Question

calculate the standard enthalpy change for the reaction at 25°c. standard enthalpy of formation values can be found in this list of thermodynamic properties.

mg(oh)₂(s) + 2hcl(g) → mgcl₂(s) + 2h₂o(g)

δh°rxn =

kj

Explanation:

Step1: Write the formula for standard enthalpy change

The formula for the standard enthalpy change of a reaction \(\Delta H_{rxn}^{\circ}=\sum n\Delta H_{f}^{\circ}(\text{products})-\sum m\Delta H_{f}^{\circ}(\text{reactants})\), where \(n\) and \(m\) are the stoichiometric coefficients.

Step2: Look up the standard enthalpy of formation values

From standard tables:

• \(\Delta H_{f}^{\circ}(Mg(OH)_2(s))=- 924.7\space kJ/mol\)
• \(\Delta H_{f}^{\circ}(HCl(g))=-92.31\space kJ/mol\)
• \(\Delta H_{f}^{\circ}(MgCl_2(s))=-641.6\space kJ/mol\)
• \(\Delta H_{f}^{\circ}(H_2O(g))=-241.82\space kJ/mol\)

Step3: Calculate \(\sum n\Delta H_{f}^{\circ}(\text{products})\)

$$
LATEXBLOCK0
$$

Step4: Calculate \(\sum m\Delta H_{f}^{\circ}(\text{reactants})\)

$$
LATEXBLOCK1
$$

Step5: Calculate \(\Delta H_{rxn}^{\circ}\)

$$
LATEXBLOCK2
$$

Answer:

\(-15.92\)