Enthalpy

ΔH = cmΔT change in chemical energy = specific heat capacity x mass x change in tempurature

kJ or kJ mol-1

the minimum energy needed by colliding reactants for a reaction to occur

the change in potential energy when products are formed from reactants

• It is where the energy change is negative (∆H > 0 kJ mol-1) • It is a reaction where energy is released • Heat energy is given out to the surroundings as the total energy of the bonds broken is less than the bonds formed • an example is burning fuels (2C2H6 + 7O2 -> 4CO2 + 6H2O), condensation, freezing

• The enthalpy change is positive (∆H > 0 kJ mol-1) • Heat energy is taken in from the surroundings: temperature falls as the total energy of the bonds broken is more than the bonds formed • an example is e.g. photosynthesis (6H2O + 6CO2 -> C6H12O6 + 6O2), melting, evaporation, dissolving salts (e.g. Ammonium nitrate)

∆H = sum of all the reactants’ bond energies - sum of all the products’ bond energies