Are all naturally occuring reactions exothermic? If a reaction is endothermic, then the reaction must take energy from the environment to occur (as far as I know), and if this is the case, then to me the reaction seems energetically unfavorable, as there is only so much energy you can get from the environment. Does this means all naturally occurring reactions, (that don't just happen once in a blue moon but at a steady rate) are exothermic? This seems pretty silly, so if not, why not?
It's not necessary that all naturally occurring reactions are exothermic. The definition of Gibbs free energy is:

$$\Delta G = \Delta H - T\Delta S$$

A spontaneous reaction needs to have $\Delta G&lt;0$, and therefore for spontaneous endothermic reactions to occur we only need that $\Delta H &lt; T\Delta S$.