Question

For a first order reaction, if the rate constant is 1 min^-1 and the reaction time is 2 min, then the ratio of final to initial concentration is ____

(a) 0.167

(b) 0.135

(c) 0.198

(d) 0.764

Answer 1

Right choice is (b) 0.135

Best explanation: –(frac{dC_A}{dt}) = kCA

Integrating between initial and final concentrations,

CA = CA0e^-kt

(frac{C_A}{C_{A0}} ) = e^-2

(frac{C_A}{C_{A0}} ) = 0.135.