Phase Changes

Phase Changes

Courtesy www.lab-initio.com

Water phase changes

Temperature remains __________during a phase change.

constant

Kinetic Energy, Potential Energy and a Heating Curve.• Since Temperature is a measure of "Average

Kinetic Energy", any change in temperature is a change in Kinetic Energy.

• Since temperature does not change during a phase change, the energy that is gained or lost is Potential Energy.

• Remember the 3 Ps. Plateau, Phase change and Potential Energy Change.

Add these abbreviations to graph!

PE = Potential energy

KE = Kinetic energy

KE

PEKE

KE

PE

Exothermic ProcessesProcesses in which energy is released as it proceeds, and surroundings become warmer

Reactants Products + energy

Endothermic ProcessesProcesses in which energy is absorbed as it proceeds, and surroundings become colder

Reactants + energy Products

Standard Temperature

Standard Temperature equals: 273 Kelvin (273 K) 0 C

Converting Celsius to Kelvin

Many problems involving temperature require that the temperature be in KELVINS!

Kelvins = C + 273

°C = Kelvins - 273

Melting point

• Melting - change from solid to liquid

• Melting point - SPECIFIC temperature when melting occurs.

• Each pure substance has a SPECIFIC melting point.• M.P. of Water = 0°C (32°F)

Boiling Point

• Boiling Point – temperature at which a liquid boils

• Each pure substance has a SPECIFIC boiling point.• Examples:• B.P. of Water = 100°C (212°F)

What’s the temperature at point B in kelvins?

What’s the temperature at point C in kelvins?

Which region is kinetic energy the highest?

III

III

IV

Which region has the lowest potential energy?

III

III

IV