CHE 142--LAB 4--Thermodynamics
Thermodynamics is the study of heat and its effects in chemistry and physics.
Today we will conduct a series of experiments which will illustrate certain important
points in thermodynamics.
1) Entropy
The creation of disorder is a universally observed occurence in all spontaneous events.
Fill 2 beakers with water, and place a drop of blue food coloring in one and a drop of
yellow in the other. Leave them untouched until the end of the lab and then observe and
explain any changes you see in terms of the concept of entropy
2) Energy of solution and conservation of energy
Examine the behavior of “hot packs”.
Hot packs contain a supersaturated solution of sodium acetate. The solution has to be
heated to get all the sodium acetate into solution. What evidence is there for
“supersaturation” when you operate the hot-pack? What evidence is there for
conservation of energy?
3) Pillar of Salt
Observe the pillar of salt demonstration given by your instructor. This also involves the
use of a supersaturated solution of sodium acetate. How ist this similar to the operation
of a hot pack?
4) Salt on Icy sidewalks
Does salt melt the ice on the sidewalk by heating it up?
Put some ice into a beaker. Put a computerized temperature probe into it and observe
the temperature. Now pour salt on the ice. What happens to the temperature?
On a salted road, there is often water instead of ice even when the temperature is well
below freezing. Based on your experiment can you suggest why this happens?
5) Chemicals reactions can give off heat
Observe the reaction of an acid with a base as demonstrated by your instructor. What
happens?
6) Supercooling
Liquids can be cooled below their freezing point and still not freeze. .If the tempeerature
goes too low, the will suddenly freeze allat once
Immerse a flask of distilled water in a salt-ice bath and lower the temperature. Let it
keep going until it is well below freezing and then observe its behavior.
7) Heat of vaporization and intermolecular forces
Intermolecular forces are what cause molecules to “stick together” in the liquid state. In
general, hydrogen bonds are stronger than simple dipole forces, and, of course, the
more hydrogen bonds, the stronger the intermolecular forces.
Using the file entitled “experiment 9”, put a drop of ethanol on one temperature probe,
and a drop of water on the other. Compare the differences in behavior between water
and ethanol.
Then dry the probes and run the experiment again. This time compare the behavior of
isopropyl alcohol with acetone.
Finally compare the behavior ot ethanol to that of isopropyl alcohol.
Build models of these four molecules.
Try to think through what is going on. For example, why are the temoperature probes
cooling down? What is it about the molecules that make some more effective at cooling
things down than others? Your answer will lie in the realm of intermolecular forces.