Calcium compounds are used in two reactions.
Reaction 1: Calcium carbonate is heated in a lime kiln. It decomposes to make calcium oxide and carbon dioxide.
CaCO3→CaO+CO2 \mathrm{CaCO_{3} \rightarrow CaO + CO_{2}} CaCO3→CaO+CO2Reaction 2: Calcium oxide reacts with water. This reaction is used in some self-heating cans.
CaO+H2O→Ca(OH)2 \mathrm{CaO + H_{2}O \rightarrow Ca(OH)_{2}} CaO+H2O→Ca(OH)2The table shows energy values from the reaction profiles for the two reactions. The energy of the reactants is set at 0 kJ/mol.
| Reaction | Energy of reactants (kJ/mol) | Energy at highest point (kJ/mol) | Energy of products (kJ/mol) |
|---|---|---|---|
| 1 | 0 | +380 | +178 |
| 2 | 0 | +40 | −65 |
Which reaction makes the temperature of the surroundings increase?
Explain your answer.
What is the activation energy for Reaction 1?
Activation energy = ...... kJ/mol
Describe the reaction profile for Reaction 2.
Include the activation energy and the overall energy change, and where their arrows should be drawn.
Explain, in terms of bond breaking and bond making, why Reaction 2 is exothermic.
The lime kiln must be heated strongly the whole time that Reaction 1 is taking place.
Explain why. Use the data in the table.
51 exam-style questions on OCR GCSE Chemistry 3.2 Energetics, covering 3.2.1 Exothermic and endothermic reactions and reaction profiles and 3.2.2 Calculating energy change from bond energies. Each one has a worked solution and a mark scheme showing where the marks go.