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Chemical reactions and how they break and form bonds between atoms. Balanced reactions, reversibility, and equlibrium.
Introduction
Molecules—like the ones that make up your body—are just collections of atoms held together by chemical bonds. In many ways, they're a lot like Tinkertoy® building projects. In fact, if you take organic chemistry, you’ll most likely buy a model set that looks suspiciously similar to Tinkertoys®:
Just as you can put Tinkertoy® wheels together in different ways using different stick connectors, you can also put atoms together in a different ways by forming different sets of chemical bonds. The process of reorganizing atoms by breaking one set of chemical bonds and forming a new set is known as a chemical reaction.
Chemical reactions
Chemical reactions occur when chemical bonds between atoms are formed or broken. The substances that go into a chemical reaction are called the reactants, and the substances produced at the end of the reaction are known as the products. An arrow is drawn between the reactants and products to indicate the direction of the chemical reaction, though a chemical reaction is not always a "one-way street," as we'll explore further in the next section.
For example, the reaction for breakdown of hydrogen peroxide (
In this example hydrogen peroxide is our reactant, and it gets broken down into water and oxygen, our products. The atoms that started out in hydrogen peroxide molecules are rearranged to form water molecules (
You may have noticed extra numbers in the chemical equation above: the
Equations must be balanced to reflect the law of conservation of matter, which states that no atoms are created or destroyed over the course of a normal chemical reaction. You can learn more about balancing reactions in the balancing chemical equations tutorial.
Reversibility and equilibrium
Some chemical reactions simply run in one direction until the reactants are used up. These reactions are said to be irreversible. Other reactions, however, are classified as reversible. Reversible reactions can go in both the forward and backward directions.
In a reversible reaction, reactants turn into products, but products also turn back into reactants. In fact, both the forward reaction and its opposite will take place at the same time. This back and forth continues until a certain relative balance between reactants and products is reached—a state called equilibrium. At equilibrium, the forward and backward reactions are still happening, but the relative concentrations of products and reactants no longer change.
Each reaction has its own characteristic equilibrium point, which we can describe with a number called the equilibrium constant. To learn where the equilibrium constant comes from and how to calculate it for a specific reaction, check out the equilibrium topic.
When a reaction is classified as reversible, it is usually written with paired forward and backward arrows to show it can go both ways. For example, in human blood, excess hydrogen ions (
Since this is a reversible reaction, if carbonic acid were added to the system, some of it would be turned into bicarbonate and hydrogen ions to restore equilibrium. In fact, this buffer system plays a key role in keeping your blood pH stable and healthy.
Attribution:
This article is a modified derivative of “Atoms, isotopes, ions, and molecules: the building blocks,” by OpenStax College, Biology (CC BY 3.0). Download the original article for free at http://cnx.org/contents/185cbf87-c72e-48f5-b51e-f14f21b5eabd@9.85.
The modified article is licensed under a CC BY-NC-SA 4.0 license.
Additional references:
Molecule. (July 2, 2015). Retrieved July 2, 2015 from Wikipedia: https://en.wikipedia.org/?title=Molecule.
Raven, P. H., Johnson, G. B., Mason, K. A., Losos, J. B., and Singer, S. R. (2014). The nature of molecules and properties of water. In Biology (10th ed., AP ed., pp. 17-30). New York, NY: McGraw-Hill.
Reece, J. B., Urry, L. A., Cain, M. L., Wasserman, S. A., Minorsky, P. V., and Jackson, R. B. (2011). Chemical reactions make and break chemical bonds. In Campbell Biology (10th ed., pp. 40-41). San Francisco, CA: Pearson.
