Heating CurveevruC gnitaeH

• Explain the plateau of heating and cooling curves.

Include: IMFs, exothermic, endothermic • Define melting and boiling point in terms of

intermolecular forces and particle size. 

Additional KEY Terms

Heating Plateau:Minimum amount of energy is needed to overcome the intermolecular forces – endothermic process.

All added heat is used to overcome these forces, NOT increase kinetic energy (temperature).

Plateau ends when all particles have phase

changed.

Cooling Plateau:Particles lose energy and slow down - pulled together by the IMFs.

Organizing into restrictive phases causes the release of stored energy – exothermic process

Freezing of Water

Freezing Point

Plateau ends when all particles have phase

changed.

Freezing of Water

Freezing Point

Melting and boiling points are a characteristic physical property.

Generally, as mass increases, melting/boiling point also increases.

(more intermolecular forces to work against)

Ionic compounds typically have higher melting point than molecular compounds.

NaCl

Sugar

160oC

801oC

IMFs must be overcome in order for a substance to change states/phases.

The greater the forces between the particles, the more energy needed to overcome these forces.

H

O

H Cl -Na +

H

O

H

Cl-

Na+

So, the greater the IMFs, the higher the melting and boiling point.

CAN YOU / HAVE YOU?

• Explain the plateau of heating and cooling curves.

Include: IMFs, exothermic, endothermic • Define melting and boiling point in terms of

intermolecular forces and particle size. 

Additional KEY Terms