Given the following data at 1 atm of pressure and 25.0 °C...ΔH°formation = +64.4 kJ/mole for Cu²⁺.ΔH°formation = -152.4 kJ/mole for Zn²⁺.ΔH°formation = 0 for both Zn and Cu²⁺ because these are in the most stable state.Calculate the standard heat of reaction for........Zn(s) + Cu2+ (aq) →Zn2+(aq) + Cu(s)
Correct answer: A. -217 kJ/mole
- A. -217 kJ/mole
- B. +217 kJ/mole
- C. -88.0 kJ/mole
- D. +88.0 kJ/mole
Explanation
To calculate the standard heat of reaction, use the formula ΔH°reaction = ΣΔH°f,products - ΣΔH°f,reactants. The enthalpies of formation are given as follows: ΔH°f(Zn²⁺) = -152.4 kJ/mole and ΔH°f(Cu²⁺) = +64.4 kJ/mole. The elements in their standard states, Zn(s) and Cu(s), have enthalpies of formation of 0 kJ/mole. Therefore, ΔH°reaction = [-152.4 kJ/mole] - [64.4 kJ/mole] = -216.8 kJ/mole, which rounds to -217 kJ/mole. Options B, C, and D do not account correctly for the given enthalpy values.
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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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