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JEE Main 2021 · ChemistryNumerical answerNumerical valueEasyCalculation

JEE Main 18 March 2021, Shift 1, Chemistry Q53

Question 53 of 90 in this shift, Chemistry question 23 of 30, Section B.

For the reaction C2H6→C2H4+H2\mathrm{C_2H_6 \rightarrow C_2H_4 + H_2} the reaction enthalpy ΔrH=\Delta_rH = __________ kJ mol−1^{-1}. (Round off to the Nearest Integer). [Given : Bond enthalpies in kJ mol−1^{-1} : C-C : 347, C=C : 611; C-H : 414, H-H : 436]

Official answer

128

NTA final key.

Chapter
Thermodynamics (Chemistry)
Topic
Enthalpy and Hess's Law
Idea tested
Bond Enthalpy Calculations

Same idea in other shifts

Asked 2× in all
  1. 3 Apr 2025, Shift 1 · Q71Given : ΔHsub⊖\Delta H^{\ominus}_{sub} [C (graphite)] = 710 kJ mol−1^{-1} ΔC−HH⊖\Delta_{C-H}H^{\ominus} = 414 kJ mol−1^{-1}…MediumNumerical value

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 42 of the 174 JEE Main shifts held from 2017 to 2026.