Chlorofluorocarbons and the environment
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Chlorofluorocarbons and the environment
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[ID] => 558138
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[post_date] => 2025-01-09 07:53:11
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[post_content] => Practice Passage (Question 1-5)
*This passage is the property of Khan Academy and has been reformatted into an AAMC-style interface in their entirety by MedLife Mastery. MedLife Mastery does not endorse and is not an affiliate of Khan Academy.
Fluorocarbons are compounds composed of carbon, hydrogen, and fluorine, and Chlorocarbons are compounds composed of carbon, hydrogen, and chlorine. Both of these compound classes prove to be potentially harmful to humans and the environment.
As an example of these harmful effects, chlorofluorocarbons (CFCs) are molecules composed of carbon, hydrogen, fluorine, and chlorine. These molecules are typically less volatile than their parent alkanes, which can be attributed to their component halides’ polarity. For example, the boiling point of methane is about -161°C, while the boiling point of dichlorodifluoromethane (Freon-12, a popular refrigerant) is about -29 °C. This decreased volatility allows some of these CFCs to reach upper levels of the atmosphere, where UV light is able to cleave C-Cl bonds in a homolytic fashion, creating free radicals capable of depleting ozone.
The polar natures of the compounds that make up these molecule classes affect their physical properties, such as boiling point. The strong intermolecular forces attributed to this polarity result in significant deviation from ideal gas behavior. Typically an ideal gas obeys the following equation:
PV=nRT
*P is pressure in atm. V is volume in liters. n is number of particles in moles. R is the constant 0.0821 (atm*L)/(mol*K). T is temperature in Kelvin.
When real gas deviations due to intermolecular forces and particle volume are accounted for, the following formula, attributed to the work of JD van der Waal, is the result:
(P+a(n/v)²)*(V-nb)=nRT
*a is an empirical value accounting for the strength of intermolecular forces.
b is an empirical value accounting for the volume occupied by gas particles.
In terms of deviation from ideal gas behavior, as the volume of a container is increased, the space occupied by real gas particles becomes less significant.
[post_title] => Chlorofluorocarbons and the environment
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[quiz_unique_key] => 578908434
[question] => The a-value for a halocarbon increases proportionally with which characteristic?
[value] => Array
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[answer] => 1
[description] => Reason for the Correct Answer:
The a-value is an empirical value accounting for the strength of intermolecular forces.
Halocarbons contain carbon, hydrogen, and a halogen.
Dipole-dipole interactions are an example of intermolecular force.
Increased polarity means the molecules would experience more intermolecular forces related to dipole-dipole interactions. Thus, the empirical a-value would need to be larger to account for increased deviation from ideal gas behavior.
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[answers] => Array
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[0] => Array
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[each_answer] => A. Polarity
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[1] => Array
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[each_answer] => B. Particle concentration
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[2] => Array
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[each_answer] => C. Nucleophilicty
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[3] => Array
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[each_answer] => D. Boiling point
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[1] => Array
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[quiz_unique_key] => 3873426850
[question] => Of the following noble gases and halide gases, which has the greatest a- value?
[value] => Array
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[answer] => 3
[description] => Reason for the Correct Answer:
This question is asking for the gas with the greatest intermolecular forces.
Intermolecular forces are forces that occur between atoms and include van der Waals forces and dipole-dipole interactions.
Fluorine is a more electronegative atom than chlorine.
Fluoromethane is a very polar molecule and would have the highest a-value of the answer choices. Fluoromethane’s polarity is related to the high electronegativity of fluorine.
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[answers] => Array
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[0] => Array
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[each_answer] => A. Chloroethane
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[1] => Array
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[each_answer] => B. Helium
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[2] => Array
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[each_answer] => C. Fluoromethane
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[3] => Array
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[each_answer] => D. Chloromethane
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[2] => Array
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[quiz_unique_key] => 83407773
[question] => Of the following noble gases and halide gases, which is most ideal?
[value] => Array
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[answer] => 1
[description] => Reason for the Correct Answer:
The most ideal gas is that which deviates least from ideal gas behavior.
Deviations from ideal gas behavior are attributed to volume of particles and intermolecular forces.
Helium has a very small gas particle and experiences almost no intermolecular forces due to its non-polar nature.
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[answers] => Array
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[0] => Array
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[each_answer] => A. Helium
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[1] => Array
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[each_answer] => B. Krypton
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[2] => Array
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[each_answer] => C. Chloromethane
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[3] => Array
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[each_answer] => D. Fluoromethane
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[quiz_unique_key] => 2261298308
[question] => Relative to the b-value for 1,1-difluoropropane, what is the b-value for 1,1-dichloropropane?
[value] => Array
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[answer] => 4
[description] => Reason for the Correct Answer:
The b-value is an empirical value accounting for the volume occupied by gas particles.
Chlorine is slightly larger than fluorine.
Relative to the b-value for 1,1-difluoropropane, the b-value for 1,1-dichloropropane is slightly greater, because the particles of 1,1-dichloropropane occupy slightly more real space.
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[answers] => Array
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[0] => Array
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[each_answer] => A. It is equal to the b-value for 1,1- difluoropropane.
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[1] => Array
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[each_answer] => B. It is slightly less than the b-value for 1,1- difluoropropane
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[each_answer] => C. It’s not possible to compare to the b-value for 1,1-difluoropropane based on the information given.
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[each_answer] => D. It is slightly greater than the b-value for 1,1- difluoropropane.
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[4] => Array
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[quiz_unique_key] => 574431310
[question] => Using the ideal gas law, what is the estimated volume of 2.00 moles of CF4 at 273K and 1 atm?
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[answer] => 1
[description] => Reason for the Correct Answer:
STP stands for standard temperature and pressure, which are 0°C (273K) and 1 atm.
The stated conditions describe 1 mole of gas at STP.
The molar volume of gas at STP is 22.4 L. This value is found experimentally. Two moles would result in double the volume, so the answer is 44.8 L.
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[answers] => Array
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[0] => Array
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[each_answer] => A. 44.80 L
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[1] => Array
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[each_answer] => B. 22.40 L
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[2] => Array
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[each_answer] => C. 42.76 L
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[3] => Array
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[each_answer] => D. 24.81 L
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[558138|3] => A
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