CHEMISTRY COMMUNITY

Jialun Chen 4F

Thank you Lyndon!

Jialun Chen 4F

I'm quite sure that you use H+ and H2O for acidic reactions but OH- and H2O for basic reactions.

Jialun Chen 4F

Matt Sanruk 2H wrote:Since it is not present in the slowest step we can assume that it is indeed zero order and does not affect the rate

I agree with Matt's rationale, the concentration of a zero-order has no effect on reaction.

Jialun Chen 4F

I think the final will most likely still be taken at the assigned location on Sunday.

Jialun Chen 4F

The specie that's being formed and used during different steps of a reaction and will not show up in the determined rate law.

Jialun Chen 4F

The two are different aspects of a reaction. The former determines the rate (or how fast) a reaction goes, while the latter considers the spontaneity of the reaction.

Jialun Chen 4F

In "Your Post", you can track the number of posts and the time of posting as well.

Jialun Chen 4F

Enaught is a fixed value for one reaction under standard condition, while E can vary as temperature or concentration of the substances in a reaction changes.

Jialun Chen 4F

There won't be any effects on the cell potential by merely changing the mass of anode or cathode.

Jialun Chen 4F

Ecellnaught depends on the difference between E cathode and E anode, yet in a concentration cell the two nodes contain the same species, thus making the difference to be 0.

Jialun Chen 4F

The test will probably be handed back next week during discussion section.

Jialun Chen 4F

In this case, the reverse direction or reactant side is favored since the reaction is spontaneous when Ecellnaught is positive.

Jialun Chen 4F

Electrolysis or electrolytic cell has a negative Ecell potential overall, which makes it nonspontaneous. Examples would include the process of making gold and other metals, such as magnesium.
*According to my TA, the Galvanic cell (spontaneous) is what we should put more emphasis on.

Jialun Chen 4F

I agree with the comments above. There's not a difference in efficiency between the two based on what I know of.

Jialun Chen 4F

Use the equation ECathode - EAnode; in a Galvanic cell, the standard setup is having anode on the left (oxidation) and cathode on the right (reduction).

Jialun Chen 4F

The second page of outline 4 (Thermodynamics) and all of the outline 5 (Electrochem).

Jialun Chen 4F

In addition to the sign of Gibbs free energy, the sign of cell potential can also serve as an indicator: if Ecell is greater than zero, the reaction is spontaneous, vice versa.

Jialun Chen 4F

Adding an inert gas (noble gases or gases that's not present in the reaction) increases the pressure of the system, but alters no concentration, thus having no effect on the overall reaction.

Jialun Chen 4F

Since DeltaG=DeltaH-T*DeltaS, in order to have a nearly equivalent DeltaG and DeltaH means an insignificant DeltaS (disorder). Thus, A has 3 solids from reactant to 3 solids from the product, indicates DeltaS of the reaction is pretty much zero. Assuming constant temperature for the four reactions, ...

Jialun Chen 4F

DeltaG's sign determines spontaneity. If positive, not spontaneous; if negative, spontaneous; if =0, at equilibrium.

Jialun Chen 4F

It depends on your preference. Some choose to continue with 14C or taking 14C along with 14BL, but you can also choose to take the lab alone.

Jialun Chen 4F

Test 2 is now week 9 during the discussion; it covers materials after midterm excluding kinetics.

Jialun Chen 4F

The sign of Gibb's free energy determines the spontaneity of a reaction.

Jialun Chen 4F

Since entropy is a measure of disorder, higher temperature means more disorder.

Jialun Chen 4F

Irreversible expansion keeps the pressure constant. It is relatively faster than reversible expansion, yet less efficient because it does less work.

Jialun Chen 4F

For a closed system, heat can be exchanged but volume remains constant. An open system has constant pressure yet a changing volume. An isolated system has no energy exchange whatsoever (eg. bomb calorimeter). So, in an isolated system, if it has no exchange of energy, can work be done? What would t...

Jialun Chen 4F

LBacker_2E wrote:My TA said it is better to use kJ for ∆H, and J for the other values. Do you think this is really important, or is it just a preference?

To me, it seems to be a personal preference. Either would work.

Jialun Chen 4F

There's no need to memorize the values. They'll be given if we even encounter related questions.

Jialun Chen 4F

For a closed system, heat can be exchanged but volume remains constant. An open system has constant pressure yet a changing volume. An isolated system has no energy exchange whatsoever (eg. bomb calorimeter).

Jialun Chen 4F

Everything for topics 1-4. I believe he said that he will begin and finish covering Gibbs free energy in the lecture this coming Wednesday and Friday. Does anyone know if we will be learning new things next week on Monday and Wednesday? I think Dr. Lavelle will go over past exam questions in class ...

Jialun Chen 4F

Andrew Liang 1I wrote:Are we expected to memorize any equations for the midterm or are they going to give all of them to us on the cover sheet?

I'm sure that all the formulas will be given on the cover sheet.

Jialun Chen 4F

My understanding is that the value is utilized to calculate entropy in the Boltzmann equation, which denotes as S=kblnW.

