Brown nitrogen dioxide and colourless dinitrogen tetroxide are in equilibrium in a sealed tube: 2NO2(g)⇌N2O4(g)\mathrm{2NO_{2}(g) \rightleftharpoons N_{2}O_{4}(g)}2NO2(g)⇌N2O4(g) The forward reaction is exothermic. The tube is moved from water at 25 ∘C25\,^\circ\mathrm{C}25∘C into iced water. What is seen, and why?
It turns paler, because the exothermic forward reaction is favoured
It turns paler, because cooling favours the side with fewer gas molecules
It turns darker, because the endothermic reverse reaction is favoured
It turns darker, because both reactions slow down so less N2O4\mathrm{N_{2}O_{4}}N2O4 forms
45 exam-style questions on Edexcel GCSE Chemistry 5.2 Reversible reactions and equilibria, covering 5.2.1 Reversible reactions and dynamic equilibrium, 5.2.2 The Haber process, and 5.2.3 Changing the position of a dynamic equilibrium. Each one has a worked solution and a mark scheme showing where the marks go.