Question

1. Model - Entropy as a State Function

   Entropy, S, as with all other state functions like internal energy, E, and enthalpy, H, is a function of the state of a system. Because measuring the absolute state of a system more difficult than measuring the changes in its states, it is the change in entropy, ΔS, in which we will be interested. This means the only aspects that will interest us will be the difference in the final and initial entropies of a system. The path by which the final state was attained is not of concern in a state function.

   Table 2. Sº for Selected Elements and Compounds at 298.15 K and 1 atm^1,2

   Substance	Al	Al	Al3+	Al2O3	C	C	CO	CO2	Cl2	Cl
   State	cr	g	aq	cr	graphite	g	g	g	g	g
   Sº, J/K·mol	28.3	164.6	-325	50.9	5.74	158.1	197.7	213.8	223.1	165.2

   Information - Standard Entropies

   Entropies unlike enthalpies of formation everything has a nonzero standard entropy. So you have to look up the standard entropies, Sº, for everything when calculating entropy change for a reaction in tables of thermodynamic data.

   How are the units of Sº different from those for the values of ΔH_fº?

   		The units of Sº and ΔHfº are both kJ/mol.
   		The units of Sº and ΔHfº are both J/mol·K.
   		The units of Sº are J/mol·K while those of ΔHfº are kJ/mol.
   		The units of Sº are kJ/mol·K while those of ΔHfº are kJ/mol.

Answer 1

Entropy is dergee of randomness while enthalpy of formation is heat change for formation of 1 mol substance from its sable constitutent elements.

(C) is correct option .

S° = J/mol-K

∆Hf = kJ/mol