Question

Distinguish between what we mean by a singledisplacement reaction and a double-displacement reaction by giving two examples of each type.

Short answer

A single-displacement reaction involves one element displacing another from a compound, with a general format: A + BC → AC + B. Examples: \(Cu + 2AgNO_{3} \rightarrow Cu(NO_{3})_{2} + 2Ag\) and \(Zn + CuSO_{4} \rightarrow ZnSO_{4} + Cu\). A double-displacement reaction involves two compounds exchanging elements, with a general format: AB + CD → AD + CB. Examples: \(Na_{2}CO_{3} + CaCl_{2} \rightarrow 2NaCl + CaCO_{3}\) and \(AgNO_{3} + NaCl \rightarrow AgCl + NaNO_{3}\).

Step-by-step solution

Definition and Examples of Single-Displacement Reactions

Single-displacement reactions are chemical reactions in which one element (usually a metal) displaces another element (usually a less reactive metal) from a compound. In these reactions, a more reactive metal will replace a less reactive metal in a compound, producing a new compound and element. The general format for a single-displacement reaction is: A + BC → AC + B. Example 1: \(Cu + 2AgNO_{3} \rightarrow Cu(NO_{3})_{2} + 2Ag\) In this example, copper (Cu) is more reactive than silver (Ag) and hence displaces silver from the compound silver nitrate (AgNO3) to form copper nitrate (Cu(NO3)2) and silver metal. Example 2: \(Zn + CuSO_{4} \rightarrow ZnSO_{4} + Cu\) In this example, zinc (Zn) is more reactive than copper (Cu) and hence displaces copper from the compound copper sulfate (CuSO4) to form zinc sulfate (ZnSO4) and copper metal.

Definition and Examples of Double-Displacement Reactions

Double-displacement reactions are chemical reactions in which two compounds (usually ionic) exchange their elements with each other, resulting in the formation of two new compounds. In these reactions, cation (positively charged ion) of one compound combines with anion (negatively charged ion) of another compound and vice versa. The general format for a double-displacement reaction is: AB + CD → AD + CB. Example 1: \(Na_{2}CO_{3} + CaCl_{2} \rightarrow 2NaCl + CaCO_{3}\) In this example, sodium carbonate (Na2CO3) and calcium chloride (CaCl2) exchange their elements to form two new compounds: sodium chloride (NaCl) and calcium carbonate (CaCO3). Example 2: \(AgNO_{3} + NaCl \rightarrow AgCl + NaNO_{3}\) In this example, silver nitrate (AgNO3) and sodium chloride (NaCl) exchange their elements to form two new compounds: silver chloride (AgCl) and sodium nitrate (NaNO3).

Key concepts

Single-Displacement Reaction

A single-displacement reaction, also known as a single replacement reaction, occurs when an element replaces another in a compound. This typically involves metals, where a more reactive metal displaces a less reactive metal from its compound. Such reactions are driven by the relative reactivity of the metals involved. For example, if element A is more chemically reactive than element B, A will replace B in the compound.

• Example: In the reaction \( Cu + 2AgNO_3 \rightarrow Cu(NO_3)_2 + 2Ag \), copper replaces silver because copper is more reactive than silver.
• Example: In the reaction \( Zn + CuSO_4 \rightarrow ZnSO_4 + Cu \), zinc displaces copper from copper sulfate due to being more reactive.

This type of reaction can be identified by its format: \( A + BC \rightarrow AC + B \).

Double-Displacement Reaction

Double-displacement reactions occur when parts of two ionic compounds are exchanged and form two new compounds. This involves the exchange of ions between the reacting compounds, each compound's cation (positive ion) swaps places with the other's anion (negative ion). This often happens in aqueous solutions where the ions are free to move.

• Example: \( Na_2CO_3 + CaCl_2 \rightarrow 2NaCl + CaCO_3 \) shows sodium carbonate and calcium chloride switching ions to form new products: sodium chloride and calcium carbonate.
• Example: \( AgNO_3 + NaCl \rightarrow AgCl + NaNO_3 \) involves silver nitrate and sodium chloride exchanging ions, resulting in silver chloride and sodium nitrate.

Such reactions can be complex, but their format is generally \( AB + CD \rightarrow AD + CB \).

Reactivity Series

The reactivity series is a vital tool used to predict the outcomes of single-displacement reactions. It ranks elements (primarily metals) according to their reactivity, from most to least reactive. This helps determine which metals can displace others from compounds in a reaction.

• Metals higher in the series are more reactive and can displace metals below them from compounds.
• The series is used to explain why, for example, zinc can displace copper in \( Zn + CuSO_4 \rightarrow ZnSO_4 + Cu \) but not vice versa.

Being familiar with this series allows you to anticipate which single-displacement reactions are possible.

Ionic Compounds

Ionic compounds are formed from the electrostatic attraction between positively charged cations and negatively charged anions. In chemical reactions such as single and double-displacement reactions, these ions are often exchanged between compounds, leading to new product formation.

• These compounds typically have high melting and boiling points due to the strong interactions between ions.
• In water, these compounds generally dissolve, separating into their constituent ions which participate freely in reactions.

Understanding ionic compounds and their behavior is crucial in predicting the outcome of many chemical reactions, especially those that occur in aqueous solutions.

Reaction Format

Understanding the format of chemical reactions is essential for writing and balancing chemical equations. Each type of reaction, whether single or double-displacement, follows a specific pattern.

• Single-displacement reactions follow the format: \( A + BC \rightarrow AC + B \).
• Double-displacement reactions follow the pattern: \( AB + CD \rightarrow AD + CB \).

These formats not only help in predicting the products formed but also in verifying that a chemical equation is balanced, meaning that the number of each type of atom is the same on both sides.