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Definitions and the First Law of Thermodynamics
Published in Marc J. Assael, Geoffrey C. Maitland, Thomas Maskow, Urs von Stockar, William A. Wakeham, Stefan Will, Commonly Asked Questions in Thermodynamics, 2022
Marc J. Assael, Geoffrey C. Maitland, Thomas Maskow, Urs von Stockar, William A. Wakeham, Stefan Will
Calorimetry is the science of measuring heat associated with physical, chemical or biological processes. These processes can either release (exothermic) or absorb heat (endothermic). We distinguish between direct calorimetry, which is explained in the following questions, and indirect calorimetry. In indirect calorimetry, the amount of heat is calculated indirectly from the measured oxygen consumption. For this purpose, a relationship between heat evolution and oxygen consumption, called the oxycaloric equivalent (–430 to –480 kJ mol−1), is exploited (Gnaiger and Kemp 1990). This is particular useful for large organisms such as humans! Direct calorimetry is performed with a calorimeter. The word calorimetry is derived from the Latin word calor, meaning “heat” and the Greek word μέτρον (metron), meaning measure.
Thermoanalytical Instrumentation and Applications
Published in Grinberg Nelu, Rodriguez Sonia, Ewing’s Analytical Instrumentation Handbook, Fourth Edition, 2019
Kenneth S. Alexander, Alan T. Riga, Peter J. Haines
Calorimetry is defined as the measurement of heat. It has been used to study reactive systems since 1780 when Lavoisier and De Laplace first studied the respiration of a guinea pig in an ice calorimeter (Lavoisier and De Laplace, 1780). The quantity of water collected and the rate of melting gives a thermodynamic and kinetic evaluation for respiration. Since that time, considerable progress has been made in the technology of calorimeters. Lavoisier was restricted to measuring exothermic reactions at 273.15 K and the sensitivity of the instrument was dependent on the accuracy of weighing the melted ice. Modern calorimeters can directly record, exo or endothermic reactions with signals as low as 5 × 10−8 W. Such sensitivity permits greater specificity in the interpretation of calorimetric data than what the ice calorimeter of Lavoisier could achieve.
Physics
Published in Keith L. Richards, Design Engineer's Sourcebook, 2017
Calorimetry is the science of measuring heat and is derived from the Latin calor meaning heat and the Greek metry meaning to measure. All calorimetric techniques are based on the measurement of heat that may be generated (exothermic process), consumed (endothermic process), or simply dissipated by the sample. There are many methods to measure such heat and since its advent in the late eighteenth century, a wide range of techniques have been developed.
Enhancement of the physical parameters due to the dispersion of functionalised gold nanoparticles in a room temperature nematic liquid crystal
Published in Liquid Crystals, 2023
Pratibha Tripathi, Rahul Uttam, Sandeep Kumar, Roman Dabrowski, Ravindra Dhar
The calorimetry technique is usually used to determine the transition temperatures and other thermodynamic parameters of materials. Initially, DSC is permitted to operate at a scan rate of 5.0°C/min for the first three cycles to stabilise the thermodynamic parameters of the system. DSC thermograms for GNPs dispersed nematic system are shown in Figure 2. DSC thermograms for pure NLC are already reported in previous publications of our group [27]. DSC thermograms suggest that nematic to isotropic transition temperature (TN-I) is 47.1°C for composite 1, and 49.6°C for composite 2 whereas 51.5°C for pure NLC [27]. Hence, the value of TN-I has decreased by 4.4°C for composite 1 and by 0.9°C for composite 2 with respect to pure NLC. When nanoparticles are dispersed in the LC host medium, firstly at low concentration, the composite system shows a reduction in the value of TN-I as compared to that of the pure NLC [27]. This is because the average spacing between mesogenic host molecules is increased due to the presence of nanoparticles in the host matrix, and hence the LC matrix is diluted. This dilution effect has been suggested by Gorkunov and Osipov [28]. The effect reduces the average strength of intermolecular interactions, and hence nematic ordering in the nematic phase [29,30], thereby decreasing the transition temperature. The ordering in the nematic phase is enhanced as the concentration of nanoparticles in the host matrix is increased 2.5 times of the initial concentration (for composite 2), and the system shows less decrement in the transition temperature. This could be due to parallel orientation of NPs along the LC, hence improving the nematic ordering of LC mesogens [28]. The microscopic textures of the pure NLC have already been reported, for both planar and homeotropic orientations of pure nematics in the earlier publications of our group [27,31,32].