Lecture 1: Gases - PDF

Lecture 1 Gases Part 1 Elements that exist as gases at 250C and 1 atmosphere 2 3  Physical Characteristics of Gases Gases assume the volume and shape of their containers. Gases are the most compressible state of matter....

Lecture 1 Gases Part 1 Elements that exist as gases at 250C and 1 atmosphere 2 3  Physical Characteristics of Gases Gases assume the volume and shape of their containers. Gases are the most compressible state of matter. Gases will mix evenly and completely when confined to the same container. Gases have much lower densities than liquids and solids. 4 Definition of pressure Force Pressure = Area (force = mass x acceleration) Pressure is the forces exerted by gas on the walls of the container Units of Pressure SI units is Pascal 1 Pascal (Pa) = 1 N/m2 1 atm = 760 mmHg = 760 torr 1 atm = 101,325 Pa=101.325 KPa 5  Gases Law Boyle’s law: The volume of a given amount of gas held at constant temperature varies inversely with the applied pressure. P a 1/V T = Constant P *V = constant n = Constant P1 * V1 = P2 * V2 6 Variation in Gas Volume with Temperature at Constant Pressure As T increases V increases 7 Charles’s and Gay-Lussac’s Law : The volume of a given amount of. gas held at constant pressure is directly proportional to the Kelvin temperature VaT V = constant *T V1/T1 = V2 /T2 Temperature must be in Kelvin T (K) = t (0C) + 273.15 8  Amonton’s Law: The pressure of a given amount of gas held at constant volume is directly proportional to the Kelvin temperature. P P1 P2 = a constant or = T T1 T2 9  RELAT- CON- LAW LAW IONSHIP STANT Boyle’s P V P1V1 = P2V2 T, n V1/T1 = Charles’ V T P, n V2/T2 Amonton’ P1/T1 = P T V, n s P2/T2 10  Avogadro’s Law V a number of moles (n) Constant temperature Constant pressure V = constant x n V1 / n1 = V2 / n2 11  Ideal Gas Equation 1 Boyle’s law: P a V (at constant n and T ) Charles’ law: V a T (at constant n and P ) Avogadro’s law: V a n (at constant P and T ) nT Va P V = constant x nT = R nT R is the gas constant P P PV = nRT 12 The conditions 0 0C and 1 atm are called standard temperature and pressure (STP). Experiments show that at STP, 1 mole of an ideal gas occupies 22.414 L. PV = nRT PV (1 atm)(22.414L) R= = nT (1 mol)(273.15 K) R = 0.082057 L atm / (mol K) 13 Gas density (d) Calculations PV = nRT m is the mass of the gas in g PV= m RT M M is the molar mass of the gas m PM d= = V RT Molar Mass (M ) of a Gaseous Substance dRT M= d is the density of the gas in g/L P 14  Dalton’s law of partial pressures: the total pressure, Ptotal, of a mixture of gases is the sum of their individual V and Tgas partial pressures are constant P11 P2 Ptotal = P1+ P2 15 Consider a case in which two gases, 1 and 2, are in a container of volume V. n1RT P1 = n1 is the number of moles of 1 V n2RT P2 = n2 is the number of moles of 2 V n1 n2 PT = P1+ P2 X1 = X2 = n1 + n2 n1 + n2 P1 = X1 PT P2 = X2 PT ni Pi = Xi PT mole fraction (Xi ) = nT 16