What’s a chemical equation and why should you balance it?
A chemical equation is usually a short way of describing a chemical reaction. The reactants are always written on the left-hand side of the equation, while the products are written on the right-hand side of the equation. In between the reactants and the products is a forward pointing arrow usually interpreted as “produces or yields.” Reaction conditions or catalysts used in the reaction are sometimes written above and below the arrow.
Now, let’s write a chemical equation to describe the reaction when hydrochloric acid (HCl) reacts with sodium hydroxide solution (NaOH). The acid is HCl and the base is NaOH. These chemicals are usually dissolved in a certain amount of water. As a result, we say that they exist in an aqueous state (aq).
If we rewrite their chemical formulas and their states, we will get something like this: HCl(aq) and NaOH (aq). When the HCl reacts with the NaOH, we will get water (H2O) and sodium chloride (NaCl), commonly called salt. We can write the complete equation as:
We can read the equation as hydrochloric acid reacts with sodium hydroxide to produce sodium chloride and water. This type of reaction is an example of a proton transfer reaction. In this case, a proton (H+) is transferred from the acid, HCl to the hydroxide ion (OH–) to form water, H2O. While the sodium ion(Na+) unites with the chloride ion (Cl–) to form salt, NaCl. Another name for this proton transfer reaction is an acid-base reacton.
The HCl and NaOH are called the reactants, while NaCl and H2O are called the products. As you can tell, the above equation is balanced. We will discuss how to balance a chemical equations next.
Why should you balance a chemical equation?
Chemical equations usually represent the atoms taking part in a chemical reaction. These atoms do have mass, and this mass is not lost or destroyed during the reaction. For this reason, we must balance chemical equations to reflect the mass of atoms involved in the reaction. Thus, the law of conservation of mass.
How do you balance a chemical equation?
To balance basic chemical equations by trial and error (inspection), you should:
- Place numbers as coefficients in front of the chemical formulas or symbols of elements.
- Never change the subscript of an element or molecule to balance a chemical equation. When you do, you will change the identity of the molecule or element.
- Keep track of polyatomic ions so that you can balance them as a group.
- Balance elements that stand alone last.
When a chemical equation is finally balanced, you should have the same number of each atom on both sides of the chemical equation.
Let’s apply the rules to balance the following chemical equation: H2 + O2 –> H2O
From the equation, hydrogen (H2) and oxygen (O2) gas reacts to make water (H2O). If you count the number of atoms on each side of the equation, you will notice that there are:
- 2 atoms of H on each side of the equation
- 2 atoms of O on the reactant side and 1 atom of O on the product side of the equation. This shows that the O is unbalanced.
To balance the O atom on the product side, you must place 2 in front of H2O. When you do, you will get 2H2O. Now, you have 2 atoms of O but 4 atoms of H. You will get 4 when you multiply the 2 in front by the subscript of H (2×2= 4).
As you can tell, the O is now balanced but the H is now unbalanced. To balance the H, you must place a 2 in front of the H on the reactant side. When you do, the final equation will look like this: 2H2 + O2 –>2H2O. If you check the number of each atom on both sides of the equation, you will notice that each atom is now balanced.
Now, you balance the following chemical equation:
If you followed through, you should notice that the above equation is already balanced.
How do you know which products are solids, liquids, or aqueous solutions?
To determine which products are solids or aqueous solutions (dissolved in water), we usually apply what we call solubility rules. These rules simply summarize which chemicals will react with one another to form soluble or insoluble compounds. The liquid state (l) is usually reserved for liquid pure water. These rules will be discussed later in another section.