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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 · 2024 · Paper I

Q6(a)(i). Moles of HCl formed per joule absorbed at 480 nm

Question

Calculate the number of moles of HCl(g) produced by the absorption of one joule of radiant energy of wavelength 480 nm in the reaction H₂(g) + Cl₂(g) → 2HCl(g) if the quantum yield of the photochemical reaction is 1.0 × 10⁶. [Given: NA = 6.022 × 10²³ mol⁻¹, h = 6.626 × 10⁻³⁴ J s, c = 2.998 × 10⁸ m s⁻¹]

Answer in brief

8.0 mol of HCl for each joule absorbed (4.0 mol of Cl₂ reacts).

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Coversquantum yieldphotochemical chain reactioneinsteinH₂–Cl₂ reactionphoton energy

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