How to Calculate Work and Heat Transfer in a Polytropic Process of Nitrogen?

[ZLing]

Homework Statement

Nitrogen at 100°C and 600 kPa expands in such a way it can be approximated by a polytropic process with n=1.2. Calculate the work and the heat transfer if the final pressure is 100 kPa.

Homework Equations

The Attempt at a Solution

I used the equation T2/T1=(P2/P1)^[(n-1)/n] to find T2. Then i used W=nCv(T1-T2) to calculate work done. Is this correct? But i don't know how to calculate the heat transfer.

 

[Chestermiller]

Homework Statement

Nitrogen at 100°C and 600 kPa expands in such a way it can be approximated by a polytropic process with n=1.2. Calculate the work and the heat transfer if the final pressure is 100 kPa.

Homework Equations

The Attempt at a Solution

I used the equation T2/T1=(P2/P1)^[(n-1)/n] to find T2. Then i used W=nCv(T1-T2) to calculate work done. Is this correct?

No. This is not the work. This is the change in internal energy. To get the work, you need to integrate PdV.

But i don't know how to calculate the heat transfer.

If you know the change in internal energy and the work, then you can use the first law to get the heat.

Chet

 

[ZLing]

No. This is not the work. This is the change in internal energy. To get the work, you need to integrate PdV.

If you know the change in internal energy and the work, then you can use the first law to get the heat.

Chet

Hi, does that mean I have to find V1 and V2 first?

 

[Chestermiller]

Hi, does that mean I have to find V1 and V2 first?

That's one way to start.

Chet