Chemistry definitions
AQA chemistry is a sneaky bitch when it asks you to define something, it’s not a matter of thinking and actually defining, it’s a matter or memorisation. I picked these definitions from mark schemes here and there, they may not be exact as AQA does give a bit of flexibility, but they should be correct. I put marks for the points, so if you’re asked for a 2 mark definition, try and say a bit more than a 1 mark one here.
Unit 1
To be constructed.
Unit 2
Reduction: a gain of electrons (1)
Reducing agent: something that donates electrons (1)
Polymerisation: the joining together of monomers (1) to form long chains (1)
Electrophile: electron pair acceptor (1)
Addition: reaction which increases number of substituents (1)
Dehydration: the elimination of water from a compound (1)
Structural isomers: compounds with the same molecular formula (1) but different structural formulae (1)
Position isomers: compounds with the same molecular formula (1) but different structures due to different positions of the same functional group on the same carbon skeleton (1)
Biofuel: a fuel made from plants or organic matter (1)
Oxidation: loss of electrons (1)
Oxidation state: the charge on the ion or element or atom (1)
Oxidising agent: a substance which accepts electrons (1)
Dynamic equilibrium: rate of forward reaction = rate of backward reaction (1) concentrations of reactants and products remain constant (1)
Compromise temperature: balance between rate and yield (1)
Activation energy: minimum energy (1) to start a reaction (1)
Catalyst: speeds up a reaction but is chemically unchanged at the end (1)
Mean bond enthalpy: enthalpy to break a covalent bond (1) varies between compounds so average value used (1)
Standard enthalpy of formation: enthalpy change when 1 mol of compound (1) is formed from its elements (1) all substances in their standard states (1)
Standard enthalpy of combustion: enthalpy change when 1 mol of a substance (1) is completely burned in oxygen (1) under standard conditions (1)
Enthalpy change: heat energy change (1) under constant pressure (1)
Stereoisomers: compounds with the same structural formula (1) but a different arrangement of atoms in space (1)
Rate of reaction: the change in concentration per unit of time (1)
Nucleophile: an electron pair donor (1)
Carbon neutral: an activity which has no net carbon emissions to the atmosphere (1)
Hess’s Law: enthalpy change is independent of the route taken (1)
Unit 3 is the ISA, so no specific definitions.
Reducing agent: something that donates electrons (1)
Polymerisation: the joining together of monomers (1) to form long chains (1)
Electrophile: electron pair acceptor (1)
Addition: reaction which increases number of substituents (1)
Dehydration: the elimination of water from a compound (1)
Structural isomers: compounds with the same molecular formula (1) but different structural formulae (1)
Position isomers: compounds with the same molecular formula (1) but different structures due to different positions of the same functional group on the same carbon skeleton (1)
Biofuel: a fuel made from plants or organic matter (1)
Oxidation: loss of electrons (1)
Oxidation state: the charge on the ion or element or atom (1)
Oxidising agent: a substance which accepts electrons (1)
Dynamic equilibrium: rate of forward reaction = rate of backward reaction (1) concentrations of reactants and products remain constant (1)
Compromise temperature: balance between rate and yield (1)
Activation energy: minimum energy (1) to start a reaction (1)
Catalyst: speeds up a reaction but is chemically unchanged at the end (1)
Mean bond enthalpy: enthalpy to break a covalent bond (1) varies between compounds so average value used (1)
Standard enthalpy of formation: enthalpy change when 1 mol of compound (1) is formed from its elements (1) all substances in their standard states (1)
Standard enthalpy of combustion: enthalpy change when 1 mol of a substance (1) is completely burned in oxygen (1) under standard conditions (1)
Enthalpy change: heat energy change (1) under constant pressure (1)
Stereoisomers: compounds with the same structural formula (1) but a different arrangement of atoms in space (1)
Rate of reaction: the change in concentration per unit of time (1)
Nucleophile: an electron pair donor (1)
Carbon neutral: an activity which has no net carbon emissions to the atmosphere (1)
Hess’s Law: enthalpy change is independent of the route taken (1)
Unit 3 is the ISA, so no specific definitions.
Unit 4
Racemic mixture: equal mixture of enantiomers (1)
Brønsted-Lowry acid: proton donor (1)
Weak acid: slightly dissociated (1)
This list is relatively incomplete.
Brønsted-Lowry acid: proton donor (1)
Weak acid: slightly dissociated (1)
This list is relatively incomplete.
Unit 5
Bidentate ligand: two atoms each donating a lone pair or electron pair (1)
Autocatalytic: a product of the reaction acts as a catalyst (1)
Heterogeneous: catalyst in a different phase from that of the reactants (1)
Ligand: a species which can donate a pair of electrons to a metal ion (1)
Co-ordinate bond: a covalent bond (1) in which both electrons are donated by one atom (1)
Homogeneous: a catalyst in the same phase as the reactants (1)
Autocatalysis: a reaction in which a product acts as a catalyst (1)
Electronegativity: the ability of an atom or element to attract electrons or electron density (1) from a covalent bond (1)
This list is relatively incomplete.
Unit 6 is the ISA, so no specific definitions.
Autocatalytic: a product of the reaction acts as a catalyst (1)
Heterogeneous: catalyst in a different phase from that of the reactants (1)
Ligand: a species which can donate a pair of electrons to a metal ion (1)
Co-ordinate bond: a covalent bond (1) in which both electrons are donated by one atom (1)
Homogeneous: a catalyst in the same phase as the reactants (1)
Autocatalysis: a reaction in which a product acts as a catalyst (1)
Electronegativity: the ability of an atom or element to attract electrons or electron density (1) from a covalent bond (1)
This list is relatively incomplete.
Unit 6 is the ISA, so no specific definitions.
