Chemistry Definitions

All definitions from the SAGS.

the mole

the SI unit for amount of substance

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, generally measured by comparing the amount of product against the amount of product that is possible

intramolecular bond

a bond which occurs between atoms within molecules

covalent bond

the sharing of at least one pair of electrons by two non-metal atoms

non-polar covalent (pure covalent)

an equal sharing of electrons

polar covalent

unequal sharing of electrons leading to a dipole forming (as a result of electronegativity difference)

electronegativity

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

ionic bond

a transfer of electrons and subsequent electrostatic attraction

metallic bonding

being between a positive kernel and a sea of delocalised electrons

intermolecular force

a force of attraction between molecules, ions, or atoms of noble gases

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 amount of energy required to start a chemical reaction

activated complex

A high energy, unstable, temporary transition state between the reactants and the products

reaction rate

the change in 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

an acid

a proton donor

a base

a proton acceptor

ionisation

the reaction of a molecular substance with water to produce ions

strong acid

an acid that ionises 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 it's ions

strong base

a base that dissociates completely in an aqueous solution

weak base

a base that only dissociates/ionises partially in an aqueous solution

amphoteric substances

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

Kw for water at 25°C

Kw = [H3O+][OH-]

pH scale

the measure of hydronium ion concentration in water at 25°C

a salt

a substance in which the hydrogen of an acid has been replaced by a cation

hydrolysis of a salt

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

neutralisation

the point where an acid and base have reacted so neither is in excess

a standrad 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

oxidising agent

a substance that accepts electrons

reducing agent

a substance that donates electrons

anode

the electrode where oxidation takes place

cathode

the electrode where reduction takes place

electrolyte

a substance that can conduct electricity by forming free ions when molten or dissolved in solution

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

closed system

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

open system

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

le châtelier’s principle

when an external stress is is applied to system in dynamic equilibrium, the equilibrium point will change in such a way as to counteract the stress