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Most Important Selected Qs for JEE AdvancedChemistryChemical Kinetics

CH ₃ CHO is thermally decomposed to CH ₄ and CO as CH ₃ CHO CH ₄+ CO and rate of reaction in terms of CH ₄ is d [ CH ₄ ] dt = K _ [ CH ₃ CHO ]^ 3 2 [ K is overall rate constant]. Mechanism: Step (I) CH ₃ CHO K ₁ C H ₃+ C HO Step (II) C H ₃+ CH ₃ CHO K ₂ CH ₄+ C H ₂ CHO Step (III) C H ₂ CHO K ₃ C H ₃+ CO Step (IV) 2 C H ₃ ~K ₄ CH ₃ CH ₃ The pre-exponential factor (A) for step I, II, III and IV are 10¹⁰, 10^6, 10^5 and

Correct answer

09

Step-by-step solution

Hint: Rate = K ₂ ( ~K ₁ 2 ~K ₄ )^ 1 2 [ CH ₃ CHO ]^ 3 2 Solution : Rate = K ₂ ( ~K ₁ 2 ~K ₄ )^ 1 2 [ CH ₃ CHO ]^ 3 2 so, K=A e^ - E₀ R T =A₂ e^ - E₂ R T ( A₁ e^ - E₁ R T 2 A₄ e^ E_i R T )^ 1 2 A=A₂ ( A₁ 2 A₄ )^ 1 2 Rate of reaction: d [ CH ₄ ] dt = K ₂ [ C H ₃ ] [ CH ₃ CHO ] Now, by steady state approximation aligned d [ C H ₃ ] dt =0= & K ₁ [ CH ₃ CHO ]- K ₂ [ C H ₃ ] [ CH ₃ CHO ] & + K ₃ [ C H ₂ CHO ]-2 ~K ₄ [ C H ₃ ]^2 ~d [ C H ₂ CHO ] dt = & 0= K ₂ [ C H ₃ ] [ CH ₃ CHO ]- K ₃ [ C H ₂ CHO ] aligned so, [ C H ₃ ]

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