Changes of State
Objectives:
• 1. Relate changes in state to changes in energy.
• 2. Compare the different states of matter in terms of
potential and kinetic energy
• 3. Describe the major events that occur along a heating
curve.
• 4. Interpret a phase diagram.
Key Terms:
• Vaporization, condensation, evaporation, equilibrium,
vapor pressure, boiling point, heat of vaporization, freezing
point, heat of fusion, sublimation, deposition, heating
curve, phase diagram
Energy and Phase Changes
• According to the kinetic-molecular theory, a substances phase
is determined by the balance of its kinetic and intermolecular
forces. What this means is that you can convert matter from
one phase to another by simply adding or deleting kinetic
energy (heat).
Changes in State
•
•
•
•
•
•
•
liquid to gas - vaporization, by process of evaporation
solid to gas - sublimation
liquid to solid - freezing
solid to liquid - melting
gas to liquid - condensation
gas to solid – deposition
triple point – where all
phases are in equilibrium
Heating Curve
• The heating curve is a representation of the phases of a substance
compared to the temperature and internal energy of a substance.
The blue lines represent the different phases of a substance while
the red lines represent the heats of fusion and vaporization.
• endothermic reactions move from left to right as the products
increase in kinetic energy and become less organized
Heat Associated with Phase Changes
•
Heat of fusion (DHfus) - the amount of heat absorbed as 1 mole of a substance melts
–
–
–
–
•
Heat of solidification (DHsolid) - the amount of heat released as 1 mole of a substance solidifies
–
–
–
–
•
occurs between B & C
exothermic
occurs at constant temperature
H2O(l) g H2O(s) DHsolid = -6.01kJ/mol
Heat of vaporization (DHvap) - the amount of heat absorbed as 1 mole of a substance solidifies
–
–
–
–
•
occurs between B & C
endothermic
occurs at constant temperature
H2O(s) g H2O(l) DHfus = 6.01kJ/mol
occurs between D & E
endothermic
occurs at constant temperature
H2O(l) g H2O(g) DHvap = 40.7kJ/mol
Heat of condensation (DHcond) - the amount of heat released as 1 mole of a substance solidifies
–
–
–
–
occurs between B & C
exothermic
occurs at constant temperature
H2O(g) g H2O(l) DHcond = -40.7kJ/mol
Heat of Solution
• Heat of solution (DHsol) - the amount of heat
absorbed or released as 1 mole of a substance
dissolves in 1L of solution
– exothermic or endothermic
– NaOH(s) g Na+(aq) + OH-(aq) DHsol = -445.1kJ/mol
– NH4NO3(s) g NH4+(aq) + NO3-(aq) DHsol = 25.7kJ/mol