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Define a Reversible Reaction
a reaction that can go either direction and can come to a state of equilibrium
Define Dynamic Equilibrium
concentrations of all reactants and products remain constant and the rate of the forward reaction is equal to the rate of the reverse reaction
Define a Closed System
no exchange of matter with the surroundings and equilibrium can only be reached in a closed system
Define Physical Equilibrium
equilibrium involving a physical process such as melting/freezing/evaporating/condensing
How do you notate the Equilibrium Constant?
Kc
What does the equilibrium constant tell us?
provides information about how far a reaction proceeds at a particular temperature
Where do the products go when forming a Kc expression?
numerator
Where do the reactants go when forming a Kc expression?
denominator
What number do you raise your concentrations to in a Kc expression?
co-efficients in reaction
How do you distinguish between the two Kc values obtained from the same reaction, one being the forward reaction value and one being the reverse reaction value?
Kc = forward Kc’ = reverse
A high Kc value =
equilibrium position lies to the right as you have mostly products in reaction mixture
A low Kc value =
equilibrium position lies to left as you have mostly reactants in reaction mixture
Greater reactants, equilibrium lies to
left
Greater products, equilibrium lies to
right
Kc>> 1 means the reaction…
proceeds almost totally towards the products
Kc<<1 means the reaction…
hardly proceeds at all towards products
State Le Chatelier’s Principle
if a system at equilibrium is subjected to some change the position of equilibrium will shift in order to minimise the effect of the change
What happens to the equilibrium position when you increase pressure?
shifts to side with fewer moles
What happens to equilibrium position when you decrease pressure?
shifts to side with more moles
Does changing pressure effect Kc value?
no
What happens to equilibrium position when you increase temperature?
shifts to endothermic side (decrease temp)
What happens to equilibrium position when you decrease temperature?
shifts to exothermic side (increase temp)
What happens to Kc value when temperature increases in an endothermic reaction?
Kc increases
What happens to Kc value when temperature increases in an exothermic reaction?
Kc decreases
What happens to Kc value when temperature decreases in an endothermic reaction?
Kc decreases
What happens to Kc value when temperature decreases in an exothermic reaction?
Kc increases
What happens to equilibrium position when the concentration of one species in a mixture is increased?
shifts to side when chemical has not been added so it is used up
Does increasing the concentration of a species in a reaction affect the Kc value?
no
How does the introduction of a catalyst affect equilibrium position?
it doesn’t however the rate of forward and reverse reaction increase equally, has no effect on Kc
How do you notate the Reaction Quotient?
Q
What does the reaction quotient tell us?
How far a reaction has proceeded at any given time before, after or at equilibrium
How does Kc differ to Q?
Q does not use equilibrium concentrations
What does it mean if Q>Kc? Where does the equilibrium position shift?
reaction mixture contains more products, therefore equilibrium position shifts to left so more products are used up.
What does it mean if Q<Kc? Where does the equilibrium position shift?
reaction mixture contains more reactants, therefore equilibrium position shifts to right so more products are made.
What does it mean if Q=Kc?
reaction is at equilibrium
What direction does a reaction proceed in regarding Gibbs Free Energy?
a reaction proceeds in the direction that involves a decrease in Gibbs free energy
Why does a reaction reach equilibrium?
At equilibrium Gibbs free energy is at its lowest
Why is movement away from equilibrium unfavourable?
it will involve an increase in Gibbs free energy
Write the equation that relates Gibbs free energy with equilibrium constant.
ΔG° = -RTlnK
Note
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