AQA GCSE Chemistry (Triple) - Paper 1 Exam-Style Flashcards: Topic 5 - Energy Changes

Vocabulary flashcards covering key concepts from the AQA GCSE Chemistry curriculum on energy changes.

Exothermic Reaction

A reaction that transfers energy to the surroundings, usually as heat — temperature increases.

Examples of Exothermic Reactions

Combustion and neutralisation reactions.

Endothermic Reaction

A reaction that takes in energy from the surroundings — temperature decreases.

Examples of Endothermic Reactions

Thermal decomposition and the reaction between citric acid and sodium hydrogencarbonate.

How can energy changes be detected?

By measuring the temperature change of the surroundings.

Reaction Profile

A diagram showing the relative energies of reactants and products and the activation energy.

Exothermic Reaction Profile - Energy Comparison

In an exothermic reaction profile, reactants have more energy than the products.

Endothermic Reaction Profile - Energy Comparison

In an endothermic reaction profile, products have more energy than the reactants.

Activation Energy

The minimum amount of energy required for particles to react.

Energy Difference between Reactants and Products

Represents the overall energy change (∆H) for the reaction.

Bond Breaking

Requires energy to be supplied; bond breaking is endothermic.

Bond Making

Releases energy; bond making is exothermic.

Overall Energy Change Formula

Energy change = Energy in (breaking) − Energy out (making).

Exothermic Reaction Example Calculation

If bond breaking requires 800 kJ and bond making releases 950 kJ, the reaction is exothermic (950 − 800 = −150 kJ → energy released).

Endothermic Reaction Example Calculation

If bond breaking requires 1200 kJ and bond making releases 1000 kJ, the reaction is endothermic (1000 − 1200 = +200 kJ → energy absorbed).

Chemical Cell

A device that uses chemical reactions to produce electricity.

Voltage of a Cell Dependence

Depends on the difference in reactivity between the two electrodes and the electrolyte used.

Non-rechargeable Battery

Over time, the reactants are used up, and the reaction stops.

Rechargeable Cell

Can have its chemical reaction reversed by applying an external electrical current.

Fuel Cell

Produces electricity by reacting a fuel (e.g. hydrogen) with oxygen, without burning it.

Overall Reaction in a Hydrogen Fuel Cell

Hydrogen + Oxygen → Water.

Advantages of Hydrogen Fuel Cells

Produce electricity efficiently, only water as waste, and can be used continuously if supplied with fuel.

Disadvantages of Hydrogen Fuel Cells

Hydrogen is hard to store and can be explosive; often produced from fossil fuels.