C3 - Reversible Reactions Flashcards
What is equilibrium of a reversible reaction?
When the amount of reactants and products reaches a certain balance and stay there
What is a reversible reaction?
A reaction where the products of the reaction can react to produce the original reactants
What has to be true for equilibrium to occur?
The reaction takes place in a closed system
What is a closed system?
When the area where the reaction is taking place doesn’t allow any reactants or products escape
What is the equilibrium position?
The ratio of the amounts of reactants and products when equilibrium is reached
How does exothermic / endothermic relate to reversible reactions?
One way of the reaction is exothermic and the other is endothermic
What 2 factors affect the equilibrium position?
Temperature and pressure
How does temperature affect the equilibrium position and why?
If you raise the temperature, the endothermic reaction will increase to use up the extra heat
If you lower the temperature, the exothermic reaction will increase to give out more heat
What is volume?
The amount of molecules in a substance
How does pressure affect the equilibrium position and why?
Most reaction have a greater volume on one side
If you raise the pressure, it will encourage the reaction that produces less volume and vice versa
How does adding a catalyst affect the equilibrium position and why?
It doesn’t affect the position because it speeds up both reactions by the same amount
What can a catalyst be used for in a reversible reaction?
Adding a catalyst means the reaction reaches equilibrium quicker
What is the Haber process?
The reversible reaction that produces ammonia gas from nitrogen gas and hydrogen gas
What is the chemical reaction for the Haber process?
N^2 + 3H^2 <–> 2NH^3
How is the nitrogen and hydrogen for the Haber process obtained?
Nitrogen is taken from the air
Hydrogen usually comes from natural gas or crude oil
What is the pressure, temperature and catalyst for the Haber process?
Pressure: 200 atmospheres
Temperature: 450 degrees C
Catalyst: iron
Describe the Haber process
H^2 and N^2 are mixed in a 3:1 ratio
The mixed gas flows into the reaction vessel where the 450C temperature and 200 atmospheres pressure is. It travels past trays of iron catalyst
Then the gasses go into the condenser where the ammonia is condensed and the unused hydrogen and nitrogen are recycled back to the start
You are left with liquid ammonia
How is the pressure set to move the equilibrium position in favour of the forward reaction and why?
The pressure is very high because there are only 2 molecules for the product and 4 molecules for the reactants
Why is the temperature of the Haber process 450C?
The forward reaction is exothermic so a lower temperature will move the equilibrium position in favour of the forward reaction
However, the temperature must still be quite high so that the rate of reaction is still high
A compromise is made and this is why the temperature is 450C
What are the 2 reasons that the catalyst is important?
Makes the reaction faster so equilibrium is reached much more quickly
Without the catalyst, the temperature would have to be raised further to get a quick enough reaction which would negatively affect the equilibrium position
