Achieve Question 7

[Sophia Hartwell 1F]

Three liquid samples of known masses are heated to their boiling points with the use of a heater rated at 400.0 W . Once the boiling points of each sample are reached, the samples are heated for an additional 3.66 min , which results in the vaporization of some of each sample. After 3.66 min , the samples are cooled and the masses of the remaining liquids are determined. The process is performed at constant pressure. The results are recorded in the table.

Liquid Boiling point (°C) Initial mass (g) Final mass (g)
C2H5OH 78.3 390.42 295.87
C4H10 −1.00 323.3 86.96
C3H6O 56.2 516.4 346.39

Calculate the molar enthalpy of vaporization, ΔHvap , and the molar entropy of vaporization, ΔSvap , for each sample. Assume that all of the heat from the heater goes into the sample.

Any walkthrough of how to find the molar entropy and enthalpy of vaporization would be super helpful!

[Charmaine Ho 2G]

To find molar enthalpy, you divide the energy supplied by the number of moles vaporized, because ΔHvap = kJ/mol
Because the energy supplied is given in watts, recall W = 1 J/s so convert 400W into kJ using 3.66 min
To find the number of moles vaporized, divide the mass difference by the molar mass

To find molar entropy, you use ΔSvap=ΔHvap/T, where T is the boiling point in Kelvin

[Sophia Hartwell 1F]

To find molar enthalpy, you divide the energy supplied by the number of moles vaporized, because ΔHvap = kJ/mol
Because the energy supplied is given in watts, recall W = 1 J/s so convert 400W into kJ using 3.66 min
To find the number of moles vaporized, divide the mass difference by the molar mass

To find molar entropy, you use ΔSvap=ΔHvap/T, where T is the boiling point in Kelvin

Ah thank you, this explanation helps me a lot.