Evaluation procedure:
At some determinant point the heat of evaluation procedure is finished and after this point heat evaluation goes on decreasing up to D. The usefulness of the method arises from the fact that peak temperature is generally featured of the material in the sample. Area of the peak BCD is proportional to the amount of reacting material. For endothermic reaction the peak EFG will be obtained as display in the idealised curve. This peak shows in which the ?T i.e. (Ts-Tr) will be negative since heat is absorbed and consequently Ts will be smaller than Tr. Remember the levels of base lines of extotherm curve, AB and DE. Both are at various levels above x-axis. This is because of the fact which heat capacity of the sample has modified as a result of the exothermic process. Same explanation could be given for the difference in levels of base lines of endotherm curve that is DE and GH. DTA curves are not only help in the identification of materials but their peak areas gives quantitative information regarding mass of sample (m), heat of reactions (enthalpy change, ? H) and factors like as sample geometry and thermal conductivity. Peak area could be express as follows if latter two factors are expressed through a factor K called calibration factor.
Peak area (A) = ± ? H m K
We will use +ve sign for endothermic reaction (?H > 0) i.e. while the temperature of the sample will lag behind the in which of the reference, and negative sign for exothermic reaction (?H < 0) the temperature of the sample will exceed that of reference, factor K is known as calibration constant that is temperature dependent. It could be determined through calibrating DTA along with a few standards. Once we know the value of K at a particular temperature, a peak area could be used for quantitative analysis to determine the mass of sample or energy (enthalpy changes) of a reaction. By this DTA curve also helps in estimating heat capacity of a sample. As you could see in Figure which there is always a difference in the base lines. The changes in heat capacity (? Cp) might be determined at a particular temperature through measuring the difference in base lines that is. displacement (d) since:
