Question

Which of the following is an unbalanced equation?
a) CaCO3 --> CaO + CO2
b) PbO2 + 2H2-->2Pb + H2O
c) 2Na+ 2H2O-->2NaOH + H2
d) CS2 + 2O2 --> CO2 + 2SO2

Answer 1

2 and 4 is unbalanced........

Answer 2

Answer:

The correct option is (b) $PbO_{2} + 2H_{2}$ →$2 Pb + H_{2}O$

Explanation:

• $CaCO_{3}$ → $CaO + CO_{2}$

In this given equation, we can see that on left hand side we have 1 Calcium atom and same on the Right hand side.

We have 1 Carbon atom on LHS and 1 on RHS.

We have 3 Oxygen atom on LHS and 3 on RHS.

Hence equation 1 is a balanced chemical equation.

• $PbO_{2} + 2H_{2}$ →$2Pb + H_{2}O$

In this given chemical equation, when we observe closely we can see that there is 1 Lead atom on LHS and 2 on RHS.

There are 2 Oxygen atoms on LHS and 1 on RHS.

There are 4 hydrogen atom on LHS and 2 on RHS.

Hence this is not a balanced chemical equation.

• $2Na + 2H_{2}O$ →$2NaOH + H_{2}$

In the above question,

There are 2 Sodium atoms on LHS and 2 on RHS.

4 hydrogen atoms are present in LHS and 4 on RHS.

And two oxygens are present on both the sides.

Hence, this is a balanced chemical equation.

• $CS_{2} + 2O_{2}$ →$CO_{2} + 2SO_{2}$

In this last given equation,

1 carbon atom is present on both the sides.

2 sulphur atom is present on both the sides.

4 oxygen atom is present on both the sides.

Hence this also is a balance chemical equation.

Therefore, equation 2 is an unbalanced chemical equation.

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