Deck 7: Making and Breaking of Bonds

Question 1

The following questions often assume that a truncated table of standard-state thermodynamic data is attached to the exam.
Specific Heat and Heat Capacity

-The same amount of heat is added to 20 gram each of iron and water. The temperature increases more in the iron than in the water. Which has the greater specific heat? Explain.

Answer 1

Water has the greater specific heat. Specific heat is the measure of the amount of heat required to raise the temperature by 1^oC of 1 g of a substance. A greater specific heat indicates that more heat will be needed to give a particular increase in the temperature of a substance relative to a substance with a lower specific heat.

Question 2

The following questions often assume that a truncated table of standard-state thermodynamic data is attached to the exam.
Specific Heat and Heat Capacity

-Metal A at 40^oC is brought into contact with Metal B at 20^oC. Assuming you have the same masses of both metals and that Metal A has a greater specific heat than Metal B, what will the final temperature be?

A) 30^oC
B) between 20^oC and 30^oC
C) between 30^oC and 40^oC
D) 40^oC
E) insufficient information given to decide

Answer 2

between 30^oC and 40^oC

Question 3

The following questions often assume that a truncated table of standard-state thermodynamic data is attached to the exam.
Specific Heat and Heat Capacity

-When 2.50 g of KClO₄ decomposes, 908 J of heat is evolved. If this heat is absorbed by 45.0 g of H₂O, what will be the temperature change of the water?

A) 0.207^oC decrease
B) 4.82^oC increase
C) 6.41^oC increase
D) 0.207^oC increase
E) none of these

Answer 3

4.82^oC increase

Question 4

The following questions often assume that a truncated table of standard-state thermodynamic data is attached to the exam.
Specific Heat and Heat Capacity

-How much energy in joules is required to heat 10.0 grams of gold from room temperature (20.0°C) to the temperature of boiling water (100.0°C) if the specific heat of gold is 0.129
?

A) 1.29 J
B) 10.3 J
C) 103 J
D) 6,200 J
E) none of the above

Question 5

The following questions often assume that a truncated table of standard-state thermodynamic data is attached to the exam.
Specific Heat and Heat Capacity

-A piece of copper metal weighing 145 grams was heated to 100°C and then dropped into 250 grams of water at 25°C. The copper metal cooled down and the water became warmer until both were at a temperature of 28.8°C. Calculate the amount of heat absorbed by the water. Assuming that the heat lost by the copper was absorbed by the water, what is the molar heat capacity of copper metal?
(C_H2O = 75.376 )

A) between 0 and 10
B) between 10 and 20
C) between 20 and 30
D) between 30 and 40
E) more than 40

Question 6

The following questions often assume that a truncated table of standard-state thermodynamic data is attached to the exam.
Specific Heat and Heat Capacity

-How much heat in joules is produced by mixing 50.0 mL of 1.0 M HBr at 25.6°C with 50.0 mL of 1.0 M KOH at 25.6°C if this reaction produces 100 mL of a solution with a temperature of 32.3°C? (Assume the heat capacity of water is 4.18
and the density of these solutions is 1.00 )

A) 6.7 J
B) 670 J
C) 1400 J
D) 2800 J
E) 5600 J

Question 7

The change in enthalpy, $\Delta$ H, for the following balanced reaction is 33.2 kJ/mol_rxn. How much heat will be absorbed by the reaction of 1.00 g of N₂ with an excess of oxygen?
N₂(g) + 2O₂(g) $\rightarrow$ 2 NO₂(g)

A) 1.19 kJ
B) 2.37 kJ
C) 33.2 kJ
D) 66.4 kJ
E) none of these

Question 8

Which of the following is a correct statement for a chemical reaction that gives off energy? The reaction is:

A) exothermic with a + $\Delta$ H
B) exothermic with a - $\Delta$ ) H
C) endothermic with a + $\Delta$ H
D) endothermic with a - $\Delta$ H
E) exothermic with a $\Delta$ H=0

Question 9

For the reaction
MnO₂(s) + CO(g) $\rightarrow$ MnO(s) + CO₂(g) $\Delta$ H = -151 kJ/ mol_rxn.
How many moles of MnO₂ are required in order for 418 kJ of heat to be released?

