Photosynthesis: in the most general sense, photosynthesis refers to any light-activated reaction for which the change in free energy (ΔGo) is positive for the reaction itself (without considering the presence of a catalyst or light). The products have higher energy than the reactants, and therefore the reaction is thermodynamically unfavorable, except through the action of light in conjunction with a catalyst.[25] Examples of photosynthetic reactions include the splitting of water to form H2 and O2, the reaction of CO2 and water to form O2 and reduced carbon compounds such as methanol and methane, and the reaction of N2 with water to yield NH3 and O2. Photocatalysis: this refers to reactions that are accelerated by the presence of a catalyst (the light itself is not the catalyst as may be erroneously implied).