Allotrope - two or more forms of the same element in which the atoms or molecules are arranged in different ways

Calorimeter - a device used for measuring the heat transferred during a reaction

Calorimetry - the process of measuring enthalpy changes of chemical reactions or physical changes

Endothermic reaction - chemical reactions which absorb heat

Enthalpy change - the heat released or taken in during any change in a system, provided that the system is kept at constant pressure

Enthalpy level diagram - a graphical representation of the enthalpy changes of processes involved in a reaction; relative enthalpy levels of different substances involved can be shown and thus their relative

Exothermic reaction - chemical reactions which release heat

Heat capacity - the amount of heat required to raise the temperature of a substance by 1 K (or 1 °C)

Internal energy - the total energy contained by a system which has two components: kinetic energy and potential energy

Joule - the unit of energy

Law of conservation of energy  - Law of conservation of energy states that energy cannot be created or destroyed, it can only be converted from one form to another

Polymorph - different forms of the same compound

Specific heat capacity - the amount of heat required to raise the temperature of 1 g of a substance by 1 K (or 1 °C)

Standard enthalpy change of combustion  - the enthalpy change when one mole of a substance is completely burnt in oxygen under standard conditions

Standard enthalpy change of formation  - the enthalpy change when one mole of a substance is formed from its elements in their standard states

Standard enthalpy change of neutralization - the enthalpy change when an acid reacts with an alkali to form one mole of water under standard conditions

Standard enthalpy change of reaction  - the enthalpy change when molar quantities of reactants as stated in the
specified equation react together under standard conditions

Surroundings - everything outside the system

System - the point of the universe, enclosed within defined boundaries, on which we focus our study

Thermochemical equation - Thermochemical equation shows the enthalpy change as well as the mole relationship