Understanding the Reaction of Magnesium with Hot Water

The reaction between magnesium and hot water is a fascinating chemical process that involves the production of hydrogen gas and magnesium hydroxide. This guide aims to provide a clear overview of the balanced equation for this reaction, the principles of balancing chemical equations, and the reaction details.

Law of Conservation of Matter and Balanced Equations

A balanced chemical equation is crucial for the accurate representation of chemical reactions. According to the law of conservation of matter, the number of atoms of each element must be the same on both sides of the equation. This means that the number of atoms of each element present in the reactants must equal the number of atoms present in the products.

The Correct Balanced Equation for Magnesium Reacting with Hot Water

Magnesium reacts with hot water to form magnesium hydroxide and hydrogen gas. The initial equation provided is:

Mg   2H2O → Mg(OH)2   H2

However, to balance this correctly, we need to re-write the water molecule, H2O, as H-OH. This allows us to balance the H atoms separately from the OH groups. Thus, the balanced equation is:

Mg   2H-OH → Mg(OH)2   H2

The equation now reflects the conservation of hydrogen and oxygen atoms. Let’s break this down further:

Mg: 1 atom on both sides H: 2 atoms on the left, 2 atoms on the right (2 in Mg(OH)2 and 2 in H2) OH: 2 groups on the left, 2 groups on the right (1 in Mg(OH)2 and 1 separate H2O) O: 2 atoms on the left, 2 atoms on the right (2 in 2H-OH and 2 in Mg(OH)2)

Specific Conditions of the Reaction

It's important to note that magnesium does not react quickly with cold water. However, when hot water is used, the reaction proceeds more rapidly. A slurry of water and magnesium turnings will yield a basic solution, as the reaction produces magnesium hydroxide, a basic salt.

Complete Reaction Equation

For a more accurate representation of the reaction, the complete equation can be written as:

Mg   2H2O → Mg(OH)2   H2

This equation shows that one atom of magnesium reacts with two molecules of water to produce one molecule of magnesium hydroxide and one molecule of hydrogen gas. The solubility of magnesium hydroxide in water is low, making the solution slightly basic.

Reactivity and Displacement

Magnesium's high reactivity allows it to displace hydrogen from water, as shown in the equation. This displacement is a consequence of magnesium's more electropositive nature compared to hydrogen. The displacement reaction can be written as:

Mg   2H2O → Mg(OH)2   H2

In summary, the reaction of magnesium with hot water is a classic example of a redox (oxidation-reduction) reaction where magnesium gets oxidized and water is reduced. Understanding the balanced equation and the principles behind it is essential for interpreting the chemical behavior of magnesium under different conditions.