Is enthelpy change during isothermal process zero?

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SUMMARY

During an isothermal process, the change in enthalpy (ΔH) is not zero, despite the temperature remaining constant. For an ideal gas, the internal energy change (ΔU) is zero, leading to the equation dH = PdV + VdP. This indicates that enthalpy is influenced by pressure and volume changes, which are significant during phase transformations such as vaporization and fusion. Therefore, enthalpy is a function of multiple variables, including pressure and state of aggregation, not solely temperature.

PREREQUISITES
  • Understanding of thermodynamic principles, specifically the first law of thermodynamics.
  • Familiarity with the concepts of enthalpy and internal energy.
  • Knowledge of ideal gas behavior and equations.
  • Basic grasp of phase transitions, including vaporization and fusion.
NEXT STEPS
  • Study the relationship between enthalpy and pressure in thermodynamic processes.
  • Explore the concept of phase transitions and their impact on enthalpy changes.
  • Learn about the implications of the first law of thermodynamics in isothermal processes.
  • Investigate real gas behavior and how it differs from ideal gas assumptions.
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Students and professionals in thermodynamics, chemical engineering, and physical chemistry who seek to understand the complexities of enthalpy changes during isothermal processes and phase transformations.

RUSI16
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is enthalpy change during isothermal process zero? if it is zero then what is the significance of enthalpies like enthalpy of vapourization or fussion since during phase transformation temperature remains constant.
 
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RUSI16 said:
is enthalpy change during isothermal process zero? if it is zero then what is the significance of enthalpies like enthalpy of vapourization or fussion since during phase transformation temperature remains constant.
H = U +PV so dH =dU + PdV + VdP. For an ideal gas, dU =0 for an isothermal process, so dH = PdV +VdP.

For melting ice which occurs at constant T, there may be negligible change in P and V, but is ΔU =0?

AM
 
RUSI16 said:
is enthalpy change during isothermal process zero? if it is zero then what is the significance of enthalpies like enthalpy of vapourization or fussion since during phase transformation temperature remains constant.
You answered your own question. Enthalpy is not just a function of temperature. It is also a function of pressure, state of aggregation, and chemical composition.
 

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