Quantrex Quantrex AcademyJEE · NEET · NDA PYQs with solutions Open app
JEE MainChemistryChemical Kinetics

Two different first order reactions, A products and B products , have half-lives in the ratio t_ 1/2, A : t_ 1/2, B = 2:1 . If t_A is the time taken for the concentration of A to reduce to 1 16 of its initial value, and t_B is the time taken for the concentration of B to reduce to 1 8 of its initial value, then the ratio t_A t_B will be :

Options

  1. A4 3
  2. B2 3
  3. C3 8
  4. D8 3

Correct answer

D. 8 3

Step-by-step solution

For a first order reaction, the time required to reduce the concentration to ( 1 2 )^n of its initial value is n t_ 1/2 . For reaction A , the concentration reduces to 1 16 = ( 1 2 )^4 . Therefore, t_A = 4 t_ 1/2, A . For reaction B , the concentration reduces to 1 8 = ( 1 2 )^3 . Therefore, t_B = 3 t_ 1/2, B . The ratio of the times is: t_A t_B = 4 t_ 1/2, A 3 t_ 1/2, B Given that t_ 1/2, A t_ 1/2, B = 2 1 , we substitute this into the equation: t_A t_B = 4 3 2 = 8 3 Answer: 8 3

Practice Chemical Kinetics on Quantrex Academy →

More from Chemical Kinetics

For a reversible reaction R P , at constant temperature, both the forward and the backward reactions are first order elementary reactions with rate constants k_f and k_b , respecti 2026For a first-order reaction R P at a given temperature, k is the rate constant. For this reaction, at the given temperature, the concentrations of R and P at a time t are [ R ] and 2026Given below are two statements: R=8.314 J K ⁻¹ mol ⁻¹ and 1 cal =4.2 J Statement I: When E_a=12.6 kcal/mol, the room temperature rate constant is doubled by a 10 ,^ C increase in t 2026Decomposition of a hydrocarbon follows the equation k = (5.5 10¹¹ , s ⁻¹) ,e^ -28000 , K T . The activation energy of reaction is __________ kJ mol ⁻¹ . (Nearest Integer) Given : R 2026For a reaction A P at T K , the half life (t_ 1/2 ) is plotted as a function of initial concentration [A]₀ of A as given below. The value of x in the given figure is _______ s (Nea 2026First order gas phase reaction A B + C p_i = initial pressure of gas A, p_t = total pressure of the reaction mixture at time t Expression of rate constant ( k ) is 2026If the half life of a first order reaction is 6.93 minutes then the time required for completion of 99 % of the reaction will be _____ minutes. (Given : 2 = 0.3010 ) 2026Consider the given graph showing variation of reactant concentration with time. Three different reactions were started with identical initial concentration of reactants. Which of t 2026 Full Chemical Kinetics list All JEE Main PYQs