Exam 18: Thermodynamics: Spontaneous and Nonspontaneous Reactions and Processes

In an experiment, 1.00 mol of sodium metal is placed in a container and reacts with an excess of chlorine gas to form sodium chloride under standard state conditions. Determine $\Delta$ S_rxn given the following information: Substance (/ - K) (s) 51.45 (g) 222.96 (s) 72.33

Of the three modes of molecular motion-vibration, rotation, and translation-which requires the greatest amount of energy to cause an excitation from the ground state to the first excited state?

Only one substance has a standard entropy of 0 J/K, and that is H⁺(aq). Why is this so?

The standard entropy of N₂(g) is 191.5 J/mol . K. Calculate the entropy per nitrogen molecule and the number of microstates for each molecule. Discuss the number of microstates in terms of the molecular motions accessible to each molecule.

A sketch of the free energy for a hypothetical chemical equilibrium is shown here. What part of the plot on the axis representing the relative quantities of reactants and products corresponds to a value of $\Delta$ G that is greater than zero?

As the temperature of a reaction with $\Delta$ S° > 0 is increased, the equilibrium constant ________

Which of the following will have the greatest standard molar entropy (S°)?

Name and state the first three laws of thermodynamics.

If 1 mol of ice melts at its melting point of 273 K, the entropy change for the ice is 22.0 J/K. If the ice melts in someone's hand at 34°C, what is the change in the entropy of the universe? Assume a final temperature for the water of 0°C. The enthalpy of fusion for ice is 6.01 kJ/mol.

As the temperature of an endothermic reaction is increased, the equilibrium constant ________

The reaction Cr(NH₃)₆³⁺(aq) + 3en(aq) $\leftrightarrow$ Cr(en)₃³⁺(aq) + 6 NH₃(aq) Where en represents ethylenediamine, has a small value for the enthalpy change, $\Delta$ H_rxn, yet the free-energy change is large because ________

Noxious NO gas can form from N₂ and O₂ gases in automobile engines at high temperatures. If the value of the equilibrium constant, K_c, for this reaction at 25°C is 1.95 *10^-31, what is the value at 2000°C? N₂(g) + O₂(g) $\leftrightarrows$ 2NO(g) Thermodynamic Properties of Nitrogen Monoxide \Delta \Delta 87.6/ 90.3/ 211/(\cdot)

Which of the following processes are reversible in the thermodynamic sense? I. Iron in the open air rusts. II. NaCl is dissolved in water and then recovered by the evaporation of the water. III. The ice in a mixture of ice and water at 0°C and 1 atm melts.

A sealed tube containing an equilibrium mixture of NO₂(g) (brown) and N₂O₄(g) (colorless) is subjected to a variety of temperatures. For the equilibrium reaction shown, the values of the $\Delta$ H°_rxn and $\Delta$ S°_rxn are also shown. What is observed in the tube with increasing temperature? 2NO₂(g) $\leftrightarrows$ N₂O₄(g) $\Delta$ H $\degree$ = -58.02 kJ/mol, $\Delta$ S=-176.5 J/mol . K

A reaction with a low enthalpy of reaction value is not spontaneous at low temperature but becomes spontaneous at high temperature. What are the signs for $\Delta$ H° and $\Delta$ S°, respectively?

Benzene is a liquid under standard conditions. The standard free-energy change for the evaporation of liquid benzene to form benzene vapor is +5.2 kJ/mol. If liquid benzene is placed in an open container under standard conditions, ________

Give an example of a spontaneous and a nonspontaneous chemical process and the sign of the entropy change for the universe for each.

Consider a reaction at a point in which the difference in free energy between the reactants and products is twice the standard free-energy change for the reaction. What expression would allow you to calculate the reaction quotient under these conditions, and what would be required for the reaction to be spontaneous?

The enthalpy and entropy of vaporization of ethanol are 38.6 kJ/mol and 109.8 J/mol · K, respectively. What is the boiling point of ethanol under equilibrium conditions, in °C?

Heat transfer from the system to the surroundings has a large effect on $\Delta$ S_surr ________