Answer:

We can write the rate law:

Rate = k[CS2]m[O3]n

Because CS2 is present in excess, [CS2] is essentially constant and we can write

Rate = k’[O3]n

Where k’ = k[CS2]m. This is the method of isolation.

We treat O3 as an ideal gas.

Rate = k’[O3]n ∞ PO3n

If n = 1 (first order), then lnPO3 versus time is linear. If n = 2 (second order), then 1/PO3 versus time is linear. The two plots are presented below.

Time (s)                                   Ozone pressure (torr)              ln(P/torr)          1/P(torr)

0                                              1.76                                         0.565               0.568

30                                            1.04                                         0.039               0.962

60                                            0.79                                         - 0.236             1.27

120                                          0.52                                         - 0.654             1.92

180                                          0.37                                         - 0.994             2.70

240                                          0.29                                         - 1.24               3.45

The plot of lnPO3 versus time is not line, whereas the plot of 1/PO3 versus time is line. Therefore, the reaction is second order in ozone concentration.