A TG curve was measured in air when an exothermic peak associated with mass loss was observed.
Yes, just consider the example of most nitrates and explosive compounds in general. After melting (endothermal) and sometimes phase changes (also endothermal), decomposition occurs and is very exothermic.
This may occur each time the resultant compounds after decomposition are more stable than the initial compound.
If your TG ios carried out in air, it can also be a rapid oxidation (like burning) of your sample, indeed producing both exothermic peak and mass loss.
Alain
Yes, just consider the example of most nitrates and explosive compounds in general. After melting (endothermal) and sometimes phase changes (also endothermal), decomposition occurs and is very exothermic.
This may occur each time the resultant compounds after decomposition are more stable than the initial compound.
If your TG ios carried out in air, it can also be a rapid oxidation (like burning) of your sample, indeed producing both exothermic peak and mass loss.
Alain
Thank you Alain for the explanation. So, it is not a combustion. Decomposition is more general definition in this case.
If athmosphere is switched from inert to air/oxigen sometimes decomposition becomes exothermic.
Decomposition can be either endothermic or exothermic, with the latter being often association with oxidation such as thermogravimetry (TGA) measured in air. However explosive substances usually include their own oxygen and can oxidise even if surrounded by an inert gas. Organic compounds decompose in air (oxygen) to give mostly carbon dioxide and water, both and particularly the latter being highly exothermic. The oxidation makes up for the energy (endothermic) required to break bonds in the original compound.
When exothermic, a reaction may be expected to occur spontaneously, however this is not usually the case since storing the material would be difficult. The parameter determining whether a reaction will occur and at what reaction rate is the activation energy. Once the activation energy is reached an exothermic reaction will be spontaneous, while an endothermic reaction will require continual energy input. With TGA activation energy is by heating, in other cases like explosives an electrical or physical impulse may give activation.
Decomposition is not always endothermic.
Examples: Decomposition of NO to N2 & O2 is exothermic (-90.25kJ/mole) N2O4 is too (-9.16 kJ/mole) as is N2O (-82.05 kJ/mole). The decomposition of ozone (O3) to oxygen (O2) is exothermic (-142.7 kJ/mole). On the other hand, the decomposition of gaseous NH3 is endothermic (+46.11 kJ/mole).
There is one kind of decomposition reaction which is always endothermic; the decomposition of gaseous diatomic or polyatomic molecules into gaseous atoms. So, for example, the decomposition of ozone (O3) to atomic oxygen (O) is endothermic (+754.81 kJ/mole).
The regular case is exothermal is the process of materials decomposition such as melting or phase changes and endothermal is the process of materials formation or solidification. The process is clear in DTA, the differential thermal analysis
Exothermal still occurs in the process of phase changes such as structure change during cooling (solid-solid phase transition, during cooling, the process is change from a structure form to another. Please see the reference, M S Omar Int J Thermophys (2010)1186–1194
Yes there is few factors influence on endo/exo character of thermal decomposition:
- structural aspects of studied material (included nitro group ect. as has been described before)
- atmosphere eg. switched from oxygen or air to inert nitrogen sometimes changed decomposition character from exo to endo
- crucible material sometimes exo peak appear when alumina crucible is used, but in aluminium endo for these same sample
both of exothermic and endothermic are depending on the chemical energy of the substances as a reactants whether this reaction is decomposition or other types of reactions.
if the chemical energy of reactants are greater than products that time the reaction is exothermic with negative ( ΔH) and that time the product is more stable than reactant
vise versa in endothermic reaction regardless the type of reactions
for example the decomposition of 2NO ------- N2 +O2 + heat----------- in this case the stability of nitrogen gas and oxygen gas is greater than nitrogen monoxide and therefor this decomposition is exothermic
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science