Question

what is \\(\delta h_{rxn}\\) for the following reaction?

\cs_2(g) + 3cl_2(g) \longrightarrow ccl_4(g) + s_2cl_2(g)\\

substance	\\(\delta h_f^\circ\\) (kj/mol)
\\(ccl_4(g)\\)	-95.7
\\(s_2cl_2(g)\\)	-19.5

-1615.0 kj/mol
-484.3 kj/mol
164.2 kj/mol
-232.1 kj/mol

Explanation:

Identify the given values and chemical equation

Using the Thermochemical Calculations and Enthalpy of Reaction knowledge points
The balanced chemical equation is:

$$ \text{CS}_2(g) + 3\text{Cl}_2(g) \longrightarrow \text{CCl}_4(g) + \text{S}_2\text{Cl}_2(g) $$

The standard enthalpies of formation \(\Delta H_f^\circ\) are:

• \(\Delta H_f^\circ[\text{CS}_2(g)] = 116.9\text{ kJ/mol}\)
• \(\Delta H_f^\circ[\text{CCl}_4(g)] = -95.7\text{ kJ/mol}\)
• \(\Delta H_f^\circ[\text{S}_2\text{Cl}_2(g)] = -19.5\text{ kJ/mol}\)
• \(\Delta H_f^\circ[\text{Cl}_2(g)] = 0\text{ kJ/mol}\) (pure element in standard state)

Apply Hess's Law formula

Using the Enthalpy of Reaction knowledge point

$$ \Delta H_{rxn}^\circ = \sum n \Delta H_f^\circ(\text{products}) - \sum m \Delta H_f^\circ(\text{reactants}) $$

Calculate sum of products and reactants

Using the Thermochemical Calculations knowledge point

$$
LATEXBLOCK0
$$

Compute the final reaction enthalpy

Using the Thermochemical Calculations knowledge point

$$ \Delta H_{rxn}^\circ = -115.2\text{ kJ/mol} - 116.9\text{ kJ/mol} = -232.1\text{ kJ/mol} $$

Answer:

• -1615.0 kJ/mol
• -484.3 kJ/mol
• 164.2 kJ/mol
• -232.1 kJ/mol (Correct answer)