Ammonia and Fertilisers

Lesson Objectives To know that ammonia is made in a reversible reaction. To be able to explain how changing the reaction conditions affects the yield of ammonia. To know that ammonia can be used to make ammonia. To be able to sort cards into evidence for and against the use of fertilisers.

Some reactions go all the way.... Others don't!

Fritz Haber

Making Ammonia: The Haber Process Some reactions can go in both directions, we say they are reversible. We show this using a split arrow “⇌” In a closed system these reactions reach an equilibrium, where there are some products and some reactants. How much product is formed depends on the reaction conditions.

Stick in your diagram, filling in the missing words and balancing the equation N2 + H2 Ý NH3

Ammonia and Fertilisers Ammonia is basic, it dissolves to give an alkali. Ammonia can be neutralised by acids to give salts that can be used as fertilisers: reacting with nitric acid gives ammonium nitrate reacting with sulphuric acid gives ammonium sulphate

In groups of 4, sort the cards into evidence for and against using nitrate fertilisers

What is the compound? Three picture clues to guess the compound.

What is this compound? CH4

What is this compound? H2O

What is this compound? NaCl

What is this compound? NH3

Learning Objectives Know that nitric acid can be made by oxidising ammonia Know that the Contact process is used to make sulphuric acid (and know the conditions used) Be able to describe the dehydrating effects of sulphuric acid on sugar and hydrated copper sulphate crystals

Ammonia can be oxidised to make nitric acid

Making Nitric Acid Nitric acid is made from the reaction of ammonia with oxygen. The first stage produces nitrogen monoxide. (The same gas is formed as a pollutant in petrol engines). A hot platinum/rhodium catalyst is used (about 850 °C). The reaction is highly exothermic and the heat given out by the reaction is sufficient to keep the reaction going. ammonia + oxygen ↓ nitric acid + water. 4NH3(g) + 8O2(g) ↓ 4HNO3(g) + 4H2O(g)

Contact Process – used to make sulphuric acid S + O2 ↓ SO2 2SO2 + O2 ∏ 2SO3 SO3 + H2O ↓ H2SO4 Sulphur is burnt in air; SO2 is reacted with excess air over a vanadium catalyst at 420°C at pressures not much above atmospheric to give over 95% conversion. SO3 is absorbed in H2SO4 rather than H2O and the reaction is exothermic and would form an acid smog.

N.B. Transition metals and transition metal compounds are often used as catalysts in industrial reactions.

Reactions with sulphuric acid Sulphuric acid can remove water from other compounds e.g. Sugar Copper sulphate crystals

http://www.youtube.com/watch?v=J1zwFwmANw4