Answer: [tex]\Delta H^{0}=-173.72[/tex] kJ/mol
Explanation: Enthalpy Change is the amount of energy in a reaction - absorption or release - at a constant pressure. So, Standard Enthalpy of Formation is how much energy is necessary to form a substance.
The standard enthalpy of formation of HCl is calculated as:
[tex]\Delta ^{0}=\Sigma H_{products}-\Sigma H_{reactants}[/tex]
[tex]Ca(OH)_{2}_{(aq)}+2HCl_{(aq)}[/tex] → [tex]CaCl_{2}_{(s)}+2H_{2}O_{(l)}[/tex]
Standard Enthalpy of formation for the other compounds are:
Calcium Hydroxide: [tex]\Delta H^{0}=[/tex] -1002.82 kJ/mol
Calcium chloride: [tex]\Delta H^{0}=[/tex] -795.8 kJ/mol
Water: [tex]\Delta H^{0}=[/tex] -285.83 kJ/mol
Enthalpy is given per mol, which means we have to multiply by the mols in the balanced equation.
Calculating:
[tex]-17.2=[-795.8+2(285.85)]-[-1002.82+2\Delta H][/tex]
[tex]-17.2=-1367.46+1002.82-2\Delta H[/tex]
[tex]2\Delta H=17.2-364.64[/tex]
[tex]\Delta H=-173.72[/tex]
So, the standard enthalpy of formation of HCl is -173.72 kJ/mol