Sunday, 21 August 2016

physical chemistry - Maximum temperature attainable by thermite reaction



In the thermite reaction 2Al(s)+FeX2OX3(s)2Fe(l)+AlX2OX3(s)

what is the maximum temperature attainable by the products? Assume reactants at 25 C and 1 atm and that all heat capacities remain constant.



I started by using Hess's law to find the enthalpy change of the reaction. I couldn't find a heat of formation for liquid iron so I assume I have to find that out. I just wrote out the equation Fe(s)+heat+enthalpy of fusionFe(s)

and figured the heat of formation for liquid iron at 25 C is around 302.71 kJ/mol.


To find the max temperature I used ΔHr=ΔTCp(products)

and came out with an equation like 14445 kJ/mol=0.147 kJ/(mol K)Tmax
This gives me a negative temperature, so I assume it is wrong. Even if I were to take the absolute value, the answer seems awfully high. I was expecting something around a few thousand degrees not near ten thousand.




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