This is the first of the five-odd gas laws you’ll need to know for the SAT II Chemistry test. Study these laws closely because you are sure to see a question or two that asks you to apply them. Boyle’s law simply states that the volume of a confined gas at a fixed temperature is inversely proportional to the pressure exerted on the gas. This can also be expressed as PV = a constant. This makes sense if you think of a balloon. When the pressure around a balloon increases, the volume of the balloon decreases, and likewise, when you decrease the pressure around a balloon, its volume will increase. Boyle’s law to can also be expressed in the following way, and this is the form of the law that you should memorize:
P1V1 = P2V2
Example Sulfur dioxide (SO2) gas is a component of car exhaust and power plant discharge, and it plays a major role in the formation of acid rain. Consider a 3.0 L sample of gaseous SO2 at a pressure of 1.0 atm. If the pressure is changed to 1.5 atm at a constant temperature, what will be the new volume of the gas? Explanation If P1V1 = P2V2, then (1.0 atm) (3.0 L) = (1.5 atm) (V2), so V2 = 2.0 L. This answer makes sense according to Boyle’s law—as the pressure of the system increases, the volume should decrease.
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