(a) Enthalpy of vaporisation (ΔΗ) - 26 k/mol.
Boiling point (T) = 35°C = (35 + 273)
K = 308 K
Now, at constant pressure
Entropy change ∆S = \(\frac{-\Delta H}{T}\)
∆S = \(\frac{26K/mol}{308K}\)
∆S = 0.0844 kJ mol−1 K−1
(b) ∆fH° = ∑∆H°Products − ∑∆H°Reacants
−1323 = {2(−393.5) + 2(−249.0)}
−{∆H°C2H4 + 0}
−1323 = −1285 − ∆H°C2H4 + 0}
∆H°C2H4 = −1285 + 1323 = 38 kJ mol−1
(c) Path functions: These are the functions whose magnitude depend on the path followed during a process as well as on the end states. E.g. work (w), heat (Q) are path functions.