For the first order reaction, half-life is 14 sec. The time requires for the initial concentration to reduce to 1/8th of its value is:
Correct answer: B. 42s
- A. 28s
- B. 42s
- C. (14)2s
- D. (14)3s
Explanation
For a first-order reaction, the half-life is the time it takes for the concentration to reduce to half its initial value. Given that the half-life is 14 seconds, we need to determine how many half-lives it takes to reduce the concentration to 1/8th of its initial value. Since (1/2)3 = 1/8, it takes 3 half-lives to reach this concentration. Therefore, the total time required is 3 x 14 = 42 seconds. Option B is correct. Option A incorrectly assumes only 2 half-lives are needed. Options C and D incorrectly manipulate the half-life duration.
Last updated
About Reaction Kinetics
Reaction kinetics relates reaction rate to concentration, temperature, surface area and catalysts. Questions cover rate laws, reaction order, rate constants, activation energy and the activated complex, including how a catalyst lowers the activation energy without changing the overall energy change or equilibrium position.
Practise Reaction Kinetics
573 free Reaction Kinetics MCQs from Chemistry, each with the correct answer and an explanation. Unlimited attempts, no account needed.
Exams that ask Chemistry questions like this
Chemistry is on 12 papers prepared for on TestUstad, and all of them draw the same bank, so this question is worth knowing for every one of them.
Related questions
100 g of a substance decays slower than 50 g of the same substance. The order of decay follows kinetics:
12.Rate of disappearance of reactant is equal to
13.Rate of reaction, when concentration of reactants are taken as unity is called
14.Order of reaction of N2O5→2N2O5+ O2
16.Which order of reaction obeys the relation t1/2= 1/Ka