AP Chemistry / Unit 6: Thermochemistry
6.5 Energy of Phase Changes
Notes
Temperature stays constant during a phase change while energy goes into breaking or forming IMFs.
- Melting and boiling are endothermic; freezing and condensing are exothermic.
- $q=n\Delta H_{fus}$ or $q=n\Delta H_{vap}$.
Practice
While water boils at 100 °C, added heat:
Temperature stays constant.
Condensation is:
Gas releases energy as it forms liquid.
Heat to melt 2 mol of ice ($\Delta H_{fus}=6.0$ kJ/mol):
$2\times6.0$.
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