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Charles Law.docx - Early scientists explored the...

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Early scientists explored the relationships among the pressure of a gas (P) and its temperature(T), volume (V), and amount (n) by holding two of the four variables constant (amount andtemperature, for example), varying a third (such as pressure), and measuring the effect of thechange on the fourth (in this case, volume). The history of their discoveries provides severalexcellent examples of thescientific method.The Relationship between Pressure andVolume: Boyle's LawAs the pressure on a gas increases, the volume of the gas decreases because the gas particlesare forced closer together. Conversely, as the pressure on a gas decreases, the gas volumeincreases because the gas particles can now move farther apart. Weather balloons get larger asthey rise through the atmosphere to regions of lower pressure because the volume of the gashas increased; that is, the atmospheric gas exerts less pressure on the surface of the balloon,so the interior gas expands until the internal and external pressures are equal.Figure[Math Processing Error]5.3.1: Boyle’s Experiment Using a J-Shaped Tube toDetermine the Relationship between Gas Pressure and Volume. (a) Initially the gas is at apressure of 1 atm = 760 mmHg (the mercury is at the same height in both the arm containingthe sample and the arm open to the atmosphere); its volume isV. (b) If enough mercury isadded to the right side to give a difference in height of 760 mmHg between the two arms, thepressure of the gas is 760 mmHg (atmospheric pressure) + 760 mmHg = 1520 mmHg and thevolume isV/2. (c) If an additional 760 mmHg is added to the column on the right, the totalpressure on the gas increases to 2280 mmHg, and the volume of the gas decreases toV/3 (CCBY-SA-NC; anonymous).The Irish chemist Robert Boyle (1627–1691) carried out some of the earliest experiments thatdetermined the quantitative relationship between the pressure and the volume of a gas. Boyleused a J-shaped tube partially filled with mercury, as shown in Figure[Math ProcessingError]5.3.1. In these experiments, a small amount of a gas or air is trapped above themercury column, and its volume is measured at atmospheric pressure and constanttemperature. More mercury is then poured into the open arm to increase the pressure on thegas sample. The pressure on the gas is atmospheric pressure plus the difference in the heightsof the mercury columns, and the resulting volume is measured. This process is repeated untileither there is no more room in the open arm or the volume of the gas is too small to bemeasured accurately. Data such as those from one of Boyle’s own experiments may beplotted in several ways (Figure[Math Processing Error]5.3.2). A simple plot of[MathProcessing Error]Vversus[Math Processing Error]P

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Term
Fall
Professor
Mr. Neilson
Tags
Robert Boyle

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