IEB CHEMISTRY DEFINITIONS

Molar mass

The mass in grams of one mole of a substance

Homogeneous mixture

A homogenous mixture of solute and solvent

Solute

A substance that is dissolved in a solution.

Solvent

A 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 that occurs between atoms within the molecules

Covalent bond

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

Non-Polar (Pure) Covalent Bond

An equal sharing of electrons

Polar covalent

The unequal sharing of electrons leading to a dipole forming

Ionic bond

Transfer of electrons and subsequent electrostatic attraction

Electronegativity

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

Metallic bond

Being between a positive kernel and a sea of delocalised electrons

Intermolecular Force

A weak 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 reaction

Reactions which transform chemical potential energy into thermal energy

Endothermic

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

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

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 a dynamic chemical equilibrium, the equilibrium point will change in such a way as to counteract the stress

Acid

BL: A proton donor

A: A substance that releases H+ions in an aqueous solution

Base

BL: A proton acceptor

A: A substance that releases OH− ions in an aqueous solution

Ionisation

The reaction of a molecular substance with water to produce ions

Strong acid

An acid the ionises completely in an aqueous solution

Weak Acid

An acid that ionises only partially in an aqueous solution

Dissociation

The splitting of an ionic compound into its ions

Strong base

A base that dissociates completely in an aqueous solution

Weak base

A base that dissociates on partially in an aqueous solution

Amphoteric (or amphiprotic) substance

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

Kw

Define Kw for water at 25°C as Kw= [H3O+][OH-]

A salt

A substance in which the hydrogen of an acid has been replaced by a cation

Hydrolysis

A reaction of an ion with water

Neutralisation/Equivalence point

The point where an acid and base have reacted 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

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 atoms 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 isomer

Compounds having the same molecular formula but different structural formula