Multiple Choice Questions (12 points, 2 each): answer the following multiple choice questions by circling the best response in each case.

1. The Cl-C-Cl bond angle in the COCl₂ molecule is approximately:

1. 92^o
2. 104.5^o
3. 114^o
4. 123^o
5. greater than 180^o

2. The hybridization of the central atom in ICl₂ ^- anion is

1. sp
2. sp²
3. sp³
4. sp³d
5. sp³d²

3. Which of the following reactions will have the largest DE value?

a. Cu(g) g Cu⁺(g) + e^-

b. Mg(g) g Mg⁺(g) + e^-

c. S(g) g S⁺(g) + e^-

d. Si(g) g Si⁺(g) + e^-

e. Cs(g) g Cs⁺(g) + e^-

4. Which of the following molecules cannot form a hydrogen bond with a water molecule?

a. NH₃

b. H₂O

c. HF

d. CH₄

e. CH₃OH

5. How many electrons can have the following quantum numbers: n = 4; l = 2; m_s = -½

a. 2

b. 3

c. 5

d. 6

e. 10

6. The heat energy that one gram of a substance needs to absorb in order for its temperature to increase by 1^oC (1 K) is called its

a. kinetic energy

b. specific heat capacity

c. heat transfer

d. calorimetry

e. enthalpy of formation

Short Answer (40 points, 4 each): answer each of the following short-answer questions

7. Calculate the temperature change that occurs when 30.0 kJ of heat is added to 1.00 kg of H₂O (s(H₂O) = 4.184 kJ/kg °C)

8. Identify (name and structure) the product(s) of the reaction between 1 mole of 2-butyne and 1 mole of chlorine (Cl₂).

9. Write electron configurations for the following atoms and ions:

Br:

N^-:

Fe³⁺:

Cu:

10a. Under what set of conditions will a reaction never be spontaneous?

b. Is it correct to say that a non-spontaneous reaction can never be made to occur? Justify your answer (briefly).

11. Does the NBr₃ molecule have a dipole moment? If so, in which direction does the dipole point? (indicate with a suitable structure/picture)

12a. Indicate the major (strongest) intermolecular force that exists in samples of each of the following compounds.

b. Circle the one that should possess the highest boiling point.

C₅H₁₁OH ________________________

NO ________________________

C₆H₁₄ ________________________

13. Iodide ion is oxidized in acidic solution to triiodide ion, I₃^-, by hydrogen peroxide.

H₂O₂ (aq) + 3I^- (aq) + 2H⁺ (aq) à I₃^- (aq) +2H₂O (l)

A series of four experiments was run at different concentrations and the initial rates of formation for I₃^- were determined.

Exp. number [H₂O₂], M [I^-], M [H⁺], M Initial rate, M/s

1 0.010 0.010 0.00050 1.15 x 10^-6

2 0.020 0.010 0.00050 2.30 x 10^-6

3 0.010 0.020 0.00050 2.30 x 10^-6

4 0.010 0.010 0.00100 1.15 x 10^-6

From these data,

(a) Obtain the reaction orders with respect to H₂O₂, I^-, and H⁺.

(b) Write the rate law

14. The reaction to form aA à Products is second order with a rate constant of 0.413 M^-1. s^-1. What is the half-life, in seconds, of the rxn if the initial concentration of A is 5.25 x 10^-3 M?

15. Consider the nitrate anion, NO₃^-

a. Write all appropriate Lewis structures.

b. Indicate the formal charges on the nitrogen and oxygen atoms for one of these structures.

16. For the following reaction, calculate the C-H bond energy given the following data.

CO(g) +2H₂(g) à CH₃OH(l) ΔH_rxn = -128 kJ

Bond D (kJ/mol)

C≡O 1072

H-H 436

C-O 358

O-H 467

Long Answer (48 points, 8 each): answer each of the following questions in the space provided

17. Next to each structure below, indicate each structure’s complete systematic name.

18. Write an equation expressing the enthalpy of formation for CuO(s). Given the following thermochemical equations:

2Cu(s) + S(s) à Cu₂S(s) DH^o = -79.5 kJ

S(s) + O₂(g) à SO₂(g) DH^o = -297 kJ

Cu₂S(s) + 2O₂(g) à 2CuO(s) + SO₂(g) DH^o = -527.5 kJ

Calculate the standard enthalpy of formation (in kilojoules per mole) of CuO(s).

