Grade 11 Physical Sciences · Matter and Materials

Calculate with the gas equations

Calculate pressure, volume or temperature of a gas using p₁V₁/T₁ = p₂V₂/T₂ or pV = nRT, with temperature in kelvin.

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Question 1.4 · November 2025 · Paper 2 · Provincial · 2 marks

Various options are provided as possible answers to the following questions. Choose the answer and write only the letter (A–D) next to the question numbers (1.1 to 1.10) in the ANSWER BOOK, for example 1.11 E.

1.4 The diagram below shows a gas syringe containing a certain gas. When the plunger is at position A the volume occupied by the gas is X and exerts a pressure P. When the plunger moves to position B the volume occupied by the gas is

\frac{1}{3}

X.

What is the DIFFERENCE in pressure exerted by the gas between points A and B?(2) Diagram for question 1.4

A $3$ P
B $\frac{2}{3}$ P
C $\frac{1}{3}$ P
D $2$ P

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More past paper questions: calculate with the gas equations

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3. Question 4.4 · November 2024 · Paper 2 · Provincial · 4 marks
Learners investigated the relationship between pressure and volume of a gas. The graph below shows the results obtained during the investigation.
4.4 Calculate the volume at $200$ kPa.(4)
Show the memo (4 ticks)Memo
1. ✓
  Formula $p_{1} V_{1} = p_{2} V_{2}$
  1 mark · Calculate with the gas equations
2. ✓
  Substitution of $p_{1} V_{1}$ $(40 \times 1 0^{3}) (12)$
  1 mark · Calculate with the gas equations
3. ✓
  Substitution of $p_{2}$ $= (200 \times 1 0^{3}) V_{2}$
  1 mark · Calculate with the gas equations
4. ✓
  Answer with unit $V_{2} = 2, 4$ cm $^{3}$
  1 mark · Calculate with the gas equations
4. Question WE7 · Siyavula Grade 11 Physical Sciences, 7.2 Ideal gas laws, Worked example 7 · 3 marks
WE7 At the beginning of a journey, a truck tyre has a volume of $30$ dm $^{3}$ and an internal pressure of $170$ kPa. The temperature of the tyre is $16$ °C. By the end of the trip, the volume of the tyre has increased to $32$ dm $^{3}$ and the temperature of the air inside the tyre is $40$ °C. What is the tyre pressure at the end of the journey?(3)
Show the memo (3 ticks)Memo
1. ✓
  Temperatures in kelvin $T_{1} = 16 + 273 = 289$ K
  $T_{2} = 40 + 273 = 313$ K
  1 mark · Calculate with the gas equations
2. ✓
  General gas equation substitution $\frac{p _{2} V _{2}}{T _{2}} = \frac{p _{1} V _{1}}{T _{1}}$
  $\frac{( 32 ) p _{2}}{313} = \frac{( 170 ) ( 30 )}{289}$
  1 mark · Calculate with the gas equations
3. ✓
  Answer with unit $p_{2} = 172, 6$ kPa
  1 mark · Calculate with the gas equations
5. Question WE6 · Siyavula Grade 11 Physical Sciences, 7.2 Ideal gas laws, Worked example 6 · 3 marks
WE6 A fixed volume of carbon monoxide ( $CO$ ) gas has a temperature of $32$ °C and a pressure of $680$ Pa. If the temperature is decreased to $15$ °C what will the pressure be?(3)
Show the memo (3 ticks)Memo
1. ✓
  Temperatures in kelvin $T_{1} = 32 + 273 = 305$ K
  $T_{2} = 15 + 273 = 288$ K
  1 mark · Calculate with the gas equations
2. ✓
  Pressure-temperature substitution $\frac{p _{2}}{T _{2}} = \frac{p _{1}}{T _{1}}$
  $\frac{p _{2}}{288} = \frac{680}{305}$
  1 mark · Calculate with the gas equations
3. ✓
  Answer with unit $p_{2} = 642, 1$ Pa
  1 mark · Calculate with the gas equations
6. Question WE1 · Siyavula Grade 11 Physical Sciences, 7.2 Ideal gas laws, Worked example 1 · 2 marks
WE1 A sample of helium occupies a volume of $160$ cm $^{3}$ at $100$ kPa and $25$ °C. What volume will it occupy if the pressure is adjusted to $80$ kPa and the temperature remains unchanged?(2)
Show the memo (2 ticks)Memo
1. ✓
  Boyle's law substitutionThe temperature stays the same: $p_{2} V_{2} = p_{1} V_{1}$
  $(80) V_{2} = (100) (160)$
  1 mark · Calculate with the gas equations
2. ✓
  Answer with unit $V_{2} = 200$ cm $^{3}$
  1 mark · Calculate with the gas equations

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