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How do smells travel to your nose? 1

DiffusionEffusionSpreading of gas molecules throughout a container until evenly distributed.

Passing of gas molecules through a tiny opening in a container

Grahams Law states that the rates of effusion and diffusion of gases at the same temperature and pressure is dependent on the size of the molecule.The bigger the molecule the slower it moves the slower it mixes and escapes.Grahams Law

Grahams LawKE = mv2Speed of diffusion/effusionKinetic energy is determined by the temperature of the gas.At the same temp & KE, heavier molecules move more slowly.Larger m smaller v6

Consider two gases at same temp.Gas 1: KE1 = m1 v12Gas 2: KE2 = m2 v22

Since temp. is same, then KE1 = KE2 m1 v12 = m2 v22 m1 v12 = m2 v22

Divide both sides by m1 v22Take square root of both sides to get Grahams Law:7Grahams LawGrahams LawRate of diffusion of a gas is inversely related to the square root of its molar mass.

The equation shows the ratio of Gas As speed to Gas Bs speed.

8This shows that the velocities of two different gases are inversely proportional to the square roots of their molar masses.This can be expanded to deal with rates of diffusion or effusionOr deal with Molar mass, masses or DensityvAvB=MBMA

Determine the relative rate of diffusion for krypton and bromine.

Kr diffuses 1.381 times faster than Br2.

Grahams LawThe first gas is Gas A and the second gas is Gas B. Relative rate mean find the ratio vA/vB.Kr83.8036Br79.9043510 A molecule of oxygen gas has an average speed of 12.3 m/s at a given temp and pressure. What is the average speed of hydrogen molecules at the same conditions?

Grahams Law

Put the gas with the unknown speed as Gas A.O15.99948H1.00794111If equal amounts of helium and argon are placed in a porous container and allowed to escape, which gas will escape faster and how much faster?Grahams Law Example problemRate of effusion of A=Rate of effusion of BMBMAGrahams Law Example Calc.Rate of effusion of He=Rate of effusion of Ar40 g4 gHelium is 3.16 times faster than Argon.Grahams Law Lab of DiffusionHCl NH350 cm50 cmNH4Cl(s)Choice 1: Both gases move at the same speed and meet exactly in the middle.

14DiffusionHCl NH3X cm(Grahams Law Ratio) X cmNH4Cl(s)Choice 2: Lighter gas moves faster; meet closer to heavier gas.

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