Unit 1 Glossary
Activated complex
The activated complex is a very unstable arrangement of atoms formed at the maximum of
the potential energy barrier, during a chemical reaction
Activation energy
is the minimum kinetic energy required by colliding particles before reaction will occur.
Active site
The active site in an enzyme contains groups of atoms which can bind to other molecules
(substrates)
Adsorption
Adsorption occurs when molecules become bonded to the surface of a catalyst
Avogadro’s constant
This is the number of atoms in one mole of an element. In particular, it is the number of
atoms in 12.0 g of the isotope carbon-12. This number is given the symbol L and has a value
of 6.02 x 1023.
Bonding electrons
are shared pairs of electrons from both atoms forming the covalent bond.
Chemical bonding
is the term used to describe the mechanism by which atoms are held together.
Chemical structure
describes the way in which atoms, ions or molecules are arranged.
Collision theory
of reactions suggests that, for a chemical reaction to occur, particles must collide.
Covalent bond
a covalent bond is formed when two atoms share electrons in their outer shell to complete
the filling of that shell.
Covalent radius
is half the distance between the nuclei of two bonded atoms of an element
Delocalised
Delocalised electrons, in metallic bonding, are free from attachment to any one metal ion
and are shared amongst the entire structure.
Desorption
Desorption occurs when the bonds between the molecules and the surface break and the
molecules leave the surface of the catalyst
Diatomic
molecules with only two atoms are described as diatomic (e.g. oxygen, O 2, and carbon
monoxide, CO.)
Dipole
an atom or molecule in which a concentration of positive charges is separated from a
concentration of negative charge.
Electronegativity
is a measure of the attraction that an atom involved in a bond has for the electrons of the
bond
Endothermic reactions
absorb heat energy from the surroundings.
Enthalpy change
for a reaction is defined as the change in energy when 1 mole of reactant is converted to
product(s), and has the symbol _H and units of kJ mol-1.
Enthalpy of combustion
is the enthalpy change that occurs when 1 mole of a substance is burned completely in
oxygen.
Enthalpy of neutralisation
is the energy change (in kJ) when an acid is neutralised to form 1 mole of water.
Enthalpy of solution
is the energy change (in kJ) when 1 mole of the substance dissolves in water.
Enzymes
Enzymes are protein moleules which act as catalysts in biological processes
Exothermic reactions
release heat energy, which is given up to the surroundings.
Formula unit
The term ’formula unit’ is a general term. A formula unit may be an atom (for all elements
which do not exist as diatomic molecules), a molecule (for all covalent molecular substances)
or the simplest ratio of atoms or ions (for network or lattice substances).
Fullerenes
are molecules of pure carbon constructed from 5- and 6-membered rings combined into
hollow structures. The most stable contains 60 carbon atoms in a shape resembling a
football.
Heterogeneous catalysis
In heterogeneous catalysis, the reactants are in a different state from the catalyst (the
catalyst is generally a solid).
Homogeneous catalysis
In homogeneous catalysis, the reactants and the catalyst are in the same state
Hydrogen bonds
are electrostatic forces of attraction between molecules containing a hydrogen atom
bonded to an atom of a strongly electronegative element such as fluorine, oxygen or
nitrogen, and a highly electronegative atom on a neighbouring molecule.
Intermolecular forces
are those which attract molecules together. They are weaker than chemical bonds.
Intramolecular forces
are forces of attraction which exist within a molecule.
Ionisation energy
The first ionisation energy is the energy required to remove one mole of electrons from one
mole of gaseous atoms (i.e. one electron from each atom). The second and subsequent
ionisation energies refer to the energies required to remove further moles of electrons.
Isoelectronic
means having the same arrangement of electrons. For example, the noble gas neon, a sodium
ion (Na+) and a magnesium ion (Mg2+) are isoelectronic.
Lattice
A lattice is a regular 3D arrangement of particles in space. The term is applied to metal ions
in a solid, and to positive and negative ions in an ionic solid.
Lone pairs
are pairs of electrons in the outer shell of an atom which take no part in bonding.
Miscible
fluids are fluids which mix with or dissolve in each other in all proportions.
Molar volume
The molar volume is the volume occupied by one mole of a substance. For gases,the units
used are _ mol-1. (Note that some texts will quote the molar volume in units of decimetres
cubed per mole (dm3 mol-1)
Periodicity
is the regular recurrence of similar properties when the elements are arranged in order of
increasing atomic number.
Poison
A catalyst poison is a substance which bonds strongly to the catalyst surface and prevent it
from working.
Polar covalent bond
a covalent bond between atoms of different electronegativity, which results in an uneven
distribution of electrons and a partial charge along the bond.
Potential energy diagram.
shows the enthalpy of reactants and products, and the enthalpy change during a chemical
reaction.
Properties
of a substance are their physical and chemical characteristics. These are often a reflection
of the chemical bonding and structure of the material.
Specific heat capacity
relates the energy change in a liquid to the change in temperature. For water it has a value
of 4.18 kJ kg-1 ÆC-1. In other words, when 1 kg of water absorbs 4.18kJ of heat its
temperature will rise by 1ÆC.
