Equilibria 6 Flashcards
dynamic equilibrium
- closed container
- either direction
- rates happen at the same time
la chandeliers principle
if a system at equilibrium is disturbed, the equilibrium moves in the direction that tends to reduce the disturbance
change in concentration
- increase the concentration of the reactant creates more products so the equilibrium moves to the right
- increase the concentration of the product = equilibrium shifts to the left
- decreasing the pressure has the opposite effect
change in pressure
- only with gases
- increasing the pressure shifts the equilibrium to the side with fewer gas molecules
change in temperature
- increasing the temperature (adding heat) shifts to the endothermic direction to absorb the heat
- decreasing the heat shifts in the exothermic direction to produce more heat
- one direction would be exothermic and then other would be endothermic
change in conditions with a catalyst
they don’t effect on the position of equilibrium but allow equilibrium to happen quicker
Ammonia
Haber process
- iron catalyst
- used to make fertiliser
- Air (nitrogen)
- methane (natural gas)
N2 + 3H2 — 2NH3 -92kJmol-1
-200 atm and 670K
Ethanol
- fermentation or hydration
- used in drugs, detergents, inks and motor fuel
- high pressure (equilibrium moves to the right) = causes ethene to polymerise and increases the costs
- low temperature (equilibrium moves to the right) = reduce the rate of reaction
Methanol
- chemical feedstock
- methanal = bakelite
- highest yield at low temperature and high pressure
- 500K and 10000kPa
equilibrium constant
- different in different reactions
- doesn’t change unless the temperature changes
effect of changing the temperature on the equilibrium constant
endothermic (decrease in temperature)
kc decrease
effect on products decrease
effect on reactants increase
equilibrium moves to the left
effect of changing the temperature on the equilibrium constant
endothermic (increase in temperature)
kc increase
effect on products increase
effect on reactants decrease
equilibrium moves to the right
effect of changing the temperature on the equilibrium constant
exothermic (decrease in temperature)
kc increase
effect on products increase
effect on reactants decrease
equilibrium moves to the right
effect of changing the temperature on the equilibrium constant
exothermic (increase in temperature)
kc decrease
effect on products decrease
effect on reactants increase
equilibrium moves to the left
effect of changing the concentration on the equilibrium constant
doesn’t change
catalyst and equilibrium constant
catalysts have no effect, affects the rates of forwards and backwards reaction
What does a closed system mean?
Nothing can enter or lose
What does a negative 🔺H mean?
Forward reaction is exothermic
Methanol
CO2 + 3H2 ↔️ CH3OH + H2O 🔺H=-49 KJmol-1
Temperature decrease
Yield CH3OH increases
Forward reaction is exothermic therefore equilibrium shifts to the right
Oppose the decrease in temperature
Methanol
CO2 + 3H2 ↔️ CH3OH + H2O 🔺H=-49 KJmol-1
Increase pressure
Yield of CH3OH increases
More molecules on the left therefore equilibrium shifts right to oppose the increase in pressure
Methanol
CO2 + 3H2 ↔️ CH3OH + H2O 🔺H=-49 KJmol-1
Catalyst added
Speeds both reaction equally
Equilibrium would be reached faster
Haber process
CH4 + 3H2 ➡️ CO + 3H2 ( reaction needed to get hydrogen)
Raw materials - air ( nitrogen ) - water - natural gas
N2 + 3H2 ↔️ 2NH3
Iron catalyst
Uses of ammonia - fertiliser - nylon - explosives
High pressure - increase yield / more moles on the left hand side / equilibrium shifts to the right
Low temperature - higher yield / forward reaction exothermic / equilibrium shifts to the right
Ethanol
Fermentation
C6H12O6 ➡️ 2C2H5OH + 2CO2
Ethanol
Stream
C2H4 + H2O ↔️ C2H5OH
Exothermic
Lower temperature = increase yield
300 degrees and 60-70 atmospheres
Phosphoric acid catalyst
Methanol
50-100 atmospheres
250 degrees
2H2 + CO ↔️ CH3OH
Production of lime
CaCO3 ↔️ CaO + CO2
Forwards reaction is endothermic
1000 degrees in the lime limekiln
Batch process
Contact process reactor
Sulphur dioxide mixed with air ( ratio 2:1) Catalyst of vanadium 450 degrees 1-2 atmospheres of pressure Exothermic
2SO2 + O2 ↔️ 2SO3
Homogeneous
All reactants and products are in the same phase
reversible reaction
forward and reverse reactions proceed at equal rates
the concentrations of reactants and products remain constant
Kc
deduced from the equation for a reversible reaction
The concentration, in mol dm–3, of a species X involved in the expression for Kc is represented by [X]
The value of the equilibrium constant is not affected either by changes in concentration or addition of a catalyst
