Question

For a first order reaction, (A) → products, the concentration of A changes from 0.1M to 0.025M in 40minutes.

Answer 1

$a = a |0| \times {e}^{ -k t} \\ 0.025 = 0.1 \times {e}^{ - kt} \\ ln( \frac{0.025}{0.1} ) = - k \times 40 \\ \\ ln(0.25) = - 40k \\ - 1.386 = - 40k \\ k = 0.03 \: min {}^{ - 1}$