Chemistry 127... Review Notes

September 14, 2004

• The exam might include a table with equation(s) and constants. Such a table might look like this.
• Claussius Clapeyron: ln(P) = - (delta H/R) * (1/T) + C
  • (I will probably not identify the terms in the equation)
• R = 8.314 J/mol K
• R = 0.08205 liter atm/mol
  • we use the first one in heat calculations, like slope of vapor pressure curve
  • we might use the second one for gas law problems and for osmotic pressure
• I'd provide values for K_b and K_f (molal boiling and freezing point constants)
• I'd provide heat capacity and heat (enthalpy) of vaporization, enthalpy of freezing and enthalpy of solution values for any species we use.
• I'll provide atomic weights (or a periodic table) if they are needed
• I will expect you to know that water has a density of 1.00 g/ml (is 1000 ml / kg)
• I will also expect you to know the normal boiling point and freezing point of water (100, 0 ^oC) and that normal barometric pressure is, of course, 1.0 atmospheres. If I use other uniits like torr or mm Hg I would provide a value (760 torr = 1 atm.)
• Generally, I would provide values for other properties

This page looks at the kind of problems (calculations) associated with the chapter and likely to show us on the exam.

this document does not cover ideas and vocabulary (the descriptive and qualitative material we have covered.) Of course that also appears on the exam, but I'm getting more questions about problems and calculations

• Chapter 10.. pages 386-387 show how to compute a dipole and to use the dipole to figure out the % ionic character of a bond.
  • The exam will NOT include any calculations of this type
  • Of course, you should understand the concept (and the link to electronegativity of the atoms involved.)
• Section 10.4 discusses the energy associated with phase changes.
  • the molar enthalpy of fusion and of vaporization (and, change sign to get molar enthalpy change for condensation and for freezing)
  • You should certainly be able to compute, for example, how much energy will it take to melt 100 gram of ice. (The molar heat of fusion for ice would be given.)
  • The formal discussion of entropy (S) and free energy (G) such as found on the top half of page 397 will NOT be included in any of the problems.
• Section 10.4 also discusses heat capacity and the energy required to change the temperature of a sample.
  • you should be able to compute the energy required to heat 3.5 moles of water from 0^oC to 45^oC. (Value for heat capacity would be given)
  • the problem could be reversed, asking what the heat capacity is if ___ Joules of energy caused the temperature to change by ___ degrees.
  • I've been asked about this a couple of times: the change in Kelvin and the change in Celsius temperature is the same.
• Section 10.5 describes how vapor pressure changes with temperature
  • the Clausius Claperyon equation will be provided for you.
  • The most useful plot is ln (natural logarithm) of pressure vs. 1/T where T is in Kelvin
    • This produces a straight line.
    • A few data points lets us find pressure at other temperatures
  • The slope is /-(delta H_vaporization R)
    • so the slope of the graph can be used to determine the molar enthalpy of vaporization.
  • You should be able to work problems such as the one from recitation quiz.
    • In practice I would work part of the problem and ask you to finish it or to comment on it. The full problem-- computing the natural log(ln) function, plotting, finding slope... -- this takes too long in an exam with many question.
• Section 10-6 to 10-10 discusses phases and crystal lattices
  • there will be no calculation from this section
  • I asked you to be able to discuss cubic and face centered cubic crystals.
  • You should also understand the idea of closely packed and the coordination number.
• Section 10-11 (Phase Diagrams)
  • there are no computational problems on the exam from this section.
  • you will probably be asked to comment of a phase diagram (explain what it shows, label the regions and the transitions.)

Chapter 11 on solutions has a number of likely problems (calculations)

• Various measures of concentration. If we told how a solution was prepared, you should be able to compute...
  • mole fraction, molarity, molality, weight %
  • you should also be able to use the density to convert from volume to mass or mass to volume. This may be needed if we want to compute both molarity and molality.
• Raoult's law P_i = X_i * P_io
  • this equation will NOT be provided, you should know it.
  • you should be able to compute vapor pressure of a component in a solution, given concentration and the vapor pressure of the pure species.
  • if there are two volatile species (vapor producing) then a separate calculation may be needed for each component.
  • the discussion of distillation -- we condense the vapor.
    • if two volatile liquids are present we can separate the mixture.
    • while we wouldn't ask you to compute such a distillation curve, you could find what the vapor looks like above a solution. It will not have the same composition as the liquid.
• Boiling point elevation and Freezing point depression
  • the equations are simple; they will NOT be provided at the exam
  • delta T = K * (molality)
    • A simple exam question might be... "what is the boiling point (freezing point) of a solution that is of some given concentration"
    • remember this is molality not molarity
    • We often go the other way, ..."if a solution freezes at -0.78 degrees, what is the molality.?" (Often, if the solution has 4.5 g/kg, what is the Molecular Weight.)
• Osmostic pressure is similar PI = n R T / V
  • what pressure can we expect for a given concentration?
  • can we measure the pressure and determine concentration (or molecular weight)?
• September 14, 2004
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