Substrate
The substrate is the reactant in a reaction catalysed by an enzyme.
Thermochemical equation
states the enthalpy change for the reaction defined, with reactants and products in the
states shown.
Van der Waals’ forces
are the intermolecular forces of attraction which result from the electrostatic attraction
between temporary dipoles and induced dipoles caused by movement of electrons in atoms
and molecules.
Viscosity
is the resistance to flow that is exhibited by all liquids.
Unit 2 Glossary
Addition
A small molecule, say AB, adds to the multiple bond so that A joins to one atom and B to the
other.
Alkanals
Alkanals are a homologous series of aldehydes based on the corresponding alkanes by
changing one of the terminal carbon atoms into a carbonyl group.
Alkanes
Alkanes are a series of saturated hydrocarbons, all of which fit the general formula
CnH2n+2.
Alkanoic acids
are a homologous series of carboxylic acids based on the parent alkanes in which one of the
terminal carbon atoms is part of a carboxyl group
Alkanols
Alkanols are a homologous series of alcohols based on the series of alkanes by replacing one
hydrogen atom by a hydroxyl group.
Alkanones
Alkanones are a homologous series of ketones based on the corresponding alkanes by
changing one of the middle chain carbon atoms into a carbonyl group.
Alkenes
Alkenes are a series of unsaturated hydrocarbons which contain one C=C bond and which fit
the general formula CnH2n.
Alkyl groups
An alkyl group is an alkane molecule minus one hydrogen atom
Alkynes
Alkynes are a series of unsaturated hydrocarbons containing one C_C bond and which fit the
general formula CnH2n-2.
Amides
Amides, containing the -CO-NH- link, can be formed in a condensation reaction between
amines and carboxylic acids.
Amino acids
Amino acids are compounds containing an amino group (-NH2) and a carboxyl group (-COOH).
Atactic
Atactic polymers (say, poly(propene)) have their side chains orientated randomly along the
backbone.
Condensation
A condensation reaction is one in which two molecules combine to form a larger molecule at
the same time eliminating a small molecule such as water.
Cured resin
A cured polyester resin sets to a rigid solid, because the curing process produces cross
linking between the linear polyester chains.
Delocalised
Delocalised electrons are shared between a number of different atoms – in benzene they
are shared between 6 carbon atoms.
Denatured
When a protein molecule loses its highly ordered three dimensional shape it is said to be
denatured.
Enzymes
Enzymes are protein molecules which act as catalysts in biological processes.
Essential
An essential (in the sense of an amino acid) is a necessary material required by living
organisms for normal growth.
Ester exchange
Ester exchange is a chemical process, sometimes called transesterification, in which one
alcohol displaces another alcohol from an ester.
Fibrous
Fibrous proteins are proteins that form long coils or align themselves in parallel to form
long, water insoluble fibers.
Functional group
The functional group is that part of a molecule which gives the substance its characteristic
properties.
Globular
Globular proteins are proteins in which long coils fold into compact roughly spherical shapes.
Homologous series
A homologous series is a family of compounds which have similar chemical properties and
which all fit the same general formula.
Hydrocarbons
are compounds containing the elements carbon and hydrogen only.
Hydrogenation
Hydrogenation is the addition of hydrogen to a carbon to carbon multiple bond
Hydrolysis
Hydrolysis is the breakdown of a molecule by reaction with water.
Isomer
Isomers have the same molecular formula but different structural formula, i.e they contain
the same number and type of atoms but the atoms are arranged differently.
Octane number
A fuel’s octane number defines its tendency to auto-ignite. A high octane number can
withstand higher temperatures without auto-ignition.
Oxidation
When applied to carbon compounds, oxidation reactions result in an increase in the oxygen
to hydrogen ratio.
Peptide
Peptide bonds are the C-N bonds resulting from the condensation reaction between a
carboxyl group of one amino acid and the amino group of a second amino acid.
Polyunsaturated
A polyunsaturated molecule has more than one carbon to carbon unsaturated bond.
Power stroke
The power stroke in a petrol engine is produced when a spark ignites the compressed
petrol/air mixture above a piston, and the controlled explosion drives the piston down to
power the engine.
Proteins
Proteins are biological polymers of small molecules called amino acids.
Redox reaction
A redox reaction is a reaction in which one reactant gains electrons and another reactant
loses electrons
Reduction
When applied to carbon compounds, reduction reactions result in a decrease in the oxygen
to hydrogen ratio.
Reforming
Reforming is a catalytic process where straight chain alkanes in the naphtha distillation
fraction are converted to branched alkanes, cycloalkanes and aromatic hydrocarbons,
without necessarily changing the number of carbon atoms. This produces a higher octane
fuel.
Saponification
Saponification is the process by which soaps are made from fats and oils in a hydrolysis
reaction.
Steam cracking
Steam cracking is used to produce ethene and propene from gaseous feedstock (ethane and
propane) or from naphtha.
