Chemistry definitions ALL

Empirical Formula

The formula that shows the simplest ratio of elements in the compound

Molar Concentration

The amount of solute per unit volume of solution

Molar Mass

The mass in grams of one mole of that substance

Mole

The amount of a substance that contains the same number of particles as 12g of Carbon - 12

Molecular Formula

The formula that shows the actual ratio of elements in a compound

Relative Atomic Mass

The mass of one atom of an element, relative to the mass of Carbon - 12

Relative Molecular Mass

The mass of a molecule, relative to the mass of Carbon - 12

Solute

Substance dissolved in the solution

Solution

A homogeneous mixture of solute and solvent

Solvent

Substance in which another substance is dissolved, forming a solution

Standard Solution

A solution for which the concentration is known and is unlikely to change for a period of time

Covalent Bonds

The sharing of at least one pair of electrons between atoms.

Electrongativity

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

InTERmolecular force

A force of attraction between molecules (ions) or atoms of noble gases

InTRAmolecular force

A bond between atoms within molecules

Ionic Bonds

The transfer of electrons and subsequent electrostatic attraction

Activated complex

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

Activation energy

The kinetic energy required to form the activated complex.

Catalyst

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

Endothermic reactions

Reactions which transform thermal energy into chemical potential energy.

Exothermic reactions

Reactions which transform chemical potential energy into thermal energy.

First law of thermodynamics (Conservation law of energy)

Energy can be converted from one form to another, but it is neither created nor destroyed.

Heat of reaction (enthalpy)

The net change of chemical potential energy of the system.

Reaction rate

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

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 Chatelier’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

Dynamic chemical equilibrium

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

Acid

A proton donor

Base

A proton acceptor

Ionisation

The reaction of a molecular substance with water to produce ions

Strong acid

An acid that ionises 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.

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 (or 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 a cation

Hydrolysis of a salt

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

Neutralisation

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

Standard solution

A solution of known concentration.

Alkali

A base that dissolves in water. All alkalis are bases, but not all bases are alkali

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 due to the presence of free (mobile) ions when molten or dissolved in solution

Electrolysis

The use of electricity to chemically decompose a compound into its component elements

Hydrocarbon

a compound containing only carbon and hydrogen atoms

Saturated compound

A compound in which all 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 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

Functional group isomerism

These molecules have the same molecular formula but different functional groups

Chain isomerism

These molecules have the same molecular formula, but their chain lengths differ

Positional isomerism

These molecules have the same molecular formula, but the position of the functional group on the main chain is different

Substitution reactions

Reactions when one atom or molecular fragment is replaced in a molecule by another