Question

In a first order reaction, `75%` of the reactants disappeared in `1.386 hr`. What is the rate constant ?
A. `3.6xx10^(-3) S^(-1) `
B. `2.8xx10^(-4) S^(-1)`
C. `17.2xx10^(-3) S^(-1)`
D. `1.8xx10^(-3) S^(-1)`

Answer 1

Correct Answer - B
75 % disintegrates i.e., 25 % is remaining
`therefore ` two half -lives have passed .
`therefore " Half" = (1.386)/(2)xx3600 s`
`therefore ` Rate constant `=(0.693xx2)/(1.386xx3600)=2.8xx10^(-4)`