SmartBook Assignment Chapter 15: Entropy and Gibbs Energy

Determine the change in entropy for the deposition of water vapor whose molar heat of sublimation is 54.2 kJ/mol at 1.0°C.

-198 J/K⋅mol

A reaction taking place at 100°C has an entropy change of 200 J/K and an enthalpy change of -20 kJ. Which of the following expressions would be used to calculate ΔG under these conditions?

-20,000 - (373)(200)

Use the information below to solve for ΔG°rxn for the simple reaction A → 2B.

-30 kJ

If we know that the entropy change for the surroundings is x J/K, and the system absorbed y kJ of heat during that reaction, what is the temperature at which this occurred (in K)?

1000y/x

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

A chemist finds that the sublimation of a compound has ΔG = -2.5 kJ at 350oC, and ΔG = +0.5 kJ at 140oC. From this information, what is a reasonable value for the temperature of sublimation?

175oC

Which equation would be used to calculate ΔG°rxn for the reaction 2A + B → 3C + D?

3(40) - 20 - 2(10) + 5

A given reaction has ΔH = -380.1 kJ/mol and ΔS = -95.00 J/K⋅mol. Calculate the temperature (in °C) below which the reaction is spontaneous.

3728

Which of the following is an application of the second law of thermodynamics?

A gas expands because matter tends to spread out.

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 250^oC vs. the same gas at 100^oC

Which of the following statements correctly reflect the relationship between the spontaneity of a reaction and the sign of ΔH? Select all that apply.

A negative value of ΔH favors spontaneity. The sign of ΔH alone is not sufficient evidence to determine the spontaneity of a process.

Select the statement that correctly describes the relationship between the entropy and spontaneity of a process.

A reaction/process in which ΔSsys > 0 and ΔSsurr > 0 will be spontaneous.

Which of the following changes are favored in a spontaneous process?

An overall decrease in the energy of the system An increase in entropy

Since entropy is typically tabulated in units of _____/ K and standard enthalpies are typically tabulated in units of _____/ mol, it is usually necessary to perform a unit conversion when calculating Gibbs free energy.

Blank 1: J or joules Blank 2: kJ, kilojoules, or kilo joules

The third law of thermodynamics states that a perfect _____ of a pure solid substance has _____ entropy at 0 K.

Blank 1: crystal or crystalline structure Blank 2: zero, 0, or no

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)

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.

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

Which of the following must be known in order to assess the spontaneity of a chemical reaction or physical process at a particular set of conditions? Select all that apply.

Change in enthalpy Change in entropy

What quantity is a measure of how spread out or dispersed a system's energy is?

Entropy

The combustion of glucose (shown below) is exothermic. C6H12O6 (s) + 6O2 (g) → 6CO2 (g) + 6H2O (g) Does this reaction cause an increase or a decrease in entropy for the system and surroundings?

Increase in the entropy of the system Increase in the entropy of the surroundings

Which of the following familiar processes is/are spontaneous under the conditions stated? Select all that apply.

Iron rusting at room temperature Ice melting at room temperature

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.

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)

What is the entropy of a system in which there is only one microstate?

S = 0

Two unknown reactions (A and B) are analyzed. It is found that reaction A is exothermic, while reaction B is endothermic. Which of these reactions is spontaneous?

Spontaneity cannot be determined from the given information.

Which of the following values must be known in order to calculate the change in Gibbs free energy using the Gibbs equation? Select all that apply.

T ΔSsys ΔHsys

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

Temperature decrease Condensation

Which of the following is a correct statement of the third law of thermodynamics?

The entropy of a perfect crystalline substance is 0 at 0 K.

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. Reason: Correct. ln20/ln10 = 1.3; the entropy increases to 130% the original value.

If the reaction shown below is to be coupled to a second reaction in order to generate an overall spontaneous process, what must be true regarding this second reaction? Fe2O3 (s) → 2 Fe (s) + 3/2 O (g); ΔG = 740.98 kJ

The free-energy change must be more negative than -740.98 kJ.

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

True or false: If a process occurs spontaneously in one direction under a certain set of conditions, it does not occur spontaneously in the opposite direction under the same conditions.

True

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

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

When highly charged ions dissolve, the entropy of the system generally decreases. 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.

The _____ of a system is a measure of the ways in which the energy of the system can be dispersed.

entropy

The second law of thermodynamics states that the total _____ of the universe will _____ for any spontaneous process.

entropy; increase

A system is in a state of _____ when ΔSuniv = 0.

equilibrium or dynamic equilibrium

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

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

If a given reversible reaction has positive values for both ΔH and ΔS, the value of ΔG will become _____ negative as temperature increases, and the formation of the _____ will be increasingly favored.

more, products

When the Gibbs free-energy change for a reaction is less than zero (negative), that reaction is ______ and the entropy change (ΔS) for the universe is ______.

spontaneous, positive

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

standard

Gibbs free energy is used most prevalently to determine the spontaneity of a reaction because it is only dependent on the ______, making it much more convenient to measure experimentally.

system

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

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

Thermodynamics tells us nothing about the _____ of a reaction.

the rate

True or false: Many nonspontaneous biochemical reactions couple with other reactions which supply enough free energy to drive them all.

true

Which of the following types of energy are forms of motional energy? Select all that apply.

vibrational rotational translational

The sign of which quantity indicates whether a reaction or process will occur spontaneously?

ΔG

Select all the options that correctly describe the free-energy change and spontaneity of the reaction CuO (s) → Cu (s) + 12 O2 (g) at 375 K if ΔH = 168 kJ/mol and ΔS = -9.63 J/K⋅mol.

ΔG = +172 kJ The reaction is not spontaneous at this temperature.

