Question

Which of the following will NOT have a standard enthalpy of formation (ΔH_f^o) equal to zero?

Select one:

a. He(s)

b. Ar(g)

c. He(g)

d. Al(s)

e. N₂(g)

Answer 1

Ans is a that is He(s)

All elements in their standard states (oxygen gas, solid carbon in the form of graphite, etc.) have a standard enthalpy of formation of zero, as there is no change involved in their formation.

As Helium naturally abundant in the gas form thats why heat of enthalpy of formation is zero for gas form not for the solid form.