Reversible reactions and equilibria Flashcards
What does the symbol with the two opposite arrows on top of each other mean?
It means that the reactions are reversible
What can reversible reactions do?
They can reach equillibrium
What conditions are required for equilibrium to be reached?
The reaction must take place in a closed container
What happens at equilibrium?
The amount of reactants is the same as the amount of products, this is because the rate of forward reaction is the same as the rate of the backwards reaction
In the Haber process what are the reactants and products?
Ammonia is made from the reaction between nitrogen gas and hydrogen gas
What must be considered when choosing the temperature at which the Haber process takes place?
Higher temp. increases rate of reaction
Higher temperature decreases the the yield of ammonia,
Higher temperature is expensive to produce
Therefore a compromise of 450*C is used
What must be considered when choosing the pressure at which the Haber process takes place at?
Higher pressure increases both the rate of reaction and yield
High pressure means leaks are more likely and it’s expensive to maintain,
Therefore a compromise of about 200 atm is used
How is equilibrium prevented from being reached?
Only about 20% of the nitrogen and hydrogen react when they and the ammonia are removed from the vessel so that equilibrium is not reached, the gases are then recycled so nothing is wasted
What problems do plants have in obtaining nitrogen?
Plants need nitrogen to grow but cannot use nitrogen gas from the air, they must use nitrates fixed from nitrogen but there aren’t enough natural nitrates
What do farmers do about the lack of natural nitrates available in the soil?
Farmers add fertiliser to the soil to provide crops with nitrates, synthetic fertilisers are used to replace natural nitrates but they are made from industrial processes that cause environmental problems
