Exam 3 Energetics

Question 1

Is it energetically favorable for ice to melt at 263 K (-10 ˚C), where ΔH is +5630 J/mol and ΔS is +20.6 J/K•mol?

Answer 1

ΔG is positive and the melting of ice at 263 K is unfavorable.

Question 2

True or False? The entropy of an open system can decrease.

Answer 2

True

Question 3

An organism takes in nutrients, often in the form of high-entropy small molecules, and from them it builds enormous, complex, highly ordered macromolecules like proteins and nucleic acids, which constructs elegantly structured cells, tissues, and organs. This is an example of what?

Answer 3

Entropy decreasing in an open system.

Question 4

In order for the entropy of an open system to decrease, it requires what?

Answer 4

An accompanying large decrease in enthalpy.

Question 5

True or False?
Living organisms spend energy to overcome entropy.

Answer 5

True

Question 6

True or False?
For these life processes to occur, the overall free energy changes in the organism must be positive; thus, life is an irreversible process

Answer 6

False

Question 7

What does it mean when an organism comes to equilibrium with its surroundings.

Answer 7

That organism is dead.

Question 8

True or False?
The portion of an energy change in process that is available, or free, to do useful work at constant T, P is the definition of Delta G.

Answer 8

True

Question 9

True or False?
The sign of ∆H for a process tells us whether that process, or its reverse, is thermodynamically favorable.

Answer 9

False it is ∆G

Question 10

True or False?
The magnitude of ∆G is an indication of how far the process is from equilibrium and how much useful work may be obtained from it.

Answer 10

True

Question 11

True or False?
A thermodynamically favored process tends in the direction that maximizes free energy because it results in a negative ∆G.

Answer 11

False. minimizing ∆G would cause it to be negative which is favored.

Question 12

True or False?
Since free energy is a state function, free energy change for any reaction will equal the free energy of the products minus that of the reactants.

Answer 12

True

Question 13

True or False?
For a reaction that is exergonic, ΔG = 0 because there is no driving force in either direction.

Answer 13

False. ΔG = 0 at equilibrium

Question 14

True or False?

The metabolic processes can occur only when each has a favorable thermodynamic driving force, that is, when ∆G < 0, within relatively narrow ranges of temperature, pH, and concentrations for ions and metabolites.

Answer 14

True

Question 15

True or False?

The concentrations of certain solutes inside cells remain relatively constant.

Answer 15

True

Question 16

True or False?

In the steady state, continuous free energy is put into the system to maintain homeostasis.

Answer 16

True

Question 17

Thermodynamic definition of entropy change at constant pressure is __________.

Answer 17

Question 18

_______represents the heat transferred from the system to the surroundings at constant pressure and some temperature T.

Answer 18

∆Hsystem

Question 19

True or False?

The negative sign represents a loss of energy by the system and a gain of energy by the surroundings.

Answer 19

True

Question 20

True or False?

Free energy is not relevant to bioenergetics because most cells and organisms live under conditions of constant pressure and temperature.

Answer 20

False. it is relevant

Question 21

Define Delta G

Answer 21

The amount of ‘free’ energy in a system to do useful work under the given conditions, specifically constant temperature

Question 22

What is the formula for free energy?

Answer 22

Question 23

What is the formula for The free energy of solute?

Answer 23

Question 24

For a typical favorable process ∆G must be what?

Answer 24

∆G must be negative, i.e. ∆G < 0

Question 25

True or false?

A decrease in energy (∆H < 0) and/or an increase in entropy (∆S > 0), makes ∆G positive.

Answer 25

False

Question 26

If Delta G is zero, then the free energy is _____, meaning the process is at _____.

Answer 26

Delta G at zero means the free energy is zero and the process is in equilibrium.

Question 27

True or False?

If delta G is positive then free energy is required to do work and the process is thermodynamically unfavorable, but so is the reverse process.

Answer 27

False. the process is thermodynamically unfavorable, but the reverse is favorable.

Question 28

If Delta G is negative then free energy is __________ and the process is thermodynamically ___________.

Answer 28

If delta G is negative then there is free energy available to do work and the process is thermodynamically favorable.

Question 29

If delta G is negative then there is free energy available to do work so the process is then ____________.

