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UPSC Civil Services (Mains)

Chemistry optional

  • 2 papers
  • 250 marks each
  • 3 h per paper
  • 5 of 8 questions, Q1 and Q5 compulsory

Paper I covers physical and inorganic chemistry.

UPSC Civil Services (Mains), Chemistry optional · 2022 · Paper I

Q5(a). Product concentration in a first-order reaction, N₂O₂ → 2NO

Question

The rate law for the reaction N₂O₂(g) → 2NO(g) is of first order in the concentration of N₂O₂. Derive an expression for the time-dependent behaviour of the product concentration [NO].

Answer in brief

[NO] = 2[N₂O₂]₀(1 − e−kt) for a start with no NO present; NO rises from zero, fastest at the start, and levels off at 2[N₂O₂]₀.

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Topic notes: rate laws, integrated rate equations and half-lives, with every Civil Services, IFoS and Geo-Scientist PYQ →

Coversfirst-order kineticsintegrated rate lawproduct concentrationhalf-lifeN₂O₂ decomposition

All parts of Question 5