Specific Heat Constant Volume Question

In summary, the equation to calculate the change of Cv is Cv = Cp - R, where Cp is the specific heat at constant pressure and R is the ideal gas constant. This equation is valid for ideal gases and can be found in tables such as Perry's Chemical Engineering Handbook. To use this equation in a spreadsheet, a curve fit can be done using the given data for Cv and Cp at different pressures and temperatures.
  • #1
Gordon Arnaut
16
0
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.
 
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  • #2
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
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
Gordon Arnaut said:
Sorry, forgot to mention the gas is air.

and the air isn't frozen, nor superheated to some obscene temperature, right? then, is not [itex]C_v[/itex], [itex]C_p[/itex], and [itex]R[/itex] constant with repect to [itex]T[/itex]? i don't follow the premise to your original question.
 
  • #5
Cp= Cv + R
 
  • #6
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
 

Attachments

  • air.zip
    4.4 KB · Views: 308
Last edited:
  • #7
Thanks, Q.

What is the underlying equation?

Regards,

Gordon.
 

What is specific heat at constant volume and how is it different from specific heat at constant pressure?

Specific heat at constant volume is the amount of heat required to raise the temperature of a unit mass of a substance by one degree while keeping its volume constant. It is different from specific heat at constant pressure, which is the amount of heat required to raise the temperature of a unit mass of a substance by one degree while allowing it to expand or contract to maintain a constant pressure.

How is specific heat at constant volume measured?

Specific heat at constant volume is typically measured using a calorimeter, which is a device that measures the heat released or absorbed by a substance during a chemical or physical process. The substance is placed in a container with a known amount of water, and the change in temperature of the water is measured to calculate the specific heat at constant volume.

What factors can affect the specific heat at constant volume of a substance?

The specific heat at constant volume of a substance can be affected by factors such as the type of substance, its temperature and pressure, and its molecular structure. Changes in these factors can lead to variations in the specific heat at constant volume, making it an important parameter to consider in many scientific applications.

How is specific heat at constant volume used in thermodynamic calculations?

Specific heat at constant volume is a key component in determining the internal energy and enthalpy of a substance in thermodynamic calculations. It is used in equations such as the First Law of Thermodynamics and the Ideal Gas Law to calculate the amount of heat required to raise the temperature of a substance or the work done on or by a substance during a process.

Why is specific heat at constant volume an important concept in chemistry and engineering?

Specific heat at constant volume is an important concept in chemistry and engineering because it allows us to understand and predict the behavior of substances during various processes. It is crucial in designing and optimizing chemical reactions and industrial processes, as well as in understanding the properties of materials and their interactions with energy.

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