A) 1.31 moles
B) 0.246 moles
C) 0.361 moles
D) 2.77 moles
E) none of these

Question 10

How much heat is produced when 0.200 mole of H₂(g) reacts with 0.300 mole of Cl₂(g) if the enthalpy of reaction for the production of one mole of HCl(g) is -92.3 kJ/mol_rxn?

A) 18.5 kJ
B) 27.7 kJ
C) 36.9 kJ
D) 55.4 kJ
E) 92.3 kJ

Question 11

How much heat in kilojoules is given off when 4.80 g of carbon are burned to produce carbon dioxide, if $\Delta$ 0H_rxn° for the combustion of carbon to form CO₂ is -394 kJ/mol_rxn?

A) 82.1 kJ
B) 158 kJ
C) 394 kJ
D) 985 kJ
E) 1.89 x 10³ kJ

Question 12

Calculate $\Delta$ wing reaction if 1.00 gram of magnesium reacts with excess fluorine to give off 46.22 kJ of heat.
Mg(s) + F₂(g) $\rightarrow$ MgF₂(s)

A) less than 300 kJ/mol_rxn
B) between 300 and 600 kJ/mol_rxn
C) between 600 and 900 kJ/mol_rxn
D) between 900 and 1200 kJ/mol_rxn
E) more than 1200 kJ/mol_rxn

Question 13

For which of the following reactions is the most heat evolved?

Question 14

Which of the following reactions is the most likely to give off heat?

A) Al(s) $\rightarrow$ Al(g)
B) Al(g) $\rightarrow$ Al³⁺(g) + 3 e^-
C) Al^-(g) $\rightarrow$ Al(g) + e^-
D) 2 Al(s) + conc. HNO₃(aq) $\rightarrow$ 2 Al³⁺(aq) + 3 H₂(g)
E) all these reactions should give off energy.

Question 15

Which of the following reactions is the most likely to give off heat?

A) Mg(s) $\rightarrow$ Mg(g)
B) Mg(g) $\rightarrow$ Mg²⁺(g) + 2 e^-
C) MgCl₂(s) $\rightarrow$ Mg²⁺(g) + 2 Cl^-(g)
D) Mg(g) + 2 Cl(g) $\rightarrow$ MgCl₂
E) all these reactions should give off energy

Question 16

Which of the following reactions is the most likely to be exothermic?

A) H₂(g) $\rightarrow$ 2 H(g)
B) 2 F(g) $\rightarrow$ F₂(g)
C) C(s) $\rightarrow$ C(g)
D) CCl₄(g) $\rightarrow$ C(g) + 4 Cl(g)
E) HCl(g) $\rightarrow$ H(g) + Cl(g)

Question 17

Which of the following reactions is the most likely to be exothermic?

A) CaCO₃(s) $\rightarrow$ CaO(s) + CO₂(g)
B) Ca(g) $\rightarrow$ Ca²⁺(g) + 2 e^-
C) Cl₂(g) $\rightarrow$ 2 Cl(g)
D) Cl(g) + e^- $\rightarrow$ Cl^-(g)
E) CaCl₂(g) $\rightarrow$ Ca²⁺(g) + 2 Cl^-(g)

Question 18

Which of the following reactions is the most likely to be endothermic?

A) 2 Na(s) + 2 H₂O(l) $\rightarrow$ 2 Na⁺(aq) + 2 OH^-(aq) + H₂(g)
B) 2 Mg(s) + O₂(g) $\rightarrow$ 2 MgO(s)
C) 2 NaCl(s) $\rightarrow$ 2 Na(s) + Cl₂(g)
D) Na⁺(g) + e^- $\rightarrow$ Na(g)
E) Cl₂(g) + 2e^- $\rightarrow$ 2 Cl^-(g)

Question 19

Which of the following reactions is the most likely to be endothermic?

