Redox reactions and electrode processes

Introduction

Redox Reactions and Electrode Processes involve the oxidation of one element and reduction of another. Electrode processes include redox reactions where chemical energy turns into electrical power. This forms the basis of an electrolytic cell. The most significant electrode process occurs when a zinc rod is immersed in a copper sulfate solution. A redox process occurs in which zinc is oxidized to Zn2+ ions, and Cu2+ ions are reduced to metal.

Redox Reactions

Redox reactions are chemical reactions where the oxidation states of the reactants change. The reaction includes two processes, a reduction reaction and an oxidation reaction. In a chemical reaction, the component being reduced is known as the oxidizing agent. In contrast, the component being oxidized is known as the reducing agent.

Types of Redox Reactions

The term redox is an abbreviation for reduction-oxidation. The different types of redox reactions are as follows:

Decomposition Reaction

A decomposition process causes a compound to be broken down into two or more parts, at least one of which must be in the elemental form.

2 H2O (l) → 2 H2 (g) + O2(g)

The above reaction is an example of a decomposition reaction. 

Combination Reaction

A chemical reaction in which the reacting elements combine to form a new compound is a combination reaction. Redox reactions include all combustion processes that require elemental dioxygen and those reactions that use elements apart from dioxygen.

C(s) + O2 (g) → CO2(g)

The above reaction is an example of a combination reaction.

Displacement Reaction

An ion (or an atom) in a compound is substituted by another element’s ion (or an atom) in a displacement reaction. Metal displacement and non-metal displacement are the two types of displacement reactions.

In the uncombined condition, metal in a combination can be replaced by another metal. Metal displacement reactions have many uses in metallurgical procedures that extract pure metals from their ores.

CuSO4 (aq) + Zn (s) → Cu (s) + ZnSO4 (aq)

Among non-metal displacement, redox reactions are hydrogen displacement and an infrequent process involving oxygen displacement.

Cl2 (g) + 2 KI (aq) → 2 KCl (aq) + I2 (s)

Disproportionation Reaction

A disproportionation reaction occurs when an element in one oxidation state is oxidized and reduced simultaneously. In a disproportionation reaction, one of the reacting compounds always includes an element that may exist in at least three oxidation states. The element in the form of a reactive substance is in an intermediate oxidation state. The reaction produces both higher and lower oxidation states of that element.

2 H2O2 (aq) → 2 H2O (l) + O2 (g)

Balancing Redox Reactions

Two approaches are implemented to balance the redox reaction chemical equations. One way is associated with the change in the oxidation number of the reducing and oxidizing agents. At the same time, the other method includes dividing the redox reaction into two half-reactions.

Significant Oxidizing Agents

Electronegative element-based molecules, For example, O2, O3 and X2 (halogens)

Compounds have an element in a more oxidized form. KMnO4, K2Cr2O7, HNO3, KClO3 are a few examples.

Metal and non-metal oxidizes. MgO, CuO, CrO3, and P4O10 are examples.

Fluorine is the most powerful oxidizing agent.

Significant Reducing Agents

All metals, such as Na, Zn, Fe, and Al

Several non-metals, including C, Hydrogen, S, and P

Hydracids such as HCl, HBr, HI, and H2S are examples of hydracids.

Few compounds include an element at its lower oxidation state. FeCl2, FeSO4, SnCl2, and Hg2Cl2 are a few examples.

Metallic hydrides such as NaH, LiH, CaH2, and others.

HCOOH is an organic chemical.

Electrode Processes

• Galvanic Cell
• When a zinc rod is dipped in copper sulfate solution, a redox reaction occurs in which zinc is oxidized to zinc ions. Copper ions are reduced to metallic copper caused by direct electron transfer from zinc to copper ions. Heat is also produced during this process
• Removal of zinc metal from copper sulfate solution is required. A redox pair is defined as the presence of both the oxidized and reduced versions of a chemical in an oxidation or reduction half-reaction
• This is illustrated by a vertical line or a slash signifying an interaction between the oxidized and reduced forms. The two redox couples in this experiment are indicated as Zn2+/Zn and Cu2+/Cu
• The following are the two half-reactions:

Oxidation Half-Reaction

Zn (s) → Zn2+ + 2e− 

Reduction Half-Reaction

Cu2+ + 2e– → Cu (s) 

Zinc loses electrons, which copper ions take up to make metallic copper. As a result, the entire redox reaction of zinc and copper is as follows:

Cu2+ + Zn (s) → Cu (s) + Zn2+

Examining the Redox Process in a Zinc and Copper Cell

Zinc electrodes emit zinc atoms, oxidizing to their ionic state because zinc ranks higher in the activity series than copper. As a result, zinc oxidizes more easily than copper.

Zn (s) → Zn2+ + 2e− 

The electron travels from the zinc anode to the copper electrode through the external wire. Eventually, the electrons shall penetrate the copper electron and interact with the copper ions in the solution to produce metallic copper. As a response, the voltmeter records a reading.

Cu2+ (aq) + 2e– → Cu(s) 

• The electrode where oxidation occurs is referred to as the anode. In this instance, the zinc anode gradually deteriorates owing to zinc metal loss while the cell is in operation. Because of electron production at the anode, the concentration of zinc ions will steadily grow. As a result, it is the negative electrode

• Electrode potential is the potential linked to each electrode. If the concentration of each species participating in the electrode reaction is unity and the reaction is carried out at 298 K, the potential of each electrode is said to be the Standard Electrode Potential. The standard electrode potential (E0 ) of a hydrogen electrode is 0.00 volts by convention
• The electrode potential value for each electrode process is a metric of the active species in the process’ inclination to persist in the oxidized/reduced state. A negative E0 indicates that the redox pair is a more effective reducing agent than the H+/H2 couple. A positive E0 means that the redox pair is a less effective reducing agent than the H+/H2 couple

Conclusion

Redox reactions and electrode processes form the basis of the working of cells, including Galvanic cells, Daniel cells, and others. Redox reactions include two simultaneous reactions: an oxidation reaction and a reduction reaction. The redox reactions occur based on oxidation numbers and the strength of reducing agents.