posted by Anonymous .
Which of the following substances have a standard heat of formation (ÄHf°) of zero?
O2(g) at 25.0 degree C and 1 atm
Fe at 1200 degree C
C2H6(g) at standard conitions
Cl2(g) at 2 atm
O2 @ 25 C and 1 atm is the only one.
Fe yes but at 25 C, not 1200.
C2H6 no since it's a compound.
Cl2 yes at 25 C and 1 atm but not at 2 atm.