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CHEM 101 Fall 09 Exam III(a) On the answer sheet (scantron) write your name, student ID number, and recitation section number. Choose the best (most correct) answer for each question and enter it on your answer sheet.

Potentially useful data: Avogadro’s Number: 6.022 × 1023 mol-1

q = c m ΔT

1. Please choose the letter “a” as your answer for this question.

2. The enthalpy change for the following reaction is -483.6 kJ:

2H2 (g) + O2 (g) → 2H2O (g) Therefore, the enthalpy change for the following reaction is __________ kJ: 4H2 (g) + 2O2 (g) → 4H2O (g) a. -483.6 b. -967.2 c. 2.34 × 105 d. 483.6 e. 967.2

3. Which of the following describes an endothermic reaction?

a. when a gas condenses b. when bonds are formed c. when the energy of bonds breaking is greater than the energy of bonds formed d. when the energy of bonds breaking is less than the energy of bonds formed e. when stronger bonds are formed and weaker bonds are broken

4. When a 6.88 g sample of CaCl2 dissolves in 250 g of water in a coffee cup calorimeter, the

temperature rises from 22.0 to 26.9°C. How much heat per mole does this process release? The specific heat of water = 4.18 J g-1 °C-1. a. 5.1 × 103 J/mol b. 8.3 × 104 J/mol c. 4.5 × 105 J/mol d. 7.7 × 102 J/mol e. 1.4 × 102 J/mol

5. A bomb calorimeter has a heat capacity of 783 J/°C and additionally contains 254 g of water.

How much energy is evolved or absorbed by the reaction when the temperature of the calorimeter goes from 23.73°C to 26.01°C? The specific heat of water = 4.18 J g-1 °C-1. a. 1.78 kJ evolved b. 2.42 kJ evolved c. 4.21 kJ evolved d. 2420 kJ absorbed e. 4210 kJ evolved

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6. Which one of the following statements is true?

a. Enthalpy is an intensive property. b. The enthalpy change for a reaction is independent of the state of the reactants and

products. c. Enthalpy is a state function. d. H is the value of q measured under conditions of constant volume. e. The enthalpy change of a reaction is the reciprocal of the ΔH of the reverse

reaction. 7. Of the following, ΔH°f is not zero for __________.

a. O2 (g) b. C (graphite) c. N2 (g) d. F2 (s) e. Cl2 (g)

8. Determine the heat of reaction for the process

Fe2O3(s) + FeO(s) → Fe3O4(s)

using the information given below:

2Fe(s) + O2(g) → 2FeO(s) ∆H° = -544.0 kJ

4Fe(s) + 3O2(g) → 2Fe2O3(s) ∆H° = -1648.8 kJ

3Fe(s) + 2O2(g) → Fe3O4(s) ∆H° = -1118.4 kJ a. -1074.0 kJ b. -22.0 kJ c. 22.2 kJ d. 249.8 kJ e. 1074.0 kJ

9. The standard enthalpies of formation for several substances are given below:

CO(g) -110.5 kJ/mol CO2(g) -393.5 kJ/mol H2O(l) -285.8 kJ/mol H2O(g) -241.8 kJ/mol H2O2 (l) -187.8 kJ/mol CH3OH(g) -200.7 kJ/mol C2H5OH(l) -277.7 kJ/mol C2H5OH(g) -235.1 kJ/mol

Determine the ∆H° for the reaction below. 2CO(g) + 4H2 (g) → C2H5OH(g) + H2O(g) a. -366.4 kJ b. -299.9 kJ c. -298.5 kJ d. -255.9 kJ e. 255.9 kJ

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10. The standard enthalpies of formation for several substances are given below: H2O(l) -285.8 kJ/mol H2O(g) -241.8 kJ/mol C2H5OH(l) -277.7 kJ/mol C2H5OH(g) -235.1 kJ/mol

