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Chemical Reaction Formula


Changes in the states of substance or system are known as reactions and can be divided into chemical and physical reactions.

Physical reaction

The equation can be represented to describe a physical reaction involving change of physical states. For example, evaporation, melting and condensation can be represented in this manner where (s) is solids, (l) is liquid and (g) is gas.


H2O(s) —-> H2O(l)


C2H5OH(l) —-> C2H5OH(g)


Chemical reaction

When atoms or group of atoms rearrange resulting in the formation of new chemical state due to the formation of chemical bonds are called Chemical reactions.

The substances undergoing changes are called reactants, written on the left-hand side of the equation, and newly formed substances are called products.


Steps in writing a chemical reaction

  •     Draft a skeleton equation wherein reactants formula is on left and products o right side of the equation.
  •    Mention the physical state of each reactant and product as (g) for gaseous, (l) for liquid, (s) for solids and (aq) for an aqueous solution     in a chemical reaction.
  •    Make sure that the equation is balanced. The number of atoms of all the elements on the left-hand side of the reactants must be equal    to the number of atoms of every element on the right-hand side of the product.

Example 1.

Sodium chloride reacts with silver nitrate to form sodium nitrate and silver chloride. Write a chemical equation for this process.


  1.    Sketch a skeleton equation where in reactants are on left and products are on the right side.

NaCl + AgNO3 —> NaNO3 + AgCl

  1.    Show the physical state of every reactant and product

NaCl(aq) + AgNO3(aq) —> NaNO3(aq) + AgCl(s)

  1.    Balance the equation

NaCl(aq) + AgNO3(aq) —> NaNO3(aq) + AgCl(s)


Example 2.

Sodium hydroxide crystals react with carbon dioxide in air to form water and a white powder sodium carbonate which is usually added to detergents as a softening agent. Write a chemical equation for this reaction.



  1.     Write a skeleton equation and keep reactants on the left side and products on the right side.

NaOH + CO2 —> Na2CO3 + H2O

  1.    Show the physical state of every reactant and product.

     NaOH(s) + CO2(g) —> Na2CO3(s) + H2O(l)

  1.    Balance the chemical equation

    2NaOH(s) + CO2(g) —> Na2CO3(s) + H2O(l)


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