Question

$H_2\left(g\right)+I_2\left(g\right)\to 2HI\left(g\right);\Delta H=51.9$ kJ

According to the above reaction, the heat of formation of $HI$ (in kJ/mol) is:

• A. $+51.9$
• B. $-51.9$
• C. $-25.95$
• D. $+25.95$

Answer 1

The correct option is D $+25.95$

The heat of formation is defined as the enthalpy change of the reaction for the formation of $1$ mole of the substance.

The following reaction is given:

$H_2\left(g\right)+I_2\left(g\right)\to 2HI\left(g\right);\Delta H=51.9$ kJ

In the above reaction, the heat involved is for the $2$ moles of $HI$.

For $1$ mole of $HI$, heat change $=\frac{51.9}{2}=25.95$

So, the heat of formation of $1$ mole of $HI$ is $+25.95$ kJ/mol.