Chemistry 9701 · AS & A Level · Atoms, molecules and stoichiometry

Atoms, molecules and stoichiometry — practice question

Changes in temperature and pressure influence the rate of chemical reactions.
(a(i))[2]

On the axes, draw a curve to represent the Boltzmann distribution of energy for particles in a sample of gaseous krypton atoms at a fixed temperature. Mark the curve $T1$ and label the axes.

(a(ii))[1]

In (a)(i), draw a second curve on the diagram to show the energy distribution of the krypton atoms at a higher temperature. Label the second curve $T2$.

(b(i))[2]

State two assumptions made by the kinetic theory when it is applied to an ideal gas.

(b(ii))[3]

A mass of 2.00 g of krypton gas, $\text{Kr}(g)$, is put into a sealed $5.00\ \text{dm}^3$ container at $120\,^{\circ}\text{C}$. Calculate the pressure, in Pa, of $\text{Kr}(g)$ in the container. Assume $\text{Kr}(g)$ behaves as an ideal gas. Show your working.

(b(iii))[2]

State and explain the conditions under which krypton behaves most like an ideal gas.

(c(i))[2]

Krypton reacts with fluorine under ultraviolet light to form krypton difluoride, $\text{KrF}_2(g)$. The reaction is $\text{Kr}(g) + \text{F}_2(g) \rightarrow \text{KrF}_2(g)$. The activation energy is $E_a = +385\ \text{kJ mol}^{-1}$ and the enthalpy change of formation of $\text{KrF}_2$ is $\Delta H_f = +60.2\ \text{kJ mol}^{-1}$. Use these details to complete the reaction profile diagram for the formation of $\text{KrF}_2$. Put labels for $E_a$ and $\Delta H_f$ on the diagram. Assume the reaction happens in one step.

(c(ii))[2]

Explain, in terms of activation energy, $E_a$, and the collision of particles, how an increase in temperature affects the rate of a chemical reaction.

Worked solution & mark scheme

This 14-mark question has a full step-by-step worked solution and mark scheme. One marking point: Correctly shaped Maxwell-Boltzmann distribution curve

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