4.13 understand the use of ΔH to represent enthalpy change for exothermic and endothermic reactions

The enthalpy change is the overall change in energy in a reaction, it is symbolised by ΔH and its unit is kJ/mol, as it is the amount of energy in kilojoules per mole of reactant. It can be positive or negative, if the reaction is exothermic, the enthalpy change is negative because the reaction gives out energy, if the reaction is endothermic, the enthalpy change value is positive because the reaction takes in energy.