Chemical Reactions

Learning Objectives

  • Understand metabolism as the sum total of all chemical reactions maintaining an organism's health and life.

  • Differentiate between anabolic and catabolic reactions:

    • Anabolic reactions: form larger molecules from smaller ones.

    • Catabolic reactions: break down larger molecules into smaller components.

  • Recognize the role of energy in chemical reactions, including types of energy involved.

The Role of Energy in Chemical Reactions

  • Energy Requirement: Chemical reactions require energy to break old bonds and form new ones.

  • Types of Energy:

    • Kinetic Energy: Energy of matter in motion (e.g., lifting a brick).

    • Potential Energy: Energy of position or stored energy (e.g., energy in a completed brick wall).

    • Chemical Energy: Form of potential energy stored in chemical bonds; it is invested when bonds are formed and released when broken.

Distinction Between Kinetic and Potential Energy

  • Kinetic Energy: Energy due to motion.

  • Potential Energy: Stored energy based on the arrangement of components.

Types of Chemical Reactions

  • Exergonic Reactions: Release more energy than they absorb (e.g., catabolism of food).

  • Endergonic Reactions: Absorb more energy than they release, requiring energy input from sources like exergonic reactions.

Forms of Energy Important in Human Functioning

  • Mechanical Energy: Stored in physical systems, powers movement (e.g., muscle movements).

  • Radiant Energy: Energy transmitted as waves; includes the electromagnetic spectrum—important for functions such as vitamin D synthesis in skin cells.

  • Electrical Energy: Involved in nerve and muscle function, supplied by electrolytes in body fluids.

Characteristics of Chemical Reactions

  • Reactants and Products: Reactants are substances that enter a reaction; products are produced.

  • Conservation of Mass: Matter is neither created nor destroyed; all components present in reactants are also in products.

  • Chemical Equations: Represent how reactants convert to products, using arrows to indicate reaction direction.

Fundamental Types of Chemical Reactions

  • Synthesis Reactions: Form larger compounds from smaller reactants (e.g., formation of ammonia from nitrogen and hydrogen).

    • General equation: A + B → AB.

  • Decomposition Reactions: Break larger compounds into smaller components (e.g., ammonia breaking down into nitrogen and hydrogen).

    • General equation: AB → A + B.

  • Exchange Reactions: Involve both synthesis and decomposition processes.

    • General exchange equation: A + BC → AB + C.

Directionality and Reversibility of Reactions

  • Any reaction can theoretically proceed in both directions under the right conditions.

  • Reversibility: Some reactions can easily reverse to return to original reactants.

    • Represented with double arrow: A + BC ⇄ AB + C.

Factors Influencing the Rate of Chemical Reactions

  • Properties of Reactants: Increased surface area facilitates faster reactions (e.g., chewing food increases surface area).

  • Temperature: Higher temperatures increase kinetic energy, leading to faster reactions.

  • Concentration and Pressure: Greater concentration or reduced volume increases likelihood of particle collisions, speeding up reactions.

  • Catalysts: Substances like enzymes increase reaction rates without being consumed, facilitating essential bodily chemical reactions.

    • Enzymes: Specific catalysts that lower activation energy needed for reactions; critical for rapid biochemical processes in the body.