How Does Enthalpy Change During the Melting Process?

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SUMMARY

The discussion centers on the enthalpy changes during the melting process of solids and liquids, specifically near the melting temperature (Tm). It is established that the enthalpy of solids is lower than that of liquids due to the energy dynamics of bond formation and breaking. When bonds are formed, energy is released, resulting in a negative enthalpy change, while breaking bonds requires energy input, leading to a positive enthalpy change. This confirms that melting is an endothermic process, as the solid phase has a lower enthalpy compared to the liquid phase.

PREREQUISITES
  • Understanding of enthalpy and its relation to phase changes
  • Familiarity with intermolecular forces and their impact on states of matter
  • Basic knowledge of thermodynamics principles
  • Concept of free energy and its comparison between solid and liquid phases
NEXT STEPS
  • Study the concept of enthalpy in detail, focusing on phase transitions
  • Research the role of intermolecular forces in determining the physical properties of substances
  • Learn about endothermic and exothermic processes in thermodynamics
  • Explore the Gibbs free energy equation and its application in phase changes
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Chemistry students, thermodynamics enthusiasts, and anyone interested in understanding the principles of phase transitions and enthalpy changes during melting processes.

geobob
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I am wondering about the enthalpies of solids and liquids near the melting temperature. I am familiar with free energy, and I know that above Tm, free energy of the solid becomes higher than liquid. However, we have been asked to think about the same question for enthalpy and draw a schematic. I was thinking that the enthalpy term should be related to intermolecular forces, so that it will always be higher for solids. Can anyone help me out with this? I don't know if it is a very simple question, but I am just a beginner.

Thank you!
 
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geobob said:
However, we have been asked to think about the same question for enthalpy and draw a schematic. I was thinking that the enthalpy term should be related to intermolecular forces, so that it will always be higher for solids.
The idea is correct, but remember that bond formation releases energy (negative enthalpy change), while bond breaking requires energy (positive enthalpy change). This is why the solid phase has a lower enthalpy than the liquid phase.

If it were the other way round (as you guessed), then melting would be exothermic - but that's not true.
 

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