Question

A first order reaction has a specific reaction rate of 10⁻² s⁻¹. How much time will it take for 20 g of the reactant to reduce to 5 g?

Options

• 238.6 second

• 138.6 second

• 346.5 second

• 693.0.second

Answer 1

138.6 second

Explanation:

Given: k = 10⁻² s⁻¹,

A₀ = 20 g,

A_t = 5 g:

For a first-order reaction:

A_t​ = A₀​e^−kt 

⇒ t = `1/k ln  (A_0)/(A_t)`

⇒ `t = 1/0.01 ln (20/5)`

= 100 ln (4)

= 100 × 1.3863

≈ 138.6 s