Dynamic equilibrium and le Chatelier's principle

Question 1

Why are equilibrium systems (ES) dynamic?

Answer 1

• When the rate of forward and reverse reactions are equal reacting at a molecular level in a closed system
• only happen in a closed system - isolated from its surroundings, so the temp, pressure + concentration of r + p are unaffected by outside influences.

Question 2

What is le Chatelier’s principle?

Answer 2

• When a system in equilibrium is subjected to an external change the system readjusts itself to maintain the effect of that change.

Question 3

What is the effect of concentration on the position of the equilibrium?

Answer 3

• If you increase the concentration of a reactant, the equilibrium shifts to the right.
• If you decrease the concentration of the reactants, the equilibrium shifts to the left.

Question 4

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

Answer 4

• Increasing the pressure shifts the equilibrium to the side with the most moles. (reduces the pressure)
• Decreasing the pressure shifts the equilibrium to the side with least moles. (raises the pressure)

Question 5

What is the effect of temp on the position of the equilibrium?

Answer 5

• Increasing temp, shifts the equilibrium in the endothermic direction (to absorb the heat)
• Decreasing the temp shifts the equilibrium in the exothermic direction

Question 6

What is the effect of a catalyst on the position of the equilibrium?

Answer 6

-No effect as it cant increase yield but equilibrium is reached faster

Question 7

what is the pressure and temp of the ethene and steam —> ethanol?

Answer 7

Pressure = 60-70 atmospheric pressure
Temp = 300C

Question 8

is the ethene and steam reaction exothermic or endothermic?

Answer 8

• It is exothermic

Question 9

What are the conditions with a compromise?

Answer 9

• Because the reaction is exo, lower temps favour the side with fewer moles so more ethene and steam are converted to ethanol at a lower temp - better yield.
• However you don’t want to time to make the product to be slow so you can’t make it too low
• Lower temp = slow ROR (compromise between max yield + faster reaction)
• Higher pressure favours the side with fewer moles of gas. Increasing pressure = increased ROR
• High pressure = expensive to produce (stronger pipes and containers to withstand the pressure)
• High pressure can be a safety issue
• Compromise between max yield and expense.