AQA GCSE Combined Science Chemistry- Energy changes paper 1

What is an exothermic reaction?

A reaction that releases energy to the surroundings, usually as heat.

What happens to temperature in an exothermic reaction?

It increases.

Give examples of exothermic reactions.

Combustion, neutralisation, some oxidation reactions.

What is an endothermic reaction?

A reaction that absorbs energy from the surroundings.

What happens to temperature in an endothermic reaction?

It decreases.

Give examples of endothermic reactions.

Thermal decomposition, reaction between citric acid and sodium hydrogen carbonate.

What is activation energy?

The minimum energy needed for particles to react.

What is the energy profile of an exothermic reaction like?

Products have less energy than reactants; energy is released.

What is the energy profile of an endothermic reaction like?

Products have more energy than reactants; energy is taken in.

What is bond breaking?

Endothermic – energy is required to break bonds.

What is bond making?

Exothermic – energy is released when new bonds form.

What is the overall energy change of a reaction? (formula)

Energy in – Energy out

What does a negative energy change mean?

The reaction is exothermic.

What does a positive energy change mean?

The reaction is endothermic.

What is the unit of energy change?

kJ/mol

What is a simple cell?

A system made of two different metals in an electrolyte that produces electricity.

How does a cell work?

The more reactive metal gives up electrons more easily, creating a flow of electricity.

What affects the voltage of a cell?

The difference in reactivity between the metals.

What does a negative energy change mean?

The reaction is exothermic.

Why does a cell stop working over time?

The reactants get used up or the ions in the electrolyte are used.

What are common errors in the temperature change practical?

• Heat loss to surroundings

• Inaccurate thermometer readings

• Delayed temperature measurements

How can accuracy be improved in this practical?

• Use insulation (e.g. polystyrene cup)

• Use a lid

• Read thermometer quickly and carefully

Why are exothermic reactions useful in real life?

self heating cans and hand warmers

Why are endothermic reactions useful in real life?

They’re used in sports injury packs to absorb heat and reduce swelling.

Why is activation energy needed in a reaction?

To break the initial bonds so the reaction can start.