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IDEAL GAS LAW. P V = n R T. Brings together gas properties. Can be derived from experiment and theory. BE SURE YOU KNOW THIS EQUATION!. The Ideal Gas Law. CHEMSAVER P 31. PV = nRT P = pressure (atm, mmHg, torr, KPa) V = volume (in Liters) n = number of moles (mol)
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IDEAL GAS LAW P V = n R T Brings together gas properties. Can be derived from experiment and theory. BE SURE YOU KNOW THIS EQUATION!
The Ideal Gas Law CHEMSAVER P 31 PV = nRT P = pressure (atm, mmHg, torr, KPa) V = volume (in Liters) n = number of moles (mol) R = Universal Gas Law Constant (on STAAR chart) T = Temperature (in Kelvins)
The Gas Constant R • Repeated experiments show that at standard temperature (273 K) and pressure (1 atm), one mole (n = 1) of gas occupies 22.4 L volume. Using this experimental value, you can evaluate the gas constant • R = PV/nT = (1 atm* 22.4 L)/(1 mol*273 K) • R = 0.0821 L ·atm / mol·K = 8.31 L ·kPa / mol·K = 62.4 L ·mmHg/ mol·K = 62.4 L· torr/ mol·K CHEMSAVER P 31
Using PV = nRT How much N2 is required to fill a small room with a volume of 960 cubic feet (27,000 L) to 0.98atm at 25 oC? Solution 1. Get all data into proper units V = 27,000 L T = 25 oC + 273 = 298 K P = 0.98 atm R = 0.0821 L ·atm / mol·K
Using PV = nRT How much N2 is required to fill a small room with a volume of 960 cubic feet (27,000 L) to 0.98atm at 25 oC? Solution 2. Now plug in those values and solve for the unknown. PV = nRT RT RT n = 1100 mol or 1.1 x 103 mol
Using Ideal Gas Law Example What is the volume of 2.30 moles of hydrogen gas at a pressure of 122 kPa and temperature of 20.0oC? Ans: V = nRT/P V = (2.30 mol)(8.31 L ·kPa / mol·K)(293K) 122 kPa = 46.0 L
Deviations from Ideal Gas Law • Real molecules have volume. The ideal gas consumes the entire amount of available volume. It does not account for the volume of the molecules themselves. • There are intermolecular forces. An ideal gas assumes there are no attractions between molecules. Attractions slow down the molecules and reduce the amount of collisions. • Otherwise a gas could not condense to become a liquid.
This implies: • If the volume of space occupied is large and the pressure is low, the behavior of a gas is very close to that of an ideal gas. • We will not deal with gases at conditions that make them non-ideal in this class.