Problem 19 - Chemistry and Chemical Reactivity

Question

A method recently suggested for the preparation of hydrogen (and oxygen) from water proceeds as follows: (a) Sulfuric acid and hydrogen iodide are formed from sulfur dioxide, water, and iodine. (b) The sulfuric acid from the first step is decomposed by heat to water, sulfur dioxide, and oxygen. (c) The hydrogen iodide from the first step is decomposed with heat to hydrogen and iodine. Write a balanced equation for each of these steps and show that their sum is the decomposition of water to form hydro- gen and oxygen.

Step-by-Step Solution

Answer

Water decomposes into hydrogen and oxygen.

Step 1: Write the Reaction for Step (a)

In Step (a), sulfuric acid and hydrogen iodide are formed from sulfur dioxide, water, and iodine. The balanced chemical equation for this reaction is: \[ \text{SO}_2 + \text{I}_2 + 2\text{H}_2\text{O} \rightarrow \text{H}_2\text{SO}_4 + 2\text{HI} \]

Step 2: Write the Reaction for Step (b)

In Step (b), sulfuric acid is decomposed by heat into water, sulfur dioxide, and oxygen. The balanced chemical equation for this step is: \[ \text{H}_2\text{SO}_4 \rightarrow \text{H}_2\text{O} + \text{SO}_2 + \dfrac{1}{2} \text{O}_2 \]

Step 3: Write the Reaction for Step (c)

In Step (c), hydrogen iodide is decomposed by heat into hydrogen and iodine. The balanced chemical equation for this step is: \[ 2\text{HI} \rightarrow \text{H}_2 + \text{I}_2 \]

Step 4: Sum the Reactions

Add the equations from all three steps together:1. \( \text{SO}_2 + \text{I}_2 + 2\text{H}_2\text{O} \rightarrow \text{H}_2\text{SO}_4 + 2\text{HI} \) 2. \( \text{H}_2\text{SO}_4 \rightarrow \text{H}_2\text{O} + \text{SO}_2 + \dfrac{1}{2} \text{O}_2 \) 3. \( 2\text{HI} \rightarrow \text{H}_2 + \text{I}_2 \) Cancel the intermediate products and reactants (sulfuric acid \((\text{H}_2\text{SO}_4)\), sulfur dioxide \((\text{SO}_2)\), hydrogen iodide \((\text{HI})\), and iodine \((\text{I}_2)\)). You are left with: \[ 2\text{H}_2\text{O} \rightarrow 2\text{H}_2 + \text{O}_2 \]

Step 5: Finalize and Verify the Result

The resulting equation from the sum of all reactions is \(2\text{H}_2\text{O} \rightarrow 2\text{H}_2 + \text{O}_2\), which shows the decomposition of water into hydrogen and oxygen. This demonstrates that the sum of the reactions correctly represents water decomposition.

Key Concepts

Balanced Chemical Equations

A balanced chemical equation is a crucial tool in chemistry. It represents a chemical reaction where the number of atoms for each element is the same on both sides of the equation. This adherence to the Law of Conservation of Mass ensures that no atoms are lost or gained in the process.
For any reaction, correctly balancing the chemical equation is essential. For example, in the decomposition of water into hydrogen and oxygen, the equation is:

• Input: 2 molecules of water – \(2\text{H}_2\text{O}\)
• Output: 2 molecules of hydrogen – \(2 ext{H}_2\) and 1 molecule of oxygen – \( ext{O}_2\).

By balancing these equations, we make sure that the chemical process can occur without any contradictions to the basic principles of chemistry.

Chemical Reactions

Chemical reactions are the processes where substances, known as reactants, are transformed into different substances, known as products. These reactions are fundamental to all chemical processes, producing countless materials and products we rely on every day. Consisting of reactants and products, reactions follow specific patterns and principles:

• Combination reactions: where multiple reactants form a single product.
• Decomposition reactions: where a compound breaks down into simpler substances, as seen in the decomposition of water.
• Single and double replacement reactions: where ions or atoms are exchanged between reactants.

The sulfuric acid decomposition is an example of a decomposition reaction. This is where a single substance breaks down into simpler substances under heat.

Sulfuric Acid Decomposition

Sulfuric acid decomposition is a classic example of a decomposition reaction. It showcases how a complex molecule can be broken down into simpler molecules with the application of heat. In the reaction:\[\text{H}_2\text{SO}_4 \rightarrow \text{H}_2\text{O} + \text{SO}_2 + \dfrac{1}{2}\text{O}_2\]

• Heat causes sulfuric acid to decompose into water, sulfur dioxide, and oxygen.
• This type of reaction is crucial for many industrial processes where sulfuric acid is used and recycled.

Understanding this process not only gives insight into chemical reactions but also into energy transfers and balance, which are critical in industrial chemistry.

Hydrogen Iodide Decomposition

The decomposition of hydrogen iodide is another important decomposition reaction. Similar to sulfuric acid decomposition, this reaction also involves breaking down a compound, but focuses on producing elemental forms:\[2\text{HI} \rightarrow \text{H}_2 + \text{I}_2\]

• Hydrogen iodide when heated decomposes into hydrogen and iodine.
• This reaction is essential for studying elemental iodine production and helps us understand molecular bond breakages.
• Heat is pivotal in these reactions, providing the necessary energy to break chemical bonds.

Together, the decomposition reactions of both sulfuric acid and hydrogen iodide illustrate basic principles of chemistry. They showcase how compounds are converted into elemental forms, which can be employed in synthesizing various products.