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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

\mathrm{C_2H_6 \rightarrow C_2H_4 + H_2}

the reaction enthalpy

\Delta_rH =

__________ kJ mol

^{-1}

. (Round off to the Nearest Integer). [Given : Bond enthalpies in kJ mol

^{-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 5× in all

3 Apr 2025, Shift 1 · Q71Given : $\Delta H^{\ominus}_{sub}$ [C (graphite)] = 710 kJ mol $^{-1}$ $\Delta_{C-H}H^{\ominus}$ = 414 kJ mol $^{-1}$ …MediumNumerical value
4 Apr 2024, Shift 1 · Q83The enthalpy of formation of ethane ( $\mathrm{C_2H_6}$ ) from ethylene by addition of hydrogen where the bond-energies of C $-$ H, C $-$ C,…EasyNumerical value
13 Apr 2023, Shift 1 · Q83 $\mathrm{A_2}+\mathrm{B_2}\rightarrow 2\mathrm{AB}$ . $\Delta H_f^0 = -200\ \mathrm{kJ\ mol^{-1}}$ AB, $\mathrm{A_2}$ and $\mathrm{B_2}$ …MediumNumerical value
26 Feb 2021, Shift 2 · Q54The average S $-$ F bond energy in kJ $\mathrm{mol^{-1}}$ of $\mathrm{SF_6}$ is __________. (Rounded off to the nearest integer) [Given :…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 108 of the 174 JEE Main shifts held from 2017 to 2026.