Jialun Chen 4F

Personally I found 4D and 4E doable, but there might be more sections out there.

Jialun Chen 4F

I think what you stated is what constitutes the difference between those two q values.

Jialun Chen 4F

I agree with McKenna. Due to the numbers given in the bond enthalpy chart being averages, this method is not as accurate relatively.

Jialun Chen 4F

The cutoff is 10^-3. Yet in cases of weak acids and bases, one may want to check the % ionization to ensure the approximation is valid (i.e, the quadratic formula is still necessary if the final percentage is >5%).

Jialun Chen 4F

Correct! Equilibrium constants change as the alteration of the temperature inside the system occurs.

Jialun Chen 4F

Correct! 25 degree Celsius is the right temperature to assume.

Jialun Chen 4F

The relationship is analogous to that of pH/pOH and [H3O+]/[OH-].
Essentially,
10^-pKa=Ka (same applies for Kb)
pKa=-log(Ka) (same applies for Kb).

Jialun Chen 4F

If K is less than 10^-3, you can drop the x in the denominator. I usually do a double-check afterwards by calculating the % ionization; if the % ionization is less than 5, you're good, otherwise, you would have to use the quadratic formula.

Jialun Chen 4F

I agree with Caroline's answer. If positive Delta H, endothermic; if negative Delta H, exothermic.

Jialun Chen 4F

Though both pKa+pKb and pH+pOH equal to 14, Ka and Kb are constants indicating how well an acid or base dissociates, while [H+] and [OH-] represents the concentration of hydronium and hydroxide ions.

Jialun Chen 4F

I'm quite sure that all values inputted in ICE Table have to be converted into molarity (mol*L^-1).

Jialun Chen 4F

All three aforementioned aspects. I recall that K remains unchanged when altering concentration and partial pressure, but when to increase or decrease the temperature, K changes.

Jialun Chen 4F

They are both units for measuring pressure. I think as long as your units in one question remain consistent, you're all set.

Jialun Chen 4F

The first two outlines should be the focus. Doing all/most of the homework problems, especially the focus questions, would definitely help a lot. Also, go back to read the textbook for any concepts that seem vague.

Jialun Chen 4F

That is correct! And I believe that in homework problems the % ionization is under 5% excluding certain outliers.

Jialun Chen 4F

Aqueous solutions should be included in the equilibrium expression. Only solid (s) and liquid (q) are excluded.

Jialun Chen 4F

Since it's a constant, not a variable, K does not have a unit. We can also think of this by perceiving the molarity units of products and reactant cancels.

Jialun Chen 4F

Correct. We perform the same calculation procedure when solving for Q and K.

Jialun Chen 4F

I think the equilibrium constant Kc does not change for the same reaction under the same temperature no matter what masses of reactants one uses.

Jialun Chen 4F

Since the change in concentration of the solvent is negligible, we don't include them in the equilibrium expression.

Jialun Chen 4F

As long as you did 5 posts weekly and make sure changed our username to your legal name plus your discussion, I think you'll be fine.

Jialun Chen 4F

I agree with the answer above. It's also one of the biological examples Dr. Lavelle expects us to memorize.

Jialun Chen 4F

You're allowed to use both, yet it depends on which one explains the concept better for you.

Jialun Chen 4F

Yes, we do. I hypothesize the VSEPR questions on the final is going to resemble those from test 2.

Jialun Chen 4F

There are two versions of naming, while the former is the older, the latter is the revised name.

Jialun Chen 4F

It means that everything inside the bracket is a part of the coordination compound.

Jialun Chen 4F

It will be handed back during your discussion session. If your discussion is on Wed, Thurs, of Fri, you will probably get the physical copy back in your discussion session next week.

Jialun Chen 4F

I agree with Mashkinadze's answer. I personally just memorize the specific strong acids/bases.

Jialun Chen 4F

Just memorize:
single bond: one sigma bond
double bond: one sigma bond, one pi bond
triple bond: one sigma bond, 2 pi bonds

Jialun Chen 4F

Since F has 3 lone pairs and one bonded pairs, the electron density is thus tetrahedral, leads to hybridization of sp3.

Jialun Chen 4F

Hybridization is not gonna be on Test 2.

Jialun Chen 4F

The positions of the cl- ions are different between cisplatin and transplatin. For cis, the two cl- are on the same side, thus dipole moments doesn't cancel. The two Cl- thus bond with the N of the guanine base pair (forming two bonds).

Jialun Chen 4F

That is correct. For instance, compounds with AX4 (tetrahedral) formula would have bond angles of 120 degrees, while AX3E (trigonal pyramidal) would have bond angles of slightly less than 120 degrees due to the lone pair.

Jialun Chen 4F

Sorry, I should've clarified: for AX2E2, the bond angle is going to be slightly less than 109.5 degrees, while AX2E is less than 120 degrees. Both VSEPR formula represents bent/angular shape.

Jialun Chen 4F

It's gonna be less than 109.5 degrees because of the lone pair.

