Thermodynamics Flashcards

Thermodynamics Overview

• Thermodynamics describes energy and matter behavior at the macroscopic level.
• It predicts the macroscopic properties of chemical reactions, indicating direction and equilibrium but not reaction speed.

Enzymatic Influence

• Enzymes speed up reactions but do not affect the equilibrium position.

Energy as a State Function

• The energy change in a reaction is independent of the conversion pathway.
• At equilibrium, the ratio of reactants to products remains consistent regardless of the mechanism.

Enthalpy

• Enthalpy change (ΔH) represents the heat generated or absorbed during a reaction: ΔH = Hproducts - Hreactants.
• A positive ΔH indicates absorbed heat, defining the reaction as endothermic.

Entropy

• Entropy measures disorder; the universe tends towards increased disorder and is also a state function.
• The entropy of a molecule includes contributions from translational, rotational, and internal motions.

Entropy and Molecular Interactions

• Condensation of two molecules into one costs translational and rotational entropy.
• Increased temperature typically results in higher system entropy.

Biological Processes

• Biological systems balance entropy and enthalpy to drive reactions.

Entropic and Enthalpic Processes

• Examples include DNA strand association (entropy decrease) and the hydrophobic effect (entropy increase).

Reaction Spontaneity

• Determining reaction spontaneity requires both enthalpy and entropy considerations.
• Gibbs Free Energy (G) combines both: ΔG = ΔH - TΔS.

Gibbs Free Energy

• A negative ΔG indicates a spontaneous reaction; stability of products over substrates is key.
• Factors influencing ΔG are enthalpy (ΔH) and entropy (ΔS).

Reaction Types

• Exergonic: ΔG < 0 (spontaneous, can be endothermic or exothermic).
• Endergonic: ΔG > 0 (not spontaneous, reverse reaction may be spontaneous).
• Equilibrium: ΔG = 0 (no net reaction).

Temperature Effects on Reactions

• Reactions with ΔH (-), ΔS (+) are spontaneous at all temperatures.
• Reactions with ΔH (-), ΔS (-) can be spontaneous only below a specific temperature.
• Reactions with ΔH (+), ΔS (+) are spontaneous above a certain temperature, while those with both ΔH (+) and ΔS (-) are unspontaneous.

Entropy Increase with Temperature

• The TΔS term grows larger as temperature rises, influencing spontaneity.

Coupled Reactions

• An unfavorable reaction can drive a favorable one if the overall ΔG remains less than zero, crucial in metabolic pathways.

ATP as Energy Currency

• ATP hydrolysis is highly exergonic and can drive endergonic reactions, linking energy release and demand.

Transport Dynamics for Molecules

• The transport of uncharged molecules follows the concentration gradient; ΔGo' is zero at equilibrium.
• For charged molecules, the electric potential difference across membranes is significant in determining ΔG, incorporating both concentration and charge.