reaction rates and equilibrium 10.4 - dynamic equilibrium and Le Chatelier's principle Flashcards
(14 cards)
What does dynamic equilibrium mean?
Both forward and reverse reactions take place at the same rate. The concentration of products and reactants don’t change. must be a closed system.
What is the position of equilibrium?
It indicates the extent of the reaction.
In a reversible reaction, if the temperature, pressure, or concentration of reactants or products is changed, then the position of equilibrium may change.
What is Le Chatelier’s principle?
When a system in equilibrium is subjected to an external change, the system readjusts itself to minimise the effect of that change.
If there are more PRODUCTS formed, where does equilibrium shift?
to the RIGHT
If there are more REACTANTS formed, where does equilibrium shift?
to the LEFT
How could you carry out a simple experiment to show the position of equilibrium could be changed by altering the concentrations.
1) Add solution of yellow potassium chromate, KrCrO4, to a beaker.
2) Add dilute sulfuric acid, H2SO4, dropwise until there is no further change. (solution turns orange)
3) Add aqueous sodium hydroxide, NaOH (aq), until there is no further change. (solution turns yellow again)
-You can repeat steps 2&3 and they will keep switching.
How does adding dilute H2SO4 turn the solution orange?
Adding dilute H2SO4 increases the concentration of H+ ions. This increases the rate of forward reaction, so causes position of equilibrium shift to minimise the change in H+ concentration.
-The shift decreases the concentration of the reactant H+
-The position of equilibrium shifts to the right, making more products.
-A new position of equilibrium is established towards products.
-the solution turns orange as Cr2O7 2- forms/
How does adding NaOH turn the solution yellow again?
When adding NaOH, the added OH- ions react with the H+ ions, decreasing the concentration of H+ ions.
The decreased concentration of the reactant H+, decreases the rate of the forward reaction, so causes the position of equilibrium to shift to minimise the change in concentration.
-the shift increases the concentration of the reactant H+ that has been removed.
-The position of equilibrium shifts to the left, making more of the H+ reactant.
-A new position of equilibrium has been established.
-Solution turns yellow as CrO4 2- forms.
Where does change in temp shift equilibrium?
-Increased temp shifts equilibrium in endothermic direction (- delta H)
-Decreased temp shifts equilibrium in exothermic reaction (+ delta H)
How could you carry out a simple experiment to show equilibrium is sensitive to changes in temp?
Cobalt Chloride CoCl2, dissolves in water to form a pink solution the process produces an equilibrium between 2 complexes of cobalt that are pink and blue. This equilibrium is sensitive to colour.
1)dissolve cobalt chloride in water in a boiling tube. Add a small quantity of HCl. Place the boiling tube in iced water. (solution is pink)
2) Set up a boiling water bath and transfer the boiling tube into it. (solution turns blue)
3) Transfer boiling tube into ice cold water, solution turns pink again.
How does increased temp turn the solution blue?
Boiling water increases heat energy of the system, causing position of equilibrium to shift to minimise change.
-As forward reaction is endothermic (+ delta H), position of equilibrium shifts to the right in endothermic direction, to take heat energy in & minimise increase in temp.
-The solution turns blue.
How does decreased temp turn the solution pink?
Decreasing temp shifts position of equilibrium to reverse, exothermic side (- delta H), on the left.
How does pressure effect position of equilibrium?
Increasing pressure shifts equilibrium to the side with fewer molecules, reducing pressure of the system.
How does catalysts effect equilibrium position?
Does not change the position. Increases the rate at which equilibrium is established (Rate of reaction)
