OCR A Level Chemistry
Definitions 2026 | Key
Terms, Concepts &
Complete Exam Revision
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Guide
Updated 2026 Questions and Answers
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Rationales
Included
, Activation Energy The minimum energy required to start a reaction by breaking bonds in the reactants
Addition Polymer A very long molecular chain formed by repeated addition reactions of many
unsaturated alkene molecules
Addition Reaction A reaction in which a reactant is added to an unsaturated molecule to make a
saturated molecule
Acid Dissociation Constant Ka= [H+(aq)][A-(aq)]/[HA(aq)]
Aliphatic Hydrocarbon A hydrocarbon where carbon atoms are joined together in straight or branched
chains
Alkali A base that dissolves in water forming OH- ions
Alkanes The homologous series with general formula CnH2n+2
Alkylammonium salt A compound where the hydrogen's on an ammonium ion have been substituted by
alkyl chains
Alkylation Addition of hydrocarbon chains to an organic compound
Alkyl group An alkane with a hydrogen atom removed e.g. CH3, C2H5
Amide A compound with a functional group made of an alcyl group, which is directly
attached to an amine
Amphoteric chemicals Chemicals that can react with both acids and bases
Anion A negatively charged ion
Anhydrous A substance that contains no water molecules
Definitions 2026 | Key
Terms, Concepts &
Complete Exam Revision
Guide
| Complete Ethics Study
Guide
Updated 2026 Questions and Answers
100% Verified Exam Prep and Comprehensive
Rationales
Included
, Activation Energy The minimum energy required to start a reaction by breaking bonds in the reactants
Addition Polymer A very long molecular chain formed by repeated addition reactions of many
unsaturated alkene molecules
Addition Reaction A reaction in which a reactant is added to an unsaturated molecule to make a
saturated molecule
Acid Dissociation Constant Ka= [H+(aq)][A-(aq)]/[HA(aq)]
Aliphatic Hydrocarbon A hydrocarbon where carbon atoms are joined together in straight or branched
chains
Alkali A base that dissolves in water forming OH- ions
Alkanes The homologous series with general formula CnH2n+2
Alkylammonium salt A compound where the hydrogen's on an ammonium ion have been substituted by
alkyl chains
Alkylation Addition of hydrocarbon chains to an organic compound
Alkyl group An alkane with a hydrogen atom removed e.g. CH3, C2H5
Amide A compound with a functional group made of an alcyl group, which is directly
attached to an amine
Amphoteric chemicals Chemicals that can react with both acids and bases
Anion A negatively charged ion
Anhydrous A substance that contains no water molecules