Jialun Chen 4F

I think melting points share the same trend as boiling points. As atom size gets larger, more polarizable, thus stronger London forces leads to higher melting point.

Jialun Chen 4F

For ion-dipole, you have an ion which carries a charge, thus it has to be considered when evaluating IMF, while dipole-dipole solely depends on dipole moment and size of the molecule.

Jialun Chen 4F

Yup, I'm quite sure that's the majority content on Test 2.

Jialun Chen 4F

The dominant force to be considered in 3F 5(c) is the dipole-dipole force, which depends on the size of the molecule; since Iodine is larger than Fluorine, Iodine experience higher diploe moment, which results in a stronger dipole-dipole force.

Jialun Chen 4F

CandiceNourian1J wrote:Do you think it will also have some information from the midterm as well? Or only new untested topics?

I don't think so, but we should know the basics from the past materials, such as drawing lewis structures.

Jialun Chen 4F

The test will be in your discussion section next week. The topic covered is everything after the midterm, which includes IMFs and VSPER models/shapes.

Jialun Chen 4F

I don't think it's necessary to know to draw a hybrid, but we are expected know the concept.

Jialun Chen 4F

Bond strength increases from single bonds to triple bonds, and bond length is the opposite, which decreases from single bonds to triples bonds.

Jialun Chen 4F

You can use that equation, but the energy version that's given by Dr. Lavelle explains the concept better for me.

Jialun Chen 4F

You're very welcome, I am glad that helped. Good luck studying!

Jialun Chen 4F

Personally, I write down the equations and concepts a notecard and I go back to them as I finish reviewing each section.

Jialun Chen 4F

It's definitely a trend you need to remember along with the atomic radius, I.E., and electron affinity. Yet it's unnecessary to memorize all the values.

Jialun Chen 4F

The first four elements, which are H, He, Li, and Be, are the exceptions to the octet rule.

Jialun Chen 4F

That's correct. The d-orbital can hold 5 pairs of or 10 electrons.

Jialun Chen 4F

All you need to bring is a pen, a scientific calculator, and your ID. Depending on your last name, the location is gonna be different, check out Dr. Lavelle's website for details.

Jialun Chen 4F

It's because the resonance hybrid is the actual representation of the structure, which has the same length. While the "alternatives" have different length in double/single bonds, but those are not actual structures.

Jialun Chen 4F

There's one difference I noted when Dr. Lavelle talked about the periodic trends. He lectured about electron affinity but didn't mention electronegativity; I searched them up and found out they're different concepts: electron affinity is the energy released when electrons are added to gas-phase atom...

Jialun Chen 4F

They don't have enough electrons to complete an octet if I recalled correctly.

Jialun Chen 4F

That's correct. Resonance refers to lewis structure have multiple bonds in different equivalent locations.

Jialun Chen 4F

The ground state is the stabilized state, the opposite of excited state. I always use the noble/inert gas to represent the inner electrons and write out the valence electrons. For example, the electron configuration for Chlorine is [Ne]3s2 3p6.

Jialun Chen 4F

I'm pretty sure that you will be fine to submit problems from either quantum or chemical bonding section, or both.

Jialun Chen 4F

E=hv is the incoming energy of electromagnetic radiation (photon). The energy needed to remove electron is the work function (represented by a greek alphabet).

Jialun Chen 4F

I got the same conclusion/answer as AArmellini did. There is no difference when I used 3 sig.figs in that problem.

Jialun Chen 4F

Lambda represents wavelength and v (squiggly) stands for frequency. It's kind easy to mix up frequency and velocity (velocity's variable is lower-case v).

Jialun Chen 4F

I agree with the answer above that E=hv is the equation used to calculate energy per photon. h is Planck's constant and v is frequency.

Jialun Chen 4F

The speed of light is in fact a constant. I used to use 2.9979*10^8 more often but figured 2.998*10^8 is more commonly applied in this class.

Jialun Chen 4F

For that' you might want to review the solubility of substances and review the definition of a spectator ion.

Jialun Chen 4F

I would recommend familiarizing yourself with all the units to play it safe. An Angstrom is simply a measurement that is equivalent to 10^-10m (or 0.1 nm if you prefer).

Jialun Chen 4F

I personally use the mole to mole conversion: 1 mole of CuSO4.5H2O contains 5 moles of H2O.

Jialun Chen 4F

There's actually something called the hill system that states C atoms and H atoms should be placed first, and others follow in alphabetical order.

Jialun Chen 4F

The test covers materials from the Review of Chemical & Physical Principles, which are some of the fundamental sections, so I believe the dilution equation is a subject that's likely to be tested.

Jialun Chen 4F

It's during your discussion. So if you have discussion on Tuesday, the test is gonna be on the same day. I recommend doing problems from the assigned homework list to prepare.

Jialun Chen 4F

It depends on the content your high school teacher covered in honors chem because unlike AP chem, honors chem can be very distinct from school to school. If you are familiar with most of the content in the fundamental section, you are probably in good shape; if not, you might want to spend a decent ...

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