# What is the missing coefficient in the balanced equation? What type of reaction is it? Mg(OH)_2 + H_2SO_4 -> MgSO_4 + ?H_2O

May 22, 2017

The stoichiometrically balanced equation is:

$M g {\left(O H\right)}_{2} + {H}_{2} S {O}_{4} \rightarrow M g S {O}_{4} + \textcolor{red}{2} {H}_{2} O$

And this is an acid-base reaction.

#### Explanation:

Chemical equations are balanced with respect to mass and charge. For every reactant particle, there is a corresponding product particle. And for every reactant charge, there must be a corresponding product charge. When you come to study $\text{redox reactions}$ we introduce the electron as a conceptual particle with a negative charge so that redox reactions can also be shown to conserve charge:

$\text{Reduction:}$

${O}_{2} \left(g\right) + 4 {e}^{-} \rightarrow 2 {O}^{2 -}$ $\left(i\right)$

$\text{Oxidation:}$

$F e \left(s\right) \rightarrow F {e}^{2 +} + 2 {e}^{-}$ $\left(i i\right)$

And we cross multiply these individual redox reactions so that the electrons do not appear in the final redox equation:

$\left(i\right) + + 2 \times \left(i i\right)$ gives.................

$2 F e \left(s\right) + {O}_{2} + \cancel{4 {e}^{-}} \rightarrow 2 F e O + \cancel{4 {e}^{-}}$

$2 F e \left(s\right) + {O}_{2} \rightarrow 2 F e O$

Charge is balanced, and mass is balanced. As is ABSOLUTELY required.

In the given example, we could write the net ionic equation, i.e.

${H}_{3} {O}^{+} + H {O}^{-} \rightarrow 2 {H}_{2} O$

Are mass and charge conserved here?