Problem 27 - Chemistry The Molecular Nature of Matter

Question

The combustion of a thin wire of magnesium metal (Mg) in an atmosphere of pure oxygen produces the brilliant light of a flashbulb, once commonly used in photography. After the reaction, a thin film of magnesium oxide is seen on the inside of the bulb. The equation for the reaction is $$ 2 \mathrm{Mg}+\mathrm{O}_{2} \longrightarrow 2 \mathrm{MgO} $$ (a) State in words how this equation is read. (b) Give the formula(s) of the reactants. (c) Give the formula(s) of the products.

Step-by-Step Solution

Answer

The equation is read as 'two magnesium plus oxygen yields two magnesium oxide.' Reactants are Mg and O2, and the product is MgO.

Step 1: Reading the Chemical Equation

This chemical equation is read as two molecules of magnesium (Mg) react with one molecule of oxygen (O2) to form two units of magnesium oxide (MgO).

Step 2: Identifying the Reactants

The reactants, which are the substances consumed in the reaction, are magnesium (Mg) and oxygen (O2).

Step 3: Identifying the Products

The products, which are the substances formed as a result of the reaction, are molecules of magnesium oxide (MgO).

Key Concepts

Combustion Reaction

Combustion reactions are a type of chemical reaction where a substance combines with oxygen to produce heat and light. Often, they involve the burning of a fuel, such as wood, gasoline, or, in this case, magnesium metal (Mg). These reactions are exothermic, which means they release energy, typically evidenced by heat and light, making them highly useful in everyday applications—from heating our homes to powering vehicles.

A classic example of a combustion reaction is the one given in the exercise, where magnesium metal burns in an atmosphere of pure oxygen. The brilliance of the light produced in this reaction is so intense that it was once utilized in flash photography. The reaction is swift and produces a noticeable change—a thin film of magnesium oxide forms as the product after the reaction. It's important to remember that for a combustion reaction to occur, a fuel (like magnesium), oxygen, and an ignition source, such as heat or a spark, are necessary. Through understanding these requirements, students can better grasp the concept of combustion reactions and their importance.

Chemical Equation

A chemical equation represents a chemical reaction using symbols and formulas. It's much like a recipe for a cooking dish, providing the necessary 'ingredients' (reactants) and the 'final dish' (products), along with their respective 'amounts' (coefficients). The equation from the exercise,
\(2 \mathrm{Mg} + \mathrm{O}_{2} \longrightarrow 2 \mathrm{MgO}\),
showcases this neatly. The numbers in front of the chemical symbols and formulas are coefficients; they tell us the ratio of molecules that participate in the reaction. Here, two atoms of magnesium react with one molecule of oxygen to produce two units of magnesium oxide. Reading and writing chemical equations accurately are pivotal skills in understanding chemical reactions. Ensuring that the equation is balanced, meaning the number of atoms of each element is the same on both sides of the equation, is essential for maintaining the law of conservation of mass.

Reactants and Products

Reactants are the starting substances in a chemical reaction, while products are the substances formed as a result. In our discussed reaction, magnesium and oxygen are the reactants because they are the substances undergoing a chemical change. Magnesium oxide, the compound that coats the inside of the bulb after the reaction, is the product.

In dissecting reactions, it's crucial to identify these constituents clearly. This identification is the first step in understanding how different substances interact chemically. For students, a useful tip is to always write down the reactants on the left side of the arrow in a chemical equation and the products on the right side. This standard format helps in visualizing the process that the reactants undergo to transform into products. Additionally, grasping the concept of reactants and products can aid students in predicting the outcomes of reactions and in learning how to balance chemical equations for maintaining the law of conservation of mass.