Determine the heat of vaporization for H2O and C2H5OH. a. 241.8 and -235.1 kJ b. 241.8 and 325.1 kJ c. 44.0 and 42.6 kJ d. -54.0 and -42.6 kJ e. -44.0 and -42.6 kJ

11. Based on the octet rule, magnesium most likely forms a __________ ion.

a. Mg2+ b. Mg2- c. Mg6- d. Mg6+ e. Mg+

12. How many valence electrons will be in the correctly drawn Lewis Structure for CCl4?

a. 32 b. 74 c. 35 d. 8 e. 11

13. How many valence electrons will be in the correctly drawn Lewis Structure for CO3

2-? a. 20 b. 22 c. 24 d. 26 e. 30

14. Determine, in order, the number of valence electrons that must be considered for the three

compounds CO2, CH3Cl, HCN. a. 16, 14, 14 b. 10, 14, 10 c. 14, 26, 14 d. 16, 14, 10 e. 22, 26, 14

15. Write the correct Lewis dot structure for O2. Which statement correctly describes the structure

of the whole molecule? a. There is a double bond and four lone pairs. b. There is a double bond and six lone pairs. c. There is a single bond and four lone pairs. d. There is a single bond and six lone pairs. e. There is a single bond, a double bond, and six lone pairs.

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16. Which of the following is an incorrect Lewis structure?

a. N

H

H

H

b. N C C O

H

H

O

HH

H

c.

Cl

C

Cl

ClCl

d. O C N

e.

17. Which of the following statements is true about cis and trans isomers of a molecule?a. The molecule must contain a carbon-oxygen double bond.b. The molecule must contain a carbon-carbon triple bond.c. The cis and trans isomers have the same melting points.d. The molecule must contain a carbon-carbon double bond.e. The cis and trans isomers have different molecular weights.

18. Which of these molecules contains the shortest carbon-carbon bond?a. C2H6b. C2H4c. C2H2d. C3H8e. C4H8

19. Which bond is longest?a. C-Ob. C-Pc. C-Hd. C-Fe. C-N

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20. Which bond is strongest? a. carbon-nitrogen triple bond b. carbon-nitrogen double bond c. carbon-hydrogen bond d. carbon-carbon triple bond e. carbon-carbon single bond

21. Given the electronegativities below, which covalent single bond is most polar?

Element: H C N O Electronegativity: 2.1 2.5 3.0 3.5 a. C–H b. N–H c. O–H d. O–C e. O–N

22. Which of the following elements is the most electronegative?

a. phosphorus b. silicon c. magnesium d. iron e. chlorine

23. What is the formal charge on carbon in CO2?

a. +2 b. +1 c. 0 d. -1 e. -2

24. Resonance structures differ by __________.

a. number and placement of electrons b. number of electrons only c. placement of atoms only d. number of atoms only e. placement of electrons only

25. How many resonance forms will ozone, O3, have?

a. -1 b. 0 c. 1 d. 2 e. -2

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chem101f09_exam3a Answer Section

MULTIPLE CHOICE

1. ANS: A PTS: 0

2. ANS: B PTS: 1

3. ANS: C PTS: 1

4. ANS: B PTS: 1

5. ANS: C PTS: 1

6. ANS: C PTS: 1

7. ANS: D PTS: 1

8. ANS: B PTS: 1

9. ANS: D PTS: 1

10. ANS: C PTS: 1

11. ANS: A PTS: 1

12. ANS: A PTS: 1

13. ANS: C PTS: 1

14. ANS: D PTS: 1

15. ANS: A PTS: 1

16. ANS: D PTS: 1

17. ANS: D PTS: 1

18. ANS: C PTS: 1

19. ANS: B PTS: 1

20. ANS: A PTS: 1

21. ANS: C PTS: 1

22. ANS: E PTS: 1

23. ANS: C PTS: 1

24. ANS: E PTS: 1

25. ANS: D PTS: 1