Thermo-Please start me off..thanks!?

Question

A piston-cylinder device contains 0.2 m3 of liquid water and 0.6 m3 of water vapor in equilibrium at 650 kPa. Heat is added at constant pressure until the temperature is 300 oC. Find the initial temperature, the total mass and the final volume.

Answer 1

JP... already helped you with a couple of these yesterday... try the same approach... use the ideal gas law

what do you know about this system

Pressure is a constant Pi=Pf= 650 kPa

n= constant- have to assume it is a closed system and no mass is added or lost. Using the physical properties for water at the initial conditions, you can calculate the mass of water that is present... Find the temperature where water has a vapor pressure of 650kPa, at that temperature find the density of water liquid and vapor, with the density and volume you can find the mass of water as a liquid and a vapor. Once you have mass you can convert to moles

V will change with T, as T goes up, V will go up

Vi= 0.8m3

Tf= 300C... need to convert to deg K

Get the ideal gas constant in the correct units from your text book, or the wikipedia link below.

Set up your equations:

PiVi=nRTi

650 kPa * 0.8m3= n (calculated as outlined above)RTi

solve for Ti- answer will be in absolute T depending upon the units for R

Same approach for final volume

PfVf=nRTf

650 kPa * Vf= n R * 300C (need to convert to K)

solve for Vf

If you still need help, go to my profile and drop me an email.

Use your text book, you should have all the information that you need...

Remember that this type of thermo is like an algebra word problem... break it into parts... what do you know, what do you need to find out... and what tools do you have to use.

http://en.wikipedia.org/wiki/Ideal_gas_l...