is a type of reaction in which energy is transferred from the reactants to the surroundings, e.g. combustion.

is a type of reaction in which energy from the surroundings is transferred to the products, e.g. photosynthesis.

Thermal energy can dissipate which means it can be transferred to the environment and wasted.

Exothermic and endothermic chemical reactions

Science

In the Carbon Cycle and Climate Change unit, pupils will build on their understanding of fuels and energetics to learn about the carbon cycle and the impact of human activity on climate.

In the Understanding chemical reactions unit, pupils learnt about how atoms move around to form new substances in chemical reactions and about some common types of chemical reactions.

This unit examines energy changes in state, exothermic and endothermic reactions, and energy transfers in various processes. It emphasises objectivity, accuracy, and precision in scientific enquiries, data interpretation, and the use of tables, graphs, and reliable methods.

Fuels and energetics

Physical activity and equipment requiring safe use

energy is transferred from the reactants to the surroundings

energy from the surroundings is transferred to the products

energy is transferred (and lost) as 'heat' to the environment

Match the following terms to their definitions.

an increase in temperature of the surroundings.

a decrease in temperature of the surroundings.

the temperature of the surroundings to remain the same.

Which of the following are reactions that are usually exothermic?

Measure 100 cm³ of copper sulfate solution into a polystyrene beaker. 

Stir the solution until all of the ammonium nitrate has dissolved.

Measure the temperature of the reaction mixture.

Record the lowest temperature reached by the solution.

The method for finding the lowest temperature of a reaction has been mixed up.
Starting with measuring the volume of solution, sort the following steps into the correct order.

The difference in temperature is –5 °C.

Energy is transferred from the surroundings to the products.

The temperature of the surroundings increased.

A pupil monitored the temperature of a reaction. The start temperature was 20°C and the end temperature 15°C. 
Which of the following statements about the reaction are correct?

True or false? After an exothermic reaction, the products of the reaction contain more energy than the reactants.

substance present at the start of a chemical reaction

substance made during a chemical reaction

when chemical bonds are broken and new substances are formed

a reversible process that does not involve breaking chemical bonds

True or false? A change of state indicates that a chemical reaction has taken place.

Which of the following are examples of chemical reactions?

magnesium + hydrochloric acid → magnesium chloride + hydrogen

magnesium chloride + hydrogen → magnesium + hydrochloric acid

magnesium chloride + hydrochloric acid → magnesium + hydrogen

hydrochloric acid + hydrogen → magnesium + magnesium chloride

Hydrogen gas and magnesium chloride are formed when magnesium reacts with hydrochloric acid. 
Which of the following represents the chemical equation for the reaction?

Burning is an example of ...
Select two correct answers. 

Calculate the mass of carbon dioxide formed when 13.5 g of calcium carbonate reacts to form 7.6 g of calcium oxide. 
calcium carbonate → calcium oxide + carbon dioxide

Content guidance

Risk assessment required - equipment

Adult supervision required

Starter Quiz