CHEMISTRY COMMUNITY

kim 2I

If Dr. Lavelle makes his final similar to the 14A final, it will be similar to the format of the midterm. The test is most likely not going to be only made up of homework problems. There will probably be a few homework problems, so the outlines will give you a good idea of what type of questions wil...

kim 2I

When you decrease the volume of the system, the overall pressure is increased. Therefore, the reaction shifts towards the side with less moles of gas and for this reaction, it would be towards the products (2 moles vs the 3 moles in the reactants).

kim 2I

The units for n is mole since it refers to the moles of electrons transferred in the redox reaction.

kim 2I

I feel like an online final would definitely be difficult for a chem test like ours, so I think it will be highly unlikely unless we receive more urgent news within the next few days.

kim 2I

Do you mean like chemical equilibria and ICE tables or knowing strong/weak acid and bases? It'd always be best to have good practice on both to do well on the final.

kim 2I

I don't think that's the case every single time. I would just remember to balance O atoms with H2O in both conditions and H atoms with H+ in acidic conditions and H2O--- --> ---OH-/OH- ---> H2O for basic conditions.

kim 2I

Examples that would require Pt(s) include only having aqueous ions to aqueous ions or aqueous ions to gases as the phase change. An exception is liquid mercury that can act as a conductor.

kim 2I

Spectator ions are usually not included in cell diagrams because they don't really have an effect on the cell.

kim 2I

The number of electrons transferred, n, can be found by looking at the two half-reactions that are combined to formed the overall reaction of the cell. Electrons being lost in the oxidation rxn should be equal to the number of electrons being gained in the reduction rxn. Therefore, if the number of ...

kim 2I

Micah3J wrote:Test 2 is on all of outline 5 right and the second half of outline 4 right?

Yep! The second half of outline 4 being 5G or page 2 of the outline.

kim 2I

I personally don't think Dr. Lavelle would expect us to derive the equation on the final although I'm sure it could be helpful to understand where the rate equation came from. Also, since that equation is provided on the equation sheet, I think he would just make us apply it in a certain problem.

kim 2I

I've been wondering the same thing. Can someone please explain this? At first I thought that if the reaction was taken place at a different temperature (not the standard of 25C or 298.15K), then you would have to use deltaG=deltaG-TS to incorporate the temperature, but why is there an equation with ...

kim 2I

When delta G is negative, the reaction is spontaneous, and when delta G is positive, the reaction is nonspontaneous. However, in terms of potentials differences (E), when the value is postive, the cell reaction is spontaneous, and when the value is negatvie, the cell reaction is nonspontaneous. This...

kim 2I

Test 2 covers what wasn't tested on the midterm, so the second page of outline 4 (5G), and outline 5.

kim 2I

Yes. Test 2 covers the second page of outline 4 (5G) and all of outline 5.

kim 2I

Since the salt bridge helps balance the ions on both sides of the solution, the solution of the anode will probably become overly postive whereas the cathode's solution will become overly negative. I think with the solution unbalanced, the transfer of electrons on the wire will most likely stop and ...

kim 2I

If the metal placed in the solutions are labeled then you could probably tell which metal will gain the electrons and which one will lose them. For example, if we know that the metals placed in the solutions are Zinc and Copper, we can figure out that Cu2+ has a greater pull for the electrons and kn...

kim 2I

Salt bridges are used to help balance out the charge in voltaic cells. As the oxidation reaction gives away the electrons from the left cell (the anode) to the right cell (the cathode), the solid metal becomes an ion that is dissolved into the solution it is placed in. Vice versa, the solution in th...

kim 2I

Yes, oxidation numbers are the charges. You should be able to figure out the oxidation number for most molecules using some of the rules based on the groups on the periodic table. Other rules such as molecules in their elemental state having the oxidation number of 0 and oxygen having the oxidation ...

kim 2I

I'm pretty sure we will mainly focus on electron transfers in these redox reactions. I wouldn't worry too much about the protons moving around.

kim 2I

Delta S total = 0 for a reversible, isothermal expansion. This means that the delta S system = - delta S surroundings based off of the equation delta total = delta S system + delta S surroundings. Delta S total = 0 since the change of entropy between the system and its surroundings is equal and oppo...

kim 2I

Just the coefficients are counted for the number of moles. When pressure is increased, the equilibrium shifts to the side where there are less moles.

kim 2I

An exothermic reactions is spontaneous because it results in an increase of entropy of the surroundings. If you think of the equation △Gr= △Hr-T △Sr, when △Hr is large enough and negative compared to △Sr, the Gibbs Free Energy would be negatvie and therefore making the reaction spontaneous.

kim 2I

Usually each TA is assigned a page/problem on the midterm so that the grading on that problem would be fair and consistent.

