Chapter 10 - Chemical equilibrium (L)
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What is chemical equilibrium?
When the forward and backwards reactions are occurring at equal rates
What 2 things must the reaction be for equilibrium to be reached?
• The reaction must be closed (i.e. nothing being added or removed) • The reaction must be reversible
What is Le Chatelier’s principle?
If a reaction is at equilibrium, and the reaction conditions are then changed, the equilibrium position will shift in the direction that opposes the applied change
What are the 3 changes that affect position of equilibrium?
• Pressure • Temperature • Concentration of reactants/products (material either added or removed)
What is the effect on equilibrium position when reactants are added?
Shifts to right to get rid of added reactants
What is the effect on equilibrium position when reactants are removed?
Shifts to left to produce more reactants
What is the effect on equilibrium position when product is added?
Shifts to left to get rid of added product
What is the effect on equilibrium position when product is removed?
Shifts to the right to produce more product
When do changes in pressure affect the position of the equilibrium?
For reactions that involve gases
What is the effect on equilibrium position when the temperature is increased on a forward exothermic reaction?
The equilibrium will move to the left (in the endothermic backwards direction) to lower the temperature
What is the effect on equilibrium position when the temperature is decreased on a forward exothermic reaction?
The equilibrium will move to the right (in the exothermic forward direction) to increase the temperature
What is the effect on equilibrium position when the pressure is increased?
The equilibrium will shift to the side with the fewer moles of gas to lower the pressure
What is the effect on equilibrium position when the pressure is decreased?
The equilibrium will shift to the side with more moles of gas
What is the effect on equilibrium position when the pressure is decreased?
The equilibrium will shift to the side with more moles of gas
What is the effect on equilibrium position when a catalyst is added?
There is no effect on the position of the equilibrium
What happens when a catalyst is added to a reaction in dynamic equilibrium?
The speed of both the forward and backwards reactions increase- it helps the reactions form equilibrium faster
What are heterogenous systems?
A system in which there are at least two different states present (e.g. gas + solid or liquid + aq)
What are homogenous systems?
A system in which all components are the same state
What factors affect the equilibrium constant?
The value of the equilibrium constant only changes if temperature changes- other changes e.g. pressure do not change the value
What is the symbol for the value of equilibrium constant?
Kc
In equilibrium law, what do the lower case letters represent?
The number of moles of the substance e.g. 6H2O The 6 would be the lower case
In equilibrium law, what do the upper case letters represent?
The concentration of a given substance in the reaction e.g. 6H2O The 6 would be the lower case, and the concentration of H2O would be the upper case
What is the formula for Equilibrium law i.e how do you work out Kc?
Kc = [C]^c [D]^d ––––––––– [A]^a [B]^b
When Kc is significantly greater than 1, what does this indicate?
More product made than reactant