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

Kinetic theory of gases — practice question

(a)[2]

Define the term specific heat capacity.

(b)

An ideal gas consisting of $N$ molecules, each with mass $m$, is enclosed in a sealed container of fixed volume $V$ and has pressure $p$.

(b(i))[1]

State an expression for the thermodynamic temperature $T$ of the gas, in terms of $V$, $N$, $p$ and the Boltzmann constant $k$.

(b(ii))[2]

Show that the mean translational kinetic energy $E_{K}$ of one molecule of the gas is $E_{K} = \frac{3}{2}kT$.

(b(iii))[2]

Explain why the internal energy of the gas is equal to the total kinetic energy of its molecules.

(c)

In part (b), the gas receives thermal energy $Q$.

(c(i))[2]

Explain, using the first law of thermodynamics, why the increase in internal energy of the gas is $Q$.

(c(ii))[2]

Use the expression in (b)(ii) together with the information in (c)(i) to show that the specific heat capacity $c$ of the gas is $c = \frac{3k}{2m}$.

(d)[2]

The container in (b) is now changed to one with no fixed volume. The gas can therefore expand, so its pressure stays constant while thermal energy is supplied. Suggest, with a reason, how the specific heat capacity of the gas would compare with the value in (c)(ii).

Worked solution & mark scheme

This 13-mark question has a full step-by-step worked solution and mark scheme. One marking point: thermal energy needed per unit mass

  • Full mark scheme, point by point
  • Step-by-step worked solution
  • Write your answer & get it marked instantly by AI