Question

For the species in the reaction below, ΔH°f is zero for ________.

2Co (s) + H2 (g) + 8PF3 (g) → 2HCo(PF3)4 (l)

A) Co (s)

B) H2 (g)

C) PF3 (g)

D) HCo(PF3)4 (l)

E) both Co(s) and H2 (g)

Answer 1

The correct option is- E) both Co(s) and H_{​​​​​​2}

Explanation:- Heat of formation (delta H_f) is the amount of heat released or absorbed to form one mole of a substance in its standard. If the substance is in its standard state then the heat of formation will be zero for that substance.

Now Co is in its standard state i.e. solid state as well as H₂ is in its standard state i.e. gaseous state. So the heat of formation for Co(s) and H₂(g) will be zero.