Thermochemistry (Enthelpy) queery

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Enthalpy (H) is defined as the sum of internal energy (U) and the work done due to expansion at constant pressure, expressed as H = U + pV. In thermochemistry, the change in internal energy is represented by the equation ΔU = q - pΔV, where q is the heat change. At constant pressure, the term pΔV becomes negligible, allowing enthalpy to simplify the calculation of heat changes. This convenience makes enthalpy the preferred measure in many thermodynamic processes.

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  • Understanding of thermodynamic principles, particularly internal energy and enthalpy.
  • Familiarity with the first law of thermodynamics.
  • Knowledge of pressure-volume work in thermodynamic systems.
  • Basic grasp of heat transfer concepts.
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  • Study the derivation of the enthalpy equation H = U + pV.
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I know that: Change in Internal Energy = Heat change - (pressure X change in volume)

and at constant volume PV is negligable.

But i heard that ENTHALPY is like internal energy but at constant PRESSURE, so PV becomes negligable and enthalpy = heat change - (PV) PLUS (PV) = heat change.

How come at constant pressure, we just use enthalpy (heat change)??

I hope you understood the question, help is very much appreciated! thankyou!
 
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Enthalphy and internal energy are two similar yet different things. Enthalpy is defined as the sum of internal energy and work due to expansion, that si:
H = U + pV
We usually use enthalpy because it is easier to keep pressure constant than to keep volume constant. Its just a matter of convenience.
 

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