Question

Describe the identifying characteristics of the following classes of reactions: decomposition, combination, singledisplacement, and double- displacement.

Short answer

Decomposition reactions involve a single compound breaking down into two or more components. Combination reactions involve two or more compounds or elements forming a more complex compound. Single-displacement reactions occur when one element replaces another in a compound. Double-displacement reactions involve the exchange of parts between two compounds to form two new compounds.

Step-by-step solution

Decomposition Reactions

Decomposition reactions are those where a single compound breaks apart into two or more elements or new compounds. It's expressed as \(AB \rightarrow A + B\). Here, AB represents a compound, and A and B could be elements or new compounds.

Combination Reactions

Combination reactions, also known as synthesis reactions, are the exact opposite of decomposition. In a combination reaction, two or more elements or compounds combine to form a more complex compound. It's generally denoted as \(A + B \rightarrow AB\). Here, again A and B could be elements or compounds.

Single-Displacement Reactions

Single-displacement reactions occur when one element displaces another in a compound. The general formula for this type of reaction is \(A + BC \rightarrow B + AC\). Here, element A replaces B in compound BC to form new compound AC.

Double-Displacement Reactions

Double-displacement reactions, also known as metathesis reactions, occur when parts of two compounds swap places to form two new compounds. The general formula is \(AB + CD \rightarrow AD + CB\). Here, AB and CD are compounds that react to form AD and CB.

Key concepts

Decomposition Reaction

Imagine you have a Lego structure representing a compound. A decomposition reaction is like taking that structure apart into individual blocks or smaller structures. In chemical terms, this means a single compound breaks down into two or more elements or simpler compounds. The general formula for this reaction is \[\begin{equation}\rAB \rightarrow A + B\rewline\end{equation}\]with AB being the original compound, and A and B representing the resulting products, which could be any combination of elements or compounds.
For example, when an electric current passes through water (\[\begin{equation}\rH_2O\rewline\end{equation}\]), it decomposes into oxygen and hydrogen gas. This type of reaction is essential in many processes, such as the breakdown of organic matter or the extraction of metals from their ores.

Combination Reaction

On the flip side, a combination reaction is like building a new Lego structure from several individual blocks. This time, two or more elements or compounds come together to form a more complex compound. The general formula is \[\begin{equation}\rA + B \rightarrow AB\rewline\end{equation}\]where A and B can be elements or compounds that combine to form AB.
An everyday example of a combination reaction is the formation of water from hydrogen and oxygen gas. Such reactions are fundamental to the creation of various materials and substances in both nature and industry.

Single-Displacement Reaction

Imagine a dance where one partner switches place with another. In single-displacement reactions, one element takes the place of another element in a compound. It follows the pattern \[\begin{equation}\rA + BC \rightarrow B + AC\rewline\end{equation}\]where element A bumps out element B from compound BC to form a new compound, AC, and releases the displaced B.
This type of reaction is often seen in metal displacement scenarios, such as when a strip of zinc metal is placed in copper sulfate solution, leading to the formation of zinc sulfate and copper metal. It's an essential type of reaction for understanding how certain elements can replace others due to their reactivity.

Double-Displacement Reaction

Double-displacement reactions can be likened to a square dance where couples exchange partners. In chemical terms, components of two compounds exchange places, resulting in the formation of two new compounds. They follow this general formula \[\begin{equation}\rAB + CD \rightarrow AD + CB\rewline\end{equation}\]where AB and CD are initial compounds that swap components to form new compounds AD and CB.
A classic example of a double-displacement reaction is the neutralization of an acid by a base, such as hydrochloric acid reacting with sodium hydroxide to produce sodium chloride and water. These reactions are significant in fields such as chemistry, environmental science, and medicine.