Chemical Kinetics for NEET UG
Kinetics is about how fast reactions go and what controls their speed. Rate laws, half-lives and the Arrhenius equation are the main tools.
ChemistryClass 1274 MCQs3 lessons13 flashcards3 memory tricks
Practise Chemical Kinetics free
What you'll learn
- Rate, rate law and order
Write a rate law, find the order of a reaction and the units of k. - First-order reactions
Use the integrated first-order equation to find time, concentration or k. - Temperature, activation energy and catalysts
Use the Arrhenius equation and explain how catalysts speed up reactions.
Key formulas
| Integrated rate law | k = (2.303/t) log([A]₀/[A]) |
|---|---|
| Half-life | t½ = 0.693/k |
| Time for 99.9% completion | ≈ 10 half-lives |
| Arrhenius equation | k = A e^(−Ea/RT) |
| Two temperatures | log(k₂/k₁) = (Ea/2.303R)(1/T₁ − 1/T₂) |
Memory tricks
For many reactions, a 10 °C rise roughly doubles the rate (Arrhenius: k = A e^(−Ea/RT)). A fridge slows spoilage.
A catalyst provides a path with lower activation energy. It does not change ΔH, ΔG or K.
For a first-order reaction t½ = 0.693/k, independent of starting concentration. Units of k: s⁻¹ (first order), mol L⁻¹ s⁻¹ (zero), L mol⁻¹ s⁻¹ (second).
Try 3 NEET-style questions
Q1. For the decomposition CH₃CHO(g) → CH₄(g) + CO(g), the experimentally found rate law is rate = k[CH₃CHO]^(3/2). The order of the reaction is
- 1
- 2
- 1.5
- 3
Show answer
Answer: (3) 1.5
The order is the exponent of the concentration term in the experimental rate law, here 3/2 = 1.5. Orders can be fractional.
Q2. The rate law of a reaction is rate = k[A]^(1/2)[B]². The overall order of the reaction is
- 2.0
- 3.0
- 2.5
- 1.0
Show answer
Answer: (3) 2.5
Overall order = ½ + 2 = 2.5.
Q3. A first-order reaction has k = 2.303 × 10⁻² s⁻¹. The time for the reactant concentration to fall to one-tenth of its initial value is
- 10 s
- 100 s
- 1000 s
- 230 s
Show answer
Answer: (2) 100 s
t = (2.303/k) log([A]₀/[A]) = (2.303/2.303 × 10⁻²) × log 10 = 100 × 1 = 100 s.
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