Question 21: The following data were obtained during the first order thermal decomposition of SO2Cl2at a constant volume.
SO2Cl2(g) → SO2(g) + Cl2(g)
| Experiment |
Time/s - 1
|
Total pressure/atm |
| 1 |
0 |
0.5 |
| 2 |
100 |
0.6 |
Calculate the rate of the reaction when total pressure is 0.65 atm.
Answer:
The thermal decomposition of SO2Cl2at a constant volume is represented by the following equation.

After time, t, total pressure,Pt = (Pº - p) + p + p
⇒ Pt = (Pº + p)
⇒ p = Pt - Pº
therefore, Pº - p = Pº - Pt - Pº
= 2 Pº - Pt
For a first order reaction,
k = 2.303/t Log Pº / Pº - p
= 2.303/t Log Pº / 2 Pº - Pt
When t= 100 s,
k = 2.303 / 100s log 0.5 / 2x0.5 - 0.6
= 2.231 × 10 - 3s - 1
When Pt= 0.65 atm,
P0+ p= 0.65
⇒ p= 0.65 - P0
= 0.65 - 0.5
= 0.15 atm
Therefore, when the total pressure is 0.65 atm, pressure of SOCl2 is
pSOCL2 = P0 - p
= 0.5 - 0.15
= 0.35 atm
Therefore, the rate of equation, when total pressure is 0.65 atm, is given by,
Rate = k(pSOCL2)
= (2.23 × 10 - 3s - 1) (0.35 atm)
= 7.8 × 10 - 4atm s - 1
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