# How to Write Chemical Equations? Writing Chemical Formulae - Examples

We all know that whenever a chemical change occurs, a new substance is formed. Such a change is referred to as a chemical reaction. In this blog, let us learn how to write chemical equations and balanced them.

What is a Chemical Equation?

A chemical reaction can be represented by writing the chemical formulae of the reactants and the products. Such representation of a chemical reaction is known as a chemical equation.

In a chemical equation, the reactants are written on the left-hand side, that is, LHS and the products are written on the right-hand side, that is, RHS with a plus sign between each of them.

The arrowhead always points towards the products and represents the direction of the reaction. Now, we know that the atoms take part in chemical reactions. And, according to the law of conservation of mass, the mass can neither be created nor be destroyed in a chemical reaction.

Thus, the total mass of the elements present in the products of a chemical reaction must be equal to the total mass of the elements present in the reactants. This means that the number of atoms of each element remains the same, both before and after the completion of a chemical reaction.

## How To Write Chemical Equations?

Let us now learn to balance a chemical equation step by step.

Let's try out this example: Fe + H2O gives Fe3O4 + H2

Is this chemical equation balanced? Come on! Let's find out. To balance a chemical equation, let us first draw boxes around each formula without changing anything inside the boxes as shown here:

Now, list the number of atoms of different elements present in the unbalanced equation on any of the sides. After listing and identifying the different atoms, start balancing the equation with the element having the maximum number of atoms in a compound.

Using this criterion, we find that Fe3O4 has the highest number of atoms, with a maximum number of oxygen atoms in it. So, let's start balancing this equation with the atom oxygen.

Here, we have 4 oxygen atoms on the right-hand side but only a single oxygen atom on the left-hand side of the equation.

Atoms of Oxygen    In Reactants         In Products

1. Initial             1 (in H2O)             4 (in Fe3O4)
2. To balance     1 x 4                       4

We must also remember that the formula of the compound or the elements involved in the reaction cannot be altered to equalize the number of atoms in the equation. This can be explained well in the given example.

Here, to balance the oxygen atoms we put the coefficient 4 before H2O as 4H2O. But the formula cannot be altered as H2O4, O4 or (H2O)4 .

This partially balances the equation as:

Fe  + 4H2O    ->   Fe3O4  +  H2

Are the oxygen atoms balanced now? Yes! They are. But, the iron and hydrogen atoms are still not balanced. Let us pick one of these atoms to proceed further. Let�s balance the hydrogen atoms now.

We can clearly observe that there are 4 hydrogen molecules (that is, 8 hydrogen atoms) on the LHS. To balance the hydrogen atoms in this equation, we will have to make the number of atoms of hydrogen 8 on the RHS as well.

Therefore, the equation would now become:

Fe  +  4H2O    ->   Fe3O4  +  4H2

Now the one element that is left unbalanced is iron, that is, Fe.

Atoms of Oxygen    In Reactants         In Products

1. Initial             1 (in Fe)                 3(in Fe3O4)
2. To balance     1 x 3                       3

To equalize Fe, we take three atoms of Fe on the LHS.

The equation has thus become:

3Fe  + 4H2O  ->   Fe3O4 + 4H2

Finally, to check the correctness of the balanced equation, let us count the atoms of each element on both sides of the equation.

3Fe + 4H2O   ->    Fe3O4 + 4H2

See. The number of atoms of each element is equal on both sides of the equation. The equation is, therefore balanced now. This method of balancing a chemical equation is called The hit and trial method as this method employs making trials to balance the equation by using the smallest whole numbers as coefficients.

A chemical equation is made more informative by mentioning the physical state of the reactants and the products along with their chemical formulae.

The gaseous, liquid, aqueous and solid states are abbreviated differently as g, l, aq and s respectively. Sometimes, the reaction conditions such as temperature, pressure, catalyst etc. are also indicated above or below the arrow in the reaction.

Let us see more examples to understand how to write chemical equations.

When a magnesium ribbon is burnt in oxygen, it gets converted to magnesium oxide. This description of a chemical reaction in sentence form is quite long. It can be written in a shorter form. The simplest way to do this is to write it in the form of a word-equation.

The word-equation for the above reaction would be:

Magnesium + Oxygen -> Magnesium oxide

The substances that undergo chemical change in the reaction: Magnesium and oxygen, are the reactants. The new substance, Magnesium oxide, formed during the reaction, is the product.

A word-equation shows change of reactants to products through an arrow placed between them. The reactants are written on the left-hand side (LHS) with a plus sign (+) between them.

Similarly, products are written on the right-hand side (RHS) with a plus sign (+) between them. The arrowhead points towards the products, and shows the direction of the reaction.

Discover more examples to learn how to write chemical equations. Chemical equations can be made more concise and useful if we use chemical formulae instead of words. A chemical equation represents a chemical reaction.

If you recall formulae of magnesium, oxygen, and magnesium oxide, the above word-equation can be written as Mg + O2->MgO

Count and compare the number of atoms of each element on the LHS and RHS of the arrow. Is the number of atoms of each element the same on both sides? If not, then the equation is unbalanced because the mass is not the same on both sides of the equation.

Such a chemical equation is a skeletal chemical equation for a reaction. This equation is a skeletal chemical equation for the burning of magnesium in air.