Deck 12: Spontaneity of Chemical Processes

Question 1

Recognize the driving force behind all chemical change: dispersal of energy and matter.

Answer 1

A process that is spontaneous in one direction is non-spontaneous in the opposite direction. Energy in the form of heat always flows from a warmer object to a colder one. The spontaneity of any process must be evaluated.

Question 2

Predict the direction of change based on the entropy changes in the system and in the surroundings.

Answer 2

The second law of thermodynamics states that in any spontaneous process, the direction of change is such that total entropy increases: ∆S_total > 0.

Question 3

Understand and calculate entropies of pure substances.

Answer 3

The third law of thermodynamics states that a pure, perfect crystal at 0ºK has zero entropy. Entropy increases as the temperature increases, when a solid melts, and when a liquid evaporates.

Question 4

Predict the direction of spontaneous change using the reaction free energy.

Question 5

Apply thermodynamics to chemical reactions and phase changes.

Question 6

Describe thermodynamically some representative energetic processes that operate in living organisms.

Question 7

Which of the following arrangements of 4 identical socks in a 4-drawer dresser has the least degree of disorder?

A) 1 pair in 1 drawer and 1 pair in another drawer
B) 2 pair in 1 drawer
C) 1 pair in 1 drawer and 1 sock in 2 other drawers
D) 1 sock in each drawer
E) 3 socks in one drawer, 1 sock in another

Question 8

Considerable energy is required to vapourize water, yet water does evaporate as demonstrated by clothes drying when hung out. The reason for this spontaneous process is

A) energy is always conserved.
B) an increase in disorder.
C) energy is released to the surroundings.
D) water has a higher vapour pressure outside rather than inside of a house.
E) an increase in order.

Question 9

The reaction shown below is exothermic:2 NO₂ (g) $\rightarrow$ N₂O₄(g)At low pressures it is NOT spontaneous, but at high pressures, significant amounts of product are formed. This is because

A) the heavier products cause greater disorder upon collisions.
B) the smaller number of product molecules leads to more disorder in the container.
C) to place the system under high pressure, the surroundings are more disordered.
D) the higher pressures make the reaction proceed more rapidly.
E) at low pressure more molecules are required to fill the same space.

Question 10

The exothermic oxychlorination of ethylene to vinyl chloride is shown below:CH₂CH_2(g) + HCl_(g) + $\frac{1}{2}$ O_2(g) $\rarr$ CH₂CHCl_(g) + H₂O_(g)What are the signs for the entropy change of the system and surroundings, respectively?

A) +ve, +ve
B) +ve, -ve
C) -ve,-ve
D) -ve, +ve

Question 11

What are the signs for the entropy change of the system and surroundings, respectively, for ethane burning, when the system is defined as ethane and oxygen?

A) <0, <0
B) <0, >0
C) 0, 0
D) >0, <0
E) >0, >0

Question 12

What are the signs for the entropy change of the system and surroundings, respectively, for water evaporating at 370ºK, when the system is defined as water?

A) <0, <0
B) <0, >0
C) 0, 0
D) >0, <0
E) >0, >0

Question 13

Given three identical cups and three identical marbles, which of the following arrangements has the greatest value of W?

A) one marble in each cup
B) two marbles in one cup, one marble in one of the other cups
C) all three marbles in one cup
D) all have the same values of W
E) two of them have the same value of W

Question 14

Which of the following samples of substances has the smallest entropy change for fusion at its melting point, T_f?

A)
B)
C)
D)
E)

Question 15

Which of the following selections has the molecules arranged in order of increasing standard entropy? (One mole of each substance is being compared.)

A) C(graphite), C₆₀(s), C(diamond)
B) Si(s), P₄(s), S₈(s)
C) C₂H₆(g), C₂H₄(g), CH₄(g)
D) Polystyrene (made of 1000 monomer units), DNA (1000 base pairs), polyethylene (1000 monomer units)
E) CH₄(g), C₂H₆(g), C₂H₄(g)

Question 16

The standard molar entropy of NO is 211 J K^-1 mol^-1. What is the standard entropy of 3 moles of NO at 10 bar?

