Exam 14: Thermodynamics: Spontaneous Processes, Entropy, and Free Energy

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?

The entropy of fusion for ice at 0°C and 1 atm is 22 J/mol · K. How many joules of heat are required to melt a typical ice cube at 0°C and 1 atm? Assume an ice cube is about 1 oz or 28 g.

Which of the following processes are spontaneous? (I)Iron in the open air rusts. (II)Liquid water in a freezer turns to ice. (III)A spark ignites a mixture of propane and air.

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.

Draw a graph of entropy versus temperature for a typical substance. Be sure to clearly label phases and phase transitions on the graph.

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, in °C?

Hydrogen iodide can theoretically be made by the reaction of hydrogen gas and iodine by the following reaction. H₂(g) + I₂(s)  2HI(g) What temperature conditions are required for the formation of HI to be favored at standard pressure? S°(H₂, g) = 130.6 J/mol · K S°(I₂, s) = 116.1 J/mol · K S°(HI, g) = 206.6 J/mol · K H (HI, g) = 26.5 kJ/mol · K

What is a microstate and how are microstates quantitatively related to entropy?

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.

When you increase the volume of a gas, the energy separation between microstates __________

What types of motion does a molecule of chlorine have?

Carbon atoms can be found in a variety of elemental forms. At sufficiently high temperature, carbon is an atomic gas. At room temperature, both tetrahedral networks in diamond and trigonal planar networks in graphite can be found. Trigonal planar networks of carbon atoms are also found in Buckminsterfullerene (C₆₀). How does the standard entropy of these forms vary per mole of carbon?

Carbon monoxide has a very weak dipole moment. In the formation of solid carbon monoxide some molecules will be reversed in their orientation from C O - - - C O to C O - - - O C. What do you expect the absolute entropy of carbon monoxide solid to be at 0 K, and why?

What is the overall standard free-energy change for the following two reactions in terms of G₁ and G₂? A + B  2C G = G₁ C + D  E G = G₂

Boltzmann derived the relationship, S = k ln W where W is the __________

Hydrogen reacts with nitrogen to form ammonia (NH₃) according to the reaction 3H₂(g) + N₂(g)  2NH₃(g) The value of H° is -92.38 kJ/mol, and that of S° is -198.2 J/mol · K. Determine G° at 25°C.

At body temperature, many proteins have a well-defined structure that is essential to their function. As the temperature is raised, however, the structure changes and the protein is no longer functional. This is referred to as protein denaturation. What can be deduced from this information about the signs of the enthalpy and entropy changes for denaturation?

Which, if any, of A through D is not true of entropy? If they are all true, select E.

Which of the following must be true for the microstates of a system? (I)The energy of each microstate equals the energy of the system. (II)The entropy of each microstate equals the entropy of the system. (III)The number of microstates equals the entropy of the system.