The question
Name: ______________________ Date: ____________ Reading a cooling curve (4 points)
Graph
Cooling curve of Compound X
A 25.0 g sample of liquid Compound X (molar mass 78.11 g/mol) at 30.0 °C is placed in a cooling bath that removes energy from it at a steady 50.0 J/s. A probe records its temperature.
Data table
| Time (s) | Compound X |
|---|---|
| 0 | 30 |
| 21.3 | 5.5 |
| 84.5 | 5.5 |
| 96.3 | -10 |
(a) Identify the freezing point of Compound X. [1 point]
(b) Calculate the molar enthalpy of fusion of Compound X, in kJ/mol. [2 points]
(c) Explain, at the particle level, why the temperature stays constant from 21.3 s to 84.5 s even though energy is still being removed. [1 point]