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Course: MCAT > Unit 3

Lesson 1: Chemical and physical sciences practice passage questions

Chlorofluorocarbons and the environment


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 -161oC, while the boiling point of dichlorodifluoromethane (Freon-12, a popular refrigerant) is about -29oC. 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:
*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:
*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.
The a-value for a halocarbon increases proportionally with which characteristic?
Choose 1 answer: