Question

recognizing enthalpy of formation
which substances have δhf = 0 kj/mol by definition? choose four correct answers.
br₂(l)
o₂(g)
h₂o(l)
he(g)
n(g)
fe(s)

Explanation:

The standard enthalpy of formation ($\Delta H_f$) of an element in its standard state is zero. The standard state of bromine is $Br_2(l)$, oxygen is $O_2(g)$, helium is $He(g)$ and iron is $Fe(s)$. Water ($H_2O(l)$) is a compound and not an element in its standard - state, and $N(g)$ is not the standard state of nitrogen (the standard state of nitrogen is $N_2(g)$).

Answer:

$Br_2(l)$, $O_2(g)$, $He(g)$, $Fe(s)$