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NCERT Class XII Chemistry
Chapter - Chemical Kinetics
Questions with Solutions

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Question : 21
Total: 39
The following data were obtained during the first order thermal decomposition of SO2Cl2 at 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.
Solution:  
‌SO2Cl2(g)→ SO2(g)+ Cl2(g)
Let‌initial‌pressureP0‌0‌0
Pressure‌at‌time‌tP0– p‌p‌p
Let initial pressure P0∝R0
Pressure at time t,Pt=P0– p+p+p=P0+p
∴‌ Pressure of reactant at time t=P0– p=2P0– Pt∝R
Using formula, k=
2.303
t
‌log‌ ‌
P0
2P0−Pt

When t=100 s,
k=
2.303
100
‌log‌
0.5
2 ×0.5−0.6

=
2.303
100
‌log(1.25)
=
2.303
100
(0.0969)
=2.2316×10−3 s−1
When Pt=0.65 atm,
∴ Pressure of SO2Cl2 at time t (p so2CI2 ),
‌‌‌‌‌R=2P0−pt
‌‌‌‌‌‌‌=2×0.50−0.65 atm $$
‌‌‌‌‌‌‌=0.35 atm
Rate at that time =k×p SO2 Cl2
=(2.2316×10−3 )×(0.35)
=7.8×10−4 atms−1
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