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
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.