The key difference between photochemical and electrochemical reaction is that photochemical reactions occur due to the absorption of light energy, whereas electrochemical reactions occur due to the absorption of electric energy.
Photochemical reactions and electrochemical reactions are two types of chemical reactions that take place in the presence of two different energy sources. However, both these reactions are often endothermic reactions.
CONTENTS
1. Overview and Key Difference
2. What is a Photochemical Reaction
3. What is an Electrochemical Reaction
4. Side by Side Comparison – Photochemical vs Electrochemical Reaction in Tabular Form
5. Summary
What is a Photochemical Reaction?
A photochemical reaction is a type of chemical reaction that is initiated by the absorption of energy in the form of light. And, this energy absorption of the molecules leads to the creation of transient excited states whose chemical and physical properties differ greatly from the original state of the molecule. The newly formed chemical species differs from the initial state by changing to new structures (via combining with each other or other molecules, via transferring electrons, hydrogen atoms, protons, etc.
When compared to the original state of the molecule, the excited state has a strong acidic nature, and it is a stronger reductant than the original state. Moreover, in the simplest photochemical process, excited states tend to emit light in the form of fluorescence.
Figure 01: Photosynthesis
The most common photochemical process on Earth is photosynthesis. Life on Earth mainly depends on the process of photosynthesis. In this process, plants can convert the energy from sunlight into stored chemical energy via forming carbohydrates (using carbon dioxide and water from the atmosphere). Also, this process releases oxygen to the atmosphere. Since most of the sunlight reaches the Earth’s atmosphere, most processes that take place on Earth are photochemical reactions.
What is Electrochemical Reaction?
An electrochemical reaction is a type of chemical reaction that is accompanied by the passage of an electric current. Mostly, this type of reactions involves the transfer of electrons between two substances (one substance is a solid, and the other substance is a liquid).
Figure 02: Electrical Cell
Generally, the occurrence of a chemical reaction happens by the liberation or absorption of heat (not any other form of energy). But, there can be many other reactions that proceed in contact with electronic conductors, separated by conducting wires. Also, this process releases electrical energy where an electric current is generated. And, this electrical energy can be used to conduct a chemical reaction by using energy as the energy source.
The most common system we know that uses electrical energy to bring about chemical reactions is an electrical cell. Here, electrolysis causes the conversion of one chemical substance into a different substance by bonding breaking and bond-forming.
What is the Difference Between Photochemical and Electrochemical Reaction?
Photochemical and electrochemical reactions are chemical reactions that take place under the influence of two different energy sources. The key difference between photochemical and electrochemical reaction is that photochemical reactions occur due to the absorption of light energy, whereas electrochemical reactions occur due to the absorption of electric energy.
Below tabulation presents more details of the difference between photochemical and electrochemical reaction.
Summary – Photochemical vs Electrochemical Reaction
Photochemical and electrochemical reactions are chemical reactions that take place in the presence of two different energy sources. The key difference between photochemical and electrochemical reaction is that photochemical reactions occur due to the absorption of light energy, whereas electrochemical reactions occur due to the absorption of electric energy.
Reference:
1. Bockris, John O’M., and Aleksandar R. Despić. “Electrochemical Reaction.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 15 Dec. 2011, Available here.
Image Courtesy:
1. “Photosynthesis en” By At09kg : original Wattcle: vector graphics – This file was derived from Photosynthesis.gif:, (CC BY-SA 4.0) via Commons Wikimedia
2. “Galvanic cell with no cation flow” By !Original: OhiostandardVector: AntiCompositeNumber – Own work (CC BY-SA 4.0) via Commons Wikimedia
