Question

Calculate the time required to decrease the concentration of reactant of first order reaction from 0.8 M to 0.1 M if rate constant is 0.1155 hour⁻¹.

Options

• 6 hour

• 12 hour

• 18 hour

• 24 hour

Answer 1

18 hour

Explanation:

For a first order reaction,

`k = 2.303/t log_10  [A]_0/[A]_t`

`therefore t = 2.303/0.1155 xx log_10  0.8/0.1`

= 19.94 × log₁₀ (8)

= 19.94 × log₁₀ (2³)

= 19.94 × 3 log₁₀ (2)

= 19.94 × 3 × 0.301

= 18.0 hour