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Equilibria

Write the balanced equation for the synthesis of AmmoniaInclude Kc expressionInclude energy level diagramhttp://www.youtube.com/watch?v=uAJDD1_Oexo

+Aims

Introduce dynamic equilibria for both chemical and physical change.

Game

+Definition 1 Chemical Equilibria

http://www.youtube.com/watch?v=tlGrBcgANSY&feature=related

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+Definition 2

Physical Dynamic Equilibria.

i.e. water

+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, be eerrransftd in or out at will.

+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 from regnye.

At equilibrium, the quantities of everything nresept in the mixture remain constant, although the reactions are still uinitconng. This is because the rates of the forward and the back reactions are aleuq.

+Chemical Equilibria

http://www.youtube.com/watch?v=0XQVXFL4uoo

http://www.youtube.com/watch?v=GS9kIj9n-BU&feature=related

+The Equilibrium Constant

This is derived from concentrations – can be gases or liquids.

NB Always [products] / [reactants]

NB2 – this is for homogeneous reactions

+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.

+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

+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.

+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.

+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.

+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.