CHM 1020--Chemistry for Liberal Studies--Spring 1999

Chemistry 1020--Lecture 15--Notes

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 (Thi-Tlo)/Thi
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 1023. 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 104 5 9.38 x 104 6 4.69 x 105 7 2.34 x 106 8 1.17 x 107

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 104 4.27 5 9.38 x 104 4.97 6 4.69 x 105 5.67 7 2.34 x 106 6.37 8 1.17 x 107 7.07

The logarithm of a number is the power of 10 equivalent to the number.

 log 1 log 100 0 log 10 log 101 1 log 100 log 102 2 log 1000 log 103 3 log 10,000 log 104 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 102 = 0.398 + 2 = 2.398
log 2500 = log 2.5 + log 103 = 0.398 + 3 = 3.398

The 0.398 is called the mantissa of the logarithm.

The number before the decimal is called the characteristic.

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