What is the difference between photochemical reactions and thermochemical reactions?

Difference between photochemical reactions and thermochemical reactions are discussed below:

THERMOCHEMICAL REACTIONS

PHOTOCHEMICAL REACTIONS

These reactions involve absorption or evolution of heat. These reactions involve absorption of light.
They can take place even in absence of light i.e. dark. The presence of light is the primary requisite for the reaction to take place.
Temperature has significant effect on the rate of a thermochemical reaction. Temperature has very little effect on the rate of a photochemical reaction. Instead, the intensity of light has a marked effect on the rate of a photochemical reaction.
The free energy change ∆G of a thermochemical reaction is always negative. The free energy change ∆G of a photochemical reaction may not be negative.
They are accelerated by the presence of a catalyst. Some of these are initiated by the presence of a photosensitizer. However a photosensitizer acts in a different way than a catalyst.

Category: Chemical Kinetics

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