Reversible Reactions Flashcards
What two things happen at equilibrium?
Rate of forward reaction = rate of backwards reaction
Concentrations of reacting substances stay constant
What happens in a dynamic equilibrium?
The forwards and backwards reactions keep going - they don’t stop at equilibrium
Describe the Haber process
It is a reversible reaction between nitrogen (from air) and hydrogen (from natural gas) to form ammonia.
N and H are passed over an iron catalyst causing the molecules to react and form ammonia
Why is 450C the temperature we use in the Haber process?
Why do we use 200 atmospheres pressure?
If the temp was too low, the reaction would be too slow. If it was too high, the equilibrium would shift to the left, producing a lower yield of ammonia.
It is a compromise temperature.
A high pressure shifts the equilibrium to the the right, producing more ammonia, but is expensive and dangerous, so we compromise the pressure as-well.
How does the temperature and pressure affect the position of equilibrium and the rate of reaction?
Increased temp: equilibrium moves in direction of endothermic reaction. Rate increased
Increased pressure: equilibrium moves in direction of fewest molecules. Rate increased
What two compounds can be used as fertilisers?
NPK ( nitrogen, phosphorus, potassium) Ammonium salts (made by reacting ammonium with the appropriate acid)
What are the differences between laboratory scale production of ammonium sulfate and industrial scale?
Laboratory needs ammonium solution and dilute sulfuric acid. Involves only a few stages (titration and crystallisation) and is small scale.
Industrial needs natural gas, air and water (raw materials to make ammonia) and sulfur, air and water (sulfuric acid).
Many stages, large scale.
How do you make a chemical cell to produce a voltage?
You need:
- zinc dipped in zinc sulfate solution
- copper dipped in copper sulfate solution (electrons flow from zinc to copper as zinc is more reactive)
- filter paper dipped in potassium chloride to form a bridge (ions pass through; completes the circuit)
- crocodile clips, wire and a voltmeter
Describe a hydrogen-oxygen fuel cell.
Hydrogen and oxygen are used to produce a voltage.
Water vapour is the only product
What are advantages and disadvantages of chemical cells and hydrogen-oxygen fuel cells?
Chemical cells:
Suitable for portable appliances, cheap.
May contain harmful substances, don’t produce voltage when one of the reactants are used up
Fuel cells:
Produce water as the only waste, always produce a voltage as long as fuel and air are supplied.
Not suitable for portables, expensive
