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Re: simultaneous equations for chemical speciation

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  • Subject: [mg100222] Re: simultaneous equations for chemical speciation
  • From: dh <dh at>
  • Date: Thu, 28 May 2009 06:50:27 -0400 (EDT)
  • References: <gvk9v0$ono$>

Hi Jem,

First, the equation:






do not add any information because they only introduce a new variable 

that does not appear anywhere else. This leaves 3 equations:




Multiplying the first 2 gives the third. Therefore, we actually have 2 




These do not have a general solution. Only under special circumstances 

we get a solution. For this problem we have Reduce. Therefore, you get 

possible solutions by:

Reduce[{h == c/(b*g), i == d/(c*g)}, {g}]


Jem & Tracy wrote:

> Hi, I am a postgrad student and completely new to mathematica, I am just 

> starting to realise the possibilities.


> I am trying to do a chemical speciation calculation.

> I have a set of simultaneous equations which represents the equilibria, 

> mass balance, and charge balance in the system.


> I want to eliminate some of the variables, and then be able to solve for 

> the remaining ones.

> My system of equations looks like this:

> a=b+c+d

> e=f+g+c+2d

> h=c/(bg)

> i=d/(cg)

> hi=d/(bg^2)

> j=mg/f

> k=lm

> n+m+b+c=g+l


> Basically, I can solve for the variable I want, but I am having trouble 

> eliminating the ones I don't want (ie. I am getting an answer that is in 

> terms of the wrong variables)

> Sofar my formula looks like:


> Solve[{a == b + c + d, e == f + g + c + 2 d, h == c/(b*g),

>   i == d/(c*g), h*i == d/(b*g^2), j == m*g/f, k == l*m,

>   n + m + b + c == g + l}, {g}]


> If I use a similar formula for the "Eliminate" function, I get error 

> mesages.


> I have been in the help files for ages, and don't really understand how 

> to do this.

> I would really appreciate some pointers!!

> Thanks



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