At 518° C, the rate of decomposition of a sample of gaseous acetaldehyde, initially at a pressure of 363 Torr, was 1.00 Torr s^-1 when 5% had reacted…

At $\displaystyle 518$° C, the rate of decomposition of a sample of gaseous acetaldehyde, initially at a pressure of $\displaystyle 363$ Torr, was $\displaystyle 1.00$ Torr $\displaystyle \mathrm{s}^{-1}$ when $\displaystyle 5$% had reacted and $\displaystyle 0.5$ Torr $\displaystyle \mathrm{s}^{-1}$ when $\displaystyle 33$% had reacted. The order of the reaction is :