[10.4] dynamic equilibrium and le chatelier's principle

Question 1

explain both parts of a dynamic equilibrium

Answer 1

• dynamic because forward and reverse reactions are both taking place
• equilibrium because:
  > reactions take place at the same rat
  > all reactants and products are present
  > concentration of all reactants and products remain constant

Question 2

what is needed for dynamic equilibrium?

Answer 2

• a reversible reaction
• a closed system
• rate of forward reaction = rate of backward reaction

Question 3

what is le chatelier’s principle?

Answer 3

when a system at dynamic equilibrium is subjected to a change, the position of equilibrium will shift to minimise the change

Question 4

what are examples of changes and actions taken by equilibrium?

Answer 4

• make it hotter = cools it back down
• increase pressure = reduce pressure
• add more of a chemical = use it up to get rid of it

Question 5

effect of concentration: adding acid

Answer 5

1. this shift decreases the concentration of the added reactant, H+ (aq)
2. position of equilibrium shifts to the right of the equation, making more products
3. a new position of equilibrium is established towards the products

• solution changes colour?

Question 6

effect of concentration: adding alkali

Answer 6

1. this shift increases the concentration of the reactant that has been removed, H+ (aq)
2. position of equilibrium shifts to the left, making more of the H+ (aq) reactant
3. a new position of equilibrium is established

• solution changes colour?

Question 7

effect of temperature: increase

scaffold answer

Answer 7

• forward reaction is exo / endo
• position of equilibrium shifts in endothermic direction to take heat energy and minimise the increase in temperature
• solution changes colour accordingly

Question 8

effect of temperature: decrease

Answer 8

• forward reaction is exo / endo
• position of equilibrium shifts in exothermic direction to give out energy and minimise the decrease in temperature
• solution changes colour accordingly

Question 9

what is the effect of pressure on the position of equilibrium?

Answer 9

• increase: POE will shift towards side with fewer gaseous molecules to try and reduce the pressure
• decrease: POE will shift towards side with more gaseous molecules to try and increase the pressure

Question 10

what is the effect of a catalyst on the POE?

Answer 10

• a catalyst does not change the POE
• it speeds up the rates of forward and reverse reactions equally
• it only increases the rate which equilibrium is established