Heat capacity calorimeters

In earlier times, ethyl ether was commonly used as an anesthetic. It is, however, highly flammable. When five milliliters of ethyl ether, C HuQC/), (d - 0.714 g/mL) is burned in a bomb calorimeter, die temperature rises from 23-5°C to 39.7°Q The calorimeter heat capacity is 10.34 k)/°C. 

Isooctane, CgHlg, is a component of gasoline. When 0.500 g of isooctane is burned, 24.06 kj of heat is given off. If 10.00 mg of isooctane is burned in a bomb calorimeter (heat capacity = 5175 J/°C) initially at 23.6°C, what is the temperature of the calorimeter when reaction is complete ... 

Acetylene, C2H2, is used in welding torches. It releases a lot of energy when burned in oxygen. One gram of acetylene releases 48.2 kj. When 0.750 g of acetylene is burned in a bomb calorimeter (heat capacity = 1.117 kJ/°C), the final temperature of the bomb is 54.5°C. What is the initial temperature of the calorimeter ... 

Naphthalene, Ci0Hs, is the compound present in moth balls. When one mole of naphthalene is burned, 5.15 X 103 kj ofheat is evolved. A sample of naphthalene burned in a bomb calorimeter (heat capacity = 9832 J/°C) increases the temperature in die calorimeter from 25.1°C to 28.4°C. How many milligrams of naphthalene were burned ... 

Report the yields, boiling ranges, and refractive indexes of the two esters. If available, the VPC and IR curves should be attached to the report. The identification number of the calorimeter and bomb, the individual and average values of the calorimeter heat capacity C(S) and the heats of combustion i Hc for the two esters, and the apparent strain energy for the cyclopropane ring should be reported. An estimate of the uncertainties in C(S), the two A//c values, and S should be given. 

High-purity benzoic acid (CgHsCOOH A// for combustion = —3227 kJ/mol) is used as a standard for calibrating bomb calorimeters. A 1.221-g sample burns in a calorimeter (heat capacity = 1365 J/°C) that contains exactly 1.200 kg of water. What temperature change is observed ... 

Isooctane, CsHis, a component of gasohne, gives off 24.06 kJ of heat when 0.500 g are burned. A 100.0-mg sample of isooctane is burned in a bomb calorimeter (heat capacity = 3085 J/°C) that contains 500.0 g of water. Both the bomb and water are at 23.6°C before the reaction. What is the final temperature of the bomb and water ... 

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. 

Hence, it is necessary to correct the temperature change observed to the value it would have been if there was no leak. This is achieved by measuring the temperature of the calorimeter for a time period both before and after the process and applying Newton s law of cooling. This correction can be reduced by using the teclmique of adiabatic calorimetry, where the temperature of the jacket is kept at the same temperature as the calorimeter as a temperature change occurs. This teclmique requires more elaborate temperature control and it is prunarily used in accurate heat capacity measurements at low temperatures. 

The heat capacity of a gas at constant pressure is nonually detenuined in a flow calorimeter. The temperature rise is detenuined for a known power supplied to a gas flowing at a known rate. For gases at pressures greater than about 5 MPa Magee et al [13] have recently described a twin-bomb adiabatic calorimeter to measure Cy. 

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]. 

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... 

Calorimeter. The P-decay energy of tritium is very precisely known (9). The thermal energy generated by the decay can thus be used with a specially designed calorimeter to measure the quantity of tritium in a system of known heat capacity. 

To measure the heat flow in a reaction, a device known as a calorimeter is used. The apparatus contains water and/or other materials of known heat capacity. The walls of the calorimeter are insulated so that there is no exchange of heat with the surrounding air. It follows that the only heat flow is between the reaction system and the calorimeter. The heat flow for the reaction system is equal in magnitude but opposite in sign to that of the calorimeter ... 

The equation just written is basic to calorimetric measurements. It allows you to calculate the amount of heat absorbed or evolved in a reaction if you know the heat capacity, Ccd, and the temperature change, At, of the calorimeter. 

Bomb calorimeter. The heat flow, q, for the reaction is calculated from the temperature change multiplied by the heat capacity of the calorimeter, which is determined in a preliminary experiment... 

The heat absorbed by the calorimeter is equal to the product of its heat capacity, Ccai, and the temperature change, At. Hence... 

Knowing the heat capacity of the calorimeter, the heat flow for any reaction taking place within the calorimeter can be calculated (Example 8.3). 

It is found that when 1.00 g of H2 is made to react completely with Cl2 in a bomb calorimeter, the temperature in the bomb (heat capacity = 9.33 kJ/°C) rises from 20.00°C to 29.82°C. How much heat is evolved by the reaction ... 

Isooctane is a primary component of gasoline and gives gasoline its octane rating. Burning 1.00 mL of isooctane (d = 0.688 g/mL) releases 33.0 kj ofheat. When 10.00 mL of isooctane is burned in a bomb calorimeter, the temperature in the bomb rises from 232°C to 66.5°C. What is the heat capacity of the bomb calorimeter ... 

WEB When one mole of caffeine (CgHlaN402) is burned in air, 4.96 X 103 kj ofheat is evolved. Five grams of caffeine is burned in a bomb calorimeter. The temperature is observed to increase by 11.37°Q What is die heat capacity of the calorimeter in J/°C ... 

Equation (4.2) can be used to determine the entropy of a substance. A pure crystalline sample is placed in a cryogenic calorimeter and cooled to low temperatures. Increments of heat, q, are added and the temperature change, AT, is measured, from which the heat capacity can be calculated from the relationship... 

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... 

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