Which of the following is the correct form of the change in the Gibbs equation for a process occurring at constant temperature?

ΔGsys = ΔHsys - TΔSsys

At a certain temperature, the change in entropy of the system is calculated to be ΔSsys. If the system is at equilibrium, what is the value of ΔSsurr under these conditions?

ΔSsurr = -ΔSsys

A particular process results in a decrease in the entropy of the system. If this process is spontaneous, what must be true about the entropy change of the surroundings?

ΔSsurr > -ΔSsys

Which of the conditions described below will result in a spontaneous reaction? Select all that apply.

ΔSsys = 30 J/K; ΔSsurr = 10 J/K ΔSsys = -20 J/K; ΔSsurr = 25 J/K

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)

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

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 J/K

Calculate the entropy change of the surroundings in J/mol⋅K when 30 kJ of heat is released by the system at 27°C.

+100

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.

+8.6 J/K

For a particular reaction ΔH° = -5. kJ and ΔS° = -100 J/K. What is the temperature (in K) at which this reaction favors the products?

50

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 Substance S° (J/K⋅mol) O2 (g) 205.0 MgO (s) 26.78 F2 (g) 203.34

57.24 J/mol⋅K

Determine the change in entropy for the melting of a solid whose molar heat of fusion is 22.3 kJ/mol at 27°C.

74.3 J/K⋅mol

Which of the following familiar processes is/are spontaneous? Select all that apply.

A teaspoon of table salt dissolving in 1 L of boiling water A ball rolling down a hill

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.

The third law of thermodynamics states that the entropy of a perfect crystal at 0 K is 0. This allows for the calculation of _____ entropies unlike standard _____ of formation, which are derived using an arbitrary reference.

Blank 1: absolute Blank 2: enthalpies

Mathematically entropy is defined by the equation S = k ln W. W represents the number of possible arrangements, where mathematically W = XN. X represents the number of _____ containing N _____.

Blank 1: cells Blank 2: molecules, atoms, or particles

In order to assess the spontaneity of a chemical reaction or physical process both the change in _____ and _____ associated with the reaction or process must be known.

Blank 1: enthalpy Blank 2: entropy

The Gibbs _____-energy change (symbolized by Δ _____ ) is a measure of the spontaneity of a process, and of the useful energy available from it.

Blank 1: free Blank 2: G

For a chemical reaction, ΔSorxn = ΣnSo(_____) - ΣnSo(_____).

Blank 1: products or final Blank 2: reactants or initial

The ΔG for a reaction that occurs under standard-state conditions is called the _____ Gibbs free energy of reaction. The term "standard state" implies a temperature of _____ oC or _____ K for the reaction.

Blank 1: standard Blank 2: 25 Blank 3: 298 or 298.15

In order to determine the spontaneity of a reaction or process, the entropy changes in both the _____ and the _____ must be considered.

Blank 1: system Blank 2: surroundings

Select the statements that correctly describe the microstates of a system, W. Select all that apply.

Entropy increases with the number of microstates. W is the number of energetically equivalent ways the particles of a system may be arranged. Increasing the temperature of a system will increase W.

Which of the following statements correctly describe general trends in standard entropy? 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 correctly reflect the relationships between ΔSsurr, ΔHsys, and T? Select all that apply.

If ΔHsys is positive, ΔSsurr will be negative. ΔSsurr is inversely proportional to temperature.

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

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

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

Which of the following statements correctly describe why the process depicted in the illustration is spontaneous? Select all that apply. (The change is occurring from left to right in the illustration, and the system remains at constant temperature.)

The process is spontaneous due to an increase in entropy. The process is spontaneous due to the dispersal of the system's energy over a larger volume.

Select all the options that describe the behavior of a reversible reaction for which both ΔH and ΔS < 0.

The reaction will become less spontaneous as the temperature increases. At low temperatures, ΔGrxn < 0. The formation of the reactants will become increasingly favored as the temperature rises.

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

The standard entropy of a substance is its absolute entropy at 1 atm. The units of standard entropy are J/mol⋅K.

Which of the following conditions are specified by standard-state conditions? Select all that apply.

The standard state of an element is its most stable allotropic form at standard-state temperature and pressure. A solution will have a concentration of 1 M. Gases are at 1 atm pressure.

True or false: The state with the largest number of possible arrangements has the greatest entropy.

True Reason: The most probable state is the one with the largest number of energetically equivalent possible arrangements: S = k ln W.

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

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

The importance of the third law of thermodynamics is that it allows us to experimentally determine _____.

absolute entropies

In order for the products to be favored in a reaction, the standard free-energy change (ΔG°) must have a ______ sign.

negative

Which of the following statements correctly describe the standard free-energy of formation (ΔG°f) for a substance? Select all that apply.

ΔG°f for any element in its most stable allotropic form at 1 atm is equal to zero. ΔG°f is the free energy change for the synthesis of 1 mole of a compound from its constituent elements in their standard states.

A reaction is found to be spontaneous only at high temperatures. Which of the following must be true? Select all that apply.

ΔHorxn > 0 ΔSorxn > 0

The reaction 4Fe (s) + 3O2 (g) + 6H2O (l) → 4Fe(OH)3 (s) is spontaneous at temperatures below 1950°C. If ΔH = -1582 kJ, calculate the entropy change for this reaction at 1950°C.

ΔS = -712 J/K

Calculate ΔSuniv and identify the following process as spontaneous, nonspontaneous, or at equilibrium. Use the values provided in the table below. CO2 (g) → CO2 (aq) at 25°C

ΔSuniv = -27.2 J/mol⋅K The reaction is nonspontaneous at this temperature.