Hydrogen iodide is made by reacting hydrogen gas with iodine gas in a closed container at 450 °C.
H2(g)+I2(g)⇌2HI(g) \mathrm{H_{2}(g) + I_{2}(g) \rightleftharpoons 2HI(g)} H2(g)+I2(g)⇌2HI(g)The forward reaction is exothermic.
Iodine gas is purple. Hydrogen gas and hydrogen iodide gas are colourless.
The mixture reaches dynamic equilibrium. The purple colour then stays the same.
Explain why the colour stays the same, even though reactions are still happening.
Predict the effect of increasing the pressure on the position of equilibrium.
Explain your answer.
The temperature of the equilibrium mixture is increased to 550 °C. The volume of the container is kept the same.
Predict how the colour of the mixture changes. Explain your answer.
A catalyst is added to a new mixture of hydrogen and iodine at 450 °C.
State and explain the effect of the catalyst on the position of equilibrium and on the time taken to reach equilibrium.
47 exam-style questions on OCR GCSE Chemistry 5.3 Equilibria, covering 5.3.1 Reversible reactions and dynamic equilibrium and 5.3.2 Changing the position of equilibrium. Each one has a worked solution and a mark scheme showing where the marks go.