The chemical changes are the modifications that occur in substances or matter from chemical reactions. They are characterized by being irreversible, as they involve the formation of new bonds that need energy or other reactions to reverse their effects..
Life and its biochemistry, for example, are made up of constant chemical changes that reveal a myriad of reactions that take place within living beings. The result is the growth, development and aging of plant and animal tissues; that as is well known, scientifically and thermodynamically, it is an irreversible process.
That is why in living creatures, from invertebrates to vertebrates, we find chemical changes even while consuming their food, since they use enzymatic reactions to degrade them and take advantage of the energy and chemical material that they extract from them..
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One of the main characteristics to recognize them in nature is to observe if a change in color occurs, or if a particular smell is produced. Thus, in the seasons of the year, it is appreciated how the trees gradually begin to change the color of their leaves; in them chlorophyll and its natural pigments undergo chemical reactions.
The reddening of the leaves in autumn is a very clear example of a chemical change. Connecting this with life, octopuses and chameleons camouflage themselves thanks to a series of chemical reactions that involve the cells of their skins; but that unlike leaves, they can reverse color changes through other reactions that “deactivate” the camouflage.
However, the different colors of the sky and clouds are not the product of chemical but physical changes: the Raleigh scattering. Meanwhile, the whitening of clothes and the removal of their stains, as well as the staining of garments with dyes, are chemical changes..
It was mentioned that the change in color and odor are two of the main characteristics that a chemical change has occurred and that, therefore, a phenomenon that involves one or multiple chemical reactions has occurred..
Next, other important characteristics that allow us to detect it directly with our senses will be addressed. The more characteristics that can be perceived, the more likely it is that we are facing a chemical change and not a physical one.
A chemical change is accompanied by an increase (exothermic reaction) or decrease (endothermic reaction) in temperature; that is, if heat is produced, or if, on the contrary, the sensation of cold is obtained, respectively. Also, sometimes the release of heat occurs parallel to the appearance of light.
The formation of gases is directly related to changes in odors. If gas forms in a liquid medium, bubbling will be observed, indicative of a chemical change.
This is due to the fact that there are molecules with high vapor pressures that are easily carried through the air, or because of the release of small molecules, such as CO.two, HtwoS, CH4, ORtwo, etc., which are end products of certain reactions.
If the reactions take place in a liquid medium and the formation of a precipitate begins to be observed, whatever its color or texture, a chemical change is said to have occurred. Likewise, it could be the case where two gases mix and form ashes or salts.
Although it is true that there are reversible reactions capable of establishing an equilibrium, the changes generated with the characteristics described so far by themselves are irreversible; They need other reactions or energy of any kind to intervene for their effects to be reversed. And even so, in many cases it is practically impossible.
This irreversibility is observed in a change of the composition, or in the deterioration of the matter. For example, a tree that burns in flames and ends in ashes, whose final composition is different from that of the tree, will not be able to reverse the chemical change that has occurred by any means; Unless time could be turned back.
Chemical changes themselves are not subject to any classification: they are perceived with our senses and it can be inferred or examined what types of chemical reactions are taking place. Thus, such changes are due to a group of inorganic, organic or biochemical reactions.
When speaking of inorganic "changes", it is said that no carbon skeleton compound is involved, but rather all transition metal complexes; oxides, sulfides, hydrides, nitrides, halogens, among other compounds.
Meanwhile, in the organic and biochemical changes carbon compounds participate, with the difference that the former usually occur outside organisms (except for the reactions carried out by drugs), and the latter within them (as regards enzymes , metabolism, biomolecules).
The papers over time lose their whiteness to turn yellowish or brown. This process is due to the oxidation of its polymers, especially lignin, which together with cellulose incorporate oxygen atoms that end up weakening their intermolecular interactions..
Fireworks represent a combustion reaction, in which a mixture of propellants, potassium nitrate, carbon and sulfur burns while electronically exciting the metallic salts that impregnate the resulting explosions with colors..
Caries generate a color change in the teeth due to their demineralization, caused by the acids generated when microorganisms digest sucrose in food. Dental enamel, which consists of a mineralogical matrix of calcium phosphates, loses its ions as acidity increases and cavities formation progresses..
The eutrophication of lakes encourages the growth of algae, which cover their surface in green as a result of a change in the chemical properties of the water; change that ends up being visible and negative for aquatic fauna.
The Alka-Seltzer when dissolved in water begin to release bubbles that demonstrate their effervescence. The gases are due to COtwo generated by the dissolution of NaHCO3, together with the citric and acetylsalicylic acids that come in the compacted tablet.
When we sweat it is inevitable, sooner or later, to perceive unpleasant odors located under the arms, on the skin, or on the feet. These bad odors are due to volatile organic molecules synthesized by microorganisms, and denote that a chemical change has occurred..
The organic decomposition of living beings or food are chemical changes that involve a series of complex reactions. Bad odors are accompanied by a change in composition, as well as color. For example, the rotting of fruits like bananas and avocados shows all these characteristics..
Although it is formally a physical reaction, without breaking chemical bonds but with the consecutive participation of an equilibrium between the H speciestwoCO3 and COtwo, The Coca-Cola Mint eruption can be taken as a reference to detect other explosions that may be purely chemical.
