Physics Help Forum How do I determine the amount of water in a sealed container to create a given pressu

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 Dec 12th 2016, 12:11 AM #1 Junior Member   Join Date: Dec 2016 Posts: 1 How do I determine the amount of water in a sealed container to create a given pressu I have a sealed container with a volume of 1 liter. I want to go from an initial pressure of p1=1 atm and an initial temperature of T1=298 to a final pressure of p2=10 atm and a final temperature of T2=453 K. I want to to use water to create the pressure. But I do not know how to determine the amount of water, how would I do that? Thanks. Last edited by bigbear312; Dec 12th 2016 at 12:14 AM.
 Dec 13th 2016, 11:09 AM #2 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,275 You can set up two equations in two unknowns: 1. For the initial condition you have gaseous air plus liquid water in the container. The number of moles of air from the Ideal Gas law is: $\displaystyle n_{a} = \frac {P_1 V_{a}}{RT_1}$ where $\displaystyle n_a$ is the number of moles of air and $\displaystyle V_{a}$ is the volume of air in the container. The volume of water at this stage is then $\displaystyle V_{w} = V - \rho_{w} n_w$ where V = size of the container or 1 liter and $\displaystyle \rho_w$ is the density of water in terms of liter/mole. Combining these two equations: $\displaystyle n_a = \frac {P_1(V-\rho_w n_w)}{R T_1}$ 2. The second equation is at the higher temperature, when the water has turned to gaseous steam. From the Ideal Gas law: $\displaystyle n_a + n_w = \frac {P_2 V}{R T_2}$ So now you have two equation with unknowns $\displaystyle n_a$ and $\displaystyle n_w$.

 Tags amount, container, create, determine, pressu, pressure, sealed, thermodynamic, water, water vapor

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