In a first order reaction concentration of reactant decreases from 20 milli mol dm-3 to 8 milli mol dm-3 in 40 minute, find rate constant of reaction?

Step-by-step solution

The rate constant for a first-order reaction follows the integrated rate law: k = 2.303 t ( [A]₀ [A]_t ) Given initial concentration [A]₀ = 20 mmol dm ⁻³ , concentration at time t[A]_t = 8 mmol dm ⁻³ , and time t = 40 minutes. Substituting the values: k = 2.303 40 ( 20 8 ) = 2.303 40 (2.5) Using (2.5) 0.3979 : k = 2.303 40 0.3979 0.02291 min ⁻¹ Rounded to two significant figures, k 0.023 min ⁻¹ . This matches option B .