Multiple Choice Questions (MCQs) for JEE Chemistry: Chemical Kinetics
Access targeted multiple-choice questions for Chemical Kinetics designed to align with the latest JEE academic syllabus for JEE Chemistry. These objective practice sets help students evaluate their conceptual understanding and improve exam readiness.
Practice Chemical Kinetics MCQs for JEE Chemistry
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Multiple Choice Questions
(a) [A]0 = [A]t + [B]t/2 + [C]t/3
(b) [A]0 = (2/3)[A]t + [B]t + [C]t
(c) [A]0 = [A]t + 2[B]t + 3[C]t
(d) [A]0 = [A]t + [B]t + [C]t
Show Answer & Explanation
Answer: (a) [A]0 = [A]t + [B]t/2 + [C]t/3
Explanation:
1. Each mole of A that reacts gives 2 mol B or 3 mol C.
2. Moles of A reacted = [B]/2 + [C]/3.
3. So [A]0 = [A]t + [B]t/2 + [C]t/3.
Teacher's Note:
1. Divide the product amount by its stoichiometric coefficient.
2. Atoms of A are conserved.
(a) C only
(b) A, B and C only
(c) B only
(d) B and C only
Show Answer & Explanation
Answer: (d) B and C only
Explanation:
1. Order = 1 - 1/2 = +1/2, so B is correct and A is wrong.
2. The rate varies as [SO3]-1/2, so it falls as SO3 accumulates (C true, D false).
Teacher's Note:
1. Add the exponents with their signs.
2. A negative exponent is an inhibiting effect.
(a) 0
(b) 3
(c) 2
(d) 1
Show Answer & Explanation
Answer: (b) 3
Explanation:
1. Doubling G alone doubles the rate: first order in G.
2. Doubling both multiplies by 8 = 23, so order in H = 3 - 1 = 2.
3. Overall order = 1 + 2 = 3.
Teacher's Note:
1. Separate the contributions of each reactant.
2. Rate multiplies by 2^n for order n.
(a) 1
(b) 2
(c) 0
(d) 3
Show Answer & Explanation
Answer: (c) 0
Explanation:
1. Fall in concentration per unit time: 0.25/0.05 = 5, 0.35/0.07 = 5, 0.30/0.06 = 5 M per min.
2. The rate is constant, so the reaction is zero order.
Teacher's Note:
1. Compare the rate over successive intervals.
2. Constant rate means zero order.
(a) -y
(b) y
(c) yR
(d) y/R
Show Answer & Explanation
Answer: (b) y
Explanation:
1. ln k = ln A - Ea x (1/RT), so the gradient is -Ea.
2. -Ea = -y, hence Ea = y.
Teacher's Note:
1. Treat 1/RT as the x variable.
2. The factor R is already in the axis.
(a) A, B, C and D only
(b) A, B and D only
(c) A and D only
(d) B and D only
Show Answer & Explanation
Answer: (b) A, B and D only
Explanation:
1. Rate of reaction is always positive (a negative sign is only used for reactants in the derivative).
2. It is a change in concentration per unit time.
3. Average and instantaneous rate are equal when the rate is constant (zero order), so C is false.
4. For heterogeneous reactions rate depends on surface area, so D is true.
Teacher's Note:
1. Check each statement separately.
2. A zero order reaction has equal average and instantaneous rates.
(a) if T1 > T2, then k1 < k2 for an exothermic reaction
(b) if T1 > T2, then k1 > k2 only for an endothermic reaction
(c) Ea1 is greater than Ea2
(d) if T1 > T2, then k1 > k2 always
Show Answer & Explanation
Answer: (d) if T1 > T2, then k1 > k2 always
Explanation:
1. With Ea > 0, k = A e-Ea/RT increases with temperature for every reaction, whether endothermic or exothermic.
2. So k1 > k2 whenever T1 > T2, and Ea1 = Ea2.
Teacher's Note:
1. Thermicity affects the equilibrium constant, not the sign of the temperature dependence of k.
2. Activation energy is temperature independent in this model.
(a) 1.4
(b) 0.8
(c) 0.04
(d) 1.2
Show Answer & Explanation
Answer: (b) 0.8
Explanation:
1. The unit s-1 shows a first order reaction: rate = k[N2O5].
2. [N2O5] = 2.4 × 10-5 / 3 × 10-5 = 0.8 mol L-1.
