Which type of reaction can be classified as both exothermic and spontaneous?

A combustion reaction is classified as both exothermic and spontaneous due to the nature of the reactants and products involved. In a combustion reaction, a fuel (often hydrocarbons) reacts rapidly with oxygen to produce heat and light. The energy released during this process is significantly greater than the energy required to break the bonds in the reactants. As a result, combustion reactions release energy, making them exothermic.

Furthermore, combustion reactions are spontaneous because they proceed without the need for outside intervention once initiated (e.g., a spark or flame). The reactants naturally favor forming products like carbon dioxide and water, leading to a decrease in Gibbs free energy, which is a hallmark of spontaneity. Thus, combustion reactions exemplify processes that release energy while also being driven by inherent thermodynamic favorability.