Question

Which is a composition reaction and which is not? a) \(\mathrm{NaCl}+\mathrm{AgNO}_{3} \rightarrow \mathrm{AgCl}+\mathrm{NaNO}_{3}\) b) \(\mathrm{CaO}+\mathrm{CO}_{2} \rightarrow \mathrm{CaCO}_{3}\)

Short answer

b is a composition reaction; a is not.

Step-by-step solution

Understand Composition Reactions

A composition reaction, also known as a synthesis reaction, occurs when two or more substances combine to form a single product. The general form is: \[ A + B \rightarrow AB \] where A and B are reactants, and AB is the product. In other words, multiple reactants form one product.

Analyze Reaction a

Consider the reaction: \[ \mathrm{NaCl} + \mathrm{AgNO}_3 \rightarrow \mathrm{AgCl} + \mathrm{NaNO}_3 \]Here, two compounds (\(\mathrm{NaCl}\) and \(\mathrm{AgNO}_3\)) react to form two new compounds (\(\mathrm{AgCl}\) and \(\mathrm{NaNO}_3\)). Since there are multiple products, this is not a composition reaction. This is an example of a double displacement reaction.

Analyze Reaction b

Consider the reaction: \[ \mathrm{CaO} + \mathrm{CO}_2 \rightarrow \mathrm{CaCO}_3 \]In this reaction, two reactants (\(\mathrm{CaO}\) and \(\mathrm{CO}_2\)) combine to form a single product (\(\mathrm{CaCO}_3\)). This fits the general form of a composition reaction.

Determine which is a Composition Reaction

Based on the analysis of each reaction: - Reaction a is not a composition reaction as it results in multiple products. - Reaction b is a composition reaction as it forms a single product from multiple reactants.

Key concepts

Composition Reaction

A composition reaction is an essential concept in the study of chemical reactions. It is also commonly referred to as a synthesis reaction. Understanding this reaction helps in identifying processes where multiple substances come together to create a single, more complex product.

In a composition reaction, you typically have two or more reactants that merge to form one unified product. This can be represented by the general equation: \[ A + B \rightarrow AB \] where \(A\) and \(B\) are reactants and \(AB\) is the resultant product. The defining characteristic of a composition reaction is the formation of a singular product from multiple reactants.

For example, the reaction of calcium oxide \((\mathrm{CaO})\) with carbon dioxide \((\mathrm{CO}_2)\) to produce calcium carbonate \((\mathrm{CaCO}_3)\) is a classic representation of a composition reaction. This aligns perfectly with the idea of synthesis, as the separate entities \((\mathrm{CaO}\) and \(\mathrm{CO}_2)\) unite to form one compound: \((\mathrm{CaCO}_3)\). This singularity in the resultant product is the hallmark of a composition reaction.

Synthesis Reaction

Synthesis reactions are a straightforward type of chemical reaction where the primary goal is creating more complex products from simpler reactants. The synthesis reaction is notably identified by its process of combining two or more reactants to result in one product.

The general form of a synthesis reaction can be represented as: \[ A + B \rightarrow AB \] This matches exactly with the composition reaction's format because both involve creating a singular product. However, the term "synthesis" emphasizes the creative aspect of forming one product, much like composing something new from simpler substances.

A great example of a synthesis reaction is when elemental sodium \((\mathrm{Na})\) combines with chlorine gas \((\mathrm{Cl}_2)\), resulting in the formation of sodium chloride \((\mathrm{NaCl})\). Here, individual elements are synthesized into a compound, demonstrating how synthesis reactions are pivotal in forming new substances.

Double Displacement Reaction

Double displacement reactions are a different class of chemical reactions where the elements of two reactants swap partners to form two new products. These reactions are also known as metathesis reactions.

The general form of a double displacement reaction is as follows: \[ AB + CD \rightarrow AD + CB \] In this type of reaction, the cations and anions of two different molecules swap places, forming two entirely different compounds. The crucial part here is the exchange, where no singular product is formed, distinguishing it from composition reactions.

Using the earlier example: \[ \mathrm{NaCl} + \mathrm{AgNO}_3 \rightarrow \mathrm{AgCl} + \mathrm{NaNO}_3 \] In this case, sodium chloride \((\mathrm{NaCl})\) and silver nitrate \((\mathrm{AgNO}_3)\) swap parts to form silver chloride \((\mathrm{AgCl})\) and sodium nitrate \((\mathrm{NaNO}_3)\). Here, the two products indicate it's a double displacement reaction, as both resulting compounds differ from the original ones, unlike the singular product in composition reactions.