Equillibrium - Topic 10

Question 1

When does dynamic equilibrium occur

Answer 1

Dynamic equilibrium occurs when forward and backward reactions are occurring at equal rates. The concentrations of reactants and products stays constant and the reaction is continuous

Question 2

What is the effect on temperature on the equilibrium

Answer 2

• If temperature is increased the equilibrium will shift to oppose this and move in the endothermic direction to try to reduce the temperature by absorbing heat.
• If temperature is decreased the equilibrium will shift to oppose this and move in the exothermic direction to try to increase the temperature by giving out heat.

Question 3

What effect would increasing temperature have on the yield of ammonia?
N2 + 3H2 ——> 2NH3 enthalpy = -280 kjmol-1

Answer 3

If temperature is increased the equilibrium will shift to oppose this and move in the endothermic, backwards direction to try to decrease temperature. The position of equilibrium will shift towards the left, giving a lower yield of ammonia.

Question 4

What does Le Chatelier’s principle state

Answer 4

Le Chatelier’s principle states that if an external condition is changed the equilibrium will shift to oppose the change

Question 5

What is the effect in pressure in equilibrium

Answer 5

• Increasing pressure will cause the equilibrium to shift towards the side with fewer moles of gas to oppose the change and thereby reduce the pressure
• Decreasing pressure will cause the equilibrium to shift towards the side with more moles of gas to oppose the change and thereby increase the pressure
• If the number of moles of gas is the same on both sides of the equation then changing pressure will have no effect on the position of equilibrium

MOLES OF GAS = BIG NUMBER infront of the compounds in a reaction

Question 6

What effect would increasing pressure have on the yield of methanol?
CO (g) + 2H2(g) CH3OH (g)

Answer 6

If pressure is increased the equilibrium will shift to oppose this and move towards the side with fewer moles of gas to try to reduce the pressure. The position of equilibrium will shift towards the right because there are 3 moles of gas on the left but only 1 mole of gas on the right, giving a higher yield of methanol

Question 7

Different industrial processes which uses equilibrium

Answer 7

• Haber process
• Contact process
• Production of methanol from CO
• Hydration of ethene to produce ethanol

Question 8

Effect on concentration on equilibrium

Answer 8

• Increasing the concentration will cause the equilibrium to shift in the direction of the lower concentration to oppose the change
• Decreasing the concentration will cause the equilibrium to shift in the direction of the higher concentration

Question 9

Effect of a catalyst on equilibrium

Answer 9

A catalyst will have no effect on the position of equilibrium but it will speed up the rate at which equilibrium is achieved this is because it speeds up the rate of the forward and backward reaction by the same amount

Question 10

Conditions of the Haber process

Answer 10

Temp: 450
Pressure: 200-1000 atm
Catalyst: iron

Question 11

How does equilibrium apply to the Haber process

Answer 11

• As the forward reaction is exothermic we would need a low temperature to produce a good yield of ammonia but this would mean that the ammonia would be produced at a slow rate this means that a compromise temp of 450 is used
• high pressure gives a good yield and a high rate but too much pressure would lead to high energy cost for pumps to produce the pressure

Question 12

Haber process reaction

Answer 12

N2 + 3H2 ⇌ 2NH3 (exothermic reaction)

Question 13

Conditions of Contact process

Answer 13

Temp: 450
Pressure: 1 to 2 atm
Catalyst: V2O5

Question 14

What only affects kc

Answer 14

Temperature nothing else

Question 15

Equation for contact process

Answer 15

Stage 1 S (s) + 02(g) → S02 (g)
Stage 2 SO2 (g) + ½/02 (g) - reversible reaction - SO3 (g)

Question 16

Effect on temp and pressure on contact process

Answer 16

Low temp gives good yield but slow rate so 450 degrees is used
High pressure gives slightly better yield and high rate but too high a pressure would lead to too high energy costs for pumps to produce the pressure

Question 17

What are the effects of pressure and temperature on haber and contact processes

Answer 17

Low temp gives good yield but slow rate: compromise moderate temp used
High pressure gives slightly better yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure

Question 18

What are the effects of pressure and temperature on haber and contact processes

Answer 18

Low temp gives good yield but slow rate: compromise moderate temp used
High pressure gives slightly better yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure

Question 19

What are the effects of temperature and pressure for production of methanol form CO and hydration of ethene

Answer 19

Low temp gives good yield but slow rate: compromise temp used
High pressure gives good yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure
For hydration only - High pressure also leads to unwanted polymerisation of ethene to poly(ethene)

Question 20

Production of methanol from CO equation

Answer 20

CO (g) + 2H2(g)- reversible reaction - СН3ОН (g)

Question 21

Conditions of production of methanol from CO

Answer 21

T= 400°C, P= 50 atm, catalyst = chromium and zinc oxides

Question 22

Conditions of production of methanol from CO

Answer 22

T= 400°C, P= 50 atm, catalyst = chromium and zinc oxides

Question 23

Equation for production of methanol from CO

Answer 23

CO (g) + 2H2 (g) - reversible reaction - СН3ОН (g)

Question 24

Equation for hydration of ethene to produce ethanol

Answer 24

C2H4 + H20 -reversible reactions - C2H5OH

Question 25

Conditions for hydration of ethene to form ethanol

Answer 25

T= 300°C, P= 70 atm, catalyst = conc H3P04

Question 26

What can having a large and small kc tell us

Answer 26

The larger the kc the equilibrium favours the products
The smaller the kc the equilibrium favours the reactants

Question 27

What can having a large and small kc tell us

Answer 27

The larger the kc the equilibrium favours the products
The smaller the kc the equilibrium favours the reactants

Question 28

What is the effect of increasing the concentration of OH ions and H ions in this reaction I2 + 2OH- (BROWN). <—> I- + IO- + H2O (COLOURLESS)

Answer 28

Increasing the concentration OH ions causes the equilibrium to shift to oppose this and move in the forward direction to remove OH ions. The position of equilibrium will shift towards the right, giving a higher yield of I’ and
IO-. ( The colour would change from brown to colourless)

Adding H+ ions reacts with the OH ions and reduces their concentration so the equilibrium shifts back to the left giving brown colour.