M3 B7 Chemical Equilibrium
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What is a reversible reaction?
A reaction that can occur in either direction
What makes equilibrium dynamic? (3)
The rate of the forward reaction is the same as the rate of the backwards reaction Concentrations of the reactants and products dont change The system must be closed
What is Le Chatelier’s principle?
When any of the conditions affecting the position of dynamic equilibrium are changed, then the position of the equilibrium will shift to minimise the change.
What is homogeneous equilibrium?
Reactants and products are in the same state
How will changing concentration of reactants affect the position of equilibrium?
Increasing the concentration of the reactants will favour the forwards reaction because this will minimise the change therefore equilibrium will shift to the right so more products will be made. Vice Versa
How will changing pressure affect the position of equilibrium
Increasing pressure favours the side with the fewest GASEOUS moles
How will changing temperature affect the position of equilibrium
increasing temperature will ALWAYS favour the endothermic reaction Decreasing temperature will ALWAYS favour the exothermic reaction
How will adding a catalyst to a reaction affect the position of equilibrium
Will have no effect on the position of equilibrium because the rates of the forwards and backwards reaction will increase equally therefore will decrease the decrease the time taken to reach dynamic equilibrium.
What is the test to investigate the change in concentration in an equilibrium reaction?
Pour a solution of yellow potassium chromate (K2CrO4) into a beaker Add dilute sulphuric acid dropwise The solution will change from yellow to orange and keep adding until no more colour change Add aqueous NaOH dropwise to change the colour from orange to yellow
Explain why the colour changed when dilute sulphuric acid was added to the yellow potassium chromate
The added H2SO4 increases the H+ ion concentration which favours the forwards reaction to minimise the change therefore equilibrium shifts to the right hence the colour change from yellow to orange.
What is the test to investigate the change in temperature of an equilibrium reaction?
Dissolve cobalt chloride in water in a boiling tube and add a small quantity of hydrochloric acid. Place the boiling tube in some iced water and the solution will turn a pink colour Transfer the boiling tube in a hot water bath and the solution will turn blue
What is the Haber Process?
The equilibrium reaction that is responsible for the production of Ammonia. N2 + 3H2 ⇌ 2NH3 (All gaseous)
What are the optimum conditions for the Haber Process?
Low temperature and high pressure
What are the problems caused by the optimum conditions for the haber process?
Low temp, slow rate High pressure, dangerous and high energy cost
What is the compromise to manage the equilibruim of the Haber Process?
Use a reasonably high temperature (450°C) Use a pressure that is above atmospheric pressure (25 - 100 atm) Use an iron catalyst to increase the rate of the reaction and allows a lower temperature to be used to lower energy costs
What is Kc?
equilibrium constant and a value that is calculated for any homogeneous reaction
What effects Kc?
Temperature ONLY
What is the equation to calculate Kc?
aA(g) + bB(g) ⇌ cC(g) + dD(g) Kc = [C] c [D] d [A] a [B] b where [ ] means concentration
What does it mean if the Kc numerical value is high?
The equilibrium lies to the right (makes more products)
What does it mean if the Kc numerical value is low?
The equilibrium lies to the left (makes less products)