AS definitions OCR


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acid A species that is a proton donor.
activation energy The minimum energy required to start a reaction by the breaking of bonds.
addition polymer A very long molecular chain formed by repeated addition reactions of many unsaturated alkene
addition polymerisation The process in which unsaturated alkene molecules (monomers) add on to a growing polymer
a very long saturated molecular chain (the addition polymer).
addition reaction A reaction in which a reactant is added to an unsaturated molecule to make a saturated molecu
adsorption The process that occurs when a gas, liquid or solute is held to the surface of a solid or, more ra
alicyclic hydrocarbon A hydrocarbon with carbon atoms joined together in a ring structure.
aliphatic hydrocarbon A hydrocarbon with carbon atoms joined together in straight or branched chains.
alkali A type of base that dissolves in water forming hydroxide ions, OH­(aq) ions.
alkanes The homologous series with the general formula: CnH2n+2.
alkyl group An alkane with a hydrogen atom removed, e.g. CH3, C2H5 alkyl groups are often shown as `R'.
amount of substance The quantity whose unit of the mole. Chemists use `amount of substance' as a means of count
anhydrous A substance that contains no water molecules.
anion A negatively charged ion.
atom economy
atomic orbital A region within an atom that can hold up to two electrons, with opposite spins.
atomic (proton) number The number of protons in the nucleus of an atom.
average bond enthalpy The average enthalpy change that takes place when breaking by homolytic fission 1 mol of a g
molecules of a gaseous species.
Avogadro constant, NA The number of atoms per mole of the carbon12 isotope
(6.02 × 1023 mol­1).
base A species that is a proton acceptor.
biodegradable material A substance that is broken down naturally in the environment by living organisms.
Boltzmann distribution The distribution of energies of molecules at a particular temperature, usually shown as a graph
bond enthalpy The enthalpy change that takes place when breaking by homolytic fission 1 mol of a given bon
gaseous species.
carbanion An organic ion in which a carbon atom has a negative charge.
carbocation An organic ion in which a carbon atom has a positive charge.

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A substance that increases the rate of a chemical reaction without being used up in the proces
cation A positively charged ion.
cis­trans isomerism A special type of E/Z isomerism in which there is a nonhydrogen group and a hydrogen atom o
bond: the cis isomer (Z isomer) has the H atoms on each carbon on the same side the trans is
atoms on each carbon on different sides of the bond.…read more

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A reaction in which the enthalpy of the products is greater than the enthalpy of the reactants, re
from the surroundings (H +ve).
enthalpy, H The heat content that is stored in a chemical system.
(standard) enthalpy change of The enthalpy change that takes place when one mole of a substance reacts completely with ox
combustion, Hc conditions, all reactants and products being in their standard states.…read more

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The breaking of a covalent bond with both of the bonded electrons going to one of the atoms, f
an anion (­ ion).
homogeneous catalysis A reaction in which the catalyst and reactants are in the same physical state, which is most freq
gaseous state.…read more

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M The mass of a mole of a substance. The units of molar mass are g mol­1.
molar volume The volume per mole of a gas. The units of molar volume are dm3 mol­1. At room temperature a
volume is approximately 24.0 dm3 mol­1.
mole The amount of any substance containing as many particles as there are carbon atoms in exact
molecular formula The number of atoms of each element in a molecule.…read more

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The two repeated steps in radical substitution that build up the products in a chain reaction.
radical A species with an unpaired electron.
rate of reaction The change in concentration of a reactant or a product in a given time.
redox reaction A reaction in which both reduction and oxidation take place.
reducing agent A reagent that reduces (adds electron to) another species.
reduction Gain of electrons or a decrease in oxidation number.…read more

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Compounds with the same structural formula but with a different arrangement of the atoms in s
stoichiometry The molar relationship between the relative quantities of substances taking part in a reaction.
stratosphere The second layer of the Earth's atmosphere, containing the `ozone layer', about 10 km to 50 km
structural formula A formula showing the minimal detail for the arrangement of atoms in a molecule.…read more


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