What is the Difference Between Photochemical and Thermal Reaction?
🆚 Go to Comparative Table 🆚The main difference between photochemical and thermal reactions lies in the energy source that drives the reactions. Here are the key differences between the two types of reactions:
- Photochemical Reactions: In these reactions, the reactants absorb photons of light, such as visible and ultraviolet radiations, to obtain energy. The absorption of light energy causes the reactant molecules to become excited, leading to the reaction. Photochemical reactions are directly affected by light and are typically endothermic, meaning they require energy to proceed.
- Thermal Reactions: Also known as dark reactions, these reactions occur by the absorption of heat energy from the surroundings. The reacting molecules are energized, and molecular collisions become effective, bringing about the reaction. Thermal reactions are not directly affected by light but are influenced by temperature. These reactions are often endothermic as well, as the reactants require heat energy to break down chemical bonds.
Some examples of thermal reactions include the decomposition of calcium carbonate into calcium oxide and carbon dioxide, and the decomposition of water molecules at 2000°C. On the other hand, a demonstration of a photochemical reaction can be seen in the mixture of hydrogen and chlorine, which remains unchanged until exposed to light, causing an explosive reaction.
Comparative Table: Photochemical vs Thermal Reaction
Here is a table comparing the differences between photochemical and thermal reactions:
| Photochemical Reaction | Thermal Reaction |
|---|---|
| Reactants receive energy as photons (e.g., UV light, visible light, IR light) | Reactants receive energy as heat |
| Examples include photosynthesis, bioluminescence, photo-degradation, vision, and photo-alkylation | Examples include thermolysis and thermal decomposition reactions |
| Initiated by light | Temperature-dependent |
| Directly affected by light | Not directly affected by light |
| Reactants need not necessarily be at a specific temperature | Temperature has a direct effect on the reaction |
Photochemical reactions occur when reactants absorb photons, leading to electron excitation and subsequent chemical reactions. On the other hand, thermal reactions involve the chemical decomposition of a substance when heat energy is applied.
- Photochemical vs Electrochemical Reaction
- Chemical vs Physical Reaction
- Chemical vs Biochemical Reactions
- Thermochemical Equation vs Chemical Equation
- Phototrophs vs Chemotrophs
- Thermal vs Heat
- Photochromic vs Thermochromic
- Nuclear Reaction vs Chemical Reaction
- Heat of Formation vs Heat of Reaction
- Photosynthesis vs Chemosynthesis
- Heat of Solution vs Heat of Reaction
- Thermochemical vs Biochemical Conversion of Biomass
- Photocatalysis vs Electrocatalysis
- Catalytic vs Non Catalytic Reaction
- Light Reaction vs Calvin Cycle
- Chemical Kinetics vs Thermodynamics
- Photodissociation vs Photoionization
- Endothermic vs Exothermic Reactions
- Thermochemistry vs Thermodynamics