Ten Examples of Chemical Changes We Experience Every Day

We live in a world made up of an innumerable number of constantly moving atoms, ions and molecules that constantly collide with each other, giving rise to innumerable changes in matter. These changes may be physical changes, such as the melting of ice in the sun or the evaporation of solvent from drying paint, but in many cases they are chemical changes or chemical reactions.

One of the most fun parts of studying chemistry is learning to recognize these changes that happen all around us, and learning to see beyond the beauty of some of these changes, as well as the simplicity of others. That is why in this article, we present a list of ten examples of chemical changes that occur around us and that we experience every (or almost every) day.

Different types of changes in matter

Before we get into the examples of chemical changes , it is important to review what chemical changes are, in order to distinguish them from the other change processes that are also constantly occurring around us.

Remember that matter can undergo different types of change processes or transformations. Broadly speaking, these changes are classified into physical changes, chemical changes, and nuclear changes or transformations.

What is a physical change?

Physical changes are those in which substances do not undergo any change in their fundamental structure. That is to say, they are transformation processes in which neither the nature nor the elemental composition change, nor the way in which the atoms and ions that make up the substances present in matter are united or linked together.

For example, the evaporation of water is a physical change because both liquid water and gaseous water are still water, despite evidence of a transformation.

What is a chemical change?

On the other hand, chemical processes or changes are transformations in which one or more chemical substances are transformed into another or different ones through a change either in their elemental composition, or in the manner and order in which they are linked to each other. yes the atoms that make them up.

That is, chemical changes consist of a process of disassembling and reconfiguring the atoms of one or more chemical substances, called reactants, to produce one or more different chemical substances, called products.

Chemical changes are easily recognizable as they involve the disappearance of one or more substances and the appearance of one or more different chemical substances. These can have radically different properties and characteristics from the original substances, making them, in some cases, very easy to recognize. For example, many chemical reactions produce drastic color changes, the sudden release of large amounts of energy in the form of heat, light, or both, or may even be marked by the appearance of impressive crystals of different colors seemingly out of nowhere.

What is a nuclear change?

In last place we have nuclear changes. Nuclear reactions are much less frequent than physical and chemical changes, but they are also of great importance. They consist of processes in which the nucleus of an atom changes in order to produce one or more new atoms. This is the type of reactions that occur in nuclear power plants, in the explosion of an atomic bomb, or in the core of stars.

Now that we’ve remembered what chemical changes are and know how to distinguish them from the other two types of changes that matter can undergo, let’s look at some specific examples of chemical changes that are constantly happening around us.

1. Milk cutting

Most of us have had the unpleasant surprise that the milk that was in the fridge has gone bad. We immediately notice this when we observe that what initially appeared to be a homogeneous white mixture has now separated into two clearly distinguishable phases, one of which is more solid and floats on an aqueous phase.

This process is due to the action of bacteria that, when growing and reproducing, carry out a series of biochemical reactions that acidify the milk. But, despite the fact that biochemical reactions are, in fact, a set of chemical reactions of different types, the reaction that we see with the naked eye occurs between the hydronium ions responsible for acidity (H 3 O + _ions ) ^and proteins of the milk that were originally dissolved in the water.

By lowering the pH of the milk (or increasing its acidity, which is the same thing), the excess hydronium ions react with the proteins, transferring protons to the protein molecules through an acid-base reaction. The protonated protein becomes less soluble and ultimately precipitates to the solid state and separates from the water.

2. Elimination of water hardness with ion exchange resins

^{Water that has a relatively high concentration of calcium (Ca 2+} ) and magnesium (Mg ^2` ) ions is known as hard water . Hard water can bring many problems to the home, including the precipitation of calcium and magnesium carbonate in the pipes which slowly clogs them to the point where no more water can pass through. They also form insoluble salts with soap molecules, preventing it from acting by removing impurities when we wash or bathe.

In places where the water is hard, special filters are often installed that remove these ions from the water, effectively “softening” it. Unlike a conventional filter, which is a porous material that does not allow particles of a certain size to pass through, filters to remove hardness from water are actually made of two special resins called ion exchange resins. These resins react through chemical reactions.

The first resin exchanges the mentioned cations (Ca ²⁺ and Mg ²⁺ ) for protons through a chemical displacement reaction such as the following:

Where M ²⁺ represents either of the two cations Meanwhile, to prevent the water from becoming acidic, another resin exchanges the anions that act as counterions for calcium and magnesium for hydroxide ions:

The hydroxide ions released on the anion exchange resin then neutralize the protons released from the cation exchange resin by another chemical reaction:

3. Fading of paints in the sun

If we go for a short walk through any town or city and look at the multiple advertisements and banners scattered on each side of the road, we will notice that the new billboards have intense and vibrant colors while those that have been exposed to the sun for longer , wind and rain have already lost most of their color. In fact, the first colors to fade are usually blue and green tones, leaving red and yellow tones, which is why many old prints exposed to the sun appear yellowish or orange.

In some cases this is due to weathering and erosion by wind and rain, but in most cases the discoloration is due to the chemical breakdown of pigments, especially blue and green shades, by the action of the sun’s ultraviolet rays.

