A first order reaction takes $20 min$ for $[A]$ to fall from $0.50$ to $0.125 M$ . Find $k$ in units of $1 0^{- 2} mi n^{- 1}$ (two decimals; use $2.303$ and $lo g 4 = 0.6020$ ).

Numerical answer type, answer in 10^-2 min^-1, tolerance 0.02.

Answer: 6.932 10^-2 min^-1

First order:

k = \frac{2.303}{t} lo g \frac{[ A ] _{0}}{[ A ]}

. Here the ratio is

0.50/0.125 = 4

, so

k = 2.303 \times 0.6020/20 = 0.06932 mi n^{- 1}

, i.e.

6.93 \times 1 0^{- 2}