Question

A first order reaction has a specific reaction rate of $10^{-2} \, sec^{-1}$. How much time will it take for $20\, g$ of the reactant to reduce to $5\, g$ ?

• A. 138.6 sec
• B. 346.5 sec
• C. 693.0 sec
• D. 238.6 sec

Answer 1

Answer: (A)

138.6 sec

Answer 2

$t _{1 / 2}=\frac{0.693}{10^{-2}}$ second

For the reduction of $20\, g$ of reactant to $5\, g$, two $t _{1 / 2}$ is required.

$t =2 \times \frac{0.693}{10^{-2}}$ second

$=138.6$ second