Question

A substance ${}^{\prime }{A}^{\prime }$ decomposes by a first order reaction starting initially with $\left[A\right]=2.00M$ and after $200min\left[A\right]=0.15M$. For this reaction what is the value of $k$ ?

• A. $1.29\times {10}^{-2}mi{n}^{-1}$
• B. $2.29\times {10}^{-2}mi{n}^{-1}$
• C. $3.29\times {10}^{-2}mi{n}^{-1}$
• D. $4.40\times {10}^{-2}mi{n}^{-1}$

Answer 1

Answer: (A)

$1.29\times {10}^{-2}mi{n}^{-1}$

Given $A\left(a\right)=2.00M,,t=200min$ and $(a-x)=0.15M$

$k=\frac{2.303}{t}\log \frac{a}{a-x}=\frac{2.303}{200}\log \frac{2.00}{0.15}$

$=\frac{2.303}{200}\times (0.301+0.824)=1.29\times {10}^{-2}mi{n}^{-1}$