Chemistry Definitions

Key definitions for OCR As Chemistry Unit 2

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Radical
A species with an unpaired electron
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Heterolytic fission
The breaking of a covalent bond with both of the bonded electrons going to one of the atoms
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Electrophile
An electron pair acceptor
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Nucleophile
An electron pair donator
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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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Substitution reaction
A reaction in which an atom or group of atoms is replaced by another atom or group of atoms
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Elimination reaction
The removal of a molecule from a saturated molecule to make an unsaturated molecule
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Fractional distillation
The separation of the components of a liquid into fractions which differ in boiling point by means of distillation, typically using a fractionating column
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Cracking
The break down of long chain saturated hydrocarbons to form a mixture of shorted chained alkanes and alkenes
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Catalyst
A substance which increases the rate of reaction without being used up in the process
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Radical subsitution
A type of substitution reaction in which a radical replaces another atom or group of atoms
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Mechanism
A sequence of steps showing the path taken by electrons in a chemical reaction
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Initiation
The first step in a radical substitution in which free radicals are generated using ultraviolet light
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Propagation
Two repeated steps in radical substitution that build up the products in a chain reaction
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Termination
The step at the end of a radical substitution in which two radicals combine to form a molecule
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Electrophilic addition
A type of addition reaction in which an electrophile is attracted to and electron rich centre and accepts a pair of electrons to form a new covalent bond
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Carbocation
A carbon atom with a positive charge
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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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Polymer
A long molecular chain built up from monomer units
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Monomer
A small molecule which combines with many other monomers to form a polymer
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Addition polymerisation
The process in which monomers add on to a polymer chain one at a time to form a very long saturated molecular chain
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Addition polymer
A long molecular chain formed by repeated addition reactions of many monomers
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Repeat unit
A specific arrangement of atoms that occurs in the structure over and over again
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Volatility
The ease with which a liquid turns into a gas
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Reflux
The continual boiling and condensing of a reaction mixture to allow the reaction to occur without the contents of the flask boiling dry
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Esterification
The reaction of an acid with a carboxylic acid to form and ester and water
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Dehyration
An elimination reaction in which water is removed from a saturated molecule to form and unsaturated one
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Nucleophilic substitution
A type of substitution reaction in which a nucleophile is attracted to an electron deficient centre and dontates a pair of electrons, forming a new covalent bond
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Atom economy
(Molecular mass of desired product/ Sum of molecular masses of all products) X100
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Exothermic
Enthalpy of products is smaller than the enthalpy of the reactants
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Endothermic
Enthalpy of products is greater than the enthalpy of the reactants
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Activation energy
The minimum energy required to start a reaction
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Standard conditions
25 *C, 1 atomospher of pressure
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Standard enthalpy change of reaction
The enthalpy change that accompanies a reaction in the molar quantities expressed in the chemical equation under standard conditions, all reactants and products being in their standard states
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Standard enthalpy change of combustion
The enthalpy change that occurs when one mole of a substance reacts completely with oxygen under standard conditions and with standard states
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Standard enthalpy change of formation
The enthalpy change that occurs when one mole of a compound is formed from its consituent elements under standard conditions and with standard states
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Specific heat capacity
The energy require to in increase the temperature of 1g of a substance by 1*C
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Average bond enthalpy
The average enthalpy change that takes place when breaking by homolytic fission one mole of a given type of bond in the molecules of a gaseous species
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Hess' Law
If a reaction can take place by more than one route, the total enthalpy change is the same for each route
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Le Chatlier'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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Dynamic equilibrium
The rate of the forwards reaction is equal to the rate of the reverse reaction in a closed system
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Adsorption
A gas, liquid or solute is held to the surface of a solid
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Greenhouse effect
The process in which the absorption and subsequent re-emission of infrared radiation by atmospheric gases warms the lower atomsphere and the planet's surface
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Hydrocarbon
A compound which contains hydrogen and carbon atoms only
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Saturated hydrocarbon
A hydrocarbon which contains single carbon-carbon bonds only
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Unsaturated hydrocarbon
A hydrocarbon which contains at least one carbon-carbon double bond
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Aliphatic hydrocarbon
A hydrocarbon with carbon atoms joined in straight or branched chains
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Alicyclic hydrocarbon
A hydrocarbon with carbon atoms joined in a circular structure
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Functional group
The part of an organic compound responsible for its chemical properties
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Homologous series
A series of compounds with the same functional group but with each successive member differing by CH2
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Alkanes
The homologous series with the general formula CnH2n+2
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Nomenclature
A system of naming organic compounds
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Alkyl group
An alkane with a hydrogen atom removed
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General formula
The simplest algebraic formula of a member of a homologous series
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Displayed formula
Shows the relative positioning of all atoms in a molecule and the bonds between them
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Structural formula
Shows the minimum detail for the arrangement of atoms in a molecule
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Skeletal formula
A simplified organic formular with hydrogen atoms removed from alkyl chains, leaving just a carbon skeleton and associated functional groups
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Structural isomers
Molecules with the same molecular formula but with different structural arrangements of atoms
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Stereoisomers
Molecules with the same structural formula but with different positions of atoms in space
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E/Z isomerism
A type of stereoisomerism in which different groups attached to each carbon in a C=C double bond may be arranged differently in space due to the restricted rotation of the C=C bond
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cis-trans isomerims
A type of E/Z isomerims in which each carbon of the C=C double bond is bonded to a hydrogen and non-hydrogen group
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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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Other cards in this set

Card 2

Front

Heterolytic fission

Back

The breaking of a covalent bond with both of the bonded electrons going to one of the atoms

Card 3

Front

Electrophile

Back

Preview of the front of card 3

Card 4

Front

Nucleophile

Back

Preview of the front of card 4

Card 5

Front

Addition reaction

Back

Preview of the front of card 5
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