Among common historical refrigerants (e.g., ammonia, carbon dioxide, sulphur dioxide, R-12), does sulphur dioxide (SO₂) have the lowest normal boiling point?
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AYes, SO₂ has the lowest boiling point
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BNo, SO₂ does not have the lowest boiling point
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CBoiling points are identical for these refrigerants
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DCannot be compared because pressure always varies
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EOnly at very high altitudes
Answer
Correct Answer: No, SO₂ does not have the lowest boiling point
Explanation
Introduction / Context:Boiling point at standard pressure is a key selection factor for refrigerants. Lower normal boiling point generally indicates stronger cooling potential at low evaporator temperatures, though toxicity, flammability, and environmental impact also matter.
Given Data / Assumptions:
- Comparison uses approximate normal boiling points at 1 atm.
- Typical references: NH₃ (ammonia), CO₂, SO₂, and R-12.
Concept / Approach:SO₂ has a normal boiling point near −10 °C, whereas ammonia is about −33 °C and R-12 about −30 °C. Carbon dioxide does not have a normal liquid boiling point at 1 atm (it sublimates at about −78.5 °C), and its critical temperature is near 31 °C; thus, at 1 atm it exists as either gas or dry ice, not a liquid. Therefore, SO₂ is not the lowest among these; in fact, it is comparatively high (warmer) among traditional refrigerants.
Step-by-Step Solution:
1) Note SO₂ boiling point ≈ −10 °C.2) Compare with NH₃ (≈ −33 °C) and R-12 (≈ −30 °C) → these are lower (colder).3) Consider CO₂ behavior at 1 atm (sublimation at −78.5 °C) → effectively a much lower temperature benchmark.Verification / Alternative check:Data tables corroborate NH₃ and R-12 having lower boiling points than SO₂ at standard pressure; CO₂ does not boil at 1 atm, indicating even stronger low-temperature behavior via sublimation reference.
Why Other Options Are Wrong:
- (a) Incorrect: SO₂ is not the lowest.
- (c) Boiling points differ widely.
- (d) While boiling point depends on pressure, standard comparisons use 1 atm.
- (e) Altitude changes pressure but does not invert the ordering cited.
Common Pitfalls:Confusing SO₂’s historical use with superior low-temperature properties; toxicity and corrosion issues limited its application.
Final Answer:No, SO₂ does not have the lowest boiling point