Problem 25 - Chemistry and Chemical Reactivity

Question

When magnesium burns in air, it forms both an oxide and a nitride. Write balanced equations for the formation of both compounds.

Step-by-Step Solution

Answer

Mg forms MgO with O2 and Mg3N2 with N2 when burned in air.

Step 1: Understand the Reactants

When magnesium burns in air, it reacts primarily with oxygen, but it can also react with nitrogen. The reactants for these processes are magnesium (Mg) and the components of air, oxygen (O_2) and nitrogen (N_2).

Step 2: Write the Equation for Magnesium Oxide Formation

Magnesium reacts with oxygen to form magnesium oxide. The chemical equation for this reaction is:\[ 2 \text{Mg} + \text{O}_2 \rightarrow 2 \text{MgO} \]

Step 3: Balance the Equation for Magnesium Oxide

The equation \( 2 \text{Mg} + \text{O}_2 \rightarrow 2 \text{MgO} \) is already balanced with respect to magnesium and oxygen atoms.

Step 4: Write the Equation for Magnesium Nitride Formation

In addition to oxygen, magnesium can react with nitrogen to form magnesium nitride. The chemical equation for this reaction is:\[ 3 \text{Mg} + \text{N}_2 \rightarrow \text{Mg}_3\text{N}_2 \]

Step 5: Balance the Equation for Magnesium Nitride

The equation \( 3 \text{Mg} + \text{N}_2 \rightarrow \text{Mg}_3\text{N}_2 \) is already balanced with respect to magnesium and nitrogen atoms.

Key Concepts

Magnesium Oxide Formation

Magnesium oxide forms when magnesium (\( \text{Mg} \)) reacts with oxygen (\( \text{O}_2 \)) from the air. This chemical reaction results in the formation of magnesium oxide (\( \text{MgO} \)).

When we write down this reaction as a chemical equation, it becomes: \[ 2 \text{Mg} + \text{O}_2 \rightarrow 2 \text{MgO} \] This equation shows that two magnesium atoms react with one oxygen molecule to produce two units of magnesium oxide.

In this process:

• Magnesium acts as a metal that easily loses electrons to form positive ions.
• Oxygen is a non-metal that typically gains electrons to form negative ions.

This transfer of electrons is what constitutes the chemical reaction, fundamentally altering the substances involved.

Magnesium Nitride Formation

Magnesium nitride (\( \text{Mg}_3\text{N}_2 \)) is another compound magnesium can form when it reacts with nitrogen (\( \text{N}_2 \)) in the air. Though less common than the formation of magnesium oxide, this reaction is notable.

The chemical equation for the formation of magnesium nitride is:\[ 3 \text{Mg} + \text{N}_2 \rightarrow \text{Mg}_3\text{N}_2 \] This equation tells us that three atoms of magnesium react with a single molecule of nitrogen to create one molecule of magnesium nitride.

In this reaction:

• Magnesium gives up electrons to nitrogen, indicating a redox reaction.
• Nitrogen, typically inert, in this case reacts due to the aggressive donating nature of magnesium's electrons.

These interactions involve the substance’s basic elemental properties and their tendency to achieve a state of lower energy.

Balancing Chemical Equations

Balancing chemical equations is essential to accurately describe a chemical reaction in a manner that adheres to the law of conservation of mass. This law states that matter cannot be created or destroyed in a chemical reaction.

To balance an equation, ensure the number of atoms for each element is equal on both the reactant and product sides of the equation.

Let's consider the magnesium oxide reaction:\[ 2 \text{Mg} + \text{O}_2 \rightarrow 2 \text{MgO} \] Count:

• 2 magnesium atoms on both reaction sides.
• 2 oxygen atoms on both reaction sides.

This confirms the equation is balanced. Similarly, look at the magnesium nitride equation:\[ 3 \text{Mg} + \text{N}_2 \rightarrow \text{Mg}_3\text{N}_2 \] Here too, you find:

• 3 magnesium atoms balanced across the equation.
• 2 nitrogen atoms balanced across the equation.

Always double-check your atom counts to ensure equations reflect the reaction correctly.

Chemical Reactions

Chemical reactions involve the transformation of one or more substances into new substances. These reactions can result in the formation of compounds like magnesium oxide and magnesium nitride.

Reactions occur due to interactions between the atoms and molecules of the reactants. In our exercise:

• Magnesium reacts with oxygen to form magnesium oxide through a burning process.
• Magnesium reacts with nitrogen to form magnesium nitride in a lesser degree.

Most reactions involve either the formation or breaking of chemical bonds, leading to energy changes in the form of heat exchange.

Understanding the basic principles of chemical reactions helps us predict the products formed when different substances interact, and allows for the controlled synthesis of desired compounds in practical applications.