chem. 1b final practice

1

Chem. 1B Final Practice

Name__________________________________________

Student Number _________________________________

All work must be shown on the exam for partial credit. Points will be taken off for

incorrect or no units and for the incorrect number of significant figures. Calculators are

allowed. On short answer problems you must show your work in order to receive credit

for the problem. If your cell phone goes off during the exam you will have your exam

removed from you.

Fundamentals (of 60 possible)

Problem 1 (of 16 possible)






Multiple Choice (of 60 possible)

Extra Credit (of 5 possible)

Final Total (of 200 possible)

2

Fundamental Questions Each of these fundamental chemistry questions is worth 5 points. You must show work

to get credit. Little to no partial credit will be rewarded. Make sure to report answers in

the correct number of significant figures and with the proper units.

1) 5 pts Draw a heating curve (Temperature vs. Heat Supplied) of H2O. Make sure

to include the value of the temperatures at boiling and freezing, clearly label

where H2O is a solid, a liquid, and a gas and indicate where ΔHvap and ΔHfus

are located.

2)

5 pts

In class we had a balloon filled with H2(g) and O2(g). The balloon did not

appear to undergo a chemical reaction until it was touched by a lit candle.

At this point the balloon turned into a fireball. Students in the front row

could feel heat from the fireball. The reaction was determined to be

O2(g) +2H2(g) 2H2O(g). Determine the signs of the following:

w<0 w>0 w=0 volume decreases

q<0 q>0 q=0 q= ΔH at constant P

ΔH<0 ΔH>0 ΔH=0 exothermic

ΔS<0 ΔS>0 ΔS=0

ΔG<0 ΔG>0 ΔG=0 spontaneous

3) 5 pts The following data was collected for the reaction

A + B C + D Ea=161molkJ

k=1.94×10-4

smolL at 30.0°C

What is k at 40.0°C?

smolL

molKJ

molJ

smolL

a

k

k

TTR

E

k

k

00149.0

2.313

1

2.303

1

3145.8

161000

1094.1ln

11ln

2

4

2

211

2

3

4) 5 pts What is wavelength associated with an electron traveling at 3.0×107

sm ?

mkgmv

h

sm

11

731

34

104.2100.31010939.9

10626.6

5) 5 pts Determine the number of orbitals that can have the following designation

3f

When n=3 l cannot equal 3 therefore no orbitals can

have this designation

n = 2

l = 0 ml = 0

l = 1 ml = -1,0,1

4 orbital

Determine the number of electrons that can have the following designation

3dz2

n=3 l=2 ml = 1 value

ms = ± ½

2 electrons

6d

n=6 l=2

ml = -2,-1,0,1,2 ms = ± ½

10 electrons

6) 5 pts Identify if the following reactions are redox reactions or not. If they are

redox reactions, specify what is oxidized and what is reduced.

Cu(OH)2(s) + 2HNO3(aq) Cu(NO3)2(aq) + 2H2O(l)

Not a redox reaction

Fe2O3(s) + 3CO(g) 2Fe(s) + 3CO2(g)

Redox Reaction

Fe +30 gained electrons

Fe is reduced

C +2 +4 lost electrons

C is oxidized

4

7) 5 pts Determine the rate law from the following mechanism.

H2S ⇌ H+ + HS

- fast equilibrium

Cl2 + HS- H

+ + 2Cl

- + S slow

Indicate if the reaction contains intermediates or catalysts and which

substances they are.

There are no catalysts and HS- is an intermediate

Rate= k2[Cl2][HS-]

Eliminate the intermediate

k1[H2S]=k-1[H+][HS

-]

H

SHClRate

H

SHHS

k

kk

k

k

22

2

1

12

1

1

8) 5 pts Circle the option that best fits each of the following descriptions:

Smallest atomic radius Na Si S Al

Largest ionic radius Na+ O

2- Mg

2+ F

-

Least polar bond C-N C-O O-H

Greatest electronegativity Al C Na N

Smallest first ionization energy K Na Mg

9) 5 pts Determine if energy is absorbed or emitted when an electron transitions

from the n=7 to the n=2 level of C5+

and the wavelength of the photon

associated with the transition?

Energy is emitted

|Energy of the transition| = energy of photon

Energy of transition

JJE

n

Z

n

ZJE

if

17

2

2

2

218

2

2

2

218

1080.17

6

2

610178.2

10178.2

Energy of photon

m

J

Js

E

hc

hcE

sm

8

17

834

1010.11080.1

1000.310626.6

5

10) 5 pts A piece of iron of mass 20.0 g at 100.°C is placed in a vessel of negligible

heat capacity but containing 50.7 g of water at 22.0°C. Calculate the final

temperature of the water. Assume that there is no energy lost to the

surroundings.

