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Saturday, 31 October

JEE Main 2025 · ChemistryMultiple choiceSingle correctMediumCalculation

JEE Main 7 April 2025, Shift 2, Chemistry Q57

Question 57 of 75 in this shift, Chemistry question 7 of 25, Section A.

A(g)→B(g)+C(g)\mathrm{A(g)\to B(g)+C(g)} is a first order reaction. Time | tt | ∞\infty psystemp_{system} | ptp_t | p∞p_\infty The reaction was started with reactant A only. Which of the following expression is correct for rate constant kk ?
  1. (1)k=1tln⁡p∞ptk=\frac{1}{t}\ln\frac{p_\infty}{p_t}
  2. (2)k=1tln⁡p∞2(p∞−pt)k=\frac{1}{t}\ln\frac{p_\infty}{2(p_\infty-p_t)}Official answer
  3. (3)k=1tln⁡p∞(p∞−pt)k=\frac{1}{t}\ln\frac{p_\infty}{(p_\infty-p_t)}
  4. (4)k=1tln⁡2(p∞−pt)ptk=\frac{1}{t}\ln\frac{2(p_\infty-p_t)}{p_t}

Official answer

Option 2

NTA final key.

Chapter
Chemical Kinetics
Topic
Rate Laws
Idea tested
First-Order Kinetics via Total Pressure

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Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.