to use Solver by dandanhuanghuang

VIEWS: 2 PAGES: 8

									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!!!
Haber Process Equilibrium
                                           guess                                          N 2 + 3H 2                     2NH 3
                 (N2)eq           x=                                      K = 4.34E-03

                                                                                                           (NH 3 )2
    This is a quartic equation!                                       (N2)o =    1            K = (NH =/(N )(H )
                                                                                                   K)
                                                                                                    3
                                                                                                        2
                                                                                                             2   2
                                                                                                                     3


                                          initial concentrations                                         (N 2 )(H 2 )3
                                                                      (H2)o =    1

                                                                                                                 (2x)2
                           left-side     right-side                                      K=                                      3
                           0.00434
                                                                                              (N 2 )o - x  (H 2 )o - 3x 
                                                                                                                        
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
Sulfur Oxides Equilibrium
                                           guess                                         2SO2 + O2                  2SO3
               (SO3)eq             x=                                     K=    5

                                                                                                       (SO3 )2
     This is a cubic equation!                                       (SO2)o =   1        K = (NH =/(N )(H )
                                                                                               K)
                                                                                               3
                                                                                                   2
                                                                                                        2   2
                                                                                                                3


                                          initial concentrations                                    (SO2 )2 (O2 )
                                                                      (O2)o =   1

                                                                                                            (x)2
                         left-side       right-side                                 K=                      2
                               5
                                                                                         (SO2 )o - x  (O2 )o - 0.5x 
                                                                                                                    
equilibrium concentrations:
                          (SO2)eq =                                ICE chart


                              (O2)eq =


                          (SO3)eq =


           calculated              K=
 from equilbrium concentrations




                                                                                                       Sinex 2008
Decomposition of PCl5
                                            guess                                           PCl 5          PCl 3 + Cl 2
       (PCl3)eq = (Cl2)eq          x=                                      K=     4.0E-03

                                                                                                     (PCl 3 )(Cl 2 )
   This is a quadratic equation!            initial concentration     (PCl5)o =     0.5        K=
                                                                                                       (PCl 5 )
                                                                                                        (x)(x)
                            left-side     right-side                                            K=
                             0.004                                                                    (PCl 5 )o -x
equilibrium concentrations:
                             (PCl5)eq =                             ICE chart


                             (PCl3)eq =


                              (Cl2)eq =


           calculated              K=
 from equilbrium concentrations




                                                                                                      Sinex 2008
Water Gas Equilibrium                                              Let's consider this reaction from either the reactant side or product side or both!
                                           guess
       C (to the right)             x=    -0.30662
                              You may want to guess x < 0
                                                                           K=       1.2
                                                                                                    CO + H 2O                       H 2 + CO2
       C' (to the left)             x = 0.306624                       (CO)o =       1
                                                                                                                       (H 2 )(CO2 )
                                          initial concentrations                                               K=
  This can be a messy quadratic!                                     (H2O)o =        0                                 (CO)(H 2O)
                          left-side      right-side                    (H2)o =       1
                              1.2           1.2                                                           How is this reaction going to shift?
                                                                      (CO2)o =       1
equilibrium concentrations:
                            (CO)eq = 1.306624
                                                                   ICE Chart
                          (H2O)eq = 0.306624
                                                                   This is an interesting reaction because K ~ 1.
                              (H2)eq = 0.693376                    We will try playing with it from just adding reactants
                                                                   or just adding products and adding both. Hence, the shift
                           (CO2)eq = 0.693376                      of the reaction could be to the right or to the left.


           calculated               K=      1.2                    When the x value goes negative, it is like multiplying
 from equilbrium concentrations                                    the C line in the ICE chart by -1, so you get
                                                                   the C' line for a shift to the left,




                                                                                                                      Sinex 2008
side or both!
To use Solver:                     The Solver must be loaded as an add-in in Excel to function!!!



                                                                         right-side                 left-side




                                                                  guess cell




                     Click on Solver…
             Solver Parameters are pre-set
                except for the value of K.



Excel 2007 - Solver is on the Data tab.




                                                                                                                Sinex 2008
How to set this up to solve the equation

1. The blue arrows show 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:



                           right-side                       K or left-side


                                          select value of
             place the guess cell here




                       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

								
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