Exothermic & Endothermic Reactions

This lesson covers:

  1. What exothermic and endothermic mean
  2. How to represent exothermic and endothermic reactions using reaction profiles (also known as energy level diagrams)
  3. What activation energy is, and how to show it on a reaction profile

True or false? Energy is stored in chemical bonds.

True

False

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True or false? Different chemical bonds hold different amounts of energy.

True

False

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If the reactant molecules in a reaction have more energy in their chemical bonds than the product molecules, will energy be absorbed or released overall? 

Absorbed 

Released 

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What is an exothermic reaction?

A reaction that releases thermal energy to the surroundings

A reaction that takes in thermal energy from the surroundings

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If an exothermic reaction occurs in a closed container, what would happen to the temperature inside the container?

The temperature would increase

The temperature would decrease

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What is an endothermic reaction?

A reaction that releases thermal energy to the surroundings

A reaction that takes in thermal energy from the surroundings

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If an endothermic reaction occurs in a closed container, what would happen to the temperature inside the container?

The temperature would decrease

The temperature would increase

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Graph showing the energy profile of an exothermic reaction with reactants and products.

What type of reaction is shown in the reaction profile above?

An exothermic reaction

An endothermic reaction

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Graph showing the energy profile of an exothermic reaction with reactants having higher energy than products.

What type of reaction is the reaction profile above?

An exothermic reaction

An endothermic reaction

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react / energy / minimum / maximum 


Activation energy is the amount of the reactant particles require in order to collide with each other and .

minimum
energy
react

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Two reaction profile diagrams showing activation energy from reactants to peak of curve for exothermic and endothermic reactions.

On reaction profile diagrams, the activation energy is always the increase in energy from the reactants to the peak of curve.


This applies to both the exothermic and endothermic diagrams.

Graph showing the progress of a reaction with energy levels of reactants and products, indicating the activation energy.

Which of the above shows the activation energy?

A

B

C

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Diagram showing the energy change of a reaction with arrows indicating different energy levels for reactants and products.

Which of the above arrows indicates the energy change of the reaction?

A

B

C

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