Recording-2025-03-14T14:03:25.422Z

Spontaneous Reactions

• Definition: Spontaneous reactions are energetically favorable processes that occur without external energy input.

• Also Known As: Exergonic reactions, which release energy.

• Key Difference: Spontaneous (exergonic) is not the same as exothermic.

  • Exothermic: Relates to heat release during the reaction.

  • Exergonic: Specifically refers to changes in free energy (Gibbs free energy).

• Characteristics:

  • Generally associated with a negative change in Gibbs free energy (ΔG < 0).

  • Typically visualized as downhill reactions in energy diagrams.

Non-Spontaneous Reactions

• Definition: Non-spontaneous reactions require energy input to proceed.

• Also Known As: Endergonic reactions, which absorb energy.

• Characteristics:

  • Typically associated with a positive change in Gibbs free energy (ΔG > 0).

  • Often visualized as uphill reactions in energy diagrams.

Gibbs Free Energy

• Gibbs Free Energy (G): A thermodynamic potential that measures the maximum reversible work that can be performed by a system at constant temperature and pressure.

• Importance in Reactions:

  • Provides insight into the feasibility of a reaction.

  • Non-spontaneous reactions can occur if coupled with spontaneous reactions.

Activation Energy

• Definition: The energy barrier that must be overcome for a reaction to proceed.

• Significance:

  • All reactions, spontaneous or non-spontaneous, have some form of activation energy.

  • Activation energy must be supplied to initiate the reaction, even for spontaneous ones.

Enzymes as Catalysts

• Role of Enzymes: Biological catalysts that speed up reactions by lowering the activation energy.

• Characteristics:

  • Not consumed in reactions; can catalyze multiple reactions sequentially.

  • Facilitate reactions by stabilizing transition states and altering energy barriers without changing free energy changes between reactants and products.

Reaction Dynamics

• Translational Motion: Molecules are constantly moving and interacting within the cytoplasm, aiding in diffusion and reaction rates.

• Bond Interactions:

  • Enzymes make covalent bonds unstable, facilitating reactions.

  • Strong binding affinity implies longer association time, but may slow down dissociation.

• Catalysis Speed: Enzymatic actions can lead to rapid substrate conversion (thousands of molecules per second).

Reaction Coupling

• Concept: Coupling spontaneous (exergonic) and non-spontaneous (endergonic) reactions to drive metabolic pathways.

• Cellular Example:

  • In cell respiration, glucose is processed stepwise to extract energy efficiently, rather than combusted all at once.

Standard Free Energy Change

• Standard Conditions: Used to compare Gibbs free energy changes in biochemical reactions under idealized conditions.

• Calculation:

  • Gibbs Free Energy (ΔG) can be calculated using gas constant, temperature, and concentration of reactants and products.

• Applications: Understanding how certain reactions can drive overall metabolic processes and energy transactions in cells.

Examples of Reactions

• Glucose + ATP → Glucose-1-phosphate + ADP:

  • Non-spontaneous reaction (+23 kJ/mol) that is driven by the release of energy from a spontaneous reaction (e.g., ATP hydrolysis -30.5 kJ/mol).

• Coupling Reactions: The overall change in Gibbs free energy can become spontaneous when combining non-spontaneous reactions with spontaneous ones.