19. The reaction 2 NO₂(g) D N₂O₄(g) has DG° = -5.40 kJ/mol of N₂O₄, at 25°C. In a reaction mixture, the partial pressure of NO₂ is 0.25 atm and the partial pressure of N₂O₄ is 0.60 atm. In which direction must this reaction proceed to reach equilibrium? Explain, using appropriate calculations.

20. When heated, ethyl chloride, CH₃CH₂Cl, decomposes in a first order reaction to give ethylene and hydrogen chloride.

CH₃CH₂Cl (g) à C₂H₄ (g) + HCl (g)

In an experiment, the initial concentration of ethyl chloride was 0.001M. After heating at 500 ⁰C for 155 s, this was reduced to 0.00067M. What is the concentration of ethyl chloride after a total of 256 s?

21.

For the structure above, report

a. the total number of lone pairs of electrons __________________

b. the total number of π-bonds __________________

c. the values of the CC₁C₂, HNH, and HOC₃ bond angles (denoted with the “arch” sign)

Bond angles

CC₁C₂ ___________________

HNH ___________________

HOC₃ ___________________

d. hybridization of the C₁ , C₂, and C₃ atoms

Hybridization

C₁ ___________________

C₂ ___________________

C₃ ___________________

22a. Using the VSEPR theory, draw the structures of

XeCl₄

BrCl₃

SCl₂

b. Circle the structure(s) with non-zero dipole moments, if any.

Equations

q = m s Δt

Answers:

Multiple choice:

1. (c); 2. (d) 3. (c) 4. (d) 5. (c) 6. (b)

Short Answers

7. q = m s Δt; 30.0 kJ = 1.00 kg x 4.184 kJ/kg ⁰C Δt; Δt = 30.0/(4.184 x1.0) = 7.2 °C

temperature will increase by 7.2 °C.

8. trans-dichloro-2-butene (major product) and cis-dichloro-2-butene (minor product)

9. Br: [Ar]3d¹⁰4s²4p⁵; N^-: 1s²2s²2p⁴; Fe⁺³: [Ar]3d⁵; Cu: [Ar]3d¹⁰4s¹

10. a)ΔS<0; ΔH>0, gives ΔG>0 b) no, it can be made to occur (ΔG= ΔH-T ΔS) by varying temperature and, thus, the entropy factor.

11. The molecule has a trigonal pyramidal structure, with electron density shifted from Br atoms towards more electronegative N-atom.

12. H-bonding, dipole-dipole, dispersion. C₅H₁₁OH has the highest boiling temperature.

13. (a) [H⁺]⁰; [I^-]¹ [H₂O₂]¹ (b) rate= k [H₂O₂][I^-]

14. t_1/2 = 1/(k x [A₀]) = 1/(0.413 M^-1s^-1 x 5.25 x 10^-3 M) = 461 s

15.

16. ΔH = Σ D(bond broken) – ΣD (bond formed)

ΔH = (C≡O) + 2(H-H) –[ 3(C-H) + C-O + O-H] = 1072 + 2x436 – 3(C-H) – 358-467 = -128

x= 416 kJ/mol = C-H bond dissociation energy

Long Answers

17 a) 2-butanol; b) trans-2-pentene; c) meta-dinitrobenzene d) methylpropen

18. 2Cu(s) + S (s) à Cu₂S (s) -79.5 kJ

SO₂ (g) à S(s) +O₂ (g) + 297 kJ

Cu₂S (s) + 2O₂ (g) à 2CuO(s) + SO₂ (g) -527.5 kJ

2Cu(s) + O₂ (g) à 2CuO(s) -310 kJ

for one mole of Cu (s) : -310/2 = -155kJ/mol

19. ΔG = 0 at equilibrium; ΔG = ΔG⁰ + RT lnQ=0; ΔG⁰ = -RTlnK

5400J/mol = 8.314 J/mol K 298.2K lnK; lnK = 2.178; K =8.8

Q = (0.60/0.25²) = 9.6; Q>K_eq, therefore, rxn must proceed in reverse direction to reach equilibrium.

20. ln[A]_t = ln[A]₀ –kt

find k: ln(0.000670) = ln(0.001) –kx 155 ; k= 2.584 x 10^-3 s^-1

find concentration after 256s using k

ln[A]_t = ln (0.0010) – 2.584 x10^-3 s^-1 x 256s

[A]_t = e^-7.5692 = 5.16 x 10^-4M

21.a) 5, b) 3 c) CC₁C₂ = 180⁰; HNH <109.5; HOC₃ <109.5

d) C₁ sp; C₂ sp³, C₃ sp²

22.