5.9 chemical equilibria

Question 1

define dynamic equilibrium

Answer 1

dynamic equilibrium refers to the state of reversible process at which the rates of forward and backward reactions are equal but not zero

Question 2

equation for equilibrium constant Kc and Kp

Answer 2

Kc = [C]^c[D]^d / [A]^a[B]^b ; Kforward / Kbackward
Kp = (Pc)^c(Pd)^d / (Pa)^a(Pb)^b

Question 3

where does the position of equilibrium lie if Kc > 1 or Kc <1

Answer 3

Kc > 1: PoE lies to the right
Kc < 1: PoE lies to the left

Question 4

what is Kc affected by (and not affected by)?

Answer 4

Kc is affected by temperature and activation energy; not affected by concentration changes

Question 5

what is the formula relating ΔG with K?

Answer 5

ΔG = - RTlnk

Question 6

where does the position of equilibrium lie if ΔG > 0 and ΔG < 0?

Answer 6

ΔG > 0: k < 1, PoE lies to the left
ΔG < 0: k > 1, PoE lies to the right

Question 7

steps to draw ICE table

Answer 7

1) write out balanced chem equation
2) initial moles, change in moles, equilibrium moles
3) write equilibirum constant equation, substitute in concentration (rmb to divide by volume)

Question 8

define le chatelier’s principle

Answer 8

le chatelier’s principle states that if a dynamic equilibrium is subjected to a change which disturbs the equilbirum, the position of the equilbirium will shift to counteract the effect of the change to re-establish equilibrium

Question 9

what is the effect of changing concentration of reactants?

Answer 9

• when conc of reactants increase, by LCP, PoE shifts to the right to decrease conc of reactants

Question 10

what is the effect of diluting the reaction mixture?

Answer 10

• conc of both reactant and products decrease
• however, side with more moles of aq decreases by a larger extent
• by LCP, PoE shifts to increase conc

Question 11

what is the effect of increasing volume of a gaseous mixture?

Answer 11

• partial pressures of both reactants and products increase
• by LCP, PoE shifts to decrease pressure by favouring direction with fewer moles of gaseous species

Question 12

what is the effect of adding an inert gas at constant VOLUME?

Answer 12

• total pressure increases
• however, partial pressures of all gases remain constant, PoE does not shift

Question 13

what is the effect of adding an inert gas at constant PRESSURE?

Answer 13

• total volume increases
• partial pressures of all gases decrease
• by LCP, PoE shifts to increase pressure by favouring direction with more moles of gaseous species

Question 14

what is the effect of increasing the partial pressure of a gaseous component?

Answer 14

• same as increasing concentration!
• when partial pressure of reactants increase, by LCP, PoE shifts to the right to decrease partial pressure of reactants

Question 15

what is the effect of adding a catalyst?

Answer 15

• no effect on PoE because catalyst increases the rate of forward and backward reaction by the sam extent by providing an alternative pathway of lower activation energy

Question 16

what is the effect of increasing temperature for an endothermic reaction?

Answer 16

• by LCP, PoE will shift right to decrease the temperature
  ** both forward and backward rates increase since equilibrium constants increase
• however, Kf increases to a larger extent than Kb

Question 17

what are the conditions and considerations for the Haber Process?

Answer 17

• 450 degrees: low temp favours forward exo reaction, but reaction is slow
• 200 atm: high pressure high yield but equipment expensive