Hydrofluorocarbons (HFCs) have been developed to replace chlorofluorocarbons (CFCs) as refrigerants. Which property of these new compounds makes them environmentally superior to CFCs?

Question

BlackTom AI · Accepted Answer

When evaluating why hydrofluorocarbons (HFCs) are considered environmentally superior to CFCs, we must compare how they behave in the atmosphere and how they impact ozone depletion.
Option 1: 'Greater reactivity leads to decomposition at elevations below the stratospheric ozone concentration maximum.' This is correct because HFCs are designed to be more reactive in the lower to mid-troposphere and lower stratosphere, causing them to break down before they can reach the upper stratosphere where ozone depletion is most critical. This shorter atmospheric lifetime reduces the chance of releasing chlorine or other ozone-depleting species.
Option 2: 'Lower reactivity makes them stable even in the intense ultraviolet light in the stratosphere.' This is incorrect. If they were more stable under UV in the stratosphere, they'd persist longer and could contribute to ozone depletion—precisely the problem CFCs posed. The environmental advantage of HFCs comes from their controlled reactivity, not from extreme stability in the stratosphere.
Option 3: 'Their higher molecular weight prevents them from reaching the stratosphere.' In reality, molecular weight alone does not reliably determine whether a compound reaches the stratosphere; transport depends more on atmospheric lifetime and volatility. This statement oversimplifies the issue and is not the mechanism by which HFCs reduce ozone impact.
Option 4: 'They do not contain fluorine.' This is factually false, as HFCs by definition contain fluorine. The presence of fluorine is a key characteristic that differentiates fluorinated refrigerants from many other compounds, and this option misstates that basic property.
Overall, the most accurate explanation among the choices is that HFCs exhibit greater reactivity leading to decomposition at elevations below the stratospheric ozone concentration maximum, limiting their potential to reach and affect the ozone layer.

Hydrofluorocarbons (HFCs) have been developed to replace chlorofluorocarbons (CFCs) as refrigerants. Which property of these new compounds makes them environmentally superior to CFCs?单项选择题

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