AS Chemistry Unit 2 Definitions

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alicyclic hydrocarbon
A hydrocarbon with carbon atoms joined together in a ring structure.
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aliphatic hydrocarbon
A hydrocarbon with carbon atoms joined together in straight or branched chains.
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alkanes
The homologous series with the general formula: CnH2n+2.
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alkyl group
An alkane with a hydrogen atom removed, e.g. CH3, C2H5; alkyl groups are often shown as ‘R’.
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dehydration
An elimination reaction in which water is removed from a saturated molecule to make an unsaturated molecule.
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displayed formula
A formula showing the relative positioning of all the atoms in a molecule and the bonds between them.
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elimination reaction
The removal of a molecule from a saturated molecule to make an unsaturated molecule.
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Esterification
The reaction of an alcohol with a carboxylic acid to produce an ester and water.
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functional group
The part of the organic molecule responsible for its chemical reactions.
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Hydrocarbon
A compound of hydrogen and carbon only.
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Nomenclature
A system of naming compounds.
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Reflux
The continual boiling and condensing of a reaction mixture to ensure that the reaction takes place without the contents of the flask boiling dry.
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saturated hydrocarbon
A hydrocarbon with single bonds only.
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Skeletal Formula
A simplified organic formula, with hydrogen atoms removed from alkyl chains, leaving just a carbon skeleton and associated functional groups.
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Structural Formula
A formula showing the minimal detail for the arrangement of atoms in a molecule.
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Structural isomer
Molecules with the same molecular formula but with different structural arrangements of atoms.
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Unsaturated hydrocarbon
A hydrocarbon containing carbon-to-carbon multiple bonds.
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Cracking
The breaking down of long-chained saturated hydrocarbons to form a mixture of shorter-chained alkanes and alkenes.
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Curly arrow
A symbol used in reaction mechanisms to show the movement of an electron pair in the breaking or formation of a covalent bond.
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Fractional ditillation
The separation of the components in a liquid mixture into fractions which differ in boiling point (and hence chemical composition) by means of distillation, typically using a fractionating column.
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heterolytic fission
The breaking of a covalent bond with both of the bonded electrons going to one of the atoms, forming a cation (+ ion) and an anion (– ion).
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homologous series
A series of organic compounds with the same functional group, but with each successive member differing by CH2.
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homolytic fission
The breaking of a covalent bond with one of the bonded electrons going to each atom, forming two radicals.
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Hydrocarbon
A compound of hydrogen and carbon only.
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Initiation
The first step in a radical substitution in which the free radicals are generated by ultraviolet radiation.
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mechanism
A sequence of steps showing the path taken by electrons in a reaction.
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Propagation
The two repeated steps in radical substitution that build up the products in a chain reaction.
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Radical
A species with an unpaired electron.
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Substitution reaction
A reaction in which an atom or group of atoms is replaced with a different atom or group of atoms.
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Termination
The step at the end of a radical substitution when two radicals combine to form a molecule.
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Addition Polymer
A very long molecular chain formed by repeated addition reactions of many unsaturated alkene molecules (monomers).
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Addition Polymerisation
The process in which unsaturated alkene molecules (monomers) add on to a growing polymer chain one at a time to form a very long saturated molecular chain (the addition polymer).
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Addition Reaction
A reaction in which a reactant is added to an unsaturated molecule to make a saturated molecule.
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Biodegradable material
A substance that is broken down naturally in the environment by living organisms.
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Carbocation
An organic ion in which a carbon atom has a positive charge.
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E/Z isomerism
A type of stereoisomerism in which different groups attached to each carbon of a C=C double bond may be arranged differently in space because of the restricted rotation of the C=C bond.
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electrophile
An atom (or group of atoms) that is attracted to an electron-rich centre or atom, where it accepts a pair of electrons to form a new covalent bond.
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electrophillic addition
A type of addition reaction in which an electrophile is attracted to an electron-rich centre or atom, where it accepts a pair of electrons to form a new covalent bond.
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Monomer
A small molecule that combines with many other monomers to form a polymer.
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cis–trans isomerism
A special type of E/Z isomerism in which there is a non-hydrogen group and a hydrogen atom on each C of a C=C double bond
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polymer
