Core Concept

Single replacement reactions (also called single displacement reactions) involve one element replacing another in a compound. These reactions follow the general form:

A+BC→AC+B\text{A} + \text{BC} \rightarrow \text{AC} + \text{B}A+BC→AC+B

Where:

• A is a single element.

• BC is a compound.

• A replaces B in BC if A is more reactive than B.

Types of Single Replacement Reactions

1. Metal Replacing Metal:

   • A metal in its elemental form replaces another metal in a compound.

   • Example: Zn+CuSO4→ZnSO4+Cu\text{Zn} + \text{CuSO}_4 \rightarrow \text{ZnSO}_4 + \text{Cu}Zn+CuSO4​→ZnSO4​+Cu

2. Metal Replacing Hydrogen:

   • A metal can replace hydrogen in acids or water (e.g., alkali metals reacting with water).

   • Example: Mg+2HCl→MgCl2+H2\text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2Mg+2HCl→MgCl2​+H2​

3. Halogen Replacing Halogen:

   • A halogen in its elemental form replaces another halogen in a compound.

   • Example: Cl2+2KI→2KCl+I2\text{Cl}_2 + 2\text{KI} \rightarrow 2\text{KCl} + \text{I}_2Cl2​+2KI→2KCl+I2​

The Activity Series

The activity series is a list of metals and halogens ranked by their reactivity. In single replacement reactions, an element can replace another element in a compound only if it is higher on the activity series.

Key Points:

• More reactive elements are at the top of the activity series.

• Less reactive elements are at the bottom.

• Metals at the top of the series (e.g., lithium, potassium) are highly reactive and can replace metals lower in the series.

• Halogens also follow an activity trend, with fluorine being the most reactive.

Predicting Reactions Using the Activity Series

1. Identify the Elements Involved:

   • Look at the single element (A) and the element it might replace in the compound (B).

2. Check the Activity Series:

   • Find both elements in the activity series.

   • If A is higher on the activity series than B, the reaction will occur, and A will replace B.

3. Write the Products:

   • Replace B with A in the compound to predict the products.

4. If A is Lower:

   • If A is lower on the activity series than B, no reaction will occur.