Question

A first order reaction has a rate constant $1.15\times 10^{-3}{s}^{-1}$ . How long will $5g$ of this reactant take to reduce to $3g$ ?

• A. 222 s
• B. 332 s
• C. 444 s
• D. 555 s

Answer 1

Answer: (C)

Here,${\left[R\right]}_0=5g,\left[R\right]=3g,k=1.15\times 10^{-3}{s}^{-1}$
For first order reaction,$t=\frac{2.303}{k}lo\frac{g{\left[R\right]}_0}{\left[R\right]}$
$\frac{2.303}{1.15\times 10^{-3}}log\frac{5}{3}=2.00\times 10^{-3}\left(log1.667\right)$
$=2.0\times 10^3\times 0.2219s=443.8\approx 444s$