A long molecular chain built up from monomer units.
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Repeat Unit
A specific arrangement of atoms that occurs in the structure over and over again. Repeat units are included in brackets, outside of which is the symbol n.
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Stereoisomers
Compounds with the same structural formula but with a different arrangement of the atoms in space.
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Activation energy
The minimum energy required to start a reaction by the breaking of bonds.
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average bond enthalpy
The average enthalpy change that takes place when breaking by homolytic fission 1 mol of a given type of bond in the molecules of a gaseous species.
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Bond enthalpy
The enthalpy change that takes place when breaking by homolytic fission 1 mol of a given bond in the molecules of a gaseous species.
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Exothermic reaction
A reaction in which the enthalpy of the products is greater than the enthalpy of the reactants, resulting in heat being taken in from the surroundings (∆H +ve).
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enthalpy
The heat content that is stored in a chemical system.
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(standard) enthalpy change of combustion
The enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions, all reactants and products being in their standard states.
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(standard) enthalpy change of formation
The enthalpy change that takes place when one mole of a compound is formed from its constituent elements in their standard states under standard conditions.
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(standard) enthalpy change of reaction, ∆Hrө
The enthalpy change that accompanies a reaction in the molar quantities expressed in a chemical equation under standard conditions, all reactants and products being in their standard states.
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enthalpy cycle
A diagram showing alternative routes between reactants and products which allows the indirect determination of an enthalpy change from other known enthalpy changes using Hess’ law.
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enthalpy profile diagram
A diagram for a reaction to compare the enthalpy of the reactants with the enthalpy of the products.
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exothermic reaction
A reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings (∆H –ve).
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Hess' law
If a reaction can take place by more than one route and the initial and final conditions are the same, the total enthalpy change is the same for each route.
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Specific heat capacity
The energy required to raise the temperature of 1 g of a substance by 1 °C.
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standard conditions
A pressure of 100 kPa (1 atmosphere), a stated temperature, usually 298 K (25 °C), and a concentration of 1 mol dm–3 (for reactions with aqueous solutions).
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standard state
The physical state of a substance under the standard conditions of 100 kPa (1 atmosphere) and 298 K (25 °C).
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catalyst
A substance that increases the rate of a chemical reaction without being used up in the process.
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Greenhouse effect
The process in which the absorption and subsequent emission of infrared radiation by atmospheric gases warms the lower atmosphere and the planet’s surface.
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heterogeneous catalysis
A reaction in which the catalyst has a different physical state from the reactants; frequently, reactants are gases whilst the catalyst is a solid.
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homogeneous catalysis
A reaction in which the catalyst and reactants are in the same physical state, which is most frequently the aqueous or gaseous state.
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stratosphere
The second layer of the Earth’s atmosphere, containing the ‘ozone layer’, about 10 km to 50 km above the Earth’s surface.
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troposphere
The lowest layer of the Earth’s atmosphere, extending from the Earth’s surface up to about 7 km (above the poles) and to about 20 km (above the tropics).
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nucleophile
An atom (or group of atoms) that is attracted to an electron-deficient centre or atom, where it donates a pair of electrons to form a new covalent bond.
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nucleophillic substitution
A type of substitution reaction in which a nucleophile is attracted to an electron-deficient centre or atom, where it donates a pair of electrons to form a new covalent bond.
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Precipitation reaction
The formation of a solid from a solution during a chemical reaction. Precipitates are often formed when two aqueous solutions are mixed together.
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Rate of reaction
The change in concentration of a reactant or a product in a given time.
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absorption
The process that occurs when a gas, liquid or solute is held to the surface of a solid or, more rarely, a liquid.
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Boltzmann distribution
The distribution of energies of molecules at a particular temperature, usually shown as a graph.
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dynamic equilibrium
The equilibrium that exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction.
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le Chatelier’s principle
When a system in dynamic equilibrium is subjected to a change, the position of equilibrium will shift to minimise the change.
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limiting reagent
The substance in a chemical reaction that runs out first.
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Other cards in this set

Card 2

Front

aliphatic hydrocarbon

Back

A hydrocarbon with carbon atoms joined together in straight or branched chains.

Card 3

Front

alkanes

Back

Preview of the front of card 3

Card 4

Front

alkyl group

Back

Preview of the front of card 4

Card 5

Front

dehydration

Back

Preview of the front of card 5
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