Tuesday, October 27, 2009
Tues-Day 2
Bio3/6- using a simplified picture that just focused on the complementary base pairs, we reviewed the DNA replication that takes place during the S part of interphase. We related our picture to what is occurring on the chromosome: the DNA replication LITERALLY forms a second identical "sister chromatid" making the chromosome go from a single-chromatid chromosome to a double-chromatid chromosome. Without this important formation of identical sister chromatids, mitosis could NOT occur because the daughter cells would not have the same number and types of chromosomes as the original cell due to the lack of DNA; thus not all of the required proteins and enzymes necessary for metabolism/homeostasis would be coded for and synthesized i.e. the new cells could not live.
We then discussed the importance of the Watson-Crick model/picture of DNA, showing how it explained/accounted for the ability of cells to reproduce identical cells with the same genetic information and also how DNA could code information that is translated into the specific amino acid sequence of all of the proteins that give an organism its specific traits and characteristics.
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.
We discussed thermochemical equations and did stoichiometric examples involving the heat/energy absorbed or released from various quantities of reactants or products.
DO NOT FORGET that the delta H value given for a reaction is PER MOLE of "reaction"; that is, for the reaction 2A + B --> 3C + D ; delta H = -255 kJ , one MOLE of reaction means that TWO moles of "A" reacted, ONE mole of "B" reacted, THREE moles of "C" formed, and ONE mole of "D" formed AND that 255 kJ of energy were released to the surroundings.
We then did some stoichiometry with the thermochemical equations, focusing on the proper placement of the energy term and noting that the quantities are treated in the exact same way as they are treated in any stoichiometry problem (especially be careful to look for limiting reactants that limit the energy absorbed or released!).
We then discussed the importance of the Watson-Crick model/picture of DNA, showing how it explained/accounted for the ability of cells to reproduce identical cells with the same genetic information and also how DNA could code information that is translated into the specific amino acid sequence of all of the proteins that give an organism its specific traits and characteristics.
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.
We discussed thermochemical equations and did stoichiometric examples involving the heat/energy absorbed or released from various quantities of reactants or products.
DO NOT FORGET that the delta H value given for a reaction is PER MOLE of "reaction"; that is, for the reaction 2A + B --> 3C + D ; delta H = -255 kJ , one MOLE of reaction means that TWO moles of "A" reacted, ONE mole of "B" reacted, THREE moles of "C" formed, and ONE mole of "D" formed AND that 255 kJ of energy were released to the surroundings.
We then did some stoichiometry with the thermochemical equations, focusing on the proper placement of the energy term and noting that the quantities are treated in the exact same way as they are treated in any stoichiometry problem (especially be careful to look for limiting reactants that limit the energy absorbed or released!).
# posted by C @ 11:59 PM 
