Transcript Properties of Matter - Broadneck High School

Heat in Changes of State
Energy Changes Accompanying Phase Changes
Gas
Energy of system
Vaporization
Condensation
Sublimation
Liquid
Melting
Freezing
Solid
Brown, LeMay, Bursten, Chemistry 2000, page 405
Deposition
Heating Curve for Water
Temperature (oC)
E
D
100
C
liquid
B
0
A
solid
Heat added
LeMay Jr, Beall, Robblee, Brower, Chemistry Connections to Our Changing World , 1996, page 487
gas
Heating Curve for Water
Temperature (oC)
vaporization
D
100
condensation
melting
C
liquid
B
0
A
solid
freezing
Heat added
LeMay Jr, Beall, Robblee, Brower, Chemistry Connections to Our Changing World , 1996, page 487
E
gas
Heating Curves
• Phase Change
– change in PE (molecular arrangement)
– temp remains constant
• Heat of Fusion (Hfus)
– energy required to melt a specific amount of a
substance at its melting point
• Heat of Vaporization (Hvap)
– energy required to vaporize a specific amount of a
substance at its boiling point
Heating Curves
140
120
Gas - KE 
Temperature (oC)
100
Boiling - PE 
80
60
40
20
0
-20
Liquid - KE 
Melting - PE 
-40
-60
-80
Solid - KE 
-100
Time
Heating Curves
• Temperature Change
– change in KE (molecular motion)
– depends on heat capacity
• Heat Capacity
– energy required to raise the temp of 1 gram of a
substance by 1°C
– water has a very high heat capacity
The quantity of a substance, the amount of heat transferred, its heat
capacity, and the temperature change are related in two ways:
q = nCpΔT where n = number of moles of substance
q = mCsΔT where m = mass of substance in grams
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Calculating Energy Changes Heating Curve for Water
140
120
H = mol x Hfus
H = mol x Hvap
Temperature (oC)
100
80
Heat = mass x t x Cp, gas
60
40
20
0
Heat = mass x t x Cp, liquid
-20
-40
-60
-80
Heat = mass x t x Cp, solid
-100
Time
Phase Diagrams
• Show the phases of a substance at different
temps and pressures.
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem