Calculate the standard enthalpy of formation of SO2(g) from the standard enthalpy changes of the

step 1 We are given two reactions, and we are asked to solve for the delta H of the other reaction. So

Calculate the standard enthalpy of formation of SO2(g) from...

Calculate the standard enthalpy of formation of $\mathrm{SO}_{2}(g)$ from the standard enthalpy changes of the following reactions: $$\begin{aligned} 2 \mathrm{SO}_{2}(g)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{SO}_{3}(g) & & \Delta H_{\mathrm{rxn}}^{\circ}=-196 \mathrm{kJ} \\ \frac{1}{4} \mathrm{S}_{8}(s)+3 \mathrm{O}_{2}(g) \rightarrow 2 \mathrm{SO}_{3}(g) & & \Delta H_{\operatorname{man}}^{\circ}=-790 \mathrm{kJ} \\ \frac{1}{8} \mathrm{S}_{8}(s)+\mathrm{O}_{2}(g) \rightarrow \mathrm{SO}_{2}(g) & \Delta H_{5}^{\circ} &=? \end{aligned}$$

Calculate the standard enthalpy of formation of $\mathrm{SO}_{2}(g)$ from the standard enthalpy changes of the following reactions:
$$\begin{aligned}
2 \mathrm{SO}_{2}(g)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{SO}_{3}(g) & & \Delta H_{\mathrm{rxn}}^{\circ}=-196 \mathrm{kJ} \\
\frac{1}{4} \mathrm{S}_{8}(s)+3 \mathrm{O}_{2}(g) \rightarrow 2 \mathrm{SO}_{3}(g) & & \Delta H_{\operatorname{man}}^{\circ}=-790 \mathrm{kJ} \\
\frac{1}{8} \mathrm{S}_{8}(s)+\mathrm{O}_{2}(g) \rightarrow \mathrm{SO}_{2}(g) & \Delta H_{5}^{\circ} &=?
\end{aligned}$$

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Key Concepts

Hess's Law

Hess's Law is the principle that the overall enthalpy change for a chemical reaction is the same, no matter how many steps the reaction is carried out in. This allows us to combine or subtract known reaction enthalpies to calculate the enthalpy change for a reaction that might be difficult to measure directly.

Standard Enthalpy of Formation

The standard enthalpy of formation is the change in enthalpy when one mole of a compound is formed from its constituent elements in their standard states. It serves as a reference value for thermodynamic calculations and can be determined indirectly through the manipulation of related reactions using Hess's Law.

Thermochemical Equations

Thermochemical equations are chemical equations that include the enthalpy change for the reaction. They provide a way to represent energy changes in chemical reactions and are essential for applying Hess's Law, as they allow the systematic addition or subtraction of reaction enthalpies to derive unknown values.

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