CAIE A-Level Physics 15.2.2 Ideal-Gas Equations of State

Practise choosing pV = nRT or pV = NkT for the data given, calculating gas variables and converting temperature, pressure and volume units consistently.

Exam points

calculate pressure, volume, temperature, amount of substance or molecule number using pV = nRT or pV = NkT
rearrange the ideal-gas equations and convert temperature, pressure and volume units consistently
choose between the mole and molecule forms of the equation of state for the data given

[Maximum number: 3]

A sealed vessel contains a mass of 0.0424 kg of an ideal gas at $227^{\circ} \mathrm{C}$ . The pressure of the gas is $1.37 \times 10^{5} \mathrm{~Pa}$ and the volume of the gas is $0.640 \mathrm{~m}^{3}$ .

Calculate:

the number of molecules of the gas in the vessel

p V=N k T

C1

$N=\left(1.37 \times 10^{5} \times 0.640\right) /\left(1.38 \times 10^{-23} \times(227+273)\right)$

C1

$=1.27 \times 10^{25}$

A1

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15.2.2—The equation of state for an ideal gas expressed as pV = nRT question 1