Q27 / 90 · JEE Main 2023 (31 Jan Shift 2) · Chemistry

Enthalpies of formation of CCl4( g),H2O(g),CO2( g) and HCl are -105,-242,-394 and -92 kJ mol-1 respectively. The magnitude of enthalpy of the reaction given below is kJmol-1. (nearest integer) CCl4( g)+2H2O(g)→CO2( g)+4HCl(g)

Correct answer: 173

Solution

Using Hess's law of constant heat summation:
Enthalpy of reaction = Enthalpy of formation of products - Enthalpy of formation of reactants
∴ΔHf°=ΔHf°CO2, g+4ΔHf°(HCl)-ΔHf°CCl4-2ΔHf°H2O,r

=[-394]+4[-92]+105-2×[242]

=-394-368+105+484

=-173 kJ/mole

Hence, the correct answer is 173.

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