Key Definitions Flashcards
Alkanes
The homologous series with the general formula: CnH2n+2.
Activation Energy
The minimum energy required to start a reaction by the breaking of bonds.
Alkyl Group
An alkane with a hydrogen atom removed, e.g. CH3, C2H5; alkyl groups are often shown as ‘R’.
Addition Polymer
A very long molecular chain formed by repeated addition reactions of many unsaturated alkene molecules (monomers).
Atom Economy
Mr of useful product x 100/ Mr of all products
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).
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.
Addition Reaction
A reaction in which a reactant is added to an unsaturated molecule to make a saturated molecule.
Biodegradeable
A substance that is broken down naturally in the environment by living organisms.
Adsorption
The process that occurs when a gas, liquid or solute is held to the surface of a solid or, more rarely, a liquid.
Alicyclic hydrocarbon
A hydrocarbon with carbon atoms joined together in a ring structure.
Boltzmann distribution
The distribution of energies of molecules at a particular temperature, usually shown as a
Aliphatic hydrocarbon
A hydrocarbon with carbon atoms joined together in straight or branched chains.
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.
Carbocation
An organic ion in which a carbon atom has a positive charge.
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.
Catalyst
A substance that increases the rate of a chemical reaction without being used ip in the process.
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.
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: the cis isomer (Z isomer) has the H atoms on each carbon on the same side; the trans isomer (E isomer) has the H atoms on each carbon on different sides of the bond.
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.
Cracking
The breaking down of long-chained saturated hydrocarbons to form a mixture of shorter-chained alkanes and alkenes.
Elimination reaction
The removal of a molecule from a saturated molecule to make an unsaturated molecule.
Dehydration
An elimination reaction in which water is removed from a saturated molecule to make an unsaturated molecule.
Empirical formula
The simplest whole-number ratio of atoms of each element present in a compound.
Displayed formula
A formula showing the relative positioning of all the atoms in a molecule and the bonds between them.
Endothermic 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).
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.
Enthalpy, H
The heat content that is stored in a chemical system.
(Standard) Enthalpy change of combustion, ∆Hcө
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.
Fractional distillation
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.
(Standard) Enthalpy change of formation, ∆Hfө
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.
Fragmentation
The process in mass spectrometry that causes a positive ion to split into pieces, one of which is a positive fragment ion.
(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.
Functional group
The part of the organic molecule responsible for its chemical reactions.
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.
General formula
The simplest algebraic formula of a member of a homologous series. For example, the general formula of the alkanes is CnH2n+2.
Enthalpy profile diagram
A diagram for a reaction to compare the enthalpy of the reactants with the enthalpy of the products.
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.
Esterification
The reaction of an alcohol with a carboxylic acid to produce an ester and water.
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.
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).
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.
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).
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.
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.
Limiting reagent
The substance in a chemical reaction that runs out first.
Homologous series
A series of organic compounds with the same functional group, but with each successive member differing by CH2.
Mechanism
A sequence of steps showing the path taken by electrons in a reaction.
Homolytic fission
The breaking of a covalent bond with one of the bonded electrons going to each atom, forming two radicals.
Molecular ion, M+
The positive ion formed in mass spectrometry when a molecule loses an electron.
Hydrocarbon
A compound of hydrogen and carbon only.
Monomer
A small molecule that combines with many other monomers to form a polymer.
Hydrolysis
A reaction with water or aqueous hydroxide ions that breaks a chemical compound into two compounds.
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.
Initiation
The first step in a radical substitution in which the free radicals are generated by ultraviolet radiation.
Nucleophilic 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.
Percentage yield
Actual amount, in mol, of product/ Theoretical amount, in mol, of product x 100
Saturated hydrocarbon
A hydrocarbon with single bonds only.
Polymer
A long molecular chain built up from monomer units.
Skeletal formula
A simplified organic formula, with hydrogen atoms removed from alkyl chains, leaving just a carbon skeleton and associated functional groups.
Propagation
The two repeated steps in radical substitution that build up the products in a chain reaction.
Specific heat capacity, c
The energy required to raise the temperature of 1 g of a substance by 1°C.
Radical
A species with an unpaired electron.
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).
Rate of reaction
The change in concentration of a reactant or a product in a given time.
Standard state
The physical state of a substance under the standard conditions of 100 kPa (1 atmosphere) and 298 K (25 °C).
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.
Stereoisomers
Compounds with the same structural formula but with a different arrangement of the atoms in space.
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.
Stratosphere
The second layer of the Earth’s atmosphere, containing the ‘ozone layer’, about 10 km to 50 km above the Earth’s surface.
