SciHawks

Physics - continued our practice of series circuits, doing problems in which we calculated the voltage/potential drop across individual resistors in a circuit, and also the energy and power output at each resistor. We finished up Circuits 4.
We then reviewed some of the quarterly questions; those who got part 1, number 8 correct will have their grades revised.
We will continue our Ohm's Law lab on Wednesday and then do a series circuit lab.

AP Chem - focused on relating catalysts and intermediates in a mechanism to their representation on an energy diagram; related the highest activation energy part of the energy diagram to the SLOW step of a reaction mechanism because, at a given temperature/average kinetic energy, the lowest fraction of molecules would meet the highest activation energy requirement step in a reaction mechanism.
We also reviewed the Arrhenius equation, and its applications.

Physics - we reviewed series circuits, focusing on the potential drop across each resistor and noting that Ohm's Law can and should be used for any individual part of the circuit, as well as for the overal V, I , and R of the circuit. Keep track of what you are using in the law by labeling everything specifically i.e. R1, I1, V1 or Rtotal, I total, V total, etc.
We then did some problems in Electrostatics 4.

AP Chem - we finished up the kinetics unit by applying the 1st order time-dependent rate law to some typical questions. We then derived the 2nd order rate law, and solved some problems with respect to that law.
We looked at each law's derivation, and each law's respective graphical applications/signatures.
We then discussed collision theory and its relation to activation energy; we then explained and applied the Arrhenius equation.

Physics - we discussed "series circuits" in which resistors are placed consecutively in a circuit and connected by metal wires. We noted that the TOTAL/equivalent resistance in a series circuit is simply the SUM of the resistances from the resistors. We also used Ohm's Law to calculate the "voltage drop" or potential difference ACROSS each of the resistors. We saw that the sum of the voltage drops equals the overall potential difference in the battery, and that each voltage drop across each resistor is directly proportional to the resistance of each resistor.
We then did some questions in the packet on series circuits and work/energy and power/rate of energy used by each resistor in a given circuit.
We then did an Ohm's law lab.


AP Chem - finished discussing the time-dependent rate equation for first order kinetic processes.
We then applied our convenient version of the formula to some typical kinetics questions.
We also analyzed the various graphs of first order processes and made inferences and predictions from them.
Enjoy the snow day; descriptive chem quiz and completion of the kinetics unit on Friday, no matter what.

Physics - we looked at the derivation of the work/energy and power equations in terms of potential difference (V), current (I), resistance (R), and time (t). We then looked at problems involving P and W/Energy in Circuits 1 and 2.

We reviewed how to calculate the number of electrons passing a point in a circuit in a given amount of time (multiply the total charge in Coulombs by 6.25 x 10^18 electrons per Coulomb).

We reviewed electric circuit diagrams.
We then expanded these diagrams by drawing in multiple resistors consecutively connected "in series".
The equivalent or total resistance of the circuit is then simply the SUM of the resistances of the individual resistors in the series circuit.
With that we can get the constant and uniform current throughout the circuit, using Ohm's Law.

We then started on the TIME-dependent equations of kinetics by looking at 0th order reactions, and 1st order reactions.
The descriptive chem quizzes will be returned tomorrow- grades from that quiz are on Blackboard.

Physics - took part II of the 2nd quarter exam.
We then further worked on the spring constant/PE of a coiled/stretched spring lab.

SNOW DAY!

Physics- handed out a practice part II exam for your quarterly, which was re-scheduled to Monday.
Take the practice test under TIMED conditions: 40 minutes.
Check Blackboard for the answer key by Sunday.

We did two periods of descriptive chemistry practice (see notes posted on Blackboard under "Descriptive Chem Help Files"). Starting Tuesday, our classes will begin with strictly timed, 5 minute descriptive chem quizzes on our double-period day. You will have to be accurate AND fast, so you should practice these frequently so that you can INSTANTLY see/judge the reaction type based on the TYPES of reactants given.

Physics - took part I of our quarterly exam.

AP Chem - we did a few examples relating the experimentally determined rate laws to the rate determining step of a proposed reaction mechanism.
We then went on (not in the 4/5 class, though) to see how rate law EXPONENTS are deduced from experimental data that show the effect of varying concentration of one reactant (one variable per experiment, the other reactant(s) concentration(s) is/are kept the same/controlled) on the reaction rate.

Physics - we reviewed for the 2nd quarterly exam.
Be sure to come to extra help if your average is sub-par this quarter.
This is your ONLY chance to undo the damage of insufficient preparation on previous exams.

