AQA A2 Chemistry Unit 5 Key Definitions
- 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
Standard Enthalpy Change
The change in enthalpy when reactants in their standard states form products that are also in their standard states
Standard State
The standard state of a substance at a given temperature is its pure, most stable form at 100kPa
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
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
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
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
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
Electron Affinity
The standard enthalpy change when an electron is added to an isolated atom in the gas phase
Enthalpy of Lattice Dissociation
The standard enthalpy change that accompanies the separation of one mole of a solid ionic lattice into its gaseous ions
Enthalpy of Lattice Formation
The standard enthalpy change that accompanies the formation of one mole of solid ionic lattice from its gaseous ions
Standard Enthalpy of Hydration
The standard molar enthalpy change for the formation of aqaueous ions from gaseous ions
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
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
Spontaneous Change
A spontaneous change is one that has a nattural tendency to occur without being driven by any external influences
Amphoteric Oxide
A amphoteric oxide is capable of reacting with both acids and bases
Oxidation
Is the loss of electrons
Reduction
Is the gain of electrons
Standard Electromotive Force (e.m.f)
The potential difference between the electrodes of a standard electrochemical cell measured under zero-current conditions
Transition Element
An element having an incomplete d sub-level either in the element or in one of its common ions
Ligand
A ligand is any atom, ion or molecule which can donate a pair of electrons to a metal ion
Co-ordination Number
The number of atoms bonded to a metal ion is the co-ordination number
Heterogeneous Catalyst
A catalyst which acts in a different phase from the reactants
Homogeneous Catalyst
A catalyst which is in the same phase as the reactants
Lewis - Acid
An electron pair acceptor
Lewis - Base
An electron pair donor
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