topic 10 Flashcards
dynamic equilibrium
when forward and backward reactions are occurring at equal rates. Concentrations of reactants and products stays constant and reaction is continuous
forward reaction ?
exothermic
backward reaction ?
endothermic
Le Chatelier’s principle
if an external condition is changed the equilibrium will shift to oppose the change
effect of increased temperature on equilibrium
equilibrium will shift to oppose this and move in the endothermic direction to try and reduce the temp by absorbing heat
effect of decreasing temperature on equilibrium
equilibrium will shift to oppose this and move in the exothermic direction to try and increase the temp by giving out heat
what temp gives higher yield
lower temps have a higher yield but result in slow rates of reaction
effect of increased pressure on equilibrium
equilibrium will shift to the side with fewer moles of gas to oppose the change and therefore reduce the pressure
effect of decreases pressure on equilibrium
equilibrium will shift to the side with more moles of gas to oppose the change and increase the pressure
effect of change in pressure if there are equal amounts of moles on both sides
no effect
lower or higher pressure for a high product yield
higher pressure gives higher yield of product and produces faster rate
cons of high pressures
expensive to produce - high energy costs for pumping
equipment is expensive
effect of concentration equilibrium
I2 + 2OH- ⇌ I- + IO- + H2O
increasing conc of OH- ions causes equilibrium to shift to oppose this and move in the forward direction to remove the OH- ions. Position of eqb shift towards the right giving a higher yield of I- and IO-.
goes from brown to colourless
What causes Kc to change?
Kc ONLY changes with TEMPERATURE. It does not change if pressure or concentration is altered.
What is said when Kc is small?
the equilibrium favours the reactants
What is the effect of changing conditions on value of Kc?
the larger the Kc the greater the amount of products.
What is the effect of catalysts on equilibrium?
No effect, but it speeds up the rate at which equilibrium is achieved
Equilibrium constant, Kc formula?
K = [C]p [D]q
[A]m [B]n
importance of equilibrium to industrial processes - haber process
pressure
temp
equation
N2 + 3H2 ⇌ 2NH3
T = 450
P = 200 - 1000 atm
catalyst = iron
Low temp gives good yield but slow rate - compromise temp used
High pressures gives a good yield and high rate - too high a pressure would lead too high energy costs for pumps to produce the pressure
importance of equilibrium to industrial processes - contact process
stage 1: S + O2 —-> SO2
stage 2: SO2 + 0.5 O2 ⇌ SO3
T = 450
P = 1 to 2 atm
catalyst V2O5
low temp gives good yield but slow rate : compromise moderate temp used
High pressure gives slightly better yield and high rate : too high pressure would lead to too high energy costs for pumps to produce the pressure
importance of equilibrium to industrial processes -production of methanol from CO
CO + 2H2 ⇌ CH3OH
T = 400
P = 50 atm
catalyst = chromium and zinc oxides
low temp gives good yield but slow rate : compromise temp used
High pressure gives slightly better yield and high rate : too high pressure would lead to too high energy costs for pumps to produce the pressure
importance of equilibrium to industrial processes - hydration of ethene to produce ethanol
CH2=CH2 + H2O ⇌ CH3CH2OH
T = 300
P = 70 atm
catalyst = concentrated H3PO4
Low temp gives good yield but slow rate : compromise temp used
High pressure gives slightly better yield and high rate : too high pressure would lead to too high energy costs for pumps to produce the pressure
High pressure also leads to unwanted polymerisation of ethene to polyethene
using a catalyst
in all cases they speed up the rate allowing lower temps to be used (lower energy costs) but have no effect on equilibrium
using high pressures - disadv
too high energy costs for pumps to produce the pressure and too high equipment costs
advantage of recycling unreacted reactants
improves overall yields of the processes
