Chemical Kinetics
Topics
Chapter tests
See all →Top questions
See all →- If the rate constant of a reaction is 0.03 s^-1, how much time does it take for 7.2 mol L^-1 concentration of the reactant to get reduced to 0.9 mol L^-1?(Given: log 2 = 0.301) Answer: 1. 69.3 s Key idea: the unit mathrms⁻¹ means first order: t=2.303/klog[A]₀/[A] . 7.2/0.9=8 , log8=3×0.301=0.903 . t=2.303×0.903/0.03... 1
- If the half-life (t_1/2) for a first order reaction is 1 minute, then the time required for 99.9% completion of the reaction is closest to : Answer: 4. 10 minutes Key idea: first order: k=frac0.693t_(1/2) and t=2.303/kloga/a-x . k=0.693\ mathrmmin⁻¹ . 99.9% complete: a/a-x=1000 ,... 1
- The rate of a reaction quadruples when temperature changes from 27^°C to 57^°C. Calculate the energy of activation.Given R = 8.314 J K^-1 mol^-1, log 4 = 0.6021 Answer: 2. 38.04 kJ/mol Key idea: logk₂/k₁=E_a/2.303RT₂-T₁/T₁T₂ . T₁=300 K, T₂=330 K, k₂/k₁=4 . E_a=2.303×8.314×0.6021×300×330/30≈38046\ J/m... 1
- Activation energy of any chemical reaction can be calculated if one knows the value of Answer: 1. rate constant at two different temperatures. Key idea: from the Arrhenius equation, logk₂/k₁=E_a/2.303R(1/T₁-1/T₂) . Knowing k at... 1
- Which plot of ln k vs 1/T is consistent with Arrhenius equation? Answer: 1. [graph option 1, see figure] Key idea: ln k=ln A-E_a/R·1/T , a straight line with negative slope -E_a/R and positive intercept ln... 1
- Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R :Assertion A : A reaction can have zero activation energy.Reasons R : The minimum extra amount of energy absorbed by reactant molecules so that thei… Answer: 1. A is false but R is true. Key idea: Activation energy is the extra energy reactants must absorb to reach the threshold energy: E_... 1