Intro to ICE Tables
PCl5, has a Ka of 6.8 x 10-4
What are the [PCl5], [PCl3] , and [Cl2] in 0.75M PCl5?
So, How Much Do We
Really Have?
Equilibrium Expressions and ICE
Tables
PCl5(g) ! PCl3(aq) + Cl2 (aq)
Molarity
PCl5 (aq) PCl3 (aq)
I
Initial concentration
C
Change in concentration
E
Equilibrium concentration
Another ICE Table
Intro to ICE Tables
PCl5, has a Ka of 6.8 x 10-4
What are the [PCl5], [PCl3] , and [Cl2] in 0.75M PCl5?
PCl5(g) ! PCl3(aq) + Cl2 (aq)
Molarity
PCl5 (aq) PCl3 (aq)
Cl2(aq)
I
0.75
0
0
C
-x
+x
+x
E
0.75 - x
x
x
(x)(x)
(0.75 - x)
=
x2
(0.75-x)
x2 + (6.8 x 10-4)x – (5.1 x 10-4) = 0
[PCl5] = 0.728
Calculate the final concentrations of the products and reactants
when 0.044M H2 mixes with 0.044M I2. (Ka = 0.16)
H2 + I2 ! 2 HI
Molarity
H2
I
0.044
C
-x
E
0.044 - x
Let “x” = the concentration
of PCl5 that dissociates
Ka =
Cl2(aq)
[Cl2]
[PCl3]
[PCl5]
= 6.8 x 10-4
Keq =
HI
I2
0.044
0
-x
+2x
2x
0.044-x
[HI]2
[H2] [I2]
0.16 =
[2x]2
[0.044 – x]2
3.84x2 + 0.014x – 3.10x10-4 = 0
x = 0.022 M
[Cl2] = [PCl3] = 0.022
x = -0.011 or x = 0.0073
-0.011 does not make sense because a negative “x”would mean the addition of reactants
[H2] = [I2] = 0.044 – 0.0073 = 0.0367
[HI] = 2 (0.0073) = 0.0146
Percent Dissociation
Calculate the percent dissociation of 0.050M HCH3CO2
HCH3CO2(aq) + H2O(l) ! H+(aq) + CH3CO2- (aq)
Ka = 1.8 x 10-5
Percent Dissociation
A 0.735M solution of a weak acid is 12.5% dissociated. What are the
[H3O+], [A-], and [HA] at equilibrium?
Let x = [HCH3CO2] that dissociates
Molarity
HCH3CO2 (aq)
[H
CH3CO2-(aq)
Molarity
HA (aq)
H+(aq)
A-(aq)
[HA] that dissociates =
I
0.050
0
0
I
0.735
C
-x
+x
x
+x
C
-0.0919
+ 0.0919
+ 0.0919
(0.735M)(0.125)
x
E
0.6431
0.0919
0.0919
= 0.0919 M
0.050 - x
E
Ka =
H+(aq)
HA(aq) + H2O(l) ! H+(aq) + A- (aq)
[CH3CO2-]
[CH3CO2H]
x = 9.5 x
10-4
=
(x)(x)
(0.050M - x)
=
0.050M
0
x2
= 1.8 x 10-5
0.050M - x
M = concentration of CH3CO2H dissociated
9.5 x 10-4 M
0
[HA] = 0.735 – 0.0919 = 0.6431 M
[H+] = [A-] = 0.0919 M
X 100 = 1.9% dissociated
In-Class Work for Quiz 2
Reaction Mechanism Questions
Reaction Mechanism Problems
Reaction Mechanisms-1
Le Châtelier’s Principle
Le Châtelier’s Principle Questions
Using Equilibrium Expressions
Equilibrium Questions 1
Due the Next Class
Time to Practice!
Equilibrium
Calculations