Substances can be combined with other substances into new substances. We call these transformations chemical reactions.
Chemical reaction It is a phenomenon where atoms remain intact. During the reactions, the initial molecules are "disassembled" and their atoms are reused to "assemble" new molecules.
In our daily lives, there are many chemical reactions involved, such as food preparation, the digestion of these foods in our bodies, combustion in automobiles, the appearance of rust, the manufacture of medicines, etc.
The form we represent the chemical reaction is called the chemical equation.
Chemical equation - is the graphical representation of the chemical reaction.
In it, we put the elements that are involved in the reaction, in abbreviated form, and how it happened, through already standardized symbols. Chemical equations represent the writing used by chemists and universally, that is, it is the same in any country.
Substances that participate in the chemical reaction are called products or reagents in the chemical equation.
Reagents (1st limb) - are the substances that are at the beginning of the reaction. They are the ones who will react, undergo the transformation.
Products (2nd limb) - are the substances resulting from the chemical reaction.
Example: Two hydrogen gas molecules join together with one oxygen gas molecule, forming two water molecules.
Note that H2 and the O2 are reagents and H2The is the product.
To represent the chemical reaction, an arrow pointing to the right side is used, indicating the transformation.
Above the arrow, some symbols are used indicating the conditions under which the reaction should occur.
∆ - heat
aq - aqueous (in water)
cat - catalyst
λ - light energy
In each substance there may be the following symbols:
↑ - gas leakage
↓ - precipitation of a solid
In chemical equations, substances can appear with their physical states:
(s) - solid
(l) - net
(g) - gas
C (s) + O2 (g) → CO2 (g)