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How do smells travel to your nose?

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Grahams Law Thomas Graham studied the effusion and diffusion of gases. Diffusion is the mixing of gases through each other. Effusion is the process whereby the molecules of a gas escape from its container through a tiny hole Thomas Graham studied the effusion and diffusion of gases. Diffusion is the mixing of gases through each other. Effusion is the process whereby the molecules of a gas escape from its container through a tiny hole

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Spreading of gas molecules throughout a container until evenly distributed. Passing of gas molecules through a tiny opening in a container

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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 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

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KE = mv 2 Speed of diffusion/effusion Kinetic energy is determined by the temperature of the gas. At the same temp & KE, heavier molecules move more slowly. Larger m smaller v

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Consider two gases at same temp. Gas 1: KE 1 = m 1 v 1 2 Gas 2: KE 2 = m 2 v 2 2 Since temp. is same, then KE 1 = KE 2 m 1 v 1 2 = m 2 v 2 2 m 1 v 1 2 = m 2 v 2 2 Divide both sides by m 1 v 2 2 Take square root of both sides to get Grahams Law:

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Grahams Law Rate 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.

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This 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 effusion Or deal with Molar mass, masses or Density This 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 effusion Or deal with Molar mass, masses or Density vAvA vAvA vBvB vBvB = = MBMB MBMB MAMA MAMA

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Determine the relative rate of diffusion for krypton and bromine. Kr diffuses 1.381 times faster than Br 2. Grahams Law The first gas is Gas A and the second gas is Gas B. Relative rate mean find the ratio v A /v B . Kr 83.80 36 Br 79.904 35

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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. O 15.9994 8 H 1.00794 1

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If 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 problem Rate of effusion of A = = Rate of effusion of B MBMB MBMB MAMA MAMA

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Grahams Law Example Calc. Rate of effusion of He = = Rate of effusion of Ar 40 g 4 g Helium is 3.16 times faster than Argon.

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Grahams Law Lab of Diffusion HCl NH 3 50 cm NH 4 Cl(s) Choice 1: Both gases move at the same speed and meet exactly in the middle.

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Diffusion HCl NH 3 X cm (Grahams Law Ratio) X cm NH 4 Cl(s) Choice 2: Lighter gas moves faster; meet closer to heavier gas.