CS2 (g) + 2O3 (g) --> CO2 (g) + 2SO2 (g) This reaction was studied using a large
ID: 795152 • Letter: C
Question
CS2 (g) + 2O3 (g) --> CO2 (g) + 2SO2 (g)
This reaction was studied using a large excess of CS2. The partial pressure of ozone as a function of time is given in the table below. Determine if the reaction is zero, first or second order with respect to ozone.
Time (s)---------------- P(O3) (torr)
0 -------------------------------1.76
30 ---------------------------- 1.04
60------------------------------ 0.79
120----------------------------- 0.52
180----------------------------- 0.37
240 -----------------------------0.29
Explanation / Answer
For a zero order reaction , rate of reaction should be independent of reactant concentration .
consider between 0 and 30 sec
rate = 1.76 -1.04 / 30 = 0.024
consider between 30 and 60 s
rate = 1.04 - 0.79 /30 = 8.33 x 10-3
Rate is not same .So this is not zero order reaction .
For first order reaction rate is proportional to reactant concentration .
consider between 0 and 30 s
rate = 0.024
consider between 30 and 60 sec
rate = 8.33 x 10-3
consider between 60 and 120 sec
rate = 0.79 -0.52 /60 = 4.5 x 10-3
so there is neither increasing constantly nor decreasing constantly .SO the reaction is not of first order .
For a second order reaction
1/ [A]t - 1/ [A]o = kt
if t is constant then the term 1/ [A]t - 1/ [A]o should be constant
consider 0 and 30 sec
1/ [A]t - 1/ [A]o = 1/1.04 - 1/1.76 = 0.39
consider between 30 and 60 sec
1/ [A]t - 1/ [A]o = 1/0.79 - 1/1,04 = 0.30
so the term 1/ [A]t - 1/ [A]o is nearly constant
consider between 60 and 120 sec
1/ [A]t - 1/ [A]o = 1/0.52 - 1/0.79 = 0.66
consider between 120 and 180 sec
1/ [A]t - 1/ [A]o = 1/0.37 - 1/0.52 = 0.77
consider between 180 and 240 sec
1/ [A]t - 1/ [A]o = 1/0.29 - 1/0.37 = 0.74
So the term 1/ [A]t - 1/ [A]o is nearly constant .
So the given reaction is second order with respect to ozone .