4. The formation of foam when adding hydrogen peroxide to a wound

Hydrogen peroxide is an aqueous solution containing about 10% to 30% hydrogen peroxide (H ₂ O ₂ ). This compound spontaneously decomposes into oxygen gas and water through a disproportionation or dismutation chemical reaction:

This reaction is very slow in a bottle of hydrogen peroxide for antiseptic use like the one we usually have in a first aid kit. However, the cells of our blood and of most eukaryotes have organelles in which there are enzymes specialized in catalytically decomposing hydrogen peroxide. Thus, when we add hydrogen peroxide to an open wound, it quickly breaks down the hydrogen peroxide, releasing oxygen gas which produces the bubbles that form the foam we see.

5. Crystallization of plastics exposed to the sun

Sunlight and its ultraviolet rays are capable of catalyzing a large number of different chemical reactions. One of them is the decomposition of the polymeric chains that form the structure of plastics. As a consequence, most of the plastic objects that we leave in the sun for a long time end up losing their plastic properties and turning into a rigid and brittle material, similar to a set of compacted crystals.

This process, which is often associated with crystallization, is a chemical change as it alters the chemical composition and connectivity between the atoms that make up the long polymer molecules.

6. The color change of food when frying or roasting it

Few things are more delicious than the blunt and caramelized flavor that forms on the surface of meats and vegetables when grilling, frying, or roasting. Like everything in the kitchen, this caramelization process occurs thanks to a series of diverse chemical processes. In this case, it involves a very complex set of chemical reactions known as Maillard reactions.

These are reactions that occur between sugars in food and amino acid residues in proteins. These are often referred to as Maillard reactions, although technically these are glycosylation or glycosylation reactions similar to those that commonly occur within living cells, but without the intervention of enzyme catalysts. Instead, Maillard reactions are driven by heat.

7. Crystallization of honey

Honey is a highly concentrated solution of different sugars in water. Despite its high concentration, all solutes usually remain dissolved. However, if we leave a bottle of honey undisturbed for a long period of time, we will most likely observe that either small sugar crystals start to appear at the bottom, or complete crystallization of all the honey is triggered. with which everything ends up becoming a single apparently solid block.

This crystallization process is often considered a chemical change. However, it can be easily reversed by slightly heating the honey, which increases the solubility of the sugars present and they dissolve again.

8. Curing of catalyzed enamels

There is a wide variety of different paints and enamels on the market, each of which has its own particular application. However, when looking for a strong, glossy and very resistant finish, we almost always opt for some type of catalyzed enamel. These enamels are nothing more than plastic resins formed by long polymers that have side chains capable of joining each other through chemical reactions. When these reactions occur, a network of interconnected molecules is formed that is extremely strong.

However, these reactions require the action of a catalyst to occur, otherwise the glaze would solidify in the jar and could not be applied to the surface. This catalyst is purchased together with the enamel, and is mixed with it in the appropriate proportion according to the amount of enamel that you want to prepare.

So, the next time you see any painter or even a manicurist, mixing a nail polish with a small amount of a transparent, colorless substance, and then applying the nail polish to any surface, let’s remember that we are about to see a catalyzed chemical reaction of cross-link formation between polymeric resins.

9. The caramelization of sugar

By heating sugar in a pan with a small amount of water, we can see that the sugar first melts, becoming a liquid. However, upon heating a bit more, we notice that it begins to turn a light brown color and release a delicious characteristic smell. Caramel has formed.

At this point, the occurrence of a chemical reaction is evident, since a compound with a different aroma from that of pure sugar is being formed, and which, in addition, has a different color, since sugar is naturally white. This process of caramel formation (or caramelization), is a chemical reaction in which the sucrose molecules of table sugar link up with each other, thus forming a polymer.

10. Curing of glues based on epoxy resins

Like catalyzed enamels, epoxy resins are made up of pre-polymerized plastics in which the polymer chains are initially free from one another. However, when mixed with a second resin that has a suitable catalyst among its components, a polymerization reaction is triggered in which the side chains of the polymers intertwine, hardening the resin.

This is the operating principle of many very hard and resistant glues.

References

Arias Giraldo, S., & López Velasco, DM (2019). Chemical reactions of simple sugars used in the food industry . Lampsakos. 22. 123–136. https://www.redalyc.org/journal/6139/613964509011/html/

Department of Inorganic Chemistry. (nd). Catalytic decomposition of hydrogen peroxide . University of Alicante. https://dqino.ua.es/es/virtual-laboratory/decomposicion-catalitica-del-peroxido-de-hidrogeno.html

Gazechim Composites Iberica. (2013, October 25). Epoxy resin . https://www.gazechim.es/noticias/actualidad/resina-epoxi/

Madsen, J. (2020, February 18). The science behind the epoxy curing process . heatexperts. https://www.heatxperts.com/es/blog/post/the-science-behind-the-epoxy-curing-process.html

VelSid. (2014, July 26). Maillard reaction . Gastronomy & Co. https://gastronomiaycia.republica.com/2010/03/11/reaccion-de-maillard/

greenhoney. (2019, November 12). Crystallized honey, the pure honey of a lifetime . https://www.verdemiel.es/blog/2019/11/12/miel-cristalizada-la-miel-pura-de-toda-la-vida/