9.19

[camrynpatterson3C]

How do we find deltaS(vap) when the temperature isn't set at the boiling point?

[Vincent Chiang 1L]

The first step is to heat the reactants to 100 degrees Celsius using the formula delta S = C(P,m)*ln(T2/T1).

[McKenna disc 1C]

Vincent is correct, but the next steps are as follows...
There's a wonderful bit in the book about this exact scenario: "Finding entropy of transition at another temperature."
We must follow 3 steps:
1. Heat the liquid to its normal boiling point.
2. Allow it to vaporize.
3. Cool the vapor back to 25 degrees celsius (or whatever the temperature of interest is).
So, yes, you use the equation Vincent suggested for the first step. ΔS= C ln (t2/t1), where T2 is the boiling point and T1 is the temperature at which you start.
For the second step, you use the equation ΔSvap= ΔHvap/Tb (where Tb is the temperature of the boiling point).
And, the same equation follows for the third step as was used in the first: ΔS= C ln (t2/t1), but T2 is the temperature to which we are cooling the substance and T1 is the temperature at which we begin.
Hope this helps.