Equilibrium

Question 1

What is meant by dynamic equilibrium? (2)

Answer 1

• Where the rate of the forward
  reaction equals the rate of the
  backwards reaction (1)
• Only in a closed system (1)

Question 2

What is Le Chateliers Principle? (2)

Answer 2

• If a reaction at equilibrium is
  subjected to change, the
  position of equilibrium will
  move to counteract change (1)
• Where shifting to the left will
  produce more reactants and
  vise versa (1)

Question 3

What happens if the reactants concentration increases? (2)

Answer 3

• Equilibrium will shift to the
  right to reduce concentration
  (1)
• More products will be made (1)

Question 4

What is the requirement for Le Chateliers principle? (2)

Answer 4

• Only work in homogeneous
  equilibria (1)
• Reactants and products in
  the same state (1)

Question 5

What happens if pressure increases? (1)

Answer 5

• Equilibrium will shift to the side
  with the fewest gas particles (1)

Question 6

What happens if temperature increases? (2)

Answer 6

• Equilibrium will shift in the
  endothermic direction (1)
• The direction of positive ΔH
  (1)

Question 7

What happens if a catalyst is added? (2)

Answer 7

• No effect on Kc (1)
• The catalyst will speed forward
  and backward reaction equally
  (1)

Question 8

Why is a medium temperature used in an exothermic reaction? (2)

Answer 8

• To have a high yield from a
  lower temperature (1)
• And a high rate of reaction (1)

Question 9

Why is a medium pressure used in a reaction? (2)

Answer 9

• To have a high yield and rate
  (1)
• But not be too expensive (1)

Question 10

What is the Kc expression? (3)

Answer 10

• The equilibrium constant (1)
• Where only gases and aqueous
  states are included (1)
• As the concentrations of solid and liquid stay constant (1)

Question 11

What is a heterogenous reaction? (1)

Answer 11

• All reactants and products in
  different states (1)

Question 12

How do you work out concentrations before Kc? (2)

Answer 12

Initial moles
Change moles
Equilibrium

Equilibrium / Volume (dm3)

Question 13

What is partial pressure? (1)

Answer 13

• The pressure of an individual gas (1)

Question 14

How do you work out partial pressure? (2)

Answer 14

• Work out mole fraction:
  number of moles / total moles (1)
• Work out partial pressure:
  mole fraction / total pressure (1)

Question 15

What is Kp? (3)

Answer 15

• Gas equilibrium constant (1)
• Uses partial pressure instead of concentration (1)
• Only gas states involved (1)

Question 16

• How would equilibrium amounts be calculated rather than concentration (2)

Answer 16

• Same number of moles on both sides of the equation (1)
• So volumes will cancel out (1)

Question 17

Why does phenolphthalein pink fade at the end of titration? (2)

Answer 17

• Equilibrium shifts to the left (1)
• So the mixture becomes more acidic (1)

Question 18

How would you confirm equilibrium has been reached in titration? (2)

Answer 18

• Repeat for longer (1)
• Kc should remain unchanged (1)

Question 19

Why is only gas involved in Kp expression? (1)

Answer 19

• Other states have no partial pressure (1)