Question

Write the balanced chemical reaction for the reaction of magnesium with hot water.
(A) $2Mg + 3{H_2}O \to 2MgOH + 3{H_2}$
(B) $Mg + 2{H_2}O \to Mg{\left( {OH} \right)_2} + {H_2}$
(C) $2Mg + 3{H_2}O \to 3MgOH + 3{H_2}$
(D) $Mg + 3{H_2}O \to 2MgOH + 3{H_2}$

Answer 1

The law of conservation of mass dictates that the quantity of each element should not change in a chemical reaction. Thus, each side of the chemical equation that is the product and the reactant side should represent the same quantity of a particular element. In a balanced equation charge on both sides of the reaction should also be conserved. Therefore, the same charge must be present on both sides of the reaction that is the same charge on the reactant side and same charge on the product side.

Complete Step by step solution
Magnesium cannot react with cold water but when magnesium is reacted with hot water, the reaction proceeds slowly. The products formed due to this reaction are magnesium hydroxide which is white in colour and hydrogen gas is released too. The reaction is as follows,
Magnesium + Water gives Magnesium hydroxide + Hydrogen gas
The unbalanced chemical equation for the same is as follows,
$Mg + {H_2}O \to MgOH + {H_2}$
We can balance a chemical equation by changing the scalar number for each chemical compound or element present in the reaction irrespective of the compound or element being present on the reactant or on the product side. A simple reaction can be balanced by trial-and-error method just by inspecting.
So, now we will balance the above reaction by trial-and-error method as follows,
$Mg + {H_2}O \to MgOH + {H_2}$
Here, we can see that on the left side that is on the reactant side the number of magnesium atoms is the same as the number of magnesium atoms on the right that is on the product side.
So, to balance the number of hydrogen and oxygen atoms we multiply water by two.
$2Mg + 2{H_2}O \to 2MgOH + {H_2}$
Now as we can see the number of hydrogen and oxygen atoms are balanced too. Hence, we can say that the equation is balanced as the quantity of chemical reactants is equal to the chemical compounds on the right side.
Therefore, the correct answer is option B.

Note
A chemical equation consists of the chemical formula of the reactants that is the formulas of compounds and symbols of elements. The chemical equation also requires the chemical formulas of the compound and elements of the products. The reactants and the products are separated by arrow and the individual compound or element is divided by a plus sign.