The convention for this example is h^ = 0 for all elements in their normal states at 298 K and 1 atm pressure. For this reaction, Zr and ZrO2 are solids and O2 is a gas. Also, AH!J98 = -262.3 kcal / mole - at 1500, the enthalpy change of the reaction is: Note: the following equation is missing from the proof p. 246.
AHo(1500) = h^, (1500)-hzr(1500)-h^(1500) = -239.9-9.6-9.6 = -259.1 kcal/mole
The enthalpy change of the reaction is ~ 3 kcal/mole higher at 1500 K than at 298 K. All things considered, though, this change is insignificant.
The effect of ACP in Equation (9.8) is analyzed for gas-phase equilibrium calculations in Problem 9.24.
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Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.