Problem 6 - Chemistry and Chemical Reactivity

Question

Select one of the alkaline earth metals and write a balanced chemical equation for its reaction with oxygen. Is the reaction likely to be exothermic or endothermic? Is the product ionic or molecular?

Step-by-Step Solution

Answer

The reaction of Mg with O2 to form MgO is exothermic and produces an ionic compound.

Step 1: Select an Alkaline Earth Metal

Alkaline earth metals are elements in Group 2 of the periodic table. Common examples include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). For this exercise, let's select magnesium (Mg) as the alkaline earth metal.

Step 2: Understand the Reaction with Oxygen

When alkaline earth metals react with oxygen, they form metal oxides. The general form of this reaction is \(M + O_2 \rightarrow MO\), where \(M\) represents the metal.

Step 3: Write the Balanced Chemical Equation

The unbalanced reaction between magnesium and oxygen can be written as: \( \text{Mg} + \text{O}_2 \rightarrow \text{MgO} \). To balance the equation, we have: \( 2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO} \).

Step 4: Determine the Nature of the Reaction

Combustion of magnesium is an exothermic reaction, meaning it releases heat. This is typical for reactions involving oxygen and metals.

Step 5: Classify the Reaction Product

The product, \(\text{MgO}\), is an ionic compound. This is because magnesium (a metal) forms ionic bonds with oxygen (a non-metal), resulting in a compound with distinct positive and negative ions.

Key Concepts

Reaction with Oxygen

Alkaline earth metals are known for their reactivity with oxygen. When these metals come into contact with oxygen, they form metal oxides. This type of reaction is essential because it shows how metals transition into compounds by bonding with oxygen atoms. The general reaction for any alkaline earth metal (

• M represents the metal and
• O₂ is oxygen

, this transition can be summarized as: \( M + O_2 \rightarrow MO \).
For instance, if we choose magnesium (Mg) from the group, the process is straightforward. Magnesium reacts with oxygen to form magnesium oxide (MgO). This transformation is not just theoretical; it's a reaction you can visibly observe through combustion where the metal burns in oxygen.

Balanced Chemical Equation

Balancing chemical equations is crucial in chemistry as it ensures the conservation of mass. It's like solving a puzzle where both sides must have the exact same quantities of each type of atom. Let's examine the equation when magnesium reacts with oxygen:

• Initial unbalanced equation: \( \text{Mg} + \text{O}_2 \rightarrow \text{MgO} \)

Balancing requires adjusting the number of atoms so that each element is equal on both sides of the reaction.

• Balanced equation: \( 2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO} \)

Here, you notice how the coefficients "2" before Mg and MgO balance the equation. This ensures that two magnesium atoms react with one oxygen molecule to yield two magnesium oxide formula units.

Exothermic Reaction

Exothermic reactions are those that release energy, often in the form of heat. When metals like magnesium react with oxygen, they undergo exothermic reactions. You can feel this energy release as an increase in temperature or observe it as the metal glows or even gives off a flame. It's because these reactions release more energy than what is consumed to break the bonds in the reactants.
Combustion, specifically, is a classic example of an exothermic reaction. When magnesium burns in air, it emits bright light and heat, which is why it feels and looks impressive. Such reactions are not only practical in generating heat but also demonstrate how chemical potential energy is transformed into thermal energy.

Ionic Compound

The product of a reaction between alkaline earth metals and oxygen is an ionic compound. But what exactly is an ionic compound? It's a substance formed when a metal bonds with a non-metal, leading to a lattice structure of oppositely charged ions. In the case of magnesium oxide (MgO), magnesium donates two electrons to achieve a positive charge, while oxygen accepts these electrons to become negatively charged.

• This results in positive Mg²⁺ ions
• and negative O^2- ions.

Because of this exchange of electrons, MgO solidifies as a stable structure. Such ionic bonds are robust, resulting in compounds with high melting and boiling points. These ionic characteristics influence how compounds behave chemically and physically.