Equillibria Flashcards
2 features of dynamic equillibria
Forward and backward reactions occur at the same rate
Concentrations of reactants and products stay constant
What does dynamic mean in terms of equillibria?
Both forward and backwars reactions are occuring simultaneously
What does “position of equillibrium” describe?
The composition of the equillibrium mixture
Eg if it shifts to the right, it is mostly reactants
Le Chatelier’s principle?
If an external condition is changed the equillibrium will shift to oppose the change
N2 + 3H2 <-> 2NH3 (exothermic, -ve enthalpy change)
What effect would increasing temperature have on yield of ammonia? (5)
Equillibrium will shift to oppose this
Move in the endothermic, backwards direction
To decrease temperature
The position of equillibria shifts towards the left giving
A lower yield of ammonia
Why is a compromise temperature needed in some equillibria?
Lower temperatures may give a higher yield of product but will also result in slow rates of reaction
Compromise temps can give a reasonable yield and rate
CO + 2H2 <-> CH3OH
What effect would increasing pressure have on the yield of methanol
Eqm will shift to oppose this and
Move towards the side with fewer moles of gas
To try to reduce the pressure
Eqm will shift to the right as there are 3 moles of gas on the left but only 1 mole of gas on the right
Giving a higher yield of methanol
Why might a compromise pressure be used?
Increased pressures may give a higher yield of product and will produce a faster rate
But they are expensive to produce, as costs for pumping in gases to make high pressures and equipment to contain high pressures are high
I2 + 2OH- <-> I- + IO + H2O
What is the effect of increasing OH- or H+ concentrations on equillibrium?
OH- conc increases would cause eqm to shift to the oppose this to remove and decrease the concentration of these ions. eqm would shift to the right, giving a higher yield of I- and IO-
adding H+ ions reacts with OH- ions to reduce their concentration, so eqm shifts back to the left to give the iodine brown colour
Effect of catalysts on the position of equillibrium?
No effect
Speeds up rate at which eqm is achieved
As it speeds up the rate of the forward and backward reactions by the same amount
Haber process equation
exo/endothermic
temperature
pressure
catalyst
N2 + 3H2 <-> 2NH3
exothermic
450°C
600atm
iron
Why is a compromise temperature used in the Haber process?
Low temp gives good yield but slow rate
Why is a compromise pressure used in the Haber process?
High pressure gives good yield and high rate, but too high leads to very high energy costs for pumps to produce the pressure
Contact process temperature
pressure
catalyst
450°C
1atm
V2O5
Production of methanol from CO equation
exo/endothermic
temperature
pressure
2 possible catalysts
CO + 2H2 <-> CH3OH
exothermic
400°C
50atm
chromium and zinc oxides
