure, Charles's law states that volume is proportional to:
- Absolute temperature
- Pressure
- Celsius temperature
- The square of temperature
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WhyCharles's law: $\frac{V}{T}=\text{constant}$, so volume is proportional to the absolute (kelvin) temperature.
3
Multiple choice · Medium
The ideal gas equation relating pressure, volume, amount and temperature is:
- $pV=nRT$
- $pV=\frac{nT}{R}$
- $pT=nRV$
- $p=nRVT$
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WhyThe ideal gas law is $pV=nRT$, where $n$ is the number of moles and $R$ the gas constant.
4
Multiple choice · Medium
A sealed rigid container of gas is heated. According to the pressure law, the pressure is proportional to:
- Absolute temperature
- Volume
- $1/T$
- Celsius temperature
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WhyAt constant volume, $\frac{p}{T}=\text{constant}$, so pressure is proportional to absolute temperature.
5
Multiple choice · Hard
A gas at $2.0\times 10^{5}\,\text{Pa}$ occupies $3.0\,\text{L}$. At constant temperature it expands to $6.0\,\text{L}$. What is the new pressure?
- $1.0\times 10^{5}\,\text{Pa}$
- $4.0\times 10^{5}\,\text{Pa}$
- $2.0\times 10^{5}\,\text{Pa}$
- $0.5\times 10^{5}\,\text{Pa}$
Tap an answer to check it.
WhyBoyle's law: $p_{1}V_{1}=p_{2}V_{2}$, so $p_{2}=\frac{2.0\times 10^{5}\times 3.0}{6.0}=1.0\times 10^{5}\,\text{Pa}$.
6
Multiple choice · Medium
The number of moles in a sample containing $N$ particles is found using the Avogadro constant $N_{A}$ as:
- $n=\frac{N}{N_{A}}$
- $n=N\,N_{A}$
- $n=\frac{N_{A}}{N}$
- $n=N+N_{A}$
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Why$n=\frac{N}{N_{A}}$, where $N_{A}\approx 6.02\times 10^{23}\,\text{mol}^{-1}$.
7
Fill in the blank · Easy
At constant temperature, the product of pressure and of a fixed mass of gas is constant.
Answer:
volume
WhyThis is Boyle's law: $pV=\text{constant}$ at fixed temperature.
8
Fill in the blank · Medium
One mole of any substance contains approximately $6.02\times 10^{}$ particles.
Answer:
23
WhyThe Avogadro constant is $N_{A}\approx 6.02\times 10^{23}\,\text{mol}^{-1}$.
9
Multiple choice · Medium
A fixed amount of ideal gas is compressed isothermally. Which statement about pressure p and volume V is correct?
- pV remains constant
- p / V remains constant
- p x V increases
- V / p doubles
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WhyAt constant temperature for a fixed amount of gas, pV is constant, so p is inversely proportional to V.
10
Multiple choice · Hard
An ideal gas at 150 kPa occupies 2.0 x 10^-3 m3. At constant temperature it is compressed to 1.2 x 10^-3 m3. What is the new pressure?
- 250 kPa
- 90 kPa
- 180 kPa
- 300 kPa
Tap an answer to check it.
WhypV constant: 150e3 x 2.0e-3 = 300; new pressure = 300 / 1.2e-3 = 2.5 x 10^5 Pa = 250 kPa.
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