Tuesday, November 18, 2008
Tues-Day 2
AP Chem- we reviewed the 0-th and 1st Laws of Thermodynamics, emphasizing the importance of understanding the SIGNS of heat and work with respect to the system. Once those signs are understood/felt, the math version of the 1st Law dE = q + w has to work and make sense. For example, if a system ABSORBS heat ( q is positive ), then the change in internal energy of the system MUST be positive due to the energy absorbed. If a system DOES WORK i.e. pushes a piston (w is negative), then that system LOSES energy (in order to do the work, it uses up some of its energy!) so the change in internal energy is negative. If both work and heat are involved, there may be a NET gain or loss of internal system energy depending on which value is greater and the sign of those values.
We then discussed ENTHALPY, which is a measure of the potential energy of the system's particles. The more stable the particles, due to MORE and STRONGER bonds, the LOWER the ENTHALPY of the system's particles. We can't measure absolute enthalpies (though we do DEFINE certain values, as you will see), we CAN via calorimetry, measure CHANGES in enthalpy, delta H, which we sometimes call the "heat of reaction" or "heat of some process".
We noted that change in enthalpy MUST BE measured ONLY under CONSTANT PRESSURE conditions and the ONLY type of work that can occur is gaseous pressure-volume work.
Try that descriptive chem set tonight; you can "grade" yourself on that tomorrow.
Bio 6- took our transcription and translation exam today. As you saw, you had already answered all of the test question types in the objectives hw. Further proof that putting in the time and effort on that homework makes the tests much more familiar and easier to handle.
Bio 7/8- took our transcription and translation exam today. As you saw, you had already answered all of the test question types in the objectives hw. Further proof that putting in the time and effort on that homework makes the tests much more familiar and easier to handle.
We then finished our Protein Synthesis lab.
We then discussed ENTHALPY, which is a measure of the potential energy of the system's particles. The more stable the particles, due to MORE and STRONGER bonds, the LOWER the ENTHALPY of the system's particles. We can't measure absolute enthalpies (though we do DEFINE certain values, as you will see), we CAN via calorimetry, measure CHANGES in enthalpy, delta H, which we sometimes call the "heat of reaction" or "heat of some process".
We noted that change in enthalpy MUST BE measured ONLY under CONSTANT PRESSURE conditions and the ONLY type of work that can occur is gaseous pressure-volume work.
Try that descriptive chem set tonight; you can "grade" yourself on that tomorrow.
Bio 6- took our transcription and translation exam today. As you saw, you had already answered all of the test question types in the objectives hw. Further proof that putting in the time and effort on that homework makes the tests much more familiar and easier to handle.
Bio 7/8- took our transcription and translation exam today. As you saw, you had already answered all of the test question types in the objectives hw. Further proof that putting in the time and effort on that homework makes the tests much more familiar and easier to handle.
We then finished our Protein Synthesis lab.
# posted by C @ 3:09 PM 
