Question

Determine whether each of the following equations represents a combination reaction, a decomposition reaction, or a combustion reaction: (a) ${\mathrm{C}}_3{\mathrm{H}}_8+$ $5{\mathrm{O}}_2⟶3{\mathrm{CO}}_2+4{\mathrm{H}}_2\mathrm{O},(\mathrm{b})2{\mathrm{NF}}_2⟶{\mathrm{N}}_2{\mathrm{F}}_4$ (c) ${\mathrm{CuSO}}_4\cdot 5{\mathrm{H}}_2\mathrm{O}⟶{\mathrm{CuSO}}_4+5{\mathrm{H}}_2\mathrm{O}.$

Short answer

(a) Combustion reaction, (b) Combination reaction, (c) Decomposition reaction.

Step-by-step solution

Identify the Reaction Type for (a)

Look at equation (a) ${\mathrm{C}}_3{\mathrm{H}}_8+5{\mathrm{O}}_2⟶3{\mathrm{CO}}_2+4{\mathrm{H}}_2\mathrm{O}$. We have a hydrocarbon ${\mathrm{C}}_3{\mathrm{H}}_8$ reacting with ${\mathrm{O}}_2$, producing ${\mathrm{CO}}_2$ and ${\mathrm{H}}_2\mathrm{O}$, which is a characteristic of a combustion reaction.

Identify the Reaction Type for (b)

Examine equation (b) $2{\mathrm{NF}}_2⟶{\mathrm{N}}_2{\mathrm{F}}_4$. This reaction takes two smaller ${\mathrm{NF}}_2$ molecules and combines them into a larger molecule ${\mathrm{N}}_2{\mathrm{F}}_4$. Therefore, it is a combination reaction.

Identify the Reaction Type for (c)

Check equation (c) ${\mathrm{CuSO}}_4\cdot 5{\mathrm{H}}_2\mathrm{O}⟶{\mathrm{CuSO}}_4+5{\mathrm{H}}_2\mathrm{O}$. This reaction involves a single compound decomposing into two products ${\mathrm{CuSO}}_4$ and $5{\mathrm{H}}_2\mathrm{O}$, so it is a decomposition reaction.

Key concepts

Combustion Reaction

A combustion reaction is a chemical process where a substance combines with oxygen to release energy in the form of light or heat. These are central to many everyday phenomena, such as burning wood or gasoline. Typically, combustion reactions involve hydrocarbons—compounds made of hydrogen and carbon—reacting with oxygen to produce carbon dioxide and water.
For instance, in equation (a):

• The hydrocarbon is propane, ${\mathrm{C}}_3{\mathrm{H}}_8$.
• When it reacts with oxygen, ${\mathrm{O}}_2$, it forms carbon dioxide, ${\mathrm{CO}}_2$, and water, ${\mathrm{H}}_2\mathrm{O}$.

Combustion reactions are exothermic; they release energy, making them useful as a source of power or heat. Common characteristics involve formation of flames, propagation of gases, and change of substances due to the high temperatures involved. In everyday terms, if it catches fire and burns, it's likely a combustion reaction!

Combination Reaction

In a combination reaction, two or more reactants combine to form a single new product. These reactions are also known as synthesis reactions. They are fundamental in constructing complex molecules from simpler ones, which is vital in the development of new materials and chemical compounds.
Looking at equation (b):

• We have two molecules of ${\mathrm{NF}}_2$
• These combine to result in a single molecule, ${\mathrm{N}}_2{\mathrm{F}}_4$.

Combination reactions are straightforward and typically involve direct interaction without the need for complex conditions. They're common in both natural processes and laboratory settings, serving roles ranging from building chemical structures to fabricating advanced materials. The simplicity of these reactions makes them a favorite for chemical demonstrations.

Decomposition Reaction

Decomposition reactions involve breaking down a single compound into two or more simpler substances. These reactions are the opposite of combination reactions, often requiring an energy input such as heat, light, or electricity to proceed.
Examination of equation (c) shows:

• ${\mathrm{CuSO}}_4\cdot 5{\mathrm{H}}_2\mathrm{O}$ is a hydrated compound.
• It breaks into ${\mathrm{CuSO}}_4$ and $5{\mathrm{H}}_2\mathrm{O}$.

Such reactions are essential for understanding chemical stability and reaction pathways. In real-world applications, decomposition reactions are used in processes like the breakdown of biomolecules in living organisms and the extraction of metals from ores. Often, the decomposition of a compound can provide insight into its structure and the forces holding it together, critical in fields like material science and inorganic chemistry.