AP Chem - took the multifarious unit exam on colligative properties, metal-ligand complex naming, solids/liquids/IMFA's.
We continue with kinetics tomorrow, and, due to the disturbingly inaccurate answers on the descritpive chem assignment, all upcoming double periods will begin with a 5 MINUTE quiz - not a second of extra time will be given.
The quiz will consist of three "predict-the-products"-and-balance chemical reactions.
You will also have to state the general and specific reaction type for each reaction.
You must do so VERY quickly and with perfect accuracy.
Each quiz will be worth 25 points.
I assumed by now that you would have to know all of these reaction types with great facility just via hw and repetition.
Those who have done so by now will be rewarded with an easy 25 points every other day.
We cannot lose class time with these quizzes so expect to have your quiz taken from you if you write anything after the 5 minute mark.
See the past posted descriptive chem files and/or come to extra help for more practice.

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!

Physics - HW due Tuesday - do ALL of the Electric Circuits 1 problems in the new unit packet.
All of these problems are Ohm's Law problems in which 2 of the 3 variables are given!

Here is a list of topics that are covered on your 2nd Quarterly/1st Semester Exam: 70% of the test questions are from quarter 2, and 30% of the test questions are from quarter 1.

Vectors
Straight-Line Motion ( d vs. t, v vs. t, and a vs. t graphs, a, v, d, t, calculations)
Projectile Motion (horizontal v, vertical v, acceleration, range, etc.)
Dynamics (normal force, applied force, incline problems, Newton's 3 Laws - inertia, Fnet = m x a, and action-reaction pairs)
Impulse, Momentum ( Fnet avg x t = change in momentum = m delta v), and Circular Motion
Work and Energy
Electrostatics

Physics - finished up the electroscope lab and the mechanical energy lab - hand those in by Tuesday (we are off on Monday!)
Did one more "system of charges" problem, and then we took part two of the electrostatics exam - the first exam to contain a "how"/"why" explanation until "then nothing would NOT BE...something has to ISN'T!"

We emphasized the difference between "rate of reaction" in change in molarity of "reaction" per second and "rate of appearance or disappearance of a product or reactant", respectively.

Did I leave anything out that we spent time on?

Enjoy the snow day everybody!

Of course, the AP Chem train has to keep chugging, so check Blackboard for a descriptive chem assignment, and the first of many part II AP Chem review questions, as we begin AP Exam prep.

Also, the New Year's vacation assignment answers are now posted, so you can review for the upcoming exam.
Questions types for Friday's test will be posted on Thursday; in the meantime, study everything covered after the last exam.

Physics - took part 1 of the Electrostatics unit exam.

AP Chem - launched the Kinetics unit by discussing the THREE possible factors that determine the number of effective collisions per second i.e. the reaction rate.
We then explained how chemical reaction rates have a range that is set by the nature of the reactants.


After that, we discussed  FOUR factors that can be varied in a gien reaction: concentration, temperature, surface area, and the addition or removal of a catalyst.


We explained how each factor affected the three primary determinants of the reaction rate: kinetic energy/force of collisions, orientation of collisions, and collision frequency.


We then discussed how reaction rates are measured in terms of change in MOLARITY per second; this unit is practical because a sample of the reacting mixture can be removed without changing the concentrations of reactants and products at the time of sampling. (However, there is NOTHING wrong or illogical about stating a reaction rate in terms of change in the number of  moles or molecules per second!)


We saw how to measure the average rate of reaction, and the instantaneous initial rate of reaction, which is the typical standard for measuring reaction rates.
We discussed how to get a single "rate of reaction", whether we are measuring the rate of disappearance of a reactant, or rate of appearance of a product. We simply divide the rate of appearance or disappearance by the coefficient of the respective product or reactant from the BALANCED chemical equation.

Physics - did two problems involving sets of charges, using trigonometry and Coulomb's Law to calculate the net force on one of the charges.
We then finished the procedure on our electroscope lab.

AP Chem - we expanded the discussion of Raoult's Law, and saw it as the basis of calcutions in distillation. We showed how Raoult can be used in conjunction with Dalton to determine the mole fractions of each component in the VAPOR/GAS phase. The formulas look very similar so you must be VERY careful to not use one when you should use the other - keep everything explicitly labeled!

Tomorrow, we dive into Kinetics - second semester college chem.

Physics - we reviewed the concept of "potential difference", measured in Volts. The potential difference between two points in an electric field is the amount of work done per Coulomb of charge moved between those two points; a Joule per Coulomb is a Volt, as is an electron-Volt per electron or per elementary charge.

