module 3: 10.4 Dynamic equilibrium and le Chatelier's principle

Question 1

where does dynamic equilibrium exist

Answer 1

In a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction and the concentrations of reactants and products do not change

Question 2

what does the effect of concentration changes do to the equilibrium

Answer 2

• if there are more products formed, the position of the equilibrium has shifted to the right
• if there are more reactants formed, the position of the equilibrium has shifted to the left

Question 3

what does the effect of temperature change do to the equilibrium

Answer 3

• Forward and reverse directions have the same value for enthalpy change - but the signs are opposite
• an INCREASE in temperature shifts the equilibrium position in the ENDOTHERMIC DIRECTION (∆H is positive)
• a DECREASE in temperature shifts the equilibrium position in the EXOTHERMIC direction (∆H is negative)

Question 4

what does the effect of pressure change do to the equilibrium

Answer 4

it favours the side where there are fewer gaseous moles.

Question 5

If the forward reaction is EXOTHERMIC (∆H is negative) what does an increase and decrease in temperature do.

Answer 5

INCREASE:

• position of equilibrium shifts to the left
• more reactants are made

DECREASE:

• position of equilibrium moves to the right
• more products are made

Question 6

If the forward reaction is ENDOTHERMIC (∆H is positive) what does an increase and decrease in temperature do.

Answer 6

INCREASE:

• position of equilibrium moves to the right
• more products are made

DECREASE:

• position of equilibrium shifts to the left
• more reactants are made

Question 7

what effect does a catalyst have on the rate of reaction

Answer 7

a catalyst has no effect on the RoR. This is due to it just decreasing the Ea, increasing the rate of the forward and reverse reactions by the same amount resulting in an unchanged position of equilibrium