a reaction that can go either direction and can come to a state of equilibrium
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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
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3
Define a Closed System
no exchange of matter with the surroundings and equilibrium can only be reached in a closed system
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4
Define Physical Equilibrium
equilibrium involving a physical process such as melting/freezing/evaporating/condensing
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5
How do you notate the Equilibrium Constant?
Kc
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What does the equilibrium constant tell us?
provides information about how far a reaction proceeds at a particular temperature
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Where do the products go when forming a Kc expression?
numerator
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Where do the reactants go when forming a Kc expression?
denominator
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What number do you raise your concentrations to in a Kc expression?
co-efficients in reaction
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10
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
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A high Kc value =
equilibrium position lies to the right as you have mostly products in reaction mixture
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A low Kc value =
equilibrium position lies to left as you have mostly reactants in reaction mixture
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Greater reactants, equilibrium lies to
left
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Greater products, equilibrium lies to
right
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Kc>> 1 means the reaction…
proceeds almost totally towards the products
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Kc<
hardly proceeds at all towards products
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17
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
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18
What happens to the equilibrium position when you increase pressure?
shifts to side with fewer moles
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What happens to equilibrium position when you decrease pressure?
shifts to side with more moles
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Does changing pressure effect Kc value?
no
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What happens to equilibrium position when you increase temperature?
shifts to endothermic side (decrease temp)
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What happens to equilibrium position when you decrease temperature?
shifts to exothermic side (increase temp)
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23
What happens to Kc value when temperature increases in an endothermic reaction?
Kc increases
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What happens to Kc value when temperature increases in an exothermic reaction?
Kc decreases
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What happens to Kc value when temperature decreases in an endothermic reaction?
Kc decreases
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What happens to Kc value when temperature decreases in an exothermic reaction?
Kc increases
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27
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
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Does increasing the concentration of a species in a reaction affect the Kc value?
no
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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
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30
How do you notate the Reaction Quotient?
Q
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What does the reaction quotient tell us?
How far a reaction has proceeded at any given time before, after or at equilibrium
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How does Kc differ to Q?
Q does not use equilibrium concentrations
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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.
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What does it mean if Q
reaction mixture contains more reactants, therefore equilibrium position shifts to right so more products are made.
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What does it mean if Q=Kc?
reaction is at equilibrium
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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
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Why does a reaction reach equilibrium?
At equilibrium Gibbs free energy is at its lowest
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Why is movement away from equilibrium unfavourable?
it will involve an increase in Gibbs free energy
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39
Write the equation that relates Gibbs free energy with equilibrium constant.
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