Chemistry: IEB definitions

chemistry

Molar mass

the mass in grams of one mole of that substance.

Solution

a homogenous mixture of solute and solvent.

Solute

the substance that is dissolved in the solution.

Solvent

the substance in which another substance is dissolved, forming a solution.

Concentration

the amount of solute per unit volume of solution.

% yield

a measure of the extent of a reaction, determined by comparing the actual amount of product against the theoretical amount of product, expressed as a percentage.

Intramolecular bond

a bond between atoms within molecules.

Intermolecular force

a force of attraction between molecules or atoms of noble gases.

Covalent bond

involves a sharing of at least one pair of electrons by two atoms.

Non-polar (pure) covalent bond

An equal sharing of electrons

Polar covalent bond

Unequal sharing of electrons which leads to a dipole forming

Ionic bonding

involves a transfer of electrons to form cations and anions which are electrostatically attracted in an ionic crystal lattice.

Metallic bonding

the attraction between positive kernels and a sea of delocalised electrons.

Electronegativity

a measure of the tendency of an atom to attract a bonding pair of electrons.

Organic molecules

molecules containing carbon atoms with the exception of carbon dioxide, carbon monoxide, diamond, graphite, carbonates (or bicarbonates), carbides (e.g. CaC₂) and cyanides (e.g. KCN).

Hydrocarbon

a compound containing only carbon and hydrogen atoms.

Saturated compound

a compound in which all of the bonds between carbon atoms are single bonds.

Unsaturated compound

a compound in which there is at least one double and/or triple bond between carbon atoms.

Functional group

an atom or a group of atoms that form the centre of chemical activity in the molecule.

Homologous series

a series of similar compounds which have the same functional group and have the same general formula, in which each member differs from the previous one by a single CH₂ unit.

Structural isomers

compounds having the same molecular formula but different structural formulae.

Heat of reaction (ΔH)

the net change of chemical potential energy of the system.

Exothermic reactions

reactions which transform chemical potential energy into thermal energy.

Endothermic reactions

reactions which transform thermal energy into chemical potential energy.

Activation energy

the minimum energy required to start a chemical reaction OR the energy required to form the activated complex.

Activated complex

a high energy, unstable, transition state between the reactants and the products.

Reaction rate

the change in amount or concentration per unit time of either a reactant or product.

Catalyst

a substance that increases the rate of the reaction but remains unchanged at the end of the reaction.

Closed system (in chemistry)

a system in which mass is conserved inside the system but energy can enter or leave the system freely.

Open system (in chemistry)

a system in which both energy and matter can be exchanged between the system and its surroundings.

Reversible reaction

A reaction in which products can be converted back into reactants

Dynamic chemical equilibrium

a reversible reaction in which the forward and the reverse reactions are taking place at the same rate, and hence the concentrations of reactants and products are constant

Le Châtelier's principle

when an external stress (change in pressure, temperature or concentration) is applied to a system in dynamic chemical equilibrium, the equilibrium point will change in such a way as to counteract the stress.

Lowry-Brønsted theory

an acid is defined as a proton donor. A base is defined as a proton acceptor.

Ionisation

the reaction of a molecular substance with water to produce ions.

Strong acid

an acid that ionizes almost completely in an aqueous solution.

Weak acid

an acid that only ionises partially in an aqueous solution.

Dissociation

the splitting of an ionic compound into its ions

Polyprotic acids

acids able to donate more than one proton.

Strong base

a base that dissociates almost completely in an aqueous solution.

Weak base

a base that only ionises partially in an aqueous solution.

Amphoteric (amphiprotic) substance

a substance that can act as either an acid or a base.

Salt

a substance in which the hydrogen of an acid has been replaced by cation.

Hydrolysis of a salt

a reaction of an ion (from a salt) with water.

Neutralisation

a chemical reaction in which an acid and base react so neither is in excess.

Standard solution

a solution of known concentration.

Redox reaction

a reaction involving the transfer of electrons.

Oxidation

the loss of electrons.

Reduction

the gain of electrons.

Reducing agent

a substance that donates electrons.

Oxidising agent

a substance that accepts electrons.

Anode

the electrode where oxidation takes place.

Cathode

the electrode where reduction takes place.

Electrolyte

a substance that can conduct electricity due to the presence of free (mobile) ions when molten or dissolved in solution.

Galvanic cell

an electrochemical cell that converts the chemical energy of spontaneous redox reactions into electrical energy.

Electrolytic cell

an electrochemical cell that uses electrical energy to cause a non-spontaneous redox reaction to occur.