Balancing Chemical Equations

A chemical equation is a symbolic representation of reactions taking place when chemicals come in contact with each other. It helps to find out the reactants, products, the phase of reactants and products (whether it is in solid, liquid or gaseous form) and the amount of each substance. In a balanced equation the number of molecules reacting (Reactants) and the number of molecules produced (Products) are represented in the form of an equation. The residuals created during the equation are also noted in the equation. When the number of atoms of each type on both side of the equation is same then the equation is said to be balanced. Grams or Moles are used to represent the quantity of reactants and products. To balance an equation it is necessary to follow three steps.

• Write down the unbalanced equation
• Balance the equation
• Specify the phase of reactants and products(whether it is in solid, liquid or gaseous form)

Step-1 : Write Down the unbalanced equation

• List the chemical formulas of reactants on the left-hand side of the equation.
• List the products on the right-hand side of equation.
• Put arrow between reactants and products to separate them and to show the direction of reaction.
• To show reactions at equilibrium arrows facing both directions have to be used.

Example for an unbalanced equation

C₃H₈   +   O₂    →    H₂O   + CO₂    (C₃H₈   & O₂   are the reactants; H₂O  & CO₂     are the products)

Step-2 : Balance the equation

•  To get the same number of atoms of every element on both sides of equation  apply  Law of    Conservation Of Mass (The law states that matter can be neither created nor destroyed ,but it can be changed from one form to another).Start balancing the element that is seen in only one reactant and product to avoid confusions. 
•  After balancing one element, continue with all the other elements one by one till all get balanced.
• Coefficients can be used in front of formulas to balance them. As subscripts can change formulas avoid using it.

In the example given in unbalanced form, C₃H₈   +   O₂    →    H₂O   + CO₂

• Three Cs are on left, but on right only one C is present
• Eight Hs on the left but only two on the right.
• Two Os on the left but three on the right

Start balancing C as it is seen in only one reactant and product.

C₃H₈   +   O₂    →     H₂O   + 3CO₂

• The C atoms on both the sides are balanced. (3 atoms)
• Eight Hs on the left but only two on the right.
• Two Os on the left but six on the right

Balance H as it is the next reactant that is seen in only one reactant and product.

C₃H₈   +   O₂    →    4 H₂O   + 3CO₂

• The C atoms on both the sides are balanced. (3 atoms)
• The H atoms on both the sides are balanced. (8 atoms)
• Two Os on the left but ten on the right

Balance the Oxygen atoms on both the sides of the equation.

C₃H₈   +   O₂    →    4 H₂O   + 3CO₂

• The C atoms on both the sides are balanced. (3 atoms)
• The H atoms on both the sides are balanced. (8 atoms)
• The O atoms on both the sides are balanced. (10 atoms)

Then the balanced equation will be

C₃H₈   +   O₂    →   4 H₂O   + 3CO₂

   (1 compound of propane combines with 5 oxygen molecules to produce 4 water and 3 Carbon dioxide compounds.)

Step 3 : Specify the states of matter of reactants and products

• For gaseous substances use (g)
• For solids use (s)
• For liquids use(l)
• For solutions in water use (aq)
• These should be mentioned immediately following the formula of substance.

C₃H₈ (g) +  5O ₂ (g) → 4 H₂O (l) + 3 CO₂ (l).

This is the balanced equation with phase of reactants and products.