Calorimeter water equivalent

A diagram of a typical run is given in figure 2 which shows the power generated by mixing of magnesium chloride with water at 200°C. In this calorimeter a heat of dilution takes 30 minutes and from an initial base line it takes about 15 minutes for the calorimeter to reach a steady state. The sensitivity of this calorimeter was equivalent to being able to detect a 2 X 10 4k... 

Knowing the so-called " water equivalent factor of the calorimeter, it is possible to determine the heat of combustion at constant volume with an accuracy better than 1%... 

Note The water equivalent factor includes the heat capacity of the ensemble which includes the calorimeter itself, water bucket with water in it, supports of the bucket, bomb, thermometer and stirring device. These values can be calculated theoretically, but much more accurate results are obtained by combustion of a sample of standard material (such as benzoic acid, supplied by the US Bureau of Standards), the heat of combustion of which has been previously accurately determined. The water equivalent values of the calorimeters and bombs supplied by the Parr Instrument Co are determined by them at the factory... 

Energy equivalent, heat capacity, or water equivalent energy required to raise the temperature of the calorimeter an arbitrary unit when multiplied by the corrected temperature rise, adjusted for extraneous heat effects, and divided by the weight of the sample, gives the gross calorific value. 

In this equation, cw stands for the heat capacity of the calorimetric vessel. Traditionally, this correction was performed via the Water Equivalent of the calorimeter. This means that the heat capacity of the calorimetric cell is described by a thermally equivalent mass of water. 

Parr adiabatic calorimeter containing a Parr double-valve oxygen combustion bomb. The water equivalent of the calorimeter was determined from the combustion of a weighed sample of benzoic acid standardized by the National Bureau of Standards (NBS). The agreement between results of any two acceptable runs was better than 0.10%. 

Bomb Pressure Correction. Any change in the operating pressure of the combustion bomb results in a change in the water equivalent (heat capacity) of the calorimeter. However, the difference is less than 1 cal./° C. when operating in the 15-450 p.s.i.g. range of pressure and is therefore negligible. 

A continuously operating mechanical stirrer ensured quick mixing of material inside the calorimeter. Similar to the location of the thermistor, a calibrating resistance coil protected with glass was kept inside the calorimeter for measuring the water equivalent of the calorimeter. Calibrated current was passed for specified time and the temperature rise was monitored for calculating the water equivalent. 

The heat of precipitation silver selenate was measured by mixing 0.04241 moles of silver nitrate dissolved in 325 g of water with 0.02122 moles of selenic acid in an isothermal calorimeter equipped with a sensitive thermometer. The acid (7.07 M) was contained initially in a bulb that was broken in order to start the reaction. The Ag2Se04 formed was shown to be crystalline by X-ray diffraction. The water equivalent was determined after each run. The experimental results and the evaluation of the standard enthalpy of formation of Ag2Se04(cr) are shown in Table A-17. 

In a typical experiment, 56.39 mg of technetium caused a temperature rise of 0.0572°C on combustion. Electrical calibration of the calorimeter shows its water equivalent to be 5847 J/K, so this experiment gives a value of ... 

The water-equivalent of the bomb, stirrer, thermometer, and calorimeter can now be calculated, as shown in the following example —... 

The value of e0 is only constant for a fixed volume V of solution inside the calorimetric vessel. The change of e0 with V is primarily due to an increase of the reaction vessel wall in contact with the liquid as the liquid volume increases [ 197,200]. This change, de0/dV, which is constant for well-designed calorimeters [197,200], can be determined by measuring e0 as a function of V. Because it has been found that as expected, e0 and d 0/dV are independent of the nature of the liquid used in the calorimeter, they are normally determined by performing electrical calibrations with the calorimeter filled with different volumes of water [200]. The energy equivalent of the calorimeter at any point during a titration can therefore be calculated from... 

The authors reacted 9 x 10 moles of MgS04(aq, 1 2000) with an equivalent amount of Na2Se03(cr) in 325 grams of water in an electrically calibrated calorimeter. Crystalline MgSe03 6H20 was formed. From the solubility product of magnesium selenite the review estimates that about 6% of the Mg remained in solution after the reaction. A correction has been applied, which changes the enthalpy of Reaction 1 in Table A-51 from - (47.49 0.13) in the paper to - (48.25 0.25) kJ-mol. ... 

The ice calorimeter is an important tool for measuring the heat capacities of liquids and solids, as well as the heats of certain reactions. This simple yet ingenious apparatus is essentially a device for measuring the change in volume due to melting of ice. To measure a heat capacity, a warm sample is placed in the inner compartment, which is surrounded by a mixture of ice and water. The heat withdrawn from the sample as it cools causes some of the ice to melt. Since ice is less dense than water, the volume of water in the insulated chamber decreases. This causes an equivalent volume of mercury to be sucked into the inner reservoir from the outside... 

In medical applications, it is of basic significance that the radiation absorption characteristics of the medium to be irradiated and that of the calorimetric absorber should be similar. Thus, calorimeters to that purpose have been constructed of water (Domen 1982), graphite (Petree and Lamperti 1967), polystyrene, polyethylene-carbon mixture (Milwy et al. 1958), and A-150 tissue-equivalent plastic (McDonald et al. 1976 Smathers et al. 1977). 

E mass of water having an equivalent thermal capacity to that of the calorimeter flask, stirrer, thermocouple, g Fd the total drag force, N... 

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