A) Mg(s) $\rightarrow$ Mg(g)
B) Na⁺(g) + Cl^-(g) $\rightarrow$ NaCl(s)
C) Na⁺(g) + e^- $\rightarrow$ Na(g)
D) H⁺(aq) + OH^-(aq) $\rightarrow$ H₂O(l)
E) 2 H₂(g) + O₂(g) $\rightarrow$ 2 H₂O(l)

Question 20

Use your understanding of the bonding in the reactants and products to explain why the following reaction is exothermic.
2 Mg(s) + O₂(g) $\rightarrow$ 2 MgO(s)

Question 21

At what temperature are standard-state enthalpy of reaction measurements most often made?

A) 0 K
B) 273.15 K
C) 0°C
D) 25°C
E) more than one of the above

Question 22

The bond strength between C and a halogen decreases down the halogen group in the periodic table. Based on this trend, predict which of the following gases has the largest (most negative) enthalpy of atom combination?

A) CCl₄
B) CBr₄
C) CF₄
D) CI₄
E) They all have the same enthalpy of atom combination

Question 23

When carbon is burned in air the following reaction takes place and releases heat.

C(s) + O₂(g) $\rightarrow$ CO₂(g)
Which of the following is responsible for the heat produced?

A) breaking oxygen-oxygen bonds
B) making carbon-oxygen bonds
C) breaking carbon-carbon bonds
D) both (a) and (c)
E) (a), (b) and (c)

Question 24

Which of the following is an exothermic process?

A) Li(g) $\rightarrow$ Li⁺ (g) + e^-
B) NH₃(g) $\rightarrow$ N (g) + 3 H
C) C(g) + 2 O(g) $\rightarrow$ CO₂(g)
D) all of these
E) none of these

Question 25

Determine the change in enthalpy for the following reaction:

A) -3088 kJ/mol_rxn
B) +544 kJ/mol_rxn
C) -544 kJ/mol_rxn
D) +9.0 kJ/mol_rxn
E) none of these

Question 26

Use enthalpies of atom combination to calculate $\Delta$ H_rxn° for the following reaction.

What would happen to the magnitude of $\Delta$ H_rxn° if the reaction consumed liquid water instead of gaseous water?

Question 27

Calculate $\Delta$ H_rxn° for the following reaction from the data given below.

A) -105.5 kJ/mol_rxn
B) -905.5 kJ/mol_rxn
C) -1274.2 kJ/mol_rxn
D) -1996.2 kJ/mol_rxn
E) none of the above

Question 28

Calculate $\Delta$ H_rxn° for the reaction:

from the following enthalpy of atom combination data.

A) less than -1000 kJ/mol_rxn
B) between -1000 and -750 kJ/mol_rxn
C) between -750 and -500 kJ/mol_rxn
D) between -500 and -250 kJ/mol_rxn
E) between -250 and 0 kJ/mol_rxn

Question 29

Both ethanol (CH₃CH₂OH) and methanol (CH₃OH) have been considered as fuels for automobiles. Which is the better fuel, on a per gram basis, when burned with oxygen?

Question 30

The following reaction occurs when sucrose (cane sugar) is metabolized by the body.

C₁₂H₂₂O₁₁(s) + 12 O₂(g) $\rightarrow$ 12 CO₂(g) + 11 H₂O(l)
Assume that $\Delta$ H_rxn° for this reaction is -5645 kJ/mol_rxn. What is the value of $\Delta$ H_ac° for sucrose?

Question 31

What is the sign of the enthalpy of reaction for the reaction:

P₄O₆(s) + 2 O₂(g) + 6 H₂O(g) $\rightarrow$ 4 H₃PO₄(s)
Assuming that all compounds are present in their most stable state at 25°C and 1 atm pressure?

A) positive
B) negative
C) impossible to determine from the data

Question 32

What is the absolute value of the enthalpy of reaction in the previous question?

A) less than 1000 kJ/mol_rxn
B) between 1000 and 1250 kJ/mol_rxn
C) between 1250 and 1500 kJ/mol_rxn
D) between 1500 and 1750 kJ/mol_rxn
E) more than 1750 kJ/mol_rxn

Question 33

Calculate the average Si-Br bond strength for an individual Si-Br bond in SiBr₄. The $\Delta$ H_ac for SiBr₄(g) is -1272 kJ/mol_rxn.

