# Misunderstood Thermodynamic question

1. Mar 31, 2012

### Abdlellah

1. The problem statement, all variables and given/known data
Plot cp as a function of temperature for O2? How does this compare with the cp expected for a diatomic ideal
gas. Add this constant value to your plot. At what temperatures does the real value of cp approach that
expected for a diatomic ideal gas.

2. Relevant equations

I plot the Cp as a function of temperature for O2?

the second part totally i misunderstand it i don't know what i should do

3. The attempt at a solution

this is what i did ( see that attachment please)

table number 2.

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2. Apr 1, 2012

### rude man

Looks to me like you plotted cp for oxygen vs. hydrogen. You were asked to plot cp for oxygen vs. cp for an ideal diatomic gas, which the problem states is a constant.

What is cp for an ideal diatomic gas?

3. Apr 1, 2012

### Abdlellah

I have just the general formula of diatomic !

4. Apr 1, 2012

5. Apr 1, 2012

### Abdlellah

Sorry I'm really bad in this :(
This is the general formula
cp = 7/2 R

What is the values of R that I have to put it.
Im thinking to calculate the Cp by taking the R value of O2 from table. But I will get only one point how I would graph it

6. Apr 1, 2012

### rude man

If I give you y = y(x) and say y = cosntant, you know how to graph it, don't you?

7. Apr 1, 2012

### Abdlellah

the value of R at 300 is 0.2 something
so i calculate it and plot it to the graph and that what i got

Last edited: Apr 1, 2012
8. Apr 1, 2012

### rude man

What happened to cp = 7R/2 where R is the theoretical, constant value of R?

9. Apr 1, 2012

### Abdlellah

i changed my answer. the R is constant at 300 K so i put the point at 300 K
is it now correct ?

#### Attached Files:

• ###### new222.JPG
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46
10. Apr 1, 2012

### rude man

The theoretical R is the same for all gases and is temperature-independent. But be aware that your units of R must be compatible with the units of your chart (the varying values of cp for O2.

Also, when you do get the right value for R, since it's temperature-independent, what is the correct way to graph it on your graph?

11. Apr 3, 2012

### Abdlellah

Oooooh I got it thank you very much :D I made the straight line cuz its constant

12. Apr 3, 2012

### rude man

Ats'a way to go!
What's your total graph look like anyway?

13. Apr 3, 2012

### Abdlellah

I'm using my iPad so I can't upload it. I'll upload it once I get home. Thank you toooooo much