(a) It can be seen that the rate of reaction between different time intervals is :
0 - 100 s, rate = [4−3.5]03Pa100=5Pas−1
100 - 200 s, rate = [3.50−,3.00]×103Pa100s=5Pas−1
200 - 300 s, rate = [3.00−2.50]×103Pa100=5Pas−1
We notice that the rate remains constant and therefore, the reaction is of zero order. Alternatively, if we plot p againts t, it is a straight line again indicating it is a zero order reaction.
(b) k = Rate = 5 Pa s−1
(c)t1/2=initialconcentrationorpressure2k
= 4.00×103Pa2×5PaS−1=400s