[sy2m]

For which of the following reactions is delta Hrxn equal to delta Hf (standard heat of formation) of the product(s)?
You do not need to look up any values to answer this question.
Select all that apply.

1) C(s) + O2 (g) --> CO2 (g)
2) Na(s)+ 1/2 Cl2(l) --> NaCl(s)
3) Na(s) + 1/2 Cl2(g) --> NaCl(s)
4) 2Na(s) + Cl2(g) --> 2NaCl(s)
5) CO(g) + 1/2 O2(g) --> CO2(g)
6) CaCO3(g) -->CaO + CO2 (g)

I know it's not 2, 4, or 6, and I am sure that 1, 3 are included. Am I right so far? How about 5?

Thank you!!!

[Astrokel]

How about 5?

What is the definition of standard heat of formation?

I know it's not 2, 4, or 6, and I am sure that 1, 3 are included.

yes