An exothermic reaction is one that transfers energy to the surroundings so…

The idea

An exothermic reaction transfers energy to the surroundings, causing a temperature rise. This occurs because the energy released when new bonds form in the products is greater than the energy absorbed when bonds break in the reactants. The excess energy is transferred to the surroundings, often as heat, which increases the temperature. Common examples include combustion, respiration, and neutralisation. They should also be able to represent the energy change on a reaction profile diagram, with products at a lower energy level than reactants.

What earns the marks

• Defines an exothermic reaction as one that transfers energy to the surroundings.
• States that the temperature of the surroundings increases.
• Explains that bond making releases more energy than bond breaking absorbs.
• Identifies examples of exothermic reactions, such as combustion or neutralisation.
• Uses a reaction profile diagram to show products at a lower energy level than reactants.

Common mistakes and how to put them right

• Confusing exothermic with endothermic.

  Put it right by remembering exothermic releases energy and raises temperature.

• Thinking the temperature of the reaction mixture always increases.

  Put it right by noting the surroundings increase in temperature, which may include the mixture itself.

• Believing energy is created.

  Put it right by stating energy is transferred from the chemical store to the thermal store of the surroundings.

Exam tips

• Use the term 'transfers energy to the surroundings' rather than 'releases energy' alone.
• Link temperature increase to the surroundings, not just the reaction mixture.
• When drawing reaction profiles, ensure the products line is lower than the reactants line for exothermic reactions.