Heating CurveevruC gnitaeH

Plateau:Energy needed to overcome the IMFs in the solid.

All added heat is used to overcome these forces, NOT increase temperature.

When all particles can move freely (no more solid) then temperature will go up.

Freezing of Water

Freezing Point

Plateau:Particles lose energy and slow down - pulled closer together by the IMFs. Organize into crystals.

Crystal particles release remaining KE which keeps the temperature constant.

Freezing of Water

Freezing Point

When all energy is lost (no more liquid), then temperature will drop.

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.