March 23, 2014

10th Chemistry New Syllabus - Balancing Chemical Equations

According to the law of conservation of mass, the total mass of the substances that are taking part in chemical reaction must be the same before and after the reaction. You know an atom is the smallest particle of an element that take part in a chemical reaction as it is the atom which account for the mass of any substance. The number of atoms of each element before and after reaction must be the same.

All the chemical equations must balance, because atoms are neither created nor destroyed in chemical reactions. A chemical equation in which the numbers of atoms of different elements on the reactants side (left side) are same as those on product side (right side) is called a balanced reaction.

Balancing a chemical equation involves finding out how many formula units of each substance take part in the reaction. A formula unit, as the name implies, is one unit – whether atom, ion, or molecule – corresponding to a given formula. One formula unit of NaCl for example is one Na+ ion and one Cl- ion; one formula unit of MgBr2 is one Mg+ ion and two Br- ions and one formula unit of H2O is one H2O molecule.

Chemical reactions and Equations

Complicated chemical equations need to be balanced using a systematic method, but simple equations can be balanced using a mixture of common sense and trial and error.
Now let us balance the chemical equation using a systematic method.

Step 1: Write the unbalanced equation using the correct chemical formula for each reactant and products. In the reaction of hydrogen with oxygen to yield water, you can write unbalanced chemical equations as
H2 + O2 - H2O……………(6)

Step 2: Compare number atoms of each element on both sides. Find
the suitable coefficients – the numbers placed before formula to indicate
how many formula units of each substance are required to balance the
equation. Only these coefficients can be changed when balancing an
equation, the formulas themselves can’t be changed. We take the
reaction of hydrogen with oxygen as an example; we can balance the
equation by adding a coefficient of 2 to both H2 and H2O. By so doing
there are 4 hydrogen and 2 oxygen atoms on each side of the equation:
2H2 + O2 - 2H2O …………..(7)

Step 3: Reduce the coefficients to their smallest whole number values,
if necessary by dividing them all by a common devisor.

Step 4: Check the answer by making sure that the numbers and kinds
of atoms are the same on both sides of the equation.

Let us work out some examples to see how equations are balanced.

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