Exothermic and Endothermic Reactions

Part 5 of our May MCAS cram series!

First, two important reminders:Energy, like matter, cannot be created or destroyed. Energy can change forms.

Exothermic Reaction

• An exothermic reaction is any reaction in which heat (energy) is released into the system as a product.

• This means the reactants have more potential energy than the products.

This is what an exothermic reaction graph looks like. Note the products line is lower than the reactants line.

Some Exothermic Reaction Examples• Candle flame• Rusting iron• Burning sugar• Formation of snow• Condensation

If the last two sound weird to you, remember: heat energy always moves from warmer to colder to achieve an energy balance.

For snow formation: heat energy leaves the water droplets to the colder surrounding area. The water droplets’ colder molecules contract and form… snow. Exothermic!

Endothermic Reaction• An endothermic

reaction is any reaction in which heat (energy) is absorbed into the system as a product.

• This means the reactants have less potential energy than the products.

This is what an endothermic reaction graph looks like. Note the products line is higher than the reactants line.

Some Endothermic Reaction Examples• Melting ice cubes• Evaporation of water• Photosynthesis• Baking bread• Cooking an egg

Again, in a system, heat energy moves from warmer to cooler. In the examples above, the products absorb heat from the system, become hotter, and react. Endothermic!

Colonel Sanders: Master Thermochemist

• Use your thermometer! Look at the temperature of the system before and after a reaction.

• If after’s temperature is higher than before’s = exothermic

• If before’s temperature is higher than after’s = endothermic

MCAS QuestionsConservation Exo/Endo

Cram Day 5

Conservation Exo/Endo

Conservation Exo/Endo

Conservation Exo/Endo

Conservation Exo/Endo

Conservation Exo/Endo

Conservation Exo/Endo