Chemistry 9701 · AS & A Level · Group 17

Group 17 — practice question

The Group VII elements chlorine, bromine and iodine each form a hydride.
(a(i))

Outline how the relative thermal stabilities of these hydrides vary from HCl to HI.

(a(ii))[3]

Explain the variation you outlined in (i).

(b)[2]

Hydrogen iodide is produced by heating hydrogen gas with iodine vapour, but the reaction is incomplete.\n\n$\text{H}_2(g) + \text{I}_2(g) \rightleftharpoons 2\text{HI}(g)$\n\nWrite an expression for $K_c$ and state the units.

(c(i))

For this equilibrium, the equilibrium constant $K_c$ is $140$ at $500\,\text{K}$ and $59$ at $650\,\text{K}$.\n\nUse this information to state and explain the effect of increasing the pressure on the equilibrium.

(c(ii))[4]

For this equilibrium, the equilibrium constant $K_c$ is $140$ at $500\,\text{K}$ and $59$ at $650\,\text{K}.\n\nUse this information to state and explain the effect of decreasing the temperature of the equilibrium.

(d)[4]

A mixture containing $0.02\,\text{mol}$ of hydrogen and $0.02\,\text{mol}$ of iodine was put into a $1\,\text{dm}^3$ flask and left until equilibrium was reached at $650\,\text{K}$. Calculate the amount, in moles, of each substance in the equilibrium mixture at $650\,\text{K}$ for $\text{H}_2(g)+\text{I}_2(g) \rightleftharpoons 2\text{HI}(g)$.

Worked solution & mark scheme

This 13-mark question has a full step-by-step worked solution and mark scheme. One marking point: Thermal stability falls down Group VII

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