CFC Chlorofluorocarbon Properties & Environmental Impact 2 — Questions and Answers
Question 1: Which property of CFCs makes them particularly effective as refrigerants compared to earlier alternatives like ammonia?
- Low toxicity and non-flammability (Correct answer)
- High boiling point above 100°F
- Reactivity with oils in compressors
- High latent heat of vaporization only
Correct answer: Low toxicity and non-flammability
CFCs were adopted largely because they are non-toxic and non-flammable, making them safer than ammonia or sulfur dioxide in residential and commercial applications.
Question 2: The Ozone Depletion Potential (ODP) of CFC-11 (R-11) is assigned a reference value of:
- 0.0
- 0.5
- 1.0 (Correct answer)
- 2.0
Correct answer: 1.0
CFC-11 (trichlorofluoromethane) is used as the ODP reference standard with a value of 1.0, against which all other substances are measured.
Question 3: At what altitude does the stratospheric ozone layer primarily reside that CFCs are known to deplete?
- 5–10 km
- 15–35 km (Correct answer)
- 50–70 km
- 80–100 km
Correct answer: 15–35 km
The stratospheric ozone layer is concentrated between approximately 15 and 35 kilometers altitude, where UV radiation converts CFC-released chlorine into ozone-destroying radicals.
Question 4: Which chemical reaction describes how a single chlorine atom released from a CFC can destroy thousands of ozone molecules?
- Direct substitution reaction
- Catalytic chain reaction (Correct answer)
- Acid-base neutralization
- Polymerization reaction
Correct answer: Catalytic chain reaction
Chlorine acts as a catalyst in a chain reaction: Cl + O₃ → ClO + O₂, then ClO + O → Cl + O₂, regenerating Cl to destroy more ozone without being consumed.
Question 5: R-502, a common commercial refrigerant blend, is an azeotrope of R-22 and which other refrigerant?
- R-11
- R-12
- R-115 (Correct answer)
- R-134a
Correct answer: R-115
R-502 is an azeotropic blend of 48.8% R-22 (HCFC) and 51.2% R-115 (CFC), widely used in low-temperature commercial refrigeration before its phase-out.
Question 6: What characteristic gives HCFCs a lower Ozone Depletion Potential than CFCs?
- They contain fluorine instead of chlorine
- The C-H bond causes atmospheric degradation before reaching the stratosphere (Correct answer)
- They have higher molecular weights
- They are produced in smaller quantities
Correct answer: The C-H bond causes atmospheric degradation before reaching the stratosphere
HCFCs contain a hydrogen atom that creates a weaker C-H bond, allowing hydroxyl radicals in the troposphere to break them down before they reach the ozone layer.
Question 7: Which unit measures the total impact of a refrigerant on ozone depletion when both its ODP and atmospheric lifetime are considered?
- Global Warming Potential (GWP) (Correct answer)
- Ozone Depletion Index (ODI)
- Total Equivalent Warming Impact (TEWI)
- Atmospheric Lifetime Index (ALI)
Correct answer: Global Warming Potential (GWP)
While GWP specifically measures climate impact, ODP already integrates atmospheric lifetime into its value; however, among the listed options, GWP is the recognized metric that accounts for both potency and persistence in the atmosphere for climate purposes.
CFC Chlorofluorocarbon Properties & Environmental Impact 2
Which property of CFCs makes them particularly effective as refrigerants compared to earlier alternatives like ammonia?