chemical equilibria, le chatelier's principle + Kc

Question 1

what is dynamic equilibrium

Answer 1

the rate of forward reaction is the same as the rate of the backward reaction in a CLOSED SYSTEM, and the concentrations of the reactants and products is constant

Question 2

what happens when position of equilibrium shifts to the
1. left
2. right

Answer 2

left = conc of reactants increase
right = conc of products increases

Question 3

what does le chatelier’s principle state?

Answer 3

if a change is made to a system in dynamic equilibrium, the position of the equilibrium moves to counteract this change

Question 4

how does the equilibrium shift when
1. increase in conc
2. decrease in conc

Answer 4

1. equilibrium shifts to the RIGHT to reduce the effect of increase of conc in the reactant
2. equilibrium shifts to the LEFT to reduce the effect of a decrease in reactant

Question 5

how does the equilibrium shift when
1. increase in pressure
2. decrease in pressure

Answer 5

1. shifts in direction with LESS moles
2. shifts in direction with MORE moles

Question 6

how does equilibrium shift when
1. temperature increases
2. temperature decreases

Answer 6

1. moves in the endothermic direction
2. moves in the exothermic direction

Question 7

what effect does a catalyst have on equilibrium?

Answer 7

catalysts only increase the rate of reaction, dont have an effect on the position of equilibrium

Question 8

what is the formula for Kc

Answer 8

[C]^c [D]^d
Kc = ——————-
[A]^a [B]^b

Question 9

formula for concentration

Answer 9

conc = moles / volume

Question 10

formula for Kp

Answer 10

pp(C)^c pp(D)^d
Kp = ————————-
pp(A)^a pp(B)^b

Question 11

method to calculate KC

Answer 11

1. ICE = initial moles, change in moles, moles at equilibrium

Question 12

what effect does an increase in temperature have on the value of Kc in endo and exo

Answer 12

An increase in temp in an ENDOthermic = Kc increases bc conc of products increases, and conc of reactants decreases
An increase in temp in an EXOthermic = Kc decreases bc product conc increases and reactant conc decreases

Question 13

what is the formula for the Haber process and is it exothermic or endothermic?

Answer 13

N₂ (g) + 3H₂ (g) ⇌ 2NH₃ (g)
exothermic

Question 14

how to maximise yield of haber process

Answer 14

• ↑↑ pressure shifts eq to right .: ↑↑ yield of ammonia bc fewer gas moles
• compromise pressure - 200atm bc high pressure = high cost
• lower temp favours exothermic .: more ammonia
• too low = slow reaction
• compromise = 400-500ºC
• iron catalyst used

Question 15

what are the reaction steps of the Contact Process

Answer 15

2SO₂ (g) + O₂ (g) ⇌ 2SO₃ (g)  ΔH = –197 kJ mol⁻¹ (exothermic)

SO₃ + H₂SO₄ → H₂S₂O₇ (oleum)

H₂S₂O₇ + H₂O → 2H₂SO₄

Question 16

how to maximise yield of contact process

Answer 16

• ↑↑ pressure shifts eq to right .: ↑↑ SO3 yield
• but Kc already high so eq already far to the right
• compromise pressure = around 1 atm
• lower temp favours SO3 production
• lower temp = too slow
• .: compromise temperature = 450ºC
• catalyst Vanadium (V) oxide (V₂O₅)