Chemical Energetics Revision Notes

Vocabulary flashcards covering key definitions, principles, and industrial processes from GCSE / IGCSE Chemical Energetics revision notes.

Physical Change

A change in which no new substance forms and that is often reversible, such as melting or boiling.

Chemical Change

A change in which one or more new substances form, atoms are rearranged, and chemical bonds are broken and formed; it is often difficult to reverse.

Exothermic Reaction

A reaction that transfers energy to the surroundings, causing the surroundings to warm up, where $\Delta H$ is negative (e.g., combustion, neutralisation, and many oxidation reactions).

Endothermic Reaction

A reaction that takes in energy from the surroundings, causing the surroundings to cool down, where $\Delta H$ is positive (e.g., thermal decomposition and some dissolving reactions).

Enthalpy Change ($\Delta H$)

The energy change of a reaction, usually measured in $kJ/mol$, calculated as $\Delta H = \text{energy in} - \text{energy out}$.

Activation Energy ($E_a$)

The minimum energy particles need for a reaction to occur.

Bond Breaking

An endothermic process that requires energy.

Bond Making

An exothermic process that releases energy.

Collision Theory

A theory stating that particles must collide with enough energy and the correct orientation for a chemical reaction to occur.

Catalyst

A substance that provides an alternative pathway with lower activation energy and is not used up, speeding up both forward and backward reactions equally without changing the equilibrium position or overall energy change.

Reversible Reaction

A reaction that can proceed in both forward and backward directions.

Dynamic Equilibrium

A state established in a closed system when the forward and reverse reactions happen at equal rates, keeping concentrations constant while reactions continue.

Le Chatelier’s Principle

The principle stating that if conditions change in a system at equilibrium, the equilibrium shifts to oppose the change.

Haber Process

An industrial process that synthesizes ammonia from nitrogen and hydrogen using an iron catalyst, balancing rate, yield, and cost with moderate temperature and high pressure.

Contact Process

A reversible and exothermic industrial process that makes sulfur trioxide from sulfur dioxide and oxygen using a vanadium(V) oxide catalyst.