- #1

- 29

- 0

## Homework Statement

I.The gas is heated at constant pressure until the volume is 4.4L at point B

II. The gas is cooled at constant volume until the pressure decreases to 1.2 atm

III. The gas undergoes an isothermal compression back to point A

a) Find the temperature at Point A,B,C

b) Find the work done on the gas ,the heat transferred to the gas and the change for each process

c) Find W,Q and delta U for the whole cycle

## Homework Equations

[/B]

delta U=Q+W

PV=nRT

1 atm=1.013x10^5 N/m^2

Cp=5/3R+R

## The Attempt at a Solution

a)

pv=nRT

Tb=PbVb/nR

Tb=2.4*4.4/(1*8.31) * 0.001* 1.013*10^5

=129K

Ta=129K/2

=64.5K

Tc=129K/2

=64.5K

b)

Wab=pv

=2.4*(4.4-2.2)* 1.013x10^5 *0.001

=535J

Qab=n*Cp*deltaT

=0.32* 8/3*R *(129-64.5K)

=457J

U=Q+W

delta Uab=457+535

=992J

Wbc=0

Since the volume keep unchange

Qbc=n*Cv*deltaT

=0.32*5/3*R*(64.5K-129K)

=-285J

U=Q+W

U=-285J

U=0

Since it is isothermic process

Wca=nRTc *ln(Vc/Va)

=0.32*8.31*64.5K*ln(4.4/2.2)

=118

Q+W=0

Q=-118J

c)

W=Wab+Wbc+Wca

=535+0+118

=653J

Q=Qab+Qbc+Qca

=457-285-118

=54J

deltaU=992-285+0

=707J