Elements
Gases
Of the three common states of matter, the gaseous state was most easily described by early scientists. As early as 1662, Robert Boyle showed how the volume of a gas, any gas, changed as the pressure applied to it was changed. Soon thereafter, the effects of temperature and the quantity of gas on volume were discovered. The result of all these studies was a set of fundamental mathematical equations known as the gas laws that applied equally well to any gas, whether pure oxygen, nitrogen, or a mixture of the two. Through careful studies of gases reacting with one another, Amedeo Avogadro later concluded that equal volumes of different gases must contain the same number of molecules. For example, 10.0 L of oxygen contained the same number of oxygen molecules as there were nitrogen molecules in 10.0 L of nitrogen.
As time passed, it became clear that one mole of any gas contained the same number of molecules, 6.02 × 1023a molecules to be exact, a number known today as Avogadro's number. One mole of anything is Avogadro's number of that thing—atoms, molecules, people, or dollars—and that would be a lot of dollars!
Pressure is the amount of force exerted on one unit of area. The example of an ocean diver should make the concept clearer: The greater the depth the diver reaches, the greater the pressure due to the weight of the overlying water. Pressure is not unique to liquids but can be transmitted by gases and solids, too. At the surface of the Earth, the weight of the overlying air exerts a pressure equal to that generated by a column of mercury 760 mm high. The two most common units of pressure in chemical studies are atmosphere and millimeters of mercury
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The English scientist Robert Boyle performed a series of experiments involving pressure and, in 1662, arrived at a general law—that the volume of a gas varied inversely with pressure.
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This formulation has become established as Boyle's law. Of course, the relationship is valid only if the temperature remains constant.
As an example of the use of this law, consider an elastic balloon holding 5 L of air at the normal atmospheric pressure of 760 mm Hg. If an approaching storm causes the pressure to fall to 735 mm Hg, the balloon expands. The product of the initial pressure and volume is equal to the product of the final pressure and volume temperature is constant.
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It is important that you realize that pressure and volume vary inversely; therefore, an increase in either one necessitates a proportional decrease in the other.
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Problem 1: Convert a pressure of 611 mm Hg to atmospheres.
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Problem 2: If a gas at 1.13 atm pressure occupies 732 milliliters, what pressure is needed to reduce the volume to 500 milliliters?
