Download JEE MCQs for JEE Chemistry: Chemical Kinetics
Explore reliable objective questions for Chemical Kinetics tailored for JEE learners. Utilizing these Chemistry multiple-choice formats ensures thorough preparation and strengthens problem-solving speed for upcoming school assessments.
Chapter-wise Objective Questions: Chemical Kinetics
Navigate directly to the 50 objective questions for Chemical Kinetics using the digital viewer below. Each practice set includes verified answer keys, allowing students to instantly cross-check their work and identify areas requiring further revision.
Multiple Choice Questions
(a) 1.5
(b) 10
(c) 2
(d) 3
Show Answer & Explanation
Answer: (c) 2
Explanation:
1. t = (2.303/k) log(100/(100 - %)).
2. t(99%) = (2.303/k) log 100 = 2 (2.303/k), t(90%) = (2.303/k) log 10 = 1 (2.303/k).
3. x = 2.
Teacher's Note:
1. Each extra '9' of completion adds one unit of 2.303/k.
2. The ratio does not depend on k.
(a) B, C and D only
(b) B and C only
(c) B and D only
(d) C and D only
Show Answer & Explanation
Answer: (a) B, C and D only
Explanation:
1. High Ea means few molecules can react, so usually slow (A false).
2. B, C and D are the standard interpretation of k = A e-Ea/RT.
Teacher's Note:
1. Read each statement against k = A exp(-Ea/RT).
2. d ln k/dT = Ea/RT2.
(a) 9.0 × 109 years
(b) 1.9 × 109 years
(c) 2.3 × 109 years
(d) 4.62 × 109 years
Show Answer & Explanation
Answer: (d) 4.62 × 109 years
Explanation:
1. Moles of U = 1/238, moles of Pb = 0.9/206, so original U = 1/238 + 0.9/206 and N0/N = 1 + (0.9/206)(238) = 2.04.
2. λ = 0.693/(4.5 × 109) y-1.
3. t = (1/λ) ln(2.04) = 6.49 × 109 × 0.7129 = 4.63 × 109 years, about 4.62 × 109 years.
Teacher's Note:
1. The lead present equals the uranium that has decayed.
2. Convert weights to moles before taking the ratio.
(a) 4.92 K
(b) 9.84 K
(c) 2.45 K
(d) 19.67 K
Show Answer & Explanation
Answer: (a) 4.92 K
Explanation:
1. For A: ln 2 = (Ea/R)(1/300 - 1/310).
2. For B: ln 2 = (2Ea/R)(1/300 - 1/T2), so 1/300 - 1/T2 = (1/2)(1/300 - 1/310) = 5.376 × 10-5.
3. 1/T2 = 3.2796 × 10-3, T2 = 304.92 K: rise = 4.92 K.
Teacher's Note:
1. Double Ea means half the required change in 1/T.
2. Use 1/300 - 1/310 = 1.0753 × 10-4.
(a) 1.73 × 10-5
(b) 3.47 × 10-5
(c) 1.73 × 10-4
(d) 3.47 × 10-4
Show Answer & Explanation
Answer: (d) 3.47 × 10-4
Explanation:
1. The concentration falls to 1/4 in 40 min, i.e. two half-lives, t1/2 = 20 min.
2. k = 0.693/20 = 0.03466 min-1.
3. Initial rate = k[X]0 = 0.03466 × 0.01 = 3.47 × 10-4 mol L-1 min-1.
Teacher's Note:
1. Rate = k x concentration.
2. Two half-lives bring 0.01 to 0.0025.
(a) 5000
(b) 1700
(c) 10000
(d) 8500
Show Answer & Explanation
Answer: (d) 8500
Explanation:
1. K = kf/kb = (Af/Ab) e(Eb - Ef)/RT = 4 e2.
2. ln K = ln 4 + 2 = 1.4 + 2 = 3.4.
3. |ΔG| = RT ln K = 2500 × 3.4 = 8500 J mol-1.
Teacher's Note:
1. Equilibrium constant is the ratio of forward to reverse rate constants.
2. ΔG = -RT ln K.
(a) 5
(b) 3.2
(c) 2.5
(d) 4.1
Show Answer & Explanation
Answer: (d) 4.1
Explanation:
1. k = 0.693/10 = 0.0693 day-1.
2. After 1/4 conversion, 3/4 is left: t = (1/k) ln(4/3) = (2 ln 2 - ln 3)/0.0693 = (1.386 - 1.1)/0.0693 = 4.1 days.
Teacher's Note:
1. ln(4/3) = ln 4 - ln 3.
2. t = (1/k) ln(a/(a - x)).
(a) A, B and C only
(b) A only
(c) C only
(d) A and C only
Show Answer & Explanation
Answer: (d) A and C only
Explanation:
1. Overall order is the sum of the exponents.
2. k[A]2 and k[A][B] have order 2.
3. k[A][B]2 is third order and k1[A] + k2[B]2 has no single order.
Teacher's Note:
1. The exponents need not equal the stoichiometric coefficients.
2. Add the powers.
(a) rate = k[A]2, k = 5 L mol-1 s-1
(b) rate = k[A][B], k = 5 L mol-1 s-1
(c) rate = k[B], k = 0.5 s-1
(d) rate = k[A], k = 0.5 s-1
Show Answer & Explanation
Answer: (d) rate = k[A], k = 0.5 s-1
Explanation:
1. Doubling [A] doubles the rate: first order in A.
2. Doubling [B] leaves the rate unchanged: zero order in B.
3. rate = k[A]; k = 0.05/0.1 = 0.5 s-1.
Teacher's Note:
1. Compare runs in which only one concentration changes.
2. Unit of k for first order is s-1.
(a) -3 d[A]/dt = d[C]/dt = k[A]^n[B]^m
(b) -d[A]/dt = d[C]/dt = k[A]^n[B]^m
(c) -(1/3) d[A]/dt = d[C]/dt = k[A]^n[B]^m
(d) (1/3) d[A]/dt = d[C]/dt = k[A]^n[B]^m
Show Answer & Explanation
Answer: (c) -(1/3) d[A]/dt = d[C]/dt = k[A]^n[B]^m
Explanation:
1. Rate of reaction = -(1/3) d[A]/dt = -(1/2) d[B]/dt = d[C]/dt = d[D]/dt.
2. It equals k[A]^n[B]^m with n and m found experimentally.
Teacher's Note:
1. Divide each rate by its coefficient.
2. Reactant terms carry a minus sign.
(a) 20
(b) 40
(c) 25
(d) 50
Show Answer & Explanation
Answer: (d) 50
Explanation:
1. The unit g per year shows a zero order reaction.
2. Amount decomposed = 2.5 g, so t = 2.5/0.05 = 50 years.
Teacher's Note:
1. The unit of k reveals the order.
2. Zero order: x = kt.
(a) 18.0 h
(b) 12.0 h
(c) 7.2 h
(d) 9.0 h
Show Answer & Explanation
Answer: (a) 18.0 h
Explanation:
1. Zero order: t1/2 = a/(2k) gives k = 0.2/(2 × 6) = 1/60 M h-1.
2. Time = (0.5 - 0.2)/k = 0.3 × 60 = 18 h.
Teacher's Note:
1. Rate is constant in zero order.
2. Time = concentration change/k.
(a) 214.4 kJ mol-1
(b) 107.2 kJ mol-1
(c) 53.6 kJ mol-1
(d) 26.8 kJ mol-1
Show Answer & Explanation
Answer: (b) 107.2 kJ mol-1
Explanation:
1. ln 4 = (Ea/R)(1/300 - 1/310) = (Ea/R)(1.0753 × 10-4).
2. Ea = 8.314 × 1.386/1.0753 × 10-4 = 1.072 × 105 J mol-1 = 107.2 kJ mol-1.
Teacher's Note:
1. ln 4 = 2 ln 2 = 1.386.
2. Convert J to kJ.
(a) A, B and C only
(b) B and C only
(c) B, C and D only
(d) C only
Show Answer & Explanation
Answer: (b) B and C only
Explanation:
1. ln(k2/k1) = (Ea/R)(1/T1 - 1/T2) needs k at two temperatures.
2. At equal concentrations the ratio of rates equals the ratio of rate constants, so B also works.
3. A single temperature or a concentration change does not give Ea.
Teacher's Note:
1. Two temperatures are needed.
2. Rates at the same composition are proportional to k.
(a) 2.3 s
(b) 1.15 s
(c) 1.5 s
(d) 2.15 s
Show Answer & Explanation
Answer: (b) 1.15 s
Explanation:
1. At t1 the pressure of A = 2u - 0.25u = 1.75u, against 2u initially.
2. 2.303 log(2/1.75) = k t, with 2.303 log(8/7) = 0.1335.
