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At 25 ° C and 1 atm pressure, the enthalpy of combustion of benzene 1 and acetylene g are - 3268 kJ mol - 1 and - 1300 kJ mol - 1 , respectively. The change in enthalpy for the reaction 3 C 2 H 2 g → C 6 H 6 l , is

Options

  1. A+ 324   kJ   mol - 1
  2. B+ 632   kJ   mol - 1
  3. C- 632   kJ   mol - 1
  4. D- 732   kJ   mol - 1

Correct answer

C. - 632   kJ   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) ΔH r = ΔH C reactant - ΔH C product = 3 ΔHc c C 2 H 2 , g - ΔH c C 6 H 6 , l = 3 × - 1300 - - 3268 = - 3900 + 3268 = - 632   kJ / mole

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