CT

CTOgHCTgFe

TmCq

qq

f

fCgJ

fCgJ

p

watermetal

25

0.2218.47.50.10045.00.20 2

11)

5 pts

What is ΔS for 2.00 mol of CO2 undergoing the following reaction at

constant pressure CO2(s,150 K) CO2(g, 195 K)?

Given the following data: Tsub = 195 K, ΔHsub =25.2molkJ ,

molK

JP sCO

C 11.47)(2

, and molK

JP gCO

C 8.34)(2

ΔS to take CO2 to sublimation point

KJ

molKJ

K

Kmol

T

TnCS 8.24

150

195ln11.4700.2ln

1

2

ΔS of sublimation (constant temperature)

KJ

KkJmol

kJsubrev

K

mol

T

Hn

T

qS 258258.0

.195

2.2500.2

KJ

KJ

KJS 2832588.24

12) 5 pts What wavelength of light is needed to excite an e- from the ground state of

a particle in a box that is 5.00×10-7

m long to the n=5 state?

Calculate the energy need for an e- to go from n=1 n=5

Jmkg

Jsnn

mL

hE if

2422

2731

23422

2

2

1078.5151000.51010939.98

10626.6

8

Calculate the wavelength of the photon

m

J

Js

E

hc Sm

0344.01078.5

10998.210626.624

834

6

Short Answer Questions

Each of the following short answer questions are worth the noted points. Partial credit

will be given. Make sure to show work, report answers to the correct number of

significant figures and use the proper units.

1a) 5 pts Consider the galvanic cell based on the following half-reactions:

Au3+

+ 3e- Au E° = 1.50 V

Tl+ + e

- Tl E° = -0.34 V

Determine the overall cell reaction and calculate E°cell.

For galvanic cell E° must be positive

Au3+

+3e- Au E° = 1.50 V

3(Tl Tl+ + e

-) E° = 0.34 V

Au3+

(aq) + 3Tl(s) Au(s) + 3Tl+(aq) E° = 1.50 V+0.34 V=1.84V

1b) 5 pts Calculate ΔG° and K for the cell reaction at 25°C.

molkJ

molJ

molC VnFEG 5321032.584.1964853 5

931026.2

ln964853

2983145.884.1

ln

K

KK

V

KnF

RTE

molC

molKJ

1c) 6 pts Calculate Ecell at 25°C when [Au

3+] =1.0×10

-2 M and [Tl

+] = 1.0×10

-4 M.

V

KVE

Au

Tl

nF

RTEK

nF

RTEE

molC

molKJ

04.2100.1

100.1ln

964853

2983145.884.1

lnln

2

34

3

3

7

2) 7 pts It takes 208.4 kJ of energy to remove one mol of electrons from the atoms

on the surface of rubidium metal. If rubidium metal is irradiated with

254-nm light, what is the maximum kinetic energy the released electrons

can have?

Calculate energy of 254 nm light

mnm

mnm 7

91054.2

10

1254

Hzm

c

c

sm

15

7

8

1018.11054.2

10998.2

JHzJshE 191534 1082.71018.110626.6

This is the energy that 1 electron would have.

Calculate the energy needed to remove 1 e-.

1922

231047.31047.3

10022.6

14.208

1

kJ

e

mol

NE

molkJ

A

Subtract the energy needed to remove the e-from the energy

provided by photon. This will give the max energy for KE.

JJJKE 191919 1035.41047.31082.7

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3a) 6 pts For each of the following

1) Write out the Lewis dot structure including all relevant resonance

structures. Make sure all structures have minimized formal charges.

2) Assign formal charges to every atom.

XeOF4

1)

2) All Formal Charges are 0

3b) 6 pts NO3-

1)

2) Formal Charges

Structure 1 (0,1,-1,-1)

Structure 2 (-1,1,0-1)

Structure 3 (-1,1,-1,0)

3c) 5 pts The following Lewis structure was drawn for a Period 3 element. Identify

the element

Since the formal charges on each of the O atoms are 0 and the

formal charge on each of the Cl atoms is 0. Therefore the formal

charge on “?” must be 0 in order for the overall charge to be 0.

This means that “?” must have 6 valence electron which makes it

an S atom.

