4 replies to this topic

[Gilnaz Pourhossein]

Hi

Can anybody please help me to find fugacity of n-Butane using the following formula:

p = 5 pa      and      T = 500° k

pv = 4155.8 - 209.9p - 5.186p² - 1.448p³ + 0.2079p⁴

I have tried to solve it using the following way but couldn't manage to do so:




any help is appreciated 

Regards

[MrShorty]

A couple of observations:

 

You take your pv=expression, appear to say that you are going to divide it by RT to get an expression for z. Then you divide the pv= expression by p to solve it for v, but call it z. You might check these steps carefully to make sure you are assigning the expression to the right variable.

 

In your integration, your integrand is (v-RT/p)dp. In the next step, you substitute v into the integrand. I observe that you seem to have left out the -209.9 term from the expression for v or z, and also neglect to include the -RT/P term.

 

Does that help?

[Gilnaz Pourhossein]

A couple of observations:

 

You take your pv=expression, appear to say that you are going to divide it by RT to get an expression for z. Then you divide the pv= expression by p to solve it for v, but call it z. You might check these steps carefully to make sure you are assigning the expression to the right variable.

 

In your integration, your integrand is (v-RT/p)dp. In the next step, you substitute v into the integrand. I observe that you seem to have left out the -209.9 term from the expression for v or z, and also neglect to include the -RT/P term.

 

Does that help?

Dear Mr/Mrs

 

Thanks for ur valuable help......

 

I have made some corrections and what I've got is as follow:

 

 

 

 

but I'm still not able to get the final result.....

 

any other tips to make me clear how to get the final result would be a great help to me.....

 

 

Thank you in advance....

[Mahdi1980]

gpn123

 

You have derived the last term of integral wrong. It is not RT/P². It is RTln P since the integral of RT/P dP is RT ln P.

Ok?

And if you replace the values of R (8.314) and T (500 K) in the result equation you can see that the first term of ln P and the last term that have lnP will be omitted since 4155.8 lnp/(8.314*500) = lnP so lnP- lnP =0

The remaining items are determined by replacing P=5 pa

So ln (fi)= -0.275

fi= exp( -0.275) =0.76

 

if you have a question please ask

 

Mahdi

[Gilnaz Pourhossein]

gpn123

 

You have derived the last term of integral wrong. It is not RT/P². It is RTln P since the integral of RT/P dP is RT ln P.

Ok?

And if you replace the values of R (8.314) and T (500 K) in the result equation you can see that the first term of ln P and the last term that have lnP will be omitted since 4155.8 lnp/(8.314*500) = lnP so lnP- lnP =0

The remaining items are determined by replacing P=5 pa

So ln (fi)= -0.275

fi= exp( -0.275) =0.76

 

if you have a question please ask

 

Mahdi

 

Dear Mahdi

 

Dorood

 

I was a bit foggy by the time i was solving this equation since it was almost twilight. Reading your post was like all the fog has lifted.

 

Thanks for all those explanations.....

 

Bedrood.....