Chemistry - Equilibria

What does a double arrow in chemical reaction mean?

Reversible reaction

If the forwards reaction is exothermic, then the backwards must be…?

endothermic

If the forwards reaction has an energy change of -956 then the backwards reaction must have an energy change of…?

+956

Define dynamic equilibrium

a state in a reversible process where the forward and reverse reactions or changes occur at the exact same rate

Dynamic equilibrium must be reached in an open/closed system

closed

At dynamic equilibrium the amounts of the reactants and products do/not change

Do not

At dynamic equilibrium the amounts of the reactants and products need/not to be equal

Need not

If there are more reactants than products, then equilibrium lies to the ….

Left hand side

If there are more products than reactants, then equilibrium lies to the ….

Right hand side

What is le chateliers principle

If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change

A + B --> C+D What happens if you increase the concentration of A and why?

The rate of the forwards reaction increases compared to the backward reaction The position of equilibrium shifts to the right, using up the excess A A is reduced, counteracting the original change

A + B --> C+D What happens if you increase the concentration of C and why?

The rate of the backward reaction increases compared to the forward reaction The position of equilibrium shifts to the right, using up the excess C C is reduced, counteracting the original change

N2 + 3H2 --> 2NH3 What happens if you increase the pressure and why?

There are 4 moles of gas on the left hand while there 2 on the right side. There are therefore fewer on the right. If you increase the pressure, the system will try to counteract the change. This means it favour the forwards reaction, producing fewer moles of gas and reducing the pressure

A + B --> C+D Forward reaction: -150kJ What happens if you increase the temperature?

The forward reaction is exothermic, producing heat. If you increase the temperature, the system will try to counteract this change This means that it will favour the exothermic backwards reaction Therefore A and B are increased

What does the haber process create

Ammonia (NH3)

Equation for the haber process

N2 + 3H2 → 2NH3

Ideal temperature for the haber process and why

450 degrees – the forward reaction of the haber process is exothermic. This means a very low temperature would produce a high yield of ammonia as the system would favour the forwards reaction. However, a low temperature would mean that the rate of collisions between particles would be very slow, so the rate of reaction would be low and ammonia would be produced slowly. For this reason, a balance must be found between yield and rate of reaction to produce a maximum amount of ammonia

Ideal pressure for the haber process and why?

200 atmospheres – less moles of gas are produced on the right hand side of the equation. This means that by increasing the pressure, the system will favour the forward reaction, producing more ammonia. However it is very expensive and dangerous to maintain a very high pressure, so 200 atmosphere is a good compromise between cost and yield

What extra thing is needed for the haber process

An iron catalyst

The two gasses needed for the haber process are…?

Nitrogen and hydrogen

How is hydrogen obtained for the haber process

Reacting natural gas with steam

How is nitrogen obtained for the haber process

Fractional distillation of liquid air (as nitrogen makes up 78%) → air is filtered to remove the dust, then cooled to -200c. Then put into a fractionating column (you should by now know how this works). Nitrogen has a lower boiling point so rises to the top, condensed, and is collected

Why can’t the yield of the haber process be 100%

It is a reversible reaction so does not go to completion

What are fertilisers

Chemicals used to add nutrients to the soil to improve the fertility of the soil and therefore gaining a higher yield of crops

What do NPK fertilisers contain

Nitrogen (N), phosphorous (P), and potassium (K)

What does this mean NPK 14:11:11 and why is this useful

That is the ratio of mass of nitrogen to phosphorus to potassium which is helpful to farmers as it shows how much of each is in the fertiliser, so can help them choose which fertiliser to use depending on what the plants need most of

What do NPK fertilisers contain (out of NPK): ammonium nitrate

nitrogen

What do NPK fertilisers contain (out of NPK): ammonium sulfate

nitrogen

What do NPK fertilisers contain (out of NPK): ammonium phosphate

Nitrogen, phosphorous

What do NPK fertilisers contain (out of NPK): potassium chloride

Potassium

What do NPK fertilisers contain (out of NPK): potassium sulfate

Potassium

What do NPK fertilisers contain (out of NPK): calcium nitrate

nitrogen

What do NPK fertilisers contain (out of NPK): single superphosphate

phosphorous

What do NPK fertilisers contain (out of NPK): triple superphosphate

phosphorous

Source of ammonium nitrate

Ammonia is made in the Haber process. This reacts in a series with water and oxygen to make nitric acid. Ammonia reacts with acids such as nitric acid to create ammonium nitrate

Source of ammonium sulfate

Ammonium is made in the Haber process. This reacts with sulfuric acid to create ammonium sulphate

Source of ammonium phosphate

Ammonium is made in the Haber process. This reacts with phosphoric acid to create ammonium phosphate

Source of potassium chloride

Mined directly and used as fertiliser

Source of potassium sulfate

Mined directly and used as fertiliser

Source of calcium nitrate

Phosphate is mined from the ground as phosphate rock, but this is insoluble so plants can't take it up and use it. Phosphate reacts with nitric acid (from ammonia) to produce phosphoric acid and calcium nitrate

Source of single superphosphate

Phosphate is mined from the ground as phosphate rock, but this is insoluble so plants can't take it up and use it. It reacts with sulfuric acid to produce calcium sulfate and calcium phosphate

Source of triple superphosphate

Phosphate is mined from the ground as phosphate rock, but this is insoluble so plants can't take it up and use it. It reacts with phosphoric acid to produce calcium phosphate