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Ch.18 - Thermodynamics: Entropy, Free Energy & Equilibrium
Chapter 18, Problem 124d

Consider the Haber synthesis of gaseous NH3 (∆H°f = -46.1 kJ/mol; ∆G°f = -16.5 kJ/mol: (d) What are the equilibrium constants Kp and Kc for the reaction at 350 K? Assume that ∆H° and ∆S° are independent of temperature.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Haber Synthesis

The Haber synthesis is a chemical reaction that combines nitrogen gas (N₂) and hydrogen gas (H₂) to produce ammonia (NH₃). This process is crucial for producing fertilizers and is represented by the equation N₂(g) + 3H₂(g) ⇌ 2NH₃(g). Understanding this reaction involves recognizing its enthalpy change (∆H°) and Gibbs free energy change (∆G°), which indicate the energy dynamics and spontaneity of the reaction.
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Born Haber Cycle

Equilibrium Constants (Kp and Kc)

Equilibrium constants, Kp and Kc, quantify the ratio of products to reactants at equilibrium for a given reaction. Kp is used for gas-phase reactions and is expressed in terms of partial pressures, while Kc is used for reactions in solution and is expressed in terms of molar concentrations. The relationship between Kp and Kc can be derived from the ideal gas law and the reaction's stoichiometry, and they are temperature-dependent.
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Kp vs. Kc Formula

Gibbs Free Energy and Temperature

Gibbs free energy (G) is a thermodynamic potential that helps predict the direction of chemical reactions. The change in Gibbs free energy (∆G) at a given temperature indicates whether a reaction is spontaneous (∆G < 0) or non-spontaneous (∆G > 0). The relationship between Gibbs free energy and equilibrium constants is given by the equation ∆G° = -RT ln(K), where R is the gas constant and T is the temperature in Kelvin, allowing for the calculation of Kp and Kc at specific temperatures.
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Related Practice
Textbook Question
Urea (NH2CONH2), an important nitrogen fertilizer, is produced industrially by the reaction Given that ∆G° = -13.6 kJ, calculate ∆G at 25 °C for the following sets of conditions. . (a) 10 atm NH3, 10 atm CO2, 1.0 M NH2CONH2 (b) 0.10 atm NH3, 0.10 atm CO2, 1.0 M NH2CONH2 Is the reaction spontaneous for the conditions in part (a) and/or part (b)?
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Textbook Question
Ammonium nitrate is dangerous because it decomposes (sometimes explosively) when heated: (a) Using the data in Appendix B, show that this reaction is spontaneous at 25 °C.
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Textbook Question

Use the data in Appendix B to calculate the equilibrium pressure of CO2 in a closed 1 L vessel that contains each of the following samples: (a) 15 g of MgCO3 and 1.0 g of MgO at 25 °C Assume that ∆H° and ∆S° are independent of temperature.

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Textbook Question
Is it possible for a reaction to be nonspontaneous yet exo-thermic? Explain.
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Textbook Question

Trouton's rule says that the ratio of the molar heat of vaporization of a liquid to its normal boiling point (in kelvin) is approximately the same for all liquids: ∆Hvap/Tbp ≈ 88 J/(K*mol) (a) Check the reliability of Trouton's rule for the liquids listed in the following table.

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Textbook Question

Trouton's rule says that the ratio of the molar heat of vaporization of a liquid to its normal boiling point (in kelvin) is approximately the same for all liquids: ∆Hvap/Tbp ≈ 88 J/(K*mol) (b) Explain why liquids tend to have the same value of ∆Hvap/Tbp.

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