Chapter 9 Homework

Question 1

For the combustion of methane, bond dissociation energies will only give a rough approximation of the change in enthalpy for this reaction.

CH4(g) + 2 O2(g)→ CO2(g) + 2 H2O(g)

Answer 1

true

Question 2

Which of the following Lewis dot structures best represents Cl −?

Answer 2

-

Question 3

Which of the following is the correct Lewis dot structure of nitric acid, HNO3?

Answer 3

-

Question 4

How many electrons must be accounted for in the Lewis dot structure for the carbonate ion?

Answer 4

24

Question 5

The water-shift reaction is used in the formation of hydrogen gas for fuel cells:

CO(g) + H2O(g) → CO2(g) + H2(g).

Calculate the ΔH of the reaction using bond dissociation energies listed below.

Single bond
H–O 459 kJ / mol
H–H 432 kJ / mol

Double bond
C–O 799 kJ / mol

Triple bond
C–O 1072 kJ / mol

Answer 5

−40.0 kJ / mol

Question 6

What is the average bond order of the highlighted S–O bond.

Answer 6

between 1 1/2 and 2

Question 7

What is the bond order of the highlighted N–O bond?

Answer 7

4/3

Question 8

For which of the following structures can a resonance structure be drawn?

Answer 8

A resonance structure for formate ion, HCO2− is

Question 9

Which resonance structure of the phosphate anion, [PO4 ]3−, is not equivalent to the other three?

Answer 9

This structure has only 8 electrons around the phosphorus atom, whereas the other structures have 10. This structure also has only single bonds between the phosphorus atom and the oxygen atoms, whereas the other structures have a double bond between the phosphorus atom and one of the oxygen atoms.

Question 10

To calculate the formal charge on an atom, “ownership” of each electron must first clearly be defined. That is, each electron must be assigned to one atom or another atom. What is the next major step in calculating the formal charge?

Answer 10

Subtract the number of electrons assigned to the Lewis dot structure from the sum of the number of valence electrons

Question 11

Three nitrogen atoms sometimes combine in the following manner, forming what is called an azide ion:

What is the overall charge of the azide ion? (Nitrogen is in Group15 (VA) of the periodic table, so a neutral nitrogen atom has 5 valence electrons.)

Answer 11

1–

Question 12

What are the formal charges for each atom in this resonance structure for sulfur trioxide? The values are listed in clockwise order, starting with the top oxygen atom and then proceeding, right to left, on the bottom row of atoms (in order from the atom marked #1 to the atom marked #4).

Answer 12

−1, 0, +2, −1

Question 13

Which of the following statements is true about the resonance structures, A–C, of the cyanate ion?

Answer 13

Structure A is the major contributor to the overall structure of the cyanate ion.

Question 14

The figure shows two possible resonance structures for boron trifluoride.

Based on the illustrations, which of the following statements is not true?

Answer 14

These two resonance structures are the only valid ones that exist.

Question 15

Arrange the following ions in the order of expected average N–O bond length with the longest first. NO2−, NO−, NO3−

Answer 15

NO3−, NO2−, NO−

Question 16

How many moles of each unique bond are formed in the combustion of propane? The reaction is:

C3H8(g) + 5O2(g) → 3CO2(g) + 4H2O(g)

Answer 16

6 moles of C=O bonds and 8 moles of O–H bonds

Question 17

Look at the energy diagram for an exothermic reaction.

Which of the following accurately describes A, B, and C?

Answer 17

A is the starting energy level of reactants; B is the amount of energy absorbed to break up the reactant molecules; C is the reactant molecules now reduced to their individual atoms