Problem 35 - Chemistry and Chemical Reactivity

Question

Write balanced equations for the reactions of aluminum with \(\mathrm{HCl}(\mathrm{aq}), \mathrm{Cl}_{2},\) and \(\mathrm{O}_{2}\).

Step-by-Step Solution

Answer

1. \(2\text{Al} + 6\text{HCl} \rightarrow 2\text{AlCl}_3 + 3\text{H}_2\); 2. \(2\text{Al} + 3\text{Cl}_2 \rightarrow 2\text{AlCl}_3\); 3. \(4\text{Al} + 3\text{O}_2 \rightarrow 2\text{Al}_2\text{O}_3\)."

Step 1: Understand the Reaction with HCl

Aluminum reacts with hydrochloric acid to produce aluminum chloride and hydrogen gas. The unbalanced chemical equation is: \( \text{Al} + \text{HCl} \rightarrow \text{AlCl}_3 + \text{H}_2 \).

Step 2: Balance the Aluminum and Chlorine Atoms

Begin by balancing the aluminum and chlorine atoms. Since there is 1 aluminum atom on both sides and 3 chlorine atoms in aluminum chloride, we need 6 hydrochloric acid molecules to have 6 chlorine atoms on the reactant side: \( 2\text{Al} + 6\text{HCl} \rightarrow 2\text{AlCl}_3 + \text{H}_2 \).

Step 3: Balance the Hydrogen Atoms

Now there are 6 hydrogen atoms on the left-hand side from 6 HCl molecules, so we need 3 hydrogen molecules on the right-hand side to balance it: \( 2\text{Al} + 6\text{HCl} \rightarrow 2\text{AlCl}_3 + 3\text{H}_2 \).

Step 4: Write the Reaction with Cl2

Aluminum reacts with chlorine gas to form aluminum chloride. The unbalanced chemical equation is: \( \text{Al} + \text{Cl}_2 \rightarrow \text{AlCl}_3 \).

Step 5: Balance the Reaction with Cl2

First balance the aluminum atoms. We have 2 aluminum atoms forming 2 aluminum chloride with 3 chlorine molecules, so the balanced equation is: \( 2\text{Al} + 3\text{Cl}_2 \rightarrow 2\text{AlCl}_3 \).

Step 6: Write the Reaction with O2

Aluminum reacts with oxygen to form aluminum oxide. The unbalanced chemical equation is: \( \text{Al} + \text{O}_2 \rightarrow \text{Al}_2\text{O}_3 \).

Step 7: Balance the Reaction with O2

Aluminum oxide has 2 aluminum atoms and 3 oxygen atoms. We need 4 aluminum atoms and 3 oxygen molecules: \( 4\text{Al} + 3\text{O}_2 \rightarrow 2\text{Al}_2\text{O}_3 \).

Key Concepts

Stoichiometry

Stoichiometry is the quantitative relationship between reactants and products in a chemical reaction. It involves using balanced chemical equations to determine the proportions in which chemicals react. To grasp stoichiometry, let's consider the reaction of aluminum with hydrochloric acid:

• We start with an unbalanced equation: \(\text{Al} + \text{HCl} \rightarrow \text{AlCl}_3 + \text{H}_2\).
• To balance this equation, we ensure that the number of atoms for each element is the same on both sides.

This process involves choosing coefficients that satisfy the law of conservation of mass. By balancing, we determine that 2 moles of aluminum react with 6 moles of hydrochloric acid to produce 2 moles of aluminum chloride and 3 moles of hydrogen gas.
Key to stoichiometry is working with the mole concept as a counting unit to measure substances. By understanding stoichiometry, it becomes easier to predict amounts of reactants needed or products formed.

Chemical Equations

Chemical equations are symbolic representations of chemical reactions, showing the reactants and the products. They serve as a basic language of chemistry, allowing us to predict what happens in a chemical reaction.
In the equations for aluminum reactions, each reaction starts as unbalanced:

• Aluminum reacting with chlorine: \(\text{Al} + \text{Cl}_2 \rightarrow \text{AlCl}_3\).
• Aluminum reacting with oxygen: \(\text{Al} + \text{O}_2 \rightarrow \text{Al}_2\text{O}_3\).

By balancing them, chemical equations communicate the quantities and identities of reactants and products. Balancing involves:

• Ensuring equal numbers of each type of atom on both sides of the equation.
• Adjusting coefficients, which are numbers placed in front of compounds.

Balanced equations are essential for stoichiometric calculations and understanding chemical reactions.

Aluminum Reactions

Aluminum is an active metal that readily reacts with many substances, including acids and gases.
1. **Reaction with Hydrochloric Acid**: When aluminum reacts with hydrochloric acid, it forms aluminum chloride and hydrogen gas. This reaction demonstrates basic metal-acid reactivity:

• \(2\text{Al} + 6\text{HCl} \rightarrow 2\text{AlCl}_3 + 3\text{H}_2\).
• Here, aluminum displaces hydrogen due to its higher reactivity.

2. **Reaction with Chlorine**: In another aluminum reaction, it combines with chlorine gas to form aluminum chloride:

• \(2\text{Al} + 3\text{Cl}_2 \rightarrow 2\text{AlCl}_3\).
• This reaction shows aluminum's ability to form ionic compounds with halogens.

3. **Reaction with Oxygen**: Aluminum also reacts with oxygen to produce aluminum oxide, a compound known for its protective layer on aluminum surfaces:

• \(4\text{Al} + 3\text{O}_2 \rightarrow 2\text{Al}_2\text{O}_3\).
• This oxidation reaction is critical in processes like corrosion resistance.

Through these reactions, aluminum showcases its diverse chemical reactivity.