Enthalpy Level Diagrams for AS Chemistry Unit 1 (Edexcel)

For all exothermic reactions, the enthalpy of a reaction is negative. This shows that the energy within the system has decreased because energy is given out. This means that the enthalpy of the reactants is greater than that of the enthalpy for the products.

For all endothermic reactions, the enthalpy for a reaction is positive. This is because energy is taken in from the surroundings and so the total energy in the system is greater at the end of the reaction…