Answer 29

Exergonic. (spontanteous)

Question 30

Is it energetically favorable for ice to melt at 283 K (+10 ˚C), where ΔH is +6770 J/mol and ΔS is +24.7 J/K•mol?

Answer 30

ΔG is negative and the melting of ice at at 283 K is favorable.

Question 31

At the melting temperature of water, 273 K (0 ℃), ∆H and T∆S terms are both equal to __________ and ∆G equals _______.

Answer 31

∆H and T∆S terms are both equal to each other @ 6010 J/mol and ∆G equals 0.

Question 32

At the melting temperature of water, ∆H and T∆S terms are both equal and ∆G is zero because ____________.

Answer 32

Ice and liquid water are in equilibrium at 273 K
Can melt a bit more ice by adding a minute amount of heat

Can freeze a bit more water by taking a minute amount of heat away

Question 33

True or False?

The melting point of any substance is the temperature at which the values for ∆H and T∆S are equal.

Answer 33

True

Question 34

True or False?

At the melting temperature of water, both ∆H or ∆S alone can tell us what will happen and which form or water is stable at any temperature.

Answer 34

False. Neither ∆H nor ∆S alone can tell us what will happen. It is their combination, expressed as ∆H - T∆S, that defines exactly which form of water is stable at any temperature.

Question 35

Explain the picture below.

Answer 35

In the fermentation of glucose to ethanol

Question 36

Explain the picture below

Answer 36

Question 37

Explain the picture below

Answer 37

Question 38

Delta H represents the sum of the heats of formation, commonly measured in kJ/mol, of the products minus the sum of those of the reactants. This called ___________

Answer 38

Enthalpy

Question 39

Entropy is a measurement of randomness or disorder. It is represented by the symbol___.

Answer 39

Delta S

Question 40

The effect of temperature on delta G for a process depends on the signs of ____ and _____.

Answer 40

Delta S and Delta H

Question 41

If Delta H is positive and Delta S is positive at low temperature then _________.

Answer 41

Delta G is positive and not favored

Question 42

If Delta H is positive and Delta S is negative at any temperature then _________.

Answer 42

Delta G is positive and not favored

Question 43

If Delta H is negative and Delta S is positive at any temperature then _________.

Answer 43

Delta G is negative and therefore favored

Question 44

If Delta H is positive and Delta S is positive at high temperature then _________.

Answer 44

Delta G is negative and therefore favored

Question 45

If Delta H and Delta S are both favored at low temperature then Delta G is _________. But if this is the case at a high temperature, then Delta G is ________

Answer 45

Delta G is negative and therefore favored; is positive and therefore unfavored.

Question 46

True or false?

Favorable processes are rapid processes.

Answer 46

False. The thermodynamic favorability of a process does not determine its rate.

Question 47

Why does the thermodynamic favorability of a process not determine its rate?

Answer 47

Because a reaction may have a large negative free energy change but still proceed at a slow rate. A good example is a diamond eventually becoming graphite.

Question 48

True or False?

A diamond is extremely hard because the carbon atoms are strongly bonded in only one direction.

Answer 48

False. The carbon atoms are strongly bonded in all directions.

Question 49

The carbon atoms of graphite are arranged in planar sheets that can easily glide against each other. This makes it structure _____.

Answer 49

Very soft.

Question 50

True or False?

Though the thermodynamic favorability of a process does not determine its rate, a catalyst may increase the rate for some reactions and influence the favored direction.

Answer 50

False.

A catalyst increases the rate for some reactions, but the favored direction is always dictated by ∆G and is independent of whether or not the reaction is catalyzed.

Question 51

True or False?

Enzymes selectively increase the rates for specific, thermodynamically favorable reactions in cells

Answer 51

True

Question 52

True or False?

The entropy of an open system cannot decrease

Answer 52

False

Question 53

True or False?

The entropy of an open system can decrease only if this change is accompanied by a small enthalpy decrease

Answer 53

False. this change can only occur if it is accompanied by a large enthalpy decrease because Energy must be expended to pay the price of organization

Question 54

How do living organisms overcome entropy?

Answer 54

By spending energy

Question 55

The magnitude of ∆G is an indication of what?

