1. +
Equilibria
Write the balanced equation for the synthesis of Ammonia
Include Kc expression
Include energy level diagram
http://www.youtube.com/watch?v=uAJDD1_Oexo

2. +
Aims
 Introduce dynamic equilibria for both chemical and physical
change.
 Game 

3. +
Definition 1 Chemical Equilibria
http://www.youtube.com/watch?v=tlGrBcgA
NSY&feature=related

4. +

5. +
Definition 2
 Physical Dynamic Equilibria.
 i.e. water

6. +
Definition 3
 The ‘closed system’….
 A closed system is one in which no substances are either
aeddd to the system or lost from it. Energy
can, however, beeerrransftdin or out at will.

7. +
Summary
 A dynamic equilibrium occurs when you have a verreslebi
reaction in a closed system. Nothing can be dddae to the
system or taken away from it apart fromregnye.
 At equilibrium, the quantities of everything nresept in the
mixture remain constant, although the reactions are
stilluinitconng. This is because the rates of the forward and the
back reactions arealeuq.

8. +
Chemical Equilibria
 http://www.youtube.com/watch?v=0XQVXFL4uoo
 http://www.youtube.com/watch?v=GS9kIj9n-
BU&feature=related

9. +
The Equilibrium Constant
 This is derived from concentrations – can be gases or liquids.
 NB Always [products] / [reactants]
 NB2 – this is for homogeneous reactions

10. +
Magnitude of Kc
 Kc is constant at constant T.
 Changing Pressure or concentration or adding a catalyst do not
change Kc.
 If Kc>>1 – rxn goes to completion.
 If Kc<<1 – rxn hardly proceeds.
 If Kc 10-2 – 102 then [reactants] and [products] are present in the
equilibirum mixture.

11. +
Your Task
 Who was Le Chatelier ?
 What did he find out about equilibria ?
 Discuss effect on Haber ( F ) or Contact ( M ) processes of altering the
following ..
 Temperature
 Pressure
 Concentration
 Catalyst
 MUST be communicated in an entertaining manner !
 http://www.chem1.com/acad/webtext/chemeq/Eq-02.html#SEC1

12. +
Key Concepts in Equilibria
Equilibrium reactions are reversible chemical reactions.
rate of the forward reaction = the rate of the reverse
reaction
At equilibrium the concentration of reactants / products
does not change with time.
 Catalysts do not affect the position of equilibrium
 Heat increases the rate of both the forward and reverse
reaction.
Only closed systems can reach equilibrium.

13. +
Le Chatelier’s Principle
 When a system at equilibrium is disturbed, the equilibrium
position will shift in the direction which tends to minimise, or
counteract, the effect of the disturbance.

14. +
Disturbances on Equilibrium
* If the concentration of a solute reactant is increased, the equilibrium position
shifts to use up the added reactants by producing more products.
* If the pressure on an equilibrium system is increased, then the equilibrium
position shifts to reduce the pressure.
* If the temperature of an endothermic equilibrium system is increased, the
equilibrium position shifts to use up the heat by producing more products.
* If the temperature of an exothermic equilibrium system is increased, the
equilibrium position shifts to use up the heat by producing more reactants.

15. +
Effect of Catalyst
 A catalyst speeds up the rate of both the forward and reverse
reactions.
 The initial slope of the concentration vs time lines will be
steeper for both reactants and products.
 A catalyst does NOT affect the equilibrium position.
 At equilibrium the concentrations of reactants and products for
the catalysed reaction are the same as for the uncatalysed
reaction.