Exergonic Reaction: Definition & Example

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  • 0:01 Exergonic Reactions
  • 0:47 Free Energy & Reactions
  • 1:42 Energy Release
  • 2:40 Lesson Summary
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Lesson Transcript
Instructor: John Williams
In living and mechanical systems, energy is needed to drive various functions. It is obtained through exergonic reactions. Learn about these reactions, the characteristics that define them, and their purpose in biological and mechanical systems through this lesson.

Exergonic Reactions

Do you know what gasoline, sugar, and lipids have in common? Each of these chemicals provides energy for various systems. Whether it's powering a car for driving or powering animal systems for living, these chemicals, and many others, store energy in their bonds that can be used once released. In order to release this energy, these chemicals must undergo exergonic reactions.

Exergonic reactions are chemical reactions that release energy in the form of heat. Typically, this energy is released when bonds are broken. More specifically, in humans, these reactions are called catabolic, which means that the molecules are being broken down into smaller components. By breaking these bonds, systems (such as the human body or the car example above) can receive the energy need to perform their functions.

Free Energy and Reactions

Energy stored in bonds is known as free energy, or energy available to do work. It is also often referred to as Gibbs free energy. When a molecule has a large amount of free energy, it becomes unstable, as the energy would prefer to be released than stored in the bonds. As a rule of thumb, the more free energy in the bond, the more unstable the molecule will be.

If a molecule is unstable, it will work to try and become stable eventually. This process can be a slow one or a fast one, but it is a certain one. Molecules that have high free energy are unstable. Therefore, the bonds that contain this energy will break easily to release heat. Because this process is certain to happen, it is also known as spontaneous reaction. Releasing the free energy stored in bonds helps the molecules involved in the reaction find energetic stability.

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