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Excelet

Using "Solver" to Solve Equilibrium Calculations

Objective: To be able to easily solve higher-order polynomials

Beware of the behavior of polynomials and the number of roots or solutions!

In chemistry, there is only one correct root for an equilibrium problem!!!

So before using the Solver, get the solution via guessing close to the value.

If you play long enough you will get the value of x by guessing!!!

To use this Excelet, Solver must be loaded in Excel.

Click on the tabs to navigate!!!

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Haber Process Equilibrium

guess

(N2)eq x = K = 4.34E-03

This is a quartic equation! (N2)o= 1 K = (NH3)2/(N2)(H2)

3

initial concentrations

(H2)o= 1

left-side right-side

0.00434

equilibrium concentrations:

(N2)eq= ICE chart

(H2)eq=

(NH3)eq=

calculated K =

from equilbrium concentrations

The formulas on this wooksheet only have named variables!

Sinex 2008

2 2 3

2

3

3

2 2

2

3

2 o 2 o

N + 3H 2NH

(NH )K =

(N )(H )

(2x)K =(N ) - x (H ) - 3x

http://academic.pgcc.edu/~ssinexhttp://academic.pgcc.edu/~ssinex

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Sulfur Oxides Equilibrium

guess

(SO3)eq x = K = 5

This is a cubic equation! (SO2)o= 1 K = (NH3)2/(N2)(H2)

3

initial concentrations

(O2)o= 1

left-side right-side

5

equilibrium concentrations:

(SO2)eq= ICE chart

(O2)eq=

(SO3)eq=

calculated K =

from equilbrium concentrations

Sinex 2008

2 2 3

2

3

2

2 2

2

2

2 o 2 o

2SO + O 2SO

(SO )K =

(SO ) (O )

(x)K =(SO ) - x (O ) - 0.5x

http://academic.pgcc.edu/~ssinexhttp://academic.pgcc.edu/~ssinex

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Decomposition of PCl5

guess

(PCl3)eq= (Cl2)eq x = K = 4.0E-03

This is a quadratic equation! initial concentration (PCl5)o= 0.5

left-side right-side

0.004

equilibrium concentrations:

(PCl5)eq= ICE chart

(PCl3)eq=

(Cl2)eq=

calculated K =

from equilbrium concentrations

Sinex 2008

5 3 2

3 2

5

5 o

PCl PCl + Cl

(PCl )(Cl )K =

(PCl )

(x)(x)K =(PCl ) -x

http://academic.pgcc.edu/~ssinexhttp://academic.pgcc.edu/~ssinex

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To use Solver: The Solver must be loaded as an add-in in Excel to function!!!

Click on Solver

Solver Parameters are pre-set

except for the value of K.

Excel 2007 - Solver is on the Data tab.

Sinex 2008

left-side

guess cell

right-side

http://academic.pgcc.edu/~ssinexhttp://academic.pgcc.edu/~ssinex

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How to set this up to solve the equation

1. The blue arrowsshow which cells or values feed into the right-side formula:

The left-side is The right-side is the

the value of K expression equal to K

and is just reading

that value in here.

2. Here are the cell references that go into the Solver Parameters:

Solver is going to vary the value of the guess cell (x),

which feeds into the right-side equation, until it gets

the right-side to equal the left-side.

Sinex 2008

select value of

K or left-side

place the guess cell here

right-side

http://academic.pgcc.edu/~ssinexhttp://academic.pgcc.edu/~ssinex