Question

Because of increasing evidence of damage to the ozone layer, chlorofluorocarbon (CFC) production was banned in 1996. However, many older cars still have air conditioners that use \(\mathrm{CFC}-12\) \(\left(\mathrm{CF}_{2} \mathrm{Cl}_{2}\right) .\) These air conditioners are recharged from stockpiled supplies of CFC-12. Suppose that 100 million automobiles each contain \(1.1 \mathrm{~kg}\) of CFC-12 and leak \(25 \%\) of their CFC-12 into the atmosphere per year. How much chlorine, in kg, is added to the atmosphere each year due to these air conditioners? (Assume two significant figures in your calculations.)

Short answer

Approximately 16 million kg of chlorine is added to the atmosphere each year.

Step-by-step solution

Calculate the amount of CFC-12 leaked per year for one car

Each car leaks 25% of the CFC-12 it contains per year. Since each car contains 1.1 kg of CFC-12, the amount leaked per car per year is \[0.25 \times 1.1 \text{ kg} = 0.275 \text{ kg/car/year}.\]

Calculate the total amount of CFC-12 leaked per year for all cars

There are 100 million cars each leaking 0.275 kg of CFC-12 per year. The total amount leaked is: \[100,000,000 \text{ cars} \times 0.275 \text{ kg/car/year} = 27,500,000 \text{ kg/year}.\]

Calculate the amount of chlorine in CFC-12

The molecular formula for CFC-12 is CF2Cl2, which indicates there are 2 chlorine atoms per molecule. The molar mass of CFC-12(M(CF2Cl2)) is \[12 \times 1 + 2 \times 19 + 2 \times 35.5 = 120.5 \text{ g/mol}.\]The mass of chlorine in one mole of CFC-12 is \[2 \times 35.5 \text{ g} = 71 \text{ g/mol}.\]The fraction by mass of chlorine in CFC-12 is \[\frac{71 \text{ g/mol}}{120.5 \text{ g/mol}}.\]

Calculate the total mass of chlorine leaked into the atmosphere per year

To find the total mass of chlorine, multiply the total mass of leaked CFC-12 by the fraction of chlorine in CFC-12: \[27,500,000 \text{ kg/year} \times \frac{71 \text{ g/mol}}{120.5 \text{ g/mol}} = 27,500,000 \text{ kg/year} \times \frac{71}{120.5}.\]Since we want the answer in kilograms, we convert grams to kilograms: \[27,500,000 \text{ kg/year} \times \frac{71}{120.5 \times 10^3} \approx 16,000,000 \text{ kg/year}.\]

State the final result with correct significant figures

With two significant figures, the total mass of chlorine added to the atmosphere each year due to these air conditioners is approximately \[16,000,000 \text{ kg/year} \approx 16 \times 10^6 \text{ kg/year}.\]

Key concepts

Chlorofluorocarbon (CFC)

Chlorofluorocarbons, commonly known as CFCs, are compounds made up of chlorine, fluorine, and carbon. They were widely used in refrigeration, air conditioning, foam blowing, and as propellants in aerosol sprays before their harmful effects on the ozone layer were discovered. CFCs are stable compounds under normal atmospheric conditions, which allowed them to slowly rise into the stratosphere, where they're exposed to ultraviolet (UV) radiation. This energy causes CFCs to release chlorine atoms, which then deplete ozone molecules. Their stability and long atmospheric lifetimes made them an insidious threat to the ozone layer.

However, the real implications of their chemistry were not understood until the 1970s and 1980s, leading to global agreements such as the Montreal Protocol to phase out their use. Despite the ban on production, CFCs continue to be released into the atmosphere from old equipment and stockpiles, impacting the ozone layer.

Atmospheric Chlorine Contribution

The atmospheric chlorine contribution refers to the amount of chlorine that is released into the Earth's atmosphere from various sources, both natural and anthropogenic. CFCs stand out among these sources since they release significant amounts of chlorine upon breakdown. In the stratosphere, this chlorine becomes a catalyst for ozone depletion. One chlorine atom can destroy thousands of ozone molecules before it is removed from the stratosphere.

Understanding the contribution of atmospheric chlorine from human-made chemicals like CFCs is crucial in evaluating their long-term environmental impact. Even after the ban on CFCs, existing CFCs continue to emit chlorine, posing a continuous threat to ozone recovery.

Environmental Impact of CFCs

The environmental impact of CFCs is significant, primarily due to their role in ozone layer depletion. The ozone layer protects life on Earth from the harmful effects of the sun's UV radiation. Depletion of this layer increases the risk of skin cancer, cataracts, and can negatively affect marine ecosystems, plants, and materials.

Unfortunately, due to their chemical stability and non-reactivity at the Earth's surface, CFCs remain in the atmosphere for decades to over a century. This long lifespan means that even after being banned, existing CFCs will continue to affect the ozone layer for many years. Efforts to reduce CFCs' environmental impact focus on proper management and disposal of old equipment containing CFCs, as well as the use of alternative compounds with less ozone depletion potential.

Stoichiometry Calculations

Stoichiometry calculations are at the heart of chemical reactions, providing a quantitative way of understanding the relationships between reactants and products. In the context of environmental chemistry, stoichiometry is used to determine the amount of harmful substances, such as CFCs, that are released into the atmosphere and the subsequent release of ozone-depleting elements like chlorine.

In the exercise provided, stoichiometric calculations were used to determine the total mass of chlorine leaked into the atmosphere from automobile air conditioners containing CFC-12. By applying the principles of stoichiometry, including molar masses and percent composition, it was possible to calculate the environmental impact in terms of chlorine release. This quantitative approach is essential for informing policies and environmental protection measures.