6.1 - 6.6 + 19.1 - Equlibria

Question 1

Define dynamic equilibrium

Answer 1

A continuous reaction in which the forward and reverse reactions are proceeding at equal rates & there is no overall change in the concentration of any reactant or product

Question 2

What are the four statements of equilibria?

Answer 2

Reaction is dynamic (forward and backward reactions are at the same rate)

Equilibrium can be approached from either direction and the final position of equilibrium will be the same

Equilibrium can only be established in a closed system

The macroscopic properties of the system do not change with time (density, concentration, colour and pressure)

Question 3

Define Le Chatelier’s Principle

Answer 3

A system at equilibrium will act to oppose any change in conditions

Question 4

If more of one compound is added to a system at equilibrium how will this affect the equilibrium?

Answer 4

Shift to opposite side to oppose change

Question 5

If the pressure is increased in a system at equilibrium how will this affect the equilibrium?

Answer 5

Shift to decrease pressure, shift to side of the equation with fewer moles of gas

Question 6

If the temperature is changed in a system at equilibrium how will this affect the equilibrium?

Answer 6

Increasing the temp will make the equilibria shift to favour the endothermic reaction

Decreasing the temp will make the equilibria shift to favour the exothermic reaction

Question 7

What effect do catalysts have on the position of equilibrium?

Answer 7

• No effect on the position of equilibrium
• But do allow equilibrium to be reached more quickly

Question 8

Define rate determining step

Answer 8

The slowest step in a reaction mechanism

Question 9

What are the considerations that need to be taken into account for equilibrium reactions in industry?

Answer 9

• Yield of product
• Time
• Cost

Question 10

As temp increases, Kc increases. Is this reaction exothermic or endothermic?

Answer 10

Endothermic

Question 11

Explain the effect equilibrium position has on equilibrium constant

Answer 11

• Changing equilibrium position has no effect on equilibrium constant
• This is because as you increase or decrease the top half of the Kc equation, the same happens on the bottom

Question 12

What are the uses of ammonia?

Answer 12

• Fertilisers
• Synthetic fibre
• Explosives
• Plastics

Question 13

What is the process used to make ammonia?

Answer 13

Haber Process

N₂ + 3H₂ ⇌ 2NH₃

∆H = -92 kJmol⁻¹

Question 14

What conditions are used for the Haber process?

Answer 14

• 670K
• 20,000kPa
• Iron catalyst
  This gives a 15% conversion rate

Question 15

What is the process used to make ethanol?

Answer 15

Hydration of ethene, obtained from crude oil

CH₂CH₂ + H₂O ⇌ CH₃CH₂OH

∆H = -46kJmol⁻¹

Question 16

What conditions are used for the hydration of ethene?

Answer 16

• 570K
• 6,500kPa
• Phosphoric acid catalyst absorbed onto silica
  This gives a 5% conversion rate

Question 17

What is the process used to manufacture methanol?

Answer 17

CO + 2H₂ ⇌ CH₃OH

∆H = -91kJmol⁻¹

Question 18

What conditions are used for the manufacture of methanol?

Answer 18

• 500K
• 10,000kPa
• Copper catalyst
  This gives a 5-10% conversion rate

Question 19

What uses are there for methanol?

Answer 19

• Starting material for the manufacture of other chemicals e.g methanal, terylene, perspex
• Motor fuel

Question 20

Define homogeneous

Answer 20

All substances in the same phase

Question 21

What is indicated about the equilibrium position if Kc > 1?

Answer 21

Equilibrium favouring right

Question 22

What is indicated about the equilibrium position if Kc < 1?

Answer 22

Equilibrium favouring left

Question 23

What is indicated about the reaction if Kc > 10¹⁰?

Answer 23

Reaction is complete

Question 24

What is indicated about the reaction if Kc < 10⁻¹⁰?

Answer 24

No reaction

Question 25

Define partial pressure

Answer 25

Partial pressure of a gas in a mixture is the fraction of the total pressure caused by each individual gas

Question 26

Partial pressure of gas A =

Answer 26

mole fraction of A x total pressure

Question 27

Mole fraction of gas A =

Answer 27

number mols of A / total number of mols in mixture

Question 28

Define homogenous

Answer 28

All reactants in the same state

Question 29

Define dynamic

Answer 29

Continuous

Question 30

Define equilibrium

Answer 30

Rates of forward and reverse reactions are equal

Question 31

Why might you not use low pressure in industry even if Le Chatelier’s indicates to?

Answer 31

Will give low production and low rate of reaction

Question 32

What can affect Kc or Kp?

Answer 32

Temperature only

Question 33

If you know the Kc of the forward reaction is x, what is the Kc of the backward reaction?

Answer 33

1/x