Why am i getting less melting enthalpy in second heating? Isn't it supposed to be higher?` what can be the possible cause behind this?
Hi Md Jarzin Shabit Zidan
Your second melting peak occurs at a lower temperature than the first, and is somewhat broader. This is typical of the melting of an impure material. Most likely you had some decomposition during the first melting.
Melting is always an endothermic process (requires heat input)
Possible Causes for the Observed Curve (Lower "Melting" Enthalpy in the Second Heating compared to the First Exotherm):
Why the "Melting" Enthalpy (second endotherm) is Lower (in magnitude) than the Initial Exotherm:
It's not that the melting enthalpy is "lower than it's supposed to be" relative to the first event. They represent different phenomena:
- Initial Exotherm: Heat released during crystallization/reaction.
- Second Endotherm (Melting): Heat absorbed to melt the formed crystals.
Note that the 2-nd heating melting enthalpy (20.8 J/g) is very close to the crystallization enthalpy (20.94 J/g), whereas the 1-st heating enthalpy is more than twice high (/7.65 J/g). It means either the crystallization conditions has not allowed complete crystallization, or the crystallizability has been partially lost.
- Badges
- Science topic
- Similar topics
- Linguistics
- Philology
- Classical Philology
- Manuscripts