Equilibrium &The Haber Equilibrium &The Haber Process Process

GCSE REVISIONGCSE REVISION

The Haber ProcessThe Haber Process

This reaction makes This reaction makes ammonia out of ammonia out of hydrogen and nitrogen.hydrogen and nitrogen.

The nitrogen comes The nitrogen comes from the air (78% N).from the air (78% N).

You donYou don’’t need to worry t need to worry about where the about where the hydrogen comes from!hydrogen comes from!

1. What does Reversible Reaction mean1. What does Reversible Reaction mean? ?

A reaction that can proceed in both directionsA reaction that can proceed in both directions

The Haber ProcessThe Haber Process The Haber process is a The Haber process is a REVERSIBLEREVERSIBLE reaction reaction

NN2(g)2(g) + 3H + 3H2(g)2(g) 2NH 2NH3(g)3(g) (+ heat) (+ heat)

nitrogen + hydrogen ammonianitrogen + hydrogen ammonia

A A reversible reaction reversible reaction is one where the is one where the productsproducts of the reaction can of the reaction can themselves themselves reactreact to produce the to produce the original reactantsoriginal reactants..

2. a. What does the Haber Process make? 2. a. What does the Haber Process make?

b. Give one use of this product b. Give one use of this product

AmmoniaAmmonia

To make fertilisersTo make fertilisers

3. 3. There are Three Raw Materials for the Haber There are Three Raw Materials for the Haber

Process. What are they?Process. What are they? Nitrogen is easily obtained from air by fractional Nitrogen is easily obtained from air by fractional

distillationdistillation Hydrogen is obtained from methane reacted with Hydrogen is obtained from methane reacted with

steam.steam. methane +  steam    carbon dioxide + hydrogen.methane +  steam    carbon dioxide + hydrogen.

CHCH44(g)   +  2H(g)   +  2H22O(g)           COO(g)           CO22(g)     +   4H(g)     +   4H22(g)(g)

The raw materials are thereforeThe raw materials are thereforeair - for nitrogen,air - for nitrogen,methane and water - for hydrogen.methane and water - for hydrogen.

4. Write the word/balanced chemical equation for the Haber 4. Write the word/balanced chemical equation for the Haber

Process.Process. nitrogen   +   hydrogen        ammonia   ( + heat)nitrogen   +   hydrogen        ammonia   ( + heat)

NN22(g)     +     3H(g)     +     3H22(g)             2NH(g)             2NH33(g)    ( + heat)(g)    ( + heat)

The Haber ProcessThe Haber Process

The HaberThe Haber

Key factsKey facts

1.1. H and N are mixed in a 3:1 ratioH and N are mixed in a 3:1 ratio

2.2. Because the reaction is reversable not all the nitrogen Because the reaction is reversable not all the nitrogen and hydrogen will convert to ammonia.and hydrogen will convert to ammonia.

3.3. The ammonia forms as a gas but cools and liquefies in The ammonia forms as a gas but cools and liquefies in the condenserthe condenser

4.4. The H and N which do not react are passed through the The H and N which do not react are passed through the system again so they are not wasted.system again so they are not wasted.

5. In a Reversible Reaction, how can the  Yield be 5. In a Reversible Reaction, how can the  Yield be

Changed?Changed? Change the conditions (use of temperature, Change the conditions (use of temperature,

pressure and catalyst).pressure and catalyst).

This is a useful summary for any reversible reactionThis is a useful summary for any reversible reactionincluding the Haber Process.including the Haber Process.

1. Increasing the temperature favours the 1. Increasing the temperature favours the endothermic reaction.endothermic reaction.

2. Increasing the pressure favours the smaller 2. Increasing the pressure favours the smaller volume.volume.

3. Using a catalyst gives the equilibrium conditions 3. Using a catalyst gives the equilibrium conditions more quickly.more quickly.

6. Why is the Haber Process run at 450 °C instead 6. Why is the Haber Process run at 450 °C instead of room temperature? of room temperature?

To increase rate of reactionTo increase rate of reaction

7. Why is the Haber Process run at High Pressure? Give 7. Why is the Haber Process run at High Pressure? Give

two reasons.two reasons. Increasing the pressure (from Le Increasing the pressure (from Le

Chatelier's Principle) makes the Chatelier's Principle) makes the equilibrium mixture have more ammonia.equilibrium mixture have more ammonia.

Increased pressure also increases the Increased pressure also increases the reaction rate.reaction rate.

8. Why is the Haber Process not run at Very High 8. Why is the Haber Process not run at Very High

Pressure?Pressure? Too expensiveToo expensive

9. Which Substance is used as a Catalyst in the Haber 9. Which Substance is used as a Catalyst in the Haber

Process?Process?

Iron catalystIron catalyst

The following questions The following questions are are HigherHigher Tier Tier onlyonly

10. Use Le Chatelier's Principle to explain what happens as a Product 10. Use Le Chatelier's Principle to explain what happens as a Product

is removedis removed If you remove a product,If you remove a product,

the equilibrium mixture changes to make more product.the equilibrium mixture changes to make more product.

It tries to get back to the composition it had before the It tries to get back to the composition it had before the product was removed.product was removed.

You can carry on removing productYou can carry on removing productuntil all the reactants have turned into product until all the reactants have turned into product

11. 11. Use Le Chatelier's Principle to explain what happens as Use Le Chatelier's Principle to explain what happens as

Heat is Removed.Heat is Removed. Heat may be treated as a reactant (for an Heat may be treated as a reactant (for an

endothermic reaction) or as a product (for an endothermic reaction) or as a product (for an exothermic reaction).exothermic reaction).

If you remove heat from an exothermic reaction If you remove heat from an exothermic reaction the equilibrium will change to produce more the equilibrium will change to produce more product. product.

If you add heat to an exothermic reaction (raise If you add heat to an exothermic reaction (raise its temperature),the reverse will happen,its temperature),the reverse will happen,and you will get less product in the equilibrium and you will get less product in the equilibrium mixture.mixture.

12. What effect does a Catalyst have on the Equilibrium 12. What effect does a Catalyst have on the Equilibrium

Composition?Composition? No effect.No effect. Equilibrium is just reached more quickly.Equilibrium is just reached more quickly.