Heat of Formation ... Please Help?

Question

Of the following which would not be considered appropriate equations to represent "standard heat of formation" processes? explain

a.C(s) + 1/2O(2)(g) ------> CO(g)

b.N(2)(g) + 3H(2)(g) ------> 2NH(3)(g)

c.CS(2)(g) ----> CS(2)(l)

d.C(g) + 4H(g) ----> CH(4)(g)

e.4CO(2)(g) + 5H(2)O(l) ------> C(4)H(10)(g) + 13/2O(2)(g)

Please Explain How to Solve The Problem.

Answer 1

The standard enthalpy of formation or "standard heat of formation" of a compound is the change of enthalpy that accompanies the formation of 1 mole of a substance in its standard state from its constituent elements in their standard states (the most stable form of the element at 101.325 kPa of pressure and the specified temperature, usually 298 K or 25 degrees Celsius). Its symbol is ΔHfO.

a: is appropriate, carbon is normally solid and O2 and CO are normally gas

b: is approprate, all are gasses at 25C and 101 kPa

c: is not appropriate becasue CS is normally a liquid at the standard conditions

d: is not appropriate since carbon is normally a solid at standard conditions

e: is approprate, water is normally a liquid and the others are normally gasses