Thermogravimetric analysis reaction stoichiometry

When heated, many solids evolve a gas. For example, most carbonates lose carbon dioxide when heated. Because there is a mass loss, it is possible to determine the extent of the reaction by following the mass of the sample. The technique of thermogravimetric analysis involves heating the sample in a pan surrounded by a furnace. The sample pan is suspended from a microbalance so its mass can be monitored continuously as the temperature is raised (usually as a linear function of time). A recorder provides a graph showing the mass as a function of temperature. From the mass loss, it is often possible to establish the stoichiometry of the reaction. Because the extent of the reaction can be followed, kinetic analysis of the data can be performed. Because mass is the property measured, TGA is useful for... 

Frequendy, it is not easy to determine the temperatures Ti,T2,..., owing to the nearly horizontal nature of the curve in those regions and the attendant indistinct beginning and ending temperatures of the reaction steps. This means also that it is not easy to determine accurately the mass loss in such cases. Because of this, some instruments also compute the trace of the first derivative of the mass curve simultaneously. This DTG (derivative thermogravimetric analysis) makes it much easier to determine where a zero slope indicates that the sample is undergoing no change in mass. Therefore, the reaction stoichiometry can be more accurately determined. 

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