3.2. Physical Chemistry: Module 3: Periodic Table and Energy: Chemistry OCR A A Level

Enthalpy Change

Enthalpy change is heat energy change and is represented by the symbol ∆H^Ө.

Enthalpy

Enthalpy is measured under standard conditions of 100 kPa pressure and a specified temperature, generally 298 K.

Activation energy

Activation energy is the minimum energy required for a reaction to take place between two colliding reactant particles.

Calorimetry

Calorimetry is an experimental method for finding enthalpy change, which works by measuring temperature change over time.

Hess’s law

Hess’s law can be used to calculate an enthalpy change using given enthalpies of formation.

Catalysts

Catalysts are used in industry because they lower the energy costs of the reaction process.

Homogeneous Catalysts

Homogeneous catalysts are catalysts that are in the same phase as the reactants.

Heterogeneous Catalysts

Heterogeneous catalysts are catalysts that are in a different phase to the species in the reaction.

Reversible reactions

Reversible reactions are reactions in which the products of a reaction can react together to reform the original reactants.