Oxidation and Reduction: Study Notes for Introductory Chemistry (Chapter 16)

Oxidation and Reduction

Introduction to Redox Chemistry

Oxidation and reduction (redox) reactions are fundamental chemical processes involving the transfer of electrons between substances. These reactions are central to many real-world applications, including energy production, corrosion, and biological processes.

• Oxidation: The loss of electrons by a substance.

• Reduction: The gain of electrons by a substance.

• Redox reactions always involve both oxidation and reduction occurring simultaneously.

Fuel Cell Technology

Hydrogen-Oxygen Fuel Cells

Fuel cells are devices that convert chemical energy directly into electrical energy through redox reactions. The hydrogen-oxygen fuel cell is a prominent example, especially in the context of environmentally friendly vehicles.

• Hydrogen fuel cells use hydrogen gas as a fuel and oxygen from the air as the oxidant.

• The only emission from a hydrogen fuel cell is water, making it environmentally friendly.

• In a hydrogen-oxygen fuel cell, hydrogen and oxygen react to form water:

$2H_2(g) + O_2(g) \rightarrow 2H_2O(g)$

• Hydrogen is oxidized (loses electrons), and oxygen is reduced (gains electrons).

• Electrons flow through an external circuit, generating electricity to power an electric motor.

Example: Hydrogen-powered vehicles use fuel cells to convert hydrogen and oxygen into water and electricity.

Electron Transfer and Covalent Bonds

In the reaction between hydrogen and oxygen, covalent bonds are formed. A covalent bond consists of a shared electron pair. However, because oxygen is more electronegative than hydrogen, the electron pair in the H–O bond is not shared equally; oxygen attracts the electrons more strongly.

• Oxygen in H2O has gained electrons compared to elemental O2.

• This electron gain is the essence of reduction.

Key Terms and Definitions

• Oxidation: Loss of electrons; increase in oxidation state.

• Reduction: Gain of electrons; decrease in oxidation state.

• Oxidizing agent: The substance that is reduced (gains electrons).

• Reducing agent: The substance that is oxidized (loses electrons).

• Electronegativity: The tendency of an atom to attract electrons in a chemical bond.

Applications and Environmental Context

Fuel Cells in Transportation

Fuel cells are being developed for use in electric vehicles as a replacement for internal combustion engines. These vehicles are currently available on a limited basis but are expected to become more widespread in the future.

• Hydrogen is stored as a compressed gas and used to generate electricity in the fuel cell.

• The only emission is water, making these vehicles environmentally friendly.

Example: The Honda FCX Clarity is a hydrogen-powered fuel cell automobile.

Summary Table: Oxidation and Reduction in Hydrogen-Oxygen Fuel Cells

Process	Reactants	Products	Electron Flow
Oxidation (at anode)	H2(g)	2H+(aq) + 2e-	Electrons released
Reduction (at cathode)	O2(g) + 4H+(aq) + 4e-	2H2O(l)	Electrons accepted

Additional info: Fuel cell technology is a practical application of redox chemistry, demonstrating the importance of electron transfer in generating clean energy.