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4a) 6 pts The bromination of acetone is acid-catalyzed:

CH3COCH3 + Br2 H CH3COCH2Br + H

+ + Br

-

[CH3COCH3]o (M) [Br2]o (M) [H

+]o (M)

Rate of Disappearance

of Br2( Lsmol )

0.30 0.050 0.050 5.7×10-5

0.30 0.10 0.050 5.7×10-5

0.30 0.050 0.10 1.2×10-4

0.40 0.050 0.20 3.1×10-4

0.40 0.050 0.050 7.6×10-5

What is the rate law? zyx HBrCOCHCHkrate ][][][ 233

Determine reaction order with respect to CH3COCH3

Use experiments 1 and 5

1

75.0log75.0log

75.040.0

30.075.0

050.0050.040.0106.7

050.0050.030.0107.55

5

x

x

M

M

MMMk

MMMk

x

x

x

zyx

Ls

mol

zyx

Ls

mol

zy HBrCOCHCHkrate ][]][[ 233

Determine reaction order with respect to Br2


When the [Br2] is double and the concentration of

[CH3COCH3] and [H+] remains the same the rate does not

change. Therefore, reaction is 0th

order with respect to [Br2]. zHCOCHCHkrate ]][[ 33

Determine reaction order with respect to H

+


1

00.4log08.4log

0.4050.0

20.008.4

050.040.0106.7

20.040.0101.35

4

z

z

M

M

MMk

MMk

z

z

z

z

Ls

mol

z

Ls

mol

]][[ 33

HCOCHCHkrate

4b) 5 pts If the rate law was determined to be

27.0

233 ][]][[ HBrCOCHCHkrate

And the following data was collected

[CH3COCH3]o (M) [Br2]o (M) [H+]o (M)

Rate of Disappearance

of Br2( Lsmol )

0.50 0.20 0.050 6.3×10-4

What is k? Remember to include units.

smol

L

Ls

mol

k

MMMk

HBrCOCHCHkrate

3.1

3.1

16.0

050.020.050.0103.6

][]][[

27.0.4

27.0

233

10

5a) 4 pts What is the electron configurations and number of unpaired e- of:

Po

Po = [Xe]6s24f

145d

106p

4 2 unpaired e

-

5b) 4 pts What is the electron configurations and number of unpaired e- of:

As2-

As2-

= [Ar]4s23d

104p

5 1 unpaired e

-

5c) 4 pts An ion having a 4+ charge and a mass of 8.286×10

-26 kg has two s electrons

with n=1, eight electrons with n = 2, and nine electrons with n = 3.

What is the atomic number of the ion?

This ion has a total of

2+8+9=19 e-

Because the charge on the ion is 4+, the ion must have 4 more

protons than electrons; therefore, the atomic number of the ion is

23, making it vanadium.

11

6a) 8 pts A technician carries out the reaction 2SO2(g) + O2(g) 2SO3(g) at 25°C

and 1.00 atm in a constant-pressure cylinder fitted with a piston. Initially,

0.0300 mol SO2 and 0.0300 mol O2 are present in the cylinder. The

technician then adds a catalyst to initiate the reaction. How much work

takes place, and is it done by the system or on the system. Assume that the

reaction goes to completion and the temperature of the system is constant.

VPw Determine the change in volume

Determine initial volume

Latm

Kmol

P

nRTV

nRTPV

molKLatm

47.100.1

29808206.00600.0

Determine final volume

Determine the limiting reagent

2

2

22 0150.0

2

10300.0 molO

molSO

molOmolSO

SO2 is the limiting reagent. All of the SO2 will be used up.

remainwillmolOmolOmolO 222 0150.00150.00300.0

formwillmolSOmolSO

molSOmolSO 3

2

3

2 0300.02

20300.0

Total moles of gas in the container after the reaction comes to completion

molmolmol 0450.00300.00150.0

Determine the volume

L

atm

Kmol

P

nRTV molK

Latm

10.100.1

29808206.00450.0

Calculate work

3

333

00037.0100

1

1

1037.047.110.1 m

cm

m

L

cmLLLV

Paatm

PaatmP 101325

1

10132500.1

JmPaVPw 3700037.0101325 3

Work is done on the system

6b) 5 pts What is the change in enthalpy for the reaction in J?

molkJ

molkJ

molkJ

molkJ

rxn

fffrxn

ffrxn

H

OHSOHSOHH

reacHprodHH

198)0()297(2)396(2

22 223

This is the amount of heat released when 1 mole of O2 reacts with 2 mol of SO2

Calculate ΔH for 0.015 mol O2

JkJmolO

kJmolO 4

2

2 100.30.31

198015.0

6c) 4 pts What is the change in internal energy for the reaction in J? Since the reaction takes place at constant pressure ΔH = q

JJJwqE 44 100.337100.3

12

Multiple Choice Questions Each of the following multiple choice questions are worth 5 points.

