Heating curve A plot of temperature

What happens when a solid is heated Typically, it melts to form a liquid. If the heating continues, the liquid at some point boils and forms the vapor phase. This process can be represented by a heating curve a plot of temperature versus time for a process where energy is added at a constant rate. 

Heating curve a plot of temperature versus time for a substance where energy is added at a constant rate. (10.8)... 

Prepare the condensing curve, a plot of the vapor temperature Tg against the amount of heat removed Q, by a series of isothermal flashes and enthalpy balances. 

The accurate determination of the linearity of the furnace heating rate is not an easy matter. From a plot of temperature versus time, as shown in Figure 6.15a, the heating rate can be estimated to 5% or better. To determine minute fluctuations of the furnace heating-rate curve, the curve in Figure 6.15b is used. A DTA curve is recorded with the reference chamber filled with an inert material (a-alumina, for example) while the sample chamber is empty. In this unbalanced condition, the fluctuations in the power input voltage are easily seen. This type of behavior is also seen if the AT thermocouples are unsymmetrically located in the furnace chamber (46). It should be noted that it is even more difficult to measure accurately heating rates of l°C/min or less. 

A lustrous metal has the heat capacities as a function of temperature shown in Table 1-4 where the integers are temperatures and the floating point numbers (numbers with decimal points) are heat capacities. Print the curve of Cp vs. T and Cp/T vs. T and determine the entropy of the metal at 298 K assuming no phase changes over the interval [0, 298]. Use as many of the methods described above as feasible. If you do not have a plotting program, draw the curves by hand. Scan a table of standard entropy values and decide what the metal might he. 

The amount of heat actually taken up by the particles was an important quantity, as tubes operate under heat transfer limited conditions near the tube inlet. Fig. 30 shows a plot of Q against r, where Q was the total energy flow into the solid particles, for the entire segment. For inlet conditions, Q varied strongly at lower r, but was almost constant at higher values. As rcut/rp decreased from 0.95 to 0.0 and the effectiveness factor increased from nearly zero to one, the active solid volume increased by a factor of 7. If the solid temperature had remained the same, the heat sink would also have had to increase sevenfold. This could not be sustained by the heat transfer rate to the particles, so the particle temperature had to decrease. This reduced the heat sink and increased the driving force for heat transfer until a balance was found, which is represented by the curve for the inlet in Fig. 30. 

A distillation curve is essentially a plot of boiling temperature (°F) vs. cumulative percent volume removed from the sample during heating (Figure 4.9). This type of plot can be used to distinguish quickly between one or several product types. 

Certain correlations are possible but it must be kept in mind that comparisons of activity in heterogeneous catalysis are likely to be treacherous. Minor differences in surface pretreatment may make major differences in properties. Nevertheless, it is clear that there are recognizable patterns of extrinsic field effects. The several kinds are shown in Fig. 22 wherein AkH is plotted against H (log scale). The curves drawn are meant to be representative, but except for relatively minor details, all of the samples studied to date fall into one of the six patterns shown. This covers over 30 different catalyst preparations, a variety of temperature-sensitive magnetic phases, and various pretreatments. Figure 22 shows one example of catalysts found to have the indicated kind of field effect. Pretreatment conditions are stated in Table IV which includes all samples on which measurements have been made. Pretreatments are abbreviated as follows (H2773q298) means that the sample had been heated in hydrogen for an hour or more at 773 K and then cooled rapidly to 298 K. One or two temperatures at which each A k pattern has been observed are also shown in Table IV. 

Below 500 K heating of the solid salt results primarily in the vaporization of the covalent molecule as a monomer. In this temperature range the only thermal decomposition, into NOz and 02, is exhibited by the solid. The vapor is more stable. The vapor pressure of Cu(N03)2 was determined by Addison and Hathaway48 by extrapolating pressure-time curves to zero time in order to subtract the pressures of N02 and 02. These vapor pressures increased from 0.32 torr at 430 K to 3.59 torr at 405 K. A plot of log P vs. 1/T is linear and yields a sublimation enthalpy of 67.0 kJ. Above 500 K both the solid and the vapor phase decompose to N02 + 02. 

---