Chemistry 0620 · IGCSE · Reversible reactions and equilibrium
Reversible reactions and equilibrium — practice question
Hydrogen iodide, HI, breaks down into iodine and hydrogen, and the reaction can proceed in both directions.
$\text{2HI(g)} \rightleftharpoons \text{I}_2\text{(g)} + \text{H}_2\text{(g)}$
A sealed gas syringe held a mixture of hydrogen iodide, iodine and hydrogen gases. When equilibrium was reached, the mixture had a pale purple colour.
(a)[2]
State what the term equilibrium means.
(b(i))[1]
Explain why the equilibrium position stays unchanged.
(b(ii))[1]
Suggest why the gaseous mixture turns darker purple even though the equilibrium position does not change.
(c(i))[1]
State what happens to the equilibrium position when the temperature is decreased.
(c(ii))[2]
State what happens to the rate of the forward reaction and the rate of the backward reaction when the temperature of the mixture is reduced.
Worked solution & mark scheme
This 7-mark question has a full step-by-step worked solution and mark scheme. One marking point: “forward reaction rate equals reverse reaction rate” …