Teacher's Note:
1. Use the unit of k to find the order.
2. Divide rate by k.
(a) 2.0 mol-1 dm3
(b) 0.5 mol-1 dm3
(c) 1.0 mol-1 dm3
(d) 1.5 mol-1 dm3
Show Answer & Explanation
Answer: (b) 0.5 mol-1 dm3
Explanation:
1. k1 = 0.693/40 = 0.01733 s-1.
2. k0 = (1.386/2)/20 = 0.03465 mol dm-3 s-1.
3. k1/k0 = 0.5 mol-1 dm3.
Teacher's Note:
1. Zero order: t1/2 = a/2k0.
2. Keep track of units.
(a) 2
(b) 3
(c) 5
(d) 4
Show Answer & Explanation
Answer: (b) 3
Explanation:
1. After n periods the fraction left is (0.8)^n.
2. (0.8)3 = 0.512 (just over 50%) while (0.8)4 = 0.410.
3. So n = 3.
Teacher's Note:
1. Compute successive powers of 0.8 until the value drops below 0.5.
2. Exactly 50% would need n = 3.1.
(a) C and D only
(b) A, C and D only
(c) B, C and D only
(d) D only
Show Answer & Explanation
Answer: (a) C and D only
Explanation:
1. log A = 5, so A = 105 min-1.
2. Ea = 2.303 x R x 2000 = 2.303 × 2 × 2000 = 9212 cal = 9.212 kcal.
Teacher's Note:
1. The intercept is log A, not A.
2. Slope = -Ea/(2.303 R).
(a) 1
(b) 2
(c) 0
(d) 3
Show Answer & Explanation
Answer: (a) 1
Explanation:
1. The second 100 s again halves the remaining reactant: constant half-life of 100 s.
2. Constant half-life means first order.
Teacher's Note:
1. 75% is two half-lives.
2. For zero order 100% would be done in 200 s.
(a) 2.5 bar
(b) data is insufficient
(c) 1.25 bar
(d) 5.0 bar
Show Answer & Explanation
Answer: (a) 2.5 bar
Explanation:
1. Let initial moles be A = 2u and C = u (mole fraction of C = 1/3); initial pressure 3u.
2. At infinity A is gone: B = 4u, C = 3u, total 7u = 35 bar, so u = 5 bar.
3. At t1 total = 17.5 bar = 3.5u. If y is the decrease in A (in units u): 3 + 2y = 3.5, y = 0.25, so p(B) = 2y u = 0.5 × 5 = 2.5 bar.
Teacher's Note:
1. Express the pressures in a unit u fixed by the final pressure.
2. Each mole of A gives 2 B and 1 °C, a net gain of 2.
(a) 4/7
(b) none of these
(c) 3/4
(d) 3/7
Show Answer & Explanation
Answer: (d) 3/7
Explanation:
1. For parallel first order paths the fractions are in the ratio of the rate constants.
2. Fraction by path 1 = k1/(k1 + k2) = 3/7.
Teacher's Note:
1. Both paths consume the same acid, so their rates add.
2. The ratio of products equals k1 : k2.
(a) A, B and D only
(b) A, C and D only
(c) A, B, C and D only
(d) A, B and C only
Show Answer & Explanation
Answer: (c) A, B, C and D only
Explanation:
1. All four are standard results of mechanism analysis.
2. For an elementary step the exponents equal the stoichiometric coefficients.
Teacher's Note:
1. Think of the rate determining step as a bottleneck.
2. Steady state and pre-equilibrium are the two usual tools.
(a) A, B and C only
(b) A and B only
(c) A only
(d) B only
Show Answer & Explanation
Answer: (b) A and B only
Explanation:
1. -dN/dt gives the number of disintegrations per unit time, called the activity or radioactivity of the sample.
