Using data in table below and S °(NaCl(s))= 72.38 J·mol-1·K-1, calculate ÄfS° for NaCl(s) in J·mol-1·K-1.
Compound S °, J·mol-1·K-1 Compound S °, J·mol-1·K-1
C(s) 5.69 H2(g) 130.6
N2(g) 191.5 O2(g) 205.0
Na(s) 51.0 Cl2(g) 223.0
Ca(s) 154.8 S(s) 31.8
To calculate the standard molar entropy change (ΔS°) for NaCl(s), we first need to determine the sum of the standard molar entropies of the individual elements in their standard states.
The equation for calculating ΔS° for the formation of NaCl(s) is:
ΔS° = ΣS°(products) - ΣS°(reactants)
The standard molar entropy for the elements in their standard states can be found in the table:
Na(s): 51.0 J·mol-1·K-1
Cl2(g): 223.0 J·mol-1·K-1
To determine the standard molar entropy change for NaCl(s), we only need the values for Na and Cl2.
ΔS° = S°(NaCl(s)) - [S°(Na(s)) + S°(Cl2(g))]
Using the given value for S°(NaCl(s)) = 72.38 J·mol-1·K-1, the equation becomes:
ΔS° = 72.38 J·mol-1·K-1 - [51.0 J·mol-1·K-1 + 223.0 J·mol-1·K-1]
Calculating this expression gives:
ΔS° = 72.38 J·mol-1·K-1 - 274 J·mol-1·K-1
ΔS° = -201.62 J·mol-1·K-1
Therefore, the standard molar entropy change (ΔS°) for the formation of NaCl(s) is -201.62 J·mol-1·K-1.