HW 3

[Ashveen Tewarie]

You guys already started with Ex. 9.1? I did sth and the final answer
I get does not differ much from the text. To determine the total
pressure the molar mass of the mixture is needed I guess. Any idea how
to determine this? Thanks!

[Josh Duckett]

I haven't started it yet - planning to start it today. I'll let you know if
I work anything out. Any big troubles with other problems?

Josh

[Josh Duckett]

I am getting a larger partial pressure than what is in the book. I am getting 473520 dyn/cm2. Is that what you got Ashveen?
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[Ashveen Tewarie]

Josh,
That's not the answer I've got. But I have already solved this
problem. Let me try to explain what I did.
Given: rho (total) =1 kg/(m^3) = rho1 + rho2, where "1" refers to O
and "2" refers to O2.

Now the eqn for Kp: Kp = (P1)^2/P2. You should now substitute for P1=
(rho1) (R/M1) T and P2= (rho2)*(R/M2) T, where R is the universal gas
constant
(R= 8.314 kJ/kmol K) and M1 and M2 are molecular or atomic weights.
Now the eqn for Kp (Kp is given) will result in an eqn that looks like
(rho1)^2/ rho2 = some Number. Thus you now have 2 eqns ( one for Kp
and one for rho_total) and 2 unknowns (rho1 and rho2). You can solve
for rho1 and get the partial pressure from P1= (rho1)* (R/M1)*T. Hope
this helps. I am now terribly stuck with 9.2 (b). The thing we should
prove seems kinda dreadful. i have written the eqn. for Kp for this
problem but i don't have a clue how to proceed.

[Josh Duckett]

Yea that's what I'm doing. I went through my work again and found a
calculation error but I'm still getting Po = 480134 dyn/cm^2. What
did you get for Rho for monatomic O? I'm using a conversion I found
online for dyne/cm^2 - I found that 1 dyne/cm^2 = 0.1 N/m^2 - is that
what you are using? I got rho_O = 0.0154 kg/m^3

Josh

[Josh Duckett]

I've gotten part of the way there for Part B. I've gotten the first
term and the P portion of the last term. I'm not sure how to
manipulate the remainder of my equation to get the 2nd term we are
supposed to end up with and the numerator of the last term.

The Kp equation will have partial pressures for 1,2,3 and 4. For each
of those you can write the partial pressure as X_n*P where P is the
total pressure, X_n is mole fraction and n=1,2,3 or 4. For
instance...

P1 = X1*P
P1 = (alpha1/(alpha1+alpha2))*P

I'm not sure if the denominator is correct or if it should include all
4 components. I think its correct that the alpha mole fractions only
have alpha in denominator and beta have only beta in denominator since
its an equilibrium and they will be going back and forth between alpha
and beta molecules. Manipulating those equations will get the first
and P portion of last terms of the proof. Incorporating the delta
with the remaining terms should finish out the proof but I haven't
worked on that yet.

Is delta* the same as delta?

[Ashveen Tewarie]

I'm getting rho_O = 0.02 kg/m^3 and I am close to the answer of the
text....
Did you use the correct Molar weights? (32 for O2 and 16 for O)

I did not have a chance to look at 9.2 b again. I will check this one
later on today. I actually started with the last Ex. (on page 85 I
guess) and the answer I get is twice the result of what the text
gives.

Delta* is the value of delta at equilibrium.

[Josh Duckett]

I figured out my error for 9.1. I'm confused on the Kp we are using in this
class. I took a fluid dynamics of combustion class last semester and we had
Kp values that are unitless and the values weren't nearly as small as we are
being given. I also took the Van't Hoff's equation and integrated it then
plugged in the values that problem 10.2 gave for deltaH, T and Kp and they
don't match if you plug them into van't Hoff's equation. Am I missing
something?

I haven't gotten any further with 9.2b. I emailed Dr. Hassan about it and
he said my mole fractions were set up wrong so I'm not sure how they should
be set up. He said the mole fraction would be based on the total number of
moles that exist in a given instant.

-----Original Message-----
From: mae...@googlegroups.com [mailto:mae...@googlegroups.com] On Behalf
Of Ashveen Tewarie

[Ashveen Tewarie]

Josh,

we should use van 't Hoff's eqn to determine Kp at the required
temperature. After integrating I get Kp = 1.7822E-12.
With this and species conservation you can get "ksi". The value of
"ksi" I'm getting is 0.5 x the value given in the text.

[Ashveen Tewarie]

Sorry, it should be Kp = 1.7822E-8

[Josh Duckett]

Thanks...my dad is having a medical emergency so I won't be responding for the next few days...didn't want to leave you all hanging

Josh

Sent from my Verizon Wireless BlackBerry

-----Original Message-----
From: Ashveen Tewarie <ashv...@gmail.com>
Date: Tue, 2 Mar 2010 04:20:45
To: MAE 562<mae...@googlegroups.com>

[Ashveen Tewarie]

Okay, wish you and your dad all the best. Take care;)

[Josh Duckett]

Thanks ashveen...I really appreciate it

Sent from my Verizon Wireless BlackBerry

-----Original Message-----
From: Ashveen Tewarie <ashv...@gmail.com>
Date: Tue, 2 Mar 2010 10:59:31
To: MAE 562<mae...@googlegroups.com>
Subject: Re: HW 3

[Josh Duckett]

Dr. Hassan gave me an extension until tomorrow - for problem 10.2 I
am getting Kp values 6 orders to small... for instance I got Kp =
1.75x10^-14 rather than 10^-8. Did you have that problem?

[Josh Duckett]

How did you set up your Kp equation to get the final number of moles
of H2O in the system? Is that what you did - use Kp to solve for
N_H20 since we already know initial value for N_H20 then use equation
3.5 to get the degree of advancement?

[Ashveen Tewarie]

That looks like a very small Kp... I got 1.78x(10^-8).
When integrating van t Hoff you have: ln(Kp2) - ln(Kp1) = -(H/R)*[(1/
T2) - (1/T1)]
Solving this should give Kp2.

[Ashveen Tewarie]

You should write the eqn. for Kp in terms of partial pressures first.
Than rewrite each partial pressure in terms of P of mixture (which is
given). The example we did in class for H2 and I2 will be helpful.
ALso use the eqn for species conservation. Keep in mind that P of mix
is given! You will end up with 3 eqns:

The eqn for Kp, species conservation and N = SIGMA (Ni). You can now
slove for the number of moles of H2O at equilibrium and determine
"ksi" to get the answer the text gives. Hope this helps

[Josh Duckett]

Thanks ashveen.

Sent from my Verizon Wireless BlackBerry

-----Original Message-----
From: Ashveen Tewarie <ashv...@gmail.com>
Date: Thu, 4 Mar 2010 06:05:52
To: MAE 562<mae...@googlegroups.com>
Subject: Re: HW 3