Exam 17: Thermodynamics: Directionality of Chemical Reactions

Use the data given to calculate the value of DG ^$\circ$ _rxn for the reaction at 25 ^$\circ$ C.

Which statement is false?

According to the Second Law of Thermodynamics,

Which statement is false?

For the reaction shown, DG ^$\circ$ = -32.8 kJ at 25 ^$\circ$ C. N2(g) + 3 H2(g) ? 2 NH3(g) a. Calculate the equilibrium constant for this reaction at 25°C. b. Is a mixture of the three gases where P_N2 = 3.5 bar, P_H2 = 1.2 bar, and P_NH3 = 0.22 bar at equilibrium? Justify your answer. c. What is the value of DG under the conditions of Part b? d. Compare the answer from Part c with DG°. Explain the difference observed.

Recovering aluminum directly from its ore, which is primarily aluminum oxide, involves the following reaction, for which thermodynamic data is tabulated below: a. Calculate DH°rxn and DS°rxn. b. Explain how you could have predicted the signs of DH°rxn and DS°rxn without any calculations. c. Without performing any further calculations, predict whether this reaction will be product-favored only above a certain temperature, or only below a certain temperature. Explain your answer. d. Calculate the temperature alluded to in Part c. e. Calculate DG° at this temperature.

At constant T and P, in which of the following situations will the reaction be product-favored at low temperature but not at high temperature?

Calculate the value of DS ^$\circ$ for the reaction shown: At 25 ^$\circ$ C the values of entropy in J K^-1 mol^-1 are ammonia, 192.77; nitrogen, 191.61; and hydrogen, 130.68.

If a chemical reaction is at equilibrium, it must be true that

Which set of conditions describes a reaction that is most likely to proceed?

Which statement correctly describes the meaning of the value of DG ^$\circ$ _rxn for a reactant-favored reaction?

Which has the highest entropy at a given temperature?

The enthalpy change for a reaction can be calculated using the equation DH°_rxn It would be possible to use DS ^$\circ$ _f values to calculate DS ^$\circ$ _rxn in a similar manner; however, this is not done in practice. a. Describe the procedure which is used instead. b. Explain why this mathematical process is possible for entropy calculations but not for enthalpy calculations.

Use the data at 25 ^$\circ$ C given below to calculate the value of DG ^$\circ$ _rxn for the reaction shown when it takes place at 120 ^$\circ$ C.

A certain reaction has DH ^$\circ$ _rxn = +177.8 kJ, and DS ^$\circ$ _rxn = +160.5 J/K. Above what temperature does it become product-favored ?

Which process is reactant-favored?

At constant T and P, in which of the following situations will the reaction never be product-favored?

Nature favors exothermic reactions because after such a reaction

What is the value of the equilibrium constant at 25 ^$\circ$ C for a reaction, if the value of DG ^$\circ$ _rxn is -47.8 kJ at 25 ^$\circ$ C?

Which process involves a decrease of entropy for the system?