Consider the reaction pathways shown below, According to Hess's Law, the enthalpy change, in kJ mol , for reaction X is:
Correct answer: B. -111 kJ/mol
- A. +111 kJ/mol
- B. -111 kJ/mol
- C. -677 kJ/mol
- D. +677 kJ/mol
Explanation
According to Hess's Law: Direct Path = Indirect Path ΔH (C → CO₂) = ΔH (C → CO) + ΔH (CO → CO₂)Calculation: -394 = X + (-283) X = -394 + 283 X = -111 kJ/mol.
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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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