We began a problem in which we deduced the net or resultant force on one charge from two other charges.

AP Chem - we manipulated the osmotic pressure formula into a more practical form to determine the molar mass of the dissolved solute that causes the osmotic pressure to increase.

We then saw how to compare a set of solutions of a given solvent, and arrange them in order of increasing or decreasing boiling or freezing point. Since k is the same for a given solvent, you just need to know how to assign the appropriate van 't Hoff factor based on whether the substance is a strong electrolyte (soluble salts and strong acids), weak electrolyte (weak acids), or non-electrolyte (ANY molecule, except an acid) and multiply "i" by the given molality.

We then looked at Raoult's Law, calculating the vapor pressure lowering effect of dissolving a non-volatile solute in a given solvent.

Physics - we discussed electric fields, and did some quantitative problems relating electric field strength to the force on a given charge.
We then went through six classic cases of representing the electric field lines/arrows/vectors for a given set of charges.
We then discussed the meaning of volts, as the work done in moving a quantity of charge. The work is equal to the change in potential energy of the charge and the quantity of charge is given in Coulombs.
We will use the term "potential difference" for the number of Volts, and relate that to the work produced by a given amount of charge.

We started an electrostatics lab during which you observed charging via conduction, and then via induction.

AP Chem - we rearranged the colligative property formula for freezing point depression and boiling point elevation. We will rearrange the osmotic pressure formula tomorrow, and then finish up the unit with Raoult's Law and any questions that you have from the break assignment.

Physics - we compared and contrasted the ELECTROSTATIC FORCE vectors with the GRAVITATIONAL FORCE vectors acting on a pair of charged objects.
The electrostatic force is generally much stronger for a charged object than any gravitational attraction to another charged object.
Furthermore, the gravitational force is ONLY attractive, whereas the electrostatic force can be either attractive (unlike charges) or repulsive (like charges).

We did a drill showing how the electrostatic force between two charged objects varies with charge and distance.

We then began to discuss the concept of "electric fields", and how to represent them with lines/arrows around a charged objects.

AP Chem - we finished phase diagrams and the common questions asked about them; we then took on properties of liquids i.e. surface tension and viscosity.
We then discussed vapor pressure, how it is measured, and how it relates to intermolecular forces and temperature of a substance. We saw that SAMPLE SIZE has nothing to do with vapor pressure at a given temperature.
We began to discuss colligative properties; tomorrow, we will do many problems from the derived formulas, using the van' t Hoff factor associated with dissociation of a given ionic compound or ionization of a given acid in solution.

Physics- we got into the electrostatics unit today, calculating the number of elementary charges in excess, from a given net charge on an object.

We also saw that when two or more charged objects are in contact, that the electrons are conducted until all of the objects have the same NET charge; this is calculated by taking the AVERAGE of the initial charges from the spheres.

We then introduced the most fundamental and important law in all of chemistry (it explains ALL of chemistry!) and physics: Coulomb's Law.

Coulomb was able to measure the Force of Electrostatic Repulsion (like charges) or Attraction (opposite charges) between charged objects.
We saw that this force is proportional to the PRODUCT of the charges (in Coulomb's);
the force also has an INVERSE SQUARED relation to the DISTANCE between the charges.

To get the law/equation, we looked at the electrostatic constant , k, and its units; k is on the reference tables.

We covered some questions from our mechanical energy / lacrosse ball lab.

We then looked at phase diagrams, discussing the important regions and phase changes that occur at various temperatures and pressures.

Physics- we explained the charging of an object via INDUCTION, and contrasted that with the charging of an object via CONDUCTION. The actual gain or loss of electrons (the "charging") occurs when the POLARIZED object is connected to the "ground"/Earth via a conducting wire (or via your hand, which then eventually conducts the electrons to the ground).

We discussed the indirect measurement of the charge, in Coulomb's, on an elementary particle i.e. an electron or a proton. The magnitude of charge on a SINGLE electron or proton is 1.6 x 10^-19 C.
Thus, an object can have ONLY A MULTIPLE of this quantity of charge, because electrons and protons cannot commonly be split or broken down further.

To determine the number of excess electrons or protons in an object, we just divide the TOTAL NET CHARGE on the object by 1.6 x 10^-19 C.


AP Chem - we discussed the various types of solids: ionic, metallic, network covalent, and molecular.
We discussed some of the physical properties of each.
Notes will be updated on Blackboard tomorrow.