as energy is released to the surroundings as heat there is a decrease in the energy of the system The combination of energy decrease and entropy increase dictates that combustion reactions are spontaneous reactions.
If there's an endothermic reaction that is spontaneous, then the reverse reaction is an exothermic reaction that's non-spontaneous. Melting ice is spontaneous at room temperature, but absorbs heat so it's endothermic. Therefore freezing of water at room temperature is an example, if you consider that a "reaction"
