Friday, October 5, 2007
Fri-Day 1 (Pep Rally: Go Jayhawks!!!)
Bio- we had our Biochemistry unit exam today. Most of you seemed comfortable with today's test. Some of you were too comfortable: if you finish a test early in my class, do NOT sit at your desk doing NOTHING; ALWAYS use the full time allotted to check and re-check your work and to EDIT and embellish (make better) your written answers; you should ALWAYS provide a labelled sketch or diagram as part of any description or explanation- that will improve your chances of getting full credit on a written response and it should occupy any remaining time for your exam.
No good test-taker takes a chance of doing nothing during a test especially since tests are the main mode of measurement of your knowledge. Any intelligent person can make an error (a misread question or a mis-marked answer); your job is to ASSUME that you made a careless error on your test and then to FIND that error as you carefully check your work. If you do not find any errors after repeated checks (time permitting), then you at least have the knowledge that you tried your very best and that you probably got a good or great score.
This advice applies to all tests in my class. Please take them very seriously and go all out on each exam; as a result, you will, by definition, become a better student and a better test-taker.
We spent our lab period working on our microscope and slide preparation skills. It was great to see that some of you were able to detect live organisms in the pond water slides that you prepared. It looked like some of them were fighting for survival!
On Tuesday, we will tidy up our labs and organize our lab folders as well as begin our new unit on "CELLS".
Have a great Homecoming weekend!
Chem 7- in our brief little period, we did complete our discussion of the cooling curve ( energy extracted/out/exothermic) of a substance noting all energy changes for each of the 5 segments of the "curve". We also applied a heat of "fusion" equation to the freezing of water (we just had to apply a negative sign because we were doing the OPPOSITE of fusion/melting).
We then began to discuss the source of a liquid's VAPOR PRESSURE (due to the fraction of molecules at a given temperature that have SUFFICIENT kinetic energy to OVERCOME their attractions to their neighboring molecules and thus ESCAPE into the GAS phase) and relate that vapor pressure to "BOILING".
The STRICT definition of boiling is when a substance's VAPOR PRESSURE is EQUAL to the ATMOSPHERIC or EXTERNAL pressure on the substance. The boiling POINT is the TEMPERATURE at which a substance boils.
We SAW that water COULD boil at room temperature (298K or 25 C) if we could LOWER the external pressure on the water from about 1 atmosphere to about .010 atmosphere via a vacuum pump. The vapor pressure of water at room temp is naturally about .010 atmosphere
so, as soon as we changed the surrounding pressure to equal .010 atm, the water started to BOIL!
The NORMAL boiling point will be the temperature at which a substance has a VAPOR PRESSURE of 1.00 atmosphere/ 101.3 kiloPascals of pressure.
So, for example, a 100 C or 373 K, the NORMAL boiling point of water, water has a VAPOR pressure of 1.00 atmosphere= 101.3 kiloPascals of pressure.
Ethanol-alcohol reaches a (normal) vapor pressure of 1.00 atmosphere at a mere 78 C or 351 K because not as much energy is required to get ALL of its molecules into the vapor phase. This is because ethanol molecules are not as strongly attracted to each other as water molecules are attracted to other water molecules. In fact, the stronger the intermolecular attraction of a given substance, the MORE energy is needed to reach a vapor pressure of 1.00 atm, thus the HIGHER the boiling point.
Of course, we will draw and discuss this more on Tuesday!
Have a great Homecoming weekend!
Chem 8/9: we finished our discussion of the cooling curve ( energy extracted/out/exothermic) of a substance noting all energy changes for each of the 5 segments of the "curve". We also applied a heat of "fusion" equation to the freezing of water (we just had to apply a negative sign because we were doing the OPPOSITE of fusion/melting).
We then began to discuss the source of a liquid's VAPOR PRESSURE (due to the fraction of molecules at a given temperature that have SUFFICIENT kinetic energy to OVERCOME their attractions to their neighboring molecules and thus ESCAPE into the GAS phase) and relate that vapor pressure to "BOILING".
The STRICT definition of boiling is when a substance's VAPOR PRESSURE is EQUAL to the ATMOSPHERIC or EXTERNAL pressure on the substance. The boiling POINT is the TEMPERATURE at which a substance boils.
We SAW that water COULD boil at room temperature (298K or 25 C) if we could LOWER the external pressure on the water from about 1 atmosphere to about .010 atmosphere via a vacuum pump. The vapor pressure of water at room temp is naturally about .010 atmosphere
so, as soon as we changed the surrounding pressure to equal .010 atm, the water started to BOIL!
The NORMAL boiling point will be the temperature at which a substance has a VAPOR PRESSURE of 1.00 atmosphere/ 101.3 kiloPascals of pressure.
So, for example, a 100 C or 373 K, the NORMAL boiling point of water, water has a VAPOR pressure of 1.00 atmosphere= 101.3 kiloPascals of pressure.
Ethanol-alcohol reaches a (normal) vapor pressure of 1.00 atmosphere at a mere 78 C or 351 K because not as much energy is required to get ALL of its molecules into the vapor phase. This is because ethanol molecules are not as strongly attracted to each other as water molecules are attracted to other water molecules. In fact, the stronger the intermolecular attraction of a given substance, the MORE energy is needed to reach a vapor pressure of 1.00 atm, thus the HIGHER the boiling point.
Of course, we will draw and discuss this more on Tuesday!
We performed the procedure for determining the heat of fusion (delta H fus) of water by melting a quantity of ice in warm water. Depending on how much ice melted and how much energy was absorbed by the ice (which is theoretically the amount of energy that was transferred FROM the warmer water TO the colder ice), we have the number of Joules of energy per number of grams of ice melted which IS the heat of fusion! We will discuss and debate this on Tuesday.
Have a great Homecoming weekend!
# posted by C @ 10:28 AM 
