3.1.6 Chemical equilibria, Le Chatelier’s principle and Kc Flashcards
In a reversible reaction at equilibrium:
forward and reverse reactions proceed at equal rates
the concentrations of reactants and products remain constant
Dynamic equilibrium
When forward and backwards reaction is happening at the same rate
And remains a constant rate
Only occur in a closed system
Conditions for equilibrium
Closed system
Sproches from any direction
Dynamic
Equilibrium reached which properties don’t change over time
Le chatelier’s principle
When a system is subjected to change the system will alter to lesser the effect of that change
Le Chatelier’s principle.
Le Chatelier’s principle can be used to predict the effects of changes in temperature, pressure and concentration on the position of equilibrium in homogeneous reactions.
Useful in altering condition in industry to increase max yield
Ethene hydrogenation
Catalyst = phosphoric acid absorbed on silica
Done in excess steam - to much steam dilutes the catalyst
Equilibrium constant kc
For reversible reactions
It indicates the position of equilibrium at certain temperatures
Kc for a reaction always has the same value endless conditions therefore position of equilibria are changed
Has varying units - you have to calculate them from mol dm-3 in the equation
Effect of changing conditions on kc
Catalyst = no effect
Conc = no effect as is a fraction
Temp does have effect - as effects quantity of react or products
Compromise conditions
Balance between rate and yield
Increasing the pressure is expensive
Talk yield
when something is 2mols in an ice table
you have to do 2x change
when talking le chatiliesr and pressure
you have to state which side has the LEAST mols for an increase
for a decrease in pressure you have to state which side has MORE mols
kc equations
always concentration !!!!! triple check for a volume
if more reactant or product is added what is the effect on the substances partial pressure and teh equations kp
NO EFFECT on kp
increases the pp as the molar fraction is increased
reason catalysts has no effect on kp
- catalysts don’t effect the position of eqm
- increases the rate of the forward and backwards reaction equally
homogenous system at equilibrium
When the products and reactants of an equilibrium reaction form a single phase
