Definitions

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Enthalpy change of reaction

Back 1

It is the heat energy absorbed or evolved when molar quantities of reactants as stated in the thermochemical equation react together under standard conditions

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Enthalpy change of combustion

Back 2

It is the energy change when one mole of a substance is completely burnt in excess oxygen under standard conditions

Usually negative

Front 3

Enthalpy change of neutralisation

Back 3

It is the energy change when one mole of water is formed during the neutralisation of an acid and an alkali under standard conditions

Always negative

Front 4

Enthalpy change of formation

Back 4

It is the energy change when one mole of compound is formed from its constituent elements in their standard states under standard conditions

Front 5

Bond dissociation energy

Back 5

It is the energy required to break one mole of covalent bond between two atoms in the gaseous state

Always positive

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Enthalpy change of atomisation

Back 6

It is the energy change when one mole of gaseous atoms is formed from its element under standard conditions

Always positive

Front 7

First ionisation energy

Back 7

It is the energy change when one mole of electrons is removed from one mole of gaseous atoms to form one mole of gaseous singly charged cations

Always endothermic

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First electron affinity

Back 8

It is the energy change when one mole of electrons is added to one mole of gaseous atoms to form one mole of gaseous anions

First EA is usually negative, second is positive

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Standard lattice energy

Back 9

It is the energy change when one mole of an ionic compound is formed from its constituent gaseous ions at standard conditions

Always exothermic

Front 10

Enthalpy change of hydration

Back 10

It is the energy change when one mole of gaseous ions is surrounded by water molecules, forming a solution at infinite dilution under standard conditions

Always exothermic

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Enthalpy change of solution

Back 11

It is the energy change when one mole of compound is dissolved by solvent such that further dilution produces no more heat change under standard conditions

LHS

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Complex ion

Back 12

It is a species that contains a central metal atom/ion surrounded by molecules/anions which forms coordinate bonds to the metal centre

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Ligands

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It is a molecule or anion with at least one lone pair of electrons that it can use to form a coordinate bond to the central atom in a complex ion

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Functions of proteins

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Structural support (alpha-keratins and collagen), movement (actin and myosin), transport (haemoglobin), regulatory (insulin), immunity (antibodies), biological catalyst (enzyme - catalase), storage of nutrients (caseins, lactal bumins and lactoglobulins)

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Secondary structure of proteins

Back 15

It is caused by the repeated coiling and folding of a polypeptide chain in a regular arrangement. The two common repeating structural patterns in proteins are alpha-helix and beta-pleated sheets. Both these structures are stabilised by hydrogen bonding betw peptide linkages of amino acids on different segments of a polypeptide chain.

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Primary structure of proteins

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It is the sequence of amino acids in a polypeptide chain and the individual amino acids are joined together by peptide linkages.

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Tertiary structure of proteins

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It refers to the three-dimensional shape of a protein molecule that results from further folding, cross-linkings and coiling of the amino acid chains caused by interactions between the R-groups of the amino acids. The four types of such interactions which stabilise the 3D shape of a protein molecule are van Der Waals' forces, hydrogen bonding, ionic bonding and disulfide linkages.

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Quaternary structure of proteins

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It is the spatial arrangement of 2 or more polypeptide chains stabilized by R-group interactions to form a large, complex protein molecule. This structure is mainly stabilised by van Der Waals' forces of attraction between non-polar R-groups on the surface of the individual polypeptide chains. There may be some stabilisation by ionic interaction and Hydrogen bonding.

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Denaturation

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It is an irreversible process whereby the protein loses its biological activity. During denaturation, the R-group interactions are destroyed, only the secondary, tertiary and quaternary structurE's are disrupted. The primary structure is still intact as no covalent bonds of the polypeptide are broken.

Resulting in the protein disintegrating to form random coils of polypeptide chains.