A) 3.66 kJ/mol
B) 254 kJ/mol
C) 318 kJ/mol
D) 636 kJ/mol
E) 1272 kJ/mol

Question 34

The disposable lighters that many smokers carry use butane as a fuel. Butane occurs as two isomers, n-butane

and isobutane

(I) Which form of butane will release the most heat when it is burned by the above combustion reaction? Explain your reasoning.
(II) Which form of butane will have the strongest bonds? Explain your reasoning.

Question 35

Use enthalpies of atom combination to calculate the change in enthalpy for
the reaction:

Is the reaction endothermic or exothermic?

Question 36

The enthalpy of atom combination for CCl₄(g) is -1306.3 kJ/mol_rxn. Calculate the average bond strength of the C-Cl bond.

A) 261.3 kJ/mol
B) 326.6 kJ/mol
C) 1306.3 kJ/mol
D) 3484.0 kJ/mol
E) 5225.2 kJ/mol

Question 37

Predict which of the following gases has the largest (most negative) enthalpy of atom combination?

A) CCl₄
B) CBr₄
C) CF₄
D) CI₄
E) They all have the same enthalpy of atom combination.

Question 38

Which of the following has the shortest carbon to halogen bond length?

A) CCl₄
B) CBr₄
C) CF₄
D) CI₄
E) All the bonds are the same length.

Question 39

Arrange the following in order of increasing enthalpy of atom combination and decreasing bond length.

A) Cl₂(g) > Br₂(g) > F₂(g) > I₂(g)
B) F₂(g) > Cl₂(g) > Br₂(g) > I₂(g)
C) I₂(g) > Br₂(g) > Cl₂(g) > F₂(g)
D) F₂(g) > Cl₂(g) > I₂(g) > Br₂(g)
E) Cl₂(g) > Br₂(g) > I₂(g) > Br₂(g)

Question 40

Arrange the following in order of increasing bond length and decreasing enthalpy of atom combination.

A) TeH₄ > SiH₄ > GeH₄ > CH₄
B) TeH₄ > GeH₄ > SiH₄ > CH₄
C) CH₄ > SiH₄ > GeH₄ > TeH₄
D) GeH₄ > CH₄ > TeH₄ > SiH₄
E) TeH₄ > SiH₄ > CH₄ > GeH₄

Question 41

Use the following data
2 H₂(g) + O₂(g) $\rightarrow$ 2 H₂O(g)   $\Delta$ H_rxn° = -483.6 kJ/mol_rxn
2 H₂(g) + O₂(g) $\rightarrow$ 2 H₂O(l)   $\Delta$ H_rxn° = -571.6 kJ/mol_rxn
To calculate $\Delta$ H_rxn° for the reaction
H₂O(l) $\rightarrow$ H₂O(g)

A) -527.6 kJ/mol_rxn
B) -44.0 kJ/mol_rxn
C) 44.0 kJ/mol_rxn
D) 527.6 kJ/mol_rxn
E) none of the above

Question 42

What is $\Delta$ H_rxn° for the reaction: 2 CO(g) + O₂(g) $\rightarrow$ 2 CO₂(g) if:
C(s) + 1/2 O₂(g) $\rightarrow$ CO(g)   $\Delta$ H_rxn° = -111 kJ/mol_rxn
C(s) + O₂(g) $\rightarrow$ CO₂(g)   $\Delta$ H_rxn° = -393 kJ/mol_rxn

A) -564 kJ/mol_rxn
B) -282 kJ/mol_rxn
C) 171 kJ/mol_rxn
D) 282 kJ/mol_rxn
E) 564 kJ/mol_rxn

Question 43

Calculate $\Delta$ H_rxn° for the reaction: C(s) + 2 H₂(g) $\rightarrow$ CH₄(g) from the following data:

A) -1855.7 kJ/mol_rxn
B) -214.6 kJ/mol_rxn
C) -75.1 kJ/mol_rxn
D) 210.9 kJ/mol_rxn
E) 1569.9 kJ/mol_rxn

