Phase Changes & Phase Diagram Lab
Select a substance, adjust pressure, and watch the heating or cooling curve build in real time. Observe flat temperature plateaus during phase transitions, explore the P-T phase diagram, and investigate how solutes shift freezing and boiling points.
Guided Experiment: Heating Curve of Water
What do you predict the heating curve of water will look like from -20°C to 120°C at 1 atm? Where will temperature remain constant, and which plateau will be longer?
Write your hypothesis in the Lab Report panel, then click Next.
Heating Curve
Phase Diagram (P-T)
Controls
Set > 0 to see colligative effects (assumes NaCl, i = 2)
Current State
Data Table
(0 rows)| # | Trial | Substance | Phase | T(°C) | P(atm) | Q(kJ) | c used(J/(mol·K)) | ΔH(kJ/mol) |
|---|
Reference Guide
Heating Curve Segments
A heating curve plots temperature against energy added at constant pressure. It has five segments for substances with a liquid phase.
During melting and boiling, temperature stays constant because all added energy breaks intermolecular bonds instead of increasing kinetic energy.
Phase Diagram (P-T)
A pressure-temperature phase diagram shows which phase is stable at each combination of P and T. Three boundary curves separate the solid, liquid, and gas regions.
Triple point is where all three phases coexist in equilibrium. Below the triple point pressure, a substance sublimes directly from solid to gas.
Critical point is where the liquid-gas boundary ends. Above this temperature and pressure, the substance becomes a supercritical fluid with no distinct liquid or gas phase.
Latent Heat
Latent heat is the energy absorbed or released during a phase change without a temperature change.
For water, the enthalpy of vaporization (40.67 kJ/mol) is about 6.8 times larger than the enthalpy of fusion (6.01 kJ/mol), which is why the boiling plateau is much longer than the melting plateau on the heating curve.
Colligative Properties
Adding a nonvolatile solute to a solvent shifts the phase boundaries. These colligative effects depend only on the number of solute particles, not their identity.
For NaCl in water (i = 2), K_b = 0.512 K kg/mol and K_f = 1.86 K kg/mol. A 0.5 m NaCl solution depresses the freezing point by about 1.86°C and elevates the boiling point by about 0.51°C.