Prentice Hall © 2003Chapter 11 The forces holding solids and liquids together are called...
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Transcript of Prentice Hall © 2003Chapter 11 The forces holding solids and liquids together are called...
• Sublimation: solid gas.• Vaporization: liquid gas.• Melting or fusion: solid liquid.• Deposition: gas solid.• Condensation: gas liquid.• Freezing: liquid solid.
Phase ChangesPhase Changes
Phase ChangesPhase Changes
• ENERGY ASSOCIATED WITH HEATING CURVES
Topics
• Vapor Pressure
• Normal Boiling Point
• Normal Freezing
• Specific Heat
• Enthalpy (Heat) of Vaporization
• Enthalpy (Heat) of Fusion
Vapor Pressure
• THE PRESSURE OF A VAPOR IN EQUILIBRIUM WITH ITS LIQUID (OR ITS SOLID)
NORMAL BOILING POINT & FREEZING POINTS
• NORMAL BOILING PT. - THE TEMPERATURE @WHICH VAPOR PRESSURE = 1 atm
• NORMAL FREEZING PT. – THE TEMPERATURE @ WHICH THE VAPOR PRESSURE OF THE SOLID AND THE LIQUID ARE THE SAME
Heat Capacity aka Specific Heat (C)
• Specific Heat (C) = the amount of energy required to raise the temperature of 1 gram of substance 1 degree celcius
Specific Heat (C) aka Heat Capacity
• Units for: specific heat (C) = J/g-oC
where J = joulesoC = temperature in oC
g = mass in grams
Specific Heat (C) Values(aka Heat Capacity)
• Example: Water
• LIQUID: CLiq = 4.18 J/ (oC . g)
• LIQUID: Csol = 2.09 J/ (oC . g)
• LIQUID: Cgas = 1.84 J/ (oC . g)
Use of Specific Heat
• q = mCT
• q = gm substance x specific heat x T
• where:
• M = mass of substance in grams
• q = amount of heat (energy)
• C = specific heat
• And T = change in temperature
Enthalpy of Vaporizationaka heat of vaporization (Hvap)
• Is the amount of heat needed to convert a liquid to a vapor at its normal boiling point
Enthalpy of Fusion aka heat of fusion (Hfus)
• Is the amount of heat needed to convert a solid to a liquid at its normal melting (freezing) point
Units for Hvap, Hfus and heat(q)
Heat of fusion Hvap = kJ/mol
Heat of vaporization Hfus = kJ/mol
Heat (q) = Joules
Therefore:
• To come up with Joules which is the unit of heat, if:
H is given, then:qvap = Hvap x moles
and
qfus = Hfus x moles
(2) Specific heat (C) is given, then: q = mCT
Sample Problem
• Calculate the enthalpy change upon converting 1 mole of ice at -25 oC to steam at 125 oC under a constant pressure of 1 atm? The specific heats are of ice, water and steam 2.09 J/g-K for ice, 4.18 J/g-K for water and 1.84 J/g-K for steam. For water, Hfus= 6.01 kJ/mol, and Hvap = 40.67kJ/mol.
• Note: The total enthalpy change is the sum of the changes of the individual steps.
Take Home Quiz
• Do Problem 11.34, page 444
• Due Wednesday at the beginning of class, Dec. 1
• Must show work for full credit
• Individual work not required
HEATING CURVES
• ENERGY ASSOCIATED WITH HEATING CURVES
• During a phase change, adding heat causes no temperature change.
Critical Temperature and Pressure• Gases liquefied by increasing pressure at some
temperature.• Critical temperature: the minimum temperature for
liquefaction of a gas using pressure.• Critical pressure: pressure required for liquefaction.
Phase ChangesPhase Changes
• Phase diagram: plot of pressure vs. Temperature summarizing all equilibria between phases.
• Given a temperature and pressure, phase diagrams tell us which phase will exist.
• Any temperature and pressure combination not on a curve represents a single phase.
Phase DiagramsPhase Diagrams
Phase DiagramsPhase Diagrams
The Phase Diagrams of H2O and CO2
Phase DiagramsPhase Diagrams