Announcements
• What’s due next week
– Lon-Capa Homework #11 (on 12/12/12)
– On #1 (Calculation of Free Energy …)
• Does not record previous try answers
• Keep track your answers
• Next Week
– wrap up equilibrium chapter and final exam review
(with demos)
1
Effect of Concentration on Equilibrium
Fe3+(aq) + SCN1-(g)
FeSCN2+(aq)
What happens if FeCl3 is added to the reaction?
• The reaction shifts right or left?
[FeSCN2+]
K= 3+
Fe
[SCN−]
2
1
Effect of Concentration on Equilibrium
Fe3+(aq) + SCN1-(g)
FeSCN2+(aq)
What happens if KSCN is added to the reaction?
• The reaction shifts right or Left?
[FeSCN2+]
K= 3+
Fe
[SCN−]
3
Effect of Concentration on Equilibrium
After equilibrium is reached, what happens if we add Na3PO4
(sodium phosphate) to the reaction?
(the PO43- will bound more strongly to form FePO4 ,
thus releasing the SCN1- )
Fe3+(aq) + SCN1-(g)
FeSCN2+(aq)
A) The reaction shifts Left (towards reactant)
B) The reaction shifts Right (towards product)
4
2
Example
N2(g) + 3H2(g)
2NH3(g)
K = 0.291 (@ 700K)
An equilibrium mixture of 0.50 M N2, 3.00 M H2, and 1.98 M
NH3 is disturbed by increasing the N2 concentration to
1.50 M. Which direction will the reaction shift?
Copyright © 2010 Pearson Prentice Hall,
Inc.
Example
• Predict the shift in equilibrium positions that
will occur when the volume is reduced
1. P4 (s) + 6 Cl2 (g)  4 PCl3 (l)
2. PCl3 (g) + Cl2 (g)  PCl3 (g)
3. PCl3 (g) + 3 NH3 (g)  P(NH2)3 (g) + 3 HCl (g)
6
3
The equilibrium constant for an exothermic reaction
(negative ∆H°) decreases as the temperature increases.
N2(g) + 3H2(g)
2NH3(g)
∆H° = -2043 kJ
K=
𝑁𝐻3 2
𝑁2 𝐻2 3
If K  as T, then
the denominator
is getting larger
the equilibrium shifts from products to reactants.
7
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