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Saturday, 31 October

JEE Main 2026 · ChemistryNumerical answerNumerical valueHardMulti-step

JEE Main 4 April 2026, Shift 2, Chemistry Q71

Question 71 of 75 in this shift, Chemistry question 21 of 25, Section B.

If 3.365 g of ethanol (ll) is burnt completely in a bomb calorimeter at 298.15 K, the heat produced is 99.472 kJ. The ∣ΔHf∘∣|\Delta H_f^\circ| of ethanol at 298.15 K is ________ ×102\times10^2 kJ mol−1\mathrm{kJ\ mol^{-1}}. (Nearest integer) Given: Standard enthalpy for combustion of graphite =−393.5 kJ mol−1=-393.5\ \mathrm{kJ\ mol^{-1}} Standard enthalpy of formation of water (l) =−285.8 kJ mol−1=-285.8\ \mathrm{kJ\ mol^{-1}} Molar mass in g mol−1\mathrm{g\ mol^{-1}} of C, H, O are 12, 1 and 16 respectively

Official answer

3

NTA final key.

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

Same idea in other shifts

Asked 7× in all
  1. 3 Apr 2025, Shift 2 · Q72A sample of n-octane (1.14 g) was completely burnt in excess of oxygen in a bomb calorimeter, whose heat capacity is 5 kJ…MediumNumerical value
  2. 5 Apr 2024, Shift 1 · Q83The heat of combustion of solid benzoic acid at constant volume is −321.30-321.30 kJ at 27∘27^\circC. The heat of combustion at constant…MediumNumerical value
  3. 8 Apr 2023, Shift 2 · Q83For complete combustion of ethene, C2H4(g)+3O2(g)→2CO2(g)+2H2O(l)\mathrm{C_2H_4(g) + 3O_2(g) \rightarrow 2CO_2(g) + 2H_2O(l)} the amount of heat produced as measured…MediumNumerical value
  4. 26 Jul 2022, Shift 1 · Q842.4 g coal is burnt in a bomb calorimeter in excess of oxygen at 298 K and 1 atm pressure. The temperature of the calorimeter rises from…MediumNumerical value
  5. 27 Jul 2022, Shift 2 · Q83A gas (Molar mass=280 g mol−1\mathrm{mol^{-1}}) was burnt in excess O2\mathrm{O_2} in a constant volume calorimeter and during combustion the…MediumNumerical value
  6. 25 Feb 2021, Shift 1 · Q53The reaction of cyanamide, NH2CN(s)\mathrm{NH_2CN_{(s)}} with oxygen was run in a bomb calorimeter and ΔU\Delta U was found to be −742.24-742.24 kJ…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.