2. Half-life and average life are times, not rates.
Teacher's Note:
1. Units of activity are becquerel or curie.
2. Rate means per unit time.
(a) 6 min
(b) 12 min
(c) 48 min
(d) 24 min
Show Answer & Explanation
Answer: (d) 24 min
Explanation:
1. Rate is proportional to concentration: r1/r2 = ek(10) = 4/3.
2. k = ln(4/3)/10 = 0.02877 min-1.
3. t1/2 = 0.693/0.02877 = 24.1 min.
Teacher's Note:
1. For first order the rate falls in the same ratio as concentration.
2. The interval is 10 min.
(a) 106.25 mm Hg
(b) 125 mm Hg
(c) 150 mm Hg
(d) 116.25 mm Hg
Show Answer & Explanation
Answer: (a) 106.25 mm Hg
Explanation:
1. If p of N2O5 reacts, total = 50 + p(4/2 + 1/2 - 1) = 50 + 1.5p. 87.5 = 50 + 1.5p gives p = 25 mm.
2. N2O5 left = 25 mm = half of 50 in 30 min, so t1/2 = 30 min.
3. At 60 min N2O5 left = 12.5 mm, reacted 37.5 mm: total = 50 + 1.5 × 37.5 = 106.25 mm Hg.
Teacher's Note:
1. Each 2 mol N2O5 gives 5 mol of gas, a net gain of 1.5 per mole reacted.
2. Find the half-life first.
(a) Rate = -d[N2]/dt = -(1/3) d[H2]/dt = -(1/2) d[NH3]/dt
(b) Rate = d[N2]/dt = d[H2]/dt = d[NH3]/dt
(c) Rate = -d[N2]/dt = -(1/3) d[H2]/dt = (1/2) d[NH3]/dt
(d) Rate = -d[N2]/dt = -3 d[H2]/dt = 2 d[NH3]/dt
Show Answer & Explanation
Answer: (c) Rate = -d[N2]/dt = -(1/3) d[H2]/dt = (1/2) d[NH3]/dt
Explanation:
1. Rate of reaction = (-1/a) d[reactant]/dt = (1/b) d[product]/dt, with a and b the coefficients.
2. Hence the first option; reactants have a minus sign and the product a plus sign.
Teacher's Note:
1. Divide by the stoichiometric coefficient.
2. Products form (positive), reactants are consumed (negative).
(a) II - ii - Q
(b) IV - iv - S
(c) I - iii - R
(d) I - iv - S
Show Answer & Explanation
Answer: (d) I - iv - S
Explanation:
1. The unit min-1 shows the reaction is first order (I).
2. First order: k = (1/t) ln[a/(a-x)] (iv), and the half-life is independent of concentration (S).
3. So I - iv - S.
Teacher's Note:
1. Check the unit of k to find the order.
2. Match formula and half-life with the same order.
(a) 4 × 10-4 s-1
(b) 10-6 s-1
(c) 2 × 10-4 s-1
(d) 10-4 s-1
Show Answer & Explanation
Answer: (d) 10-4 s-1
Explanation:
1. ln(k2/k1) = 4606 (1/400 - 1/500) = 4606 × 5 × 10-4 = 2.303.
2. k2/k1 = 10, so k2 = 10-4 s-1.
Teacher's Note:
1. Slope = -Ea/R.
2. ln 10 = 2.303.
(a) A, C and D only
(b) A, B, C and D only
(c) B, C and D only
(d) A, B and D only
Show Answer & Explanation
Answer: (b) A, B, C and D only
Explanation:
1. Total = 400 + 2x = 1000, x = 300 mm, so A left = 100 mm = 1/4 in 20 min, i.e. 2 half-lives; t1/2 = 10 min and k = 0.693/10 = 0.0693 min-1.
2. At 30 min A left = 400/8 = 50 mm, x = 350 mm, so p(C) = 350 mm.
3. Total = 400 + 2(350) = 1100 mm. All four are correct.
Teacher's Note:
1. Pressure rise = 2x for this stoichiometry.
2. 30 min is 3 half-lives.
(a) 3.47 × 10-3 min-1 and 200 min
(b) 6.93 × 10-2 min-1 and 20 min
(c) 6.93 × 10-3 min-1 and 300 min
(d) 6.93 × 10-3 min-1 and 200 min
Show Answer & Explanation
Answer: (d) 6.93 × 10-3 min-1 and 200 min
Explanation:
1. First order with t1/2 = 100 min: k = 0.693/100 = 6.93 × 10-3 min-1.
2. 75% completion = two half-lives = 200 min.