A) 202 J K^-1 mol
B) 606 J K^-1
C) 624 J K^-1
D) 633 J K^-1
E) 606 J K^-1 mol^-1

Question 17

An important reagent in organic chemistry is thionyl chloride, SOCl₂. One synthetic route would be to react SO₂ with HCl in the gas phase to produce SOCl₂ and water. What is the entropy change for this reaction? (J/K•mole SOCl₂)? (S? = 309.7(SOCl₂), 248.2(SO₂), 186.9(HCl), 188.8(H₂O) in J/K•mole)

A) -123
B) 123
C) -246
D) -146
E) 61.5

Question 18

One process water can undergo is dissociation, the equation for which is shown below:H₂O _(l) $\rarr$ H⁺ (aq) + OH^- (aq)As temperature increases to 90°C,

A) there will be no shift in the position of equilibrium.
B) more reactants will be present at equilibrium.
C) the extent of dissociation will be less.
D) the extent of dissociation will be greater.
E) the water will vapourize rather than dissociate.

Question 19

A reaction will NEVER be spontaneous when

A) $\Delta$ G° > 0.
B) $\Delta$ H°< 0 and $\Delta$ S° > 0.
C) $\Delta$ H°< 0 and $\Delta$ S° < 0.
D) $\Delta$ G=0.
E) $\Delta$ G > 0.

Question 20

Isomerization of hydrocarbons is important in the refining of petroleum. A simple example is that of butane, which has only two isomers: Which of the following statements is most correct?

A) At standard temperatures, n-butane is the preferred isomer.
B) At temperatures less than 450, n-butane is the preferred isomer.
C) At temperatures greater than 450ºK, n-butane is the preferred isomer.
D) At ambient temperatures, a sample of n-butane and isobutene which was at equilibrium would contain barely any butane.
E) A 1:1 mixture of butane and isobutane is at equilibrium at room temperature.

Question 21

Consider the following chemical reaction:CaSO₄(s) + 2H₂O (g) $\rarr$ CaSO₄ - 2H₂O (s)This reaction is exothermic.

A) The reaction is spontaneous at all temperatures.
B) The reaction is never spontaneous.
C) The reaction is spontaneous at low temperature.
D) The reaction is spontaneous at high temperature.
E) There is not sufficient information given to assess the spontaneity of the reaction.

Question 22

Consider the following unbalanced reaction:CO₂(g) + H₂O(g) (\rarr\) O₂(g) + C₃H₈(g)This reaction is endothermic.

A) The reaction is spontaneous at all temperatures.
B) The reaction is never spontaneous.
C) The reaction is spontaneous at low temperature.
D) The reaction is spontaneous at high temperature.
E) There is not sufficient information given to assess the spontaneity of the reaction.

Question 23

Which of the following energy producing technologies has no effect on the environment?

A) nuclear power
B) geothermal power
C) hydroelectric power
D) solar power
E) No energy producing technology is free from effects on the environment.

Question 24

A child plays with a deck of cards and leaves the room. You politely pick up and organize the cards. Which of the following is true during the action of organizing the cards?

A) You become more ordered.
B) The universe becomes more ordered.
C) The deck of cards becomes more disordered.
D) You become more disordered.
E) The ordering of a deck of cards is spontaneous.

Question 25

Which of the following processes generate thermal pollution?
I. Hydroelectric generation of electricity
II. Nuclear generation of electricity
III. Coal powered generation of electricity
IV. Natural gas/oil powered generation of electricity
V. Wind farms

A) all of the above
B) I, II, III, and IV
C) III and IV
D) II, III, IV and V
E) II, III, IV

Question 26

The process of storing energy for short term in the body is by making ATP. What type of bond is made or broken in this process?

A) making of a phosphate ester (P-O-P) bond
B) breaking of a phosphate ester bond
C) addition of water to ADP
D) the forming of a C=O bond
E) the forming of a C=C bond

Question 27

How does your body perform non-spontaneous reactions?

