Chemical Equilibirum Flashcards
What are the rules in an equilibrium system?
- The rate of forward reaction is equal to the rate of backward reaction
- The concentration of reactants and products do not change
What does an equilibrium system being dynamic mean?
At equilibrium, both the forward and backwards reactions are taking place. As fast as the reactants are becoming products, the products are becoming reactants. Therefore, in an equilibrium system the concentrations of the reactants and products remain unchanged even though the forward and reverse reactions are still taking place
What must a system be for it to remain in equilbirum?
Closed
What is le Chatelier’s principle?
When a system in equilibrium is subjected to an external change the system readjusts itself to minimise the effect of that change
What does changing the concentration of a reactant or product in equilibrium do?
Change the rate of forwards or reverse reaction. The position of equilibrium will then shift to counteract this
What happens if the concentration of A or B increases?
The equilibrium shifts to the right (towards C and D)
What happens if the concentration of A or B decreases?
Equilibrium shifts to the left (towards A and B)
What happens if the concentration of C or D increases?
Equilibrium shifts to the left (towards A and B)
What happens if the concentration of C or D decreases?
The equilibrium shifts to the right (towards C and B)
What is used to investigate the changes of equilibrium position with concentration?
The equilibrium between chromate ions and CrO4 2-
SEPERATE NOTES!
What will changing the temperature of a system do to the equilibirum?
Change its position - the direction in which the equilibrium shifts depends on the sign of ΔH
What does an increase in temperature do to the equilibirum?
Shift it in the endothermic direction - ΔH is positive
What does a decrease in temperature do the equilibrium?
Shift the equilibrium in the exothermic direction - ΔH is negative
What is used to investigate the change in equilibrium with temperature?
Cobalt chloride dissolved in water
SEPARATE NOTES!!!
If the forward reaction is exothermic, what does an increase in temperature do?
Position of the equilibrium shifts to the left and more reactants are made
If the forward reaction is exothermic, what does a decrease in temperature do?
Position of the electrons shifts to and the right and more products are made
If the forward reaction is endothermic, what does an increase in temperature do?
Position of equilibrium shifts to the right and more products are made
If the forward reaction is endothermic, what does a decrease in temperature do?
Position of equilibrium shifts to the left and more reactants are made
What effect does an increase in pressure have on an equilibrium?
The equilibrium shifts to the side with fewer gaseous moles
If the number of gaseous molecules is the same on both sides, what does an increase in pressure do?
Nothing
What effect does a catalyst have on the equilibrium position?
It does not change the position of equilibrium - it speeds up the rates of forward and reverse reactions equally. However, it does increase the rate at which equilibrium is established
What is the Haber process?
A process in how to make ammonia
N2 (g) + 3H2 (g) <=> 2NH3 (g)
What is the change in enthalpy for the Haber process?
- 92 kJ mol^-1
Is the Haber process exothermic or endothermic?
Exothermic
What conditions would ideally make the highest yield of ammonia in the Haber process?
- A low temperature will push the equilibrium towards the ammonia
- A high pressure will push the equilibrium towards the ammonia
Why can’t a low temperature be used in the Haber process?
It would produce a high yield but it would do so very slowly. It would take a long time for significant amounts of ammonia to form and the rate may be so slow equilibrium can’t even be established
Why can’t a high pressure be used in the Haber process?
A very high pressure requires a very strong container and a large quantity of energy, increasing the cost of the process. Safety is also a concern, as a failure in steelwork could cause the leaking of hot gases including toxic ammonia
What are the Haber process compromise conditions?
- Temperatures high enough to give a reasonable rate of reaction without shifting the equilibrium position too far to the right
- Pressure that is not a safety concern and not too expensive to run
these conditions are 350-500 degrees and 100-200 atm
What is the notation for the equilibrium constant?
Kc
How do you calculate Kc?
For the general reversible equation : aA + bB <=> cC + dD
where [ ] means concentration of
What does a Kc value of 1 indicate?
The position of the equilibrium is halfway between the reactants and products
What does a Kc value greater than 1 mean?
A position of equilibrium towards the products
What does a Kc value less than 1 mean?
A position of equilibrium towards the reactants
