Problem 113 - Chemistry Matter and Change

Question

Write a balanced equation for the following reactions. (Chapter 9) a. Zinc displaces silver in silver chloride. b. Sodium hydroxide and sulfuric acid react to form sodium sulfate and water

Step-by-Step Solution

Answer

a. \( Zn + AgCl \rightarrow Ag + ZnCl_2 \) b. \( 2NaOH + H_2SO_4 \rightarrow Na_2SO_4 + 2H_2O \)

Step 1: Identify the reactants and products

For this reaction, the reactants are Zinc (Zn) and Silver chloride (AgCl). After the displacement, the products are Silver (Ag) and Zinc chloride (ZnCl₂).

Step 2: Write the unbalanced equation

We will start by writing the unbalanced equation using the reactants and products' correct chemical symbols and formulas: Zn + AgCl → Ag + ZnCl₂

Step 3: Balance the equation

The equation is already balanced since each reactant (Zn and Cl) has the same number of atoms on both sides of the equation. Thus, the final balanced equation is: \[ Zn + AgCl \rightarrow Ag + ZnCl_2 \] b. Sodium hydroxide and sulfuric acid react to form sodium sulfate and water:

Step 1: Identify the reactants and products

In this reaction, the reactants are Sodium hydroxide (NaOH) and Sulfuric acid (H₂SO₄). The products of the reaction are Sodium sulfate (Na₂SO₄) and Water (H₂O).

Step 2: Write the unbalanced equation

Start by writing the unbalanced equation using the correct chemical symbols and formulas of the reactants and products: NaOH + H₂SO₄ → Na₂SO₄ + H₂O

Step 3: Balance the equation

To balance the equation, we need to make sure that the number of atoms on both sides of the equation is equal. We can balance the NaOH on the left side by adding a coefficient of 2: 2NaOH + H₂SO₄ → Na₂SO₄ + H₂O Now, we have: - 2 Na atoms, 2 O atoms, and 2 H atoms on the left side, and 2 Na atoms, 4 O atoms, and 2 H atoms on the right side. Since there is the same number of Na and H atoms on both sides, and the number of O atoms on both sides is different, we can add a coefficient of 2 in front of H₂O to balance the equation: 2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O Now, we have: - 2 Na atoms, 2 O atoms, and 2 H atoms on the left side and 2 Na atoms, 4 O atoms, and 2 H atoms on the right side. Thus, the final balanced equation is: \[ 2NaOH + H_2SO_4 \rightarrow Na_2SO_4 + 2H_2O \]

Key Concepts

Chemical Reactions

A chemical reaction is a process that involves the transformation of one or more substances into different substances. This process occurs because chemical bonds between atoms are broken and new bonds are formed. When zinc displaces silver in silver chloride, and when sodium hydroxide reacts with sulfuric acid, these are examples of chemical reactions.

Understanding chemical reactions involves knowing that:

• There is an initial set of materials called reactants.
• The reaction process converts these reactants into new materials called products.
• The rearrangement of atoms happens without any loss, which is governed by the law of conservation of mass. This law states that no atoms are lost or gained during a chemical reaction; they are merely rearranged.

In order to describe these reactions, chemists write chemical equations. An equation shows the substances involved as reactants transforming into products. Having a balanced chemical equation is important as it reflects the stoichiometry of the reaction, ensuring that atoms are conserved from reactants to products.

Reactants and Products

Reactants and products are the building blocks of chemical reactions. Reactants are substances that start a chemical reaction, while products are substances that are formed as the result of a chemical reaction.

When writing a balanced chemical equation:

• Identify the reactants and products first. For the zinc and silver chloride reaction, the initial substances are zinc (Zn) and silver chloride (AgCl).
• Write the correct chemical formula for each reactant and product. After zinc displaces silver, the products are silver (Ag) and zinc chloride (ZnCl₂).
• In the reaction of sodium hydroxide with sulfuric acid, the reactants are sodium hydroxide (NaOH) and sulfuric acid (H₂SO₄), forming sodium sulfate (Na₂SO₄) and water (H₂O) as products.

Reactants and products must be balanced according to the stoichiometry of the reaction. Balancing is crucial because it ensures the conservation of mass, reflecting that the atoms of the reactants are rearranged to form the products without any atom being lost or created.

Stoichiometry

Stoichiometry is the quantitative relationship between reactants and products in a chemical reaction. It is essential for balancing chemical equations and understanding the precise ratios of substances involved.

To apply stoichiometry:

• Write the unbalanced equation using known reactants and products. Initially, the unbalanced equation appears as that between sodium hydroxide (NaOH) and sulfuric acid (H₂SO₄), yielding sodium sulfate (Na₂SO₄) and water (H₂O).
• Count the number of atoms for each element on both sides of the equation. Ensure that the same number of atoms for each element is present in both reactants and products.
• Adjust the coefficients (the numbers before each chemical formula) to balance the equation. For example, in the NaOH and H₂SO₄ reaction, you place a coefficient of 2 before NaOH and H₂O to balance the sodium and oxygen atoms accordingly.

This act of balancing reflects the stoichiometry of the reaction, showing that the law of conservation of mass holds true. Balanced equations help predict how much of each reactant is needed or how much of a product will form, making stoichiometry a crucial tool in chemical calculations and experiments.