Thermodynamics, Finding Work and Heat transfer

  • #1

Homework Statement


Two-tenghts Kmol of Nitrogen in a piston cylinder assembly undergoes two processes in a series as follows...

Process 1-2: Constant pressure at 5 bar from V1=1.33m^3 to V2 = 1m^2
Process 2-3: Constant volume to P3=4bar

Assuming ideal gas behavior and neglecting kinetic and potential energy effects, determine the work and heat transfer for each process in KJ

The Attempt at a Solution



What i have so far is W = f(5 dV, v, 1,1.33) = -1.65KJ. -f=integral

and then Q = ^U + W and I can figure out ^U. The problem i have is with my answer for W. Do i use the equation i presented, or am i suppose to use pV^n = constant. I guess i am just a little confused on what equation is used when.

Thank You
 

Answers and Replies

  • #2
Redbelly98
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Welcome to Physics Forums.

Homework Statement


Two-tenghts Kmol of Nitrogen in a piston cylinder assembly undergoes two processes in a series as follows...

Process 1-2: Constant pressure at 5 bar from V1=1.33m^3 to V2 = 1m^2
Process 2-3: Constant volume to P3=4bar

Assuming ideal gas behavior and neglecting kinetic and potential energy effects, determine the work and heat transfer for each process in KJ

The Attempt at a Solution



What i have so far is W = f(5 dV, v, 1,1.33) = -1.65KJ. -f=integral

and then Q = ^U + W and I can figure out ^U. The problem i have is with my answer for W. Do i use the equation i presented, or am i suppose to use pV^n = constant. I guess i am just a little confused on what equation is used when.

Thank You
pV^n = constant is only used when Q=0, i.e. for adiabatic processes. That is not the case here -- these paths follow either p=constant or V=constant.

Okay, you got W. So if you calculate ΔU, then you can get Q.

What are the temperatures at the three points 1, 2, and 3? That would help you calculate U at each point, and therefore ΔU for each path.
 

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