Equilibrium and reversible reactions
The reaction between nitrogen and hydrogen to form ammonia is reversible.
The reaction mixture can reach a dynamic equilibrium.
Which of these statements describes what is happening at equilibrium?
Put ticks (✓) in the boxes next to the two correct statements.
Now write out the out the three conditions needed for dynamic equilibrium into your book
The concentrations of nitrogen, hydrogen and ammonia are constant
The concentration of ammonia is increasing.
The forward and reverse reactions happen at the same time
All of the nitrogen and hydrogen react to make ammonia.
The forward and reverse reactions happen at the same rate.
The reaction between nitrogen and hydrogen has stopped.
True
False
Economic considerations
to be economically viable need to make as ammonia as possible as as possible and the conditions are a between these two factors.
Now write out the conditions for the Haber process into your exercise book.
compromise
quickly
much
Temperature.
Higher temperature shifts equilibrium to as the reverse reaction is so the higher the temperature the the yield.
At lower temperature the rate of reaction is too
so a medium temperature of about 450°C is used.
Write out why a temperature of 450oC is used
compromise
exothermic
left
lower
endothermic
slow
right
Pressure
higher pressure shifts equilibrium to the side with (LHS (4) gas moles vs RHS (2) gas moles).
The higher the pressure the the yield because forward reaction decreases
higher the pressure the tougher the reaction vessel has to be so that it does not burst
higher pressure increases .
medium pressure of atmospheres
Write out why a pressure of 200 Atm is used.
higher
right
compromise
fewer
200
cost
pressure
Catalyst
catalyst gives more product in same
catalyst allows use of temperature for same rate
catalyst does not change position
(Note a catalyst provides an reaction pathway of lower energy so a greater proportion of the particles the activation energy so the frequency of collisions increases even though the total number of collisions is not changed).
Write out why an iron catalyst is used.
exceed
lower
equilibrium
activation
successful
alternative
time
N₂ + 3H₂ ⇌ 2NH₃
The reaction is exothermic in the forward direction
If Hydrogen is added equilibrium will shift to the
If f Nitrogen is added equilibrium will shift to the
If ammonia is added equilibrium will shift to the
If the pressure is increased the equilibrium will shift to the
If the temperature is increased the equilibrium will shift to the
Write these out as a set of model answers.
exothermic
left
right
endothermic
increase
2
right
3
Nothing to write here just for practice.
equilibrium shifts to the because reverse reaction is
Equilibrium shifts to the because there are fewer moles of products () than there are of reactants () and an in pressure shift equilibrium to the side with fewer moles of gas.
Nothing to write here just for practice.
