Constant calorimeter

The p V work temi is not nomially measured. It can be eliminated by suspending the calorimeter in an evacuated space (p = 0) or by holding the volume of tire calorimeter constant (dF= 0) to give... 

With most non-isothemial calorimeters, it is necessary to relate the temperature rise to the quantity of energy released in the process by determining the calorimeter constant, which is the amount of energy required to increase the temperature of the calorimeter by one degree. This value can be detemiined by electrical calibration using a resistance heater or by measurements on well-defined reference materials [1], For example, in bomb calorimetry, the calorimeter constant is often detemiined from the temperature rise that occurs when a known mass of a highly pure standard sample of, for example, benzoic acid is burnt in oxygen. 

Find the heat capacity of the calorimeter (calorimeter constant). 

Some of the heat transferred to the surroundings during an exothermic reaction are absorbed by the calorimeter and its parts. In order to account for this heat, a calorimeter constant or heat capacity of the calorimeter is required and usually expressed in J °C 1. 

An important variation of the adiabatic principle is isoperibol calorimetry. Well-defined heat leaks, minimized by efficient calorimeter construction and experiment design, are compensated for by calculation and/or extrapolation. The isoperibol design holds the temperature of the immediate environment surrounding the calorimeter constant. The word isoperibol literally means "constant temperature environment. ... 

Calculate the heat transfer, Q, from a bomb calorimeter (constant volume) or a steady flow calorimeter (constant pressure), Qp, from theory or experimental data. 

The heat capacity of a calorimeter is determined by adding a known amount of heat and measuring the rise in temperature of the calorimeter and of the solution it contains. This heat capacity of a calorimeter is sometimes called its calorimeter constant. 

A 5.1-gram piece of gold jewelry is removed from water at 100.0°C and placed in a coffee-cup calorimeter containing 16.9 g of water at 22.5°C. The equilibrium temperamre of the water and jewelry is 23.2°C. The calorimeter constant is known from calibration experiments to be 1.87 J/°C. What is the specific heat of this piece of jewelry The specific heat of pure gold is 0.129 J/g °C. Is the jewelry pure gold ... 

When 3.16 g of salicylic acid, C HgOj, is burned in a bomb calorimeter containing 5.00 kg of water originally at 23.00°C, 69.3 kj of heat is evolved. The calorimeter constant is 3612 J/°C. Calculate the final temperature. 

The calorimeter constant is determined from the data for the combustion of benzoic acid... 

Catalyst samples were ground into fine powder, freed of moisture, and sealed in glass bulbs, which were ultimately broken within a Dewar-flask calorimeter. A heater, Beckmann thermometer, sample holder, and stirrer were introduced into the calorimeter through an evacuated lid. The dissolutions were carried out at 160° in equivolume mixtures of H2SO4 and H3PO4. The calorimeter constant was reproducible within 0.05% the over-all precision of the determinations is estimated to be within 1 cal./g. 

This is choice (A). If you neglected to use the calorimeter constant, you might choose choice (B) in error. If you solved this equation incorrectly, you might choose choice (C). Choice (D) could be chosen incorrectly if the 15° temperature change was ignored. 

The calorimeters wifli carrier gas are also used. " Evaporation of substance is accelerated by a stream of gas (for example, nitrogen) at reduced pressure. The heat loss by a calorimeter, due to evaporatioit is compensated by an electrical current to keep temperature of calorimeter constant and equal to flic temperature of the thermostating bath. 

More sophisticated models, with a greater number of calorimeter parts, their temperatures and interconnections lead to similar relationships between AT and Cp but involve more internal device parameters. It follows that if a more complicated model of the calorimeter is required, a greater number of calibrating runs are needed to fix the calorimeter constants before the calibrating factor for the cyclic heat capacity, and the phase lag will be known for any frequency. 

Note that in contrast to our earlier equations relating and AT, there is no mass or number of moles term here for the quantity of material. The calorimeter constant is the heat capacity of a particular olyect (or set of objects) rather than that of a material. It may help to think of it as the heat capacity per calorimeter and then realize that we have just one calorimeter. For someone who routinely uses the same calorimeter, this approach is much simpler than the alternative, which... 

Once the calorimeter constant is known, we are ready to use the calorimeter for our actual measurement. We place known amounts of reactant(s) into the calorimeter, initiate the reaction, and then measure the resulting temperature change of the calorimeter. The calorimeter constant allows us to determine the amount of heat released or absorbed in the reaction. Example Problem 9.5 shows how this process works. 

The calibration step allows us to determine the calorimeter constant. Once this is known, the amount of heat evolved from the fuel can be determined by using Equation 9.5. Finally, we divide this heat by the mass of fuel that generated it to arrive at the requested energy density. 

Resistive heating is used to calibrate a calorimeter. When 300.0 J of heat is added to the system, its temperature change is 2.45 C. What is the calorimeter constant for this apparatus ... 

Anthracite 35 kj/g Subbituminous 31 kj/g Bituminous 28 kJ/g Lignite 26 kJ/g An unknown sample of one of these coals is burned in an apparatus with a calorimeter constant of 1.3 kJ/ C. When a 0.367-g sample is used, the temperature change is 8.75 C. Which type of coal is the sample ... 

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