R1 - R3 Definitions

(currently only R3)

Exothermic

A reaction in which energy is transferred from the system to the surroundings

Endothermic

A reaction in which energy is transferred from the surroundings to the system

Specific heat capacity

The amount of energy required to increase the temperature of a 1 kg substance by 1 degree K (or C)

Standard enthalpy change of combustion (2 marks!)

The enthalpy change when 1 mole of substance burns (combines vigorously with oxygen) under standard conditions

Standard enthalpy change of reaction (2 marks!)

The enthalpy change when molar quantities of reactants in their standard states react to form products in their standard states under standard conditions

Standard enthalpy change of formation (2 marks!)

The enthalpy change when 1 mole of a substance in the standard state (1 atm of pressure and 298.15 K) is formed from its pure elements under the same conditions

Standard enthalpy change of neutralisation (2 marks!)

The enthalpy change when solutions of an acid and alkali react together under standard conditions to produce 1 mole of water

Hess’ law

States that the total enthalpy change in a chemical reaction is independent of the route by which the chemical reaction takes place, as long as the initial and final conditions are the same

Bond enthalpy

The energy required to break 1 mole of chemical bonds in the gaseous state

Average bond enthalpy

The enthalpy change when 1 mole of molecules is broken in the gaseous state and averaged for the bond in similar compounds

(In)complete combustion

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Standard enthalpy of atomisation

The enthalpy change when 1 mole of an element in its standard state is atomised to produce 1 mole of gaseous atoms

Standard enthalpy change of hydration

The enthalpy change when 1 mole of gaseous ions is dissolved in water to give 1 mole of aqueous ions and a solution of indefinite dilution

Standard enthalpy change of solution

The enthalpy change when 1 mole of an ionic substance is dissolved sufficient water to form an indefinite dilution

Entropy

A measure of the amount of disorder of the particles in a system.

Gibbs free energy

The energy associated with a chemical reaction that can be used to do work, and is equal to ΔH−TΔS where enthalpy is H, T is temperature in K, and S is the entropy of the system