IB Chem Unit 7 (Phase diagram and change)

Solid

• Molecules packed tightly together

• Defined volume, defined shape

The temperature and kinetic energy are low

Liquid

• Molecules packed moderately-tightly together

• Defined volume, undefined shape

  • Takes the shape of its container

Temperature is higher, kinetic energy is medium

Gas

• Molecules are far apart 

• Undefined volume, undefined shape

Temperature and kinetic energy are high

how to determine the phase of a substance

• The phase of a substance depends on temperature and pressure

• Temperature is a measurement of the average kinetic energy in a sample

• Therefore, the hotter a substance is the faster the molecules move

• Adding or removing heat to/from a substance causes phase changes

  • From solid to liquid

Solid → Liquid

• Melting

• Endothermic

  

Liquid → Solid

• Freezing

• Exothermic

  

Liquid → Gas

• Vaporization

• Endothermic

  

Gas → Liquid

• Condensation

• Exothermic

  

Solid → Gas

• Sublimation

• Endothermic

  

Gas → Solid

• Deposition

• Exothermic

  

Phase Diagram

• Phase diagrams represent phase changes as a function of temperature & pressure.

Relate temperature and pressure to physical state

Normal boiling/melting point pressure

• 101 kPa

• 1.0 atm

• 760 mmHg

Triple Point

• Point on the phase diagram where solids, liquids and gasses all exist at the same time.

Critical Point

• Point where the liquid can no longer be distinguished from a gas 

• Vapor cannot be liquefied 

• Occurs at extremely high temperature and pressure