“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  www.dictionary.com Phase Changes “Latent” Heat of Fusion “Latent” Heat of Vaporization

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

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

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

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

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

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

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

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.