1. Edexcel Additional Science
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DTT Booster
Edexcel Additional Science
THERAPY Topic 5 – Exothermic and Endothermic Reactions   
Commissioned by The PiXL Club Ltd. October 2016
© Copyright The PiXL Club Ltd, 2016
This resource is strictly for the use of member schools for as long as they remain members of The PiXL Club. It may not be copied, sold nor transferred to a third party or used by the school after membership ceases. Until such time it may be freely used within the member school.
All opinions and contributions are those of the authors. The contents of this resource are not connected with nor endorsed by any other company, organisation or institution.
The PiXL Club Ltd, Company number

2. How to deliver the DTT Booster
Administer the short diagnosis test.
Mark the test (peer assess).
Work through the therapy slides completing the model questions and answers.
Complete the question slides for students to self assess.
Administer the final test (peer assess).

3. Conduction and convection
Edexcel Exothermic and Endothermic Reactions
To work out if a reaction is exothermic or endothermic, you often have to look at the temperature change. This means you have to know the temperature at the start of the reaction and at the end of the reaction.
Whenever chemical reactions take place, ENERGY is involved. This is because energy is always TRANSFERRED to or from the surroundings.
There are two types of reactions:
Exothermic reactions give out heat to
the surroundings (gets hot)
Endothermic reactions take in heat from the surroundings (gets cold)
Model Question
Which of these reactions represents an exothermic reaction?
Which of these reactions represents an endothermic reaction?
Which reaction has the largest energy change?
Reaction
Start temp (°C)
Final temp (°C) 1 19 27 2 18 3 16 4 25
CLICK to reveal MODEL ANSWER
Remember:
Ex = heat out (as in exit)
En = heat in (as in entrance)
No change = no reaction
1) one or four 2)three 3)one
P1.1.3a/P1.1.1

4. Conduction and convection
Edexcel Exothermic and Endothermic Reactions
To work out if a reaction is exothermic or endothermic, you often have to look at the temperature change. This means you have to know the temperature at the start of the reaction and at the end of the reaction.
Whenever chemical reactions take place, ENERGY is involved. This is because energy is always TRANSFERRED to or from the surroundings.
There are two types of reactions:
Exothermic reactions give out heat to
the surroundings (gets hot)
Endothermic reactions take in heat from the surroundings (gets cold)
Model Question
Which of these reactions represents an exothermic reaction?
Which of these reactions represents an endothermic reaction?
Which reaction has the largest energy change?
Reaction
Start temp (°C)
Final temp (°C) 1 19 27 2 18 3 16 4 25
Remember:
Ex = heat out (as in exit)
En = heat in (as in entrance)
No change = no reaction
1) one or four 2)three 3)one
P1.1.3a/P1.1.1

5. Conduction and convection
Edexcel Exothermic and Endothermic Reactions
We can measure exothermic reactions because they give a rise in temperature as the reaction happens.
Model Question
Explain how a hand warmer works.
Model Answer
The hand warmer contains a salt solution that forms crystals when activated.
A small metal disc in the plastic pack is used to start the exothermic change.
The crystals spread through the solution, giving off heat energy.
Some hand warmers can be used many times by boiling it in water to re-dissolve the crystals.
Salt solution
Metal disc
Everyday examples include:
Explosions
Other important examples include:
Combustion
Neutralisation
Oxidation reactions (eg: respiration)
Displacement
CLICK to reveal MODEL ANSWER
FIREWORKS -
GAS
P1.1.3a/P1.1.1

6. Conduction and convection
Edexcel Exothermic and Endothermic Reactions
We can measure exothermic reactions because they give a rise in temperature as the reaction happens.
Model Question
Explain how a hand warmer works.
Model Answer
The hand warmer contains a salt solution that forms crystals when activated.
A small metal disc in the plastic pack is used to start the exothermic change.
The crystals spread through the solution, giving off heat energy.
Some hand warmers can be used many times by boiling it in water to re-dissolve the crystals.
Salt solution
Metal disc
Everyday examples include:
Explosions
Other important examples include:
Combustion
Neutralisation
Oxidation reactions (eg: respiration)
Displacement
FIREWORKS -
GAS
P1.1.3a/P1.1.1

7. Conduction and convection
Edexcel Exothermic and Endothermic Reactions
We can measure endothermic reactions because they give a drop in temperature as the reaction happens.
Model Question
Explain how an ice pack works.
Model Answer
Ice packs contain two bags, The inner one contains ammonium nitrate and the outer one water.
When the outer bag is squeezed, the inner bag bursts and the ammonium nitrate dissolves, taking the energy in from its surroundings.
Outer bag containing water
Inner bag containing ammonium nitrate
An everyday example includes:
Photosynthesis
These reactions are much less common, but one important example is:
Dissolving ammonium nitrate in water (sports injury packs)
CLICK to reveal MODEL ANSWER
P1.1.3a/P1.1.1

8. Conduction and convection
Edexcel Exothermic and Endothermic Reactions
We can measure endothermic reactions because they give a drop in temperature as the reaction happens.
Model Question
Explain how an ice pack works.
Model Answer
Ice packs contain two bags, The inner one contains ammonium nitrate and the outer one water.
When the outer bag is squeezed, the inner bag bursts and the ammonium nitrate dissolves, taking the energy in from its surroundings.
Outer bag containing water
Inner bag containing ammonium nitrate
An everyday example includes:
Photosynthesis
These reactions are much less common, but one important example is:
Dissolving ammonium nitrate in water (sports injury packs)
P1.1.3a/P1.1.1

