Previously in Chem104

1

• Previously in Chem104
• A new chapter Equilibrium
• Writing equilibrium expressions
• observing LeChateliers Principle
• Calculating equilibrium constants, K

• TODAY
• A new wrinkle on Equilibrium
• Q

Q, from the Q continuum, Star Trek ,The Next
Generation No, not that Q ..
2

• TODAY
• A new chapter Equilibrium
• Writing equilibrium expressions
• observing LeChateliers Principle
• Calculating equilibrium constants, K

• TODAY
• A quick recap of Mondays concepts
• Magnitudes of Keq
• Q the reaction quotient
• Q how to use it

3
A quick recap on equilibrium expressions
For this reaction
Cu(H2O)62 Cl-
CuCl(H2O)5 H2O
But if reaction goes BOTH to right and to left,
which are reagents and which are products?
By convention reagents are species to the left
of arrow products are species to the right of
arrow
4
A quick recap on equilibrium behavior
5
A quick recap on equilibrium expressions
You watched
Cu(H2O)62 Cl-
CuCl(H2O)5 H2O
You wrote
CuCl(H2O)5
Keq
0.28
Cu(H2O)62Cl
When CuCl(H2O)5 0.8 M, Cu(H2O)62 0.4 M,
Cl 7.1M
You know
Pure liquids and solids dont appear in Keq
expression
6
Are Your Eyes Misleading You?
What is in the graduated cylinder?
Visible electronic spectra
7
Are Your Eyes Misleading You?
What is in the graduated cylinder?
Recall equilibrium concentrations
CuCl(H2O)5
0.8 M
Keq
0.28
0.4 M x 7.1M
Cu(H2O)62Cl
If Keq 1, product concentrations are
similar to reagent concentrations
8
How large must Keq be for reaction to be
complete?
Consider these reactions
Ni(H2O)62 6 NH3
Ni(NH3)62 6H2O
Keq
2.0 x 108
Ni(en)32 6 NH3
Ni(NH3)62 3 en
Keq
7.3 x 109
9
How large must Keq be for reaction to be
complete?
Consider this reaction
Ni(H2O)62 6 NH3
Ni(NH3)62 6H2O
Keq
2.0 x 108
10
What is Keq for this reaction ?
Ni(H2O)62 3 en
Ni(en)32 6 H2O
K1 2.0 x 108
Ni(H2O)62 6 NH3
Ni(NH3)62 6H2O
Ni(en)32 6 NH3
Ni(NH3)62 3 en
K2 7.3 x 109
K K1 x K2
Ni(H2O)62 3 en
Ni(en)32 6 H2O
K K1 x K2 (7.3 x 109)(2.0 x 108) 1.5 x
1018
11
This Keq seems huge! What is ratio of rgt. Ni
to prdt. Ni species
Ni(H2O)62 3 en
Ni(en)32 6 H2O
K 1.5 x 1018
12
What happens if the concentrations are equal
CuCl(H2O)5 0.8 M, Cu(H2O)62 0.8 M, Cl
0.8M
for this reaction
Cu(H2O)62 Cl-
CuCl(H2O)5 H2O
You investigate by calculation
CuCl(H2O)5
0.8 M
1.25
Cu(H2O)62Cl
0.8 M x 0.8 M
But you know Keq 0.28 ? 0.8 what does this
mean?
Its not at equilibrium!!
13
So under these concentration conditions
CuCl(H2O)5 0.8 M, Cu(H2O)62 0.8 M, Cl
0.8M
CuCl(H2O)5
1.25 gt 0. 28 Keq
Cu(H2O)62Cl
This tells you one definite thing theres too
much in numerator, or, theres too much product
How will reaction system species behave?
Cu(H2O)62 Cl-
CuCl(H2O)5 H2O
CuCl(H2O)5 decreases, Cu(H2O)62 increases,
Cl increases
14
This is Q!!! Ratio of Concentrations under
Non-Equilibrium conditions
products
Q
reagents
aA bB
cC dD
CcDd
Q
AaBb
Q the Reaction Quotient
15
The reaction quotient Q can be determined for
any set of concentrations
Possible outcomes