Use the given the standard enthalpies of formation to determine the heat of reaction of the following reaction:2 Ag₂S(s) + 2 H₂O (l) → 4 Ag(s) + 2 H₂S(g) + O₂(g)ΔH°f Ag₂S(s) = -33 kJ/moleΔH°f H2S(g) = -21 kJ/moleΔH°f H₂O(l) = -286 kJ/mole
Correct answer: D. +596 kJ
- A. +232.4 kJ
- B. +423.5 kJ
- C. +518.0 kJ
- D. +596 kJ
Explanation
To determine the heat of reaction, apply Hess's Law: ΔH°reaction = ΣΔH°f(products) - ΣΔH°f(reactants).First, identify the standard enthalpies of formation for each compound involved in the reaction:ΔH°f (Ag2S(s)) = -33 kJ/molΔH°f (H2S(g)) = -21 kJ/molΔH°f (H2O(l)) = -286 kJ/molΔH°f (Ag(s), O2(g)) = 0 kJ/mol (since they are in their standard states)Calculate the heat of reaction:ΔH°reaction = [4(0) + 2(-21) + 0] - [2(-33) + 2(-286)]ΔH°reaction = [0 - 42] - [-66 - 572]ΔH°reaction = -42 + 638 = +596 kJThus, the correct answer is +596 kJ. The other options result from common calculation errors such as incorrect stoichiometry or neglecting the contribution of some enthalpies.
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About Thermochemistry and Energetics of Chemical Reactions
Thermochemistry measures energy changes in chemical reactions and distinguishes exothermic from endothermic processes. Work covers systems, surroundings and state functions, internal energy, the first law of thermodynamics, enthalpy and Hess's law, including the sign conventions used when heat enters or leaves a system.
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