3. k = log(64/49) = 2 log(8/7) = 2 × 0.0580 = 0.1160 s-1, so t1 = 0.1335/0.1160 = 1.15 s.
Teacher's Note:
1. Use the same log base on both sides.
2. A falls from 2u to 1.75u.
(a) k = k'
(b) k = 2k'
(c) 2k = k'
(d) k = 4k'
Show Answer & Explanation
Answer: (c) 2k = k'
Explanation:
1. d[NO2]/dt = 2 × (-d[N2O5]/dt) because 4 NO2 form for 2 N2O5 used.
2. So k'[N2O5] = 2k[N2O5], k' = 2k.
Teacher's Note:
1. NO2 forms twice as fast as N2O5 disappears.
2. Use the stoichiometric ratio 4 : 2.
(a) k4 < k3 and k2 < k1, if T2 > T1
(b) k4 > k3 and k2 > k1, if T2 < T1
(c) k4 < k3 and k2 > k1, if T2 < T1
(d) k4 > k3 and k2 > k1, if T2 > T1
Show Answer & Explanation
Answer: (d) k4 > k3 and k2 > k1, if T2 > T1
Explanation:
1. If T2 > T1, raising the temperature raises k with or without catalyst: k2 > k1 and k4 > k3.
2. If T2 < T1 both pairs fall, so k2 < k1 and k4 < k3. Only the first option is consistent.
Teacher's Note:
1. The direction of the temperature change decides the sign of the change in k.
2. A catalyst does not reverse the temperature trend.
(a) 1
(b) 5
(c) 10
(d) 100
Show Answer & Explanation
Answer: (b) 5
Explanation:
1. Runs 1 and 2: rate independent of [B]. Runs 1 and 3: doubling [A] doubles the rate. So rate = k[A], k = 6.93 × 10-3/0.10 = 0.0693 min-1.
2. Since rate = -(1/2) d[A]/dt, -d[A]/dt = 2k[A], so the first order constant for A is 0.1386 min-1.
3. t1/2 = 0.693/0.1386 = 5 min.
Teacher's Note:
1. Rate of reaction differs from rate of consumption of A by the factor 2.
2. Half-life of A uses the constant for A.
(a) first order with respect to cane sugar
(b) second order
(c) third order
(d) zero order with respect to cane sugar
Show Answer & Explanation
Answer: (a) first order with respect to cane sugar
Explanation:
1. Water is present in large excess, so its concentration is effectively constant.
2. Rate = k[sucrose][H2O] reduces to k'[sucrose], a pseudo first order law.
Teacher's Note:
1. Such reactions are called pseudo first order.
2. Molecularity is two but the order is one.
(a) The order with respect to B is 2
(b) The order with respect to B is 1
(c) The total order of the reaction is 4
(d) The order with respect to A is 2
Show Answer & Explanation
Answer: (a) The order with respect to B is 2
Explanation:
1. Doubling A alone doubles the rate: order in A = 1.
2. Both doubled gives 8 times: 2 × 2^m = 8, so m = 2.
3. Order in B is 2 and total order 3.
Teacher's Note:
1. Separate the contributions of A and B.
2. 2.4/0.3 = 8.
(a) 2
(b) 1
(c) 3
(d) 0
Show Answer & Explanation
Answer: (a) 2
Explanation:
1. Half-time independent of [A]: the reaction is first order in A, a = 1.
2. Between pH 5 and 4 [H+] increases 10 times and the half-time falls 10 times, so rate is proportional to [H+]: b = 1.
3. a + b = 2.
Teacher's Note:
1. In a buffer [H+] is constant, so the reaction behaves as pseudo first order.
2. Half-time is inversely proportional to the effective rate constant.
(a) Ef = 60 kJ mol-1; Eb = 100 kJ mol-1
(b) Ef = 30 kJ mol-1; Eb = 70 kJ mol-1
(c) Ef = 80 kJ mol-1; Eb = 120 kJ mol-1
(d) Ef = 70 kJ mol-1; Eb = 30 kJ mol-1
Show Answer & Explanation
Answer: (c) Ef = 80 kJ mol-1; Eb = 120 kJ mol-1
Explanation:
1. ΔH = Ef - Eb = -40 kJ.