Peppermint offers nucleation sites for small bubbles of CO to form.two, which absorb part of the COtwo dissolved by interfering with its interactions with water molecules. Thus, the COtwo dissolved it concentrates in multiple small bubbles, which oppose the increasing surface tension of the water caused by sugar and other compounds.
The result is that the CO bubblestwo they escape dragging the water that does not want to "release" them. This causes the characteristic foam of these peppermint rashes to appear, as seen in the image above..
Explosions are usually very vigorous combustion reactions, from which smoke, light and heat are released. Wherever an explosion occurs, you are facing a chemical change.
Wood is essentially made up of cellulose and lignin, both organic polymers. Its carbon atoms react vigorously with the oxygen in the air, causing CO and CO.two, depending on how complete the combustion is and the degree of oxygenation.
This is a chemical change because the polymers of the wood cannot return to their initial state, in addition to the release of heat, light and smoke.
The redness or tanning of our skin, when under intense sun, indicates that there was a change in its composition due to the reaction of the melanin contained in its cells, which oxidize and decompose.
Starting from the purple cabbage juice, an experiment can be set up to show color changes as a function of pH. It is easy to reproduce in any laboratory or kitchen.
If this juice is added to different test tubes, they are labeled, and different substances are added to them, from acidic (vinegar) to alkaline (detergent), there will be a range of colors (upper image).
This is because purple cabbage juice contains natural acid-base indicators, which respond to changes in pH. The more acidic the solution, the redder it will appear; and if on the contrary it is very basic, it will turn yellowish.
When an egg is fried or cooked, we allow the heat to denature its proteins, breaking its bonds and forming others while losing its original structure..
Leather colors can fade due to oxygen in the air and UV radiation, which cause the chemical bonds between the dyes and the organic material to break..
The change in color that is observed in breads and sweets, as well as its evident increase in volume compared to raw dough, is indicative of several chemical changes.
First, by the uplift caused by yeast and baking powder; and second, by the Maillard reaction, where proteins and sugars react with each other to turn the mixture golden..
Metals rust, so they lose their luster, darken and begin to corrode when the oxide layers formed can no longer adhere or bond with the metal interior. The most representative corrosion is that of iron, due to the characteristic brown color of its oxide.
Inside the batteries or cells, chemical reactions occur that generate electricity, electrical currents that run through an external circuit and activate their devices. In essence the anode loses electrons (oxidation), these electrons activate the device (remote control, phone, watch, pointer, etc.), and then end up at the cathode (reduction).
If a mosquito bites us and we kill them instantly or within a few minutes, we will notice that the blood is light red. Meanwhile, if a few hours elapse and we kill this same mosquito, we will see that the blood is dark, it will even present brown tones.
This change in color is indicative that the blood has undergone chemical reactions within the mosquito..
One of the most impressive chemical changes is seen in the famous iodine clock reaction. It is so called because its speed can be controlled by modifying the concentration of the reactants. The reaction comes to an end when an intense, very dark blue color appears, in great contrast to the initial transparency observed..
This color (top image) is due to interactions between starch and the anion complex I3-. One of its versions starts from iodate, IO3-, and bisulfite, HSO3-:
IO3- + 3HSO3- → I- + 3HSO4-
The I- reacts with the IO3- of the medium to generate iodine:
IO3- + 5I- + 6H+ → 3Itwo + 3HtwoOR
And this in turn reacts with more bisulfite:
Itwo + HSO3- + HtwoO → 2I- + HSO4- + 2H+
Once the HSO is over3-, the second reaction will predominate until there is an excess of Itwo, which will join the I- to form the I3-. And finally, the I3- will interact with starch molecules darkening the solution.
Again, and finally, a specific chemical reaction is named but with changes too visible to be left out: elephant toothpaste (top image). In certain videos the amount of foam is such that you could literally brush an elephant's mouth.
This reaction is based on the catalytic decomposition of hydrogen peroxide, HtwoORtwo (hydrogen peroxide), with iodide ions, I-, from soluble salts such as NaI or KI. The first reaction that occurs is, according to the following chemical equation:
HtwoORtwo + I - → HtwoO + IO -
The IO species - subsequently reacts with the HtwoORtwo in a second reaction:
IO - + HtwoORtwo → HtwoO + Otwo + I -
Where catalyst I is regenerated - (not consumed).
Note that the final products are HtwoOr metwo. If detergent and colorants are added to the reaction mixture, the water together with the oxygen will foam vigorously, which will rise through the container and shoot upwards, against gravity..
When paper is burned, carbon dioxide, water vapor, and ash are produced. These three substances are chemically different from the first substance, so it is a chemical change.
When an apple is chopped and left in the open, it turns from being an ivory color to being brown or ocher. This is called oxidation..
When food spoils, a chemical change occurs. For example, rotten eggs go through a decomposition process that causes them to change color and smell..
Yogurt is the result of a chemical change involving milk and certain bacteria, such as Streptococcus thermophilus and the Lactobacilli bulgaricus.
When a bottle of champagne or a soft drink is opened, a bubbling is observed. This bubbling means that the carbonic acid in the drink has broken down, releasing the carbon dioxide..
The creation of wine from grapes is a fermentation process. This is an example of an anaerobic chemical reaction in which sugar is transformed into ethyl alcohol and carbon dioxide..
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