Difference between Enthelpy and Heat

In summary, the conversation discusses the relationship between enthalpy and heat, with one participant questioning if they are the same thing. The other participant explains that while they are closely related, enthalpy is a specific type of heat that is determined by the energy released or absorbed during chemical reactions. Enthalpy is also a function of state, while heat is not, and they can only be equal in reversible isobaric reactions. Work done to the system can affect enthalpy, but not necessarily lead to a heat flow.
  • #1
gsingh2011
115
1
I searched this on google but I couldn't find anything. Is enthalpy the same thing as heat? There is a formula, q=m[tex]\Delta[/tex]H, 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[tex]\Delta[/tex]T and q=m[tex]\Delta[/tex]H, then does ms[tex]\Delta[/tex]T=m[tex]\Delta[/tex] so [tex]\Delta[/tex]H=s[tex]\Delta[/tex]T?
 
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  • #2
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.
 
  • #3
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
 
  • #4
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.
 

Related to Difference between Enthelpy and Heat

What is the difference between Enthalpy and Heat?

Enthalpy and heat are closely related concepts in thermodynamics. Both describe energy in a system, but they have different definitions and applications.

How are Enthalpy and Heat defined?

Enthalpy is defined as the total heat content of a system at constant pressure. It is represented by the symbol H and is measured in Joules (J). Heat, on the other hand, is defined as the transfer of energy between two systems due to a temperature difference. It is represented by the symbol Q and is also measured in Joules (J).

What are the units used to measure Enthalpy and Heat?

As mentioned before, Enthalpy is measured in Joules (J). Heat is also measured in Joules (J) as it is a form of energy. However, in some cases, it can also be measured in calories (cal) or British Thermal Units (BTUs).

How are Enthalpy and Heat related?

Enthalpy and heat are related through the equation Q = mCΔT, where Q is the heat transferred, m is the mass of the substance, C is the specific heat capacity, and ΔT is the change in temperature. Enthalpy is also related to heat through the equation H = U + PV, where U is the internal energy, P is the pressure, and V is the volume.

In what situations are Enthalpy and Heat used?

Enthalpy is commonly used in chemical reactions to measure the amount of heat released or absorbed. Heat, on the other hand, is used to describe the transfer of energy between systems, such as in heating and cooling processes. Both are important in understanding and analyzing thermodynamic processes and systems.

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