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

Kinetic theory of gases — practice question

Hydrogen gas is made up of molecules, and each molecule has a mass of $3.34 \times 10^{-27}\,\text{kg}$. Hydrogen can be treated as an ideal gas. A spherical balloon holds $0.0160\,\text{mol}$ of hydrogen gas at a temperature of $282\,\text{K}$. At this temperature, the gas volume in the balloon is $1.87 \times 10^{-4}\,\text{m}^{3}$.
(a)[2]

State Newton’s law of gravitation in words.

(b)[2]

According to one basic assumption of the kinetic theory of gases, no forces act between gas molecules except during collisions. State two other basic assumptions of the kinetic theory of gases.

(c(i))[2]

Determine the gas pressure.

(c(ii))[2]

Estimate the mean separation of the hydrogen molecules in the gas.

(d(i))[2]

Use your answer in (c)(ii) to calculate the mean gravitational force between neighbouring molecules in hydrogen gas.

(d(ii))[1]

Using the weight of a molecule as a guide, suggest with a reason whether your answer in (d)(i) agrees with the kinetic theory of gases assumption that there are no forces exerted between molecules.

Worked solution & mark scheme

This 11-mark question has a full step-by-step worked solution and mark scheme. One marking point: “(gravitational) force varies directly with the product of the masses” …

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