Based off the enthalpy of formation of a substance, how can you tell if its ther

Question

Based off the enthalpy of formation of a substance, how can you tell if its thermodynamically stable?

For example how would you order these substances by stability?

Thermodynamic Properties of Some Substances (at Substance }1? (kJ/mol) (kJ/mol) So (J/mol·K) Al(s) Al2- CO CO209) +28.3 +50.9 +197.7 +213.7 +202.8 +173.8 +69.9 +188.8 +192.5 +210.8 +240.1 +205.1 0 0 (1675.7 1582.3 110.5 393.5 137.2 -394.4 0 0 2(g) H F(a) H20(L)-2 H20()- N Hs(g) 271.1 285.8 -241.8 273.2 237.1 228.6 -16.5 +86.6 +51.3 0 3(g) -46. 1 +90.3 NO2) +33.2 0209) 0

Explanation / Answer

For "stability" we care mainly in fhe free energy, that is, the energy "free" for the reacction

then

all those G <0, are stabnle

if G = 0, those are elemental states / equilibrium

if G > 0, then this is not stable

so

NO, NO2, are not stable at STP conditions

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