Practise 16 real Federal Board questions on Reaction Kinetics from 2023 to 2026. See the answer and explanation as soon as you answer.
Reaction Kinetics is one of the 19 main chapters in our Federal Board FSC Chemistry question bank (11th and 12th class), and about 3% of its real questions come from it. Tayyari Karo has 16 real questions on this chapter from 2023 to 2026; 7 are multiple choice and marked instantly, and the rest are short and long questions with a model answer. By difficulty: 6 hard, 6 medium, 4 easy.
Work through the questions below, then open the explanation for each one. Redo the ones you missed a few days later.
These are real past-paper questions. Think of your answer first, then open the explanation.
Which factor does NOT affect rate of reaction?
Answer: D. Color of reactants
The color of reactants has no bearing on reaction rate; temperature, concentration and catalysts are established rate factors.
Identify the step in the mechanism of free radical chlorination of ethane: CH₃-CH₃+Cl• ⟶ CH₃-CH₂•+HCl
Answer: B. Propagation
A radical reacting with a molecule to generate a new radical and a stable product, continuing the chain, is a propagation step.
A catalyst increases the rate of reaction by:
Answer: D. Lowering activation energy
Catalysts provide an alternate pathway with lower activation energy, speeding up the reaction without being consumed.
For a reaction "A ⟶ Product", doubling the concentration of 'A' quadruples the rate. The reaction order is:
Answer: C. 2ⁿᵈ order
Rate ∝ [A]ⁿ. Doubling [A] gives 4× rate ⇒ 2ⁿ = 4 ⇒ n = 2, second order.
When NaOH solution reacts with aluminum in different physical states, most rapid reaction should occur with:
Answer: A. Aluminum powder
Powdered Al has the largest surface area exposed to NaOH, so the reaction rate is fastest with aluminum powder.
The rate equation determined experimentally for this reaction: (CH₃)₃CBr + H₂O → (CH₃)₃COH + HBr, rate = K[(CH₃)₃CBr]. Hence it is:
Answer: D. Pseudo first order reaction
Although water is also a reactant, it is present in huge excess so its concentration stays essentially constant; the reaction appears first order overall — a pseudo first order reaction.
Phosgene is a toxic gas prepared by the reaction of CO with Cl₂: CO(g)+Cl₂(g)→COCl₂(g). Data: Exp1 [CO]=1.000 [Cl₂]=0.100 rate=1.29×10⁻²⁹; Exp2 [CO]=0.100 [Cl₂]=0.100 rate=1.30×10⁻³⁰; Exp3 [CO]=0.100 [Cl₂]=1.000 rate=1.30×10⁻³⁰. a. Calculate the rate constant (k). b. Using half-life method calculate t½ of reaction.
Determining orders: Comparing Exp1&2 ([Cl₂] const, [CO] ×10): rate ratio = 1.29×10⁻²⁹/1.30×10⁻³⁰ ≈ 9.9 ≈ 10¹, so order w.r.t. CO = 1.
Comparing Exp2&3 ([CO] const, [Cl₂] ×10): rate stays the same (1.30×10⁻³⁰), so order w.r.t. Cl₂ = 0.
Rate law: Rate = k[CO]¹[Cl₂]⁰ = k[CO]
a. Rate constant: using Exp1: 1.29×10⁻²⁹ = k(1.000) → k = 1.29×10⁻²⁹ s⁻¹
b. Half-life: since the reaction is first order overall (order 1 in CO), t½ = 0.693/k = 0.693/(1.29×10⁻²⁹) ≈ 5.37×10²⁸ s (using the first-order half-life formula, independent of initial concentration).
Explain the occurrence of a chemical reaction with reference to molecular collisions, activation energy, formation of activated complex and enthalpy changes in the reaction.
According to collision theory, a chemical reaction can only occur when reactant particles collide with each other; however, not every collision leads to a reaction — only effective collisions, which need both (a) sufficient kinetic energy, at least equal to the activation energy (Eₐ) — the minimum energy required to break existing bonds and initiate reaction — and (b) the correct orientation of colliding molecules.
When a collision has enough energy and proper orientation, the reactant molecules momentarily form an unstable, high-energy, transient species called the activated complex (transition state), in which old bonds are partially broken and new bonds are partially formed. …
The full model answer is in the app.
| Session | Questions |
|---|---|
| 2026 Annual | 4 |
| 2025 1st Annual | 3 |
| 2025 2nd Annual | 2 |
| 2024 Annual | 3 |
| 2023 Annual | 4 |
16 real Federal Board (FBISE) Chemistry questions on Reaction Kinetics from 2023 to 2026, for 11th and 12th class. Each one shows the session it came from.
No. We could not find an official FBISE marking scheme for these papers, so the answers and explanations are written by Tayyari Karo for practice. Check anything important with your teacher or textbook.
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