The gas phase decomposition of dinitrogen pentoxide at $335K$

$N_2{O}_5(g)2N{O}_2(g)+\frac{1}{2}{O}_2(g)$

is first order in $N_2{O}_5$ with a rate constant of $4\mathrm{.}70{10}^{-3}{s}^{-1}.$

If the initial concentration of $N_2{O}_5$ is $0\mathrm{.}215M,$ the concentration of $N_2{O}_5$ will be M after $256$ s have passed.

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