Question

which substance has δhf defined as 0 kj/mol?
○ h₂o (s)
○ ne (l)
○ f₂ (g)
○ co₂ (g)

Explanation:

The standard enthalpy of formation ($\Delta H_f$) of an element in its standard state is 0 kJ/mol.

• $H_2O$(s) is a compound, not an element in standard state, so its $\Delta H_f

eq 0$.

• Ne(l): Neon's standard state is gas (Ne(g)), so Ne(l) is not in standard state, $\Delta H_f

eq 0$.

• $F_2$(g): Fluorine is a diatomic gas in its standard state (elemental form, gaseous), so $\Delta H_f = 0$.
• $CO_2$(g) is a compound, $\Delta H_f

eq 0$.

Answer:

C. $F_2$(g)