Question

A first order reaction is $20\%$ complete in $10$ minutes. What is the specific rate constant for the reaction?

• A. $0.0970\, min.^{-1}$
• B. $0.009 \,min.^{-1}$
• C. $0.0223 \,min.^{-1}$
• D. $2.223 \,min.^{-1}$

Answer 1

Answer: (C)

$0.0223 \,min.^{-1}$

Answer 2

$a-x=\frac{80}{100}\times a=0.8a$, $t=10 \, min$. $k=\frac{2.303}{t} log$ $\frac{a}{a-x}$ $=\frac{2.303}{10} log$ $\frac{a}{0.8a}$ $k=0.233\, log$ $\frac{10}{8}=0.2303\left(1-0.9030\right)$ $=0.2303\times 0.0970=0.0223$ $min.^{-1}$