Haber Process & NPK Fertilisers Flashcards

All 25 cards in this deck

What are the raw materials for the Haber process?

Nitrogen and hydrogen.

In the Haber process, what is the source of the nitrogen and what is the source of the hydrogen?

Nitrogen from the air; hydrogen from natural gas (methane).

What conditions are used in the Haber process?

An iron catalyst, about $450^\circ$C and about $200$ atmospheres.

What is the balanced symbol equation for the reaction in the Haber process?

$N_2 + 3H_2 \rightleftharpoons 2NH_3$

What are the steps to separate the ammonia and deal with the unreacted gases in the Haber process?

e.g. the mixture leaving the reactor contains ammonia, nitrogen and hydrogen

1. Cool the gas mixture.
2. Ammonia liquefies (condenses) and is removed as a liquid.
3. The remaining nitrogen and hydrogen are recycled back to the reactor.

What is the atom economy of the forward reaction in the Haber process?

$100\%$ — the equation shows only one product, ammonia.

What does it mean to say the Haber process reaches a dynamic equilibrium?

The forward and reverse reactions happen at the same rate, so the amounts of nitrogen, hydrogen and ammonia stay constant.

What does the symbol $\rightleftharpoons$ in the Haber process equation tell you?

The reaction is reversible — some ammonia breaks back down into nitrogen and hydrogen.

What effect does increasing the pressure have on the yield of ammonia in the Haber process?

It increases the yield — there are fewer gas molecules on the product side ($4 \rightarrow 2$), so equilibrium shifts to the right.

What effect does increasing the temperature have on the yield of ammonia in the Haber process?

It decreases the yield — the forward reaction is exothermic, so equilibrium shifts to the left.

True or false? Once the Haber process reaches equilibrium, both reactions have stopped.

False. Both the forward and reverse reactions carry on, but at the same rate.

True or false? At equilibrium in the Haber process there are equal amounts of reactants and products.

False. The amounts stay constant, but they are not necessarily equal.

What is the trade-off that decides the temperature used in the Haber process?

A lower temperature gives a higher yield of ammonia but a slower rate, so about $450^\circ$C is a compromise between yield and rate.

Why is a pressure of about $200$ atmospheres used in the Haber process rather than a much higher pressure?

Higher pressure gives a higher yield, but high-pressure equipment and the energy to compress the gases are very expensive (and less safe).

True or false? Using the iron catalyst increases the percentage yield of ammonia.

False. The catalyst speeds up the reaction (equilibrium is reached sooner) but does not change the position of equilibrium or the yield.

On a graph of percentage yield of ammonia against temperature at constant pressure, what does the line do?

The yield falls as the temperature increases.

Which three elements do NPK fertilisers contain compounds of?

Nitrogen, phosphorus and potassium.

e.g. potassium nitrate supplies K and N.

True or false? Ammonium nitrate on its own supplies all three of the NPK elements.

False. Of N, P and K it contains only nitrogen; NPK fertilisers are formulations of several salts.

Which two types of substance used in fertiliser manufacture are made from ammonia?

Ammonium salts (e.g. ammonium sulfate) and nitric acid.

How are potassium chloride, potassium sulfate and phosphate rock obtained?

By mining (quarrying).

What property of phosphate rock means it cannot be used directly as a fertiliser?

It is insoluble in water, so plants cannot absorb it.

Give three ways industrial production of a fertiliser salt differs from its laboratory preparation.

Industrial production is on a much larger scale, is quicker, and is a continuous process (the laboratory method is small scale, slower and must be repeated in batches).

True or false? An NPK fertiliser is a formulation — a mixture of salts blended to give appropriate percentages of the elements.

True. NPK fertilisers are formulations of various salts, not a single compound.

Which salt useful as a fertiliser is named as the product when phosphate rock (calcium phosphate) is treated with nitric acid?

Calcium nitrate.
It is formed along with phosphoric acid.

What fertiliser products are named when phosphate rock (calcium phosphate) is treated with sulfuric acid, and when it is treated with phosphoric acid?

Sulfuric acid: single superphosphate (calcium phosphate and calcium sulfate).
Phosphoric acid: triple superphosphate (calcium dihydrogenphosphate).