Using the Heat Capacity

The thermal conductivity of soHd iodine between 24.4 and 42.9°C has been found to remain practically constant at 0.004581 J/(cm-s-K) (33). Using the heat capacity data, the standard entropy of soHd iodine at 25°C has been evaluated as 116.81 J/ (mol-K), and that of the gaseous iodine at 25°C as 62.25 J/(mol-K), which compares satisfactorily with the 61.81 value calculated by statistical mechanics (34,35). 

Use the heat capacity of a substance to calculate the heat required to raise its temperature by a given amount (Example 6.3). 

Thermodynamic representation of transitions often represents a challenge. First-order phase transitions are more easily handled numerically than second-order transitions. The enthalpy and entropy of first-order phase transitions can be calculated at any temperature using the heat capacity of the two phases and the enthalpy and entropy of transition at the equilibrium transition temperature. Small pre-tran-sitional contributions to the heat capacity, often observed experimentally, are most often not included in the polynomial representations since the contribution to the... 

Using the heat capacity data and enthalpy data listed at the beginning of this appendix, it is possible to perform the energy balance. The minor components in the tail-gas stream are grouped together in the calculation under the heading other gases . 

Using the heat capacities, C° for A, B, C and D to calculate the enthalpy required to raise their temperatures from T to T2 T < T2) we can establish, directly from the cycle... 

You could use the heat capacity equations to get the enthalpy changes for the gases, AH 29g, i.e.,... 

We calculate the energy of combustion for methane, using the heat capacity of the calorimeter (11.3 kJ/°C) and the observed temperature increase of 7.3°G. 

An inefficient but simple procedure is to assume a value of T (Tf is a reasonable first guess), solve Equations 1 through 4 successively, and then evaluate the left side of Equation 5 (which equals AW for the assumed temperature and must be positive when T = Tp). The value of T is then decreased by a small fixed amount, such as 0.5°C, and the procedure is repeated until the sign of AW changes from positive to negative from one T to the next. TTie true T (for which AW = 0) must lie between the two last assumed values and may be estimated by linear interpolation. When calculating specific enthalpies, use the heat capacity formulas for pentane and hexane given in part (b). 

Tables which show only values for the stable phases at 1 bar pressure are multiphase tables. Multiphase tables can always be recognized by the presence of solid lines, indicating phase transitions, on the table. They are prepared in a manner similar to tables for condensed phases. The functions are evaluated in the same manner as for a solid up to the first transition point then the enthalpy and entropy of transition are added and the integration is continued using the heat capacities of the next phase. At each transition, the above process is repeated.

Aqueous solutions. For the special but very important case of aqueous solutions, a rough rule in the absence of experimental data is to use the heat capacity of the water only. For example, a 21.6% solution of NaCl is assumed to have a heat capacity of 0.784 cal/(g)CC) the experimental value at 25 C is 0.806 cal/(g)(°C). 

The coefficients for some gaseous compound in the above equations are listed in Table 11.3.45 It is found that the heat capacity of a real gas is almost the same as its ideal state if the pressure is not too high. Therefore, it is proper to use the heat capacity of an ideal gas for a practical gas when the pressure is low. The approximate method to calculate the heat capacity can also be used if empirical data is not readily available.6... 

The amount of heat given off by the system (in the sealed compartment) raises the temperature of the calorimeter and its water. The amount of heat absorbed by the water can be calculated using the specific heat of water similarly, we use the heat capacity of the calorimeter to find the amount of heat absorbed by the calorimeter. The sum of these two amounts of heat is the total amount of heat released by the combustion of 1.000 gram of ethanol. We must then scale that result to correspond to one mole of ethanol. 

Dependence upon radiation for heat removal in the case of the old form of reactor was essential since even with the large excesses of air used the heat capacity of the total exit products was insufficient to remove the heat of reaction, especially when die air-naphthalene mixture had been preheated to approximately 350° C. prior to entering the catalyst zone. With the present method of temperature control and heat removal the heat of reaction amounts to about 10,000 B.t.u. per pound of naphthalene fed to the converter. As the proportion of naphthalene burned to com-... 

Then using the heat capacities reported in the NIST Chemistry WebBook and Eq. 8.5-5, the Gibbs free energ - of reaction at any other temperature can be obtained. 

The first partial derivative is the definition of the heat capacity, Cp, Notice this heat capacity is the extensive heat capacity of the reactor contents. Normally we express this quantity as an intensive heat capacity times the amount of material in the reactor. We can express the intensive heat capacity on either a molar or mass basis. We choose to use the heat capacity on a mass basis, so the total heat capacity can be expressed as... 

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