Energy of a reaction: exothermic, endothermic, bond energies

Exothermic: the system gives out energy to the surroundings ($Q < 0$ for the system) and the temperature of the surroundings rises — combustion, acid-base neutralisation, hydration of $\ce{CaO}$. Endothermic: the system takes in energy ($Q > 0$) and the temperature of the surroundings falls — dissolving $\ce{NH4NO3}$, electrolysis, photosynthesis.