Multiple Choice
Given the thermochemical equation: 2 O_3(g) → 3 O_2(g)ΔH = -284 kJ, what is the enthalpy change for this reaction per mole of O_3(g)?
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8. Thermochemistry
Thermochemical Equations
Multiple Choice
Given the reaction: 2 H_2S(g) + 3 O_2(g) → 2 SO_2(g) + 2 H_2O(g), what is the standard enthalpy change (ΔH°) for this reaction? (Use the following standard enthalpies of formation: ΔH_f°(H_2S(g)) = -20.6 kJ/mol, ΔH_f°(O_2(g)) = 0 kJ/mol, ΔH_f°(SO_2(g)) = -296.8 kJ/mol, ΔH_f°(H_2O(g)) = -241.8 kJ/mol)
A
+535.2 kJ
B
-1107.6 kJ
C
+1107.6 kJ
D
-535.2 kJ
Verified step by step guidance1
Write down the balanced chemical equation: \(2 \mathrm{H_2S}(g) + 3 \mathrm{O_2}(g) \rightarrow 2 \mathrm{SO_2}(g) + 2 \mathrm{H_2O}(g)\).
Recall the formula for the standard enthalpy change of a reaction using standard enthalpies of formation: \(\Delta H^\circ_{\text{reaction}} = \sum \Delta H^\circ_f (\text{products}) - \sum \Delta H^\circ_f (\text{reactants})\).
Calculate the total enthalpy of formation for the products by multiplying the standard enthalpy of formation of each product by its coefficient and summing: \(2 \times \Delta H^\circ_f(\mathrm{SO_2}(g)) + 2 \times \Delta H^\circ_f(\mathrm{H_2O}(g))\).
Calculate the total enthalpy of formation for the reactants similarly: \(2 \times \Delta H^\circ_f(\mathrm{H_2S}(g)) + 3 \times \Delta H^\circ_f(\mathrm{O_2}(g))\).
Subtract the sum of the reactants' enthalpies from the sum of the products' enthalpies to find \(\Delta H^\circ_{\text{reaction}}\): \(\Delta H^\circ = [2 \times (-296.8) + 2 \times (-241.8)] - [2 \times (-20.6) + 3 \times 0]\) (do not calculate the final value here).
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