What are chemical reactions?
Chemical reactions are thermodynamic processes that transform matter. In this process, two or more chemical substances, also called reactive substances, change their molecular structure and chemical bonds to consume or release energy. This way, they manage to generate new chemical structures other than the initial ones; these are called products.
These processes can occur naturally and spontaneously in nature, and they can be generated through human intervention in a controlled environment, such as a laboratory.
Chemical reactions are expressed through chemical equations, which are formulas describing the reagents involved, as well as the result or product obtained. These equations also usually describe the conditions under which the chemical reaction occurs – that is, if they are in the presence of heat, light, etc.
What concepts are associated with chemical reactions?
- Matter: everything that takes up space and has mass, shape, weight, and volume and is therefore perceptible.
- Atoms: the smallest unit of matter that has the characteristics of a chemical element.
- Chemical element: a type of matter made up of atoms of the same kind.
- Molecule: a group of atoms that are the same or different that are held together. When they are separated, this affects or destroys the properties of the substance.
- Bond: what establishes interactions between atoms and molecules.
- Chemical compound: a substance that is made up of the combination of two or more elements from the periodic table.
- Chemical substance: matter with a defined chemical composition; the result of the combination of two chemical elements that is made up of molecules and atoms. Its elements cannot be separated by any physical means.
- Products: substances that result from the chemical reaction and which fulfill a certain function. They are made up of one or more chemical compounds.
What are the characteristics of chemical reactions?
- In a chemical reaction, atoms do not change; what changes are the bonds between them.
- Most chemical reactions occur in aqueous solutions.
- They can be reversible if the products become reactants again, or irreversible when the products do not go back to being the reactants that gave rise to them.
- Reactions can be simple when they require a single step for the reactants to be converted into products, or complex when there are several steps between the reactants and the product; intermediate compounds may also be formed in the latter case.
How does a chemical reaction occur?
A chemical reaction occurs when moving molecules hit each other, breaking their bonds and producing an exchange of atoms that form new products. Another way a chemical reaction can occur is through the vibration of substances; when they do so with sufficient energy, they can be broken down into smaller molecules.
What explains the law of conservation of matter?
The law of the conservation of matter is fundamental in all natural sciences, but especially in chemistry. It states that, in any chemical reaction, mass is conserved. This means that the matter consumed in the process is equal to the mass resulting from the products formed.
The approach states the following: in an isolated system, during every ordinary chemical reaction, the total mass in the system remains constant – that is, the mass of the reactants consumed is equal to the mass of the products obtained.
This law was originally proposed by Russian scientist Mikhail Lomonosov in 1748. It wasn’t until 40 years later that it was really developed by French chemist Antoine-Laurent de Lavoisier. That’s why the law is also called the Lomonosov-Lavoisier Law. In short, while mass cannot be created or destroyed, it can be transformed, just as the entities associated with it can change form.
What types of chemical reactions are there?
- Synthesis reaction (combination): when two or more reagents combine to form a more complex product.
- Displacement, substitution, or exchange reaction: in this type of reaction, elements of the compounds are replaced to create new ones. They can be simple when one element displaces another, or double when elements are exchanged.
- Decomposition reactions: when a chemical compound is divided into simpler substances. These types of reactions are the opposite of synthesis reactions.
- Oxidation-reduction reactions: when an electron transfer or exchange occurs. While one compound loses electrons (oxidizes), the other gains them (reduces).
- Acid-base reactions: in this type of reaction, a basic substance is neutralized with an acidic one, and the result is a neutral compound and water.
- Combustion reactions: these are similar oxidation-reduction reactions, though they differ in that oxidation occurs quickly in combustion. For it to happen, a combustible material combines with oxygen and gives off energy.
- Exothermic and endothermic reactions: the former give off heat from the reactive process, and the latter require it.
- Endoluminous and exoluminous reactions: the former need light to occur; the latter emit light.
- Exo-electric and endo-electric reactions: the former transfer electrical energy out, and the latter require it.