Chapter 1: Introduction to Chemical Reactions

Continuation of Chemistry Chapter 2 PowerPoint

Introduction to Chemical Reactions

  • Chemical Reaction Definition:

    • A process where either a covalent bond or ionic bond is formed or broken.

  • Types of Chemical Reactions:

    • Overview: Understand the functions and appearances of reactions.

    • Major Types of Reactions: Three essential types: decomposition reactions, synthesis reactions, and exchange reactions.

Decomposition Reactions

  • Definition:

    • The breakdown of a large molecule into smaller fragments.

    • Term: Catabolism

      • A specific type of decomposition reaction that releases kinetic energy.

      • Exergonic Reaction: A type of catabolic reaction that releases energy necessary for cellular work.

  • Example of Catabolic Reaction:

    • Ingestion of meals containing large complex molecules broken down into smaller parts for absorption and energy.

  • Hydrolysis Reaction:

    • Definition: The decomposition reaction involving water.

      • Hydro translates to water and lysis means breakdown.

    • Equation Explanation:

      • Reactants on the left and products on the right, with the general representation of decomposition as:
        AB
        ightarrow A + B

    • Example with Sodium Chloride (NaCl):

      • When water is added to salt (NaCl), it disintegrates into sodium (Na) and chlorine (Cl).

      • This reaction releases energy, contributing to electrolyte conduction.

Synthesis Reactions

  • Definition:

    • Forming larger molecules from smaller ones. (Opposite of decomposition.)

    • Equation Representation:

      • AB+CD→AC+BD

    • Energy Consumption in Synthesis:

      • Requires energy input to build larger structures.

  • Example: Building a Lego set utilizes energy to assemble pieces into a complete set.

  • Specific Type: Dehydration Synthesis Reaction

    • Definition: Removal of water from reactants to allow formation of larger molecules.

    • Example: In dehydration synthesis, small products produce water as they combine.

  • Terms for Synthesis Reactions:

    • Anabolism: Synonymous with synthesis; involves constructing larger molecules and requires energy (endergonic reaction).

Exchange Reactions

  • Definition:

    • Simultaneous synthesis and decomposition reactions where molecules are exchanged.

    • Example equation:

      • AB+CD→AC+BD

  • Application: Useful for neutralizing strong acids/bases within the body; acts as buffers.

Reversible Reactions

  • Definition:

    • Reactions that can occur in both directions, allowing for synthesis and decomposition interchangeably.

  • Equilibrium:

    • A balanced state where synthesis and decomposition occur at equal rates.

Enzymes

  • Definition:

    • Biological catalysts that are typically proteins and facilitate chemical reactions by lowering activation energy.

  • Key Characteristics of Enzymes:

    • Reusable: Not consumed in reactions.

    • Specific: Each enzyme typically interacts with specific substrates (reactants).

    • Mechanism: Lock and Key fit model, where the specific substrate binds to an active site on the enzyme.

      • Example Illustration:

        • Substrate one binds to an enzyme but not substrate two.

  • Alteration Feature:

    • While enzymes may change shape during interactions, they return to a normal state afterward.

Environmental Influence on Enzymes

  • Denaturation:

    • The alteration of enzyme shape due to inappropriate pH and temperature causing loss of function.

    • Example of Denaturation:

      • Salivary amylase functions at neutral pH (7) but denatures in acidic environments (like the stomach).

    • Optimal Conditions:

      • Enzymes require specific pH and temperature ranges for proper functioning.

Energy

  • Definition:

    • The capacity to perform work.

    • Types of Energy:

      • Potential Energy: Energy stored, not currently doing work (e.g., water behind a dam).

      • Kinetic Energy: Energy of motion, actively performing work (e.g., water flowing).

  • Exergonic vs. Endergonic Reactions:

    • Exergonic: Net release of energy (related to catabolism).

      • Condition: Energy released is greater than the activation energy.

    • Endergonic: Requires energy absorption for reaction (related to anabolism).

      • Condition: Requires energy to initiate the reaction.

Understanding pH

  • Definition of pH:

    • Measurement of hydrogen ion concentration.

    • Formula: pH = - ext{log}[H^+]

    • Represented as moles per liter (mol/L).

  • pH Scale Interpretation:

    • Scale ranges from 0 to 14:

      • 0-7 = Acidic (high H+ concentration);

      • 7 = Neutral;

      • 7-14 = Basic (lower H+ concentration).

  • Visual Representation:

    • Acidic substances are strong H+ donors (like vinegar), while bases may cause harm (like ammonia).

Review Questions

  • 1. Ionic bond breakdown releases blank:

    • Answer: Electrolytes (conduct electricity in water).

  • 2. Type of bond between different water molecules:

    • Answer: Hydrogen bond.

  • 3. Bond formed by equal sharing of electrons:

    • Answer: Nonpolar covalent bond.

  • 4. Term for denatured enzyme due to environmental changes:

    • Answer: Denatured or denaturation.

  • 5. pH comparison (higher concentration of hydrogen ions):

    • Answer: pH of 2 is greater than pH of 5 in hydrogen ion concentration.