Synthesis gas
Synthesis gas is a mixture of carbon monoxide and hydrogen obtained by steam reforming
methane or coal.
Tetraethyl lead
Tetraethyl lead (Pb(C2H5)4) was added to petrol to increase its octane number to prevent
auto-ignition. After the introduction of catalytic converters, lead additives are no longer
used since lead is toxic and poisons the catalyst.
Theoretical yield
The theoretical yield is the maximum possible amount of product in a reaction, i.e. all of the
reactant(s) have been converted into product.
Thermoplastic polymers
Thermoplastic polymers melt or soften on heating. They consist of polymer chains which
have only weak forces (typically van der Waals’) between them.
Thermosetting plastics
Thermosetting plastics do not soften or melt on heating (see thermoplastic polymers) on
account of a highly cross-linked structure.
Triglycerides
Triglycerides are molecules formed through the condensation of one glycerol molecule with
three fatty acid molecules.
Unsaturated
An unsaturated molecule has at least one carbon to carbon double bond. An unsaturated
hydrocarbons does not contain the maximum number of hydrogen atoms for a given carbon
atom framework.
Volatile
A volatile substance evaporates very easily to form a gas.
Unit 3 Glossary
Acid
An acid is a substance which produces H+(aq) ions in solution and has a pH of less than 7.
Alkali
An alkali is a substance which produces OH-(aq) ions in solution and has a pH of greater than
7.
Batch processes
These involve mixing one batch of reactants in a vessel, allowing the reaction to complete,
then removal of the products, before reloading with a fresh batch of reactants.
Capital costs
Capital costs are incurred in the initial building of the plant and associated infrastructure.
Cash flow
Cash flow is the movement of money into and out of a business, and is a measure of
profitability.
Continuous processes
These take place in a plant where reactants are fed in continuously at one end, and products
are removed continuously from the other.
Dissociate
A molecule is said to dissociate when it splits up to form ions.
Dissociation
Dissociation occurs when molecules of a substance split up to form ions, on dissolving in
water.
Dynamic equilibrium
A dynamic equilibrium is achieved when the rates of two opposing processes become equal,
so that no net change results
Electrodes
The electrodes (one negative and one positive) dip into the electrolyte and form the
connection to the electric wires. Any chemical reactions occur at their surfaces.
Electrolysis
Electrolysis is the decomposition of a salt, acid or base either molten, or in solution, by the
passage of direct electrical current.
Electrolyte
Electrolytes are liquids containing ions which are free to move, and are therefore capable of
conducting electricity.
Electrolytic cell
An electrolytic cell is the equipment used to carry out electrolysis.
Equilibrium
chemical equilibrium is the state reached by a reaction mixture when the rates of forward
and reverse reactions have become equal
Feedstock
Feedstocks are the reactants from which other chemicals can be extracted or synthesised.
Fixed costs
Fixed costs are incurred irrespective of whether a plant is operating at maximum or only at
partial capacity.
Half-life
is the time taken for the activity or mass of a radioisotope to halve.
Hess’s law
The enthalpy change for a chemical reaction is independent of the route taken, providing
the starting point and finishing point is the same for both routes.
Ion-electron equations
An ion-electron equation is a half-equation, either an oxidation or a reduction, which in
combination of the opposite type, can be part of a complete redox equation.
Ionic product of water
Neutral
A neutral solution is neither acidic nor alkaline and has a pH = 7.
Nuclear chain reaction
is a self-sustaining series of processes in which neutrons from one fission reaction cause
multiple fission reactions in nearby nuclei.
Nuclear fission
is the splitting of a heavy nucleus into smaller fragments, caused by bombardment with
neutrons.
Nuclear fusion
is the combination of small nuclei into a larger nucleus accompanied by the release of
energy.
Oxidation
An oxidation is a loss of electrons by a reactant in any reaction.
Oxidising agent
An oxidising agent is a substance which accepts electrons.
Pilot plant
A pilot plant is a small scale chemical plant, built with similar materials to a fullscale one, to
investigate the chemical and engineering aspects of a process before a full-scale plant is
built.
Radioisotopes
of an element are isotopes which undergo radioactive decay.
Raw materials
Raw materials are the initial starting materials from which the a process’s feedstock is
derived.
Reducing agent
A reducing agent is a substance which donates electrons.
Reduction
A reduction is a gain of electrons by a reactant in any reaction.
Salts
Salts can be defined as one of the products of the neutralisation of an acid by a base. Salts
are formed when the hydrogen ions of an acid are replaced by metal ions or ammonium ions.
Stoichiometry
Stoichiometry means literally ’measuring elements’ and is concerned with the quantities of
substances reacting and the quantities of substances produced as derived from the
balanced equation, i.e. it is concerned with mole relationships.
Strong
A solution is strong when the solute is completely dissociated into ions. There are no
molecules of the original solute present.
Variable costs
Variable costs are dependent on a plant’s output.
Weak
A solution is weak when the solute is only partially dissociated into ions. Molecules of the
solute exist in equilibrium with the dissociated ions.