9. Conduction and convection
Edexcel Exothermic and Endothermic Reactions
Model Question
Is the chemical reaction occurring when you strike a match exothermic or endothermic?
Model Answer
Exothermic, we can feel and see the energy released as heat and light
Some ideas for you to be clear about:
Chemical bonds hold the energy of a molecule.
If we break a bond we have to put energy in!
If we make a new bond energy is released!
CLICK to reveal MODEL ANSWER
For an exothermic reaction
During a chemical reaction bonds are broken and new bonds form.
If you put in more energy breaking bonds than is released making new bonds the reaction is endothermic
If you release more energy than you put in the reaction is exothermic
More energy is released than put in
Energy is released by our reaction. This energy is released to the surroundings – We can feel this energy as heat.
P1.1.3a/P1.1.1

10. Conduction and convection
Edexcel Exothermic and Endothermic Reactions
Model Question
How would you draw a diagram to show an endothermic reaction?
Model Answer
For an endothermic reaction
CLICK to reveal MODEL ANSWER
More energy is put in than released
Reactants
Energy
Products
This graph shows the energy contained in the molecules of the reaction not the energy of the solution or the surroundings.
Energy is taken in by our reaction. This energy is taken from the surroundings – We can feel this energy loss as a cooling of the surroundings.
After an exothermic reaction is over the molecules formed contain less energy in their bonds than at the start of the reaction.
We can show this on a chart.
As you can see, after the reaction the products contain less energy than the reactants – a drop shows that energy is lost from the chemicals and released to the surroundings
P1.1.3a/P1.1.1

11. Conduction and convection
Edexcel Exothermic and Endothermic Reactions
Model Question
Two reactions were carried out in a test tube, in which reaction would you feel the test tube warming up?
Model Answer
Tube A
Exothermic
CLICK to reveal MODEL ANSWER
Endothermic
The size of the energy gap is important!
The bigger the gap the bigger the energy change
In the two diagrams opposite you can see that the energy change for the endothermic reaction is greater than that for the exothermic
P1.1.3a/P1.1.1

12. Conduction and convection
AQA Exothermic and Endothermic Reactions
Writing a plan could involve:
Listing apparatus
Writing a method
Giving measurements
Listing and explaining control variables
Explaining how to reduce safety risks
CLICK to reveal MODEL ANSWER
Model Answer - HINTS
Think about what apparatus is required and how you will use it to take the measurements. Use any diagram to help list what must be kept the same for a fair test.
Model Question
A group of students carried out an investigation where they changed the type of metal hydrogencarbonate and reacted it with hydrochloric acid. They measure the temperature at the start and the lowest temperature and then calculate the temperature difference.
Explain how they could have carried out the experiment and how they kept it a fair test.
Metal
hydrogencarbonate
Staring
temperature (◦C)
Final
Temperature
difference (◦C) A 20 10 B 9 11 C 21 15 6 D 12 8 E 14 7
P1.1.3a/P1.1.1

13. Conduction and convection
AQA Exothermic and Endothermic Reactions
Writing a plan could involve:
Listing apparatus
Writing a method
Giving measurements
Listing and explaining control variables
Explaining how to reduce safety risks
Model Answer - HINTS
Think about what apparatus is required and how you will use it to take the measurements. Use any diagram to help list what must be kept the same for a fair test.
Model Question
A group of students carried out an investigation where they changed the type of metal hydrogencarbonate and reacted it with hydrochloric acid. They measure the temperature at the start and the lowest temperature and then calculate the temperature difference.
Explain how they could have carried out the experiment and how they kept it a fair test.
Metal
hydrogencarbonate
Staring
temperature (◦C)
Final
Temperature
difference (◦C) A 20 10 B 9 11 C 21 15 6 D 12 8 E 14 7
P1.1.3a/P1.1.1

14. Edexcel Exothermic and Endothermic Reactions
Explain what is meant by an exothermic reaction and give an example of such a reaction.
Explain what is meant by an endothermic reaction and give an example of such a reaction.
Use the table to answer the following questions a) Which reaction is exothermic? b) Which reaction is endothermic? c) What can you conclude from reaction C?
Which graph, A or B, shows an endothermic change?
5. Different metals are added to hydrochloric acid and the temperature rise is recorded. List the factors that you would need to keep the same in order to make the investigation fair.
Reaction
Start temp (°C)
Final temp (°C) A 19 29 B 20 18 C 21 D 25

15. Edexcel Exothermic and Endothermic Reactions
Explain what is meant by an exothermic reaction and give an example of such a reaction.
A reaction that gives out energy to the surroundings
2. Explain what is meant by an endothermic reaction and give an example of such a reaction.
A reaction that takes in energy from the surroundings
3. Use the table to answer the following questions a) Which reaction is exothermic? A and D b) Which reaction is endothermic? B c) What can you conclude from reaction C?
It does not react
Which graph, A or B, shows an endothermic change? B
Different metals are added to hydrochloric acid and the temperature rise is recorded. List the factors that you would need to keep the same in order to make the investigation fair.
Metal – same mass, surface area
Acid – same type, concentration/volume/same starting temperature
Reaction
Start temp (°C)
Final temp (°C) A 19 29 B 20 18 C 21 D 25

16. Final test DTT Booster Students now complete the final test.
Compare this to what they achieved in the diagnostic test.