Chemistry

Chemistry definitions Gr12 IEB

Molar Mass

The mass in grams of one mole of that substance

Molar Concentration

The amount of solute per unit volume of solution

Electronegativity

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

Heat of Reaction

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

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

A Closed System

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

An 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

Acid (Lowry-Bronsted model)

Is defined as a proton donor

Base (Lowry-Bronsted model)

Is defined as a proton acceptor

Ionisation

The reaction of a molecular substance with water to produce ions

A Strong Acid

An acid that ionises almost completely in a aqueous solution

A Weak Acid

An acid that only ionises partially in an aqueous solution

Dissociation

The splitting of an ionic compound into its ions

A Strong Base

A base that dissociates almost completely in an aqueous solution

A Weak Base

A base that only ionises partially in an aqueous solution

An Amphoteric (or amphiprotic) Substance

A substance that can act as either an acid or base

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A substance in which the hydrogen of an acid has been replaced by a cation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

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

A 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

An Oxidising Agent

A substance that accepts electrons

A Reducing Agent

A substance that donate electrons

An Anode

The electrode where oxidation takes place

A Cathode

The electrode where reduction takes place

An Electrolyte

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

A Hydrocarbon

A compound containing only carbon and hydrogen atoms

A Saturated Compound

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

An Unsaturated Compound

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

A Functional Group

An atom or group of atoms that form the centre of chemical activity in the molecule

A 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