Chemical equation

• Reaction between two or more elements, resulting in the formation of a chemical bond between atoms and the formation of a chemical compound either by releasing or consuming energy can be represented by formula of entities.

Thus a chemical equation is a short form that is used to describe a chemical reaction.

• The substances that undergo the change are called reactants and the substances that are formed as a result of chemical change are called products.

Example:

Carbon burns in air to form carbon dioxide gas releasing heat in the process.

Carbon is the reactant. Carbon dioxide is the product. Heat energy is released in the conversion.

Chemical equation:

C + O₂ CO₂ + Heat released

• The reactants and products are separated by an arrow (→) mark.
• The reactants are on the left side of the arrow and products on the right.
• The symbol ∆ above the arrow mark means that the reactants must be heated for the reaction to take place.

1. Reaction of Hydrogen with Oxygen forming water. 2H₂ + O₂ → 2H₂O

2. Potassium chlorate undergoing decomposition on heating to form potassium chloride and oxygen.

3. 2KCIO₃ 2KCI + 3O₂

4. Reaction of Silver nitrate with hydrogen chloride forming silver chloride and nitric acid.

5. AgNO₃ + HCl → AgCl + HNO₃

6. Zinc reacts with dilute hydrochloric acid to form zinc chloride and liberates hydrogen.

7. Zn + 2HCl → ZnCl₂ H₂

Balancing a Chemical Equation:

According to Law of mass action:

• Matter can neither be created nor destroyed but can be changed from one form to another.
• Therefore the number of atoms of reactants should be equal to the number of atoms of products.

Balancing a chemical equation:

Step 1:

• Write the correct skeletal equation containing formula of one molecule of each reactant and product.
• Reactants are written on the left hand side and products on the right hand side separated by an arrow which shows the direction of reaction.

Step 2:

• To balance the equations apply the Law of conservation of mass.
• Start by balancing an element that appears in only once in reactant and product.
• Once one element is balanced, proceed to balance other elements until all are balanced.
• Balance chemical formulae by placing coefficients in front of them.

Note:

• The chemical formulae of compounds should not be changed by adding or removing subscripts.

Example:

The chemical reaction between hydrogen and oxygen forming water.

The unbalanced equation is written as

H₂ + O₂ → H₂O

• If the chemical equation for the reaction is written like this it shows that one oxygen atom is destroyed but according to Law of mass action matter can neither be created nor be destroyed.
• The equation should be balanced so that there are equal numbers of atoms of each element on the reactant and product side.

1. Put 2 in front of water molecule.

H₂ + O₂ → 2H₂O

Now:

2. Put 2 in front of Hydrogen molecule.

2H₂ + O₂ →  2H₂O

Equation is balanced.

• Write the balanced chemical equation for reaction of Lithium oxide with water.

Li₂O + H₂O → LiOH

Put 2 in front of LiOH.

Li₂O + H₂O → 2LiOH

The chemical equation is balanced.

• Balance the given chemical equation:

FeCl₃ + NaOH → Fe(OH)₃ + NaCl

• Put 3 in front of NaOH.

FeCl₃ + 3NaOH → Fe(OH)₃ + NaCl

• Put 3 in front of NaCl.

FeCl₃ + 3NaOH → Fe(OH)₃ + 3NaCl