Calculating Pressure Change in Combustion Cylinder

[Soaring Crane]

1) A combustion cylinder (containing a fixed number of moles of gas initially at 9.00atm ) with a moveable piston is maintained at a constant temperature changes volume from 2.00 L to 6.0 L. Determine the change in pressure during this action.

P1 = 9.00 atm
V1 = 2.00 L
P2 = ?
V2 = 6.0 L

Use P1V1 = P2V2, where P2 = (P1*V1)/(V2) = (9.00atm*2.00L)/(6.0 L) = 3.0 atm??

delta P (change in P) = P2 - P1 = 3.0 atm - 9.00 atm = -6.0 atm?? (correct significant digits?)

2) A combustion cylinder (containing a fixed number of moles of gas initially with a pressure of 4.00atm ) with a fixed piston changes temperature from 9.00 kelvin to 4.00 kelvin. Determine the change in pressure during this action.

P1 = 4.00 atm
T1 = 9.00 K
P2 = ?
T2 = 4.00 K

Use P1/T1 = P2/T2, where P2 = (P1*T2)/(T1) = (4.00 atm)(4.00 K)/(9. 00K) = 1.7778 atm??

Change in pressure (delta P) = P2 - P1 = 1.78 atm - 4.00 atm = -2.22 atm?

Thank you for any help.

 

[Leong]

i think it is ok as i don't see any mistakes.

 

[lightgrav]

The only thing to worry about is whether your gas CONDENSES as it cools to 4 Kelvin. At such low Temperatures, almost nothing acts like an IDEAL gas.

 

[Soaring Crane]

Well, exactly what formula/method would you use if it wasn't an ideal gas?

 

[Pengwuino]

Well if he was not given any more information, you must assume it uses the ideal gas law... you would need experimental values otherwise i believe.

 

[kp]

use the Van Der Waals equation for real gases.