Chemical Kinetics
Rate laws, order of reaction, Arrhenius equation
Key Concepts
- Rate of reaction: change in concentration per unit time
- Rate law: rate = k[A]^m[B]^n (order determined experimentally, not from equation)
- First-order kinetics: radioactive decay, many reactions in solution
- Arrhenius equation: k increases with temperature
- Activation energy (E_a): energy barrier that reactants must overcome
Important Formulae
| First-order half-life | t₁/₂ = 0.693/k |
| First-order integrated rate law | ln[A] = ln[A]₀ − kt |
| Second-order half-life | t₁/₂ = 1/(k[A]₀) |
| Arrhenius equation | k = Ae^(−Ea/RT) |
| Temperature effect on k | ln(k₂/k₁) = (Ea/R)(1/T₁ − 1/T₂) |
Quick Tips
- Molecularity: number of species in elementary step (integer, max 3); order: determined from experiment (can be fraction).
- Rate-determining step is the slowest step of a mechanism.
- For a 10°C rise in temperature, reaction rate approximately doubles (thumb rule).
Sample Practice Questions
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The overall order of reaction A + B → C where rate = k[A][B]² is:
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Answer: 3
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For a first-order reaction, after 2 half-lives, fraction remaining:
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Answer: 1/4
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The rate constant k has units mol L⁻¹ s⁻¹. The order of reaction is:
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Answer: Zero
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Photochemical reactions are initiated by:
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Answer: Light (photons)
Practice Questions
Practice 20 randomly selected NEET questions on Chemical Kinetics. Answers are revealed after each question.
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What are the key concepts in Chemical Kinetics for NEET?
Rate of reaction: change in concentration per unit time; Rate law: rate = k[A]^m[B]^n (order determined experimentally, not from equation); First-order kinetics: radioactive decay, many reactions in solution; Arrhenius equation: k increases with temperature; Activation energy (E_a): energy barrier that reactants must overcome.
Which formulae are important for Chemical Kinetics in NEET?
First-order half-life: t₁/₂ = 0.693/k; First-order integrated rate law: ln[A] = ln[A]₀ − kt; Second-order half-life: t₁/₂ = 1/(k[A]₀); Arrhenius equation: k = Ae^(−Ea/RT); Temperature effect on k: ln(k₂/k₁) = (Ea/R)(1/T₁ − 1/T₂).
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