Heat capacity calibration

R.L. Bohon, AnalChem 35 (12), 1845-52 (1963) CA 60,1527 (1964) Approx heats of expin, Qv were detd on mg amounts of propints and expls by differential thermal analysis (DTA). Small-screw-cap metal cupsi sealed with a Cu washer served as constant vol sample containers the initial cup pressure could be controlled from 0 to approximately lOOOpsia. The calibration constant was calcd for each run from the total heat capacity of the cup and the relaxation curve, thereby compensating for equipment variations. 

There are two steps in the calculation. First, calibrate the calorimeter by calculating its heat capacity from the information on the first reaction, Cca) = qc, /AT. Second, use that value of Cc-1 to find the energy change of the neutralization reaction. For the second step, use the same equation rearranged to gcal = Cca AT, but with AT now the change in temperature observed during the reaction. Note that the calorimeter contains the same volume of liquid in both cases. Because dilute aqueous solutions have approximately the same heat capacities as pure water, assume that the heat capacity is the... 

The heat capacity of an object is the ratio of the heat supplied to the temperature rise produced. Heat transfers are measured by using a calibrated calorimeter. 

When 0.113 g of benzene, C6H6, burns in excess oxygen in a calibrated constant-pressure calorimeter with a heat capacity of 551 J-(°C) I, the temperature of the calorimeter rises by 8.60°C. Write the thermochemical equation for... 

A calorimeter was calibrated with an electric heater, which supplied 22.5 kj of energy to the calorimeter and increased the temperature of the calorimeter and its water bath from 22.45°C to 23.97°C. What is the heat capacity of the calorimeter ... 

A calorimeter is calibrated with an electrical heater. Before the heater is turned on, the calorimeter temperature is 23.6 °C. The addition of 2.02 X 10 J of electrical energy from the heater raises the temperature to 27.6 °C. Determine the total heat capacity of this calorimeter. 

C06-0017.A coffee-cup calorimeter is calibrated using a small electrical heater. The addition of 3.45 kJ of electrical energy raises the calorimeter temperature from 21.65 °C to 28.25 °C. Calculate the heat capacity of the calorimeter. 

The results of the calibrations and the evaluation of the total heat evolved are given in Table 5.4-16. The product ArU and the heat capacity of the reaction mixture increased by about 20 % during the reaction period. The total amount of heat released per unit mass of reaction mixture is 190 kJ/kg indicating a moderate heat effect. However, the adiabatic temperature rise dTaj = AHKmcf)) is quite significant (109 "C). This is due to the relatively low heat capacity of the reaction mixture. 

In principle all parameters of the model can be entered in the parameter estimation procedure. For the time being we limit the parameters to be calibrated to the ground thermal conductivity, ground heat capacity and borehole filling conductivity. 

It must be noted that although the calibration cell is very different from the adsorption cell [Fig. 18, cells (1) and (2)3, the heat capacity of both cells is not very different, as the similar values of the time constant of the calorimeter containing one cell or the other indeed show (350 sec in the case of the calibration cell and 400 sec in the case of the adsorption cell) (55). This is explained by the fact that in both eases, the calorimeter cell is almost completely filled with a metal. However, the glass tube which is immersed in the calorimeter cell and the pressure changes which occur in the course of the adsorption experiments may be the sources of variable thermal leaks. The importance of these leaks was appreciated by means of the following control experiments. 

Low-temperature thermometers are obtained by cutting a metallized wafer of NTD Ge into chips of small size (typically few mm3) and bonding the electrical contacts onto the metallized sides of the chip. These chips are seldom used as calibrated thermometers for temperatures below 30 mK, but find precious application as sensors for low-temperature bolometers [42,56], When the chips are used as thermometers, i.e. in quasi-steady applications, their heat capacity does not represent a problem. In dynamic applications and at very low temperatures T < 30 mK, the chip heat capacity, together with the carrier-to-phonon thermal conductance gc d, (Section 15.2.1.3), determines the rise time of the pulses of the bolometer. 

Adiabatic calorimetry uses the temperature change as the measurand at nearly adiabatic conditions. When a reaction occurs in the sample chamber, or energy is supplied electrically to the sample (i.e. in heat capacity calorimetry), the temperature rise of the sample chamber is balanced by an identical temperature rise of the adiabatic shield. The heat capacity or enthalpy of a reaction can be determined directly without calibration, but corrections for heat exchange between the calorimeter and the surroundings must be applied. For a large number of isoperibol... 

The melting transition of ultra-pure metals is usually used for calibration of DSC instruments. Metals such as indium, lead, and zinc are useful and cover the usual temperature range of interest. Calibration of DSC instruments can be extended to temperatures other than the melting points of the standard materials applied through the recording of specific heat capacity of a standard material (e.g., sapphire) over the temperature range of interest. Several procedures for the performance of a DSC experiment and the calibration of the equipment are available [84-86]. A typical sensitivity of DSC apparatus is approximately 1 to 20 W/kg [15, 87]. 

Scenario A student constructed a coffee cup calorimeter (see Figure 1). To determine the heat capacity of the calorimeter, the student placed 50.0 mL of room temperature distilled water in the calorimeter. A calibrated temperature probe recorded the temperature as 23.0°C. The student then added 50.0 mL of warm distilled water (61.0°C) to the calorimeter and recorded the temperature every 30 seconds for the next three minutes. The calorimeter was then emptied and dried. Next, the student measured the temperature change when 50.0 mL of... 

Let us return to the thermal decomposition of Fe(CO)(l,3-C4H6)2. Once the calibration constant is known, the enthalpy of the net process 9.10 can be calculated as the product of s and the area (A + B). The next step is to correct this value to 298.15 K by using heat capacity data. This exercise is, however, complicated by the cyclobutadiene polymerization. Brown et al. analyzed the reaction products by mass spectrometry and found several oligomers, in particular the dimer (C4H6)2 and the trimer (C4H6)3 [163]. With such a mixture, it is difficult to ascribe the observed enthalpy change to a well-defined chemical reaction. This is discussed in the paper by Brown and colleagues, who were nevertheless able to recommend a value for the standard enthalpy of formation of the iron-olefin... 

A marginal but very important application of the drop calorimetric method is that it also allows enthalpies of vaporization or sublimation [162,169] to be determined with very small samples. The procedure is similar to that described for the calibration with iodine—which indeed is a sublimation experiment. Other methods to determine vaporization or sublimation enthalpies using heat flow calorimeters have been described [170-172], Although they may provide more accurate data, the drop method is often preferred due to the simplicity of the experimental procedure and to the inexpensive additional hardware required. The drop method can also be used to measure heat capacities of solids or liquids above ambient temperature [1,173],... 

The heat flux and energy calibrations are usually performed using electrically generated heat or reference substances with well-established heat capacities (in the case of k ) or enthalpies of phase transition (in the case of kg). Because kd, and kg are complex and generally unknown functions of various parameters, such as the heating rate, the calibration experiment should be as similar as possible to the main experiment. Very detailed recommendations for a correct calibration of differential scanning calorimeters in terms of heat flow and energy have been published in the literature [254,258-260,269]. 

Examples are water for the calibration of viscometers, sapphire as a heat-capacity calibrant in calorimetry, and solutions used for calibration in chemical analysis... 

Heat transfers are measured by using a calibrated calorimeter. The heat capacity of an object is the ratio of the heat supplied to the temperature rise produced. Molar heat capacities of liquids are generally greater than those of the solid phase of the same substance. Molar heat capacities increase as molecular complexity increases. 

Strategy First, calibrate the calorimeter. To do so, calculate the heat capacity from the information on the first reaction. For this step, use the expression... 

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