Chemistry - Unit 2e - Reversible reactions and Inustrial processes

What happens during a reversible reaction?

As the reactants react, their concentration falls and the forward reaction will slow down. But as more products are made, their concentrations rise and the backwards reaction speeds up

What is equalibrium in a reversible reaction?

When reactions are going at same rate so the concentrations of reactants and products dont change

If there are more products than reactants…..

If there are more reactants than products….

…the reaction is going in forwards direction

…the reaction is going in backwards direction

How are reversible reactions endothermic and exothermic?

It will be exothermic in one direction and endothermic in the other. The energy transferred from surroundings by endothermic reaction is equal to energy transferred to surroundings during exothermic reaction

What happens when you heat a reversible reaction?

It will go the endothermic direction

What are the 3 conditions that could be kept the same that determines the direction of the reaction?

Temperature, pressure or concentration

What is the haber process used for?

To produce ammonia from hydrogen and nitrogen, which is used to make fertilisers

What reaction takes place in the haber process?

N(2) + 3H(2) reversible symbol 2NH(3) (+heat)

How does the habour process work?

Nitrogen is obtained from air (78% nitrogen). Hydrogen comes from reacting methane with steam to form hydrogen and carbon dioxide. These reactants are passed over an iron catalyst where high temperatures (350 -450) and high pressure(150-200 atmospheres) are used. Because its reversible, some ammonia converst back to hydrogen and nitrogen. The ammonia is produced in gas form so its liquified as it cools in the condenser and is removed. Any unused nitrogen and hydrogen is recycled to be used again. Ammonia produces is used to make ammonium nitrate - a very nitrogen-rich fertiliser

How can you test for ammonia?

Ammonia form an alkaline solution when it dissolves in water and an alkaline will turn damp red litmus paper blue

How do we use the contact process to make Sulfuric acid?

First make sulfer dioxide by reacting sulfer with the air(oxygen). Sulfer dioxide is oxidised to make sulfer trioxide. Oleum is then produced by dissolving sulfer trioxide in concentrated sulfer acid. Then Oleum is converted into sulferic acid by adding water

What are the 3 conditions kept when making sulfer dioxide?

Reaction in step 2 is reversible. So conditions are a compramise between rate of reaction and yeild and cost.

Temp. - quite high temp of 450c to form sulfer trioxide at kinda quick rate but acceptable yield

Pressure - high pressure is expensive so its just above atmospheric pressure

Catalyst - Vanadium pentoxide catalyst is used that doesnt change direction of reaction

How is sulfuric acid used?

Combine with ammonia to make ammonium sulfate for a fertiliser.

Also used to make paints, plastics and detergents

Concentrated sulfuric acid can remove water from hydrated salts

Also removes ‘elements of water’ from sugars such as sucrose

Whats the water in a lattice called?

Water of crystalisation

describe the dehydration of hydrated copper sulfate

Add concentrated sulfuric acid to hydrated copper sulfate and the water is removed. The blue hydrated crystals turn into white, anhydrous copper sulfate powder - very exothermic reaction

Describe the dehydration of sugars?

Add concentration of sulfuric acid to sugar for the mixture to turn yellow then brown. Sulfuric acid removes hydrogen and oxygen(water) from sugar, forming water. Solid carbon is left which turns solution black. The water formed will dilute sulfuric acid which generate lots of heat which boils the water. Steam produced by boiling water causes carbon to rise out of beaker

How can you test for ammonium ions?

Add source of OH- ions and gently heat. if ammonia gas is rpoduced them ammonium ions are present

Describe how fertiliser damages lakes and rivers?

• fertiliser runs of into waterways

• level of nitrogen in water goes up

• algae bloom is formed from excess nitrogen which blocks sunlight from plants below

• Plants cant photosynthesis so they die and aerobic bacteria feeds on dead plants

• Bacteria will multiply and require loads of oxygen from water

• Oxygen dependant aniamls and planst now die

Whats eutrophication?

“too much of a good thing’