<< Chapter < Page Chapter >> Page >

Free and activation energy

After learning that chemical reactions release energy when energy-storing bonds are broken, an important next question is the following: How is the energy associated with these 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 quantify these energy transfers. 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. Free energy specifically refers to the energy associated with a chemical reaction that is available after the losses are accounted for. In other words, free energy is usable energy, or energy that is available to do work.

If energy is released during a chemical reaction, then the change in free energy, signified as ∆G (delta G) will be a negative number. A negative change in free energy also means that the products of the reaction have less free energy than the reactants, because they release some free energy during the reaction. Reactions that have a negative change in free energy and consequently release free energy are called exergonic reactions . Think: ex ergonic means energy is ex iting the system. These reactions are also referred to as spontaneous reactions, and their products have less stored energy than the reactants. An important distinction must be drawn between the term spontaneous and the idea of a chemical reaction occurring immediately. Contrary to the everyday use of the term, a spontaneous reaction is not one that suddenly or quickly occurs. The rusting of iron is an example of a spontaneous reaction that occurs slowly, little by little, over time.

If a chemical reaction absorbs energy rather than releases energy on balance, then the ∆G for that reaction will be a positive value. In this case, the products have more free energy than the reactants. Thus, the products of these reactions can be thought of as energy-storing molecules. These chemical reactions are called endergonic reactions and they are non-spontaneous. An endergonic reaction will not take place on its own without the addition of free energy.

There is another important concept that must be considered regarding endergonic and exergonic reactions. Exergonic reactions require a small amount of energy input to get going, before they can proceed with their energy-releasing steps. These reactions have a net release of energy, but still require some energy input in the beginning. This small amount of energy input necessary for all chemical reactions to occur is called the activation energy    .

Enzymes

A substance that helps a chemical reaction to occur is called a catalyst, and the molecules that catalyze biochemical reactions are called enzymes . Most enzymes are proteins and perform the critical task of lowering the activation energies of chemical reactions inside the cell. Most of the reactions critical to a living cell happen too slowly at normal temperatures to be of any use to the cell. Without enzymes to speed up these reactions, life could not persist. Enzymes do this by binding to the reactant molecules and holding them in such a way as to make the chemical bond-breaking and -forming processes take place more easily. It is important to remember that enzymes do not change whether a reaction is exergonic (spontaneous) or endergonic. This is because they do not change the free energy of the reactants or products. They only reduce the activation energy required for the reaction to go forward ( [link] ). In addition, an enzyme itself is unchanged by the reaction it catalyzes. Once one reaction has been catalyzed, the enzyme is able to participate in other reactions.

Questions & Answers

information for blood vessels
Sumit Reply
helps pump blood through body
scott
arteries carry blood away from the heart while veins return it to the heart
Reverian
veins have thinner outer walls because blood pressure in them is very low compared to arteries with thicker outer walls to withstand the higher blood pressure.
Oliver
cell, tissue, organ, organism, organ system,
Gheida Reply
please what are the characteristics of a good respiratory system?
Salomon Reply
thin wall ,a moist inner surface ,a huge combined surface area and a rich blood supply.
Nchimunya
Help me am confused what is the cell membrane as a partially permeable membrane
Janelle Reply
it is the ability of a molecules to cross a cell membrane depending on their both size and chemical properties.
Andrews
Based on my previous understanding of biological systems, a cell membrane is a semi-permeable membrane made up of a phospholipids bi-layer. The polar head consisting of phosphate and the hydrophobic end made up of lipids.
Abayomi
Smallest bone of rabbit is
Sahrukh Reply
difference between catebolism and anebolism
Anthvanath Reply
identify the causes of infertility in human beings
Rodrick Reply
Describe how a healthy pregnancy could be maintained
Rodrick
Huaman largest bone
Sahrukh
How I can test DNY
Salamin Reply
Samllest bone
Sahrukh
How can I determine my child
AlfredOfficial Reply
by DNA tests
lasford
thanks
AlfredOfficial
How to test
Salamin
How many bones of 1 year childrean
R.k Reply
208
Rani
A baby's body has about 300 bones at birth. These eventually fuse (grow together) to form the 206 bones that adults
Manali
Somebudy seys me 300
R.k
A baby's body has about 300 bones at birth. These eventually fuse (grow together) to form the 206 bones that adults h
Manali
I ask you about beby bones
R.k
i cann't say about 1 year baby's bones bt on birth baby has 300 bones
Manali
Ok thank you goodnight
R.k
good night
Manali
have a sweat dream
Rani
it's 300 bones because it a baby
Jasper
babies have 300 bones in which it fuses to become 206 as an adult.
Andrews
it has 300 bones ,nchimunya
Nchimunya
figure of male reproduction
Rani Reply
front view of male reproductive system
Rani
front view of male reproductive system
Rani
what is Actin? I don't understand this definition
Rhonda Reply
Actin is a family of globular multi-functional proteins that form microfilaments. 
Lauren
difference between throat and lyrnx
Lone
what is the difference between a vaccine and a antiserum
Silver Reply
An antiserum contains antibodies already produced and is used to pass on immune responses. A vaccine contains a substance that stimulates the production of antibodies to create an immune response.
Nana
A vaccine a preparation of antigens for one (or more) diseases that is given to stimulate active immunity and protect against the disease (s). while an antiserum either neutralizes the "infection " or stimulates your immune system to attack an infection.
Oliver
what is deoxyribonucleic acid
Carlene Reply
A negatively charged molecule; polymer of nucleotides found in the nucleus of a cell ... DNA.
Abayomi
guys u needs your help i am in this conversation but i don't understand what you guys were talking about please i need your help.
Asali
Hi
Janelle
hi
Oliver
hello
Rani
how are you doing?
Jasper
DNA is genetic material which is present in cell DNA is made up of nitrogen base,phosphate group and pentose sugar.
Manali
hi
Jasper
give a front view of male reproductive system
Rani
to maintain certain biological activities of cell
jeeni Reply

Get the best Human biology course in your pocket!





Source:  OpenStax, Human biology. OpenStax CNX. Dec 01, 2015 Download for free at http://legacy.cnx.org/content/col11903/1.3
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Human biology' conversation and receive update notifications?

Ask