Question

Cyclopropane rearranges to form propene $\, \, \, \, \, \, \, \triangle \, \, \longrightarrow \, \, CH_3 - CH = CH_2$ This follows first order kinetics. The rate constant is $2.714 \times 10^{-3} \, s^{-1}.$ The initial concentration of cyclopropane is $0.29\, M$. What will be the concentration of cyclopropane after $100 \,s$?

• A. $0.035 \,M$
• B. $0.22\, M$
• C. $0.145\, M$
• D. $0.0018\, M$

Answer 1

Answer: (B)

$0.22\, M$

Answer 2

$k = \frac{2.303}{t} \, log \, \frac{a}{(a-x)}$
( a - x) is the concentration left after 100 s.
\hspace15mm 2.7 \times 10^{-3} = \frac{2.303}{100} \, log \, \frac{0.29}{(a-x)}
\Rightarrow \hspace15mm \frac{0.27}{2.303} = log \, \frac{0.29}{(a-x)}
\Rightarrow \hspace15mm 0.117 = log \, \frac{0.29}{(a-x)}
\Rightarrow \hspace15mm (a-x) = 0.22 \, M