Chemistry 1020Lecture 15Notes
Review:
Chapter 4—Energy
 Definition of energy; relationship to work.
 First Law of Thermodynamics
 Mechanical energy; kinetic and potential
 Internal energy
 Heat as a form of energy
 Units of energy: Joule and calorie
 Measuring heat with a calorimeter
 Combustion reactions: writing and balancing.
 Predicting heats of reaction from bond energies
 Calculating energies per mole and energies per mass
 Comparing energy yields of fuel sources
 Interconverting energy forms
 Heat conversion to work—maximum efficiency (T_{hi}T_{lo})/T_{hi}
 Second Law of thermodynamics
 Entropy and randomness
 Major energy sources—historical development
 Comparison of fuel sources; advantages and disadvantages
Chapter 5—Water
 Heating curve for water;
 Specific heats of solids and liquids
 Heats of fusion and vaporization
 Unusual properties of water
 High bp and mp
 High heats of fusion and vaporization
 High specific heat
 Ice density less than liquid density
 Electronegativity
 Polarity of Molecules
 Review Lewis Dot structures
 Review molecular geometry
 Water as a solvent
 Ionic compounds
 Polyatomic ions
 Structure and nomenclature
 Covalent compounds
 Hydrogen bonding
 Amphipathic molecules—soaps and detergents
 Water sources—impurities in natural waters
 High salt
 microbial contamination
 hard water
 Water purification
 distillation
 reverse osmosis
 ion exchange
For Spring Break, you should read Chapter 6, and review Logarithms
(Appendix 3)
Introduction to Logarithms
We often deal with numbers that are very large or very small. The number
of molecules in a mole is 6.23 x 10^{23}. The diameter of a hydrogen atom is 1.06
x 10^{10} m. For this purpose, it is convenient to express numbers in exponential
form.
Often we have to deal with a range of numbers over many powers of ten,
sometimes trying to represent graphically relationships. Suppose you were a biologist
measuring the rate of growth of bacterial cells with time, and using a microscope and
appropriate dilutions of the bacterial growth solution, you collect the following data:
Time
(hours) 
Number of cells 
1 
150 
2 
750 
3 
3750 
4 
1.88 x 10^{4} 
5 
9.38 x 10^{4} 
6 
4.69 x 10^{5} 
7 
2.34 x 10^{6} 
8 
1.17 x 10^{7} 
One way of graphing this data would look as follows:
Note you cannot get all the data on one graph.
Another method is to plot the logarithm of the number of cells:
Time
(hours) 
Number of cells 
Logarithm of Number of
cells 
1 
150 
2.18 
2 
750 
2.88 
3 
3750 
3.57 
4 
1.88 x 10^{4} 
4.27 
5 
9.38 x 10^{4} 
4.97 
6 
4.69 x 10^{5} 
5.67 
7 
2.34 x 10^{6} 
6.37 
8 
1.17 x 10^{7} 
7.07 
The logarithm of a number is the power of 10 equivalent to the number.
log 1 
log 10^{0} 
0 
log 10 
log 10^{1} 
1 
log 100 
log 10^{2} 
2 
log 1000 
log 10^{3} 
3 
log 10,000 
log 10^{4} 
4 
log 0.1 
log 10^{1} 
1 
log 0.01 
log 10^{2} 
2 
log .001 
log 10^{3} 
3 
log .0001 
log 10^{4} 
4 
What about a number that is not an even power of 10?
For example: log 25 = log 2.5x10 = log 2.5 + log 10
The log of 2.5 can be looked up in a log table, or more easily, by
entering 2.5 on your calculator, then pushing the log button.
log 2.5 = 0.398
Note the pattern:
 log 25 = log 2.5 + log 10 = 0.398 + 1 = 1.398
 log 250 = log 2.5 + log 10^{2} = 0.398 + 2 = 2.398
 log 2500 = log 2.5 + log 10^{3} = 0.398 + 3 = 3.398
The 0.398 is called the mantissa of the logarithm.
The number before the decimal is called the characteristic.