Question 44

Given the following data
3 H₂(g) + N₂(g) $\rightarrow$ 2 NH₃(g)   $\Delta$ H_rxn° = -92.4 kJ/mol_rxn
2 H₂(g) + O₂(g) $\rightarrow$ 2 H₂O(l)   $\Delta$ H_rxn° = -571.7 kJ/mol_rxn
Calculate $\Delta$ H_rxn° for the following reaction:
4 NH₃(g) + 3 O₂(g) $\rightarrow$ 2 N₂(g) + 6 H₂O(l)

A) -1899.9 kJ/mol_rxn
B) -1715.1 kJ/mol_rxn
C) -1530.3 kJ/mol_rxn
D) -479.3 kJ/mol_rxn
E) 1530.3 kJ/mol_rxn

Question 45

Hydrogen peroxide is a good oxidizing agent because it is a good source of molecular oxygen: 2 H₂O₂(aq) $\rightarrow$ 2 H₂O(l) + O₂(g). Calculate $\Delta$ H_rxn° for this reaction from the enthalpies of the following reactions.
2 H₂(g) + O₂(g) $\rightarrow$ 2 H₂O(l)   $\Delta$ H_rxn° = -571.66 kJ/mol_rxn
H₂(g) + O₂(g) $\rightarrow$ H₂O₂(aq)   $\Delta$ H_rxn° = -187.8 kJ/mol_rxn

A) -759.5 kJ/mol_rxn
B) -383.9 kJ/mol_rxn
C) -196.0 kJ/mol_rxn
D) -98.0 kJ/mol_rxn
E) 196.0 kJ/mol_rxn

Question 46

Calculate $\Delta$ H_rxn° for the reaction
N₂(g) + O₂(g) $\rightarrow$ 2 NO(g)
From the enthalpies of the following reactions.
N₂(g) + 2 O₂(g) $\rightarrow$ 2 NO₂(g)   $\Delta$ H_rxn° = 66.4 kJ/mol_rxn
2 NO(g) + O₂(g) $\rightarrow$ 2 NO₂(g)   $\Delta$ H_rxn° = -114.2 kJ/mol_rxn

A) -180.6 kJ/mol_rxn
B) -47.8 kJ/mol_rxn
C) 47.8 kJ/mol_rxn
D) 180.6 kJ/mol_rxn
E) $\Delta$ H_rxn° is impossible to calculate from the information given

Question 47

Calculate the heat of combustion of propane, C₃H₈,
C₃H₈(g) + 5 O₂(g) $\rightarrow$ 3 CO₂(g) + 4 H₂O(g)
from the enthalpies of the following reactions.
3 C(s) + 4 H₂(g) $\rightarrow$ C₃H₈(g)   $\Delta$ H_rxn° = -103.85 kJ/mol_rxn
C(s) + O₂(g) $\rightarrow$ CO₂(g)   $\Delta$ H_rxn° = -393.51 kJ/mol_rxn
H₂(g) + 1/2 O₂(g) $\rightarrow$ H₂O(g)   $\Delta$ H_rxn° = -241.83 kJ/mol_rxn

Question 48

Calculate the heat required to transform 18 g of ice at 0°C to water vapor at 100°C using some or all of the data given below.
H₂O(s) $\rightarrow$ H₂O(l)   $\Delta$ H_rxn° = 6.03 kJ/mol_rxn
H₂O(l) $\rightarrow$ H₂O(g)   $\Delta$ H_rxn° = 40.67 kJ/mol_rxn
2 H₂(g) + O₂(g) $\rightarrow$ 2 H₂O(g)   $\Delta$ H_rxn° = -484 kJ/mol_rxn
H₂O(liquid, 0°C) $\rightarrow$ H₂O(liquid, 100°C)   $\Delta$ H_rxn° = 7.53 kJ/mol_rxn

A) 40.67 kJ
B) 46.70 kJ
C) 54.23 kJ
D) 296 kJ
E) none of these

Question 49

(Note that some of these are the same problems as found in the section headed Enthalpies of Atom Combination. However in this section all problems are worked using Enthalpies of Formation.)

-For which of the following substances is the enthalpy of formation, $\Delta$ H_f S1° , equal to zero?

