Question

What is the value of rate constant of first order reaction, if it takes 15 minutes for consumption of 20% of reactants?

Options

• 1.38 × 10^-2 min^-1

• 1.48 × 10^-2 min^-1

• 1.07 × 10^-2 min^-1

• 1.84 × 10^-2 min^-1

Answer 1

1.48 × 10^-2 min^-1 

Explanation:

Given, t = 15 min tor 20% of reactant to react.

For first order reaction,

Rate constant (k) = `2.303/"t" log  (["R"_0])/(["R"])`

where,

[R₀] = original amount of reactant

[R] = reactant remaining unreacted

So, [R₀] = 100

[R] = 80 (20% reacted)

k = `2.303/(15 "min") log [100/80]`

= 1.48 × 10^-2 min^-1