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 balanced equation is \( 2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO} \). The reaction is exothermic, and the product is ionic.

Step 1: Selecting an Alkaline Earth Metal

Choose an alkaline earth metal, which is in Group 2 of the periodic table. Common examples are magnesium (Mg), calcium (Ca), or barium (Ba). For this exercise, we'll select magnesium (Mg) as the alkaline earth metal.

Step 2: Writing the Chemical Equation

Write the unbalanced chemical equation for the reaction of magnesium with oxygen. This involves magnesium (Mg) and oxygen (O2) reacting to form magnesium oxide (MgO). The unbalanced reaction is: \( \text{Mg} + \text{O}_2 \rightarrow \text{MgO} \).

Step 3: Balancing the Chemical Equation

Balance the chemical equation by ensuring that the number of atoms for each element is the same on both sides of the equation. The balanced equation is: \[ 2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO} \] This shows that two moles of magnesium react with one mole of oxygen to form two moles of magnesium oxide.

Step 4: Determining the Reaction Nature

This type of reaction, where a metal reacts with oxygen to form an oxide, is typically exothermic, meaning it releases heat. This is because a large amount of energy is released when strong ionic bonds are formed in the product.

Step 5: Identifying the Product Type

The product formed, magnesium oxide (MgO), is ionic. This is because magnesium (Mg), a metal, loses electrons to oxygen (O2), a non-metal, forming ionic bonds between Mg2+ and O2- ions.

Key Concepts

Chemical Equation Balancing

Chemical equation balancing is crucial in ensuring that the law of conservation of mass is upheld during a chemical reaction. When reacting substances form new products, the number of atoms for each type must remain constant on both sides of the equation. This balance reflects that atoms are neither created nor destroyed. By adjusting coefficients before each chemical formula, we achieve a balanced equation. For instance, in the reaction between magnesium (Mg) and oxygen (O2), the unbalanced equation is:\[ \text{Mg} + \text{O}_2 \rightarrow \text{MgO} \]The equation isn't balanced because the number of oxygen and magnesium atoms are not equal on both sides. To balance it, we place coefficients to ensure each type of atom matches. The balanced equation is:\[ 2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO} \]This reflects that two magnesium atoms react with one molecule of oxygen, forming two units of magnesium oxide, thus ensuring the law of conservation of mass.

Exothermic Reaction

An exothermic reaction releases energy, mostly in the form of heat. These reactions occur because the energy needed to break the bonds in the reactants is less than the energy released when new bonds form in the products. As such, the environment usually feels warmer.
In the context of alkaline earth metals reacting with oxygen, such as the magnesium and oxygen example, the reaction to form magnesium oxide is exothermic:\[ 2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO} + \text{energy} \]The strong ionic bonds formed in magnesium oxide release a significant amount of energy. This heat emission makes the reaction exothermic.

Ionic Compounds

Ionic compounds form when metals and non-metals exchange electrons, resulting in a bond between oppositely charged ions. Alkali earth metals, like magnesium, typically form ionic compounds when they react. In the example of magnesium reacting with oxygen, magnesium transfers electrons to oxygen, creating ions: - Magnesium becomes a cation (Mg²⁺), losing two electrons. - Oxygen becomes an anion (O^2-), gaining those electrons.
This exchange forms a stable ionic compound, magnesium oxide (MgO). Ionic compounds, like MgO, exhibit high melting and boiling points due to the strong attractions between the positive and negative ions. This makes them solid at room temperature, with bright, crystalline structures, often dissolving in water to conduct electricity when molten or dissolved.