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-   -   Internal energy equals to average kinectic energy ? (http://www.physicsforums.com/showthread.php?t=661201)

 Outrageous Dec27-12 11:09 PM

Internal energy equals to average kinectic energy ?

For ideal gas , can I assume Cv dT = nkT (3/2)
, thank you

 Andrew Mason Dec28-12 12:47 PM

Re: Internal energy equals to average kinectic energy ?

Quote:
 Quote by Outrageous (Post 4210583) For ideal gas , can I assume Cv dT = nkT (3/2) , thank you
No. Molar heat capacity, Cv = 3R/2 only for ideal monatomic gases. You are also mixing temperature change with temperature here.

Using molar heat capacity 3R/2 for a monatomic ideal gas:

$\int_{Ti}^{Tf} nC_vdT = \frac{3}{2}nR(T_f - T_i) = \frac{3}{2}nR\Delta T = \frac{3}{2}Nk\Delta T$

AM

 Outrageous Dec29-12 03:41 AM

Re: Internal energy equals to average kinectic energy ?

Quote:
 Quote by Andrew Mason (Post 4211000) No. Molar heat capacity, Cv = 3R/2 only for ideal monatomic gases. You are also mixing temperature change with temperature here. Using molar heat capacity 3R/2 for a monatomic ideal gas: $\int_{Ti}^{Tf} nC_vdT = \frac{3}{2}nR(T_f - T_i) = \frac{3}{2}nR\Delta T = \frac{3}{2}Nk\Delta T$ AM
Thanks for compact explanation.

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