Difference Between Thermochemical and Photochemical Reaction:
The following are the points of difference between Thermochemical and Photochemical Reaction.
| Thermochemical Reaction | Photochemical Reaction |
|---|---|
| These reactions proceed with the absorption or evolution of heat. | These reactions proceed with the evolution or absorption of light. |
| These reactions can take place in the dark also. | The presence of light is essential for these reactions. |
| The temperature has a significant effect on these reactions and rate of reaction. | The temperature has no significant effect on these reactions but the intensity of light affects the rate of reaction. |
| ΔG is always negative for spontaneous reactions. | In photochemical reactions ΔG may or may not be negative for spontaneity. For example, ΔG is +ve for (i) Photosynthesis in plants (ii) Ozonization of oxygen. |
| Thermochemical activation is not of selective nature. | Photochemical activation is highly selective, i.e., absorbed photons of light excite only a particular atom, or molecule, or group of atoms, which then becomes the site for the photochemical reactions. |
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