Dalton’s+Law+of+Partial+Pressure

Dalton ’s Law of Partial Pressure: PT = P1 + P2 +P3 +… John Dalton was the chemist who came up with the atomic theory. He also came up with this law of partial pressure. Dalton’s law of partial pressure determines the total pressure of a gas mixture. This total pressure is found by adding the pressures of each gas in the mixture: the partial pressures. This law can be used with an infinite number of partial pressures. Dalton’s law of partial pressure is virtually common sense; each different gas that makes up a gas mixture exerts a specific pressure as the particles collide with container walls, so of course all of these pressures added together are the total pressure. Problem: A flask contains a mixture of hydrogen and oxygen. The pressure being exerted by these gases is 785 mm Hg, as determined by a manometer. If the partial pressure of the hydrogen in the mixture is 395 mm Hg, what is the partial pressure of the oxygen? Whenever a problem asks for partial pressure, the equation used is Dalton’s law of partial pressure. Because there are only two gases used in the problem, the equation only needs to go up to P2. PT = P1 + P2 PT = total pressure P1 = partial pressure of gas #1 P2 = partial pressure of gas #2 Now you need to figure out what you’re solving for. The problem asks for the partial pressure of Oxygen, the second gas mentioned. So you know you need to solve for P2. PT = P1 + **P2** To solve for P2 you need to isolate it, get it on one side. PT – P1 = P2 Then you need to substitute the values in for the variables. PT is the pressure exerted: 785 mm Hg. P1 is the partial pressure of hydrogen: 395 mm Hg. 785 mm Hg – 395 mm Hg = P2   Now solve. You should get 390 mm Hg. P2 = 390 mm Hg  The equation is solved. :[]



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