AQA A2 Chemistry Unit 5 Key Definitions

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  • Created by: Ellie
  • Created on: 22-03-15 15:41

Enthalpy Change

Enthalpy change is the amount of heat taken in or given out at constant pressure during any physical or chemical change

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Standard Enthalpy Change

The change in enthalpy when reactants in their standard states form products that are also in their standard states

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Standard State

The standard state of a substance at a given temperature is its pure, most stable form at 100kPa

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Standard Enthalpy of Formation

The enthalpy change under standard conditions when one mole of a compound is formed from its elements with all reactants and products in their standard states

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Ionisation Enthalpy

Is the standard molar enthalpy change for the removal of an electron from a species in the gas phase to form a positive ion and an electron, both also in the gas phase

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Enthalpy of Atomisation

Is the standard enthalpy change that accompanies the formation of one mole of gaseous atoms from the element in its standard state

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Bond Dissociation Enthalpy

The standard molar enthalpy change that accompanies the breaking of a covalent bond in a gaseous molecule to form two gaseous free radicals

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Free Radical

A species that results from the homolytic fission of a covalent bond. It contains an unpaired electron, since homolytic fission results in the splitting of the electron pair in a covalent bond, one electron going to each partner

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Electron Affinity

The standard enthalpy change when an electron is added to an isolated atom in the gas phase

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Enthalpy of Lattice Dissociation

The standard enthalpy change that accompanies the separation of one mole of a solid ionic lattice into its gaseous ions

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Enthalpy of Lattice Formation

The standard enthalpy change that accompanies the formation of one mole of solid ionic lattice from its gaseous ions

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Standard Enthalpy of Hydration

The standard molar enthalpy change for the formation of aqaueous ions from gaseous ions

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Enthalpy of Solution

The standard enthalpy change that occurs when one mole of an ionic solid dissolves in enough water to ensure that the dissolved ions are well seperated and do not interact with one another

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Mean Bond Enthalpy

The average of several values of the bond dissociation enthalpy for a given type of bond, taken from a range of different compounds

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Spontaneous Change

A spontaneous change is one that has a nattural tendency to occur without being driven by any external influences

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Amphoteric Oxide

A amphoteric oxide is capable of reacting with both acids and bases

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Is the loss of electrons

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Is the gain of electrons

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Standard Electromotive Force (e.m.f)

The potential difference between the electrodes of a standard electrochemical cell measured under zero-current conditions

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Transition Element

An element having an incomplete d sub-level either in the element or in one of its common ions

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A ligand is any atom, ion or molecule which can donate a pair of electrons to a metal ion

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Co-ordination Number

The number of atoms bonded to a metal ion is the      co-ordination number

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Heterogeneous Catalyst

A catalyst which acts in a different phase from the reactants

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Homogeneous Catalyst

A catalyst which is in the same phase as the reactants

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Lewis - Acid

An electron pair acceptor

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Lewis - Base

An electron pair donor

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