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Equilibrium Law Calculations

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... small we can use a simplification to make calculating x simple ... Setting up the RICE chart is the same, but the calculation of Kc is now slightly different ... – PowerPoint PPT presentation

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Title: Equilibrium Law Calculations


1
Equilibrium Law Calculations
  • (with RICE charts)

2
Example 14.7 - pg. 567 H2 I2 ? 2HI
  • Read 566 (from Calculating Kc) to 568. Follow
    the sample calculation carefully.

H2
I2
HI
1
1
2
0.100
0.100
0
-0.08
-0.08
0.16
0.02
0.02
0.16
Ratio, Initial, Change, Equilibrium
64
3
PE 9 - pg. 568 PCl3 Cl2 ? PCl5
PCl3
Cl2
PCl5
1
1
1
0.2
0.1
0
-0.08
-0.08
0.08
0.12
0.02
0.08
Ratio, Initial, Change, Equilibrium
33.3
Q - Try 14.38, 14.39 pg. 589
4
RE 14.38 - pg. 589 2HBr ? H2 Br2
HBr
H2
Br2
2
1
1
0.500
0
0
0.130
0.130
-0.260
0.240
0.130
0.130
0.293
5
RE 14.39 - pg. 589 CH2O ? H2 CO
CH2O
H2
CO
1
1
1
0.100
0
0
-0.020
0.020
0.020
0.020
0.020
0.080
0.0050
6
14.9 - pg. 570 CO H2O ? CO2 H2
  • Read 570-1. Follow sample calculation carefully.

CO
H2O
CO2
H2
1
1
1
1
0.100
0
0
0.100
-x
-x
x
x
0.10 - x
0.10 - x
x
x
4.06
x/0.10-x 2.01, x 0.201-2.01x, 3.01x
0.201 x0.0668
PE 11, 14.40, 14.41 pg. 589 (notice for 14.41)
7
PE 11 - pg. 571 H2 I2 ? 2HI
H2
I2
HI
1
1
2
0.200
0.200
0
-x
-x
2x
0.2 - x
0.2 - x
2x
49.5
2x/0.2-x 7.04, 2x 1.408-7.04x, x0.156
H2 (I2 also) 0.2 - 0.156 0.044 M
HI 2(0.156) 0.312 M
8
14.40 - SO3 NO ? NO2 SO2
SO3
NO
NO2
SO2
1
1
1
1
0.150
0
0
0.150
-x
-x
x
x
0.15 - x
0.15 - x
x
x
0.50
.707x/0.15-x, 0.106-0.71xx, x0.062
SO3, NO 0.15 - 0.062 0.088 M
NO2, SO2 0.062 M
9
14.41 - CO H2O ? CO2 H2
CO
H2O
CO2
H2
1
1
1
1
0.010
0.010
0.010
0.010
x
x
-x
-x
0.01x
0.01x
0.01 - x
0.01 - x
0.40
.6325(0.01-x)/(0.01x), x0.00225
CO, H2O 0.010 0.00225 0.0123 M
CO2, H2 0.010 - 0.00225 0.0078 M
10
Equilibrium calculations when Kc is very small
  • Thus far, problems have been designed so that the
    solution for x is straightforward
  • If the problems were not so carefully designed we
    might have to use quadratic equation (or
    calculus) to solve the problem.
  • If Kc is very large or very small we can use a
    simplification to make calculating x simple
  • Setting up the RICE chart is the same, but the
    calculation of Kc is now slightly different
  • Read pg. 572, 573

11
Equilibrium calculations when Kc is small
  • Looking at the equilibrium law for 14.10

4x3
small Kc
0.100 - 2x2
For Kc to be small, top must be small, bottom
must be large (relative to top) For top to be
small, x must be small If x is small, then 0.100
- 2x ? 0.100 Notice that we can only ignore x
when it is in a term that is added or
subtracted. Can we ignore x in 4x, 3x, 0.1-3x,
3x-x, x21?
We can for these
?
?
?
Try PE 12 (573). Concentrations are initial.
12
PE 12 - pg. 573 N2 O2 ? 2NO
N2
O2
NO
1
1
2
0.033
0.00810
0
-x
-x
2x
0.033-x
0.00810-x
2x
4.8 x 10-31
13
PE 12 - pg. 573 N2 O2 ? 2NO
4.8 x 10-31
  • Small Kc Thus numerator is small and x must be
    small x is negligible when adding or subtracting

4.8 x 10-31
2x2
1.28 x 10-34
2x
1.13 x 10-17
This is the equilibrium NO2
14
2HCl ? H2 Cl2 Kc 3.2 x 1034 determine
equil, if initial are 2.0 M, 1.0 M, 0 M
HCl
H2
Cl2
2
1
1
2
1
0
x
x
-2x
2-2x
1x
x
3.2 x 1034
x (3.2 x 1034)(4) 1.3 x 1033 equil are 2,
1 and 1.3 x 1033
15
RE 14.42 - pg. 590 2HCl ? H2 Cl2
HCl
H2
Cl2
2
1
1
2
0
0
x
x
-2x
2-2x
x
x
0.293
16
2Na 2H2O ? 2NaOH H2
Na
H2O
NaOH
H2
2
2
2
1
0.100
0
0
0.100
-2x
-2x
2x
x
0.10-2x
0.10-2x
2x
x
0.10-2x2 0.10-2x2
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