S = n(C2H4) / n(C3H6) It was given that selectivity is 5 of ethylene to propylene, so S = 5. Ethylene is a produce in the first equation, and propylene is a product in the second equation. This means that the first equation produces 5 times more mols than the second equation. 5 = (S1 - S2) / S2 then just by looking at that you can pick some numbers that make that true, so the simplest ones are S1 = 6, and S2 = 1 therefor, S1 = 6*S2 If I am wrong someone correct me please, this is my guess after they skipped a lot of steps :(
My textbook, "Elementary Principles of Chemical Processes, 4th edition, Felder" indicates that the extent of reaction is dimensionless. My professor along with class thought this must of been a mistake, but he contacted the author, and was convinced that it is in fact, dimensionless. Will it mess me up to assume that there is a unit? I don't see why it would be unitless, because saying the extent of reaction is 30, doesn't really tell us anything
There should be a unit as firstly the equation is: moles out = moles in + (stoichiometric coefficient x extent of reaction)... Now any equation where you are adding or subtracting two variables to give another, they all have to have the same units. If the extent of reaction was dimensionless you could not add it to the amount of moles in which would have units of moles or moles per unit time etc. Best way to think of it and it'd help you further on in Chemical Engineering is any two things added together have to have the same units and it's one thing my professor has stressed to pay attention to the units it can help you solve problems and avoid silly mistakes.
Unfortunately, no, because the Extent of Reaction Method is used using stoichiometric ratios (the reason there is a 2 in front of zai 2 etc.) and the only time we can use stoichiometric ratios is when we work in moles (n), or at least thats what my book says!
Hey, how you see that the extent of reaction 1 is 6 times exent reaction of 2? How do you find £1? I dont understand how you go from S=£1-£2/£2 to £1=6£2
We know that n(C2H6) = 100 - £1 - £2 And from fractional conversion we find n(C2H6) as 30 Then, substituting we get ¹ £1 + £2 = 70 Now, how I've done it is that we know the selectivity is 5 then n(C2H4) / n(C3H6) = 5 n(C2H4) = 5* n(C3H6) = 5* £2 (From C3H6 Balance) We substitute this in C2H4 Balance so we get 5*£2 = £1 - £2 >> 6*£2 = £1 Going back to our first equ we substitute to get £1 + £2 = 70 >>> 7*£2 = 70 After that, you have found extent of 2nd rection, you use it to fing 1st and then everything else. Sorry for being late
I'd like to know why we cant just simply do this: There's 5 moles of ethylene forming for every mole of propylene. We know that a total of 70 moles of ethane reacts. So we can just do 5/6 x 70 = moles of ethylene formed and 1/6 x 70 for the moles of propylene formed?
Great question. In this case, the ethylene is also a reactant in the second equation, so some of what is produced is also consumed. That is why it becomes a bit more difficult and you need to go through these steps. Thanks for the question!
9 hours in class on this and this video taught me more in 8 minutes. Super good video!
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thank you for all your work. These videos are helping me a great deal.
I missed this stuff...i wish all mass balance questions were this easy. Extent of reaction approach is definitely easier than the black box.
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This is Perfect and straight to the point...thank you♡
how did we get that 6?
S = n(C2H4) / n(C3H6)
It was given that selectivity is 5 of ethylene to propylene, so S = 5. Ethylene is a produce in the first equation, and propylene is a product in the second equation. This means that the first equation produces 5 times more mols than the second equation.
5 = (S1 - S2) / S2
then just by looking at that you can pick some numbers that make that true, so the simplest ones are S1 = 6, and S2 = 1
therefor,
S1 = 6*S2
If I am wrong someone correct me please, this is my guess after they skipped a lot of steps :(
I so appreciate this work !!
hi, if theres a recycle stream will na0 be the fresh feed or the amt entering reactor ie including recycle
Very good video. Thank you.
My textbook, "Elementary Principles of Chemical Processes, 4th edition, Felder"
indicates that the extent of reaction is dimensionless. My professor along with class thought this must of been a mistake, but he contacted the author, and was convinced that it is in fact, dimensionless. Will it mess me up to assume that there is a unit? I don't see why it would be unitless, because saying the extent of reaction is 30, doesn't really tell us anything
There should be a unit as firstly the equation is: moles out = moles in + (stoichiometric coefficient x extent of reaction)... Now any equation where you are adding or subtracting two variables to give another, they all have to have the same units. If the extent of reaction was dimensionless you could not add it to the amount of moles in which would have units of moles or moles per unit time etc. Best way to think of it and it'd help you further on in Chemical Engineering is any two things added together have to have the same units and it's one thing my professor has stressed to pay attention to the units it can help you solve problems and avoid silly mistakes.
My professor said something like this. He was talking about the unit going on the stoichiometric coefficient in front of the extent of reaction.
why is initial C2H4 canceled out from the second equation? I dont understand that.
Thanks for the question. It is marked out because that is the term for how much C2H4 we started with, which was zero.
@@LearnChemE Appreciate your time, thank you!
Thanks this was a helpful video
Can you use the same equation for mass flow?
Unfortunately, no, because the Extent of Reaction Method is used using stoichiometric ratios (the reason there is a 2 in front of zai 2 etc.) and the only time we can use stoichiometric ratios is when we work in moles (n), or at least thats what my book says!
How to find the degrees of freedom?
Try this video: ua-cam.com/video/tW1ft4y5fQY/v-deo.html
nice video
very helpful , thanks :)
WOW What does he tell right now?
Thx very mush
Hey, how you see that the extent of reaction 1 is 6 times exent reaction of 2? How do you find £1? I dont understand how you go from S=£1-£2/£2 to £1=6£2
We know that
n(C2H6) = 100 - £1 - £2
And from fractional conversion we find n(C2H6) as 30
Then, substituting we get
¹ £1 + £2 = 70
Now, how I've done it is that we know the selectivity is 5 then
n(C2H4) / n(C3H6) = 5
n(C2H4) = 5* n(C3H6) = 5* £2 (From C3H6 Balance)
We substitute this in C2H4 Balance so we get
5*£2 = £1 - £2 >> 6*£2 = £1
Going back to our first equ we substitute to get
£1 + £2 = 70 >>> 7*£2 = 70
After that, you have found extent of 2nd rection, you use it to fing 1st and then everything else.
Sorry for being late
Pardon me ?
I'd like to know why we cant just simply do this: There's 5 moles of ethylene forming for every mole of propylene. We know that a total of 70 moles of ethane reacts. So we can just do 5/6 x 70 = moles of ethylene formed and 1/6 x 70 for the moles of propylene formed?
Great question. In this case, the ethylene is also a reactant in the second equation, so some of what is produced is also consumed. That is why it becomes a bit more difficult and you need to go through these steps. Thanks for the question!
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