A) H₂(l)
B) H₂O(g)
C) O₃(g)
D) F₂(g)
E) Na(g)

Question 50

(Note that some of these are the same problems as found in the section headed Enthalpies of Atom Combination. However in this section all problems are worked using Enthalpies of Formation.)

-Determine the change in enthalpy for the following reaction:
SnO₂(s) + 2 H₂(g) $\rightarrow$ Sn(s) + 2 H₂O(l)
$\Delta$ H_f ° SnO₂(s) = -580.7 kJ/mol_rxn $\Delta$   H_f ° H₂O(l) = -285.83 kJ/mol_rxn

A) -3088 kJ/mol_rxn
B) + 544 kJ/mol_rxn
C) -544 kJ/mol_rxn
D) + 9.0 kJ/mol_rxn
E) none of these

Question 51

(Note that some of these are the same problems as found in the section headed Enthalpies of Atom Combination. However in this section all problems are worked using Enthalpies of Formation.)

-Use enthalpies of formation to calculate $\Delta$ H ° for the following reaction.
C(s) + H₂O(g) $\rightarrow$ CO(g) + H₂(g)
What would happen to the magnitude of $\Delta$ H ° if the reaction consumed liquid water instead of gaseous water?

Question 52

(Note that some of these are the same problems as found in the section headed Enthalpies of Atom Combination. However in this section all problems are worked using Enthalpies of Formation.)

-Calculate $\Delta$ H ° for the following reaction from the data given below.
4 NH₃(g) + 5 O₂(g) $\rightarrow$ 4 NO(g) + 6 H₂O(g)

A) -105.5 kJ/mol_rxn
B) -905.4 kJ/mol_rxn
C) -1274.2 kJ/mol_rxn
D) -1996.2 kJ/mol_rxn
E) none of the above

Question 53

(Note that some of these are the same problems as found in the section headed Enthalpies of Atom Combination. However in this section all problems are worked using Enthalpies of Formation.)

-Calculate $\Delta$ H ° for the reaction

3 NO₂(g) + H₂O(l) $\rightarrow$ 2 HNO₃(aq) + NO(g)
From the following enthalpy of formation data.

A) less than -1000 kJ/mol_rxn
B) between -1000 and -750 kJ/mol_rxn
C) between -750 and -500 kJ/mol_rxn
D) between -500 and -250 kJ/mol_rxn
E) between -250 and 0 kJ/mol_rxn

Question 54

(Note that some of these are the same problems as found in the section headed Enthalpies of Atom Combination. However in this section all problems are worked using Enthalpies of Formation.)

-The following reaction occurs when sucrose (cane sugar) is metabolized by the body.
C₁₂H₂₂O₁₁(s) + 12 O₂(g) $\rightarrow$ 12 CO₂(g) + 11 H₂O(l)
Given that $\Delta$ H ° for this reaction is -5645 kJ/mol_rxn, what is the value of $\Delta$ H_f ° for sucrose?

Question 55

(Note that some of these are the same problems as found in the section headed Enthalpies of Atom Combination. However in this section all problems are worked using Enthalpies of Formation.)

-Both ethanol (CH₃CH₂OH) and methanol (CH₃OH) have been considered as fuels for automobiles. Which is the better fuel, on a per gram basis, when burned with oxygen?

Question 56

(Note that some of these are the same problems as found in the section headed Enthalpies of Atom Combination. However in this section all problems are worked using Enthalpies of Formation.)

-What is the sign of the enthalpy of reaction for the reaction P₄O₆(s) + 2 O₂(g) + 6 H₂O(g) $\rightarrow$ 4 H₃PO₄(s)
Assuming that all compounds are present in their most stable state at 25°C and 1 atm pressure?

A) positive
B) negative
C) impossible to determine from the data

Question 57

(Note that some of these are the same problems as found in the section headed Enthalpies of Atom Combination. However in this section all problems are worked using Enthalpies of Formation.)

-What is the magnitude of the enthalpy of reaction in the previous question?

