Thermodynamics Overview

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Questions and Answers

Which of the following statements accurately describes entropy?

  • A measure of the amount of disorder or randomness in a system. (correct)
  • A measure of the amount of energy available to do work.
  • A measure of the total energy content of a system.
  • A measure of the amount of heat energy lost during a reaction.

What is the relationship between entropy and the second law of thermodynamics?

  • The second law states that entropy always decreases in a closed system.
  • The second law states that entropy is a measure of the energy lost from a system.
  • The second law states that entropy is a constant value in a closed system.
  • The second law states that entropy always increases in a closed system. (correct)

Which of the following is NOT a characteristic of an exergonic reaction?

  • The reaction requires energy input from the surroundings. (correct)
  • The Gibbs free energy change (ΔG) is negative.
  • The reaction is spontaneous.
  • The reaction releases free energy.

What is the significance of the Gibbs free energy change (ΔG) in determining if a reaction is exergonic or endergonic?

<p>If ΔG is positive, the reaction is endergonic. (B)</p> Signup and view all the answers

How does the first law of thermodynamics relate to the concept of energy transfer in biological systems?

<p>The first law states that energy can be transferred and transformed, but not created or destroyed. (A)</p> Signup and view all the answers

Which of the following processes is an example of an exergonic reaction?

<p>Cellular respiration (B)</p> Signup and view all the answers

Why is it impossible to have 100% efficiency in energy transfer?

<p>Because some energy is always lost as heat due to the second law of thermodynamics. (A)</p> Signup and view all the answers

How do cells use energy to maintain their structure and fight the natural tendency towards disorder?

<p>By carrying out endergonic reactions that require energy input. (A)</p> Signup and view all the answers

What is the difference in Gibbs free energy between the reactants and products in an exergonic reaction?

<p>The products have a lower Gibbs free energy than the reactants. (D)</p> Signup and view all the answers

What is the sign of the change in Gibbs free energy (ΔG) for an exergonic reaction?

<p>Negative (C)</p> Signup and view all the answers

Which of the following statements is TRUE about endergonic reactions?

<p>Endergonic reactions require energy input. (C)</p> Signup and view all the answers

What is the term for the process where an endergonic reaction is coupled to an exergonic reaction to make the overall reaction spontaneous?

<p>Metabolic coupling (D)</p> Signup and view all the answers

Which of the following is an example of an endergonic reaction?

<p>The synthesis of ATP from ADP and inorganic phosphate. (C)</p> Signup and view all the answers

Which of the following conditions are considered 'standard biochemical conditions'?

<p>25°C, 1M concentrations, 1 atm pressure, pH 7 (B)</p> Signup and view all the answers

What is meant by the statement 'if a reaction is endergonic in one direction then it must be exergonic in the other'?

<p>A reaction that requires energy input in one direction will release energy in the reverse direction. (A)</p> Signup and view all the answers

How does the change in Gibbs free energy (ΔG) relate to the equilibrium constant (K) of a reaction?

<p>ΔG is inversely proportional to K. (A)</p> Signup and view all the answers

Flashcards

Gibbs Free Energy

A measure of the amount of usable energy in a system.

ΔG

Change in Gibbs free energy calculated as Gfinal – Ginitial.

Exergonic Reaction

A reaction that releases energy, marked by ΔG < 0.

Endergonic Reaction

A reaction that requires energy, marked by ΔG > 0.

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Coupled Reactions

Reactions where endergonic ones link to exergonic ones to utilize energy.

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Standard Biochemical Conditions

Conditions for ΔG calculation set at 25°C, 1M, 1 atm, pH 7.

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Energy in Reactions

Endergonic reactions must be exergonic in reverse; energy shifts between forms.

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Glucose and ATP Reaction

Glucose + ATP → glucose-6-phosphate + ADP + Pi; ΔG = -4.1 kcal/mol.

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First Law of Thermodynamics

Energy cannot be created or destroyed, only transformed.

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Entropy

A measure of disorder or randomness in a system.

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Enthalpy

Total heat content of a system, equals internal energy plus pressure-volume work.

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Second Law of Thermodynamics

Energy transfer increases the universe's entropy; 100% efficiency is impossible.

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Equilibrium in Reactions

State where ΔG = 0; no net flow in either direction.

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Energy Transformation

The process of changing energy from one form to another.

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Study Notes

Thermodynamics

  • The laws of thermodynamics describe energy transformations in the universe.
  • The first law of thermodynamics states that energy in the universe is constant, meaning it can be transferred and transformed but not created or destroyed. This is also known as the principle of conservation of energy.
  • Entropy is a thermodynamic quantity representing the unavailability of a system's thermal energy for conversion into mechanical work. It is often interpreted as the degree of disorder or randomness in the system.
  • Enthalpy is a thermodynamic quantity equivalent to the total heat content of a system. It equals the internal energy of the system plus the product of pressure and volume.
  • The second law of thermodynamics states that during energy transfer or transformation, some energy is unusable and often lost as heat.
  • 100% efficiency of energy transfer is impossible.
  • In many life-important processes such as photosynthesis and oxidation of glucose, the efficiency is only about 42%.
  • Every energy transfer or transformation increases the entropy (disorder) of the universe.
  • Systems tend to proceed from ordered (low-entropy) states to disordered (high-entropy) states.
  • The entropy of the system plus its surroundings is unchanged by reversible processes.
  • The entropy of the system plus its surroundings increases for irreversible processes.

Exergonic and Endergonic Reactions

  • An exergonic reaction proceeds with a net release of free energy and is spontaneous.
  • ∆G is negative.
  • An endergonic reaction absorbs free energy from its surroundings and is non-spontaneous.
  • ∆G is positive.
  • When ∆G = 0, the process is at equilibrium, with no net flow in either the forward or reverse direction.

ATP

  • ATP is the energy currency of cells.
  • ATP is involved in the transfer of chemical energy.
  • ATP stores energy.
  • Phosphoanhydride bonds in ATP have a large negative ΔG of hydrolysis.
  • ATP is hydrolyzed to couple with something that needs it.

Coupling Reactions

  • Endergonic reactions are coupled with exergonic reactions.
  • If a reaction is endergonic in one direction, it must be exergonic in the other.

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