Calcium carbonate must be heated strongly and continuously to decompose it.
CaCO3→CaO+CO2\mathrm{CaCO_{3} \rightarrow CaO + CO_{2}}CaCO3→CaO+CO2
Which statement about the reverse reaction, CaO+CO2→CaCO3\mathrm{CaO + CO_{2} \rightarrow CaCO_{3}}CaO+CO2→CaCO3, is correct?
It is endothermic, as bonds must be broken before any reaction can happen
It is endothermic, as a reaction and its reverse have the same energy change
It is exothermic, as the energy taken in by the forward change is given out
It is exothermic, as calcium oxide and carbon dioxide only make bonds and break none
94 exam-style questions on Edexcel GCSE Chemistry 8.2 Heat energy changes in chemical reactions, covering 8.2.1 Exothermic and endothermic changes, 8.2.2 Bond breaking, bond making and overall energy change, 8.2.3 Calculating energy change from bond energies, and 8.2.4 Activation energy and reaction profiles. Each one has a worked solution and a mark scheme showing where the marks go.