Unit 1 Glossary

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, O2, 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