2. With Ef = 2x, Eb = 3x: 2x - 3x = -40, x = 40.
3. Ef = 80 kJ mol-1, Eb = 120 kJ mol-1.
Teacher's Note:
1. ΔH equals Ef minus Eb.
2. Exothermic means Eb is larger.
(a) 106.25 mm Hg
(b) 116.25 mm Hg
(c) 175.0 mm Hg
(d) 136.25 mm Hg
Show Answer & Explanation
Answer: (a) 106.25 mm Hg
Explanation:
1. Total = 50 + 1.5p (p = N2O5 reacted); 87.5 gives p = 25 mm, half of 50: t1/2 = 50 min.
2. At 100 min (two half-lives) N2O5 left = 12.5 mm, p = 37.5 mm: total = 50 + 56.25 = 106.25 mm Hg.
Teacher's Note:
1. Two half-lives leave one quarter.
2. Use the pressure gain 1.5 per unit of N2O5 reacted.
(a) 30
(b) 8
(c) 3
(d) 9
Show Answer & Explanation
Answer: (d) 9
Explanation:
1. t = (2.303/k) log(c0/c).
2. t1/8 = (2.303/k) log 8 = (2.303/k)(0.9); t1/10 = (2.303/k)(1).
3. 10 × 0.9 = 9.
Teacher's Note:
1. log 8 = 3 log 2 = 0.9.
2. The ratio is independent of k.
(a) 9k
(b) 3k
(c) k
(d) k/3
Show Answer & Explanation
Answer: (c) k
Explanation:
1. The rate constant depends only on temperature (and catalyst).
2. Changing a concentration changes the rate, not k.
Teacher's Note:
1. Rate triples but k stays the same.
2. Do not confuse rate and rate constant.
(a) 33.68 h
(b) 29.77 h
(c) 12.8 h
(d) 67.37 h
Show Answer & Explanation
Answer: (a) 33.68 h
Explanation:
1. Partial decay constant = fraction x total decay constant, so partial half-life = t1/2/fraction.
2. For β-minus: 12.8/0.38 = 33.68 h. (For β-plus 67.37 h, electron capture 29.77 h.)
Teacher's Note:
1. The three paths are parallel first order processes.
2. Smaller fraction means longer partial half-life.
(a) A and B only
(b) A and D only
(c) A, B, C and D only
(d) A, B and D only
Show Answer & Explanation
Answer: (d) A, B and D only
Explanation:
1. Let p0 be the initial pressure; each 3 atm of A gives 4 atm of products, so total at infinity = (4/3)p0 = 4 and p0 = 3 atm.
2. After 20 min, if 3y atm of A has reacted, total = 3 + y = 3.5, y = 0.5, so A left = 3 - 1.5 = 1.5 atm = half.
3. So t50% = 20 min, t75% = 40 min, t87.5% = 60 min. t99% = 20 log2(100) = 133 min, not 64/3 min.
Teacher's Note:
1. Find p0 from the final pressure first.
2. Each half-life is 20 min.
(a) -1.25 × 10-4
(b) -5.00 × 10-4
(c) -2.50 × 10-4
(d) -3.75 × 10-4
Show Answer & Explanation
Answer: (b) -5.00 × 10-4
Explanation:
1. -d[SO2]/dt = 2 (-d[O2]/dt) from the stoichiometry 2 : 1.
2. d[SO2]/dt = -5.00 × 10-4 mol L-1 s-1.
Teacher's Note:
1. SO2 is used up twice as fast as O2.
2. Keep the minus sign for a reactant.
(a) is halved
(b) is doubled
(c) is quadrupled
(d) remains the same
Show Answer & Explanation
Answer: (b) is doubled
Explanation:
1. Rate is first order in B.
2. Doubling [B] doubles the rate.
Teacher's Note:
1. The order, not the stoichiometric coefficient, matters.
2. The coefficient 2 does not enter the rate law here.
(a) 2 : 3 : 4
(b) 1 : 2 : 3
(c) 1 : 3 : 5
(d) 1 : 1 : 1
Show Answer & Explanation
Answer: (d) 1 : 1 : 1
Explanation:
1. The rate constant of a reaction depends only on temperature (and catalyst).
2. The temperature is constant, so k is the same at all three times: 1 : 1 : 1.
Teacher's Note:
1. Do not confuse the rate constant with the rate.
2. The rate falls as A is used up, k does not.
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Chemical Kinetics Objective Questions & Solutions for JEE Chemistry
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FAQs
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