Difference between Enthelpy and Heat

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Discussion Overview

The discussion centers on the relationship between enthalpy and heat, exploring whether they are equivalent concepts. Participants examine the definitions and implications of enthalpy in various contexts, including thermodynamic processes and chemical reactions.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • One participant questions whether enthalpy is the same as heat, noting the formula q=mΔH and expressing confusion over the definitions.
  • Another participant suggests that enthalpy can be viewed as a specific type of heat related to energy changes during chemical bond formation or breaking.
  • A different participant challenges the correctness of the formulas q = ΔH·m and q = m·s·ΔT, introducing an alternative relationship involving ΔH, temperature, and entropy (ΔH = T·ΔS + ΔG).
  • One participant clarifies that enthalpy is a state function while heat is not, indicating that they cannot be considered the same in general terms. They specify conditions under which enthalpy equals heat, particularly in reversible isobaric processes, and highlight exceptions such as explosive reactions.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between enthalpy and heat, with no consensus reached on whether they are equivalent. Some participants propose specific conditions under which they may align, while others challenge the definitions and relationships presented.

Contextual Notes

Limitations include potential misunderstandings of thermodynamic principles, the dependence on specific conditions for the equivalence of enthalpy and heat, and unresolved mathematical relationships among the variables discussed.

gsingh2011
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I searched this on google but I couldn't find anything. Is enthalpy the same thing as heat? There is a formula, q=m\DeltaH, so it seems like they should be different, but from what I've learned H just seems like heat to me... Also, if q=ms\DeltaT and q=m\DeltaH, then does ms\DeltaT=m\Delta so \DeltaH=s\DeltaT?
 
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They're very closely related. One way to think of it is that enthalpy is a specific type of heat, given by the energy released (or absorbed) by the breaking/formation of chemical bonds. I'm sure someone else can expand on this; I don't want to get into a ton of detail on it just because, well, I don't know a ton of details on it.
 
Are you sure q = delta H.m and q = mS delta T are correct ?
What I learned is delta H = T.delta S + delta G
 
Enthalpy is a function of state, heat isn't. Hence they cannot be the same in general.
Enthalpy is only equal to heat in reversible isobaric reactions if the only work done is volume work (-p Delta V). E.g. if energy is supplied by an electric current, this will change enthalpy but not necessarily lead to a heat flow. Often, reversibility is not crucial as long as the work done to the system is still (-p Delta V). It is clear that this won't hold e.g. in an explosion, when a piston moves so rapidly that shock waves are formed.
 

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