# Homework Help: Ideal gases thermodynamic enthalpy and internal energy change

1. Jan 21, 2012

### xzibition8612

1. The problem statement, all variables and given/known data
See attachment ecxample001.

2. Relevant equations

See attachment D11.

3. The attempt at a solution
In the first equation (Cp/R = a+bT+cT^2...etc.), Cp/R is the constant pressure specific heat. The general formula for enthalpy change is h2-h1 = integral[Cp]dT, so does Cp/R = Cp except Cp/R is the constant pressure specific heat on a molar basis?

Then in the next line of formula in the solution (h2-h1 = R/M integral (a+bT...)dT) how did it go from Cp/R to R/M? I'm totally lost in this. And by the formula do I seriously plug in these huge numbers (from D11)? I tried plugging it in and get keep getting somethign to the 17th power. I'm also very confused on the units, as there's a lot of variables and I'm not very clear on them and what they represent. Any help would be appreciated. Thanks!

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• ###### D11 001.jpg
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2. Jan 21, 2012

### LawrenceC

It looks like the numbers in the chart are intended to be between 1 and 25 in absolute value. Values for b are premultiplied by 1000. C by 1M and d by 1B. So the value d for CO2 would be 2.002X10^-9.

3. Jan 21, 2012

### xzibition8612

thanks i know that from the chart. So how did the problem go from cp/R to R/M?

4. Jan 21, 2012

### LawrenceC

Enthalpy change is integral of CpdT. They give you Cp/R as function of temperature on a molar basis. So Cp is R times the polynomial. The M comes from the fact it is a mass basis.

5. Jan 21, 2012

### xzibition8612

So R/M is merely a conversion factor to get Cp molar basis back to the regular Cp?
Thanks a lot man.