Pathology and Laboratory Medicine Book



Chemical Reaction

Aka: Chemical Reaction, Entropy, Thermodynamics
  1. See Also
    1. Redox Reaction (Oxidoreductase Process, Oxidation-Reduction)
    2. Energy Metabolism
    3. High Energy Molecule
  2. Definitions
    1. Chemical Reaction
      1. Chemical change in which two or more substances are modifed to result in one or more new substances
      2. Reactions affect the rearrangement of atoms or molecules
      3. Results in substances with different properties from the original substances
    2. Thermodynamics
      1. Energy relationships between different states of a system
      2. Properties (heat, work, Temperature, equilibrium) affect the conversion from one state to another
  3. Physiology
    1. Thermodynamics
      1. Energy is conserved (First Law of Thermodynamics)
        1. Energy is equivalent on each side of a chemical equation
      2. Entropy (Second Law of Thermodynamics)
        1. Natural, normal progression and breakdown from a state of order to one of disorder and randomness
        2. Measured as the amount of heat or energy unavailable to do work
        3. Examples: Heat flows to colder regions, Chemical Reactions favor energy loss
    2. Chemical Reaction
      1. Reaction Direction
        1. Reactions follow pathways of net energy loss or release, and stable substances with stronger bonds
        2. When reactions involve a cascade of sub-reactions, the net result is energy loss and stability
        3. Complex biosynthesis in organisms (including humans) requires significant energy loss
        4. Two-way reactions typically involve different mechanisms and enzymes for the different directions
        5. In vivo reactions are limited to the cells that contain the needed substrates and enzymes
          1. Many reactions are limited to certain tissues (e.g. liver, Muscle)
        6. Only one reaction direction is typically active at one time (to prevent wasted activity)
          1. For example, Glycolysis and Gluconeogenesis do not occur simultaneously
          2. Biosynthesis of a substance often occurs in different organs than its biodegradation
          3. Simultaneous, bidirectional reactions result in wasted energy, typically lost as heat
      2. Reaction Rate
        1. Rate is largely determined by the energy needed to trigger the reaction (energy of activation)
        2. Rate increases with warmer Temperatures and higher substrate concentrations, and when enzyme facilitated
        3. Rate decreases with colder Temperatures and higher reaction product concentrations
        4. Rate is independent of the potential energy loss from a given reaction
    3. Enzymes (Proteins) and Ribozymes (RNA) facilitate Chemical Reactions
      1. Lower the energy of activation for a specific reaction, significantly speeding the overall reaction
  4. References
    1. Goldberg (2001) Biochemistry, Medmaster, Miami, p. 4-12

Thermodynamics (C0039808)

Definition (NCI) The branch of physics concerned with the conversion of different forms of energy.
Definition (MSH) A rigorously mathematical analysis of energy relationships (heat, work, temperature, and equilibrium). It describes systems whose states are determined by thermal parameters, such as temperature, in addition to mechanical and electromagnetic parameters. (From Hawley's Condensed Chemical Dictionary, 12th ed)
Definition (CSP) branch of chemistry concerned with heat and other energetic characteristics of chemical reactions and states.
Concepts Occupation or Discipline (T090)
MSH D013816
English Thermodynamic, Thermodynamics, thermodynamic, thermodynamics
Swedish Termodynamik
Czech termodynamika
Finnish Termodynamiikka
Polish Termodynamika
Norwegian Varmelære, Termodynamikk
French Thermodynamique
German Thermodynamik
Italian Termodinamica
Dutch Thermodynamica
Portuguese Termodinâmica
Spanish Termodinámica
Derived from the NIH UMLS (Unified Medical Language System)

Entropy (C0376522)

Definition (MSH) The measure of that part of the heat or energy of a system which is not available to perform work. Entropy increases in all natural (spontaneous and irreversible) processes. (From Dorland, 28th ed)
Concepts Phenomenon or Process (T067)
MSH D019277
English Entropies, Entropy, entropy (thermodynamics), entropy
Swedish Entropi
Czech entropie
Finnish Entropia
Polish Entropia
Norwegian Entropi
French Entropie
German Entropie
Italian Entropia
Dutch Entropie
Portuguese Entropia
Spanish Entropía
Derived from the NIH UMLS (Unified Medical Language System)

chemical reaction (C0596319)

Definition (CSP) chemical change in which the atoms or molecules of two or more substances are rearranged to form one or more additional substances, often having different properties.
Concepts Phenomenon or Process (T067)
English chemical reactions, chemical reaction
Derived from the NIH UMLS (Unified Medical Language System)

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