Reversible and irreversible Reactions Introduction Dr Seemal Jelani

Reversible and irreversible Reactions Introduction Dr Seemal Jelani 1

Irreversible reaction The reactants react to form the products which cannot revert back into reactants One example is reaction of hydrogen gas and iodine vapor to form hydrogen iodide • Fuel and oxygen reacts to form CO 2 and H 2 O • H 2 O + I 2 2 HI Dr Seemal Jelani 2

Reversible reaction • The reactants react with other reactants to form products, the products are reacting with other products to form reactants Dr Seemal Jelani 3

Reversible Reactions 09/09/2020 Some chemical reactions are reversible. In other words, they can go in either direction: A + B e. g. Ammonium chloride NH 4 Cl C + D Ammonia + hydrogen chloride NH 3 + HCl When a reversible reaction occurs in a closed system (Where nothing can escape), equilibrium is reached when both reactions occur at exactly the same rate in each direction. The relative amounts of all the reacting substances at equilibrium depend on the Dr conditions of the reaction. Seemal Jelani 4

Making Ammonia 09/09/2020 Guten Tag. My name is Fritz Haber and I won the Nobel Prize for chemistry. I am going to tell you how to use a reversible reaction to produce ammonia, a very important chemical. This is called the Haber Process. Nitrogen + hydrogen Ammonia N 2 + 3 H 2 2 NH 3 Fritz Haber, 1868 -1934 To produce ammonia from nitrogen and hydrogen you have to use three conditions: Nitrogen Hydrogen • High pressure • 450 O C • Iron catalyst Mixture of NH 3, H 2 and N 2. This is cooled causing NH 3 to liquefy. Dr Seemal Jelani Recycled H 2 and N 2 5

Haber Process Summary 09/09/2020 A low temperature increases the yield of ammonia but is too slow A high temperature improves the rate of reaction but decreases the yield too much A high pressure increases the yield of ammonia but costs a lot of money To compromise all of these factors, these conditions are used to make a reasonable Yield of ammonia, quickly: Nitrogen Hydrogen • 200 atm pressure • 450 O C • Iron catalyst Mixture of NH 3, H 2 and N 2. This is cooled causing NH 3 to liquefy. Dr Seemal Jelani Recycled H 2 and N 2 6

Uses of Ammonia 09/09/2020 Ammonia is a very important chemical as it can be used to make plant fertilisers and nitric acid: Ammonia gas Oxygen Hot platinum catalyst Nitrogen monoxide Cooled Nitrogen monoxide Water and oxygen Nitric acid More ammonia can then be used to neutralise the nitric acid to produce AMMONIUM NITRATE (a fertiliser rich in nitrogen). Ammonia + nitric acid NH 3 + HNO 3 Ammonium nitrate NH 4 NO 3 The trouble with nitrogen based fertilisers is that they can also create Dr Seemal Jelani 7 problems – they could contaminate our drinking water.