Chemical eqm: Le Chatelier's pirnciple

Question 1

Define Le Chatelier’s Principle

Answer 1

• effect of changing conditions on a system at eqm
• can be predicted by this principle
• states that if system in eqm is subjected to change
• eqm position of system will shift
• minimize effect of change

Question 2

4 Changing conditions

Answer 2

• conc of reactants and products
• temp of mixture
• pressure of gaseous reactants/products
• addition of catalyst

Question 3

Effect on changing conc on POE

Answer 3

• reactant added to/removed from eqm
• POE shifts to remove/replace reactant (until new eqm is reached)
• vice versa

Question 4

Le Chatelier Principle (conc of reactants/products)

Answer 4

• [reactant] increase, POE shift right to reduce [reactant] and increase [product] (vie versa)
• if [product] increase, POE shift left to increase [reactant] (vice versa)

Question 5

Effect of changing pressure on POE (only gaseous system)

Answer 5

• depends on no. of gaseous molecules
• high to low pressure
• pressure of system increase, POE move towards side with fewer gas molecules (vice versa)
• no. of gas molecules same on both sides, pressure no effect on POE

Question 6

Effect of temperature on POE

Answer 6

• Exothermic (enthalpy negative)

- Endothermic (enthalpy positive)

Question 7

Effect of temperature on POE (exo)

Answer 7

• releases heat
• Rise in temp: POE shifts left, remove excess heat produced by forward reaction
• Drop in temp: POE shifts right, produce more heat

Question 8

Effect of temperature on POE (endo)

Answer 8

• absorbs heat
• Rise in temp: POE shifts right, absorbs excess heat produced
• Drop in temp: POE shifts left, produce more heat

Question 9

Effect of adding catalyst on POE

Answer 9

• speeds up chemical reaction
• remains chemically unchanged
• lowers Ea of both forward and backward rxtns
• increases rate of both forward and backward rxtn by same extent
• eqm position achieved faster