NAME: ______________________________________________ LAB SECTION: _____________
NAME: Wenjia Zhang
HOMEWORK #3
REFRIGERANT GASES and THE OZONE LAYER
Follow the instructions to fill in this table.
A. Lewis structures (2 points) Draw the Lewis structures for each chemical in the next section. Use what you learned in Homework #2 to draw your Lewis structures correctly. The structural formulas tell you how the atoms are connected. For example:

B. Category (1 point) Label each chemical as a CFC, HCFC, HFC, HFO, or halon in the top right box.
C. Ozone-depleting potential (0.5 point) Rank each chemical based on its ozone-depleting potential. Use the same ideas that we covered in Lecture 9 and assign each chemical a score of 0, 1, or 2.

Score

0

1

2

Meaning

This chemical does not destroy the ozone layer

This chemical causes only moderate damage to the ozone layer

This chemical is very harmful to the ozone layer

D. Ozone-destroying product formed in the stratosphere (0.5 point) If the chemical does destroy ozone, what part of the molecule is responsible for the ozone destruction? The options are Cl atoms, Br atoms, or none.

Note:

Everyone gets +1 free point, so the total points add up to 25!

1.

2.

3.

4.

5.

6.

Fall 2020 – CHEM 1001 – Homework #3

Page 1 of 1

molecular formula = C2H3F3
structural formula = CH3CF3

CFC, HCFC, HFC,
HFO, or halon?

ozone-depleting
potential (0, 1, or 2)

ozone-destroying
product (Cl, Br, or
none)

molecular formula = C2HCl2F3
structural formula = CCl2FCHF2

CFC, HCFC, HFC,
HFO, or halon?

ozone-depleting
potential (0, 1, or 2)

ozone-destroying
product (Cl, Br, or
none)

molecular formula = C3H2F4
structural formula = CHFCHCF3

CFC, HCFC, HFC,
HFO, or halon?

ozone-depleting
potential (0, 1, or 2)

ozone-destroying
product (Cl, Br, or
none)

molecular formula = C2Br2F4
structural formula = CBrF2CBrF2

CFC, HCFC, HFC,
HFO, or halon?

ozone-depleting
potential (0, 1, or 2)

ozone-destroying
product (Cl, Br, or
none)

H C

H

C C

H

F F

CH2FCHFCH3

The non-C atoms to the right of
each C tell you which atoms are
connected to that carbon

C atoms
structural formula: Lewis structure:

H

H

H

H C

H

C C

O

H H

CH3CH(OH)CH3

the “CH(OH)” in the structural
formula tells us that the H and the
OH are both connected to the
middle C

C atoms
H

H

H

H
structural formula: Lewis structure:

molecular formula = C2Cl5F
structural formula = CCl3CCl2F

CFC, HCFC, HFC,
HFO, or halon?

ozone-depleting
potential (0, 1, or 2)

ozone-destroying
product (Cl, Br, or
none)Science of Contemporary Issues

Lecture 9

CFCs, Replacements & The Montreal Protocol

Chapman Cycle with Catalyst

The catalyst disrupts the cycle and removes ozone at a faster rate than it can be created

Ok, Where Are the Other Free Radicals?

chlorofluorocarbons

Contain Cl
Contain F

Contain C
(backbone)

dichlorodifluoromethane
methane = CH4

How many valence e− are
there in this Lewis structure?

A. 4
B. 8
C. 24
D. 28
E. 32

Where Do The CFCs Come From?

How a Refrigerator Works

Compressor:
Cold gaseous refrigerant → Hot liquid refrigerant

Outer Coils:
Hot liquid refrigerant → Warm liquid refrigerant

Inner Coils:
Warm liquid refrigerant →

Cold gaseous refrigerant

HEATS UP THE HOUSE

COOLS DOWN THE FOOD

BACK
SIDE

INSIDE

Refrigerant Gases
CFCs

chlorofluorocarbons
HCFCs

hydrochlorofluorocarbons

HFCs
hydrofluorocarbons

HFOs
hydrofluoroolefins

olefins:
chemicals with C-C double bonds

 release Cl in
stratosphere

 ligher than air
 long lifetime (100 yrs)

 shorter lifetime (10 yrs)
 less likely to reach

stratosphere

and  zero ozone-
destroying
potential

 greenhouse
gases

 zero ozone-destroying potential
 much shorter lifetime (11 d) = less

potent greenhouse gas

Halon Fire Extinguishers
Halons are chemicals made of C, Br, and Cl and/or F

that are used in fire extinguishers (the “Cousins” of CFCs)

CBrClF2
(Halon 1211)

CBrF3
(Halon 1301)

• Used by the military and in aircraft
• Illegal elsewhere after the Montreal Protocol

 release free radical Br atoms
in the stratosphere

Difluoroethane – HFC

boiling point
−25 oC

Will this chemical destroy the ozone layer?

C2H4F2

A. Yes, it will cause a lot of damage
B. Yes, it will cause medium damage
C. No, it does not contain Cl or Br
D. No, but it is a greenhouse gas
E. I don’t care – I want to know how any of this relates

to the ozone destruction and Chapman Cycle!!

Estimating Ozone Depleting Potential

• Cl or Br atoms in molecule
• Long atmospheric lifetime

These properties increase ozone-depleting potential:

• They do not contain Cl or Br
• They do not last long in the atmosphere

(they have a short atmospheric lifetime, usually contain C-H
bonds and/or C=C bonds)

Molecules will not lead to ozone depletion if:

Discovery of Ozone Depletion!

1995 Nobel Prize

Experimental

analyses show that as

ClO• concentrations

increase, ozone

concentration

decreases.

Chapman Cycle with Catalyst

The catalyst disrupts the cycle and removes ozone at a faster rate than it can be created

Here’s Out Catalyst – Ruins Cycle

0

100

200

300

400

500

600
F-

F

O
-F

B
r-

B
r

O
-C

l

O
-B

r

C
l-

C
l

C
-B

r

O
-O

in
O

zo
n

e

C
-C

l

H
-B

r

H
-C

l

C
-F

O
=O H
-F

B
o

n
d

S
tr

e
n

gt
h

(
kJ

/m
o

l)

Atoms Connected by Bond

Bond Strengths and Reactivity

weaker bonds than O3 stronger bonds than O3

related to F related to Cl

related to Br O2 or O3

λ ≤ 242 nm

λ ≤ 320 nm

2Cl. + 2O3




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