1. “Latent” Heat of Fusion “Latent” Heat of Vaporization
Students will be able to calculate energy required during phase changes.
la·tent
Adjective : present but not visible, apparent, or actualized; existing as potential 
Phase Changes
“Latent” Heat of Fusion
“Latent” Heat of Vaporization

2. fp and mp should occur at same temp
Melting
Freezing
Process of changing from a solid to a liquid
Endothermic
Process of changing from a liquid to a solid
Exothermic l s °C
Time
melting point
fp and mp should occur at same temp l s
freezing point

3. bp and cp should occur at same temp
Boiling
Condensing
Process of changing from a liquid to a gas
Endothermic
Process of changing from a gas to a liquid
Exothermic g l °C
Time g l
boiling point
bp and cp should occur at same temp
condensing point

4. Heat of Fusion (Hf)
heat required to melt one mole of a substance at its melting point
J/mole
kJ/mole

5. Heat of Vaporization (Hv)
Heat required to vaporize one mole of a substance at its boiling point
J/mole
kJ/mole

6. Heat of Combustion (Hcomb)
Heat required to burn one mole of a substance
J/mole
kJ/mole

7. Energy involved in physical changes:
= E = m · T ∙ c l s
Melting  E = (Hf)(mole)
Vaporize/Boil  E = (Hv)(mole)

8. Ex: If the Hf of water is 6. 01 kJ/mol and Hv is 40
Ex: If the Hf of water is 6.01 kJ/mol and Hv is 40.7 kJ/mol, how much energy is needed to melt 45.23g?
Convert grams to moles
2. Calculate E

9. If 537.5 J of energy is used, how many grams of CO2 can be vaporized?
Hf = 0.52 kJ/mol
Hv = 3.29 kJ/mol
E = (Hv)(mole)
Solve for moles. (Be sure energy measurements are the SAME.)
2. Convert moles to grams.