Chemical equations must be balanced to equate the number of atoms of reactants and products. As the law of conservation of mass states, “Mass can neither be created nor be destroyed but can be changed from one form to another.” Hence, the total mass of the reactant must be equal to the total mass of the products.
For example,
Na + H2O → NaOH + H2 ( Unbalanced equation )
The total mass of the reactants is 23+18= 41grams whereas the total mass of the products is 40+2=42 grams. This means that this equation needs to be balanced.
2Na + 2H2O → 2NaOH + H2 ( Balanced equation )
Now, the reactants have a total mass of 82grams {(23×2=46) + (18 x 2=36)} and the products formed must have 82grams {(40×2=80) + (2 x 1=2)}.
Rules for Balancing Chemical Equations
- Write reactants and products involved in the reaction correctly.
- Count and write atoms present in reactants and products.
- If carbon is present in your equation, try balancing it first and hydrogen and oxygen at the end.
- Never change the subscripts of atoms to balance the equation.
- Always mention the physical state of the elements and compounds.
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