Problem 9 - Chemistry The Central Science In Si Units

Question

Write "true" or "false" for each statement. (a) We balance chemical equations as we do because energy must be conserved. (b) If the reaction \(2 \mathrm{O}_{3}(g) \rightarrow 3 \mathrm{O}_{2}(g)\) goes to completion and all \(\mathrm{O}_{3}\) is converted to \(\mathrm{O}_{2}\), then the mass of \(\mathrm{O}_{3}\) at the beginning of the reaction must be the same as the mass of \(\mathrm{O}_{2}\) at the end of the reaction. (c) You can balance the "water-splitting" reaction \(\mathrm{H}_{2} \mathrm{O}(l) \rightarrow \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g)\) by writing it this way: \(\mathrm{H}_{2} \mathrm{O}_{2}(l) \rightarrow \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g)\).

Step-by-Step Solution

Answer

(a) False, (b) True, (c) False.

Step 1: Evaluate Statement (a)

This statement claims we balance chemical equations to conserve energy. In fact, the primary reason for balancing chemical equations is to obey the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction. Although energy conservation is important, it is not the principal reason chemical equations are balanced. Hence, statement (a) is false.

Step 2: Evaluate Statement (b)

This statement considers the mass of reactants and products before and after a reaction. The law of conservation of mass states that the mass of the reactants must equal the mass of the products in a chemical reaction. Thus, if all \( \mathrm{O}_3 \) is converted to \( \mathrm{O}_2 \), their masses must be equal. Hence, statement (b) is true.

Step 3: Evaluate Statement (c)

This statement provides an incorrect way of balancing the water-splitting reaction. The correct decomposition of water \( \mathrm{H}_2 \mathrm{O} \) into \( \mathrm{H}_2 \) and \( \mathrm{O}_2 \) involves writing \( 2 \mathrm{H}_2 \mathrm{O}(l) \rightarrow 2 \mathrm{H}_2(g) + \mathrm{O}_2(g) \). Writing it with \( \mathrm{H}_2 \mathrm{O}_2 \) is incorrect, as this changes the substance involved in the reaction. Hence, statement (c) is false.

Key Concepts

Conservation of Mass

The law of conservation of mass is a fundamental principle in chemistry. This law asserts that during a chemical reaction, matter is not created or destroyed. Rather, it changes form. This means that the total mass of the reactants (the starting substances) must equal the mass of the products (the substances formed) in a chemical reaction.
For example, if you begin with 10 grams of reactants, you should have 10 grams of products after the reaction is complete. This concept is crucial because it ensures that atomic matter is accounted for at all stages of a chemical reaction.
Understanding this principle allows chemists to predict the amounts of products that will be generated from given reactants. It also enables chemists to ensure that chemical equations are accurately representative of what occurs in the real world. Remember, no atoms are lost; they are merely rearranged.

Balancing Chemical Equations

Balancing chemical equations is an essential skill in chemistry. The fundamental purpose is to reflect the law of conservation of mass. In a balanced chemical equation, the number of atoms for each element is the same on both sides of the equation. This ensures that matter is conserved throughout the chemical process.
To balance an equation, one often starts by writing the unbalanced equation based on the reactants and products of the reaction. Then, we adjust the coefficients (the numbers before the molecules) to make sure that each type of atom has the same quantity on both sides.
The coefficients represent the relative number of moles of a substance. By mastering balancing equations, students gain deeper insights into the stoichiometry and relationships between reactants and products. A balanced equation provides valuable information, such as the proportions of reactants needed and the amount of product that can be formed.

Chemical Equation Representation

Chemical equations are vital tools in representing chemical reactions. They provide a concise way of showing which substances react and what they transform into during the reaction.
A chemical equation consists of reactants on the left, products on the right, and an arrow pointing from reactants to products to show the direction of the reaction. For example, in the reaction \( 2 \mathrm{H}_2 + \mathrm{O}_2 \rightarrow 2 \mathrm{H}_2 \mathrm{O} \), hydrogen and oxygen are reactants, and water is the product.
Chemical equations must be correctly written and balanced to accurately reflect the law of conservation of mass. In some cases, additional symbols may be used to show the state of the substances, such as (s) for solids, (l) for liquids, (g) for gases, and (aq) for aqueous solutions. By understanding chemical equation representation, one can predict the outcomes of reactions and ensure that they are both feasible and accurately understood.