1. AP Questions: putting it all together

2. Equilbrium Constant and EXTERNAL EFFECTS
Formation of stalactites and stalagmites
CaCO3(s) + H2O(liq) + CO2(g) fg Ca2+(aq) + 2 HCO3-(aq)

3. The outcome is governed by LE CHATELIER’S PRINCIPLE
EQUILIBRIUM
Temperature, catalysts, and changes in concentration/ pressure affect equilibria.
The outcome is governed by
LE CHATELIER’S PRINCIPLE
“...if a system at equilibrium is disturbed, the system tends to shift its equilibrium position to counter the effect of the disturbance.”

4. Equilibrium constant, K, and Concentration
Concentration changes
Δ [ X ]
no change in K
only the position of equilibrium changes.

5. Butane-Isobutane Equilibrium

6. Butane Isobutane
At equilibrium K = 2.5
[iso] = 1.25 M
[butane] = 0.50 M
An additional 1.50 M butane is added.
When the system comes to equilibrium again, what are [iso] and [butane]?

7. Butane e Isobutane Solution
Calculate Q immediately after adding more butane and compare with K.
Q is LESS THAN K. Therefore, the reaction will shift to the ____________.

8. Butane e Isobutane Q is less than K, shifts right toward isobutane.
Set up ICE table
[butane] [isobutane]
Initial
Change
Equilibrium
1.25
- X X
2.00 – x x

9. Butane e Isobutane x = 1.07 M At the new equilibrium position,
[butane] = 0.93 M and
[isobutane] = 2.32 M.
Equilibrium has shifted toward isobutane.

10. Equilibrium Constant and Catalyst
Add catalyst: NO change in K
A catalyst only affects the RATE it approach equilibrium.
Catalytic exhaust system

11. Pressure and Equilibrium N2O4(g) e 2 NO2(g)
Increase P in the system by reducing the volume
(constant Temp). e

12. Increase P (decreased V). Therefore, reaction shifts LEFT
N2O4(g) e 2 NO2(g)
Increase P (decreased V).
In gaseous system the equilibrium will shift to the side with fewer molecules (in order to reduce the P).
Therefore, reaction shifts LEFT
P of N2O and P of NO2 .

13. Temperature Effects on Equilibrium
Figure 16.6

14. Temperature Effects on Equilibrium
Kc (273 K) =
Kc (298 K) =
N2O4 (colorless) + heat e 2 NO2(brown) ∆Ho = kJ (endo)

15. Every T has a unique K Temperature change = change in K
Consider the fizz in a soft drink
H2CO3(aq) + HEAT e CO2(g) + H2O(l)
K = [CO2] / [H2CO3]
Increase T. What happens to equilibrium position? To value of K?
K increases as T goes up because [CO2] increases and [H2CO3] decreases.
Decrease T. Now what?
Equilibrium shifts left and K decreases.

16. NH3 Production
N2(g) + 3 H2(g) e 2 NH3(g) + heat
K = 3.5 x 108 at 298 K
What is the advantage of using the above system to produce ammonia?

17. Le Chatelier’s Principle
Change T - changes K
causes change in P or concentrations at equilibrium
Use a catalyst: K not changed.
Reaction comes more quickly to equilibrium.
Add or take away reactant or product: K does not change
Reaction adjusts to new equilibrium “position”