Chemical equations are different from those of classical mathematics. Mathematical equations establish equality between two numbers or between two elements. These numbers or elements are placed to the right and left of the equal sign (=) and can be inverted without altering the equation, since they mathematically have the same value. The chemical equations, on the other hand, describe the way in which atoms and molecules combine together to obtain a reaction. Instead of the equal sign, an arrow is used to show that substances are mixed in the chemical reaction to form new substances. The substances that are introduced into the reaction, called reagents, must appear on the left side of the arrow, while the elements to the right of the arrow are the so-called products of the reaction.
Steps
Method 1 of 1: Write a Chemical Equation
Step 1. Learn the atomic symbols used
Atoms are the building blocks of chemistry. The periodic table of the elements can be consulted in any textbook or textbook of chemistry. Note that capital letters are used to indicate elements, either alone or followed by a lowercase letter. For example, C is the symbol for carbon, He is the symbol for helium.
Step 2. Learn that some atoms alone are unstable and must be combined with another atom of the same type
These pairs of atoms are called diatomics. For example, an oxygen atom (O) is unstable. The air that people breathe contains the diatomic pair O2, which is stable.
Step 3. Observe how the atoms combine together to form molecules
Molecules are indicated by writing in sequence the atoms that compose them and making each atomic symbol follow a number in subscript to indicate how many units of that particular type of atom are present in the molecule. For example, the methane molecule consists of one carbon atom (C) and four hydrogen atoms (H4) and is denoted by CH4.
Step 4. Determine the type of reaction you want to describe
It is not enough to write a sequence of atoms and molecules to obtain a reaction. Reactions take place thanks to the entropy principle. This principle states that everything in nature seeks the lowest possible state of energy. If the reactants that are introduced are capable of combining themselves into atoms and molecules in order to reach a lower energy state, the reaction takes place thanks to entropy.
Step 5. Choose the reagents of the equation, which you will write to the left of the arrow
For example, in order to rust iron and obtain ferrous oxide, two reagents are needed: iron (Fe) and oxygen (O2).
Step 6. Determine the products of the reaction
Write the products to the right of the arrow. In the iron rust example, the product will be ferrous oxide. The equation is thus completed by writing Fe + O2 -> Fe2O3.
Step 7. Balance the equation
Atoms are neither created nor destroyed. The atoms of each reagent element must appear in the same quantity among the reaction products. In other words, to the left and right of the arrow there must be the same number of atoms for each element. Therefore, the equation Fe + O2 -> Fe2O3 for iron rust cannot be correct. One iron atom and two oxygen atoms enter the reaction, but two iron and three oxygen atoms result as products of the reaction. To correct this imbalance, adjust the quantity and proportions of the incoming atoms. With some trial and error, you can observe that 4 Fe + 3 O2 -> 2 Fe2O3 is the lowest number of incoming atoms that can be used to reach equilibrium. Four iron atoms and six oxygen atoms enter as reactants and the same amount, ie four iron atoms and six oxygen, arises as a product of the reaction.