Answer 55

The magnitude of ∆G is an indication of how far the process is from equilibrium and how much useful work may be obtained from it

Question 56

True or False?

Q, symbolizes the mass action expression for a system that is at equilibrium

Answer 56

False. Q, symbolizes the mass action expression for a system that is not at equilibrium

Question 57

True or False?

the free energy of any component of the system increases from its standard value with a logarithmic dependence on its activity which is valued by the molar concentration of the solute A.

Answer 57

True The free energy of solute A is expressed by the following equation.

Go_A : the standard free energy for solute A at chemical standard state*

(pressure =1 bar, T = 25 ℃ (298.15 K), and solutes at concentrations of 1 M each)

R: the gas constant

T: temperature in units of kelvin

Question 58

True or False?

Standard state is a precisely defined reference state which can be used to compare thermodynamic properties

Answer 58

True

Question 59

Since free energy is a state function, free energy change for any reaction will equal the _______ minus that of the _______.

Answer 59

the free energy of the products minus that of the reactants

Question 60

True or false?

For a reaction at equilibrium, ΔG = 0 because there is no driving force in either direction.

Answer 60

True.

Question 61

True or False?

This reaction is at equilibrium when G6P and F6P are both at 1 M because ∆G°is positive. Therefore, the equilibrium must lie to the right, with a higher concentration of F6P than G6P

Answer 61

False.

This reaction is Not at equilibrium when G6P and F6P are both at 1 M because ∆G°is positive. This is an endergonic reaction and so reverse reaction is favored under standard conditions. Therefore, the equilibrium must lie to the left, with a higher concentration of G6P than F6P

Question 62

True or False?

The metabolic processes can occur only when each has a favorable thermodynamic driving force, that is, when ∆G < 0, within relatively narrow ranges of temperature, pH, and concentrations for ions and metabolites.

Answer 62

True

Question 63

True or False?

In a steady state ∆G > 0. Over time, the system is maintained in a higher state of order than its surroundings

Answer 63

False. ∆G is less than 0, negative.

Question 64

True or False?

In an equilibrium state, over time, any difference in entropy (state of disorder) between the system and the external environment tends to disappear.

Answer 64

True

Question 65

What are the conditions of a steady state?

Answer 65

• Constant state requires continual work
• Free energy is continuously put into the system to maintain homeostasis.
• Over time, the system is maintained in a higher state of order than its surroundings

Question 66

True or False?

In an equilibrium state, net free energy enters and escapes the system.

Answer 66

False.

Net free energy neither enters nor escapes the system

Question 67

Ionic compounds are maintained at constant concentrations in cells, but only through continually moving ions across the cell membrane. What is this an example of ?

Answer 67

Steady - state

Question 68

True or false?

Steady-State = Dynamic Equilibrium where all reactions in the body are interrelated, and the system as a whole is in a steady-state condition rather than equilibrium.

Answer 68

True.

Question 69

Give another example of steady-state in dynamic equilibrium other than ionic compounds.

Answer 69

The sodium-potassium pump. It uses active transport to move molecules from a high concentration to a low concentration.

Question 70

True or False?

Simple diffusion is an example of steady-state in dynamic equilibrium.

Answer 70

True. Diffusion means the movement of particles from an area of high concentration to an area of low concentration. Dynamic means that things continue to happen - the particles don’t stop moving!

The reverse of this is Equilibrium which means that a balanced situation has been achieved (particles are evenly spread out).

Question 71

True or False?

Thermoregulation is an example of steady-state in dynamic equilibrium.

Answer 71

True.

With thermoregulation entropy is low internally but high externally and it is an active process that requires energy to keep your internal temperature constant regardless of external affects.

Question 72

How does a thermodynamically unfavorable reaction become favorable?

Answer 72

By the coupling of unfavorable and favorable reactions

Question 73

How does coupling make a thermodynamically unfavorable reaction become favorable?

Answer 73

Question 74

True or False?

Living systems couple favorable and unfavorable processes to drive the unfavorable process forward.

Answer 74

True.

Coupling of this kind is used to drive unfavorable chemical reactions, pump metabolites across membranes against a concentration gradient, transmit nerve impulses, contract muscles, etc.

