John Dalton (1766 – 1844) - Developed the Law of Partial Pressures (abt. 1801)
Partial Pressures The PRESSURE created by the collision of one gas in a mixture of gases is called the Partial Pressure of the gas Dalton said that molecules of different gases in a mixture act independently of one another in exerting a force on the wall of the container. In other words, the frequency of collisions of one gas is independent of the presence of other gases
Dalton’s Law of Partial Pressures DALTON’S LAW OF PARTIAL PRESSURES states the following: The sum of the partial pressures of all the components in a gas mixture is equal to the total pressure of the gas mixture In other words: Ptotal = Pgas1 + Pgas2 + Pgas3 + …
P tot = P He + P Ne + P ar P tot = 1 atm + 2 atm + 3 atm = 6 atm
Partial Pressure Problem A diving tank contains a mixture of Oxygen and Nitrogen. The pressure exerted by these gases Is 7.2 atm. The partial pressure of the Nitrogen Is 5.76 atm. What is the pressure exerted by The Oxygen in atm. & KPa? P tot = P O2 + P N2 7.2 atm = P 02 + 5.76 atm P O2 = 1.44 atm P O2 = 1.44 x 101.3 = 145.87 Kpa
Partial Pressure Problem 2 The gases carbon dioxide, oxygen and Argon are mixed in a tank. All gases have the same Partial pressure, and the total pressure of the Tank is 48,420 Pascals. What is the partial pressure of O 2 ? Sol’n:P tot = P CO2 + P O2 + P Ar 48,420 = 3P (since they’re all equal) P O2 = 48,420/3 = 16,140 Pascal
Diffusion and Effusion Diffusion: Movement of one gas through another gas from a area of High concentration to an area of low concentration When you smell the skunk in the backyard or the fish in The kitchen its diffusion of gas molecules that bring the Smell to your nose
Effusion: A process closely related to diffusion. It’s the movement of molecules or atoms through a tiny Hole, one so small that only one molecule at a time can Pass through An example of effusion is the deflation of a helium filled balloon overnight.
Graham’s law of effusion In 1846 Thomas Graham studied the rates at which Different gases move through a small opening into a Vacuum. What he discovered was…. GRAHAM’S LAW ALSO APPLIES TO DIFFUSION ! Gases with smaller MW effuse (or diffuse) more rapidly Than gases with larger MW’s Slowerfaster
Graham’s law of effusion Problem: Arrange the following gases from highest to lowest rate of diffusion lowest rate of diffusion He Cl 2 Ne O 2 H 2 N 2 Kr H2 He Ne N2 O2 Cl2 Kr
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