Question

The species which by definition has zero standard molar enthalpy of formation at 298 K is :

• A. $B{r}_2\left(g\right)$
• B. $C{l}_2\left(g\right)$
• C. $H_{2}O\left(g\right)$
• D. $C{H}_4\left(g\right)$

Answer 1

The correct option is B $C{l}_2\left(g\right)$

The species which by definition has zero standard molar enthalpy of formation at 298 K is $C{l}_2\left(g\right)$. $C{l}_2$ is gas at room temperature.

$B{r}_2$ is in liquid state at this temperature.

Hence, option B is correct.