Question 75

List and define the 3 types of thermodynamic systems.

Answer 75

Open systems - Can exchange matter and energy with surroundings.

Closed systems - Can exchange energy (e.g. heat or work) but not matter with surroundings.

Isolated systems - Can exchange neither matter nor energy with surroundings

Question 76

True or False?

Surroundings are anything defined as part of the system.

Answer 76

False

Question 77

True or False?

Living systems are closed systems.

Answer 77

False.

Living systems are open systems because they can exchange both energy (e.g., heat) and material (e.g., nutrients and excreted wastes) with their environments.

Question 78

True or False?

A system must have defined boundaries.

Answer 78

True.

Question 79

Define a system.

Answer 79

Any part of the universe that we choose to study

(i.e., a cell, a Petri dish containing nutrients and millions of cells, the whole laboratory in which this dish rests, or the entire Earth)

Question 80

The 1st law of thermodynamics states that ___________.

Answer 80

Although energy can be transferred between the system and the surroundings in different ways (i.e., in the form of heat or work), in the chemical processes, energy can be neither created nor destroyed.

Question 81

True or False?

In an Isolated system, Total energy is constant.

Answer 81

True

Question 82

True or False?

In a Closed or Open systems, Energy is not conserved

Answer 82

False

Question 83

As the system loses energy by doing some work on its surroundings, an equal amount of energy must be absorbed by the surroundings. This is due to what?

Answer 83

The 1st law of thermodynamics, energy can neither be created nor destroyed.

Question 84

True or False?

Energy can be converted from one form to another

Answer 84

True

Question 85

In EXOTHERMIC reaction, HEAT is a ___ while in a ENDOTHERMIC reaction, HEAT A _______

Answer 85

EXOTHERMIC = HEAT AS PRODUCT

ENDOTHERMIC = HEAT AS REACTANT

Question 86

This is what type of reaction?

Answer 86

Exothermic Reaction

The system releases energy to the surrounding in the form of heat.

Question 87

A Catalyst works by_____.

Answer 87

Reducing the activation energy of a reaction.

Question 88

True or False?

the Enthalpy, ∆H is defined as A measure of the total energy of a thermodynamic system.

Answer 88

True

Question 89

define Enthalpy.

Answer 89

The heat exchanged between the system and the surroundings at constant pressure (which is the typical condition of living systems).

• The negative sign indicates that the reaction releases energy

Question 90

True or False?

The energy within a system increases as the energy is transferred as heat to the surroundings.

Answer 90

False. Energy within the system decreases because heat is escaping.

Question 91

True or False?

A State function Depends only on the initial and final states of the system it describes and is Independent of the pathway taken to get from the initial to the final state.

Answer 91

True

Question 92

When we place an ice cube in a glass of water at room temperature, it melts. Why doesn’t the rest of the water freeze instead?

Answer 92

Because in fact, all the water has not reached the freezing point at the same time (due to water’s high heat of vapporation). Even a microscopic fraction of a degree above freezing keeps the water from freezing, so until the water reaches a temperature slightly below the freezing point, it remains liquid.

Question 93

When we touch a flame to a piece of paper, the paper burns to carbon dioxide and water. Why can’t we mix carbon dioxide and water to form paper?

Answer 93

Because heat is what causes CO₂ to form but CO₂ is not a component of paper.

Question 94

What is the thermodynamically favored direction for a process?

Answer 94

Thermodynamically favored processes or reactions are those that involve both a decrease in the internal energy of the components (ΔH° < 0) and an increase in entropy of the components (ΔS° > 0). These processes are necessarily “thermodynamically favored” (ΔG° < 0) or negative.

Question 95

A process is at equilibrium when:

Answer 95

• It is the lowest energy state of the system
• The forward and reverse rates of the process are equal

Question 96

True or False?

Irreversible processes are set up far from an equilibrium state, and then proceed away from that state

Answer 96

False

Irreversible processes are set up far from an equilibrium state, but then proceed towards the euilibrium state.

Question 97

True or False?

Thermodynamics does not indicate in which direction a process is favorable

Answer 97

False. Thermodynamics does indicate in which direction a process is favorable. That is the whole purpose of thermodynamics.

