Chemistry 2.6 Reversible Reactions, Industrial Processes and Important Chemicals

Reversible reaction

A reaction that occurs in both directions where products can react to reform the original reactants and is shown using ⇌

Forward and backward reactions

In A plus B ⇌ C plus D the forward reaction forms C plus D and the backward reaction forms A plus B

Changing direction of a reversible reaction

Change temperature pressure or concentration of reactants or products

Energy change in reversible reactions

If the forward reaction is exothermic the backward reaction is endothermic with the same energy change

Haber process reaction

Nitrogen reacts with hydrogen to form ammonia N2 plus 3H2 ⇌ 2NH3

Uses of ammonia

Used mainly to make nitrogen based fertilisers

Sources of nitrogen and hydrogen

Nitrogen comes from air and hydrogen comes from natural gas or other sources

Conditions of the Haber process

High temperature around 450 degrees Celsius high pressure around 200 atmospheres and an iron catalyst

Steps in the Haber process

Purified gases react some ammonia forms some breaks down mixture is cooled ammonia liquefies and unreacted gases are recycled

Dynamic equilibrium in the Haber process

Forward and backward reactions occur at the same rate once equilibrium is reached

Effect of increased pressure in the Haber process

Equilibrium shifts to the right to produce more ammonia because there are fewer gas molecules

Effect of lower temperature in the Haber process

Lower temperature favours the forward exothermic reaction producing more ammonia

Disadvantages of low temperature and high pressure

Low temperature slows the reaction rate and high pressure requires lots of energy

Aims when choosing Haber conditions

To maximise rate of reaction and yield of ammonia

Test for ammonia gas

Moist red litmus paper turns blue because ammonia is alkaline

Test for ammonium ions

Add hydroxide ions and test for ammonia gas produced

Ionic equation for ammonium ions

NH4 plus plus OH minus forms NH3 and water

Reactions used to make fertilisers from ammonia

Neutralisation reactions

Examples of nitrogenous fertilisers

Ammonium sulfate (NH4)2SO4 and ammonium nitrate NH4NO3

Making ammonium sulfate

React ammonia or ammonium hydroxide with sulfuric acid

Making ammonium nitrate

React ammonia or ammonium hydroxide with nitric acid

Advantages of fertilisers

Increase crop growth and yield and increase farmer profit

Disadvantages of fertilisers

Can cause eutrophication change soil pH have many manufacturing stages and cause baby blue syndrome

Strong acid

A strong acid completely dissociates in water to release H plus ions

Sulfuric acid formula

H2SO4

Contact process

The industrial manufacture of sulfuric acid

First step of the Contact process

Sulfur is burned in air to form sulfur dioxide

Second step of the Contact process

Sulfur dioxide reacts with oxygen to form sulfur trioxide in a reversible reaction using a catalyst

Conditions of the reversible step in the Contact process

Vanadium five oxide catalyst temperature around 450 degrees Celsius and pressure around 2 atmospheres

Final step of the Contact process

Sulfur trioxide reacts with water to form sulfuric acid

Uses of sulfuric acid

Used to make fertilisers chemicals refine petroleum process metals make rayon and in lead acid batteries

Dehydrating agent

A substance that removes water from other compounds

Sulfuric acid as a dehydrating agent with sugar

Removes water from glucose in a highly exothermic reaction leaving carbon and steam

Effect of sulfuric acid on hydrated copper sulfate

Blue hydrated crystals turn into white anhydrous powder