Chapter 5C - Changes to Equilibrium

Question 1

When might yield need to be optimised?

Answer 1

• important industrial processes involve reversible reactions
• position of equilibrium needs to be shifted to the right

Question 2

Define position of equilibrium

Answer 2

Relative concentration of reactants and products at equilibrium

Question 3

What conditions affect the position of equilibrium?

Answer 3

• Change in concentration of reactants/products at a constant volume and temperature
• dilution
• pressure
• temperature

Question 4

What is Le Chatelier’s Principle?

Answer 4

• A reaction mixture will remain at equilibrium unless changes to conditions are made and can be predicted by this principle
• When a system is subjected to a stress, the system will shift in a direction so as to relieve the stress and partially oppose the change

Question 5

When might Le Chatelier’s principle be applied?

Answer 5

Industrial process can set conditions to maximise the yield.

Question 6

How can the concentration of an equilibrium mixture be changed?

Answer 6

• addition of reactants/products
• removal of reactants/products

Question 7

What is the affect of concentration change on the position of equilibrium?

Answer 7

Cause the system to shift in a direction which partially opposes the change

Question 8

If concentration of reactants is increased…

Answer 8

• The reaction favours the forwards direction (net forwards reaction)
• position of equilibrium shifts to the right to partially oppose increased concentration of reactants and produce more products

Question 9

If concentration of reactants is decreased…

Answer 9

• The reaction favours the backwards direction (net backwards reaction)
• position of equilibrium shifts to the left to partially oppose decreased concentration of reactants and produce more reactants to re-establish equilibrium

Question 10

If concentration of products is increased…

Answer 10

• The reaction favours the backwards direction (net backwards reaction)
• position of equilibrium shifts to the left to partially oppose increased concentration of products and produce more reactants to re-establish equilibrium

Question 11

If concentration of products is decreased…

Answer 11

• The reaction favours the forwards direction (net forwards reaction)
• position of equilibrium shifts to the right to partially oppose decreased concentration of products and produce more products to re-establish equilibrium

Question 12

Define Pressure

Answer 12

• Collisions between particles and walls
• proportional to volume

Question 13

How can the pressure of a gaseous equilibrium mixture be changed?

Answer 13

By increasing or reducing the volume of the reaction chamber at a constant temperature

Question 14

What is the affect of decreased volume of a gaseous equilibrium mixture?

Answer 14

• pressure increases
• concentration of all reactants and products increase
• causes system to shift in a direction that produces fewer moles (particles) of gas to partially oppose the change.
• formation of ____ will decrease pressure as less ____ than ____ molecules.

Question 15

What is the affect of increased volume of a gaseous equilibrium mixture?

Answer 15

• pressure decreases
• concentration of all reactants and products decrease
• causes system to shift in a direction that produces more moles (particles) of gas to partially oppose the change.
• formation of ____ will increase pressure as less ____ than ____ molecules.

Question 16

What will occur if there are the same number of particles on both sides of the equation and pressure is changed?

Answer 16

There will no change in equilibrium position with pressure change
The system will not shift.

Question 17

Change in temperature

Answer 17

• the system will shift in a direction so as to relieve the change in temperature and partially oppose the change
• depends whether forwards reaction is exothermic/endothermic
• only stress that changes the equilibrium constant K

Question 18

What is the affect of increasing the temperature of an exothermic reaction?

Answer 18

• net backwards reaction
• The position of equilibrium will shift left to decrease the temperature and partially oppose the change
• K decreases as more reactants are produced.

Question 19

What is the affect of decreasing the temperature of an exothermic reaction?

Answer 19

• net forwards reaction
• The position of equilibrium will shift right to increase the temperature and partially oppose the change
• K decreases as more products are produced.

Question 20

What is the affect of increasing the temperature of an endothermic reaction?

Answer 20

• net forwards reaction
• The position of equilibrium will shift right to decrease the temperature and partially oppose the change
• K decreases as more products are produced.

Question 21

What is the affect of decreasing the temperature of an endothermic reaction?

Answer 21

• net backwards reaction
• The position of equilibrium will shift left to increase the temperature and partially oppose the change
• K decreases as more reactants are produced.

Question 22

What is the affect of the addition of a catalyst?

Answer 22

• Does not change position of equilibrium or K

Question 23

What is Dalton’s Law?

Answer 23

• Partial pressure is the pressure each gas exerts in a mixture of gases
• Ptotal = P1 + P2 + P3…

Question 24

What is the affect of an addition of an inert gas?

Answer 24

• increases the total pressure of a gaseous mixture
• partial pressure and mol/volume of the gases involved in the equilibrium reaction do not change
• does not affect equilibrium position or K

Question 25

What are the **common inert gases**?

Answer 25

* Noble gases e.g He, Ne, Ar * Nitrogen Gas N2

Question 26

How does the **dilution of an aqueous solution** affect the position of equilibrium?

Answer 26

* concentration of all reactant and products decrease * the system is no longer at equilibrium * the system will shift in a direction that produces a greater number of particles, hence increasing the concentration of the reaction mixture to reastablish equilibrium

Question 27

What will occur if there are the **same number of particles on both sides** of the equation and the **solution is diluted**?

Answer 27

There will no change in equilibrium position with pressure change The system will not shift