Graham’s Law of effusion Review Notes on Graham’s law of effusion Guided practice

Combined Gas Law P1V1T2 = P2V2T1

Ideal Gas Law PV = nRT

ST: 273 K SP: 1 atm, 760 torr, 760 mmHg, 101.3 kPa STP Conditions ST: 273 K SP: 1 atm, 760 torr, 760 mmHg, 101.3 kPa

Values of R with Constants 0.0821atm*L/k*mol 62.4mmHg*L/K*mol and 62.4torr*L/K*mol 8.31kPa*L/k*mol

Dalton’s Law of Partial Pressure PT = P1 + P2 + P3 …

Graham’s Law of Effusion Notes

Diffusion vs. Effusion vs. Osmosis Diffusion: the natural tendency of gas to spread out to uniformly fill the area. Cookies baking can be smelled throughout the house. Effusion: the process in which a gas flows through a small hole in a container. Balloons deflate over time Osmosis: the ability of water to flow through a semi permeable membrane to equalize concentrations

Graham’s Law of Effusion Is there a way to predict how long it will take to effuse? That’s what Graham determined. Must relate one gas to another. Thought: who can get up and move faster? Little kids or their grandparents? Same thing for gases – the lighter/smaller the faster!

Rate of effusion = MMB MMA MMB the molar mass of the heaviest compound. MMA the molar mass of the lightest compound.

Relating rate to time MMB = TimeB MMA TimeA Because B weighs more, it will take longer for it to get moving.

Relating rate to volume MMB = VolumeA MMA VolumeB Since A moves the fastest and is small enough to escape, more of A will get out than B.

What is the rate of effusion of He to N2? MM of He = 4g/mol MM of N2 = 28g/mol 28 4 = Meaning He effuses 2.646 times faster than N2. 2.646

Why are the rates of CO & N2 the same? They have the same molar mass!

Which effuses faster, H2 or Cl2? How much faster? MM H2 = 2g/mol MM Cl2 = 70.9g/mol Therefore H2 effuses faster! 70.9 = 2 5.954

If it takes 90s for Ar to effuse, how long will it take Cl2? MM = 40 MM = 70.9 MMB = TimeB MMA TimeA 70.9 = X 40 90 1.33135 = X/90 120 sec = X

If 10.5 mL of an unknown gas effuses in the same amount of time as it takes 15.7 mL of F2 to effuse, what is the MM of the unknown gas? MMB = VolumeA MMA VolumeB Since fluorine has more volume escaping it is A – always want ratios set up to be greater than 1 X = 15.7 38 10.7 X/38 = 1.467289 X/38 = 1.4672892 X = 38 (1.4672892) = 81.81 g/mol