# Definitions

### Hydrocarbon

A compound containing only carbon and hydrogen atoms.

### Functional Group

A group of atoms in an organic molecule responsible for the chemical characteristics of a compound.

### Homologous Series

A series of compounds with the same general formula, similar chemical properties and containing the same functional group.

### Saturated Hydrocarbon

A hydrocarbon containing only single bonds.

### Curly Arrows

A symbol used in mechanisms to show the movement of electron pairs.

### Exothermic Reaction

Reaction where the enthalpy of the products is less than the enthalpy of the reactants, resulting in heat being released into the surroundings. Exothermic is bond making.

### Endothermic Reaction

Reaction where the enthalpy of the products is greater than the enthalpy of the reactants, resulting in heat being taken in from the surroundings. Endothermic is bond breaking.

### Incomplete Combustion

Combustion that occurs in a limited supply of oxygen, forming carbon monoxide.

A species with an unpaired electron.

### Nucleophile

Contains a lone pair of electrons which can be donated.

### Electrophile

An atom or group of atoms that are attracted to an electron-rich region, where it accepts a pair of electrons.

### Homolytic Fission

Breaking of a covalent bond to form two radicals, each with an unpaired electron.

### Heterolytic Fission

Breaking of a covalent bond to form two oppositely charged ions.

### Structural Isomer

Molecules with the same molecular formula but with a different structural formula.

### Stereoisomer

Molecules with the same structural formula but with a different arrangement of atoms in space.

### E/Z Stereoisomer

A type of stereoisomer where different groups attached to each carbon in a $C=C$ bond are arranged differently in space, due to the restricted rotation of the double bond.

### Atom Economy

This is a measure of the amount of waste produced during a reaction. It is defined as:
$$\text{atom economy} = \frac {\text{Mr of desired product}}{\text{Sum of Mr of all products}} \times 100$$

### Percentage Yield

This is a measure of how much of the reactants is turned into products. It is defined as:
$$\text{yield} = \frac {\text{actual product, mol}}{\text{theoretical product, mol}} \times 100$$

### Standard Enthalpy change of formation

This is the enthalpy change when one mole of a compound is formed from its constituent elements, in their standard states, under standard conditions.

### Standard enthalpy change of combustion

The enthalpy change when a reaction occurs in the molar quantities stated in the balanced equation, in their standard states, under standard conditions.

### Standard Conditions

A temperature of 298K, an atmosphere of 100kPa and a concentration of $1 mol\,dm^{-3}$ for solutions.

### Average Bond Enthalpy

The average change in enthalpy that occurs when the covalent bonds in one mole of gaseous are broken.

### Activation Energy

The minimum energy required in order to start a reaction.

### Catalyst

Provides an alternative reaction route in order to lower the activation energy without being consumed itself.

### Le Chatelier's Principle

This states that when a system in equilibrium is subjected to change, the position of equilibrium will shift in order to minimise the effect of the change.