Contents
- 1 Key Concepts of Chemical Kinetics:
- 1.1 1. Rate of Reaction:
- 1.2 2. Factors Affecting Reaction Rate:
- 1.3 3. Rate Law and Order of Reaction:
- 1.4 4. Half-Life (t₁/₂):
- 1.5 5. Activation Energy (Ea):
- 1.6 6. Reaction Mechanism:
- 1.7 Applications of Chemical Kinetics:
- 1.8 UNIT – I – Advanced Chemical Kinetics – SCYA5202
- 1.9 Resonance Chemistry Chemical Kinetics
- 1.10 An Introduction to Chemical Kinetics
- 1.11 CHEMICAL KINETICS
- 2 1. Resonance in Chemistry
- 3 2. Chemical Kinetics
Chemical Kinetics - Resonance Chemistry
Chemical Kinetics:
Chemical kinetics is the branch of chemistry that deals with the study of the speed or rate of chemical reactions and the factors affecting them. It helps understand how quickly a reaction proceeds and the mechanisms behind it.
Key Concepts of Chemical Kinetics:
1. Rate of Reaction:
The rate of a chemical reaction is the change in concentration of reactants or products per unit time.
Formula:
Rate=−Δ[Reactant]Δt=Δ[Product]Δt\text{Rate} = \frac{-\Delta [\text{Reactant}]}{\Delta t} = \frac{\Delta [\text{Product}]}{\Delta t}Rate=Δt−Δ[Reactant]=ΔtΔ[Product]
where,
- Δ[Reactant]\Delta [\text{Reactant}]Δ[Reactant] = Change in concentration of reactant
- Δt\Delta tΔt = Change in time
- The negative sign indicates the decrease in concentration of reactants.
2. Factors Affecting Reaction Rate:
- Concentration: Higher concentration generally increases the rate.
- Temperature: Increase in temperature usually speeds up the reaction.
- Surface Area: More surface area leads to a faster reaction (applicable for solids).
- Catalysts: Catalysts lower the activation energy and speed up the reaction.
- Nature of Reactants: Reactions involving ionic compounds are faster than those with covalent bonds.
3. Rate Law and Order of Reaction:
-
Rate Law: Expresses the relationship between the rate of a reaction and the concentration of reactants.
Rate=k[A]m[B]n\text{Rate} = k [A]^m [B]^nRate=k[A]m[B]n
where,
kkk = Rate constant
[A][A][A] and [B][B][B] = Concentration of reactants
mmm and nnn = Reaction order with respect to A and B -
Order of Reaction: The sum of the powers of the concentration terms in the rate law.
4. Half-Life (t₁/₂):
The time taken for the concentration of a reactant to reduce to half of its initial value.
- For a first-order reaction:
t1/2=0.693kt_{1/2} = \frac{0.693}{k}t1/2=k0.693
5. Activation Energy (Ea):
The minimum energy required for reactants to undergo a chemical reaction.
- Arrhenius Equation:
k=Ae−EaRTk = A e^{-\frac{E_a}{RT}}k=Ae−RTEa
where,
kkk = Rate constant
AAA = Frequency factor
EaE_aEa = Activation energy
RRR = Gas constant
TTT = Temperature in Kelvin
6. Reaction Mechanism:
The step-by-step sequence of elementary reactions leading to the overall reaction.
Applications of Chemical Kinetics:
- Understanding reaction mechanisms.
- Designing chemical processes in industries.
- Studying the stability and shelf-life of pharmaceuticals.
- Environmental studies like the rate of pollutant degradation.
If you need more help with specific problems or concepts in Chemical Kinetics, feel free to ask!
UNIT – I – Advanced Chemical Kinetics – SCYA5202
Resonance Chemistry Chemical Kinetics
An Introduction to Chemical Kinetics
CHEMICAL KINETICS
Let’s break down two major concepts in Physical Chemistry: Resonance and Chemical Kinetics — often studied together in school-level or entrance exams like NEET, JEE, and CBSE.

1. Resonance in Chemistry

Definition:
Resonance is a way to describe delocalized electrons within certain molecules or polyatomic ions where bonding cannot be expressed by a single Lewis structure.
It represents the blending of two or more valid Lewis structures (called resonating structures) for a molecule.

Key Points:
-
Resonance structures differ only in the position of electrons, not atoms.
-
The actual structure is a resonance hybrid, which is more stable than any individual structure.
-
Resonance adds stability to a molecule.

Examples:
-
Ozone (O₃):
-
Two resonance structures:
mathematicaO=O–O
O–O=O
-
The actual bond length is between single and double bonds.
-
-
Benzene (C₆H₆):
-
Alternating double bonds:
makefileKekulé structures:
C1=C2–C3=C4–C5=C6 C1–C2=C3–C4=C5–C6
-

Resonance Rules:
-
All resonance forms must be valid Lewis structures.
-
Atom positions remain fixed.
-
The molecule is represented by the resonance hybrid.

2. Chemical Kinetics

Definition:
Chemical kinetics is the branch of chemistry that studies the rate of a chemical reaction, the factors affecting it, and the mechanism of the reaction.

Key Concepts:
Concept | Explanation |
---|---|
Rate of Reaction | Change in concentration of reactants or products per unit time |
Rate Law | Rate = k [A]^m [B]^n (m and n are orders of reaction) |
Order of Reaction | The sum of powers of concentrations in the rate law |
Molecularity | Number of molecules colliding in a single step |
Rate Constant (k) | A constant at a given temperature |
Activation Energy (Ea) | Minimum energy needed to initiate a reaction |

First Order Reaction Formula:
Rate=k[A]\text{Rate} = k [A] Rate=k[A] k=2.303tlog([A]0[A]t)k = \frac{2.303}{t} \log\left(\frac{[A]_0}{[A]_t}\right)k=t2.303log([A]t[A]0)

Example: Decomposition of N₂O₅
2N2O5→4NO2+O22N_2O_5 \rightarrow 4NO_2 + O_22N2O5→4NO2+O2
This follows first-order kinetics.

Factors Affecting Reaction Rate:
-
Concentration
-
Temperature
-
Catalyst
-
Surface area
-
Nature of reactants

Difference Between Resonance and Kinetics
Feature | Resonance | Chemical Kinetics |
---|---|---|
Deals with | Electron delocalization | Reaction rate and mechanism |
Type | Structural/Conceptual | Dynamic/Quantitative |
Stability | Explains stability of molecules | Explains how fast reactions proceed |
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