Question

Which of the following type(s) of reaction(s) generally has/have the same number of reactants and products? I. Single-displacement reaction II. Double-displacement reaction III. Combination reaction A. I only B. II only C. II and III D. I and II

Short answer

D. I and II

Step-by-step solution

- Understand the Types of Reactions

Identify the characteristics of each of the given reaction types: single-displacement, double-displacement, and combination reactions.

- Single-displacement Reaction

In a single-displacement reaction (I), one element displaces another in a compound. General form: \[A + BC \rightarrow AC + B\]. There are two reactants and two products.

- Double-displacement Reaction

In a double-displacement reaction (II), the ions of two compounds exchange places to form two new compounds. General form: \[AB + CD \rightarrow AD + CB\]. There are two reactants and two products.

- Combination Reaction

In a combination reaction (III), two or more substances combine to form a single product. General form: \[A + B \rightarrow AB\]. There are generally two reactants forming one product.

- Compare Reactants and Products

Compare the number of reactants and products for each type of reaction. Single-displacement and double-displacement reactions each have the same number of reactants and products. Combination reactions do not.

- Identify the Correct Options

Based on the comparison, single-displacement and double-displacement reactions have the same number of reactants and products. Hence, the correct options are I and II.

Key concepts

Single-Displacement Reaction

In a single-displacement reaction, also known as a single-replacement reaction, one element replaces another element in a compound. The general form of this reaction is: \[A + BC \rightarrow AC + B\]Where:

• A is a single element.
• BC is a compound.
• AC is a new compound formed.
• B is the displaced element, now a free element.

The key point is that the reaction involves two reactants and yields two products: one element and one compound. Single-displacement reactions often occur in solutions where metals replace metals or non-metals replace non-metals based on reactivity. For example:\[Zn + CuSO_4 \rightarrow ZnSO_4 + Cu\]Here, zinc (Zn) displaces copper (Cu) in copper sulfate (CuSO_4) to form zinc sulfate (ZnSO_4) and free copper (Cu).

Double-Displacement Reaction

Double-displacement reactions, or double-replacement reactions, involve the exchange of ions between two compounds to form two new compounds. The general form of this reaction is:\[AB + CD \rightarrow AD + CB\]Where:

• AB and CD are the original compounds.
• AD and CB are the new compounds formed.

In these reactions, the cations and anions of the two reactants switch places. These reactions are common in aqueous solutions where the reactants are typically ionic compounds. For example:\[Na_2SO_4 + BaCl_2 \rightarrow BaSO_4 + 2NaCl\]In this example, sodium sulfate (Na_2SO_4) and barium chloride (BaCl_2) react to form barium sulfate (BaSO_4) and sodium chloride (NaCl). Double-displacement reactions are characterized by two reactants and two products.

Combination Reaction

A combination reaction, also called a synthesis reaction, involves two or more reactants combining to form a single product. The general form of this reaction is:\[A + B \rightarrow AB\]Where:

• A and B are the reactants.
• AB is the product formed.

These reactions are usually exothermic, releasing energy in the form of heat or light. Combination reactions are straightforward since they typically involve simple compounds or elements reacting to form a more complex compound. For example:\[2H_2 + O_2 \rightarrow 2H_2O\]In this example, hydrogen (H_2) and oxygen (O_2) gases react to form water (H_2O). Note that combination reactions generally form only one product, distinguishing them from other reaction types.

Reaction Types Comparison

When comparing different reaction types, it's essential to focus on the number of reactants and products. Let's break down the key characteristics:

• Single-displacement reactions involve one element replacing another in a compound, with two reactants and two products.
• Double-displacement reactions involve the exchange of ions between two compounds, resulting in two reactants and two products.
• Combination reactions involve multiple reactants forming a single product.

From this understanding, we can determine that both single-displacement and double-displacement reactions maintain the same number of reactants and products. Combination reactions, however, differ as they combine several reactants into one product. This comparison clarifies why single-displacement and double-displacement reactions have equal numbers of reactants and products, while combination reactions do not.