Question

select which of the following standard enthalpy of formation values is not zero at 25°c: check all that apply. s₈(rhombic) h(g) br₂(l) pb(s) ne(g) none of the above

Explanation:

The standard enthalpy of formation ($\Delta H_f^\circ$) is zero for elements in their standard states at 25°C. Rhombic sulfur (S₈(rhombic)) is the standard state of sulfur; neon (Ne(g)) is a noble gas in its standard gaseous state; lead (Pb(s)) is a metal in its standard solid state; bromine (Br₂(l)) is a halogen in its standard liquid state. Hydrogen exists as H₂(g) in its standard state, so H(g) (atomic hydrogen gas) is not the standard state, meaning its $\Delta H_f^\circ$ is non-zero.

Answer:

$\square$ H(g)