Log in sanjaecuvilie 9 years agoPosted 9 years ago. Direct link to sanjaecuvilie's post “I understand that one of ...” I understand that one of the ways to speed up a chemical reaction is to slice the solute into smaller pieces, this way it is more exposed to the solvent. However, what i fail to comprehend is how this method INCREASES the surface area of the solute. Wouldn't making the solute smaller DECREASE the surface area? • (1 vote) Phoebe 8 years agoPosted 8 years ago. Direct link to Phoebe's post “It increases the surface ...” It increases the surface area : volume ratio--there's the same amount of matter but more surface as more of it is exposed. Surface area is the area of all the surfaces added together. A cube with length 1, width 1, and height 2 has 4 2x1 rectangles and 2 1x1 rectangles, which is 10 in total. Cut it in half and you have two cubes, each with 6 1x1 rectangles (half the height, same length and width). 2 x 6 = 12 so you now have a surface area of 12 instead of 10. (15 votes) arehartdallon 9 years agoPosted 9 years ago. Direct link to arehartdallon's post “can radioactive elements ...” can radioactive elements set on fire? • (4 votes) Davin V Jones 9 years agoPosted 9 years ago. Direct link to Davin V Jones's post “Sure, they pretty much ac...” Sure, they pretty much act the same chemically as their stable isotopic counterparts. (5 votes) Julian Delgadillo Marin 8 years agoPosted 8 years ago. Direct link to Julian Delgadillo Marin's post “Are all Hidrogen atoms eq...” Are all Hidrogen atoms equal to each other? Like totally equal no diference? • (0 votes) Orian Stephens 4 years agoPosted 4 years ago. Direct link to Orian Stephens's post “Being as they are the sam...” Being as they are the same thing, if there is a difference, it would be so minuscule. But yes, There really isn't a genuine difference between multiple hydrogen atoms. (5 votes) sophiasalguerooo 4 years agoPosted 4 years ago. Direct link to sophiasalguerooo's post “Why do atoms come togethe...” Why do atoms come together? • (4 votes) RowanH 4 years agoPosted 4 years ago. Direct link to RowanH's post “Do you mean why several a...” Do you mean why several atoms come together in a molecule? They are more stable this way because when a bond is formed(by sharing electrons between atoms) energy is released. (4 votes) Jack Friedrich 9 years agoPosted 9 years ago. Direct link to Jack Friedrich's post “Where are Hydrogen and Ox...” Where are Hydrogen and Oxygen atoms found as single atoms? • (2 votes) sanjaecuvilie 9 years agoPosted 9 years ago. Direct link to sanjaecuvilie's post “Oxygen and Hydrogen atoms...” Oxygen and Hydrogen atoms are diatomic, meaning they can never be found alone in nature. If they fail to find another element to bond to, they are forced to bond with themselves. (7 votes) amalone0702 3 years agoPosted 3 years ago. Direct link to amalone0702's post “Are two atoms of the same...” Are two atoms of the same element identical? • (3 votes) Charles LaCour 3 years agoPosted 3 years ago. Direct link to Charles LaCour's post “They do not have to be. ...” They do not have to be. An element can have what are called isotopes. The element is defined by the number of protons in the atomic nucleus but there may be different numbers of neutrons. For example the all of the isotopes of carbon have 6 protons but there are isotopes with 6, 7 and 8 neutrons. (3 votes) Sheesh2212 3 years agoPosted 3 years ago. Direct link to Sheesh2212's post “How do you even balance B...” How do you even balance BIG equations? • (4 votes) ZaynaC 4 years agoPosted 4 years ago. Direct link to ZaynaC's post “Are all reactions reversi...” Are all reactions reversible? • (2 votes) Amrita 4 years agoPosted 4 years ago. Direct link to Amrita's post “Hi! your answer is no.All...” Hi! your answer is no.All reactions are not reversible.Mainly chemical reactions are not reversible. Examples include,germination of a seed,curdling of milk,etc. Hope this might help. Have a nice day. (5 votes) Joon's Moonchild 6 years agoPosted 6 years ago. Direct link to Joon's Moonchild's post “How do you know that the ...” How do you know that the product can also turn back into its reactant and vise versa? • (3 votes) tyersome 6 years agoPosted 6 years ago. Direct link to tyersome's post “Are you asking about expe...” Are you asking about experimental evidence? What would you expect to happen if you made a pure solution of the product(s) of a reversible reaction? What would you expect to happen if the reaction was irreversible? Does that help? (2 votes) roselene reynolds 4 years agoPosted 4 years ago. Direct link to roselene reynolds's post “how do you get the chemic...” how do you get the chemical reaction for Na(s)+H2O(L) which yields to NaOH(aq)+H2(g)? • (3 votes) Mahnoor Umar 4 years agoPosted 4 years ago. Direct link to Mahnoor Umar's post “2Na + 2H2O ----> 2NaOH + ...” 2Na + 2H2O ----> 2NaOH + H2 (2 votes)Want to join the conversation?
The apple example above is a good one--cutting something in half means new surface is exposed that was previously on the inside.
This is the balanced chemical reaction.
