Endothermic reactions - energy is taken from surroundings - supplied to break bonds.
Exothermic reactions - energy is released - so new bonds are formed.
The energy needed to break bonds is the activation energy for a reaction.
Energy level diagrams the difference in enery between products and reactants.
The energy change is represented by delta H (ΔH).
ΔH is negative on the diagram when it is an exothermic reaction. (because the products are at a lower energy level than the reactants and the temperature of the surroundings increases.)
ΔH is positive on the diagram when it is an endothermic reaction. (because the products are at a higher energy level than the reactants and the temperature of the surroundings decreases.)
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