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Question: Answered & Verified by Expert
Calculate the half-life of the first-order reaction
C2H4OgCH4g+COg
if the initial pressure of C2H4Og is 80 mm and the total pressure at the end of 20 minutes is 120 mm.
ChemistryChemical KineticsJEE Main
Options:
  • A 40 min
  • B 120 min
  • C 20 min
  • D 80 min
Solution:
2725 Upvotes Verified Answer
The correct answer is: 20 min

According to the question,
p0-p+p=120 mm
or p0+p=120 mm
or p=120-80=40 mm.
For a first order reaction,
k=1tlnp0p0-p=120ln8080-40=120ln2 …(i)
But we know that t12=1n2k …(ii)
From equations (i) and (ii)
k=120kt12
t12=20 min.

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