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JEE Main 202225 JuneEvening Shift
Exam
JEE Main
Year
2022
Date
25 June
Shift
Evening Shift
Subject
Chemistry
Chapter
Thermodynamics (C)

JEE Main 2022 · 25 June · Evening Shift · Chemistry · Thermodynamics (C)

At 25 ° C and 1atm pressure, the enthalpy of combustion of benzene...

At 25°Cand1atm25 ° C and 1atm pressure, the enthalpy of combustion of benzene \left(1\right) and acetylene (g)\left(g\right) are −3268kJmol−1and−1300kJmol−1- 3268kJ{mol}^{- 1} and - 1300kJ{mol}^{- 1}, respectively. The change in enthalpy for the reaction 3C2H23{C}_{2}{H}_{2}\left(g\right)→C6H6(l)\to {C}_{6}{H}_{6}\left(l\right), is

Options

  1. A+324kJmol−1+ 324kJ{mol}^{- 1}
  2. B+632kJmol−1+ 632kJ{mol}^{- 1}
  3. C−632kJmol−1- 632kJ{mol}^{- 1}
  4. D−732kJmol−1- 732kJ{mol}^{- 1}

Correct answer

C. −632kJmol−1- 632kJ{mol}^{- 1}

Step-by-step solution

Standard enthalpy of combustion is defined as the enthalpy change when one mole of a compound is completely burnt in oxygen with all the reactants and products in their standard state under standard conditions (298K and 1 bar pressure)

ΔHr=(ΔHC)reactant−(ΔHC)product{\Delta H}_{r} = {\left({\Delta H}_{C}\right)}_{reactant} - {\left({\Delta H}_{C}\right)}_{product}

=3[ΔHcc(C2H2,g)]−[ΔHc(C6H6,l)]= 3\left[{\Delta Hc}_{c}\left({C}_{2}{H}_{2}, g\right)\right] - \left[{\Delta H}_{c}\left({C}_{6}{H}_{6}, l\right)\right]

=3×(−1300)−(−3268)= 3 \times \left(- 1300\right) - \left(- 3268\right)

=−3900+3268=−632kJ/mole= - 3900 + 3268 = - 632kJ / mole

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