Thermodynamics and Thermochemistry 2 Question 8
8. The species which by definition has zero standard molar enthalpy of formation at $298 \mathrm{~K}$ is
(2010)
(a) $\mathrm{Br}_{2}(g)$
(b) $\mathrm{Cl}_{2}(g)$
(c) $\mathrm{H}_{2} \mathrm{O}(g)$
(d) $\mathrm{CH}_{4}(g)$
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Solution:
- Elements in its standard state have zero enthalpy of formation. $\mathrm{Cl}{2}$ is gas at room temperature, therefore $\Delta H{f}^{\circ}$ of $\mathrm{Cl}_{2}(g)$ is zero.
