Question

UCI Chemistry researchers, Prof. F. Sherwood Rowland and Dr. Mario Molina werefirst to discovered in 1973 that chlorofluorocarbons (CFCs) were depleting the Earth’sozone layer when released into the atmosphere. Once they reach the stratosphere, Clis released from the CFCs molecules by interaction with UV light. Free Cl atoms areable to react with ozone in a catalytic cycle that converts O3into the more stable O2.It is estimated that a single Cl atom is able to react with∼100000 O3molecules.Although CFCs production was banned in 1996, there are still a substantial numberof motor vehicle air conditioners (MVACs) that use CFC-12 (CF2Cl2) as refrigerant.The average CFC-12 emission rate from operating MVACs has been estimated tobe 59.5 mg per hour per vehicle (Zhang et al.Environ. Sci. Technol. Lett.2017).How much chlorine, in kg, is added to the atmosphere in a year due to 100 millionMVACs using CFC-12 as refrigerant?

Answer 1

Answer:

15.27895 x 10⁶kg of chlorine radical is added to the atmosphere in a year due to 100 million MVACs                                                                                              

Explanation:

Chlorofluorocarbons (CF₂Cl₂) from refrigerants produce chlorine radicals according to the following equation

         CF₂Cl₂ → CF2Cl  + Cl ⁻ .........(1)

From equation 1, one mole of CF₂Cl₂ produces one mole of Chlorine radical

From the question,

The emission rate of CF₂Cl₂ is 59.5mg/hour/MVAC

In one day the emission rate would be 59.5 x 24hours

                                                                  = 1428mg/day

In one year, the emission rate would be 1428mg/day x 365days

                                                                 =  521220mg/year

                                                                   = 521.220g/year/MVAC

Therefore the emission rate for 100 million MVAC using CF₂CL₂ in a year is

                                                                    = 52122 x 10⁶g/year/MVAC

                                                                    = 52122 x 10³kg/year/MVAC

The molar mass of CF₂CL₂                       = 120.913g/mol

No of moles  of CF₂CL₂                              = mass/ molar mass

                                                                     = 52122 x 10⁶g / 120.913g/mol

                                                                      = 431 x 10⁶ moles of CF₂Cl₂

From equation 1,  since one mole of CF₂Cl₂ produces one mole of Chlorine radical, it implies that

431 x 10⁶ moles of CF₂Cl₂ would produce 431 x 10⁶ moles of chlorine radical,

Therefore, to find the mass of chlorine radical produced, we use the formula

No of moles of chlorine radical  = mass/ molar mass

431 x10⁶ moles = mass of chlorine radical /molar mass of chlorine radical

431 x 10⁶ moles = mass/ 35.45g/mol

mass of chlorine =  431 x 10⁶ moles x 35.45 g/mol

                            =    15278.95 x 10⁶ g

In Kg, the mass    =   15,278.95 x 10³kg of cholrine radical

                             =   15.27895 x 10⁶ Kg of chlorine radical