Thermodynamics and Thermochemistry 2 Question 8

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

(2010)

(a) Br2(g)

(b) Cl2(g)

(c) H2O(g)

(d) CH4(g)

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Solution:

  1. Elements in its standard state have zero enthalpy of formation. $\mathrm{Cl}{2}isgasatroomtemperature,therefore\Delta H{f}^{\circ}of\mathrm{Cl}_{2}(g)$ is zero.