3.2.3 Chemical equilibrium Flashcards
Explain dynamic equilibrium.
When the rate of the forward reaction is equal to the rate of the reverse reaction and the concentrations of the products and the reactants do not change. Only exists in a closed system.
What is Le Chatelier’s principle? (Don’t need to know definition for exam).
When a system in dynamic equilibrium is subjected to a change, the position of the equilibrium will shift to minimise the change.
What changes affect the equilibrium?
-Concentration
-Pressure (only for gaseous)
-Temperature
What happens when you change the concentration of one of the reactants?
If you increase conc. of R1, then more of R2 will react with R1 to compensate for the change in conc. This will shift the equilibrium to the right.
What happens when you increase the concentration of the product?
Equilibrium will shift to the left to increase the decomposition of the product (favours the reverse reaction).
What happens when you decrease the concentration of the product?
Equilibrium will shift to the right to favour the forward reaction, so that more of the product will be formed.
What happens when you increase the pressure?
Equilibrium shifts to the side with the fewest gaseous moles.
What happens when you decrease the pressure?
Equilibrium shifts to the side with the most gaseous moles.
What would happen if you increased/decreased the pressure if there were an equal amount of gaseous moles?
There would be no change to the equilibrium position.
How would the presence of a catalyst affect the equilibrium position?
The presence of a catalyst wouldn’t affect the position of equilibrium, as it increases the rate of the forward and reverse reactions equally.
What happens when you increase the temperature?
The equilibrium will shift in the direction of the endothermic reaction (absorbs heat).
What happens when you lower the temperature?
The equilibrium will shift in the direction of the exothermic reaction (produces heat).
What is the Haber process?
The production of ammonia.
N2+3H2 ⇌ 2NH3
What are the ideal conditions for the Haber process?
Want to favour forward reaction.
-High pressure
-Low temperature
What issues are there with the ideal conditions for the Haber process?
-A very high pressure is incredibly dangerous.
-A low temperature would mean that the rate would be very low (reaction would take too long)
What are the actual conditions of the Haber process?
-Pressure: 200 ATM
-Temp: 400-500 °C
-Fe catalyst
Why are the actual conditions of the Haber process known as ‘compromise conditions’?
-The lower pressure will favour the side with the most gaseous moles (reverse reaction).
-The higher temperature doesn’t favour the forwards reaction.
-Therefore lower yield.
-However, catalyst and high temp will increase rate, so will obtain products quickly.
What is the yield of the Haber process under compromised conditions?
15%
What is the equilibrium constant?
Kc
What is the equation for the equilibrium constant?
Kc = [Products] / [Reactants]
What does it mean in terms of equilibrium position if the Kc value is small?
The concentration of the reactants is higher, therefore the equilibrium has shifted to the left (favours reverse).
What does it mean in terms of equilibrium position if the Kc value is large?
The concentration of the products is higher, therefore the equilibrium has shifted to the right (favours forward).
What is the Kc expression for:
3A ⇌ 2B + C
Kc = [B]^2 [C] / [A]^3
What factor can affect the value of Kc?
Temperature
