Chemistry

# Chemistry - Standard Atmospheric Pressure Corresponds to...

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Standard Atmospheric Pressure - Corresponds to the typical pressure at sea level. This pressure is equal to 1.01325 x 10 5 Pa, 760 mm Hg, 760 torr, 1 atm, and 101.325 kPa 10.3 The Gas Laws The four variables needed to define the physical state of a gas are temperature, T, pressure, P, volume, V, and the amount of gas, which is usually expressed in moles, n. Boyle's Law - The volume of a fixed quantity of gas maintained at constant temperature is inversely proportional the pressure. V = constant x 1/P; PV = constant. Charles' Law - The volume of a fixed amount of ga maintained at constant pressure is directly proportional to its absolute temperature (on the Kelvin scale). V = constant x T; V/T = constant Avogadro's Hypothesis - Equal volumes of gases at the same temperature and pressure contain equal number of molecules. From this, Avogadro's Law was established, which said t he volume of a gas maintained at constant temperature and pressure is directly proportional to the number of moles of the gas. Gay-Lussac's law of combining volumes , provided the basis for both of these, which said that at a given temperature and pressure the volumes of gases that react with on another are in the ratios of small whole numbers. 10.4 The Ideal-Gas Equation The Ideal-Gas Equation - PV = nRT; Made by combining the three gas laws, An ideal gas is a hypothetical gas whose pressure, volume, and temperature behavior is completely described by the ideal-gas equation. The term R is called the gas constant , whose value depends on the units of P,V, n, and T. Temperature is expressed in Kelvins, Pressure in atm's, Volume in liters, and the quantity of gas, n , in moles. Standard Temperature and Pressure (STP) - 0 degrees Celsius and 1 atm. 10.5 Further Applications of the Ideal-Gas Equation The ideal gas law can also be used to determine the density of a gas, by multiplying both sides of the equation (n/V) = (P/RT) by M, the molar mass, which is the number of grams in one mole of a substance. The resulting equation (nM/V) is equivalent to m/V (mass divided by volume), which is the same thing as density. Thus, the density of gas is given by the equation PM/RT. 10.6 Gas Mixtures and Partial Pressures Dalton's Law of Partial Pressures - The total pressure of a mixture of gases equals the sum of the pressures that each would exert if it were present alone. The pressure exerted by a particular component of a mixture of gass is called the partial pressure . The law has the equation P t = n t (RT/V), where P t is the total pressure exerted by the gas(es), and n t is the total number of moles in the gas(es) Partial Pressures and Mole Fractions - Because each gas in a mixture behaves independently, we can relate the amount of a given gas in a mixture to its partial pressure. For a mixture, n 1 /n 2 is called the mole fraction of gas 1, which is denoted as X 1 . The mole fraction, X, expresses the ratio of the number of moles of one component to the total number of moles in the mixture. The

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Chemistry - Standard Atmospheric Pressure Corresponds to...

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