Endothermic and Exothermic Chemical Reactions

Content Objective: PS.3b

Learning Target: use evidence and scientific reasoning to differentiate (tell the difference) between a chemical reaction that requires an input of energy (endothermic) and one that releases energy (exothermic)

Language Objective: I can define and identify the endothermic and exothermic reactions.

Directions:

• watch the video

  • write down key details and/or examples of endothermic and exothermic reactions

• use the slides to write key information on the notes sheet.

• answer the interactive questions

Share the key details from the video.

Recall:

Chemical changes involve the breaking and making of chemical bonds. Any time there is a chemical reaction, there will also be a change in energy.
Let's discuss two types of chemical change that are classified by whether the reaction absorbs or releases heat energy: endothermic reactions and exothermic reactions.

Multiple Choice

During chemical reactions, bonds are...

• broken only

• formed only

• both broken and formed

• none of the above are correct

ENDOTHERMIC REACTIONS - "endo" is a prefix that can mean "inner" or "absorbing"

If the total energy required to break bonds in the reactants is more than the total energy released when new bonds are formed in the products, the reaction is endothermic.

You can remember this because the prefix endo- means inner or absorbing.

So, an endothermic reaction takes thermal energy in or absorbs thermal energy from the surroundings; making the temperature of the surroundings decrease.


Energy used to break bonds > Energy released to form bonds

Endothermic Reaction Example

Instant cold packs are an example of an endothermic reaction that you might be familiar with. Inside, there is solid ammonium nitrate. There is also a separate bag of water. To activate the reaction, you squeeze the bag of water to cause it to break. The water is then able to mix with the ammonium nitrate and cause an endothermic reaction.

​An instant cold pack contains ammonium nitrate and water. When the chemicals are mixed, it causes an endothermic reaction.

Remember:
An endothermic chemical reaction absorbs heat from the environment.

EXOTHERMIC REACTIONS - "exo" is a prefix that means "outside"

If the total energy required to break bonds in the reactants is less than the total energy released when new bonds are formed in the products, the reaction is exothermic.

In other words, an exothermic reaction releases heat energy into the surroundings. This causes an increase in temperature. You can remember this because the prefix exo- means outside or external.
The heat goes out of the reaction; making the temperature of the surroundings increase.


Energy used to break bonds < Energy released to form bonds

Exothermic Reaction Example

Burning the wax of a candle is an example of an exothermic reaction because heat from the flame is released to the environment.

Remember:
An exothermic chemical reaction releases heat to the environment.

Multiple Choice

If a chemical reaction is EXOTHERMIC, the temperature of the surrounding would....

• stay the same

• increase

• decrease

Multiple Choice

During an endothermic reaction in a beaker if we are part of the surroundings and touched the beaker, it would feel _______. 

• warm

• cold

Multiple Choice

The illustration shows cell respiration. Is the overall reaction of cell respiration an Endothermic or an Exothermic reaction?

• endothermic

• exothermic

Multiple Choice

A student mixed two chemicals to allow them to react. The temperature before the reaction was 25 ° C. The temperature after the reaction was 18° C. Which of the following is true?

• The temperature did not change.

• It is an endothermic reaction

• It is an exothermic reaction

• Energy is released from the reaction into the surrounding.

Multiple Choice

What type of reaction occurs in a hand warmer?

• exothermic

• endothermic

Multiple Choice

What instrument would you use to detect an endothermic or exothermic reaction?

• triple beam balance

• ruler

• thermometer

Glue your notes in your notebook, please.