# Specific Heat Constant Volume Question

1. Apr 6, 2007

### Gordon Arnaut

Can someone give me the equation to calculate the change of Cv (specific heat at constant volume with change in temperature.

For example the equation to do this with Cp (specific heat at constant pressure) is:

Cp = 1.9327e-10*T^4 - 7.9999e-7*T^3 + 1.1407e-3*T^2 - 4.4890e-1*T + 1.0575e+3

Regards,

Gordon.

2. Apr 6, 2007

### siddharth

Look up the equation for the given substance in a table. For example, Perry's Chemical Engineering Handbook. What substance is the equation for cp valid for? If it's an ideal gas, you can use the ideal gas constant to get a relationship between cp and cv.

3. Apr 6, 2007

### Gordon Arnaut

Sorry, forgot to mention the gas is air.

Yeah, I can get Cv once I know Cp, by subtracting R:

Cv = Cp - R.

I was just wondering if there was an equation because I want to use it in a spreadsheet.

Regards,

Gordon.

4. Apr 6, 2007

### rbj

and the air isn't frozen, nor superheated to some obscene temperature, right? then, is not $C_v$, $C_p$, and $R$ constant with repect to $T$? i don't follow the premise to your original question.

5. Apr 6, 2007

Cp= Cv + R

6. Apr 6, 2007

### Q_Goest

Hi Gordon,
Attached is the output from a spreadsheet that gives Cv and Cp at various pressures and temperatures. Just do a curve fit.

Edit: Pressure in PSIA

#### Attached Files:

• ###### air.zip
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Last edited: Apr 6, 2007
7. Apr 6, 2007

### Gordon Arnaut

Thanks, Q.

What is the underlying equation?

Regards,

Gordon.