Exothermic & Endothermic

Exothermic reaction definition

Reaction that releases energy to surroundings

Exothermic temperature change

Temperature of surroundings increases

Exothermic energy profile

Products have lower energy than reactants

Exothermic examples

Combustion, neutralisation, respiration

Exothermic sign

Negative energy change (ΔH < 0)

Endothermic reaction definition

Reaction that absorbs energy from surroundings

Endothermic temperature change

Temperature of surroundings decreases

Endothermic energy profile

Products have higher energy than reactants

Endothermic examples

Thermal decomposition, photosynthesis, dissolving ammonium nitrate

Endothermic sign

Positive energy change (ΔH > 0)

Energy profile diagrams

Show energy of reactants vs products

Activation energy

Minimum energy needed for reaction to start

Activation energy on diagram

Peak of curve above reactants

Bond breaking

Endothermic (energy absorbed)

Bond forming

Exothermic (energy released)

Overall energy change

Depends on difference between energy absorbed and released

Key idea

If more energy released than absorbed → exothermic; if more absorbed → endothermic