Question 98

True or False?

Irreversible process are often called “spontaneous”, or favorable.

Answer 98

True

Question 99

Why do chemical and physical processes have thermodynamically favored directions?

Answer 99

Because a Systems natural inclination is to go toward the lowest-energy state by releasing energy as heat

Question 100

True or False?

Systems have a natural tendency to become less ordered (the increase in entropy, S).

Answer 100

True.

Question 101

True or False?

Diffusion as an entropy-driven process that although there is practically no energy change, in terms of heat and work, the process is unfavorable.

Answer 101

False. Diffusion is a favorable process despite no energy change.

Question 102

True or False?

The opposite process of diffusion never occurs.

Answer 102

True. This is why diffusion is a favored process despite no energy change.

Question 103

The 2nd law of thermodynamics states that ______.

Answer 103

The entropy of an isolated system will tend to increase to a maximum value because Systems have a natural tendency to become less ordered (entropy, S).

Question 104

True or False?

For a favorable process in an open system, such as a living cell, ∆Suniverse must increase.

Answer 104

True. This is due to the 2nd law of thermodynamics: Systems have a natural tendency to become less ordered.

∆S_universe = ∆S_system + ∆S_{surroundings > 0}

Question 105

True or False?

The 2nd law of thermodynamics states that in all processes involving energy changes under a given set of conditions of temperature and pressure, some energy is dissipated unproductively

Answer 105

True

Question 106

Give 3 examples of high entropy

Answer 106

Question 107

Give 3 examples of low entropy

Answer 107

Question 108

True or false?

Entropy is available for performing work.

Answer 108

False.

Entropy is NOT available for performing work becaue it is the energy that is dissipated unproductively during energy changes.

Question 109

True of False?

Energy transformations lead to an increase in entropy in a system

Answer 109

True

Question 110

True or False?

Answer 110

True

Question 111

Ice and water are at equilibrium at what temperature?

Answer 111

273K

Question 112

Define the steady-state.

Answer 112

Steady state refers to the maintenance of constant internal concentrations of molecules and ions in the cells and organs of living systems.

• A dynamic steady state = internal composition at both cellular and gross levels are relatively constant, but different from equilibrium concentrations.
• Continuous flux of mass and energy results in the constant synthesis and breakdown of molecules via chemical reactions.
• Steady state can be thought of as homeostasis at a cellular level.

Question 113

A system with __________ and __________ will never be spontaneous.

Answer 113

positive enthalpy . . . negative entropy

• a positive enthalpy in combination with a negative entropy will always result in a positive value for Gibb’s free energy.

ΔG=(+)−T(−)=+

This means these are the conditions that will always result in a nonspontaneous reaction.

Question 114

True or False?

An equilibrium constant greater than one would indicate that the equilibrium concentration of products is greater than the equilibrium concentration of reactants, consistent with a spontaneous reaction.

Answer 114

True

Question 115

If the reaction quotient (Q) is less than the equilibrium constant (K), what is true about the Gibbs free energy?

Answer 115

It is less than zero.

If Q is less than K, then the reaction has not yet reached the equilibrium state. It will proceed spontaneously in the forward direction. Since it is proceeding spontaneously in the forward direction, this must mean that the ΔG (Gibbs free energy) must be negative, or less than zero.

Question 116

Of the following reactions, which of the following is only spontaneous at high enough temperatures?

a) ∆H –, ∆S + b) ∆H +, ∆S – c) ∆H –, ∆S – d) ∆H +, ∆S +

Answer 116

d) ∆H +, ∆S +

Question 117

If a reaction has a positive value for its enthalpy and a negative value for its entropy, which of the following is true?

The reaction is at equilibrium

The reaction is spontaneous

Not enough information to tell

The reaction is nonspontaneous

Answer 117

The reaction is nonspontaneous.

• Given the equation for free energy, (delta)G = (delta)H-T(delta)S, we can determine that the reaction is nonspontaneous at all temperatures if H is positive and S is negative. This combination would always lead to a positive G value, meaning that free energy is required for the reaction to take place and it is therefore nonspontaneous.

Question 118

What must be true of a spontaneous process?

