What reaction illustrates $\Delta H^\circ_\mathrm f$ for $\ce{CaCO3}$?
Answer: $\ce{Ca(s) + C(s) + 3/2O2(g) -> CaCO3(s)}$.
Ok so why isn't it: $\ce{2Ca(s) + 2C(s) + 3O2(g) -> 2CaCO3}$
Or
$\ce{Ca(s) + C(s) + O3(g) -> CaCO3}$ ?
For example in another similar question:
Choose the reaction that illustrates $\Delta H^\circ_\mathrm f$ for $\ce{Ca(NO3)2}$.
Answer: $\ce{Ca(s) + N2(g) + 3 O2(g) -> Ca(NO3)2(s)}$
Can someone confirm this assumption of mine: it's ok to use fractions in these types of equations to blance it out as long as it's in oxygen's coefficient.
As that assumption correct?