A) coupling these reactions with spontaneous reactions
B) Non-spontaneous reactions do not occur in our body.
C) by directly using sugars or fats for energy for these reactions
D) by only using ADP
E) All reactions in the body are spontaneous.

Question 28

The following reaction has a $\Delta$ G_rxn = 2872 kJ/mol. How is it that this reaction happens in plants on a regular basis?
6 CO_2(g) + 6 H₂O_(l) $\rarr$ C₆H₁₂O_6(aq) + 6 O_2(g)

A) $\Delta$ G says that the reaction is spontaneous.
B) This reaction is coupled with spontaneous reactions.
C) Energy is released to compensate for $\Delta$ G.
D) This reaction happens in humans not plants.
E) It happens is small amounts so that not much energy is needed.

Question 29

Liquids composed of different molecules have different degrees of order. Compare the liquid phases of H₂S and H₂O and suggest which is more "ordered."

Question 30

Ammonium nitrate, [NH₄][NO₃], dissolves spontaneously, even though the process is sufficiently endothermic to make it useful in "cold packs". Explain this phenomenon from the order-disorder perspective.

Question 31

State whether the disorder of each of the following systems increases or decreases in the stated process without consulting any tables:
i. 2 S _(s) + 3 O_{2 (g)} $\rightarrow$ 2 SO_{3 (g)}
ii. CO_{2 (g)} $\rightarrow$ CO_{2 (s)}
iii. heating water from 5 °C to 75 °C

Question 32

State whether the disorder of each of the following systems increases or decreases in the stated process without consulting any tables:
i. 6 CO_2(g) + 6 H₂O_(l) $\rightarrow$ C₆H₁₂O_6(aq) + 6 O_2(g)
ii. CH_4(g) + 2 O_2(g) $\rightarrow$ CO_2(g) + 2 H₂O_(l)
iii. CH₃CH₂OH_(l) $\rightarrow$ CH₃CH₂OH_(g)

Question 33

Compare the vapourization of H₂S and H₂O. For which of these will you expect the greater increase in disorder and why?

Question 34

What is the total entropy change when 40.5 g of ice ( $\Delta$ H_fus = 6.01 kJ/mole) melts at 0^oC?

Question 35

What is the total entropy change when 43 ml of water ( $\Delta$ H_fus = 6.01 kJ/mole, density 0.9981 g ml^-1) freezes at 0^oC?

Question 36

Consider a 1 kg block of ice melting in a 35^oC chamber ( $\Delta$ H_fus = 6.01 kJ/mole). Determine the total entropy change for the ice and the chamber.

Question 37

Calculate the entropy change for the fusion of 1 mole of hydrogen sulphide, mp = -85.6°C and ∆H_fus = 2.39 kJ/mole.

Question 38

Calculate the entropy change of the universe for 1 mole of solid water melting at -5°C.

Question 39

What is the entropy change in the surroundings when the system is a 2.2 kg block of ice that melts in a swimming pool (surrounding) whose temperature is 31°C?

Question 40

What is the entropy change in the surroundings when a 25 g piece of ice, the system, melts in the mouth of a human (surrounding) which maintains a temperature of 37°C?

Question 41

Write the definition of the 3 Laws of Thermodynamics.

Question 42

What is the entropy change for the reaction of graphite (S˚=5.74 J/mol•K) and hydrogen (S˚=130.68) to produce methane (S˚=186.2)?

Question 43

In adjusting the acidity of swimming pool water, concentrated aqueous HCl is added. What is the entropy for the chloride ions after 0.5 L of 12.0 M HCl is added to a swimming pool of 9.6 x 10⁴ L (about 25,000 gallons)? (S° Cl^- _(aq) = 56.5 J/mole • K)

Question 44

One mole of SF₆ (g) (S°= 291.82 J/mole•K) is at STP. When released into a large room, the final concentration is 1 PPM by volume. What is the entropy change for the SF₆ upon this expansion?

