WHY does the 2nd law of Thermodynamics work?

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SUMMARY

The discussion centers on the Second Law of Thermodynamics, specifically addressing the concept of entropy and its implications for energy transformations in chemical reactions. Participants explore the equation G = H - TS, where G represents the energy available for work, H is the enthalpy of the reaction, and TS accounts for the temperature and entropy. The conversation highlights the paradox of spontaneous reactions that increase disorder, such as the melting of ice, and the necessity of breaking molecular bonds, which requires energy input. Ultimately, the discussion emphasizes the importance of understanding the interplay between energy, entropy, and molecular arrangements in thermodynamic processes.

PREREQUISITES
  • Understanding of thermodynamic principles, specifically the Second Law of Thermodynamics
  • Familiarity with the Gibbs free energy equation (G = H - TS)
  • Knowledge of enthalpy and entropy concepts in chemical reactions
  • Basic grasp of molecular behavior during phase changes (e.g., solid to liquid)
NEXT STEPS
  • Research the implications of the Second Law of Thermodynamics in real-world systems
  • Study the Gibbs free energy and its role in predicting reaction spontaneity
  • Explore the relationship between temperature, entropy, and phase changes in detail
  • Investigate specific examples of spontaneous reactions and their thermodynamic properties
USEFUL FOR

Students of chemistry, physicists, and anyone interested in the principles of thermodynamics and energy transformations in chemical processes.

Pjoseph
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Dear All

Can't get my head around this.

Entropy of the universe (system+surroundings) always increases.
But why?
G = H - TS
G = Energy available for work
H = Enthalpy of reaction
How can the energy available be greater than the enthalpy of the reaction?
There must be some input from the 'rearrangement' of the molecules?
Ok I can accept that.
When S is positive for a chemical reaction there is more energy from the work than H dictates.
How can it come from a a reaction becoming more disordered?
This requires breaking bonds eg. Solid to liquid which REQUIRES energy. Logically more disordering reactions should be less spontaneous due to the additional energy required to break up the ordered molecules.

Thereby making it more difficult to break things up than to put them together.
Please Help
 
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Welcome Pjosheph.
Pjoseph said:
This requires breaking bonds eg. Solid to liquid which REQUIRES energy. Logically more disordering reactions should be less spontaneous due to the additional energy required to break up the ordered molecules.
Thereby making it more difficult to break things up than to put them together.
Please Help
One must keep a 'tally' of the total energy & entropy properly. Consider what happens when you put a cube of ice on a hot pan -both kept inside a sealed box. Does the ice melt spontaneously? Also, does the entropy decrease as the volume decreases upto 4 C?
 

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