Equilibria

Question 1

Reversible Reaction

Answer 1

A reaction where the products can react to remake the reactants

Question 2

Dynamic Equilibria

Answer 2

• A reversible reaction where the forwards and backwards reactions happen at the same rate
• Concentration remains constant (but not necessarily equal on both sides)

Question 3

4 Conditions needed for equilibria

Answer 3

• Reaction must happen in a closed system
• Equilibrium can be achieved from either direction (reactants –> products or products –> reactants)
• Dynamic process (reached when rate is equal)
• The properties of the system don’t change (e.g. temperature, pressure, concentration)

Question 4

Le Chatelier’s Principle

Answer 4

If a system at equilibrium is disturbed, the equilibrium moves in the direction that tends to reduce the disturbance

Question 5

Effect of Concentration on equilibrium

Answer 5

• Increasing concentration of reactants moves equilibrium to products (and vice versa)
• Decreasing concentration of reactants moves equilibrium to reactants (and vice versa)

Question 6

Effect of Pressure on equilibrium

Answer 6

• Changing the pressure of a system will only impact reactions involving gases
• Increasing pressure causes equilibrium to move to the side with fewer moles of gas
• Decreasing pressure causes equilibrium to move to the side with more moles of gas

Question 7

Effect of Catalysts on Equilibrium

Answer 7

• No effect
• Increases the of the forwards and backwards reactions by an equal amount

Question 8

Haber Process

Answer 8

• N2 from the air and H2 from natural gases are pumped into the compressor through pipes
• Gases are compressed to roughly 200 atm in the compressor
• Pressurised gases are pumped into a tank containing iron bed catalysts at 450 degrees celcius
• Some of the N2 and H2 react to form ammonia
• The unreacted H2 and N2 are passed through a cooling tank and the ammonia is liquified and stored in pressurised tanks
• The unreacted H2 and N2 is recycled back into the system

Question 9

Haber Process Optimum Conditions

Answer 9

• Low temperature (shifts equilibrium to products)
• High pressure (shifts equilibrium to products)

Question 10

What is the issue with the Haber Process Optimum Conditions?

Answer 10

• At low temperature the rate of reaction is slow so it takes too long to produce ammonia
• At high pressure it is expensive to maintain the equipment used for the reaction (not economical)

Question 11

Haber Process Compromise Conditions

Answer 11

• 670K (450 degrees celcius)
• 200 atm
• Iron Catalyst

Question 12

Production of Ethanol

Answer 12

Optimum Conditions:
- High Pressure
- Low Temperature
- Excess Steam - increases the concentration of reactants which shifts equilibrium to products

Question 13

What are the issues with the production of ethanol Conditions?

Answer 13

• High Pressure causes ethene to polymerise
• Low Temperature reduces reaction rate
• Too much steam dilutes the catalyst

Question 14

Production of Ethanol Compromise Conditions

Answer 14

• 570K
• 6500 kPa

Question 15

Production of Methanol

Answer 15

Optimum Conditions:
- Low Temperature
- High Pressure

Compromise Conditions:
- 500K
- 10,000 kPa