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What is equilibrium
When the rate of the forward reaction is equal to the rate of the backward reaction
What is dynamic equilibrium
When the reaction has not stopped but both the forwards and backwards reactions are still occurring at the same time.
What is Kc
The equilibrium constant
What is the equilibrium constant expression
for the reaction
aA + bB ⇌ cC +dD
The equilibrium expression is
Cc Dd
Aa Bb
What does a high Kc mean
The equilibrium lies to the right
Proportionally more products than reactants
The reaction almost goes to completion
What does a low Kc mean
The equilibrium lies to the left
Proportionally more reactants than products
The reaction has barely taken place
What is the reaction quotient (Q)
When the concentrations of reactants and products are taken at any given time and substituted into the equilibrium constant expression. Kc is used when the concentrations of reactants and products are at equilibrium.
What does Q show us in relation to Kc
Q = Kc the reaction is at equilibrium so there is no net reaction
Q < Kc reaction proceeds to the right in favour of products
Q > Kc reaction proceeds to the left in favour of products
How does changes in concentration affect the equilibrium
If an increase in concentration of one of the reactants occurs, the rate of the forwards reaction increases. According to le chateliers principle the equilibrium will re-establish itself where it is in favour of the products. This opposes the change.
How do changes in pressure affect the equilibrium
Only has an affect if the reactants and products are in a gaseous state.
If a reaction is subjected to increased pressure the equilibrium will shift to oppose the change by moving in favour of the side with the least molecules.
How do changes in temperature affect the equilibrium
If the forward reaction is exothermic, a decrease in temperature will favour the exothermic reaction as it wants to oppose the loss of heat
Increasing the temperature will favour the backwards endothermic reaction.
How does addition of a catalyst affect the equilibrium
It speeds up both the forward and the backwards reaction equally so it has no affect on the position of equilibrium.
What is homogenous equilibria
Where the reactants and products are all in the same phase.
How does Gibbs free energy show the state of equilibrium
ΔG = negative then the reaction proceeds in the forwards direction
ΔG = positive then the reaction proceeds in the backwards direction
ΔG = 0 the reaction is at equilibrium
How are Gibbs free energy and the equilibrium constant related
ΔG° = -RTln(K),
ΔG° is standard Gibbs free energy change,
R is the gas constant
T is temperature,
ln is the natural logarithm,
K is the equilibrium constant."
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