The conversion of methyl isonitrile to acetonitrile in the gas phase at $250C$

$C{H}_{3}NC(g)longrightarrowC{H}_{3}CN(g)$

is first order in $C{H}_{3}NC.$

During one experiment it was found that when the initial concentration of $C{H}_{3}NC$ was $0\mathrm{.}0270M,$ the concentration of $C{H}_{3}NC$ dropped to $0\mathrm{.}00753M$ after $267\mathrm{.}0s$ had passed.

Based on this experiment, the rate constant for the reaction is

$s^{-1}.$