Chapter 17 - Chemical Equilibrium Flashcards
Reversible reaction
One in which the products react to give back the reactants, i.e, the reaction goes in both directions
Static equilibrium
The whole system is at rest, e.g, a meter stick in balance
Dynamic equilibrium
Reactants are continuously forming products and the products are continuously forming reactants; and the rate of the forwards reaction is equal to the rate of the backwards reaction
Chemical equilibrium
State of dynamic balance in a reversible reaction where the rate of the forward reaction is the same as the rate of the backwards reaction
Once the equilibrium has been reached there is no further change in the __________ of either reactants or products
Once the equilibrium has been reached there is no further change in the CONCENTRATION of either reactants or products
Scientists want the position of equilibrium to be ‘_______________’ as possible in order to ___________ the amount of products produced
Scientists want the position of equilibrium to be ‘AS FAR TO THE RIGHT’ as possible in order to MAXIMISE the amount of products produced
Le Chatelier’s Principle
If a stress (different conditions) is applied to a system at equilibrium, the system readjusts to relieve the stress applied
What are the ‘stresses’ that can be applied to a system at equilibrium?
Temperature
Concentration
Pressure
Catalysts
What happens if the temperature of a system at equilibrium is decreased?
The reaction that adds heat to the reaction (the exothermic one) will be favoured, i.e, goes in the exo direction
What happens if the temperature of a system at equilibrium is increased?
The reaction that absorbs heat (the endothermic one) will be favoured, i.e, goes in the endo direction
What is important to note about changing the pressure of a system at equilibrium?
Changing the pressure of a system at equilibrium only applies to reactions involving gases. Also only applies when there are a different number of molecules in the forward and reverse reactions
What happens if the pressure of a system at equilibrium is reduced?
The system favours/goes to the side with the greater number of molecules (take up more room)
What happens if the pressure of a system at equilibrium is increased?
The system favours/goes to the side with the smaller number of molecules (i.e brings a reduction in volume)
What happens to a system at equilibrium when the concentration of ‘X’ increases?
The system goes in the direction that removes ‘X’
What happens to a system at equilibrium when the concentration of ‘X’ decreases?
The system goes in the direction that forms ‘X’
What are the three ‘conditions’ of the effect of catalysts on reactions in equilibrium?
○ It must be a positive catalyst for both the forward and backwards reactions
○ It will not change the amount of each reactant and product at the point of equilibrium
○ The catalyst speeds up the rate at which the position of equilibrium is reached, but does not actually change that position
Ammonia can be manufactured by combining…
…nitrogen with hydrogen using an iron catalyst
What is the effect of pressure on the Haber Process?
At high pressure, the reaction is forced to the right and so increases the yield of ammonia.
However, this is expensive to generate and is dangerous, so a compromise pressure of about 200 atmospheres is used
What is the effect of temperature on the Haber Process?
The forward reaction is exothermic, so if we lower the temperature the forward reaction will increase.
However, lower temperatures decrease the rate of reaction and the process is uneconomically slow, so a compromise temperature of about 500°C is used
According to Le Chatelier’s Principle, what area the best conditions to maximise the yield of ammonia in the Haber Process?
High pressure and low temperature
What is the catalyst used in the reaction to make sulfuric acid?
vanadium pentoxide
What is the effect of pressure on the Contact Process?
High pressure forces the reaction to the right and so gives an increased yield of SO₃.
However, this is costly and the sulfur dioxide will liquefy at high pressure, so a pressure of just above atmospheric pressure is used
What is the effect of temperature on the Contact Process?
The forward reaction is exothermic so lowering the temperature will favour the forward reaction.
However, if we lower the temperature, the rate of reaction will decrease so 450°C is used
What does a larger value of Kc indicate?
The further the reaction has gone to completion, i.e, how far the equilibrium is to the right
What does a lower value of Kc indicate?
Only a small fraction of the reactants have been converted into products i.e the equilibrium lies on the left
Once equilibrium has been established for a given reaction, the value of Kc…..
….is constant for that given reaction
What is the only factor that can change the value of Kc for a reaction that has established equilibrium?
A change in temperature
