Tuesday, February 1, 2011
Tues-Day 2
Physics - completed the problems in Circuits 3; this gave us further practice relating resistance, current, voltage, energy, and power.
We also did another "number of electrons passing a point in the circuit" in a given amount of time (you can use either of the two formulas); the key is getting the charge, q, in Coulomb's by multiplying the current, I, by the time, t, first.
We did a resistance problem, given constant temperature, we need the resistivity of the wire/material, the length of the wire, and the cross-sectional area of the wire. The resistivities of various metals AT 20 degrees Celsius are given in the reference table. However, the resistivity (and thus resistance) of a metal will INCREASE with increasing temperature because the electrons will crash more frequently into more rapidly vibrating/higher temperature atoms, and thus be slowed down i.e. resistance will increase.
AP Chem - did two more examples of kinetics problems from mechanism to predicted rate law to check for consistency with experimental rate law. A proposed mechanism must pass BOTH the balanced equation requirement, and the consistency with experimental (rate law) requirement.
We noted that catalyst can appear in rate law equations even though catalysts do not appear in the net balanced equation. Catalysts are NOT spectators, they DO participate in the reaction pathway.
In contrast, intermediates that appear in a rate determining step would have to be substituted for in a rate law because there is no way to manipulate intermediate concentrations in a beaker at the start of the reaction (i.e. initial conditions).
In 10/11, we added to common redox reactions to our descriptive chemistry arsenal: those involving acidified solutions of dichromate ion or of permanganate ion (will introduce this in 4/5 tomorrow).
We began to go over some of the unbelievable misconceptions, and test-taking errors in order to improve your performance on all future tests.
We also did another "number of electrons passing a point in the circuit" in a given amount of time (you can use either of the two formulas); the key is getting the charge, q, in Coulomb's by multiplying the current, I, by the time, t, first.
We did a resistance problem, given constant temperature, we need the resistivity of the wire/material, the length of the wire, and the cross-sectional area of the wire. The resistivities of various metals AT 20 degrees Celsius are given in the reference table. However, the resistivity (and thus resistance) of a metal will INCREASE with increasing temperature because the electrons will crash more frequently into more rapidly vibrating/higher temperature atoms, and thus be slowed down i.e. resistance will increase.
AP Chem - did two more examples of kinetics problems from mechanism to predicted rate law to check for consistency with experimental rate law. A proposed mechanism must pass BOTH the balanced equation requirement, and the consistency with experimental (rate law) requirement.
We noted that catalyst can appear in rate law equations even though catalysts do not appear in the net balanced equation. Catalysts are NOT spectators, they DO participate in the reaction pathway.
In contrast, intermediates that appear in a rate determining step would have to be substituted for in a rate law because there is no way to manipulate intermediate concentrations in a beaker at the start of the reaction (i.e. initial conditions).
In 10/11, we added to common redox reactions to our descriptive chemistry arsenal: those involving acidified solutions of dichromate ion or of permanganate ion (will introduce this in 4/5 tomorrow).
We began to go over some of the unbelievable misconceptions, and test-taking errors in order to improve your performance on all future tests.
# posted by C @ 2:24 PM 
