Reaction-solution calorimeters

Figure 8.1 Scheme of a Dewar vessel isoperibol reaction-solution calorimeter. A ampule containing the sample B ampule breaking system C calorimeter head D temperature sensor E stirrer F electrical resistance G Dewar vessel H plunger of the ampule breaking system I, J inlets K plug connecting the calibration resistance to the calibration circuit. 

Various substances and reactions have been used to test the accuracy of reaction-solution calorimeters [3 9,40]. The solution of tris(hydroxymethyl)amin-omethane (THAM orTRIS) in 0.1 mol dm-3 HCl(aq), which was first proposed by Wadso and Irving [133] in 1964 and recommended by the Standards Committee of the U.S. Calorimetry Conference in 1966 [134,135], is perhaps the most widely used method. Several problems encountered in the use of the THAM+HC1 (aq) reaction to assess the accuracy of reaction-solution calorimeters have been... 

Figure 8.5 The vessel of the LKB 8700 reaction-solution calorimeter. A thermistor B heater used for calibration C stirrer/ampule holder D glass ampule E sapphire pin. Adapted from [132].

The accuracy of a titration calorimeter is normally assessed using the reactions of NaOH(aq) with HCl(aq) or HCICUjaq) [209,210], The dissolution of crystalline tris(hydroxymethyl)aminomethane (THAM) in HCl(aq) has also been employed when the apparatus is equipped with a system for the introduction of solid samples (e.g., an ampule breaking device) [210]. As mentioned in chapter 8, the latter method is commonly recommended for testing conventional reaction-solution calorimeters [39,40]. 

Kullberg measured the heat evolved when small amounts of red HgO(cr) were dissolved in solutions of 0.3 and 1 M KSeCN in a reaction solution calorimeter. The HgO(cr) was contained in a thin-walled glass ampoule, which could be broken inside the calorimeter... 

Calorimetry is the basic experimental method employed in thennochemistry and thennal physics which enables the measurement of the difference in the energy U or enthalpy //of a system as a result of some process being done on the system. The instrument that is used to measure this energy or enthalpy difference (At/ or AH) is called a calorimeter. In the first section the relationships between the thennodynamic fiinctions and calorunetry are established. The second section gives a general classification of calorimeters in tenns of the principle of operation. The third section describes selected calorimeters used to measure thennodynamic properties such as heat capacity, enthalpies of phase change, reaction, solution and adsorption. 

M. V Kilday. Systematic Errors in an Isoperibol Solution Calorimeter Measured with Standard Reference Reactions. J. Res. Natl. Bur. Stand. 1980, 85, 449—465. 

The design and operation of solution calorimeters is an extensive topic. Reference (125) reviews modem calorimetry and identifies earlier discussions. The thermometric titration type of calorimeter has been perfected during the past fifteen or twenty years. It is especially useful for measuring heats of reaction that take place in several steps. The availability of advances in thermometry has had a major effect on calorimetry. 

In this experiment 500 mL of solution A, with a precisely known concentration in the neighborhood of 0.25 M, is reacted with 50 mL of solution B at a concentration sufficient to provide a slight excess over the amount required to react with solution A. The reaction is carried out in the solution calorimeter shown in Fig. 1. The calorimeter is a vacuum Dewar... 

In the high-temperature region, the main method of measurement is the drop calorimetry, where the sample is heated to the chosen temperature outside the calorimeter in a furnace and the heat capacity is calculated from the temperature dependence of the enthalpy changes measured after dropping the sample into the calorimeter. The application of this technique affects, however, the behavior of the sample heated in the furnace (decomposition, reaction with the crucible, etc. should be avoided) as well as at the cooling from the furnace temperature to that of the calorimeter. Sometimes the sample does not complete its phase transition at cooling (e.g. at the temperature of fusion, a part of the sample crystallizes while the other part becomes glassy). In such a case, the drop calorimeter must be supplemented by a solution calorimeter in order to get the enthalpy differences of all the samples to a defined reference state. 

Kilday MV. Systematic errors in an isoperibol solution calorimeter measure with standard reference reactions. J Res Natl Bur Stand 1980 85 449-465. 

Dan and coworkers synthesized and characterized two complexes of general formula [Ln(Ala)2(Im)(H20)](C104)3 (Ln = Pr, Gd Ala = alanine Im = imidazoles). By using a solution-reaction isoperibol calorimeter, standard enthalpies of reaction at 298.15 K, were determined. Standard enthalpies of formation of the two complexes at 298.15 K were also calculated [185]. 

Heat accumulation calorimeters allow a rise in temperature of the reaction system for exothermic reactions or a decrease in temperature for endothermic reactions. A reaction is followed by measurement of a temperature change as a function of time, although modern calorimeters allow the signal to be converted into power. An adiabatic solution calorimeter is typical of this class. 

Solution calorimeters are usually adiabatic calorimeters. They are mainly used for the study of rapid reactions, for example, heats of solution, heat capacity of liquids, heat capacity of solids by a method of mixtures, or the enthalpy change of rapid reactions in solution. A schematic diagram is shown as Figure 3. The temperature sensor, plus a means of electrical calibration and a device for mixing reactants are all enclosed within a Dewar flask, or other adiabatic assembly. 

A number of photocalorimeters have been applied to study radiation-activated processes involving organometallic compounds. In general, these instruments are classical (reaction-solution, heat-flux or DSC) calorimeters to which an optical system has been adapted. Comprehensive reviews of photocalorimetric methods, including examples of applications to organometallic systems, have been published by Teixeira." " ... 

Figure 5.1 An adiabatic heat-of-solution calorimeter. The reaction vessel contains acid. Pushing down on the handle at the top punctures the upper seal and pushes out the bottom of the sample container, allowing the sample to dissolve.

The following reaction was carried out in an adiabatic solution calorimeter by Wagman and... 

Fig. 1. Schematic diagram of experimental apparatus for measuring AS (H /H2) (A) computer, (B) electrochemical workstation, (C) solution-reaction isoperibol calorimeter,...

Figure 3.41. Simple solution calorimeter for measuring the reaction enthalpy AH solution calorimetry is, for example, used for determination of the hydration heat of cement.

Reviews of batch calorimeters for a variety of applications are published in the volume on Solution Calorimetry [8] cryogenic conditions by Zollweg [22], high temperature molten metals and alloys by Colinet andPasturel [19], enthalpies of reaction of inorganic substances by Cordfunke and Ouweltjes [16], electrolyte... 

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]. 

Thermochemistry is concerned with the study of thermal effects associated with phase changes, formation of chemical compouncls or solutions, and chemical reactions in general. The amount of heat (Q) liberated (or absorbed) is usually measured either in a batch-type bomb calorimeter at fixed volume or in a steady-flow calorimeter at constant pressure. Under these operating conditions, Q= Q, = AU (net change in the internal energy of the system) for the bomb calorimeter, while Q Qp = AH (net change in the enthalpy of the system) for the flow calorimeter. For a pure substance. 

Boiling point elevation (ATb) Increase in the boiling point caused by addition of a nonvolatile solute, 269-271 Bomb calorimeter Device used to measure heat flow, in which a reaction is carried out within a sealed metal container, 202-203... 

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