Is Heat Capacity the Same for All Materials?

[thentangler]

Hi there,
I have a quick question. According to duLong and petit's law, the heat capacity at constant volume for most solids at high temperatures is 3R. (I.e) Cv=3R.
Where R is the gas constant. Does this mean that the heat capacity is the same for all materials?
I thought each material at a unique heat capacity. Can somebody explain?
Thank You

 

[Jano L.]

Hello thentangler,
For solids in high enough temperatures above the Debye temperature, the heat capacaity is 3R per mole.

Check the table of temperatures here

http://en.wikipedia.org/wiki/Debye_model#Debye_versus_Einstein

For long organic molecules, the heat capacity can be much larger than 3R per mole, because they have many active degrees of freedom.

 

[Borek]

Note: it is specific heat capacity per mole that is (almost) identical.

 

[thentangler]

So suppose I encounter a material that is a classical solid, would it be safe to substitute 3R for its specific heat when I am calculating its Q per mole?

 

[Borek]

Define "safe". Dulong–Petit law is an approximation. Sometimes it works, sometimes it doesn't. If you can't find specific heat capacity and you use 3R you should always spell it out, as it is possible you are way off.

 

[thentangler]

Aahh, thank you Borek. The limitations of classical physics I suppose. :)