KCET2026ChemistryChemical Kinetics
For a 1st order change R P , the concentration of Reactant R changes from 0.1 M to 0.025 M in 40 minutes. The rate of reaction when the concentration of R is 0.01 M is ____
Options
- A1.73 10⁻⁵ M min ⁻¹
- B3.47 10⁻⁴ M min ⁻¹
- C3.47 10⁻⁵ M min ⁻¹
- D1.73 10⁻⁴ M min ⁻¹
Correct answer
B. 3.47 10⁻⁴ M min ⁻¹
Step-by-step solution
The concentration of the reactant changes from 0.1 M to 0.025 M , which is 1 4 of the initial concentration. This corresponds to 2 half-lives. 2 t_ 1/2 = 40 min t_ 1/2 = 20 min The rate constant k for a first-order reaction is: k = 0.693 t_ 1/2 = 0.693 20 = 0.03465 min ⁻¹ The rate of reaction when [R] = 0.01 M is: Rate = k[R] Rate = 0.03465 0.01 = 3.465 10⁻⁴ M min ⁻¹ Rate 3.47 10⁻⁴ M min ⁻¹ Answer: 3.47 10⁻⁴ M min ⁻¹