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Potential energy is not only associated with the location of matter (such as a child sitting on a tree branch), but also with the structure of matter. A spring on the ground has potential energy if it is compressed; so does a rubber band that is pulled taut. The very existence of living cells relies heavily on structural potential energy. On a chemical level, the bonds that hold the atoms of molecules together have potential energy. Remember that anabolic cellular pathways require energy to synthesize complex molecules from simpler ones, and catabolic pathways release energy when complex molecules are broken down. The fact that energy can be released by the breakdown of certain chemical bonds implies that those bonds have potential energy. In fact, there is potential energy stored within the bonds of all the food molecules we eat, which is eventually harnessed for use. This is because these bonds can release energy when broken. The type of potential energy that exists within chemical bonds, and is released when those bonds are broken, is called chemical energy    ( [link] ). Chemical energy is responsible for providing living cells with energy from food. The release of energy is brought about by breaking the molecular bonds within fuel molecules.

The molecular formula of octane (top), which is a chain of eight carbons and eighteen hydrogens, fuels a racecar speeding along a track (bottom).
The molecules in gasoline (octane, the chemical formula shown) contain chemical energy within the chemical bonds. This energy is transformed into kinetic energy that allows a car to race on a racetrack. (credit “car”: modification of work by Russell Trow)

Visit this site and select “A simple pendulum” on the menu (under “Harmonic Motion”) to see the shifting kinetic (K) and potential energy (U) of a pendulum in motion.

Free energy

After learning that chemical reactions release energy when energy-storing bonds are broken, an important next question is how is the energy associated with chemical reactions quantified and expressed? How can the energy released from one reaction be compared to that of another reaction? A measurement of free energy    is used to quantitate these energy transfers. Free energy is called Gibbs free energy (abbreviated with the letter G) after Josiah Willard Gibbs, the scientist who developed the measurement. Recall that according to the second law of thermodynamics, all energy transfers involve the loss of some amount of energy in an unusable form such as heat, resulting in entropy. Gibbs free energy specifically refers to the energy associated with a chemical reaction that is available after entropy is accounted for. In other words, Gibbs free energy is usable energy, or energy that is available to do work.

Every chemical reaction involves a change in free energy, called delta G (∆G). The change in free energy can be calculated for any system that undergoes such a change, such as a chemical reaction. To calculate ∆G, subtract the amount of energy lost to entropy (denoted as ∆S) from the total energy change of the system. This total energy change in the system is called enthalpy    and is denoted as ∆H . The formula for calculating ∆G is as follows, where the symbol T refers to absolute temperature in Kelvin (degrees Celsius + 273):

Questions & Answers

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Mirabel Reply
what are hormones
what is meant by th word photosynthesis
it is the process where by chloropherious plant manufacture their food with the presence of sunlight , chlorophyll and water etc.
what is biology
stallon Reply
is the study living things
and non living things
what is water circle?
Faith Reply
please i asks whether this biology is for university
Sky Reply
for secondary
Copulation means coming together of male and female in the present of sexual Intercourse.
what are the adaptive features of nervous system
Please what is ovulation
Adusei Reply
What is cell division?
What is copulation?
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what is a metaborism
Beatrice Reply
this is a specialized part of the cell eg Nucleus
David Reply
what are adaptive features of nervous system
what are the organelles?
Faith Reply
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mana Reply
reproduction is the process by which living organisms give rise to young ones of their own kind
What is evolution
the production of new forms of life over time as documented in the fossil record.
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Kevin Reply
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Rita Reply
what is a melanin?
Judith Reply
what is telophase
melanin in that black color we posse in our skins
it is a substance that gives the colour black to the hair
melanin is a dark brown or blacksubstance that is a natural part of people's skin, hair, and eyes

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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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