Answer 118

ΔG must be less than 0 and K must be greater than Q

• Change in free energy must always be negative for a spontaneous process. Additionally, Q must be less than K so that the reaction will proceed in the forward reaction, toward equilibrium.

Question 119

Na(s) + 1/2 Cl2(g) → NaCl (s)

The Standard Heat of formation for NaCl is -411.1 kJ

Which of the following descriptions accurately describes the reaction above?

Answer 119

It is favorable and driven by change in enthalpy only.

Here we are told that the reaction has a favorable enthalpy change (- means energy is released). Qualitatively we can see that the reaction will have an unfavorable change in entropy because the product, being a solid, is more ordered than the reactants which are both solid and gaseous. Thus we can conclude that the reaction is favorable because of the favorable change in enthalpy, which helps to overcome the unfavorable change in entropy.

Question 120

Calcium carbonate is formed from calcium oxide and carbon dioxide.

CaO(s)+CO2(g)→CaCO3(s)

Given that this reaction is spontaneous at low temperatures and non-spontaneous at high temperatures, what must be true about the change of enthalpy (ΔH) and the change of entropy (ΔS)?

Answer 120

ΔH is less than 0 and ΔS is also less than 0.

• For this particular reaction, ΔS is negative because the total number of moles of gas decreases from reactants to products. Since the reaction is spontaneous at lower temperatures, then ΔG must be negative when T is small. Since the -TΔS term would be positive for all values of T, the only way ΔG can be negative is if ΔH is negative. At higher temperatures, the positve -TΔS term would outweigh the negative ΔH term, resulting in a positive ΔG and a non-spontaneous reaction.

Question 121

Which of the processes A–D will lead to a positive change in the entropy of the system? If all of these processes lead to a positive change in the entropy of the system, select E.

a. Sodium chloride crystals form as saltwater evaporates.
b. Helium gas escapes from the hole in a balloon.
c. Stalactites form in a cave.
d. Water freezes in a freezer.
e. All of these lead to a positive change in entropy of the system, as they are all spontaneous.

Answer 121

b. Helium gas escapes from the hole in a balloon.
* positive change in the entropy of the system means what leads to more disorder.

Question 122

Which of the following processes will lead to a decrease in the entropy of the system?

a. Salt crystals dissolve in water.
b. Air escapes from a hole in a balloon.
c. Iron and oxygen react to form rust.
d. Ice melts in your hand.
e. None of these lead to a negative change in the entropy of the system, as they are all spontaneous.

Answer 122

c. Iron and oxygen react to form rust.
* Decrease in entropy = less disorder

Question 123

Indicate which one of the following reactions results in a negative ΔSsys.

a. H2O(g) ⇔ H2O(s)
b. CaCO3(s) ⇔ CaO(s) + CO2(g)
c. CuSO4(H2O)5 (s) ⇔ CuSO4(s) + 5H2O(g)
d. 14O2(g) + 3NH4NO3(s) + C10H22(l) → 3N2(g) + 17H2O(g) + 10CO2(g)
e. CO2(aq) ⇔ CO2(g)

Answer 123

Any side with more gas has more entropy.

a. H2O(g) ⇔ H2O(s)

Question 124

Indicate which one of the following reactions result in a positive ΔSsys.

a. AgNO3(aq) + NaCl(aq) ⇔ AgCl(s) + NaNO3(aq)
b. H2O (g) + CO2 (g) ⇔ H2CO3 (aq)
c. H2(g) + I2(g) D 2 Hl(g)
d. C2H2O2(g) ⇔ 2 CO(g) + H2(g)
e. H2O(g) ⇔ H2O(l)

Answer 124

d. C2H2O2(g) ⇔ 2 CO(g) + H2(g)

Because of the ranking for posite Delta S of a system

1. GAS > Liquid > Solid - gas wins over any other

2. Molecular Size
3. Number of Molecules

4. Dissolved > undissolved

5. Temperature

D is correct because of 1 and 4.

Question 125

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

a. NH3(g)
b. He(g)
c. C(s, graphite)
d. H2O(l)
e. CaCO3(s)

Answer 125

a. NH3(g)

Because is a gas and has more moles of gas than He

Question 126

Indicate which of the following has the highest entropy at 298 K.

a. 0.5 g of HCN
b. 1 mol of HCN
c. 2 kg of HCN
d. 2 mol of HCN
e. All of the above have the same entropy at 298 K.

