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Ask iit jee aieee pet cbse icse state board community Community Discussion Question: Cp/Cv
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rajat (284)

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for a mixture of n1 moles of a monoatomic gas and n2 moles of a diatomic gas has its Cp/Cv = 1.5
find the ratio n1/n2

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neeleshv (119)

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We have
mix= (n11+ n22)/n1+n2
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chimanshu_007 (11604)

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is the ans 5/8

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joyfrancis (1504)

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On mixing the two gases
Umix = Ugas1 + Ugas2
(n1+n2)CvmixT = n1Cvgas1T + n2Cvgas2T----(i)
now it is given that the mix =3/2
we have Cvmix=R/-1
             Cvmix=2R(on putting gamma=3/2)
also, Cvgas1=3R/2
and Cvgas2=5R/2
on substituting all these values in equation 1 we get
(n1+n2)2R=n1(3R/2) + n2(5R/2)
n2/2=n1/2
n1/n2=1
thanks

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him26.89 (207)

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Cp={5R/2(n1)+7R/2(n2)}/{n1+n2}
Cv={3R/2(n1)+5R/2(n2)}/{n1+n2}
&Cp/Cv=1.5
=>  n1/n2=1
i think its absolutely right.
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chirag (384)

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him26.89, I would like to correct you, your answer is wrong...
 
Ans.:-n1/n2=3/5
 
Soln.:-
 
=Cpn1+Cp'n2/n1+n2
 
1.5=1.66*n1+1.4n2/n1+n2
 
1.5n1+1.5n2=1.66*n1+1.4n2
 
therefore,
 
1/6n1=1/10n2
 
therefore,
 
n1/n2=3/5...
 
Hope it is correct.......
 
Please rate for my efforts....
 
Thanx....
 



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chirag (384)

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neeleshv, your formula is absolutely incorrect...

Hope you correct it, I have written it down....

But, btw atleast you gave it a try......

Hope you rate me........



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joyfrancis (1504)

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hi chirag
you have made a mistake you have taken Cp=1.66 which is wrong and the formula given by neeleshv is correct.

check my solution

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chirag (384)

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Joyfrancis you are absolutely wrong, Cp or Cv cannot be equal to 1.66, since it is in terms of R...
 
Neelshv's formula is also wrong....
 
I have corrected my answer, now it is absolutely correct... Initially I had made a mistake by not considering Cv in the denominator... My formula is absolutely correct.. Hope you check it in H. C. Verma....
 
Ans.:-n1/n2=1/2
 
Soln.:-
 
mix=Cpn1+Cp'n2/Cvn1+Cv'n2
 
For monoatomic gas, Cp=2.5R, Cv=1.5R
For Diatomic gas, Cp'=3.5R, Cv'=2.5R
 
1.5=2.5R*n1+3.5Rn2/1.5Rn1+2.5R' 2
 
4.5n1+7.5n2=5*n1+7n2
 
therefore,
 
0.5n1=0.5n2
 
therefore,
 
n1/n2=1/1........
 
Please rate for my efforts....
 
Thanx....



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Anjishnu (25)

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so can't we use the formula mix=(1n1 + 2n2)/(n1+n2)
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srini (395)

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hey........
Did you get the formula by just using cp=cp1*n1+cp2*........

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joyfrancis (1504)

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hey chirag
how did you get this gamma=Cpn1+Cp'n2/n1+n2...can you please explain

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magiclko (4215)

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joyfrancis is absolutely correct... nd the formula given by neeleshv is also correct... joyfrancis has given the proof...
chirag how have u got that formula... pls enlighten us too....

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chirag (384)

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Anjishnu,
mix=(1n1 + 2n2)/(n1+n2), this formula is absolutely wrong.....
correct formula is ,
mix=Cpn1+Cp'n2/Cvn1+Cv'n2
 
Joyfrancis, initially, I had made a mistake by not considering Cv in the denominator....
Sorry, it' was my mistake, but i have posted the corrected soln already.....
 
Magiclko,regarding the proof can you please refer H. C. Verma part II page 75 Solved example 10...
I will not be able to write the whole proof due to typing constraints....Please co-operate... If still you are unable to g