Topic 15 - Dynamic Equilibria, Calculations Involving Volumes of Gases Flashcards
5.19C - What is the Haber process?
A reversible reaction between nitrogen and hydrogen to form ammonia.
5.20 - What is a reversible reaction and dynamic equilibrium?
Reversible reactions reach dynamic equilibrium when in closed systems where substances can’t enter or leave.
In a dynamic equilibrium, the forward and backwards rate of reaction happen at the same rate and the concentration of reacting substances don’t change.
5.20C - What factors affect the rate of attainment of equilibrium in the Haber process?
Pressure - high pressure increases the equilibrium yield of ammonia. The equilibrium moves to the right as it is the side with fewer molecules will have a higher pressure. This decreases time taken to reach equilibrium.
Temperature - the forward reaction is exothermic and the backwards reaction is endothermic. As temperature increases the position of equilibrium moves to the left ( endothermic side ). This decreases time taken to reach equilibrium.
Catalyst - An iron catalyst is used to increase the rate of reaction. It doesn’t affect the equilibrium as catalysts don’t form products. This decreases time taken to reach equilibrium.
Concentration - if the concentration of a reacting substance is increased, the equilibrium moves to the opposite side to counteract the effect. This decreases time taken to reach equilibrium.
5.21 - How are reaction pathways chosen for industrial processes?
Manufacturers choose the reaction conditions that produce an acceptable amount of yield in a certain amount of time. It isn’t profitable if the reaction is fast but is expensive.
In the Haber process, the pressure used is 200atm because it is a compromise as high pressures are expensive to maintain.
Temperature is 450°C, as it gives an acceptable amount of ammonia in a certain time.
Iron catalysts are used as they increase the rate of reaction.
Factors such as availabilty, cost, energy, rate of reaction, equilibrium position, atom economy and yield are taken into account when choosing a pathway.
5.22C - What are fertilisers?
Once plants absorb all the minerals in the soil, it may not grow properly due to deficiency diseases.
Fertilisers replace these mineral ions needed by plants and promote plant growth.
The minerals nitrogen, phosphorus and potassium ( NPK ) are used to promote plant growth.
These minerals must be provided as soluble compounds as plants only absorb mineral ions dissolved in water.
5.23C - How is the Haber process used to manufacture ammonium nitrate?
Ammonium nitrate is a nitrogen-rich fertiliser.
Ammonia is manufactured by the Haber process, where nitrogen and hydrogen react in a reversible reaction.
Nitric acid is also manufactured by reacting ammonia with oxygen to give nitric acid and water.
Ammonia sulfate is also manufactured as it is a nitrogenous fertiliser, it is made by reacting ammonia with dilute sulfuric acid.
5.24C - Describe and compare the production of making a fertiliser in a laboratory and in a factory
Ammonia sulfate can be prepared in a laboratory and can be industrially produced.
For the laboratory preparation, ammonia solution and dilute sulfuric acid are bought from chemical manufacturers, as it is small scale, it is then titrated and crystallised.
This is a batch process, as a small amount is made and the apparatus is cleaned and another small amount is made.
The industrial production of ammonia sulfate is large scale, raw materials like sulfur and air make sulfur trioxide and water is reacted with it to make sulfuric acid.
Water and natural as forms hydrogen and air reacts with hydrogen to form ammonia. Ammonia is reacted to sulfuric acid to make ammonium sulfate.
This process takes several stages and is a continuous process, where reactants are fed to reactants and products are removed and it is rarely stopped to clean the equipment.
Batch processes are difficult to automate while continuous processes are usually automated, so less people needed to make the same product.
