topic 6 chemical equilibria, Le Chatelier's principle and Kc

Question 1

reversible reactions

Answer 1

Some reactions are reversible, where the reactants react to form products, which can then react to reform the original reactants. It is represented using a double arrow. In each reaction system, one reaction will be endothermic and the opposite reaction will be exothermic.

Question 2

what are the 2 key features of dynamic equilibrium?

Answer 2

In a reversible reaction at equilibrium:
-The forward and reverse reactions proceed at equal rates
-The concentrations of reactants and products remain constant.

Question 3

Le Chatelier’s principle

Answer 3

Le Chatelier’s principle can be used to predict the effects of changes in temperature, pressure and concentration on the position of equilibrium in homogeneous reactions.

Question 4

what happens when concentration of reactants INCREASES/ products INCREASES?

Answer 4

REACTANTS INCREASES:
- equilibrium shifts to the RIGHT to oppose the change and reduce the concentration of the added reactant

PRODUCT INCREASE:
- equilibrium shifts to the LEFT to oppose the change and reduce the concentration of the added product

Question 5

what happens when the pressure is increased/decreased?

Answer 5

PRESSURE INCREASED:
- equilibrium shifts to the side with FEWER GAS MOLECULES
- as fewer moles of gas exert less pressure
- to oppose the change and decrease the overall pressure

PRESSURE DECREASES:
- equilibrium shifts to the side with more GAS MOLECULES
- more moles of gas exert more pressure
- opposes the change and increases the overall pressure

IF THERE ARE EQUAL MOLES ON BOTH SIDES CHANGE IN PRESSURE = NO EFFECT ON EQUILIBRIUM

Question 6

what happens to equilibrium when temperature is increased/decreased?

Answer 6

• the forward reaction is exothermic

INCREASED TEMPERATURE means adding heat:
-the equilibrium will shift to the LEFT/RIGHT in the endothermic direction to absorb this heat
-to oppose the change and decrease the temperature

DECREASED TEMPERATURE means removing heat:
- the equilibrium will shift to the LEFT/RIGHT in the exothermic direction to produce more heat, to counteract the decrease in temperature
- to oppose the change and increase the temperature

Question 7

effect of catalyst on the position of equilibrium

Answer 7

catalysts have no effect on the position of equilibrium, they cant increase yield or do not have effect the number of particles, but using a catalyst speeds up the rate of reaction and equilibrium is reached faster