Anybody having trouble remembering the difference between vaporisation, condensation, freezing, sublimation and the likes can look forward to this post/notes. It is not that students cannot understand the concepts, but usually student fail to recall the name of the phase change processes at crucial moments. And by crucial moments, I mean exams. Hence, Berry Berry Easy wants to impart another set of essential notes, this time on “Phases and Phase Change”
STPM Form 6 – Terminology and Concepts : Phases and Phase Change
Difference between the three phases:
| Solid | Liquid | Gas |
| Least kinetic energy (vibration and rotational forms and do not change their positions) | More energetic than solid, yet not as energetic than gas (translation, vibrational and rotational forms) | Most kinetic energy (translation, vibrational and rotation forms) |
Solid
Solid – a state having both a definite shape (fixed lattice structure) and a definite volume.
Unit cell – repeating structure subunits of a solid molecule (fixed lattice structure / crystal structure).
| Solid | |
| Simple cubic | One atom per repeating unit cell |
| Body-centred cubic | Two atoms per repeating unit cell |
| Face-centred cubic | Four atoms per repeating unit cell |
Liquid
Liquid – a state having a definite volume but no definite shape.
| Liquid | ||||
|
Intermolecular forces |
Hydrogen bond | Polar interaction | Dipole moments | Van der Waals |
| Strongest | Strong yet weaker than hydrogen bond | Strong yet weaker than hydrogen bond and polar interaction | Weakest | |
Surface tension – the resistance of a liquid to an increase in its surface area.
Viscosity – the resistance of a liquid to flow / the resistance to flow by an object through the liquid.
Summary of phase change (berry berry important)
| Phase Change | Term |
| Liquid to gas | Vaporisation |
| Gas to liquid | Condensation |
| Solid to liquid | Melting |
| Liquid to solid | Freezing |
| Solid to gas | Sublimation |
| Gas to solid | Deposition |
Isothermal – conditions where the temperature of a system does not change.
Triple point – all three phases (solid, liquid and gas) can coexist simultaneously in the equilibrium
Critical point – highest temperature and pressure at which a liquid may be observed.
Supercritical fluid – Beyond critical point, it is impossible to distinguish between a gas and liquid.
Normal boiling point – temperature at which a material boils when the pressure is 1.00 atm.
Adapted from The Berkeley Review (2001) pg 65
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