~christina~

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**[SOLVED] 2 Thermodynamic questions**

**1. Homework Statement**

1.

a) Determine the work done on a fluid that expands from i to f as indicated in picture below.

b) How much work is performed on the fluid if it is compressed from f to i along the same path?

http://img340.imageshack.us/img340/6344/82457490fq4.jpg [Broken]

2. An ideal gas initially at Pi, Vi and Ti is taken through a cycle as shown.

a) find the net work done on the gas per cycle

b) What is the net energy added by heat to the system per cyle

c) Obtain a numerical value for the net work done per cycle for 1.00 mol of gas initially at 0C

**2. Homework Equations**

[tex]\Delta E_{int}= Q+ W [/tex]

**3. The Attempt at a Solution**

**1.**

**a)Determine the work done on a fluid**

I thought that work was the area under the curve...but acording to my book for constant pressure.. I think it is

[tex]P_i(V_f-V_i) [/tex]

Now I'm thinking that If I find the are under the curve then it would be=>

(4-1m^3)(2x10^6Pa)+ (2-1m^3)(6x10^6-2x10^6)+ 1/2(3-2m^3)(6x10^6-2x10^6)=

(6x10^6)+(4x10^6)+ (2x10^6)= 1.2x10^7 J

**b) How much work is performed on the fluid if it is compressed from f to i along the same path?**

here I'm not sure what they want, when they say that the fluid is compressed along the same path. I assume that would mean that the pressure changes? But how would that look on the graph? Am I supposed to draw a new graph?

_________________________________________________________________________

I would say work done is = area of the cyclic cycle thus:

(3Pi-Pi)(3Vi-Vi)= 4J

if it is cyclic I think that the net energy added by heat would be =

Not sure how I would do this if they say that there is 1.00mol of gas at 0C.

I know that [tex]Q=nc\Delta T[/tex] but if you don't have the final temp then how do you do the question, and also if you don't have c?

I need help on kowing whether I'm correct or not and need help on parts c for #2 and also on part b) of #1.

Please help me out.

Thank you.

here I'm not sure what they want, when they say that the fluid is compressed along the same path. I assume that would mean that the pressure changes? But how would that look on the graph? Am I supposed to draw a new graph?

_________________________________________________________________________

**2.****a) net work done on the gas per cycle**I would say work done is = area of the cyclic cycle thus:

(3Pi-Pi)(3Vi-Vi)= 4J

**b) What is the net energy added by heat to the system per cyle**if it is cyclic I think that the net energy added by heat would be =

**Q= -W**because the [tex]E_{int}= 0[/tex] thus would it would be -4J ?**c) Obtain a numerical value for the net work done per cycle for 1.00 mol of gas initially at 0C**Not sure how I would do this if they say that there is 1.00mol of gas at 0C.

I know that [tex]Q=nc\Delta T[/tex] but if you don't have the final temp then how do you do the question, and also if you don't have c?

I need help on kowing whether I'm correct or not and need help on parts c for #2 and also on part b) of #1.

Please help me out.

Thank you.

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