When must kelvin be used?

Every time a gas law or pV equals nRT is applied; Celsius is only used to report the final answer.

Why does a deep bubble grow?

Pressure falls as the bubble rises, so at constant temperature its volume rises in proportion.

S5 Physics Gas Laws, Paper 3: the ideal gas equation in use

2026-11-02

Uses pV equals nRT for volume, pressure and amount, then tackles a rising bubble, a warming tyre and the Celsius slip in ten graded items.

Focus　Convert to kelvin, cubic metres and pascals before substituting, then convert the answer back to the units asked for.

01　Paper details (check answers afterwards)

Item	Detail
Questions	10
Suggested time	25
Difficulty mix	Foundation 4 · Intermediate 3 · Challenge 2 · Error redo 1
Chapter	Chapter: S5 Physics: Gas Laws
Level	Four basic, three advanced, two challenge and one error-repair item

02　Questions (10 items)

Foundation1.5 mol of an ideal gas is at 300 K and 100 kPa. Find its volume, with R as 8.31.
Foundation2 mol of an ideal gas occupies 0.02 cubic metres at 250 K. Find the pressure.
FoundationAt constant pressure 2 L of gas is heated from 300 K to 450 K. Find the new volume.
FoundationAt constant volume a gas is at 200 kPa and 300 K. Find the pressure at 250 K.
IntermediateA gas of 0.05 cubic metres at 150 kPa and 300 K is compressed to 0.02 cubic metres at 400 K. Find the new pressure.
Intermediate32 g of oxygen, molar mass 32 g per mol, is at 300 K and 1.0 times ten to the five pascals. Find the volume.
IntermediateA sealed bottle holds gas at 2.0 times ten to the five pascals at 27 C. Find the pressure at 127 C.
ChallengeA bubble of 1 cubic centimetre sits 20 m under water, where the pressure is atmospheric plus rho g h with g as 10. Find its volume at the surface at constant temperature.
ChallengeA tyre is at 220 kPa and 25 C, rising to 55 C after a run at constant volume. Find the new pressure.
Error redoA student substitutes 27 for 300 in pV equals nRT and gets 4.5 L for 2 mol at 27 C and 1.0 times ten to the five pascals. What is the correct volume?

03　Answers and one-line notes

#	Answer	One-line note
1	0.0374 cubic metres, that is 37.4 L	From pV equals nRT the volume is 1.5 times 8.31 times 300 over 100000, about 0.0374 cubic metres.
2	207750 Pa, about 207.8 kPa	Pressure is nRT over V, so two times 8.31 times 250 over 0.02 gives 207750 pascals.
3	3 L	At constant pressure volume over temperature is fixed, so 2 times 450 over 300 gives 3 L.
4	166.7 kPa	At constant volume pressure over temperature is fixed, so 200 times 250 over 300 is about 166.7 kPa.
5	500 kPa	The combined gas law gives 150 times 0.05 times 400 over 0.02 times 300, that is 500 kPa.
6	0.0249 cubic metres, that is 24.9 L	Thirty two grams of oxygen is one mole, so the volume is 8.31 times 300 over 100000, about 24.9 L.
7	2.67 times ten to the five pascals	Volume is fixed, so 300 K becomes 400 K and the pressure rises to about 2.67 times ten to the five pascals.
8	3 cubic centimetres	The pressure at depth is 100000 plus 1000 times 10 times 20, that is 300000 pascals, so the bubble expands three times, to 3 cubic centimetres.
9	242.1 kPa	Kelvin must be used, so 298 K becomes 328 K and the pressure rises to about 242.1 kPa.
10	0.0499 cubic metres, that is 49.9 L	The gas equation needs kelvin, so 300 K gives about 49.9 litres rather than 4.5 litres.

04　What to do after marking

After marking, redo only the wrong items and write down which step went wrong (formula, unit, or misread number).
Repeat the same item two days later; move to the next paper only when both attempts are correct.
Parents only need the answer and note columns; there is no need to explain every item.

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Questions and answers are written originally by the TutorZone team and are not taken from any school, publisher or examination authority paper. Every value is checked by computer.