What is a photochemical reaction?
What actually is a photochemical reaction?
A photochemical reaction is a reaction that can only proceed in the presence of light.
This implies that a photochemical reaction is a reaction in which the rate is influenced by the presence of light.
Reaction rate actually depends on a few factors like temperature, pressure, and concentration but some reactions are majorly influenced by light.
What are the basic laws of photochemistry?
The first law of photochemistry
The second law of photochemistry
Stark-Einstein law of photochemistry
2nd law of photochemistry
we will talk about these laws of photochemistry at the end of this article.
What does a photochemical reaction mean?
Photochemical reactions start with the absorption of the photons from light. When the reactant particles absorb the energy from the light, they get excited and move from the ground state to the excited state.
Photochemical reactions remain in the ground state unless excited by the presence of light, this only signifies that the reactant particles only collide when their energy is increased by the photons coming from the light.
What is the first step of photochemical reaction?
The first step in a photochemical reaction is the absorption of energy by the particles; the molecules get excited and then collide to form products.
We should remember that one of the factors that increase the rate of reactions among other factors is the presence of light.
A few reactions respond to the presence of light and thus are called photochemical reactions.
What are the types of photochemical reactions?
Since we have established the fact that photochemical reactions are influenced by light, there is a need to state the types of photochemical reactions we have.
1. Photo-dissociation reaction
This is a dissociation reaction that is influenced by light. A dissociation reaction involves the splitting of a single compound into two products.
For example, the splitting of the ozone is a photo-dissociation reaction.
This is the photodissociation of the oxygen equation.
O3 + hv ===O2 + [o]
Another example of a photodissociation reaction is the splitting of water vapor into hydrogen and oxygen
2H2O + hv === 2H2 + O2
Also, the decomposition of silver bromide and silver halide is another good example of a photodissociation reaction.
AgBr + hv ====Ag + Br
2. Photos addition reaction
The photoaddition reaction involves two separate atoms coming together to form a single product.
A + B + hv ===AB
3. Photo-substitution reactions
The irradiation of lumogen red in ethyl acetate is an Example of Photo-substitution reactions.
4. Photo-redox reactions
these are redox reactions hastened by the presence of light. A redox reaction is one that involves oxidation and reduction occurring simultaneously
Example of photo-redox reactions is the reduction of electron poor alkenes.
Photochemical reaction examples
The following are some examples of photochemical reaction equations
1. Photosynthesis in plants
The photochemical reactions of photosynthesis start at the chloroplast that contains the chlorophyll. Actually the thylakoid membrane is the chloroplast is the site of photochemical reaction in green leaves and plants.
2. Decomposition of silver halides.
2AgBr == 2Ag + Br2
This is a photochemical reaction used in photography .This is actually an example of a photochemical decomposition reaction.
3. Depletion of ozone layer.
This is a photochemical reaction in the atmosphere
4. Halogenation of alkanes
This is a photochemical reaction in organic chemistry
5. Reaction of chlorine with water
Cl2 + H2O == HOCl + HCl
This is a photochemical reaction applied in making beaches.
The above are 5 examples of photochemical reactions
The above are 5 examples of photochemical reactions are model types and are very important to us.
Photochemical and thermal reactions
What’s the difference between thermal and photochemical reaction
Photochemical and thermal reactions
Photochemical and thermal reactions are not really the same though the two different reactions are influenced by light and heat respectively.
Photochemical reactions are reactions that the reactant particles collide faster by absorbing photons from the light energy.
On the other side, thermal reactions are reactions in which the particles collide faster by absorbing heat from heat energy.
This is to say that thermal reactions occur faster by absorbing heat. The heat energy increases the average kinetic energy of the particles which increases the frequency of collision but in photochemical reactions, the reactants gain light energy and this increases the frequency of collision.
In thermal reactions particles are sensitive to 8heat or better put respond to heat while the particles or molecules in photochemical reactions respond to light energy.
What’s the difference between thermal and photochemical reaction?
In conclusion, photochemical reactions proceed in the presence of light white in thermal reactions, particles collide when heat is applied.
Basic laws of photochemistry
How man laws do we have in photochemistry?
There are just two laws of phochemistry
First law of photochemistry
The 1st law of photochemistry is called the Grotttus-Draper law , the law states that light must be absorbed by reactants before a photochemical reaction will take place.
The first law of photochemistry is a very foundational and important law in photochemistry because the theory stems from
Second law of photochemistry
The 2nd law of photochemistry is called the Stark-Einstein law.
The stark-Einstein law states that for each photon of light absorbed by a chemical reactions only one molecule will be activated for subsequent reactions.
What the law is saying is that each molecule or atom will absorb one photon of light each for a photochemical reaction to occur.
The number of molecules or atoms activated is equal to number of photons activated.
What is the principle of photochemistry?
The principle of photochemistry involves absorption of energy, the particles get excited ,collide faster and reaction occurs.
What is the importance of chemistry?
Applications of photochemistry include the following:
1.decontamination of drinking water
2.DNA damage detection
3.Production of hydrogen fuel
4. Environmental monitoring
in answering the question; what is a photochemical reaction? I have talked about the concept of photochemical reactions, basic laws of photochemistry.