# Exambusters Study Cards 11 Gases

 State Normal atmospheric pressure in five standard units
 1 atm 760 torr 101.3 kilopascals 14.7 lbs/square inch
 definition: Pressure
 force/area
 barometer
 An instrument, invented by Torricielli in 1643, which measures atmospheric pressure. An evacuated glass tube in which a column of mercury rises or falls with changing pressure.
 manometer
 An instrument used to measure pressure of gases in a closed container.
 State three postulates of the Kinetic-Molecular Theory of Gases
 1. Matter is composed of very small particles; a gas is mostly empty space. 2. Particles are in constant random motion. 3. Collisions are elastic.
 State the formula for Graham’s Law of Diffusion.
 In a mixture of gases A, B: ; (RA)(MWA)1/2 = (RB)(MWB)1/2 ; MW = Molecular Weight R = Rate of diffusion
 Do heavy or light gases diffuse faster?
 Light gases diffuse faster.
 Charles’ Law
 V1/T1 = V2/T2   Volume and temperature have a direct relationship when pressure and moles of gas remain constant.   V = volume T = Kelvin
 Solve this problem: At 300 K, a gas has a volume of 10 liters. Find the volume at 400 K
 Use Charles’ Law: V1/T1 = V2/T2 V2 = 13.3 L
 Boyle’s Law
 (P1)(V1) = (P2)(V2) Pressure and volume have an inverse relationship when temperature and moles of gas remain constant.   P = Pressure V = Volume
 A sample of gas has a volume of 25 L at 800 torr. Find the volume at 400 torr.
 Use Boyle’s law: (P1)(V1) = (P2)(V2) ; V2 = 50 L
 Combined Gas Law
 P1V1/T1 = P2V2/T2 ; Moles of gas constant P = Pressure V = Volume T = Kelvin
 Dalton’s Law of Partial Pressures
 In a gas mixture, the total pressure equals the sum of the partial pressures of each component.   Ptotal = P1 + P2 + P3 …..
 Ideal Gas Law
 PV = nRT   P = Pressure (atmospheres) V = Volume (liters) n = # of moles R = 0.0820 (L atm)/(mol K) T = temperature in K
 How many moles of H2 gas are there in 20 L at 4 atm and 400K?
 Use the Ideal Gas Law: PV = nRT   n = 2.44 moles
 STP
 Standard temperature (0 C, 273 K) and standard pressure (1 atm or 760 torr)
 Gay-Lussac’s Law of Combining Gas Volumes
 When only gases are involved in a reaction, the volumes of reactants and products are in a small, whole number ratio.