Chemical Reactions: Classification, Kinetics, and Redox Principles

Classification of Chemical Reactions

Criteria for Classification

• Energy: Endothermic (absorbs heat, ΔH > 0) and Exothermic (releases heat, ΔH < 0).
• Kinetic: Reaction speed (Slow vs. Fast reactions).
• Direction: Reversible vs. Irreversible reactions.
• Nature of Reagents: Acid-base and Oxidation-reduction (Redox).

Factors Affecting Reaction Rates

• Concentration: Increasing concentration increases reaction rate.
• Temperature: Increasing temperature increases reaction rate.
• Surface Area: Increasing the contact surface between reactants increases reaction rate.

Reaction Directionality

A reaction proceeds until the limiting reagent is consumed in a closed system. Reversible reactions are characterized by occurring in both directions.

Properties of Acids and Bases

Acids

• Sour taste and corrosive nature.
• Solutions tend to be thinner.
• Change the color of natural dyes.
• Lose properties when reacting with a base.

Bases

• Bitter taste and corrosive nature.
• Oily or slippery touch when concentrated.
• Degreasing power.
• Change the color of natural dyes.
• Lose properties when reacting with an acid.

Acid-Base Definitions

• Strong Acid/Base: Substances that dissociate completely in aqueous solution.
• Weak Acid/Base: Substances that exist in equilibrium.
• Hydronium (H₃O⁺): Formed in acidic solutions.
• Electrolytes: Substances that dissociate into hydroxyl ions (OH⁻) and cations in water.
• Neutralization: The reaction between hydrogen ions and hydroxyl ions to form water.

The pH Scale

• Acidic: pH < 7
• Basic: pH > 7
• Neutral: pH = 7

Redox Reactions

Redox reactions involve the exchange of electrons between reagents:

• Oxidation: The process where a substance loses electrons.
• Reduction: The process where a substance gains electrons.
• Reducing Agent: The species that is oxidized (loses electrons).
• Oxidizing Agent: The species that is reduced (gains electrons).

The oxidation number of an atom in a compound is defined as the charge the atom would possess if the compound were purely ionic.