Your answers need to be filled in on the Scantron provided. Note: Your Scantrons will not be returned to you, therefore, for

your records, you may want to mark your answers on this sheet.

On the Scantron you need to fill in your perm number, test version,

and name. Failure to do any of these things will result in the loss

of 1 point. Your perm number is placed and bubbled in under the

“ID number”. Do not skip boxes or put in a hyphen. In addition,

leave bubbles blank under any unused boxes. The version number

(A) is bubbled in under the “test form.”

1. As the number of bonds between two carbon atoms increases, which one of the

following decreases?

A) the bond energy

B) the bond length

C) the number of electrons between the carbon atoms

D) all of these

E) none of these

2. Of the following five ions or molecules, which is the strongest reducing agent?

A) Cl2

B) Fe2+

C) Cr2+

D) F-

E) H2

3. Ammonium metavanadate reacts with sulfur dioxide in acidic solution as follows

(hydrogen ions and H2O omitted):

xVO3

– + ySO2 xVO

2+ + ySO4

2–

The ratio x : y is

A) 2 : 1

B) 1 : 1

C) 1 : 3

D) 1 : 2

E) None of the Above

4. Cations are _________ than/as their parent atom.

A) the same size

B) larger

C) smaller

13

5. Which of the following statements is(are) true?

I. An excited atom can return to its ground state by absorbing electromagnetic radiation.

II. The energy of an atom is increased when electromagnetic radiation is emitted from it.

III. The energy of electromagnetic radiation increases as its frequency increases.

IV. An electron in the n = 4 state in the hydrogen atom can go to the n = 2 state by

emitting electromagnetic radiation at the appropriate frequency.

V. The frequency and wavelength of electromagnetic radiation are inversely

proportional to each other.

A) III, IV, V

B) I, II, IV

C) II, III, IV

D) III, V

E) I, II, III

6. Which of the following statements is false?

A) The spin quantum number of an electron must be either +1/2 or –1/2.

B) An orbital can accommodate at most two electrons.

C) In the usual order of filling, the 6s orbital is filled before the 4f orbital.

D) The electron density at a point is proportional to 2 at that point.

E) A 2p orbital is more penetrating than a 2s; that is, it has a higher electron density

near the nucleus and inside the charge cloud of a 1s orbital.

7. The following reaction has a G° value of 42.6 kJ/mol at 25°C.

HB(aq) + H2O(l) H3O+(aq) + B

–(aq)

Calculate Ka for the acid HB.

A) 3.41 10–8

B) 14.0

C) 42,600

D) –17.2

E) 1.63

8. Consider an atom traveling at 1% of the speed of light. The de Broglie wavelength is

found to be 3.31 10–3

pm. Which element is this?

A) P

B) He

C) Ca

D) F

E) Be

14

9. Using the following bond energies:

Bond Bond Energy (kJ/mol)

CC 839

C-H 413

O=O 495

C=O 799

O-H 467

estimate the heat of combustion for 1 mol of acetylene:

C2H2(g) + 5/2O2(g) 2CO2(g) + H2O(g)

A) –447 kJ

B) +365 kJ

C) –1228 kJ

D) 1228 kJ

E) +447 kJ

10. At constant pressure, the reaction

2NO2(g) N2O4(g)

is exothermic. The reaction (as written) is

A) never spontaneous.

B) always spontaneous.

C) spontaneous at low temperatures but not at high temperatures.

D) spontaneous at high temperatures but not at low temperatures.

11. At 25°C, the following heats of reaction are known:

2C2H2 + 5O2 4CO2 + 2H2O H = –2600.0 kJ

C + O2 CO2 H = –394 kJ

2H2 + O2 2H2O H = –572 kJ

At the same temperature, calculate H for the following reaction:

2C + H2 C2H2 H = ?

A) 2422 kJ

B) 226 kJ

C) -2422kJ

D) -226 kJ

E) none of these

12. The rate constant k is dependent on

A) the temperature.

B) the concentration of the reactant.

C) the order of the reaction.

D) the concentration of the product.

E) none of these

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Answer Key

1. B

2. C

3. A

4. C

5. A

6. E

7. A

8. C

9. C

10. C

11. B

12. A

chem. 1b final practice

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