2.3- Equilibria Flashcards
Two features of dynamic equilibrium?
Forward and backward reactions are occurring at equal rates
The concentrations of reactants and products stay constant
What does the term ‘dynamic’ mean?
Both forward and backward reactions occurring simultaneously
What does the expression ‘position of equilibrium’ mean?
Describes the composition of the equilibrium mixture
If the position of equilibrium favours the reactants (also described as ‘towards the left’) then the equilibrium mixture will contain mostly reactants
What is Le Chatelier’s principle?
If an external condition is changed the equilibrium will shift to oppose the change (and try to reverse it)
What is the effect of temperature on equilibrium?
If temperature is increased the position of equilibrium will shift to oppose this and move in the endothermic direction to try and reduce the temperature by absorbing heat
If temperature is decreased the position of equilibrium will shift to oppose this and move in the exothermic direction to try and increase the temperature by giving out heat
Effect of pressure on equilibrium?
Increasing pressure will cause the position of equilibrium to shift towards the side with fewer moles of gas to oppose the change and thereby reduce the pressure
Decreasing pressure will cause the position of equilibrium to shift towards the side with more moles of gas to oppose the change and thereby increase the pressure
If the number of moles of gas is the same on both sides of the equation then changing pressure will have no effect on the position of equilibrium
Advantages and disadvantages of having lower temperatures?
Low temperatures may give a higher yield of product but will also result in slow rates of reaction.
Often a compromise temperature is used that gives a reasonable yield and rate
Advantages and disadvantages of increasing pressure?
Increasing pressure may give a higher yield of product and will produce a faster rate.
High pressures, however, leads to too high electrical energy costs for pumps to produce the pressure and too high equipment costs to have equipment that can withstand high pressures
Effect of catalysts on equilibrium?
No effect on the position of equilibrium, but it will speed up the rate at which equilibrium is achieved
Lower energy costs as lower temperatures can be used
Why do catalysts not affect the position of equilibrium?
Speeds up the rates of both the forward and backward reactions by the same amount
Effect of concentration on equilibrium?
If you increase the concentration of a reactant, the equilibrium tries to get rid of the extra reactant by making more product so equilibrium position shifts to the right (vice versa)
Equation for formation of ethanol?
C2H4 (g) + H2O (g) —> C2H5OH (g)
DH = negative
Conditions and catalyst used for formation of ethanol reaction?
Temperature= 300°C Pressure= 70 atm Catalyst= concentrated H3PO4
Reasons for conditions for ethanol formation reaction?
Low temperature gives good yield but slow rate so compromise temperature used
High pressure gives good 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 poly(ethene)
Uses of methanol and ethanol?
Fuels
