Calculate the ∆H_rxn for the following thermochemical equation: 

When given the following: 

• A. -296.8 kJ
• B. -148.4 kJ
• C. 148.4 kJ
• D. 296.8 kJ

Answer: (B)

Verified step by step guidance

1. Identify the given thermochemical equation: \(\mathrm{S (s) + \frac{3}{2} O_2 (g) \rightarrow SO_3 (s)}\) and the enthalpy change for the formation of \(SO_3\) from its elements, which is given as \(\Delta H = -296.8 \text{ kJ}\) for the formation of 2 moles of \(SO_3\).
2. Recognize that the given enthalpy change corresponds to the reaction forming 2 moles of \(SO_3\), but the target reaction forms only 1 mole of \(SO_3\). Therefore, you need to adjust the enthalpy change proportionally.
3. Set up a proportion to find the enthalpy change for the formation of 1 mole of \(SO_3\): \(\Delta H_{\text{rxn}} = \frac{1}{2} \times (-296.8 \text{ kJ})\).
4. Calculate the adjusted enthalpy change (without final numerical evaluation here) to find \(\Delta H_{\text{rxn}}\) for the reaction as written.
5. Interpret the sign of \(\Delta H_{\text{rxn}}\) to understand whether the reaction is exothermic (negative \(\Delta H\)) or endothermic (positive \(\Delta H\)).