Answer 126

c. 2 kg of HCN

because total grams per mol is 27 and there are 1000 moles in 1 kg. so 2 kg of HCN = 54,000 moles of HCN.

a. 0.5 g of HCN = 1 grams HCN is equal to 0.03700230968417 mole.
b. 1 mol of HCN = 27 grams
d. 2 mol of HCN = 54 grams

Question 127

In a spontaneous process, which of the following always increases?

a. the entropy of the system
b. the entropy of the surroundings
c. the entropy of the universe
d. the entropy of the system and the universe
e. the entropy of the system, surroundings and the universe

Answer 127

c. the entropy of the universe

ΔSuniverse depends on both ΔSsystem and ΔSsurroundings. ΔSsystem is reflected by ΔSº, (system entropy) while ΔSsurroundings is reflected by ΔHsystem (system enthlpy)

Question 128

The dissolution of ammonium nitrate in water is a spontaneous endothermic process. It is spontaneous because the system undergoes __________.

Answer 128

b. an increase in entropy.

• If you know it’s spontaneous, then either entropy or enthalpy (or both) must be favorable. If you know one is NOT favorable, then the other must certainly be favorable.
• An endothermic process means that the enthalpy, delta H, isn’t favorable so delta H must have a positive value. For this reaction to be spontaneous and therefore favored as it states, Delta S, entropy, would have to be largely positive, i.e. increase in entropy.
• This change in entropy is large enough that the mathematical product of the temperature (which must be very high) and change in entropy in the Gibbs free energy equation is larger than the change in enthalpy. Therefore, the Gibbs free energy is negative, and the reaction is spontaneous.

Question 129

Which of the following must be true for a spontaneous exothermic process?

a. only that ΔSsys < 0
b. only that ΔSsys > 0
c. both ΔSsys < 0 and the magnitude of ΔSsys < the magnitude of ΔSsurr
d. both ΔSsys < 0 and the magnitude of ΔSsys > the magnitude of ΔSsurr
e. either ΔSsys > 0, or else ΔSsys < 0 but the magnitude of ΔSsys < the magnitude of ΔSsurr

Answer 129

e. either ΔSsys > 0, or else ΔSsys < 0 but the magnitude of ΔSsys < the magnitude of ΔSsurr

Since Enthalpy is favorable (exothermic), then entropy could be either favorable or unfavorable. But if it’s unfavorable, it must not be bad enough to win over the good enthalpy.

A spontaneous, exothermic process means enthlaphy is favored.

Question 130

Suppose a chemical reaction is found to be spontaneous, but with ΔSsys < 0. What must be TRUE of the reaction?

Answer 130

ΔSsurr > 0 and the magnitude is ΔSsurr > ΔSsys. In other words, the system loses entropy but the surroundings gain entropy, and the gain by the surroundings outweighs the loss by the system.

• ΔSsys < 0 means that the entropy is not favored

Question 131

Which of the following statements about equilibrium are true?

I. ΔGsys = 0

II. ΔSsys = 0

III. ΔSuniverse = 0

Answer 131

I. ΔGsys = 0

III. ΔSuniverse = 0

Question 132

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 ΔH° and ΔS°, respectively?

Answer 132

Both are positive.

This is because “low enthlapy” = delta H is positive;

“Not spontaneous at low temperature but becomes spontaneous at high temperature” = delta S is positive (# 1 and #2a)

1. Entropy factor increases at higher temp

2. A temperature “flip” means entropy and enthalpy disagree.

a. If so, high Temp = entropy control,

b. low temp = enthalpy control.

Question 133

When entropy is favorable, (positive), enthalpy must be______.

Answer 133

Unfavorable (positive)

Question 134

True or False?

Delta G decreases with increasing Delta H (bond energy) and with increasing entropy.

Answer 134

False. Delta G INCREASES with increasing Delta H and DECREASES with increasing entropy.

Question 135

True or False?

Spontaneous reactions occur with energy to spare.

Answer 135

True.