Organic chemistry
| Term | Definition |
|---|
| Homologous series | A series of organic compounds that can be described by the same general formula, in which one member differs from the next by a CH₂ group. |
| Functional group | A bond or an atom or a group of atoms that determines the physical and chemical properties of a group of organic compounds. |
| Saturated compound | A compound in which there are no multiple bonds between C atoms in the hydrocarbon chain. |
| Unsaturated compound | A compound with one or more multiple bonds (double or triple) between C atoms in the hydrocarbon chain. |
| Structural isomers | Organic molecules with the same molecular formula but different structural formulae. |
| Polymer | A large molecule composed of smaller monomer units covalently bonded to each other in a repeating pattern. |
Boiling point, vapour pressure and melting point are defined in the lesson on physical properties of organic compounds.
Reaction rates and equilibrium
| Term | Definition |
|---|
| Reaction rate | The change in concentration of reactants or products per unit time. |
| Activation energy | The minimum energy needed for a reaction to take place. |
| Catalyst | A substance that increases the rate of a chemical reaction without itself undergoing a permanent change. |
| Exothermic reaction | A reaction that releases energy (ΔH < 0). |
| Endothermic reaction | A reaction that absorbs energy (ΔH > 0). |
| Chemical equilibrium | A dynamic equilibrium in a closed system when the rate of the forward reaction equals the rate of the reverse reaction. |
Le Chatelier’s principle is in the lesson on chemical equilibrium calculations.
Acids and bases
| Term | Definition |
|---|
| Arrhenius acid / base | An acid produces hydrogen ions (H⁺) or hydronium ions (H₃O⁺) when it dissolves in water; a base produces hydroxide ions (OH⁻) when it dissolves in water. |
| Lowry–Brønsted acid / base | An acid is a proton (H⁺) donor; a base is a proton (H⁺) acceptor. |
| Ampholyte (amphiprotic substance) | A substance that can act as either an acid or a base (e.g. H₂O, HCO₃⁻). |
| Strong / weak acid | A strong acid ionises completely in water; a weak acid ionises incompletely, forming a low concentration of H₃O⁺. |
| Concentrated / dilute acid | A concentrated acid contains a large amount of acid in proportion to the volume of water; a dilute acid contains a small amount. |
| Hydrolysis | The reaction of a salt with water. |
| Equivalence point | The point at which the acid and base have completely reacted in the mole ratio of the balanced equation. |
| Endpoint | The point in a titration where the indicator changes colour. |
Electrochemistry
| Term | Definition |
|---|
| Oxidation | A loss of electrons (an increase in oxidation number). |
| Reduction | A gain of electrons (a decrease in oxidation number). |
| Oxidising agent | A substance that is reduced (gains electrons). |
| Reducing agent | A substance that is oxidised (loses electrons). |
| Anode / cathode | The anode is the electrode where oxidation takes place; the cathode is the electrode where reduction takes place. |
| Galvanic cell | A cell in which chemical energy is converted into electrical energy (a spontaneous reaction). |
| Electrolytic cell | A cell in which electrical energy is converted into chemical energy (a non-spontaneous reaction). |
| Electrolysis | The chemical process in which electrical energy is used to bring about a non-spontaneous chemical change. |
Memory aids: OIL RIG — Oxidation Is Loss, Reduction Is Gain (of electrons). AN OX, RED CAT — oxidation at the anode, reduction at the cathode. The oxidising agent is itself reduced.