Teacher's Note:
1. 75% always needs two half-lives for first order.
2. k = 0.693/t1/2.
(a) 8
(b) 24
(c) 3
(d) 5
Show Answer & Explanation
Answer: (a) 8
Explanation:
1. Each complex ion [Fe(C2O4)2(H2O)2]2- loses 5 electrons (1 for Fe(II) to Fe(III) and 4 for two oxalates to 4 CO2).
2. MnO4- + 8H+ + 5e → Mn2+ + 4H2O, so one MnO4- oxidises one complex ion and uses 8 H+.
3. Ratio of rates = 8.
Teacher's Note:
1. Balance the electrons first.
2. Count only the H+ taken by permanganate.
(a) 1 × 10-3
(b) 1 × 10-4
(c) 1 × 10-6
(d) 1 × 10-5
Show Answer & Explanation
Answer: (b) 1 × 10-4
Explanation:
1. The rate is proportional to [H+].
2. For HX, [H+] = 1 M; for HA the rate is 1/100, so [H+] = 0.01 M.
3. Ka = [H+]2/[HA] = (0.01)2/(1 - 0.01) = 1.0 × 10-4.
Teacher's Note:
1. Strong acid is fully ionised.
2. Use Ka = x2/(c - x).
(a) A, B and D only
(b) B only
(c) A and B only
(d) A, B and C only
Show Answer & Explanation
Answer: (c) A and B only
Explanation:
1. P = A(experimental)/A(theory). P = 4.5 means the experimental frequency factor is 4.5 times that predicted by simple collision theory.
2. Ea is not affected by P (A true, B true).
3. C is the opposite and D is incorrect, since the reaction proceeds without a catalyst.
Teacher's Note:
1. P greater than 1 is possible when the theory underestimates A.
2. Ea comes from the temperature dependence of k.
(a) 0.5
(b) 2
(c) 1
(d) 4
Show Answer & Explanation
Answer: (c) 1
Explanation:
1. Rate of reaction = (1/2) d[NH3]/dt = -d[N2]/dt.
2. So -d[N2]/dt = (1/2)(2.0 × 10-4) = 1.0 × 10-4, hence p = 1.
Teacher's Note:
1. Divide each rate by its stoichiometric coefficient.
2. Two moles of NH3 form for every mole of N2 used.
(a) dependent on the initial concentration of A
(b) independent of temperature
(c) independent of time
(d) independent of the mechanism of the reaction
Show Answer & Explanation
Answer: (c) independent of time
Explanation:
1. d[B]/dt = 3k1[A] and d[C]/dt = 4k2[A].
2. The ratio 3k1/(4k2) contains no [A] or t, so it is independent of time (and of the initial concentration).
3. It does depend on temperature through k1 and k2.
Teacher's Note:
1. [A] cancels in the ratio.
2. k1 and k2 usually have different activation energies.
(a) 5.00 × 10-5
(b) 1.00 × 10-4
(c) 1.38 × 10-4
(d) 3.45 × 10-5
Show Answer & Explanation
Answer: (c) 1.38 × 10-4
Explanation:
1. k = (2.303/t) log(800/50) = (2.303/(2 × 104)) log 16.
2. log 16 = 1.204, so k = 2.303 × 1.204/(2 × 104) = 1.386 × 10-4 s-1.
Teacher's Note:
1. 800/50 = 16 = 24, which is four half-lives.
2. k = 4 × 0.693/t.
(a) 1
(b) 0
(c) 3
(d) 2
Show Answer & Explanation
Answer: (d) 2
Explanation:
1. t1/2 is proportional to p1-n.
2. Doubling p roughly halves t1/2 (3.52 → 1.82 → 0.93), so p1-n = p-1.
3. 1 - n = -1, n = 2.
Teacher's Note:
1. For zero order the half-life would increase with pressure; for first order it stays constant.
2. Use two successive readings to find the exponent.
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Multiple Choice Questions (MCQs) for JEE Chemistry Chemical Kinetics
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