1. Solving Problems NOT AT Equilibrium

2. The Reaction Quotient
Ratio of Products to Reactants of a Reaction NOT NECESSARILY at equilibrium.
The formula is the same as the equilibrium constant.
Q = [Products]coefficient [Reactants] coefficient
Compare value to equilibrium constant

3. Solving for Q (Reaction Quotient)
In an experiment, mol NOCl, mol NO(g) and mol Cl2 are mixed in 2.0 L flask.
2NOCl(g) NO(g) + Cl2(g)
What is the value of the reaction quotient, Q?
Which direction will the reaction proceed to reach equilibrium if Kc = 1.55 x 10-5? 3

4. Q vs Keq If Q < K If Q>K If Q = K system is at equilibrium
Products Not Enough
Forward Reaction Favored
If Q>K
Products Too Much
Reverse Reaction Favored
If Q = K system is at equilibrium
Neither Reaction Favored
[Products]
[Reactants]

5. Reaction Quotient Problem
0.035 moles of SO2, moles of SO2Cl2, and moles of Cl2 are combined in an evacuated 5.00 L flask and heated to 100oC. 
SO2Cl2(g)  SO2(g) + Cl2(g)
      
What is Q before the reaction begins? 
Which direction will the reaction proceed in order to establish equilibrium if Kc = at 100oC?

6. EQUILIBRIUM PROBLEM

7. EQUILBRIUM PROBLEM (con’t)

8. Le Chatelier’S Principle

9. Le Chatelier’s Principle
“If a system at equilibrium is disturbed by a change in temperature, pressure, or the concentration of one of the components, the system will shift its equilibrium position so as to counteract the effect of the disturbance. “
-Le Chatelier's Principle (1888)
3 Types of Stress or Disturbance
Change in concentrations
Change in pressure
Change in temperature

10. Fe2O3(s) + 3 CO(g) 2 Fe(s) + 3 CO2(g)
Early Inspiration
Fe2O3(s) + 3 CO(g) 2 Fe(s) + 3 CO2(g)
The reduction of iron oxide
by carbon monoxide
The smoke emitted contained
a lot of CO and iron
production was slow.
How could we remedy this?

11. Disrupting Equilibrium
Synthesis of ammonia from hydrogen and nitrogen

12. STRESS 1- Change in Concentration
Favored
Rev
Fwd
Adding product makes Q > K
Removing reactant makes Q > K
Adding reactant makes Q < K
Removing product makes Q < K
Determine the effect on Q, this will tell you the direction of shift

13. Practice Problem
The following reaction is at equilibrium in a reaction vessel when more CO (g) is added to the system.
2 CO2 (g)   2 CO (g) + O2 (g)
Which direction will the reaction shift?
Will the forward or reverse reaction be favored?
What will eventually happen to the concentration of O2 (g)?
What will eventually happen to the concentration of CO2 (g)?
What will happen to the concentration of each substance when equilibrium is re-established? 13

14. Practice Problem 2
The reaction below is allowed to reach equilibrium. Ammonia gas is removed from the reaction vessel.
  N2 (g) + 3 H2 (g) 2 NH3 (g)
Will the forward or reverse reaction be favored?
What will happen to the concentration of N2 in the vessel?
What will happen to the concentration of H2 in the vessel?
Why would running water through the reaction chamber remove the ammonia but not nitrogen or hydrogen? Hmm… 14

15. STRESS 2- Change Pressure
System will shift to minimize the total volume if pressure is increased.
System will move in the direction that has the fewest moles of gas.
If moles of gas molecules is equal, the system will not be affected.
Because partial pressures (and concentrations) change a new equilibrium will be reached.

16. Practice Problem
The following reaction is at equilibrium in a 5.0 L chamber. The volume of the chamber is decreased to 3.0 L. The temperature is held constant. (Imagine if there were 15 moles of each substance at equilibrium)
2 SO3(g) 2 SO2 (g) + O2 (g)
What will happen to the pressure in the chamber?
Will the forward or reverse reaction be favored?
What will happen to the moles of SO2 in the chamber?
What will happen to the moles of SO3 in the chamber?
Will the new Keq or Kp value be larger or smaller than before? 16

17. STRESS 3- Change in Temperature
Affects the rates of both the forward and reverse reactions – speeds up both reactions, so equilibrium is reached faster.
The direction of the shift depends on whether the reaction is exothermic (- ∆H) or endothermic (+ ∆H)
Think of heat as a product if exothermic:
Reactant Product + Heat
Think of heat as a reactant if endothermic:
Reactant + Heat Product

18. Practice Problem The reaction below has a enthalpy of – 57 kJ.
2 NO2(g) N2O4(g)     
Is the reaction exothermic or endothermic? 
If the temperature of the reaction chamber is increased, will the forward or reverse reaction be favored?
What will happen to the concentration of NO2 gas?
What will happen to the concentration of N2O4 gas? 18

19. Practice Problem 2
The following reaction was at equilibrium and the concentrations of the reactants and products were measured. When the temperature was increased, the concentration of NO increased.
N2(g) + O2(g) 2 NO (g)     
Is the reaction exothermic or endothermic?  Explain.
What happened to the concentration of N2 gas?
What happened to the concentration of O2 gas?
Will the Keq at the higher temperature be greater or less than the previous Keq at the lower temperature? 19

20. Haber-Bosch Process 3 H2(g) + N2(g) 2 NH3 (g) + heat
What conditions would increase ammonia production?