What is the final pressure when two gases at different pressure are mixed?

My question deals with pressure. The valve between a 5-L tank containing a gas at 9 atm and a 10-L tank containing a gas at 6 atm is opened. What is the final pressure in the tanks? I cannot seem to find an equation for that problem...can you help?
Mellissa Mortensen 3/17/99

Rather than searching for an equation someone else has worked out for you, break the problem into several simpler pieces.

• Imagine that the 10 L tank contains nothing. Could you calculate the final pressure of the gas from the 5 L tank after the valve is opened?

  P1 = 9 atm V1 = 5 L		P2 = ? V2 = 15 L

• Imagine that the 5 L tank contains nothing. Could you calculate the final pressure of the gas from the 10 L tank after the valve is opened?

  P1 = 6 atm V1 = 10 L		P2 = ? V2 = 15 L

• If the gases from the two tanks are ideal, their molecules behave independently when they are mixed. So will the pressure exerted by one gas on the walls of the container affect the pressure exerted by the other gas?
• Then how will the total pressure be related to the "partial pressures" each gas in the mixture exerts?

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Author: Fred Senese senese@antoine.frostburg.edu

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