pressure/temperature relation

[hostie]

I was just wondering: if there is a hypothetical pot enclosed on all sides such that steam from boiling water creates pressure at a certain temperature, then the temperature is increased, will the pressure increase in proportion to this temperature?

[Bone Daddeo]

Yes. The law of Gay-Lussac tells us that pressure is directly proportional to temperature (Kelvin) when volume is held constant.

 

P1/T1=P2/T2

[morp]

The answer is yes and no.Dependenig on the liquid the prssure will at first no rise witkh temp.Above the boiling temp. the pressure will increase rapidly with temp. Above the "Critical point" the liquid/vapor will behave as a gas, GAS LAWS Will apply.

IF your question is a bit more precise i can gi!ve a more precise answer.

 

Morp

[hostie]

Thanks guys,

 

My story is this: one container, 1/3 filled with boiling water constantly boiling with 240*F on a pressure gauge. then the temperature of the stove is increased, indicating on the gauge that the temperature inside the pot is 255*F. Now, I know that 255*F boiling constantly would be 15psi, what is the psi for 240*F? Should be just scaled down with t1/p1=t2/p2

 

{*****} <-- lid

| . . .. .|

|. . .. . | <-- gas (evaporated water)

|~~~~| <-- boiling water

````````

^--- container on stove.

[Bone Daddeo]

Thanks Morp. I assumed we had 100% water vapor in the system produced by boiling water. Your problem Hostie is a horse of a different color and Gay-Lussac will not work. This is a vapor pressure problem. You need to use the Antoine Equation.

 

Following Morp's lead, start by looking at the phase diagram for water. It will show you the phase/phases of water for a given temperature and pressure. You'll immediately see that the relationship between pressure, temperature and phase is not a simple one - which is why the Antoine Equation is not a simple one either. Then look at a vapor pressure table for water to see it numerically and you'll see why we just look up values for water when we need them .

Edited June 8, 2009 by Bone Daddeo

[hostie]

Oooooh, I remember phase diagrams from my Material Science class! Of course, it's so simple now. I was thinking on thermodynamic tangent... Thank you two so much, you're my heroes