Wednesday, January 19, 2011
Tues-Day 1
Physics - we explained the factors that cause electrical resistance: the "resistivity" of the material, which is a property due to the chemical nature of the substance i.e. its degree of attraction for electrons within the material, the length of the material/wire, and the cross-sectional area of the material/wire.
We discussed the measurement of electrical energy or work due to the flow of charge through a wire (current) having a potential difference, V, and a particular resistance to the flow of charge, R.
The relation is that Work or energy = V x I x t , and because Power is the RATE of work or W/t, we can see that P = V x I.
We used Ohm's Law to substitute for V or I in the above equations to get more work and power equations.
The quarterly exam is Thursday and Friday! Do ALL of the packet questions, and ask me about anything that you cannot easily answer.
We began a lab on measuring spring constants, and determining the elastic potential energy in a compressed or stretched spring.
AP Chem - we saw that experimentally determined rate laws can be related to the RATE-DETERMINING/SLOW step of a proposed reaction mechanism.
We showed mathematically that the number of molecules/particles of a given substance colliding in the rate determining step must match the EXPONENT of the concentration of that given substance in the rate law.
We discussed the TWO requirements for a plausible mechanism:
1. The sum of the elementary steps MUST add up to the overall net balanced equation
2. The rate law for the proposed SLOW/rate determining elementary step must MATCH the EXPERIMENTALLY DETERMINED rate law.
Again, you can NEVER just take the coefficients from the balanced net equation, and use them in the rate law- that would assume a ONE STEP mechanism, which can NEVER be assumed, even if that were coincidentally true!
We discussed the measurement of electrical energy or work due to the flow of charge through a wire (current) having a potential difference, V, and a particular resistance to the flow of charge, R.
The relation is that Work or energy = V x I x t , and because Power is the RATE of work or W/t, we can see that P = V x I.
We used Ohm's Law to substitute for V or I in the above equations to get more work and power equations.
The quarterly exam is Thursday and Friday! Do ALL of the packet questions, and ask me about anything that you cannot easily answer.
We began a lab on measuring spring constants, and determining the elastic potential energy in a compressed or stretched spring.
AP Chem - we saw that experimentally determined rate laws can be related to the RATE-DETERMINING/SLOW step of a proposed reaction mechanism.
We showed mathematically that the number of molecules/particles of a given substance colliding in the rate determining step must match the EXPONENT of the concentration of that given substance in the rate law.
We discussed the TWO requirements for a plausible mechanism:
1. The sum of the elementary steps MUST add up to the overall net balanced equation
2. The rate law for the proposed SLOW/rate determining elementary step must MATCH the EXPERIMENTALLY DETERMINED rate law.
Again, you can NEVER just take the coefficients from the balanced net equation, and use them in the rate law- that would assume a ONE STEP mechanism, which can NEVER be assumed, even if that were coincidentally true!
# posted by C @ 12:10 PM 
