Introduction to Thermodynamics and Spontaneous Reactions
Energy Principles
First Law of Thermodynamics: Energy cannot be created or destroyed, only transformed.
Applies to biological reactions in the body.
Energy is primarily derived from the sun, mainly in the form of light energy.
Exit as heat.
Spontaneous Reactions:
Occur without external energy input (e.g., no heat or ATP required).
Often exothermic, releasing energy.
Example: Falling marbles on the floor; no energy needed for scattered arrangement.
Thermodynamics in Biology
Thermodynamics: Study of energy transformations.
Photosynthesis: Plants convert light energy into chemical energy (e.g., glucose).
Humans and animals consume plants/animals for energy.
This energy provides the heat that supports metabolic processes.
Key Concepts in Spontaneous Reactions
Entropy (ΔS): Measure of disorder or randomness.
Second Law of Thermodynamics: Total entropy (disorder) of an isolated system tends to increase.
Higher entropy: More spontaneous reactions.
Example: Ice melting increases disorder, releasing heat.
Enthalpy (ΔH): Measure of heat content of a system.
Exothermic Reactions: Release heat (ΔH < 0). Favorable for spontaneity.
Endothermic Reactions: Absorb heat (ΔH > 0). Not favorable unless compensated by increased entropy.
Free Energy Change (ΔG):
Determines spontaneity of reactions:
ΔG < 0: Spontaneous (exergonic).
ΔG > 0: Non-spontaneous (endergonic).
Relation:( ext{ΔG = ΔH - TΔS} )
T = temperature in Kelvin
When ΔH is negative (heat released) and ΔS is positive (increase in disorder), ΔG is negative leading to spontaneity.
Concept Visualization
Energy Graph:
Going uphill signifies a non-spontaneous reaction (requires energy).
Going downhill signifies a spontaneous reaction (energy is released).
Comparison of Reactions
Spontaneous Reactions: No energy is needed, they often release heat and increase entropy.
E.g., glucose oxidation to carbon dioxide and water is spontaneous.
Non-Spontaneous Reactions: Require energy input to occur, typically exhibit positive ΔG.
Example: Formation of sucrose from glucose and fructose requires energy input.
Reactions in Biological Systems
Coupled Reactions: Spontaneous reactions can drive non-spontaneous ones by coupling with ATP breakdown.
Metabolism: Totality of chemical reactions including:
Catabolic Pathways: Break down molecules, releasing energy (e.g., digestion).
Anabolic Pathways: Build larger molecules from smaller ones, requiring energy.
Four stages of catabolism:
Digestion
Acetyl CoA production
Citric Acid Cycle
ATP Production (via Electron Transport Chain)
Summary of Reaction Favorability
Spontaneous Conditions:
ΔH negative (exothermic)
ΔS positive (increased disorder)
Cannot have both ΔH and ΔS positive or negative simultaneously for spontaneity.
Changes in temperature can influence ΔG by:
Making a reaction spontaneous if conditions allow for an increase in entropy.
Study Strategies
Review concepts of exergonic and endergonic reactions, understanding their thermodynamic manifestations.
Familiarize with definitions of metabolic pathways and their sequencing in ATP production.
Understand the visual representation of energy transactions in spontaneous vs. non-spontaneous reactions (hills).
Reflect on analogies given - like energy transfer compared to a machine needing power to operate.
Practice applying the laws of thermodynamics to hypothetical scenarios for better comprehension.