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) \( \text{Zn} + 2\text{AgCl} \rightarrow 2\text{Ag} + \text{ZnCl}_2 \) b) \( 2\text{NaOH} + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{SO}_4 + 2\text{H}_2\text{O} \)

Step 1: Write the Unbalanced Equation for Reaction (a)

In reaction (a), zinc displaces silver in silver chloride. Write the unbalanced chemical equation for this single displacement reaction: \[ \text{Zn} + \text{AgCl} \rightarrow \text{Ag} + \text{ZnCl}_2 \]

Step 2: Balance the Equation for Reaction (a)

First, count the number of atoms of each element on both sides of the equation for reaction (a):- Zn: 1 atom on both sides- Ag: 1 atom on both sides- Cl: 2 atoms in \( \text{ZnCl}_2 \) on the right side, so we need 2 \( \text{AgCl} \) on the left.Balance by adjusting coefficients:\[ \text{Zn} + 2\text{AgCl} \rightarrow 2\text{Ag} + \text{ZnCl}_2 \]

Step 3: Write the Unbalanced Equation for Reaction (b)

In reaction (b), sodium hydroxide reacts with sulfuric acid to form sodium sulfate and water. Write the unbalanced chemical equation: \[ \text{NaOH} + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{SO}_4 + \text{H}_2\text{O} \]

Step 4: Balance the Equation for Reaction (b)

First, count the atoms on each side of the equation for reaction (b):- Na: 2 in \( \text{Na}_2\text{SO}_4 \) on right, so 2 \( \text{NaOH} \) on left- H: 2 in \( \text{H}_2\text{SO}_4 \) and 2 in 2 \( \text{H}_2\text{O} \) on right- O: 4 in \( \text{SO}_4 \) and 2 in \( \text{H}_2\text{O} \) equal totals on both sidesBalance by adjusting coefficients:\[ 2\text{NaOH} + \text{H}_2\text{SO}_4 \rightarrow \text{Na}_2\text{SO}_4 + 2\text{H}_2\text{O} \]

Key Concepts

Single Displacement Reaction

In a single displacement reaction, one element successfully replaces another element in a compound. This type of reaction is characterized by the general formula:

• A + BC → B + AC

In the exercise example, zinc (Zn) replaces silver (Ag) in silver chloride (AgCl). When the zinc is introduced, silver is displaced out of its compound, forming zinc chloride (ZnCl₂) and elemental silver (Ag) as products.
Single displacement reactions often involve metals where a more reactive metal displaces a less reactive one from its compound. The reactivity series of metals is a handy tool to predict whether a single displacement reaction will occur. Remember, not all metals can displace each other; only a more reactive metal can displace a less reactive one.

Double Displacement Reaction

Double displacement reactions involve the exchange of ions between two compounds to form two new compounds. Generally outlined as:

• AB + CD → AD + CB

In the given exercise, sodium hydroxide (NaOH) and sulfuric acid (H₂SO₄) react with each other to form sodium sulfate (Na₂SO₄) and water (H₂O).
Here, the sodium (Na) from sodium hydroxide swaps places with the hydrogen (H) from sulfuric acid, resulting in the formation of sodium sulfate and water. These reactions often occur in solutions and result in the formation of a precipitate, water, or a gas as one of the products. They are key in many industrial processes and everyday reactions.

Chemical Equation Balancing

Balancing chemical equations is crucial to accurately represent a chemical reaction. This process ensures the law of conservation of mass is followed, which states that matter cannot be created or destroyed. To balance an equation, you must ensure the same number of each type of atom appears on both sides. Steps to Balance:

• List all elements in the reaction.
• Count the number of atoms of each element in reactants and products.
• Adjust coefficients to balance the atoms for each element.

The coefficients indicate the number of molecules or formula units involved in the reaction. Always start balancing with the compound that has the most complex formula, then adjust the simpler ones. This practice ensures you comply with stoichiometry and that the reaction is depicted accurately.

Stoichiometry

Stoichiometry is the mathematical portion of chemistry that relates reactants' and products' quantities in a chemical reaction. It is based on the principle that each chemical reaction follows fixed proportions of reactants to products. By understanding and applying stoichiometry, you can:

• Predict the amount of product formed from a given amount of reactant.
• Determine the amount of reactants required to produce a desired product amount.
• Calculate the yields of reactions.

Balanced chemical equations are necessary for stoichiometry calculations because they define the precise ratios of molecules or moles of substances in a reaction. This discipline is essential for industrial applications, laboratory analyses, and any scenario where quantitative chemical information is necessary.