Chemical Equation
According to Law of Conservation of Mass, mass can neither be created nor destroyed in a chemical reaction. To obey this law, the total mass of elements present in reactants must be equal to the total mass of elements present in products.
In this part of the lesson, you will learn step by step method of balancing the chemical equation of reaction between iron and water. In the previous section of this lesson, it was explained that mass of product and mass of reactants are not equal in this reaction. Hence, it is not obeying the law of conservation of masses and hence it needs to be balanced.
How to Balance a Chemical Equation
To balance the given or any chemical equation, follow these steps:
Fe + H2O → Fe3O4 + H2
Step 1: Write the number of atoms of elements present in reactants and in products in a table, as shown here.
| Name of atom | No. of atoms in reactant | No. of atoms in product |
|---|---|---|
| Iron | 1 | 3 |
| Hydrogen | 2 | 2 |
| Oxygen | 1 | 4 |
Step 2: Balance the atom which is the maximum in number, on either side of chemical equation.
In this equation, the number of oxygen atom is the maximum on RHS.
To balance the oxygen one needs to multiply oxygen on LHS by 4, so that number of oxygen atoms becomes equal on both sides.
Fe + 4 × H2O → Fe3O4 + H2
Step 3: Now, the number of hydrogen atoms becomes 8 on LHS, which is more than that on RHS. To balance it, one needs to multiply the hydrogen on RHS by 4.
Fe + 4 × H2O → Fe3O4 + 4 × H2
Step 4: After that number of oxygen and hydrogen atoms becomes equal on both sides. The number of iron is one on LHS, while it is three on RHS. To balance it, multiply the iron on LHS by 3.
3 × Fe + 4 × H2O → Fe3O4 + 4 × H2
Step 5: Now the number of atoms of each element becomes equal on both sides. Thus, this equation becomes a balanced equation.
| Name of atom | No. of atoms in reactant | No. of atoms in product |
|---|---|---|
| Iron | 3 | 3 |
| Hydrogen | 8 | 8 |
| Oxygen | 4 | 4 |
After balancing, the above equation can be written as follows.
3Fe + 4H2O → Fe3O4 + 4H2
More Examples
Balance the given equations.
(a) H2 + O2 → H2O
Answer: 2H2 + O2 → 2H2O
(b) Fe + H2O → Fe2O3 + H2
Answer: 2Fe + 3H2O → Fe2O3 + 3H2
(c) CO2 + H2O → C6H12O6 + O2
Answer: 6CO2 + 6H2O → C6H12O6 + 6O2
(d) Fe2O3 + C → Fe + CO2
Answer: 2Fe2O3 + 3C → 4Fe + 3CO2
For balancing most of the chemical equations, you can do some guesswork and balance them on the go, as shown in these examples. But when you are a novice, try to make a table and write number of atoms of elements of reactants and products, as shown in the first example. Gradually, you will learn the tricks and can easily balance a given equation.
Writing the symbols of Physical States of substances in Chemical equation:
By writing the physical states of substances, a chemical equation becomes more informative.
- Gaseous state is represented by symbol g
- Liquid state is represented by symbol l
- Solid state is written by symbol s
- Aqueous solution is written by symbol aq
Writing the condition in which reaction takes place: The condition is generally written above and/or below the arrow of a chemical equation.
Thus, by writing the symbols of physical state of substances and condition under which reaction takes place, a chemical equation can be made more informative.
Summary
| Balanced Equation | Number of atoms of each elements is equal on both sides of equation. |
|---|---|
| Law of Conservation of Mass | Mass cannot be created and cannot be destroyed. |