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Exothermic and Endothermic Reactions and the Haber Process

In this worksheet, students learn about the energy changes during chemical reactions and how a reversible reaction system, like the Haber process, works.

Key stage:  KS 4

Curriculum topic:  Chemistry: Rate and Extent of Chemical Change

Curriculum subtopic:  Factors that Influence Reaction

Difficulty level:  

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QUESTION 1 of 10

During chemical reactions energy transfer takes place to and from the surroundings. This transfer is in the form of thermal energy, i.e. heat. A chemical reaction can be either exothermic or endothermic.

 

Exothermic Reactions

Exo- means 'out', so exothermic reactions release heat to their surroundings. The picture shows an example of an exothermic reaction:

 

 

Clearly, this looks like an explosion. Explosions are exothermic reactions, but a reaction can be exothermic without exploding. Any increase in temperature indicates an exothermic reaction. If you were to hold a container where an exothermic reaction takes place, you would feel the heat and a thermometer inside the container would show an increase in temperature. Examples of exothermic reactions are combustion (burning) and neutralisation.

 

Endothermic Reactions  

Endo- means 'inside', so endothermic reactions take in energy from their surroundings. Be careful, because this can be confusing: if you were to hold a container where an endothermic reaction takes place, you would feel your hands getting cold, as the reaction would take heat from the container and...even your hands if you kept holding it! A thermometer in the container would show a decrease in temperature.

The graph below shows the difference in energy levels in reactants and products of an endothermic reaction:

 

As you can see, the energy of the products is far higher than the energy of the reactants. Examples of endothermic reactions are electrolysis and thermal decomposition.  

 

The Haber Process  

Some reactions are reversible, which means the products can react to produce the reactants again! The Haber Process is an example; it is used in the industry to produce ammonia, a compound of nitrogen and hydrogen. Ammonia is a colourless gas used in the production of fertilisers, nylon, dyes, cleaning products and explosives.

The chemical equation below shows the Haber Process (note that a double arrow is used to show reversibility):

 

The forward reaction in the Haber Process is exothermic, i.e. when ammonia is produced heat is released. This means an increase in temperature shifts the equilibrium to the reverse reaction, so less ammonia is produced. However, if the temperature is too low, not enough ammonia will be produced.

 

The Haber Process is illustrated in the diagram below:

What type of reactions release thermal energy into the surroundings?

endothermic

exothermic

Choose two examples of exothermic reactions from the options below:

neutralisation

thermal decomposition

combustion

electrolysis

What would you see if you place a thermometer in a container where an endothermic reaction takes place?

The temperature would increase.

The temperature would decrease.

The temperature would remain stable.

Compare the energy of the reactants and the energy of the products in an endothermic reaction. 

The energy of the reactants and products in an endothermic reaction is equal.

The reactants in an endothermic reaction have higher energy than the products.

The products in an endothermic reaction have higher energy than the reactants.

A group of students perform a chemical reaction. The thermometer shows an increase in temperature.

What type of reaction was that?

What type of a reaction is the Haber Process?

reversible

irreversible

What type of energy changes occur in a reversible reaction?

The energy of the reactants is higher than the energy of the products.

The reverse reaction is always the endothermic one.

One direction is exothermic and the other endothermic, but that differs according to the reaction.

How would you describe ammonia?

a white solid

a colourless gas

a blue liquid

What would be a potential problem if the temperature during the Haber Process is kept too low?

Ammonia would be produced uncontrollably.

Not enough ammonia would be produced.

What type of catalyst is used in the Haber Process?

iron

mercury

magnesium

  • Question 1

What type of reactions release thermal energy into the surroundings?

CORRECT ANSWER
exothermic
EDDIE SAYS
Exothermic reactions release thermal energy into their surroundings.
  • Question 2

Choose two examples of exothermic reactions from the options below:

CORRECT ANSWER
neutralisation
combustion
EDDIE SAYS
Neutralisation and combustion are exothermic reactions, because they release heat into the surroundings.
  • Question 3

What would you see if you place a thermometer in a container where an endothermic reaction takes place?

CORRECT ANSWER
The temperature would decrease.
EDDIE SAYS
A thermometer in a container where an endothermic reaction takes place would show a decrease in temperature.
  • Question 4

Compare the energy of the reactants and the energy of the products in an endothermic reaction. 

CORRECT ANSWER
The products in an endothermic reaction have higher energy than the reactants.
EDDIE SAYS
The energy levels in the products of an endothermic reaction are higher than the energy in the reactants, because energy is taken in while the reaction is taking place.
  • Question 5

A group of students perform a chemical reaction. The thermometer shows an increase in temperature.

What type of reaction was that?

CORRECT ANSWER
exothermic
EDDIE SAYS
An increase in temperature is shown in exothermic reactions.
  • Question 6

What type of a reaction is the Haber Process?

CORRECT ANSWER
reversible
EDDIE SAYS
The Haber Process is a reversible reaction.
  • Question 7

What type of energy changes occur in a reversible reaction?

CORRECT ANSWER
One direction is exothermic and the other endothermic, but that differs according to the reaction.
EDDIE SAYS
One direction is exothermic and the other endothermic, but that differs according to the reaction. This means that in the Haber Process that you learned about here, the forward reaction is exothermic, but that is not always the case with all reversible reactions.
  • Question 8

How would you describe ammonia?

CORRECT ANSWER
a colourless gas
EDDIE SAYS
Ammonia is a colourless gas.
  • Question 9

What would be a potential problem if the temperature during the Haber Process is kept too low?

CORRECT ANSWER
Not enough ammonia would be produced.
EDDIE SAYS
The forward reaction in the Haber Process is exothermic, i.e. when ammonia is produced heat is released. This means an increase in temperature shifts the equilibrium to the reverse reaction, so less ammonia is produced. However, if the temperature is too low, not enough ammonia will be produced.
  • Question 10

What type of catalyst is used in the Haber Process?

CORRECT ANSWER
iron
EDDIE SAYS
An iron catalyst is used in the Haber Process for efficient ammonia production.
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