Equilibrium I Flashcards
What is a reversible reaction?
Is one that goes in both directions at the same temperature
What is meant by term equilibrium?
A system is in equilibrium when there is no further change in the concentrations of the reactants and products
what happens in a dynamic equilibrium?
in a dynamic equilibrium, the rates of the forward and reverse reaction are equal. Therefore there is no further change in the concentrations of the reactants and products
What is le Chatelier’s principle?
when the conditions of a system in equilibrium is alters in such a way as to try to restore the original conditions
what happens if a system at equilibrium is heated?
the temperature rises and the system reacts to remove the heat energy and bring the temperature down.
This means that heat energy must be converted to chemical energy
Where does an increase in temperature shift equilibrium ?
to the endothermic side
What happens when temperature shifts in the endothermic direction?
a decrease in the equilibrium yield for an exothermic reaction
An increase in the equilibrium yield for the endothermic reaction
When temperature decreases what happens to the energy?
the chemical energy is converted to heat energy , restoring the temperature
why does an increase in temperature speed up the endothermic reactions in the equilibrium more than the exothermic?
This is because the Ea for the reaction on endothermic is greater than that for the reaction in the exothermic direction. The reaction with high Ea are more sensitive to temperature changes than reactions with lower Ea
When does the effect of pressure apply to in equilibrium?
only applies to equilibrium reactions involving gases
What is pressure caused by?
pressure is caused by the bombardment of the gas molecules on the walls of the container
At a given temperature, what does the pressure depend on?
only on the number of gas molecules in a given volume
What is the pressure of an equilibrium system increased by?
reducing the volume or
adding more gas into the same volume
Results in more molecules per cm^3
If the pressure is increased, according to le chatelier’s principle what will happen?
That the system will react in order to try to bring the pressure down again towards the original value. This can only happen if equilibrium shifts to the direction with fewer gas molecules
A decrease in pressure will result in what?
the equilibrium shifting towards the side of the equation with more gas molecules.
When does the effect of equilibrium apply to a system?
It applies to a system in which the reactants are dissolved in a solvent, usually water
What happens if the concentration of one of the substances in the equilibrium reaction is increased according to le chatelier’s?
position will shift to remove some of that substances
What happens to equilibrium if the concentration of one of the species is decreased?
the position will shift to produce more of that species
How does a catalyst work?
By providing an alternative route that has a lower Ea than that of an uncatalysed reaction. Faster ROR
How does a catalyst affect the position of equilibrium?
has no effect on the position of equilibrium but it will speed up the rate at which the
equilibrium is achieved.
Why are catalysts important in industrial processes?
As many reactions are extremely slow at room temperature
How can the overall yield of industrial processes be improved?
Recycling unreacted reactants back into the reactor can improve the overall yields of all these processes
Give 4 examples of industrial processes using the concept of equilibrium
Haber process
Contact process
Production of methanol from CO
Hydration of ethene to produce ethanol
key details of haber process
N2 + 3H2 2NH3 H = -ve exo
T= 450oC, P= 200 – 1000 atm, catalyst = iron
Low temp gives good yield but slow rate: compromise temp used
High pressure gives good yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure
key details of production of methanol from CO
CO (g) + 2H2(g) CH3OH (g) H = -ve exo T= 400oC, P= 50 atm, catalyst = chromium and
zinc oxides
Low temp gives good yield but slow rate: compromise temp used
High pressure gives good yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure
key details of the contact process
Stage 1 S (s) + O2 (g)SO2 (g)
Stage 2 SO2 (g) +1⁄2O2 (g) SO3 (g) H = -98 kJ mol-1
T= 450oC, 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 a pressure would lead to too high energy costs for pumps to produce the pressure
key details of hydration of ethene to produce ethanol
CH2=CH2 (g) + H2O (g) CH3CH2OH(l) H = -ve
T= 300oC, P= 70 atm, catalyst = conc H3PO4
Low temp gives good yield but slow rate: compromise temp used
High pressure gives good yield and high rate: too high a pressure would lead to too high energy costs for pumps to produce the pressure
High pressure also leads to unwanted polymerisation of ethene to poly(ethene)
what does kc stand for?
equilibrium constant
how do you work out kc
products over reactants , moles become powers
