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Combustion

Posted 21 dic 2016, 10:50 GMT-5 Chemical Reaction Engineering, Studies & Solvers 5 Replies

Net One
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Can anyone help?

Calculate the equilibrium composition for the reaction H2O to H2 + ½ O2 for the
ratios on n(H)/n(O) = 1.5. The temperature is 2500K, and the pressure is 3 atm.

I have done it for n(H)/n(O) = 2, which was much easier as H20 cancelled out however cannot do it with a ratio of 1.5.

Thanks
5 Replies Last Post 22 dic 2016, 15:18 GMT-5
Lasse Murtomäki
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Posted: 8 years ago 22 dic 2016, 02:49 GMT-5
Three variables: n(H2), n(O2), n(H2O)
Three constraints:
1. Ideal gas law for the total amount nTOT = n(H2) + n(O2) + n(H2O); p·V = nTOT·R·T
2. n(H)/n(O) = 1.5
3. Reaction equilibrium constant.

The rest is algebra. (Ideal gas law applies very well in your conditions.)

Best wishes
Lasse
Three variables: n(H2), n(O2), n(H2O) Three constraints: 1. Ideal gas law for the total amount nTOT = n(H2) + n(O2) + n(H2O); p·V = nTOT·R·T 2. n(H)/n(O) = 1.5 3. Reaction equilibrium constant. The rest is algebra. (Ideal gas law applies very well in your conditions.) Best wishes Lasse
Net One
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Posted: 8 years ago 22 dic 2016, 07:04 GMT-5
How exactly do I use the equation p·V = nTOT·R·T for this since we are not given any volume.
Do I have to find the volume and if so what do I do after finding that.
Very confused with this problem. Been stuck on it for 1 week now.

Many thanks
Net One
How exactly do I use the equation p·V = nTOT·R·T for this since we are not given any volume. Do I have to find the volume and if so what do I do after finding that. Very confused with this problem. Been stuck on it for 1 week now. Many thanks Net One
Dave Greve
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Posted: 8 years ago 22 dic 2016, 09:30 GMT-5
The problem you are describing is equilibrium thermochemistry. I don't have the Comsol reaction chemistry module but I have encountered this sort of problem in research on chemical vapor deposition.

This is a classic problem in chemical engineering. Briefly, if you know the standard free energy of all the species involved it's a matter of algebra. If there are only three possible components the algebra will be easy. (And you don't need a finite element application to solve).

However- at 2500 K there are lots of other possible species, sometimes present in very small concentrations. Do you care about atomic oxygen and hydrogen? Ozone? Molecular radicals?

Is this just a starting point for a chemical kinetics problem?

D W Greve
DWGreve Consulting


The problem you are describing is equilibrium thermochemistry. I don't have the Comsol reaction chemistry module but I have encountered this sort of problem in research on chemical vapor deposition. This is a classic problem in chemical engineering. Briefly, if you know the standard free energy of all the species involved it's a matter of algebra. If there are only three possible components the algebra will be easy. (And you don't need a finite element application to solve). However- at 2500 K there are lots of other possible species, sometimes present in very small concentrations. Do you care about atomic oxygen and hydrogen? Ozone? Molecular radicals? Is this just a starting point for a chemical kinetics problem? D W Greve DWGreve Consulting
Lasse Murtomäki
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Posted: 8 years ago 22 dic 2016, 11:24 GMT-5
I would take, say, 1 m3 volume.

But this is not a Comsol problem at all.

BR
Lasse
I would take, say, 1 m3 volume. But this is not a Comsol problem at all. BR Lasse
Dave Greve
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Posted: 8 years ago 22 dic 2016, 15:18 GMT-5
If you want only the answer to this particular problem, use the on-line calculator

www.crct.polymtl.ca/equiweb.php
If you want only the answer to this particular problem, use the on-line calculator http://www.crct.polymtl.ca/equiweb.php

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