What is the molar entropy of fusion (delta)Sf (f in subscript) for lead (Pb) in Joules ?

Question

Can you also include the steps?

Answer 1

Entropy is measured in units of joules/(degree K), and the *molar* entropy is measured in units of joules/((degree K)*mole), not just joules.

*I* would get the molar entropy for the fusion of lead by going to the NIST on-line database of thermodynamic properties at the first source below, and look up the melting point of Pb (second source below). Doing this, I find that Pb melts at a temperature between 600 K and 601 K .

I would then look up the molar entropies of solid Pb and liquid Pb at ~601K at the third and fourth sources below. Doing this, I find that:

S_solid(600 K) = 84.34 J/(K*mol)
S_liquid(601K) = 92.33 J/(K*mol)

The molar entropy of fusion is simply given by:

delta-S_fusion = S_liquid - S_solid = 7.99 J/(K*mol)



If this is some sort of homework problem, though, I suspect that you were given a set of thermodynamic data for a series of reactions, and that by adding and subtracting some combination of those reactions, you can obtain the net reaction:

Pb(solid) = Pb(liquid)

at the melting temperature of Pb. The molar entropy of this reaction is then given by the same combination of sums and differences of the reaction entropies as you performed to get the net reaction above.