Chemical Equilibrium
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37 Terms
reversible reaction
reaction where reactants react to form products then react to give the reactants back
N.B!!! chemical equilibrium
dynamic state where the RATE OF the forward reaction is equal to the RATE OF the reverse reaction
Q: Why is chemical equilibrium known as a dynamic state?
forward and reverse reaction CONTINUE to occur and DO NOT STOP
Q: does a reaction at equilibrium ever cease?
Never, it's in a dynamic state- rate of forward reaction equals rate of reverse reaction.
N.B!!! once equilibrium is reached...
... concentrations of reactants and products remain constant (don't have to be the same, just constant)
Equilibrium "lies" on the right
Concentration products is greater than concentration reactants
Equilibrium "lies" on the left
Concentration reactants is greater than concentration products
N.B!!! Le Chatelier's principle
if a stress is applied to a system AT EQUILIBRIUM, the system shifts to oppose the applied stress
Going toward a concentration...
... increases it
Going away from a concentration...
... decreases it
If equilibrium looking to decrease temperature...
... it goes in endothermic
If equilibrium looking to increase temperature...
... it goes in exothermic
Negative delta H...
... forward reaction is exothermic
Positive delta H...
... forward reaction is endothermic
Pressure only affects equilibrium if:
1. it's a gaseous reaction (all reactants and products are gases).
2. and if there are an unequal number of molecules on each side.
Q: What affect does a catalyst have in equilibrium?
None, it can bring a reaction to equilibrium faster but doesn't affect the actual state of equilibrium. It speeds up the forward and reverse reactions equally.
Q: Give 2 industrial applications of Le Chatelier's principle
1. Manufacture of ammonia (Haber process)
2. Manufacture of sulfuric acid (Contact process)
Q: According to Le Chatelier's principle, what conditions should be used to maximise the yield of ammonia/sulfuric acid obtained?
1. High pressures
2. Low temperatures
Q: Why are these conditions not used in practise during the Haber/Contact process?
High pressures are dangerous
Low temperatures make the rate of reaction too slow
Haber process compromised conditions
Compromise pressure 200 atm used
Compromise temperature 500°C used
Q: 2 uses of ammonia
1. Explosives
2. Cleaning products
What catalyst is used for the Haber process?
Iron
What catalyst is used for the Contact process?
Vanadium
Q: Why is a platinum catalyst not used for the Contact process?
Platinum easily "poisoned"
Contact process compromised conditions
Compromise pressure 1-2 atm used
Compromise temperature 450°C used
Q: 2 uses of sulfuric acid
1. Car batteries
2 Paints
Q: What is meant by equilibrium constant (Kc)?
Relationship between concentration of reactants and products at equilibrium.
Equilibrium constant formula
Kc = [C]^C [D]^D / [A]^A [B]^B
Only factor that affects Kc?
Temperature
In Kc concentration of...
... products on top and reactants in bottom
Kc greater than 1
Equilibrium lies on right
Kc less than 1
Equilibrium lies on left
Increase in Kc
forward reaction being favoured (more products being made)
Decrease in Kc
reverse reaction being favoured (more reactants being made)
...write out what the graph shows e.g. as temperature increases, Kc increases
then use one of the pieces of info to establish what side of rxn is being favoured and apply let chateliers principle to other piece of info then piece the two answers together e.g. "Kc increases" means forward rxn is favoured
"temperature increases" so equilibrium shifts to decrease temperature in the endothermic direction to use heat up.
piecing together, forward rxn is endothermic