Question 45

Determine the change in entropy and if the following unbalanced reaction is spontaneous or non-spontaneous with respect to entropy.Ba(OH)₂ $\rightarrow$ 8H₂O_(s) + NH₄NO_3(s) $\rightarrow$ Ba(NO₃)_2(s) + H₂O_(l) + NH_3(aq)

Question 46

An electric heater releases 1200 J of energy every second. How much does the entropy of the surroundings increase when the heater runs for 10 minutes in a room that is at 25°C?

Question 47

Hydrogen sulphide is a toxic gas, which fortunately has the distinctive odour of rotten eggs. What is the entropy (J/K) of 0.01 mole of H₂S (S?=205.8 J/K.mole) which occupies a volume of 10⁶ L at a temperature of 298°K?

Question 48

Calculate the free energy for the oxychlorination of ethylene to vinyl chloride, CH₂CHCl, under standard conditions.
$\Delta$ G° = 53.6(CH₂CHCl), -95.3(HCl), 68.49(CH₂CH₂), -228.7(H₂O) kJ/molThe equation of reaction is:
CH₂CH_{2 (g)} + HCl _(g) + EQ \F(1,2) O_{2 (g)} $\rightarrow$ CH₂CHCl _(g) + H₂O _(g)

Question 49

Calculate the free energy for the oxychlorination of ethylene to vinyl chloride, CH₂CHCl, under standard conditions at 100^oC given the thermodynamic data below collected at 25^oC:
$\Delta$ G^o = 53.6(CH₂CHCl), -95.3(HCl), 68.49(CH₂CH₂), -228.7(H₂O) kJ/mol
$\Delta$ H^o = 37.2(CH₂CHCl), -92.3(HCl), 52.4(CH₂CH₂), -241.8(H₂O) kJ/molThe equation of reaction is:
CH₂CH_{2 (g)} + HCl _(g) + $\frac{1} {2}$ O_{2 (g)} $\rarr$ CH₂CHCl _(g) + H₂O _(g)

Question 50

The conversion of calcite,CaCO_3(s), to CaO_(s) and CO_2(g) is NOT favourable at ambient temperatures. At what temperature will this decomposition of CaCO₃ become spontaneous?

Question 51

Determine if the following unbalanced reaction is spontaneous or non-spontaneous at standard conditions.
( $\Delta$ G° = -857, SiO₂; 0, Si; 0, Al; -1582 kJ/mol)
SiO_2(s) + Al_(s) $\rightarrow$ Al₂O_3(s) + Si_(s)

Question 52

What is the reaction quotient for the following unbalanced cell reaction?Ba(OH)₂.08H₂O_(s) + NH₄NO_3(s) $\rightarrow$ Ba(NO₃)_2(s) + H₂O_(l) + NH_3(aq)

Question 53

Determine Gibb's Free Energy and if the following unbalanced reaction is spontaneous or non-spontaneous at standard conditions.
Ba(OH)₂.8H₂O_(s) + NH₄NO_3(s) $\rightarrow$ Ba(NO₃)_2(s) + H₂O_(l) + NH_3(aq)

Question 54

Determine Gibb's Free Energy and if the following unbalanced reaction is spontaneous at 0^oC.
Ba(OH)₂.8H₂O_(s) + NH₄NO_3(s) $\rarr$ Ba(NO₃)_2(s) + H₂O_(l) + NH_3(aq)

Question 55

At what identical concentration of H⁺ and CH₃CO₂^- (?G°_f = -372.5 kJ) will the dissociation of 1 M acetic acid, below, ( $\Delta$ G°_f (CH₃CO₂H (aq)) = -399.6 kJ) become spontaneous at room temperature?
CH₃CO₂H (aq) $\rightarrow$ H⁺(aq) + CH₃CO₂^-(aq)

Question 56

The possible isomerization for ethanol to methyl ether is shown below:
What is
a) the value of the reaction quotient when ?G=0 and
b) will the predominant species be ethanol or methyl ether?

Question 57

Complete the following table for determining at what relative temperature (high or low, or at none) a reaction will be spontaneous.

