Quantrex Quantrex AcademyJEE · NEET · NDA PYQs with solutions Open app
MHT CET202611 April 2026Evening ShiftChemistryThermodynamics (C)Actual

The bond dissociation enthalpy of H ₂ , Cl ₂ and HCl are 434 , 242 and 431 kJ mol ⁻¹ respectively. Calculate the enthalpy of formation of HCl.

Options

  1. A-93 kJ mol ⁻¹
  2. B245 kJ mol ⁻¹
  3. C93 kJ mol ⁻¹
  4. D-245 kJ mol ⁻¹

Correct answer

A. -93 kJ mol ⁻¹

Step-by-step solution

The reaction for the formation of HCl is: 1 2 H ₂(g) + 1 2 Cl ₂(g) HCl (g) The enthalpy of formation is given by: _f H = BE ( reactants ) - BE ( products ) _f H = [ 1 2 BE ( H ₂) + 1 2 BE ( Cl ₂) ] - BE ( HCl ) Substituting the given values: _f H = [ 1 2 (434) + 1 2 (242) ] - 431 _f H = (217 + 121) - 431 _f H = 338 - 431 = -93 kJ mol ⁻¹ Answer: -93 kJ mol ⁻¹

Practice Thermodynamics (C) on Quantrex Academy →

More from Thermodynamics (C)

Identify the INCORRECT statement 2026The standard enthalpies of formation of CH₄ (g), CO₂ (g) and H₂ O(l) are -74.8 kJ mol ⁻¹ , -393.5 kJ mol ⁻¹ and -285.8 kJ mol ⁻¹ respectively. Then the enthalpy change for the give 2026For an ideal gas undergoing an isothermal change, there is 2026Ozone is formed by the reaction O _ 2(g) + O _ (g) O _ 3(g) , H = -107.2 kJ . Given O=O bond energy is 498.0 kJ mol ⁻¹ , the average bond energy of ozone is: 2026H and S for a reaction are 35.5 kJ mol ⁻¹ and 83.6 J K ⁻¹ respectively. Assuming that H and S do not vary with temperature, the reaction is spontaneous when: 2026The heat of combustion of carbon to CO ₂ is -393.5 kJ mol ⁻¹ . The heat released on the formation of 35.2 g of CO ₂ by combustion of C is: 20265 moles of a gas is allowed to pass through a series of changes as shown in the graph, in a cyclic process. The processes C A , B C and A B respectively are 20251 mole of an ideal gas is allowed to expand isothermally and reversibly from 1 L to 5 L at 300 K. The change in enthalpy (in kJ ) is ( R =8.3 ~J ~K ⁻¹ ~mol ⁻¹ ) 2025 Full Thermodynamics (C) list All MHT CET PYQs