A) less than 1000 kJ/mol_rxn
B) between 1000 and 1250 kJ/mol_rxn
C) between 1250 and 1500 kJ/mol_rxn
D) between 1500 and 1750 kJ/mol_rxn
E) more than 1750 kJ/mol_rxn

Question 58

(Note that some of these are the same problems as found in the section headed Enthalpies of Atom Combination. However in this section all problems are worked using Enthalpies of Formation.)

-For which of the following substances is the enthalpy of formation, $\Delta$ H_f°,
Equal to zero?

A) H₂(g)
B) H₂O(g)
C) O₃(g)
D) H(g)
E) Na(g)

Question 59

(Note that some of these are the same problems as found in the section headed Enthalpies of Atom Combination. However in this section all problems are worked using Enthalpies of Formation.)

-For which of the following substances is the enthalpy of formation, $\Delta$ H_f S1° , equal to zero?

A) H₂O(l)
B) H₂O(s)
C) Cl(g)
D) P₄(s)
E) CO₂(g)

Question 60

The reaction below shows two isomers of benzene, a compound with the formula C₆H₆. The structure of benzene was a point of great controversy in the late 1800's and the two structures shown in the reaction were the chief contenders.


Which of the following statements is correct?

A) Isomer 1 is more stable than isomer 2
B) Isomer 2 is more stable than isomer 1
C) Isomer 2 has overall stronger bonds than isomer 1
D) Isomer 2 has stronger bonds and is more stable that isomer 1
E) Isomer 1 has weaker bonds and is more stable than isomer 2

Question 61

Retailers purchase gasoline by weight so they get a constant amount of gasoline per dollar (as long as the price is constant). We buy gasoline by volume. The enthalpy of combustion of 1.00 L of gasoline is -3.539 x 10⁴ kJ at 15.6^oC when gasoline has a density of 0.73722 g/mL. What would the enthalpy of combustion of 1.00 L of gasoline be at 32.2^oC when gasoline has a density of 0.72210 g/mL?

A) -3.466 x 10⁴ kJ
B) -3.539 x 10⁴ kJ
C) -2.592 x 10⁴ kJ
D) -2.373 x 10⁴ kJ
E) None of the above

Question 62

Which of the following is not true for an exothermic reaction?

A) Heat flows from the reaction system to the surroundings.
B) The temperature of the surroundings rise.
C) The enthalpy change for the reaction is negative.
D) The products have a higher energy than the reactants.
E) The bonds in the products are stronger than the bonds in the reactants.

Question 63

Write a balanced equation for the combustion of carbon disulfide to form carbon dioxide and sulfur dioxide, draw the Lewis structures of all reactants and products, and calculate $\rightarrow$ H_rxn° for this reaction.
_____ CS₂(g) + _____ O₂(g) $\rightarrow$ _____ CO₂(g) + _____ SO₂(g)

Question 64

Use the following standard enthalpies of atom combination to
$\Delta$ H_ac° H₂(g) = -435.30 kJ/mol_rxn   $\Delta$ H_ac F₂(g) = -157.98 kJ/mol_rxn
$\Delta$ H_ac° N₂(g) = -945.41 kJ/mol_rxn   $\Delta$ H_ac° C(s) = -716.68 kJ/mol_rxn
$\Delta$ H_ac° O₂(g) = -498.34 kJ/mol_rxn   $\Delta$ H_ac° NH₃(g) = -1171.8 kJ/mol_rxn
$\Delta$ H_ac° H₂O(g) = -926.3 kJ/mol_rxn   $\Delta$ H_ac° HF(g) = -567.7 kJ/mol_rxn

-What is $\Delta$ H_rxn° for the following reaction?
3 N(g) $\rightarrow$ 3/2 N₂(g)

A) +710 kJ/mol_rxn
B) -710 kJ/mol_rxn
C) +1418 kJ/mol_rxn
D) -1418 kJ/mol_rxn
E) -473 kJ/mol_rxn

Question 65

Use the following standard enthalpies of atom combination to
$\Delta$ H_ac° H₂(g) = -435.30 kJ/mol_rxn   $\Delta$ H_ac F₂(g) = -157.98 kJ/mol_rxn
$\Delta$ H_ac° N₂(g) = -945.41 kJ/mol_rxn   $\Delta$ H_ac° C(s) = -716.68 kJ/mol_rxn
$\Delta$ H_ac° O₂(g) = -498.34 kJ/mol_rxn   $\Delta$ H_ac° NH₃(g) = -1171.8 kJ/mol_rxn
$\Delta$ H_ac° H₂O(g) = -926.3 kJ/mol_rxn   $\Delta$ H_ac° HF(g) = -567.7 kJ/mol_rxn

-What is the bond energy of N N?

