Chem 2

Which of the following compounds are expected to be soluble in carbon tetrachloride (CCl4) based on structure? Select all that apply.

C6H6 CO2

Which, if any, of the following processes is spontaneous under the specified conditions?

CO2(s) → CO2(g) at 0°C, 1 atm pressure

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

Condensation Temperature decrease

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)

H2O (g) (ii) H2O2 (g)

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?

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

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?

ln20ln10ln20ln10 = 1.3; the entropy increases to 130% the original value.

Will HCl (g) or NaCl (s) be more soluble in the solvent CH3OCH3? Why?

The dipole-dipole forces in an HCl/CH3OCH3 solution are similar in strength to the dipole-dipole forces between CH3OCH3 molecules. HCl (g) will be more soluble in CH3OCH3.

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

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

Rank the following compounds in order of decreasing standard entropies. (Place the compound with the highest entropy at the top of the list).

g,g,l,l

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.

ΔSsys = nR lnVfinalVinitialVfinalVinitial = 1.5 mol × 8.314JK⋅mol8.314JK⋅mol × ln2.0L1.0L2.0L1.0L = 8.6 J/K

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

ΔSsys= nR ln VfinalVinitialVfinalVinitial ΔSsys = k ln Wfinal - k ln Winitial

Miscible liquids are liquids that ______.

are soluble in each other in all proportions

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.

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

Which has the largest entropy?

O2(g)

what is entropy of a system

is a measure of how dispersed or spread out its energy is.

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?

0.34

Calculate the standard entropy change for the following reaction at 25°C. Use the values provided in the table below. 2CO2 (g) → 2CO (g) + O2 (g)

173.6 J/mol⋅K

In the following reaction, there is one species for which the standard entropy is not known. Use the given value for the change in entropy of the reaction and the values for standard entropy that are listed in the table below to solve for the missing standard entropy at 25°C. O2 (g) + 2MgF2 (s) → 2MgO (s) + 2F2 (g); ΔS°rxn = 140.76 J/mol⋅K

57.24 J/mol⋅K

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

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

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

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

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

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

describe the change in entropy when a solution is formed?

Entropy usually increases when a solution forms because there are more interactions between particles in a solution. Reason: If there are more interactions between particles, there will be more ways of dispersing energy. The entropy of a solution is usually higher than that of the pure solvent.

Ethanol and water are miscible. What does this mean?

Ethanol and water are soluble in each other in all proportions.

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

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

______ is the process of stabilizing the particles of an ionic solute in aqueous solution by surrounding them with water molecules, which form ion-dipole interactions.

Hydration

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

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

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?

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

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

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

describe the change in entropy when a solution is formed? Select all that apply.

The particles in a solution generally have a greater freedom of movement than the particles in a pure solute. Entropy usually increases when a solution forms because there are more interactions between particles in a solution.

Which of the following options correctly describe standard entropy? 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.

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

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

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.

Wfinal = 24= 16 microstates ΔSsys = k ln 24

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

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

I2I2 (s) has a very low solubility in H2OH2O (I) because the weak _____ forces between I2I2 and H2OH2O are not strong enough to replace the _____ between the H2OH2O molecules.

dipole-induced dipole; hydrogen bonds

The measure of the degree of dispersion of the energy of a system is called

entropy

What is defined as a measure of the randomness or disorder of a system?

entropy

A solution forms when the attractive between the solute and solvent are similar in to the solvent-solvent and solute-solute attractions and are therefore able to replace them.

forces, type

The entropy of gaseous molecules is _____ the entropy of these molecules in a condensed phase. Therefore, reactions producing a greater number of gas molecules typically result in a positive change in entropy.

greater than

A solution usually has a _____ entropy than either the pure solvent or pure solute because in the solution there are a _____ number of interactions between particles and therefore _____ ways to distribute the energy of the system.

higher; greater; more

The stabilization of a solute in aqueous solution by interaction of the solute with water molecules is known as ______.

hydration

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.)

increase, energy

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.

increases, increase, increase

The most probable state is the one with the

largest number of possible arrangements.

When a sky diver free-falls through the air, the process is

spontaneous

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

standard

Which of the following is an example of a nonspontaneous process?

water freezing at room temperature