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Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: adam1v on December 03, 2005, 06:49:26 AM

Title: Stuck with y= cp/cv
Post by: adam1v on December 03, 2005, 06:49:26 AM

Hi there.
I was wondering if someone could help.
I have been asked 2 small questions for homework, which i am stuck with.
Firstly, show that cp-cv = r.
I have managed to do this as the teacher has gave us some clues in class.
THe second question is show that gamma = Cp/Cv ?

Would anyone be able to help me out with the second question?
Ideally id like someone to do the question for me, and add their own comments below each line so i could follow it?

thanks in advance,

regards
Adam

Title: Re:Stuck with y= cp/cv
Post by: adam1v on December 03, 2005, 06:56:54 AM

since the rules dont like people posting 6-5 homework questions, i will show what i have found out, but i dont understand it, so if it is correct, could someone elaborate on it?

hi found this (http://books.google.com/books%3Fq%3Dgamma%2B%253D%2Bcp/cv&sig=EWyS8tisOlKhIsHn2muQFLomXGs&pli=1&auth=DQAAAG4AAAB_cQse_qoNE2ZaLID42U_qhyXe4JKy4DaYfJLrbd-LfTRk6ke0jXazOH-XQdDwHxBoGC_DcGoXhPBquX0F277fSsy5Behg_HnDuWVB8AS-157Bo5g-Y5GvvUM6Nj2tFxwnqthFSIUVjNOD9mZx0LI9) from google.

Title: Re:Stuck with y= cp/cv
Post by: Donaldson Tan on December 03, 2005, 04:15:56 PM

the google link is dead.

i am rather surprised by your 2nd question, because by definition, gamma is the ratio of heat capacity at constant pressure to heat capacity at constant volume.

regarding your 1st question, i shall give you the benefit of the doubt.

considering 1 mole of gas,

Cp = (dH/dT)
Cv = (dU/dT)

H = U + PV = U + RT (ideal gas: PV = RT)
dH = dU + RdT
dH - dU = RdT
dH/dT - dU/dT = R
Cp - Cv = R

Title: Re:Stuck with y= cp/cv
Post by: adam1v on December 12, 2005, 01:38:33 PM

Quote from: geodome on December 03, 2005, 04:15:56 PM

i am rather surprised by your 2nd question, because by definition, gamma is the ratio of heat capacity at constant pressure to heat capacity at constant volume.

Thanks for all your help Geo. I have now answered both questions, but regarding the second question,
Gamma = Cp/CV, is that not correct then?Cp being specific heat capacity at contstant pressure and Cv specific heat capacity at constant volume?

Adam

Title: Re:Stuck with y= cp/cv
Post by: Donaldson Tan on December 13, 2005, 02:25:08 AM

by definition, gamma is the ratio of heat capacity at constant pressure (Cp) to heat capacity at constant volume (Cv), so gamma = Cp/Cv

Title: Re:Stuck with y= cp/cv
Post by: adam1v on December 13, 2005, 02:07:48 PM

i know lol  ???

thats what ive said in the original post?

Ive done it now anyhow :)