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. |
