Second Law of Thermodynamics

Definition

The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time, and it will eventually reach a maximum value at equilibrium. This principle highlights the directionality of energy transformations and the inevitable increase in disorder within a system, which plays a crucial role in understanding coupled reactions, free energy changes, and biological processes.

5 Must Know Facts For Your Next Test

1. The second law indicates that natural processes tend to move towards a state of greater disorder or entropy, which is vital for understanding how energy flows in biological systems.
2. In biological contexts, this law explains why organisms require a constant input of energy to maintain order and perform work against entropy.
3. The concept of free energy is closely tied to the second law; only reactions that lead to an increase in overall entropy are spontaneous.
4. In coupled reactions, the energy released from an exergonic reaction can be used to drive an endergonic reaction, illustrating the balance between entropy and energy transfer.
5. The second law has profound implications for metabolism, as living organisms are constantly transforming energy while increasing the universe's total entropy.

Review Questions

• How does the second law of thermodynamics apply to the concept of coupled reactions in biological systems?
  • The second law of thermodynamics emphasizes that for any reaction, the overall entropy must increase. In coupled reactions, a spontaneous exergonic reaction releases energy that can drive a non-spontaneous endergonic reaction. This illustrates how organisms can harness energy transformations while adhering to thermodynamic principles. Ultimately, the coupling allows biological systems to function efficiently despite the natural tendency towards increased disorder.
• Discuss how the second law of thermodynamics influences the concept of free energy in chemical reactions.
  • The second law directly impacts free energy by establishing that only those reactions that increase overall entropy are spontaneous. The change in Gibbs free energy ($$\Delta G$$) determines if a reaction can occur without external energy input. A negative $$\Delta G$$ indicates a process that releases free energy and contributes to increased entropy, aligning with the second law. Understanding this relationship helps predict reaction behavior under various conditions.
• Evaluate the significance of the second law of thermodynamics in understanding metabolic pathways in living organisms.
  • The second law of thermodynamics is crucial for grasping how metabolic pathways operate within living organisms. It explains that organisms must continuously acquire energy to counteract the natural trend toward increased entropy and maintain order. By converting energy from food into usable forms through various biochemical reactions, cells can sustain life processes. This requires careful regulation and coupling of reactions to ensure that the overall entropy increases in compliance with thermodynamic principles while allowing life to thrive.

Related terms

Entropy:

A measure of the disorder or randomness in a system, often associated with the unavailability of a system's energy to do work.

Enthalpy:

A thermodynamic quantity that represents the total heat content of a system, equal to the internal energy plus the product of pressure and volume.

Coupled Reactions: Reactions in which the energy released from one reaction is used to drive another reaction, often involving an unfavorable reaction being driven by a favorable one.