Enthalpy

Enthalpy change

• When bonds break or form during a reaction, energy is often released or absorbed as heat, this heat change at a constant pressure is known as an enthalpy change

Exothermic vs Endothermic

• Exothermic - release heat and have a negative enthalpy change (∆H), temperature of surroundings increases

• Endothermic - absorbs heat from surroundings and have a positive enthalpy change, temperature of of surroundings decreases

Enthalpy Diagrams

Standard conditions

• temperature = 298K, Pressure = 101kPa

Types of standard enthalpy changes

• Standard enthalpy of formation - the enthalpy change when 1 mole of a substance is formed from its constituent elements under standard conditions with all reactants and products in their standard states

• Standard enthalpy of combustion - enthalpy change when 1 mole of a substance is completely burned in oxygen