Understanding Hess Law: Enthalpy Summation vs. Heat Change in Chemical Reactions

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SUMMARY

Hess's Law states that the total enthalpy change of a chemical reaction is the sum of the enthalpy changes for each step of the reaction. The discussion contrasts enthalpy changes (dH) with heat changes (dQ) in chemical reactions, questioning the validity of summing heat changes in the same manner as enthalpy. The consensus is that while Hess's Law applies to enthalpy, heat changes do not necessarily follow the same additive property due to differences in thermodynamic principles. Additionally, the discussion touches on the distinctions between thermodynamic and kinetic stability.

PREREQUISITES
  • Understanding of Hess's Law and its application in thermodynamics
  • Familiarity with concepts of enthalpy (dH) and heat (dQ)
  • Basic knowledge of chemical reaction mechanisms
  • Concepts of thermodynamic stability versus kinetic stability
NEXT STEPS
  • Study the principles of thermodynamics, focusing on enthalpy and heat transfer
  • Explore the differences between thermodynamic and kinetic stability in chemical reactions
  • Learn about the applications of Hess's Law in calculating reaction enthalpies
  • Investigate the role of state functions in thermodynamic processes
USEFUL FOR

Chemistry students, educators, and professionals interested in thermodynamics, particularly those studying reaction mechanisms and stability concepts.

syamdcs
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You people heard about hess law means that sum of all enthalpies of chemical reactions takes place but why we only call sum of all enthalpies?

1)
A----B dH1
B----C dH2 HESS LAW
DH = dH1 + dH2

2)
A----B dQ1
B----C dQ2 ?
DQ = dQ1 + dQ2
In the above representations one is associated with enthapy and another is heat
whethe second one is valid or not?if so why?
 
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Welcome to the forums syamdcs,

According to the rules of the forum, you must show your work/attempt before we can offer any assistance. Also, in future, could you please post homework questions in the appropriate forum. Thanks.
 
please i will like u to give me some major diferences btw thermodynamic and kinetic stability
 

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