Question
Consider the first order reaction R P. The fraction of molecules decomposed in the given first order reaction can be expressed as
JEE Main
Chemistry
Chemical Kinetics
2026
JEE Main 2026 (04 April Shift 1)
JEE Main Chemistry Question (2026) — Solution
Options
- A. 1 - e^ k_1 t
- B. 1 + e^ k_1 t
- C. 1 + e^ -k_1 t
- D. 1 - e^ -k_1 t
Answer
D. 1 - e^ -k_1 t
Step-by-step solution
For a first order reaction, the concentration of reactant at time t is given by [R]_t = [R]_0 e^ -k_1 t The amount of reactant decomposed is [R]_0 - [R]_t = [R]_0 - [R]_0 e^ -k_1 t = [R]_0 (1 - e^ -k_1 t ) The fraction of molecules decomposed is [R]_0 - [R]_t [R]_0 = [R]_0 (1 - e^ -k_1 t ) [R]_0 = 1 - e^ -k_1 t Answer: 1 - e^ -k_1 t
Related: Chemistry — Chemical Kinetics · All PYQ Banks