Spontaneity & exo/endothermic

[106036120]

Are all exothermic reactions spontaneous?

[505989311]

No they are not all spontaneous. This is because there could be a high activation energy required to start the reaction.

A logical example is burning wood or paper. It is an exothermic reaction because it releases heat; however, not all paper or wood spontaneously burns due to the activation energy required to start the reaction.

[alexia11]

Not all exothermic reactions are spontaneous. A negative Delta G means that a reaction is spontaneous. The change in enthalpy can contribute to this but an exothermic reaction is not the only factor deciding if a reaction is spontaneous.

[Averie Moore 2F]

The Gibbs free energy of the reaction determines if it is spontaneous by calculation of a negative value.

[Holiday Parsons 2D]

On top of the other answers: refer to the equation (in standard conditions). There are some values you can put into that equation that show a relationship between the variables that represent exothermic reactions that don't have to be spontaneous such as when is negative and the other variables represent a non-spontaneous process (e.g, low values in entropy but with a higher temperature).