Question 58

One of the more important industrial chemicals is hydrogen. One process for hydrogen production is called "steam reforming", in which hydrocarbons react with water to give hydrogen and CO. The equation of reaction for reforming methane is written below:
CH_{4 (g)} + H₂O _(g) $\rightarrow$ CO _(g) + 3 H_{2 (g)}
a) Calculate the free energy change for this reaction at standard conditions.
b) Estimate the temperature at which the process becomes spontaneous.

Question 59

Calcite, CaCO_3(s), can be converted to CaO_(s) and CO_2(g). Determine the pressure of CO₂ at 1150 K at which the reaction is no longer spontaneous.

Question 60

One process for hydrogen production is called "steam reforming", in which hydrocarbons react with water to give hydrogen and CO. The equation of reaction for reforming methane is written below.
CH_{4 (g)} + H₂O _(g) $\rightarrow$ CO _(g) + 3 H_{2 (g)}
What is the free energy change, $\Delta$ G, for reforming methane at 298^oK when the partial pressure of the products is 5.0 x 10^-5 atm and the partial pressure of the reactants is 1.0 atm?

Question 61

What are the signs of ΔH, ΔS, and ΔG for the process of ice melting at 10˚C and 1 atm?

Question 62

Given the following chemical reaction at 298^oK:3 O_2(g) $\rightarrow$ 2 O_3(g) ?G? = 344 kJ/mole, what would be ?G if the partial pressure of O₂ = 0.20 bar and O₃ = 0.0001 bar?

Question 63

An explosive that is also used as fertilizer is ammonium nitrate. Calculate $\Delta$ G $\degree$ for one of the decomposition reactions this fertilizer can undergo.
( $\Delta$ G $\degree$ = -183.9 (NH₄NO₃), 103.7 (N₂O), -228.7 (H₂O) in kJ/mol)
NH₄NO_3(s) $\rightarrow$ N₂O_(g) + 2 H₂O_(g)

Question 64

At 45 $\degree$ C, what is the vapour pressure of Iodine?
(I_2(s): $\Delta$ H $\degree$ = 0, S $\degree$ = 116.1 J/mol.K) (I_2(g): $\Delta$ H $\degree$ = 62.4 kJ/mol, S $\degree$ = 260.7 J/mol.K)

Question 65

Estimate how many moles of ATP would be required to ride a bicycle at 35 km/hour for 1 hour, an activity that would require about 1500 kJ of energy, givenATP $\rightarrow$ ADP + H₂O, ?G° = -30.6 kJ

Question 66

Glucose (MM = 180g/mole) is metabolized at a rate of about 38% efficiency. How many grams of glucose would supply the energy to ride a bicycle at 35 km/hour for 1 hour, an activity that would require about 1500 kJ of energy?

Question 67

Palmitic acid, C₁₅H₃₁CO₂H undergoes complete combustion with $\Delta$ G_rxn ^o of -9790 kJ mol^-1. Using bond energies, estimate the entropy change associated with this reaction.

Question 68

Chemical energy stored in glucose can be used to convert ADP to ATP; under normal physiological conditions the process, shown below, is 38.3 % efficient:
C₆H₁₂O₆ + 6O₂ + 36 ADP + 36 H₃PO₄ $\rightarrow$ 6CO₂ + 36 ATP + 42 H₂O $\Delta$ G° = Given that the reaction: ADP + H₃PO₄ $\rightarrow$ ATP + H₂O requires 30.6 kJ mol^-1 determine $\Delta$ G° for the reaction of glucose and ADP above.

Question 69

The formation of ATP from ADP requires 30.6 kJ/mol. The oxidation of the fat, palmitic acid, to carbon dioxide yields -9790 kJ/mol of energy. Yet your body is only able to produce 130 ATP units per 1 palmitic acid unit. What is the percent yield for this biological process?

Question 70

A person exercises for 30 minutes and burns 800 kJ of free energy. How many moles of ATP (-30.6 kJ/mol) does this represent and based on 38% efficiency, how many grams of glucose were burned if 1 mole of glucose can make 36 ATPs?