Heat of formation of MgF2/AlF3 vs. MgO/Al2O3
Referring to:
https://engineering.purdue.edu/~propulsi/propulsion/comb/pro...
Can someone please explain to me why there is a switch in the rankings of heat of formation produced per gram of reactant when we compare Al/Mg
fluorides vs. Al/Mg oxides? I don't have a university chemistry background (just Year 12) so if the explanation is complicated you'll have to point me
in the direction of a reference available online for me to read 
So, for the flourides, Mg > Al hands down:
1) Mg + F<sub>2</sub> -> MgF<sub>2</sub> ΔH<sub>f</sub> = -2862 cal/g
2) 2Al + 3F<sub>2</sub> -> 2AlF<sub>3</sub> ΔH<sub>f</sub> = -844 cal/g
Why is the heat of formation of AlF<sub>3</sub> so poor? I'd have expected it to be much more comparable to MgF<sub>2</sub>.
For the oxides, Al > Mg:
1) 4Al + 3O<sub>2</sub> -> 2Al2O<sub>3</sub> ΔH<sub>f</sub> = -4000 cal/g
2) 2Mg + O<sub>2</sub> -> 2MgO ΔH<sub>f</sub> = -3610 cal/g
Oops corrected chemical formulae subscripts.
[Edited on 23-5-2011 by IndependentBoffin]
I can sell the following:
1) Various high purity non-ferrous metals - Ni, Co, Ta, Zr, Mo, Ti, Nb.
2) Alkex para-aramid Korean Kevlar analogue fabric (about 50% Du Pont's prices)
3) NdFeB magnets
4) High purity technical ceramics
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
