STPM Chemistry Form 6 Notes – Terminology and Concepts : Phases and Phase Change

by BerryBerryTeacher

in Berry Reference (Notes)

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 – 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).

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 – a state having a definite volume but no definite shape.


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 fluidBeyond 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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