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Q.
$H _{2}+ Cl _{2} \longrightarrow 2 HCl , \Delta H=-194 \,kJ$
In the above reaction the heat of formation of $HCl$ is :
AFMCAFMC 2000
Solution:
Heat of formation is the amount of heat absorbed or liberated when one mole of a substance is formed from its constituent element.
When $2$ moles of $HCl$ is formed heat liberated = $194 kJ$
$\therefore $ When $1\, mol$ of $HCl$ is formed heat liberated
$=\frac{194}{2}=97 \,kJ$
$\therefore \Delta H_{f}=-97 \,kJ$