Understanding Enthalpy and Entropy: Key Factors in Chemical Reactions

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SUMMARY

The discussion focuses on the relationship between enthalpy and entropy in chemical reactions, emphasizing that enthalpy change is constant for a specific compound as long as the reaction occurs, while free energy changes vary with temperature and pressure. The conversation highlights that higher temperatures can increase the rate of unfavorable reactions, affecting the overall enthalpy. Additionally, it clarifies that to determine the spontaneity of a reaction, one must consider free energy changes rather than relying solely on entropy values.

PREREQUISITES
  • Understanding of enthalpy and its relation to bond energies
  • Knowledge of free energy changes in chemical reactions
  • Familiarity with the concepts of temperature and pressure effects on reactions
  • Basic principles of thermodynamics
NEXT STEPS
  • Research the Gibbs Free Energy equation and its applications
  • Study the impact of temperature on reaction kinetics
  • Explore the relationship between enthalpy, entropy, and spontaneity
  • Learn about the TdS term in thermodynamic equations
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Chemistry students, educators, and professionals interested in thermodynamics and the principles governing chemical reactions.

yifan
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I've got two questions here.
Why is the enthalpy cahnge for a specific compound differs when temperature, pressure is different?
Can we use the entropy change to deduse whether an reaction can happen naturally?
Thank u
 
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The enthalpy change pertains to the level of the chemical equation and thus it is constant as long as the reaction takes place; since enthalpy changes pertains to bond energies. What you are referring to, I believe is, free energy changes. Free energy changes differ at different temperatures and pressures, which can be due to several reasons. For one, the rate of the unfavorable reaction will be increased relative to the favorable reaction at higher temperatures, thus the enthalpy of the reaction as a whole will be different at different temperatures since different proportions, relating to the chemical equation, of products will be formed (think enthalpy change per mole). Also at higher temperatures the value of TdS becomes significant. In order to calculate the spontaneity of a reaction one needs to know this free energy change, entropy value will not be sufficient.


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That is great, thank u again. :smile:
 

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