Class 11 NEET Chemistry Chemical Thermodynamics

H2+Cl2→2HCl
=434+242−(431)×2
∆H‌reaction ‌=−186kJ
Heat of formation is the amount of heat absorbed or evolved when one mole of substance is directly obtained from its constituent element.
Hence, enthalpy of formation of HCl=‌

−186

2

kJ
=−93kJmol−1