Related Experiment Video
Updated: May 31, 2026
06:15
Preparation of Binary and Ternary Deep Eutectic Systems
Published on: October 31, 2019
Phase transitions in the urea/n-nonadecane system by calorimetric techniques
A López-Echarri1, I Ruiz-Larrea, A Fraile-Rodríguez
1Departamento de Física de la Materia Condensada, Facultad de Ciencia y Tecnología, Universidad del País Vasco, Apartado 644, 48080 Bilbao, Spain.
Summary
This study investigates the calorimetric properties of urea and n-nonadecane mixtures during structural phase transitions. Calorimetric analysis reveals anomalies and discusses their influence on phase transition mechanisms.
Area of Science:
- Physical Chemistry
- Materials Science
Background:
- Urea and n-nonadecane mixtures exhibit complex phase behavior.
- Understanding their structural phase transitions is crucial for materials science applications.
Purpose of the Study:
- To perform a calorimetric study of urea/n-nonadecane and its deuterated derivatives around their structural phase transition temperatures.
- To compare results obtained from differential scanning calorimetry (DSC), temperature-modulated (AC) calorimetry, and adiabatic calorimetry.
Main Methods:
- Differential Scanning Calorimetry (DSC)
- Temperature-Modulated (AC) Calorimetry
- Adiabatic Calorimetry
Main Results:
- Identified a main phase transition peak for urea/n-nonadecane at specific temperatures (158.5, 149.4, 154 K).
- Observed small specific heat anomalies at lower temperatures, with reported entropic and enthalpic changes.
- Demonstrated the influence of heating/cooling rates and thermal history on specific heat profiles, including thermal hysteresis and latent heat.
Conclusions:
- The study characterizes the order of phase transitions using thermal hysteresis and latent heat.
- A preliminary analysis of urea and alkyl chain contributions to specific heat and their impact on phase transition mechanisms is presented.
Related Concept Videos
01:15¹H NMR of Conformationally Flexible Molecules: Variable-Temperature NMR
The axial and equatorial protons in cyclohexane can be distinguished by performing a variable-temperature NMR experiment. In this process, except for one proton, the remaining eleven protons are replaced by deuterium. The deuterium substitution avoids the possible peak splitting caused by the spin-spin coupling between the adjacent protons. The remaining proton flips between the axial and equatorial positions.
00:52¹H NMR of Conformationally Flexible Molecules: Temporal Resolution
At room temperature, the chair conformer of cyclohexane undergoes rapid ring flipping between two equivalent chair conformers at a rate of approximately 105 times per second. These two chair conformers are in equilibrium. The rapid ring flipping results in the interconversion of the axial proton to an equatorial proton and an equatorial to the axial proton. Such interconversions are too rapid and cannot be detected on the NMR timescale. Hence, the NMR spectrometer cannot distinguish between the...
02:39Phase Transitions: Melting and Freezing
Heating a crystalline solid increases the average energy of its atoms, molecules, or ions, and the solid gets hotter. At some point, the added energy becomes large enough to partially overcome the forces holding the molecules or ions of the solid in their fixed positions, and the solid begins the process of transitioning to the liquid state or melting. At this point, the temperature of the solid stops rising, despite the continual input of heat, and it remains constant until all of the solid is...
02:41Constant Volume Calorimetry
Calorimeters are useful to determine the heat released or absorbed by a chemical reaction. Coffee cup calorimeters are designed to operate at constant (atmospheric) pressure and are convenient to measure heat flow (or enthalpy change) accompanying processes that occur in solution at constant pressure. A different type of calorimeter that operates at constant volume, colloquially known as a bomb calorimeter, is used to measure the energy produced by reactions that yield large amounts of heat and...
01:19Calorimetry
When objects at different temperatures are placed in contact with each other but isolated from everything else, they attain thermal equilibrium. A container that prevents heat transfer in or out is called a calorimeter, and the use of a calorimeter to make measurements is called calorimetry. Generally, these measurements involve heat or specific heat capacity. The term "calorimetry problem" is used for any problem where the specified objects are thermally isolated from their surroundings. An...
01:23Urea Cycle
The urea cycle describes how liver cells convert ammonia to urea. Ammonia is a toxic waste product of protein catabolism. Land animals must convert ammonia into the less toxic urea which can be safely eliminated by the kidneys through urine. Marine animals excrete ammonia directly, and the surrounding water dilutes the ammonia to safe levels.