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Boyle's law, which summarizes these observations, states that: the volume of a certain amount of gas, which is maintained at a constant temperature, is inversely proportional to the pressure exerted, which is summarized in the following expression:
P.V = constant or P = 1 / V
Example:
An inflated balloon with a volume of 0.55L at sea level (1.0 atm) is allowed to rise to a height of 6.5 km, where the pressure is about 0.40 atm.
Assuming that the temperature remains constant, what is the final volume of the balloon?
Reasoning and solution:
Note that the number of moles and the temperature of the gas remain constant, so Boyle's law is used. From the equation:
P1V1 = P2 V2
Where P1 = 1 atm, V1 = 0.55L and P2 = 0.40 atm, as well
V2 = V1 x (P1 / P2) = 0.55 L x (1 atm / 0.40 atm) = 1.4 L
When the pressure is reduced (at a constant temperature), the volume increases. The final volume is greater than the initial volume, so the answer is reasonable.