Question

Give an example of a combination redox reaction, a decomposition redox reaction, and a displacement redox reaction.

Short answer

Combination: \( 2H_2 + O_2 \rightarrow 2H_2O \); Decomposition: \( 2H_2O_2 \rightarrow 2H_2O + O_2 \); Displacement: \( Zn + CuSO_4 \rightarrow ZnSO_4 + Cu \).

Step-by-step solution

Understanding Redox Reactions

A redox reaction involves the transfer of electrons between two species. This process includes oxidation (loss of electrons) and reduction (gain of electrons). We will identify and give examples for combination, decomposition, and displacement types of redox reactions.

Example of a Combination Redox Reaction

A combination redox reaction involves two elements or compounds combining to form a single compound. For instance, when hydrogen gas reacts with oxygen gas to form water: \( 2H_2 + O_2 \rightarrow 2H_2O \). In this reaction, hydrogen is oxidized (from 0 to +1) and oxygen is reduced (from 0 to -2).

Example of a Decomposition Redox Reaction

A decomposition redox reaction involves a single compound breaking down into two or more products, often with one element being oxidized and another reduced. An example is the decomposition of hydrogen peroxide into water and oxygen: \( 2H_2O_2 \rightarrow 2H_2O + O_2 \). Here, oxygen is both oxidized (from -1 to 0) and reduced (from -1 to -2).

Example of a Displacement Redox Reaction

A displacement redox reaction involves an element in a compound being replaced by a more reactive element. For example, when zinc is dropped into a copper(II) sulfate solution: \( Zn + CuSO_4 \rightarrow ZnSO_4 + Cu \). Zinc is oxidized (from 0 to +2), and copper is reduced (from +2 to 0).

Key concepts

Oxidation

Oxidation is a fundamental concept in redox reactions that involves the loss of electrons by a molecule, atom, or ion. When a substance undergoes oxidation, it increases its oxidation state. Think of it as losing negativity or gaining positivity. For example, when zinc oxidizes during a displacement reaction, it loses electrons and its oxidation state rises from 0 to +2.
Key ideas about oxidation include:

• The substance that oxidizes acts as a reducing agent because it donates electrons to another species.
• Oxidation doesn't necessarily involve oxygen; it refers to electron transfer.
• Tracking oxidation involves understanding oxidation states, which indicate the degree of oxidation in chemical compounds.

Reduction

Reduction complements oxidation and involves the gain of electrons, decreasing the oxidation state of a molecule, atom, or ion. When a substance is reduced, it is essentially gaining negativity or losing positivity. In the example of zinc displacing copper, copper is reduced as it gains electrons, lowering its oxidation state from +2 to 0.
Important points about reduction:

• The substance being reduced is called an oxidizing agent because it receives electrons from another species.
• Reduction can occur without the presence of oxygen; it's about electron acquisition.
• Understanding reduction requires careful consideration of the changes in oxidation numbers.

Combination Redox Reactions

Combination redox reactions occur when two or more elements or compounds unite to create a single compound. A classic example is the formation of water from hydrogen and oxygen. During this process, hydrogen undergoes oxidation (its state changes from 0 to +1), and oxygen undergoes reduction (its state changes from 0 to -2).
Key Features of Combination Redox Reactions:

• Always involve a synthesis process, where reactants come together to form a more complex product.
• Typically involve simple elements or compounds merging.
• Both oxidation and reduction occur simultaneously, reflecting a transfer of electrons.

Decomposition Redox Reactions

Decomposition redox reactions are characterized by a compound breaking down into simpler substances. For instance, hydrogen peroxide decomposing into water and oxygen exemplifies this type. In such reactions, a single reactant yields multiple products, with parts of the compound experiencing oxidation and reduction.
Features of Decomposition Redox Reactions:

• Involve breaking down compounds into less complex components.
• Electron transfer causes changes in the oxidation states of the respective elements involved.
• Typically result in the release or formation of simpler molecules such as gases.

Displacement Redox Reactions

Displacement redox reactions occur when an element in a compound is replaced by a more reactive free element. A notable example is when zinc metal reacts with copper(II) sulfate, resulting in the formation of zinc sulfate and copper metal. Here, zinc loses electrons, becoming oxidized, while the copper ion gains electrons, being reduced.
Understanding Displacement Redox Reactions:

• Usually involve a more reactive metal displacing a less reactive metal in a compound.
• These reactions showcase a series of redox processes driven by reactivity differences.
• Commonly observed in electrochemical cells and metal extraction processes.