CHEM113 15.3

The entropy of a substance in a gas phase is much higher than its entropy in the liquid or solid phase.

A reaction that results in an overall increase in the number of gas molecules has a positive sign for ΔSrxn. Select the statement that correctly explains why.

The entropy would increase, but it would be less than double the original entropy.

An atom of hydrogen is bound to a metal surface (but free to move across it) with 10 possible sites of attachment. What would be the effect of increasing the size of the metal surface to 20 possible sites?

increases, increase, increase

As temperature increases, entropy ______ due to a(n) ______ in the number of available energy states, and thus a(n) ______ in the number of possible arrangements of molecules within those energy states.

a liquid evaporates a solid sublimes a molecular substance dissolves in water

Entropy will generally increase when ______. (Select all the options that complete this sentence correctly.)

ΔSsys = k ln 2^4 Wfinal = 2^4= 16 microstates

Four particles initially in one flask are allowed to also expand into a second flask. Select the correct value(s) for the number of microstates (W) and change in entropy of the system. Recall that W = XN where X is the number of cells and N is the number of particles. Select all that apply.

2NO2 (g) vs. N2O4 (g) C3H8 (g) vs. C2H6 (g)

In which cases do the substance(s) on the left have a higher entropy than the substance(s) on the right? Select all that apply. Multiple select question.

A gas at 250oC vs. the same gas at 100oC A more complex substance vs. a simpler substance in the same phase, if their molar masses are similar

Select all the options in which the first species of each pair has a higher standard entropy.

standard

The ____ entropy of a substance is its absolute entropy at 1 atm.

n= number of moles R= ideal gas constant Vfinal= final volume Vinitial= initial volume

The change in entropy for a system can be calculated using the equation below. Match each variable with the correct term. ΔSsys = nR ln Vfinal/Vinitial

increase, energy

The dissolution of a molecular solute typically results in a(n) ______ in entropy because the system's molecules and ______ are dispersed into a larger volume. (Assume that the solute is not an acid or base.)

the number of microstates is difficult to determine for a real process

The equation ΔSsys = nR ln Vfinal/Vinitial is much more frequently used than the Boltzman equation ΔSsys = k ln Wfinal/Winitial because _____.

+8.6 J/K ΔSsys = nR lnVfinal/Vinitial = 1.5 mol × 8.314J/K⋅mol × ln2.0L/1.0L = 8.6 J/K

Two 1.0-L flasks are connected by a stopcock with 1.5 moles of an ideal gas restrained in one flask. Determine the change in entropy (ΔSsys), when the stopcock is open and the gas is allowed to expand into both flasks at a constant temperature.

There is an increase in the entropy of the system as temperature increases. The kinetic energy of the particles in the system increases.

What effect does increasing the temperature of a gas have on its entropy, and why?

+0.34 J/K Reason: ΔSsys = nR lnVfinalVinitial = 0.10 mol × 8.314/JK⋅mol × ln3.0/L2.0L = 0.34 J/K

What is the change in entropy (ΔSsys), for the expansion of 0.10 mole of an ideal gas from 2.0 L to 3.0 L at constant temperature?

A tire is punctured, releasing the gas trapped inside. A crystal of sodium chloride is heated from 275 K to 290 K. An ice cube melts at 273 K.

Which of the following changes would result in an increase in the entropy of the system? Select all that apply.

The units of standard entropy are Jmol⋅KJmol⋅K. The standard entropy of a substance is its absolute entropy at 1 atm.

Which of the following options correctly describe standard entropy? Select all that apply.

It is difficult to determine the number of different possible arrangements (W). Tabulated standard entropy values are used to calculate entropy changes instead.

Which of the following options correctly explain why the equation S = k ln W is rarely used to calculate the change in entropy of a system? How is ΔS determined?

ΔSsys= nR ln Vfinal/Vinitial ΔSsys = k ln Wfinal - k ln Winitial

Which of the following options correctly show how to calculate the entropy change of a system? Select all that apply.

Temperature decrease Condensation

Which of the following processes or changes will lead to a decrease in entropy? Select all that apply.

H2CO3 (aq) → H2O (l) + CO2 (g) N2O4 (g) → 2NO2 (g)

Which of the following reactions/processes are predicted to have a positive value for ΔSrxn? Select all that apply.

N2O4 (g) → 2NO2 (g) H2CO3 (aq) → H2O (l) + CO2 (g)

Which of the following reactions/processes are predicted to have a positive value for ΔSrxn? Select all that apply.

C2H6O (l) → C2H6O (s) 4Fe (s) + 3O2 (g) → 2Fe2O3 (s)

Which of the following reactions/processes have a negative sign for ΔSrxn? Select all that apply.

For elements with two allotropic forms, the one that is more mobile will have a greater value for standard entropy. For two monatomic species, the one with the larger molar mass will have a higher standard entropy.

Which of the following statements correctly describe general trends in standard entropy? Select all that apply.

The energy of the particles increases during these phase changes. The number of possible arrangements of the particles increases.

Which of the following statements correctly explain the increase in entropy that occurs when substance changes from solid to liquid, or liquid to gas? Select all that apply.

The mobility of the particles increases much more when this phase change occurs. Vaporization of a substance

Which phase change will have a more dramatic increase in entropy? Select the statement that best explains why.

The dissolution of ions with low charges typically results in an increase in the entropy of the system. The mobility of H2O molecules in such a solution is reduced since they are arranged in a specific way around the dissolved ions. When highly charged ions dissolve, the entropy of the system generally decreases.

Which statements correctly describe the changes that occur when an ionic solid dissolves in water? Select all that apply.

(ii) H2O2 (g) (i) H2O (g)

in each of the following pairs, which species will have a greater value for standard entropy? (i) F (g) vs. H2O (g) (ii) H2O2 (l) vs. H2O2 (g)