We explain what a chemical change is and what its characteristics are. Also, examples and differences with a physical change.
What is a chemical change?
Chemical changes are a type of alteration in the matter that modifies its chemical constitution, that is, that it alters its nature and not only its form. This means that chemical changes, also called chemical reactions or chemical phenomena, imply rupture and formation of the chemical links of substances or chemical compounds to form new substances or compounds.
The chemical reactions occur when two or more are chemically combined substances (called reagents or reactants) that change their chemical structure in the process, and can consume (endothermic reactions) or release (exothermic reactions) Energy, to generate two or more new substances (called products). Some chemical reactions are dangerous for the human being, as they can involve or produce toxic or corrosive compounds. Other reactions, such as certain exothermic reactions, can cause explosions.
In the chemical industry Many materials that we use in everyday life are produced through controlled chemical reactions. Some reactions occur spontaneously and others must be generated by humans in industrial plants or in chemical laboratories.
Chemical reactions require a stipulated time to occur, which varies depending on the nature of the reactants and the conditions in which the reaction occurs.
Thus, the factors that affect the speed of chemical reactions generally tend to be:
- Temperature rise the rise of temperature it tends to increase the speed of chemical reactions.
- Increased pressure. Increasing the pressure usually increases the speed of chemical reactions. This generally occurs when substances that are sensitive to changes in Pressure, how are the gases. In the case of liquids Y solid, pressure changes do not cause major changes in the speed of your reactions.
- Aggregation state in which the reagents are. Solids tend to react more slowly than liquids or gases, although the speed will also depend on the reactivity of each substance.
- Use of catalysts. They are substances that are used to increase the speed of chemical reactions. These substances do not take part in the reactions, they only control the rate at which they occur. There are also substances called inhibitors, which are used in the same way but cause the opposite effect, that is, they slow down reactions.
- Light energy (Light). Some chemical reactions are accelerated when light is shined on them.
- Reagent concentration. Most chemical reactions occur faster if they have a high concentration of their reagents.
Examples of chemical change
The production of salts from battery acid is a chemical change.
Any chemical reaction is a perfect example of chemical change, even those that occur in our bodies. Some examples are:
- The breathing. It is a biological process of chemical change, in which oxygen is taken from the air and it is used to react with the glucose that we obtain from food, generating high levels of chemical energy (ATP) and amounts of carbon dioxide (CO2) waste, which must be expelled from the organism.
- Acid rain. Occurs in environments where atmosphere it is very polluted. It is usually the result of chemical changes that occur between the water stored in the clouds and other gases dispersed in the air, whose content of sulfur oxide or nitrogen oxide generates sulfuric acid or nitric acid that fall along with the rain.
- The formation of salts. The reaction that occurs inside the batteries is produced between an acid and a metal. For example, in batteries that use lead Y sulfuric acid lead (II) sulfate is produced, a salt of color White.
- The decomposition of ozone. The molecule ozone decomposes into oxygen molecules by the action of certain types of light.
Chemical change and physical change
Physical changes in matter do not alter its composition, that is, they do not modify the chemical structure of substances, so that through a physical change no substances can be decomposed or formed. Physical changes only change physical properties of substances such as shape, form, density and the aggregation states (solid liquid gas). On the other hand, physical changes are usually reversible, since they alter the shape or the state of matter, but not its composition.
For example, by boiling water we can convert a liquid into a gas, but the steam resulting is still made up of water molecules. On the contrary, if we freeze the Water, it passes to the solid state, but it is still chemically the same substance. Another example is the liquefied gas that we use in our lighters, which is usually butane (C4H10) or propane (C3H8) transformed into a liquid state by applying high pressure, but without altering its chemical composition.
Chemical changes alter the distribution and bonding of the atoms of matter, making them combine in a different way, thus obtaining substances different from the initial ones. When a chemical change occurs, you always get the same amount of matter that you had in the beginning, even if it is in different proportionsSince matter cannot be created or destroyed, only transformed.
For example, if we react water (H2O) and potassium (K), we will obtain two new substances: potassium hydroxide (KOH) and hydrogen (H2). This is a reaction that normally releases a lot of energy, therefore it is very dangerous.