Question

Describe the type of reaction for each reaction shown. (a) \(2 \mathrm{H}_{2} \mathrm{O} \longrightarrow 2 \mathrm{H}_{2}+\mathrm{O}_{2}\) (b) \(2 \mathrm{Ca}+\mathrm{O}_{2} \longrightarrow 2 \mathrm{CaO}\) (c) \(2 \mathrm{NaN}_{3}(\mathrm{s}) \longrightarrow 2 \mathrm{Na}(\mathrm{s})+3 \mathrm{N}_{2}(g)\)

Short answer

Reaction (a) is a decomposition reaction, (b) is a synthesis reaction, and (c) is a decomposition reaction.

Step-by-step solution

Analyzing Reaction (a)

The reaction given is \( 2 \mathrm{H}_{2} \mathrm{O} \longrightarrow 2 \mathrm{H}_{2} + \mathrm{O}_{2} \). In this reaction, water (\( \mathrm{H}_{2} \mathrm{O} \)) is decomposing into hydrogen gas (\( \mathrm{H}_{2} \)) and oxygen gas (\( \mathrm{O}_{2} \)). This is an example of a **decomposition reaction**, where a compound breaks down into two or more simpler substances.

Analyzing Reaction (b)

The reaction given is \( 2 \mathrm{Ca} + \mathrm{O}_{2} \longrightarrow 2 \mathrm{CaO} \). Here, elemental calcium (\( \mathrm{Ca} \)) reacts with oxygen gas (\( \mathrm{O}_{2} \)) to form calcium oxide (\( \mathrm{CaO} \)). This reaction is a **synthesis (or combination) reaction**, where two or more reactants combine to form a single product.

Analyzing Reaction (c)

The reaction given is \( 2 \mathrm{NaN}_{3} (\mathrm{s}) \longrightarrow 2 \mathrm{Na} (\mathrm{s}) + 3 \mathrm{N}_{2} (g) \). Sodium azide (\( \mathrm{NaN}_{3} \)) decomposes into metallic sodium (\( \mathrm{Na} \)) and nitrogen gas (\( \mathrm{N}_{2} \)). This is another example of a **decomposition reaction**, where a single compound breaks down into multiple products.

Key concepts

Decomposition Reaction

A decomposition reaction occurs when a single compound breaks down into two or more simpler substances. This type of chemical reaction is essential for various industrial and biological processes.
In decomposition reactions, a compound typically needs energy to break the bonds holding its atoms together. Common forms of energy that drive these reactions include heat, light, or electricity.
For example, in exercise (a), the decomposition of water ( H_{2}O) into hydrogen ( H_{2}) and oxygen ( O_{2}) gases is catalyzed by electricity in a process called electrolysis.

• This reaction demonstrates a key principle of decomposition reactions: breaking down complex molecules to form simpler ones.
• Each product in a decomposition reaction is typically more stable than the original compound.
• Decomposition reactions are critical in recycling materials and in combustion processes.

Synthesis Reaction

A synthesis reaction, also known as a combination reaction, involves two or more entities combining to form a singular, more complex product. These reactions are fundamental in the creation of new compounds and materials.
Synthesis reactions are usually exothermic, meaning they release energy, predominantly in the form of heat or light. This release of energy occurs as stronger, new bonds form during the process.
In exercise (b), elemental calcium ( Ca) reacts with oxygen ( O_{2}) to form calcium oxide ( CaO).

• In this reaction, two simple substances combine to create a solid compound, calcium oxide.
• Synthesis reactions are vital in forming complex compounds from simpler chemicals.
• Such reactions are also crucial in biological processes like protein synthesis and the photosynthesis of glucose in plants.

Compound Breakdown

Compound breakdown is a broader concept within chemical reactions where more complex chemical substances are simplified into simpler substances, often in the context of decomposition reactions.
In chemistry, understanding how compounds break down is vital for controlling and utilizing reactions effectively. Decomposition reactions, shown in steps (a) and (c) of our original problems, illustrate this concept well.
For instance, sodium azide ( NaN_{3}) breaking down into sodium ( Na) and nitrogen ( N_{2}) looks simple, but it's critical for various applications such as airbag deployment.

• This breakdown happens under conditions that favor the release of pressure and gases quickly and effectively.
• The breakdown of compounds is essential for many scientific fields, from material science to environmental chemistry.
• Understanding these reactions helps us create desired products while managing unwanted by-products in industrial processes.