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

Kinetic theory of gases — practice question

(a)[1]

Use one assumption of the kinetic theory of gases to explain why the molecules of an ideal gas have zero potential energy.

(b(i))[1]

The mean translational kinetic energy $E_{K}$ of one molecule of an ideal gas is written as $E_{K} = \frac{1}{2} m\langle c^{2} \rangle = \frac{3}{2}kT$, where $m$ is the mass of a molecule and $k$ is the Boltzmann constant. State what the symbol $\langle c^{2} \rangle$ means.

(b(ii))[1]

State the meaning of $T$ in the expression $E_{K} = \frac{1}{2} m\langle c^{2} \rangle = \frac{3}{2}kT$.

(c(i).1)[3]

An iron cylinder of fixed volume $4.7 \times 10^{4}\,\text{cm}^{3}$ contains an ideal gas at pressure $2.6 \times 10^{5}\,\text{Pa}$ and temperature $173^{\circ}\text{C}$. The gas is heated, and $2900\,\text{J}$ of thermal energy is transferred to it. Calculate the number $N$ of molecules in the cylinder.

(c(i).2)[1]

Calculate the rise in average kinetic energy of one molecule during the heating process.

(c(ii))[3]

Use your answer in part (c)(i).2 to determine the final temperature $T$, in kelvin, of the gas in the cylinder.

(i)[1]

Find the increase in average kinetic energy of one molecule during the heating process.

(ii)[3]

Use your answer in (i) part 2 to determine the final temperature $T$, in kelvin, of the gas in the cylinder.

Worked solution & mark scheme

This 14-mark question has a full step-by-step worked solution and mark scheme. One marking point: no intermolecular forces (therefore no potential energy)

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