Is delta H a state function?(Hess Law?)

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SUMMARY

Delta H, or enthalpy change, is indeed a state function, as established by Hess's Law, which states that the total enthalpy change for a reaction is the same regardless of the pathway taken. While work (W) is path-dependent, at constant pressure, it can be treated as a state function, leading to the conclusion that delta H is a state function. The discussion highlights the apparent contradiction between the path dependency of work and the state function nature of delta H, ultimately resolving it by recognizing the conditions under which these properties apply.

PREREQUISITES
  • Understanding of thermodynamic concepts, specifically enthalpy and internal energy.
  • Familiarity with Hess's Law and its applications in chemical reactions.
  • Knowledge of state functions versus path-dependent functions in thermodynamics.
  • Basic principles of work in both physics and chemistry contexts.
NEXT STEPS
  • Study Hess's Law in detail, focusing on its implications for enthalpy changes in chemical reactions.
  • Explore the relationship between internal energy (delta U) and work (W) at constant pressure.
  • Investigate the differences in sign conventions for work in physics versus chemistry.
  • Examine case studies where enthalpy changes are calculated using different reaction pathways.
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Chemistry students, educators, and professionals in thermodynamics or physical chemistry who seek to deepen their understanding of state functions and enthalpy changes in chemical reactions.

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is delta H a state function??(Hess Law?)

Is delta H a state function?

We know that delta H=delta U+W (at const P)
so,
we also know that W is path dependent function.So delta H being a sum of delta U and a path dependent function must not be a state function.(point 1)

But there is this Hess Law which allows you to add 2 chemical reactions along with their enthalpy changes.
Lets say water is formed from H2 and O2.lets say water is again formed from H2 and O2 but in a different path.according to Hess law,delta H is same in both cases.
Now doesn't that make delta H a state function?(point 2)

Don't point 1 and point 2 contradict?
Thank You.
 
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sachin123 said:
We know that delta H=delta U+W (at const P)
so,
we also know that W is path dependent function.

What if W is no longer path dependent when you fix P?
 


oh.so even W is a state function in this case then.
so that makes H a state function in general.
Thank you Mapes
 


Also may I extend this and ask,
why are different sign conventions used for 'Work' in physics and chemistry?
in physics we take W +ve when work is done by the system and correspondingly we take it -ve in chemistry.Is there any significance?
 


however i read a text saying that, 'delta H has a defined value for a particular change, regardless of whether or not it's at constant pressure'.

in this case, W is not a state function. then how is it possible?
 

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