What is chemical kinetics?

Chemical kinetics is the branch of chemistry that studies the speed (rate) of reactions and the mechanism of reactions. In simple words – kinetics describes how fast or slow a reaction is and how it proceeds.

What is reaction rate?

Reaction rate means the change in the concentration of a reactant or product with time.

\[
\text{Rate} = -\frac{\Delta [\text{Reactant}]}{\Delta t} = \frac{\Delta [\text{Product}]}{\Delta t}
\]

Meaning if the reactant is decreasing or the product is increasing, then we can calculate its rate.

Factors affecting reaction rate.

1.Concentration:
Higher concentration → more collisions → faster reaction.

2.Temperature:
As temperature increases, the energy in the molecules increases → the reaction is faster.

3.Catalyst:
Catalyst speeds up the reaction, but is not consumed.

4.Surface Area:
Finely divided or powdered reactants have a larger surface area → the rate is faster.

5.Nature of Reactants:
Ionic reactions are fast, while covalent reactions are comparatively slow.

Units of Rate Constant (k)

Reaction Order	Unit of k
Zero Order	mol L⁻¹ s⁻¹
First Order	s⁻¹
Second Order	L mol⁻¹ s⁻¹

Real Life Examples of Kinetics.

• To study the speed of food spoilage
• To check the reaction time of medicine.
• optimizing industrial reactions
• Enzyme-catalyzed biological reactions society

Example Problem:

Question: If in a first-order reaction the reactant is reduced by 50% in 30 min, what will be the rate constant?
Solution:
For first order,

\[
k = \frac{2.303}{t} \log \left( \frac{a}{a – x} \right)
\]

\[
k = \frac{2.303}{30} \log \left( \frac{1}{0.5} \right) = 0.0231 \, \text{min}^{-1}
\]

FAQs

Q1. What is the main purpose of kinetics?
Kinetics tells us the speed of a reaction and how it happens — that is, how fast or slow a reaction takes place.

Q2. What does the rate constant (k) depend on?
The rate constant depends on temperature and the presence of a catalyst, but not on concentration.

Q3. What is a zero-order reaction?
In a zero-order reaction, the rate does not depend on the concentration of the reactant.

Q4. How does a catalyst affect a reaction?
A catalyst lowers the activation energy, which makes the reaction faster.