Question

For which equation, does the enthalpy of reaction represent `DeltaH_f^@` for methanol? `1.` `CO(g) + 2H_2(g) rarr CH_3OH(l)` `2.` `C(g) + 2H_2O(g) rarr CH_3OH(l)+1/2H_2(g)` `3.` `C(s) + 2H_2(g) +1/2O_2(g) rarr CH_3OH(l)` `4.` `C(g) + 2H_2(g) rarr CH_3OH`

Answer 1

`"Option 3"`

Explanation:

The standard enthalpy of formation is the enthalpy associated with the formation of 1 mole of substance from its constituent elements in their standard states under specified conditions. And of course the standard states of the given elements are as carbon graphite, dihydrogen, and dioxygen gas.

And thus, the enthalpy of formation of methanol is the enthalpy associated with the following reaction:

`C(s) + 2H_2(g) + 1/2O_2(g) rarr CH_3OH(l) +DeltaH_f^@`

I included the enthalpy term, because typically this definition is used in thermochemical scenarios.