Liquid calorimeter

In a method used by Thomsen the given liquid, e.g. a solution, was used as the calorimeter liquid and heat given to it by the combustion of hydrogen or by a chemical reaction (e.g. the dilution of sulphuric acid, in a vessel immersed in the liquid. A known mass of heated solid can also be immersed in the liquid in a calorimeter. Schiff enclosed the liquid in a platinum vessel of cross-shaped section, containing a thermometer. This was heated to a given temperature and then put into the calorimeter, and stirred round in the water. The liquid was in layers only 1 cm. thick and a rapid equalisation of temperature was thus ensured. Schlesinger heated the liquid electrically and deduced the rise in temperature from the measured increase in volume and the coefficient of expansion. Specific heats of liquids at low temperatures ca,n be determined by a modification of the Nernst calorimeter, in which the liquid in a small steel vessel contained in a... 

The enthalpies of reactions (2), (3), and (5) were determined in a variable temperature calorimeter with an isothermal jacket (Fig. 1). The calorimeter was constructed in accordance with the recommendations given in [24, 26]. A cylindrical calorimeter casing was made of 0.2-mm-thick nickel sheet. The calorimeter liquid was 2 kg of distilled water. The evaporation of the water was prevented by pouring 8.4 g of vaseline oil on its surface. 

Tensile test device, liquid nitrogen (thermostat), calorimeter vessel,0liquid nitrogen (calorimeter liquid), calibration heater, outflow tube for gaseous nitrogen,... 

This type of calorimeter may be known from school or university, where it is often used to demonstrate the experimental determination of heat capacities. Figure 7.9 shows the construction of a mixing calorimeter. Here the calorimeter liquid fills a vessel that is thermally insulated from the surroundings as thoroughly as possible. 

Classic mixing calorimetry represents the historically most important means for the determination of heat capacities. For this purpose, a sample of temperature Ts is introduced directly into the calorimeter liquid, which has the temperature Tini. Thereupon the calorimeter liquid assumes the temperature Tfin after... 

This balance, however, only applies to the ideal case in which the entire heat lost by the sample serves to heat the calorimeter liquid without any losses. In reality, the calorimeter vessel and other components are heated as well, apart from the thermal leakage, so that only part of the heat raises the temperature of the calorimeter liquid. Under such circumstances,... 

Mixing calorimetry with water as the calorimeter liquid was already introduced in the mid-eighteenth century for the measurement of heat capacities. Calibration was done likewise with water until the mid-nineteenth century. For this purpose, a given mass of water m (specific heat capacity =1 cal g at that time) of known temperature %, was poured into the calorimeter, and the subsequentiy established temperature of the mixture Tg was measured. Thus,... 

But, of course, the other reactant may also be a solid or a gas. Moreover, the calorimeter liquid may consist of a molten metal in which solid metals are subsequently dissolved. In another type of calorimeter, a mixture of reactants or a certain substance is enclosed in the reaction vessel, and the heat flow rate and... 

Calorimeter vessel, calorimeter liquid (reagent 1),(3) stirrer with ampoule breaker, 0 ampoule with reagent 2... 

The heat of adsorption is an important experimental quantity. The heat evolution with each of successive admissions of adsorbate vapor may be measured directly by means of a calorimeter described by Beebe and co-workers [31]. Alternatively, the heat of immersion in liquid adsorbate of adsorbent having various amounts preadsorbed on it may be determined. The difference between any two values is related to the integral heat of adsorption (see Section X-3A) between the two degrees of coverage. See Refs. 32 and 33 for experimental papers in this area. 

All calorimeters consist of the calorimeter proper and its surround. This surround, which may be a jacket or a batii, is used to control tlie temperature of the calorimeter and the rate of heat leak to the environment. For temperatures not too far removed from room temperature, the jacket or bath usually contains a stirred liquid at a controlled temperature. For measurements at extreme temperatures, the jacket usually consists of a metal block containing a heater to control the temperature. With non-isothemial calorimeters (calorimeters where the temperature either increases or decreases as the reaction proceeds), if the jacket is kept at a constant temperature there will be some heat leak to the jacket when the temperature of the calorimeter changes. 

A liquid serves as the calorimetric medium in which the reaction vessel is placed and facilitates the transfer of energy from the reaction. The liquid is part of the calorimeter (vessel) proper. The vessel may be isolated from the jacket (isoperibole or adiabatic), or may be in good themial contact (lieat-flow type) depending upon the principle of operation used in the calorimeter design. 

Accurate enthalpies of solid-solid transitions and solid-liquid transitions (fiision) are usually detennined in an adiabatic heat capacity calorimeter. Measurements of lower precision can be made with a differential scaiming calorimeter (see later). Enthalpies of vaporization are usually detennined by the measurement of the amount of energy required to vaporize a known mass of sample. The various measurement methods have been critically reviewed by Majer and Svoboda [9]. The actual teclmique used depends on the vapour pressure of the material. Methods based on... 

Solution calorimetry covers the measurement of the energy changes that occur when a compound or a mixture (solid, liquid or gas) is mixed, dissolved or adsorbed in a solvent or a solution. In addition it includes the measurement of the heat capacity of the resultant solution. Solution calorimeters are usually subdivided by the method in which the components are mixed, namely, batch, titration and flow. 

Various flow calorimeters are available connnercially. Flow calorimeters have been used to measure heat capacities, enthalpies of mixing of liquids, enthalpy of solution of gases in liquids and reaction enthalpies. Detailed descriptions of a variety of flow calorimeters are given in Solution Calorimetry by Grolier [17], by Albert and Archer [18], by Ott and Womiald [H], by Simonson and Mesmer [24] and by Wadso [25]. 

Recent developments m calorimetry have focused primarily on the calorimetry of biochemical systems, with the study of complex systems such as micelles, protems and lipids using microcalorimeters. Over the last 20 years microcalorimeters of various types including flow, titration, dilution, perfiision calorimeters and calorimeters used for the study of the dissolution of gases, liquids and solids have been developed. A more recent development is pressure-controlled scamiing calorimetry [26] where the thennal effects resulting from varying the pressure on a system either step-wise or continuously is studied. 

Magee J W, Blanco J C and Deal R J 1998 High-temperature adiabatic calorimeter for constant-volume heat capacity of compressed gases and liquids J. Res. Natl Inst. Stand. Technol. 103 63... 

Figure 12-26. The SIMULAR reaction calorimeter. Features include pumped liquid feed, gas mass flow control, gas evolution measurement, and distillation equipment. (Source Hazard Evaluation Laboratory Ltd.)...

If two liquids are mixed together, there is in general a change of intrinsic energy (AU) and a change of free energy (A ). The heat absorbed when 1 mol of [1] and x mols of [2] are mixed in a calorimeter is the increase of intrinsic energy, and is usually denoted by QOz) ... 

Page 14, line 2 The method of Nernst, Koref, and Lindemann, by the use of the copper-calorimeter, determines the mean specific heat over a range of temperature. The mode of procedure is the same as in ordinary calorimetry, except that a hollow block of copper, the temperature of which is determined by means of inserted thermoelements, is used instead of a calorimetric liquid, and the method therefore made applicable to very low temperatures. 

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