A) 237 kJ/mol
B) 158 kJ/mol
C) 473 kJ/mol
D) 946 kJ/mol
E) 1892 kJ/mol

Question 66

Use the following standard enthalpies of atom combination to
$\Delta$ H_ac° H₂(g) = -435.30 kJ/mol_rxn   $\Delta$ H_ac F₂(g) = -157.98 kJ/mol_rxn
$\Delta$ H_ac° N₂(g) = -945.41 kJ/mol_rxn   $\Delta$ H_ac° C(s) = -716.68 kJ/mol_rxn
$\Delta$ H_ac° O₂(g) = -498.34 kJ/mol_rxn   $\Delta$ H_ac° NH₃(g) = -1171.8 kJ/mol_rxn
$\Delta$ H_ac° H₂O(g) = -926.3 kJ/mol_rxn   $\Delta$ H_ac° HF(g) = -567.7 kJ/mol_rxn

-What is the $\Delta$ H_rxn° for the following reaction as written?
4 NH₃(g) + 3 O₂(g) $\rightarrow$ 2 N₂(g) + 6 H₂O(g)

A) -1266 kJ/mol_rxn
B) -1184 kJ/mol_rxn
C) -196 kJ/mol_rxn
D) +767 kJ/mol_rxn
E) none of the above

Question 67

Use the following standard enthalpies of atom combination to
$\Delta$ H_ac° H₂(g) = -435.30 kJ/mol_rxn   $\Delta$ H_ac F₂(g) = -157.98 kJ/mol_rxn
$\Delta$ H_ac° N₂(g) = -945.41 kJ/mol_rxn   $\Delta$ H_ac° C(s) = -716.68 kJ/mol_rxn
$\Delta$ H_ac° O₂(g) = -498.34 kJ/mol_rxn   $\Delta$ H_ac° NH₃(g) = -1171.8 kJ/mol_rxn
$\Delta$ H_ac° H₂O(g) = -926.3 kJ/mol_rxn   $\Delta$ H_ac° HF(g) = -567.7 kJ/mol_rxn

-What is the bond energy, H₂N-H, for one of the N-H bonds in NH₃(g)?

A) 391 kJ/mol
B) 645 kJ/mol
C) 737 kJ/mol
D) 846 kJ/mol
E) 1173 kJ/moI

Question 68

Use the following standard enthalpies of atom combination to
$\Delta$ H_ac° H₂(g) = -435.30 kJ/mol_rxn   $\Delta$ H_ac F₂(g) = -157.98 kJ/mol_rxn
$\Delta$ H_ac° N₂(g) = -945.41 kJ/mol_rxn   $\Delta$ H_ac° C(s) = -716.68 kJ/mol_rxn
$\Delta$ H_ac° O₂(g) = -498.34 kJ/mol_rxn   $\Delta$ H_ac° NH₃(g) = -1171.8 kJ/mol_rxn
$\Delta$ H_ac° H₂O(g) = -926.3 kJ/mol_rxn   $\Delta$ H_ac° HF(g) = -567.7 kJ/mol_rxn

-How much heat is absorbed or evolved when just enough H₂(g) reacts with just enough F₂(g) to produce 0.200 mol of HF(g)?

A) 54 kJ of heat is absorbed
B) 54 kJ of heat is evolved
C) 108 kJ of heat is absorbed
D) 108 kJ of heat is evolved
E) 216 kJ of heat is absorbed

Question 69

Consider the following data for heats of atom combination of three substances in the liquid and gaseous states.


Explain the relative magnitudes of the differences between the enthalpies of atom combination of the liquid and gaseous states of these three compounds.