Solid R is orange. Gases S and T are colourless.
R(s)⇌S(g)+T(g) \mathrm{R(s) \rightleftharpoons S(g) + T(g)} R(s)⇌S(g)+T(g)The forward reaction is endothermic. A sealed container holding all three substances at equilibrium is warmed and allowed to reach a new equilibrium.
What is observed?
The amount of orange solid stays the same, because temperature does not affect solids.
Less orange solid remains, because the endothermic forward reaction is favoured.
More orange solid forms, because the exothermic reverse reaction is favoured.
All of the orange solid disappears, because the forward reaction goes to completion.
124 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.