Physics 9702 · AS & A Level · Kinetic theory of gases

Kinetic theory of gases — practice question

The pressure $p$ multiplied by the volume $V$ of an ideal gas is described by $pV = \frac{1}{3}Nm\langle c^{2} \rangle$, where $m$ is the mass of a single molecule of the gas.
(a(i))[1]

State what the symbol $N$ stands for.

(a(ii))[1]

State what is meant by the symbol $\langle c^{2} \rangle$.

(b)[2]

The quantity $pV$ is also represented by $pV = NkT$. Deduce an expression for the mean kinetic energy of a molecule of the ideal gas, in terms of the Boltzmann constant $k$ and the thermodynamic temperature $T$.

(c(i))[2]

A cylinder holds $1.0\ \text{mol}$ of an ideal gas. The cylinder volume stays fixed. Calculate the energy needed to increase the gas temperature by $1.0\ \text{kelvin}$.

(c(ii))[2]

The cylinder volume is now free to increase so that, on heating, the gas stays at constant pressure. Explain whether the energy needed to raise the gas temperature by $1.0\ \text{kelvin}$ is now different from your answer in (i).

Worked solution & mark scheme

This 8-mark question has a full step-by-step worked solution and mark scheme. One marking point: $N$ denotes the total number of molecules

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