Chemical Equation

A chemical equation is a representation of a chemical reaction using chemical symbols and formulas. It shows the reactants on the left-hand side of the equation, the products on the right-hand side of the equation, and the relative amounts of each species involved in the reaction.

For example, the chemical equation for the reaction between hydrogen gas (H2) and oxygen gas (O2) to form water (H2O) is:

2H2(g) + O2(g) → 2H2O(l)

In this equation, the numbers in front of the chemical species represent the stoichiometric coefficients, which indicate the relative amounts of each species involved in the reaction. The reactants are on the left-hand side of the equation, and the products are on the right-hand side of the equation, separated by an arrow.

The chemical equation is a concise way of summarizing the key details of a chemical reaction, including the types of reactants and products, the stoichiometry of the reaction, and the physical state of the species involved.

How to balance chemical equations

To balance a chemical equation, follow these steps:

Step 1: Write the unbalanced chemical equation.

Step 2: Count the number of atoms of each element on both sides of the equation.

Step 3: Start balancing the elements one at a time. Begin with the most complex molecule or the one with the largest number of atoms.

Step 4: Use stoichiometric coefficients to balance the equation. Place the coefficient in front of each species so that the number of atoms of each element is equal on both sides of the equation.

Step 5: Verify that the equation is balanced by counting the number of atoms of each element on both sides of the equation.

Step 6: If necessary, check that the physical state of each species is the same on both sides of the equation. If not, add the appropriate state symbol (s, l, g, aq) to the equation.

Step 7: Finally, make sure that the stoichiometric coefficients are in the simplest whole number ratio.

Example

Example 1

Here is an example of balancing the chemical equation for the reaction of hydrogen gas with oxygen gas to form water:

Step 1: Write the unbalanced equation.

H2(g) + O2(g) → H2O(l)

Step 2: Count the number of atoms of each element on both sides of the equation.

Reactants: 2 H, 2 O Products: 2 H, 1 O

Step 3: Balance the oxygen atom first.

H2(g) + O2(g) → 2H2O(l)

Step 4: Count the number of atoms of each element on both sides of the equation.

Reactants: 2 H, 2 O Products: 4 H, 2 O

Step 5: Balance the hydrogen atom.

2H2(g) + O2(g) → 2H2O(l)

Step 6: Check that the physical state of each species is the same on both sides of the equation.

Step 7: Verify that the stoichiometric coefficients are in the simplest whole number ratio.

The balanced equation for the reaction of hydrogen gas with oxygen gas to form water is

 2H2(g) + O2(g) → 2H2O(l).

Example 2

Balancing the combustion of methane (CH4) with oxygen (O2) to produce carbon dioxide (CO2) and water (H2O).

CH4 + O2 → CO2 + H2O

To balance this equation, we first count the number of atoms of each element on both sides of the equation. On the left side, there is 1 carbon atom, 4 hydrogen atoms, and 2 oxygen atoms. On the right side, there is 1 carbon atom, 2 hydrogen atoms, and 3 oxygen atoms.

To balance the equation, we can start by adjusting the number of oxygen atoms by adding a coefficient of 2 in front of the O2 on the left side:

CH4 + 2O2 → CO2 + H2O

Now we have 4 oxygen atoms on both sides, but the number of hydrogen atoms is still not balanced. We can balance the hydrogen atoms by adding a coefficient of 2 in front of the H2O on the right side:

CH4 + 2O2 → CO2 + 2H2O

Now the equation is balanced, with 1 carbon atom, 4 hydrogen atoms, and 4 oxygen atoms on both sides.

Example 3

Balance this chemical equation for the reaction in which nitrogen (N2) and hydrogen (H2) combine to form ammonia (NH3):

N2 + H2 → NH3

 First count the nitrogen atoms on both sides of the arrow. There are two nitrogen atoms in the reactants so there must be two in the products as well. Place the coefficient 2 in front of NH3 to balance nitrogen:

N2 + H2 → 2 NH3

Now count the hydrogen atoms on both sides of the arrow. There are six hydrogen atoms in the products so there must also be six in the reactants. Place the coefficient 3 in front of H2 to balance hydrogen:

N2 + 3 H2 → 2 NH3

Example 4
Balance this chemical equation for the reaction in which carbon dioxide (CO2) and water (H2O) combine to form glucose (C6H12O6) and oxygen (O2):

CO2 + H2O → C6H12O6 + O2

To balance this equation, we need to adjust the coefficients in front of the chemical formulas so that the number of atoms of each element is equal on both sides of the equation.

First, let's count the number of atoms of each element on both sides of the equation. On the left side, there are 1 carbon atom, 3 oxygen atoms, and 2 hydrogen atoms. On the right side, there are 6 carbon atoms, 12 hydrogen atoms, and 8 oxygen atoms.

To balance the carbon atoms, we can add a coefficient of 6 in front of the CO2 on the left side:

6CO2 + H2O → C6H12O6 + O2

Now we have 6 carbon atoms on both sides of the equation. To balance the hydrogen atoms, we can add a coefficient of 6 in front of the H2O on the left side:

6CO2 + 6H2O → C6H12O6 + O2

Now we have 12 hydrogen atoms on both sides of the equation. Finally, we can balance the oxygen atoms by adding a coefficient of 6 in front of the O2 on the right side:

6CO2 + 6H2O → C6H12O6 + 6O2

Now we have 12 oxygen atoms on both sides of the equation.

The balanced equation is:

6CO2 + 6H2O → C6H12O6 + 6O2

This balanced equation tells us that 6 molecules of carbon dioxide and 6 molecules of water react to produce 1 molecule of glucose (C6H12O6) and 6 molecules of oxygen.