Hello Everyone, thank you for joining me for another post on general chemistry topics! Today's topic is exothermic and endothermic reactions.
Why you should understand Exothermic and Endothermic Reactions: Exothermic and Endothermic conditions describe the transfer of Enthalpy during a reaction.
Key Ideas
- Defining Exergonic and Endergonic
- How they compare with Exothermic and Endothermic
- Graphing: Exergonic and Endergonic graphs compared to the Endo/Exothermic graphs
Defining Exergonic and Endergonic
Exergonic and Endergonic reactions describe the movement of energy during a reaction. If a reaction is favorable in energy movement (from high energy to low energy) it is considered spontaneous. A reaction in which energy is lost (the reaction goes from a high energy state to a low energy state) is considered an exergonic reaction. Exergonic reactions lose energy during the reaction and are spontaneous. A reaction where energy is gained requires some form of energy input and is considered nonspontaneous. Endergonic reactions are nonspontaneous and require energy to occur.
How they compare with Exothermic and Endothermic
While the words Endergonic and Exergonic may seem very similar to exothermic and endothermic; the two groups are very different.
Exothermic and endothermic reactions only describe the movement of heat. Just because a reaction is labeled as exothermic or endothermic does not mean you can predict it's spontaneity. Exothermic reactions are not always spontaneous. Endothermic reactions are not always nonspontaneous.
Exergonic and endergonic reactions specifically describe the movement of energy during a reaction. The movement of energy during a reaction directly corresponds with the spontaneity of a reaction. An exergonic reaction will always be spontaneous and an endergonic reaction will always be nonspontaneous.
Graphing: Exergonic and Endergonic graphs compared to the Endo/Exothermic graphs
Below are the graphs of both exergonic/endergonic reactions and endothermic/exothermic reactions.
The graphs of endergonic and exergonic reactions will always have Gibbs Free Energy as an axis.
The graphs of exothermic and endothermic reactions will always have Potential energy as an axis. This is because potential energy is stored in the molecules as vibrational energy. Remember: breaking a bond requires energy, it doesn't release energy. The addition or removal of heat increases and decreases the potential energy of a reaction (adding heat creates more vibrations while removing heat decreases vibrations).
Further explanation of potential energy as an axis: An exothermic reaction releases heat. This means that initially, the reaction contains more heat and the molecules are vibrating more rapidly. As the heat is released, the molecules lose potential energy as their vibrations decrease.
Summary
- Exergonic reactions lose energy during the reaction and are spontaneous.
- Endergonic reactions are nonspontaneous and require energy to occur.
- Exothermic reactions are not always spontaneous.
- Endothermic reactions are not always nonspontaneous.
- An exergonic reaction will always be spontaneous and an endergonic reaction will always be nonspontaneous.
- Breaking a bond requires energy, it doesn't release energy.
I hope you've found this post on exergonic and endergonic reactions helpful. If you have any questions feel free to comment on this post, email me, or comment on the video I've linked below.
- Saren
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