Question

Determine whether each of the following equations represents a combination reaction, a decomposition reaction, or a combustion reaction: (a) \(2 \mathrm{NaHCO}_{3} \longrightarrow\) \(\mathrm{Na}_{2} \mathrm{CO}_{3}+\mathrm{CO}_{2}+\mathrm{H}_{2} \mathrm{O},(\mathrm{b}) \mathrm{NH}_{3}+\mathrm{HCl} \longrightarrow \mathrm{NH}_{4} \mathrm{Cl}\) (c) \(2 \mathrm{CH}_{3} \mathrm{OH}+3 \mathrm{O}_{2} \longrightarrow 2 \mathrm{CO}_{2}+4 \mathrm{H}_{2} \mathrm{O}\)

Short answer

(a) Decomposition; (b) Combination; (c) Combustion.

Step-by-step solution

Analyze Reaction (a)

The given reaction is \(2 \mathrm{NaHCO}_{3} \longrightarrow \mathrm{Na}_{2}\mathrm{CO}_{3}+\mathrm{CO}_{2}+\mathrm{H}_{2}\mathrm{O}\). In this reaction, a single compound (\(\mathrm{NaHCO}_{3}\)) breaks down into multiple products (\(\mathrm{Na}_{2}\mathrm{CO}_{3}\), \(\mathrm{CO}_{2}\), and \(\mathrm{H}_{2}\mathrm{O}\)). This is characteristic of a decomposition reaction, where one reactant yields two or more products.

Analyze Reaction (b)

The reaction \(\mathrm{NH}_{3}+\mathrm{HCl} \longrightarrow \mathrm{NH}_{4}\mathrm{Cl}\) involves two simple reactants (\(\mathrm{NH}_{3}\) and \(\mathrm{HCl}\)) combining to form a single product (\(\mathrm{NH}_{4}\mathrm{Cl}\)). Such a process, where two or more reactants form a single product, is known as a combination reaction.

Analyze Reaction (c)

In the reaction \(2 \mathrm{CH}_{3}\mathrm{OH}+3 \mathrm{O}_{2} \longrightarrow 2 \mathrm{CO}_{2}+4 \mathrm{H}_{2}\mathrm{O}\), an organic compound (\(\mathrm{CH}_{3}\mathrm{OH}\)) reacts with oxygen (\(\mathrm{O}_{2}\)) to produce carbon dioxide (\(\mathrm{CO}_{2}\)) and water (\(\mathrm{H}_{2}\mathrm{O}\)). This is a typical combustion reaction, where a hydrocarbon and oxygen react to form \(\mathrm{CO}_{2}\) and \(\mathrm{H}_{2}\mathrm{O}\).

Key concepts

Combination Reaction

A combination reaction, also known as a synthesis reaction, occurs when two or more substances come together to form a single, new product. This type of reaction can be quite straightforward and is often seen in basic chemical chemistry studies. For instance, in the reaction \(\mathrm{NH}_{3}+\mathrm{HCl} \rightarrow \mathrm{NH}_{4}\mathrm{Cl}\), two substances—ammonia (NH\(_3\)) and hydrochloric acid (HCl)—combine to form ammonium chloride (NH\(_4\)Cl).

Here are a few key characteristics of combination reactions:

• Simplicity: Usually involves simple reactants and results in a relatively simple product.
• Energy: These reactions commonly release energy in the form of heat or light.
• Examples: Formation of water from hydrogen and oxygen is a combination reaction (\(2\:\mathrm{H}_2 + \mathrm{O}_2 \rightarrow 2\:\mathrm{H}_2\mathrm{O}\)).

Combination reactions are fundamental in understanding how different materials can interact to form compounds with entirely new properties.

Decomposition Reaction

A decomposition reaction is essentially the reverse of a combination reaction. In a decomposition reaction, a single compound breaks down into two or more simpler substances. This type of reaction involves a single reactant, which often requires the input of energy in the form of heat, light, or electricity.

For example, the reaction \(2 \mathrm{NaHCO}_{3} \rightarrow \mathrm{Na}_{2}\mathrm{CO}_{3} + \mathrm{CO}_{2} + \mathrm{H}_{2}\mathrm{O}\) is a classic example of a decomposition reaction. In this case, sodium bicarbonate breaks down into sodium carbonate, carbon dioxide, and water.

Here are some characteristics of decomposition reactions:

• Complex to Simple: A single reactant forms multiple products.
• Energy Input: Often requires energy input (like heating) to break chemical bonds.
• Common in Nature: Decomposition occurs naturally as part of processes such as the breakdown of organic matter.

Understanding decomposition reactions is crucial for interpreting many natural and industrial processes.

Combustion Reaction

Combustion reactions are a subset of chemical reactions where a hydrocarbon reacts with oxygen to produce carbon dioxide and water. These reactions are exothermic, meaning they release energy, usually in the form of heat or light. This is why these reactions are responsible for fires and explosions.

In the reaction \(2 \mathrm{CH}_{3}\mathrm{OH} + 3 \mathrm{O}_{2} \rightarrow 2 \mathrm{CO}_{2} + 4 \mathrm{H}_{2}\mathrm{O}\), methanol (\(\mathrm{CH}_{3}\mathrm{OH}\)) combusts in the presence of oxygen to produce carbon dioxide and water.

Key traits of combustion reactions include:

• Reactivity: High-energy release makes these reactions very reactive.
• Oxidation Process: Combustion involves oxidation, which is the addition of oxygen to a substance.
• Applications: Provides energy in engines, power plants, and heating systems.

Combustion reactions are essential for various technological and industrial applications as they provide a significant source of energy used in daily life.