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Module 3. Lesson 1 - Enthalpy Changes in Chemistry. Starter. When a chemical reaction takes place heat may be given out or taken in. Can you remember the word we use when heat is given out? Can you remember the word we use when heat is taken in?. AfL - Energy level diagrams.

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Module 3

Module 3

Lesson 1 - Enthalpy Changes in Chemistry


Starter
Starter

  • When a chemical reaction takes place heat may be given out or taken in.

  • Can you remember the word we use when heat is given out?

  • Can you remember the word we use when heat is taken in?


Afl energy level diagrams
AfL - Energy level diagrams

Which diagram do you think is endothermic and which is exothermic?

Heat given out

Heat taken in


Change in energy
Change in energy

  • Chemical reactants have a certain amount of chemical energy stored within them.

  • When the reaction has taken place they have either more or less energy stored within them than before.


Objectives
Objectives

Must

Recall and use the terms ENDOTHERMIC and EXOTHERMIC

Should

Describe examples of ENDOTHERMIC and EXOTHERMIC reactions.

Could

Explain ENDOTHERMIC and EXOTHERMIC reactions using energy level diagrams.


Exothermic demos
Exothermic Demos

  • Chlorine gas reacting with sodium metal (video)

  • Concentrated sulphuric acid and sugar (demo)


Definitions
Definitions

  • In your notes write down a definition of an exothermic reaction;

    AND

  • Describe what happened in the two experiments you have just seen.

    Be prepared to share your answers –

    I could ask you!


Exothermic reactions
Exothermic Reactions

Correct definition:

An exothermic chemical reaction where the products have less energy than the reactants. Energy is given out to the surroundings (temperature goes up).


Endothermic demos
Endothermic Demos

  • Dissolving ammonium nitrate

  • Reaction between ammonium nitrate and barium hydroxide.


Definitions1
Definitions

  • In your notes write down a definition of an endothermic reaction;

    AND

  • Describe what happened in the two experiments you have just seen.

    Be prepared to share your answers –

    I could ask you!


Endothermic reactions
Endothermic Reactions

Correct definition:

An endothermic chemical reaction is where the products have more energy than the reactants. Energy is taken in from the surroundings (temperature goes down).


Afl which of the following statements is correct
AfL - Which of the following statements is correct?

  • The products of a chemical reaction have more energy than the reactants so an exothermic reaction must have taken place.

  • The products of a chemical reaction have less energy than the reactants so an endothermic reaction must have taken place.

  • The products of a chemical reaction have less energy than the reactants so an exothermic reaction must have taken place.


Which of the following statements is correct
Which of the following statements is correct?

The products of a chemical reaction have less energy than the reactants so an exothermic reaction must have taken place.

Q - How can we illustrate this?


Energy level diagrams copy into your notes
Energy level diagrams – copy into your notes

Endothermic Exothermic

Heat given out

Heat taken in

Energy level of products is higher than reactants so heat taken in.

Energy level of products is lower than reactants so heat given out.




Plenary can you recall
Plenary – Can you recall?

  • Draw an energy profile for an exothermic reaction marking clearly the activation energy.


Homework
Homework

  • Question booklet.


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