kim 2I

You should know the most common strong acids and bases and think of all else as being a weak acid/base. For the strong acids, you should know HCl, HNO3, H2SO4, HBr, HI, HClO4 and for the strong bases, you should know LiOH, NaOH, KOH, Ca(OH)2, Ba(OH)2, and Sr(OH)2. You probably won't be tested direct...

kim 2I

As far as I know, Dr. Lavelle doesn't do curves on the tests, so seeing how you did in comparison to other students would be difficult. For the midterm and final, Dr. Lavelle let's us know the average class score, so you'll be able to get an idea of how well/poorly you did on those exams.

kim 2I

An example of a closed system would be and ice pack used to reduce swelling on injuries (energy can be transferred in and out of the system) and an example of an isolated system would be a thermos with hot liquid in it (no heat/energy/matter can go in and out of the system into the surroundings).

kim 2I

For calculations regarding entropy, the temperature should be in K. The change in entropy is measured in joules per kelvin, so a celsius calcuation would result in a different answer.

kim 2I

The right date and time should be 2/9 Sunday 2-5 since there was a change for conflicting midterms.

kim 2I

Topics on the midterm would include everything we've learned from week 1 to the end of this week (week 5). ALl of thermodynamics should be on the test!

kim 2I

Last time I went, they asked for your last chem discussion section, so make sure you remember that as well!

kim 2I

That makes a lot more sense. Thank you! What's the concept behind spectator ions allowing us to "cancel" them out like that?

kim 2I

When the volume decreases (increase in pressure), the reaction will shift to where there are less moles of gas.
When the volume increases (decrease in pressure), the reaction will shift to where there are more moles of gas.

kim 2I

When referring to the change in temperature, you do not have to worry about the units (Kelvin or celsius) on the temperature. The change would be the same regardless and would not affect your calculations.

kim 2I

R is Rydberg's constant so it can't have a change, but volume (V) and moles (n) can have a change since when the moles of gas changes, the volume changes as well.

kim 2I

From what I remember, only the midterm and the final are cumulative. Test 2 should only cover what comes after the midterm, not everything before.

kim 2I

The reaction should be 2HD(g) --> H2(g) + D2(g). Therefore, there is an equal number of moles on each side.

kim 2I

I believe you can pick them up at 3034 Young Hall.

kim 2I

I think Khan Academy's videos are the most helpful for me, but there are other resources such as Chemistry Libretexts.

kim 2I

You should always balance your chemical reactions before doing any sort of calculations so that the molar ratios are accurate. If by unbalanced you're referring to the fact that the reaction hasn't reached equilibrium yet, then the K cannot be calculated since K represents the EQUILIBRIUM constant. ...

kim 2I

Yes. Solids and liquids stay out of the equilibrium constant.

kim 2I

What you said about the "position" of Q being changed relative to K due to the greater concentration of products is true, but it might be better to say that Q would end up being more than K since the reaction is now going in the reverse direction (or favoring the reactants to the left).

kim 2I

I thought I understood how to find the equation for the equilibrium constant K, but when I saw the answer for this Self-test on page 401 in the textbook, I didn't really understand it. What is the net ionic equation for the reaction 2AgNO3(aq) + 2NaOH(aq) --> Ag2O(s) + 2NaNO3(aq) + H2O(l)?

kim 2I

Since strong acids and bases dissociate completely, it allows us to find the molarities of all the components that take place in the neutralization reaction through the balanced equation.

kim 2I

Dr. Lavelle's lectures aren't Bruincasted, so even though attendance isn't required, going to lecture is the best way to learn and to get well-organized notes from his powerpoints.

kim 2I

Actually doing the modules are helpful as well! Watch the videos and at the very least, take the post-assessments.

kim 2I

If the K value is large (K>10^3), then it means there are more products at equilibrium and that the "equilibrium sits to the right."
If the K value is small (K<10^-3), then it means there are more reactants at equilibrium and that the "equilibrium sits to the left."

kim 2I

When calculating K, all the components should be in the same "form/units." Therefore, the concentration of the gas would have to be calculated using the Ideal Gas Law of PV=nRT (divide by V on both sides, moles (n) over V = concentration, therefore, conc=P/RT). Finally the Kc can be calcul...

kim 2I

Since the "ICE" box is related to calculations with the equilibrium constant as well, you do not include solids and liquids. The rule applies to both types of problems as it refers to the same type of reactions.

kim 2I

The reaction will continue until the ratio is reached and will STILL continue even after equilibrium is reached. The products will go back to being reactants and vice versa at the same rate throughout.

kim 2I

I would recommend buying the 7th edition textbook. I have the 6th edition solutions manual and for the most part, the questions/homework problems are aligned with each other (6th and 7th edition) but there are definite changes throughout the book. If you want to make sure you get credit for your hom...

kim 2I

Joanne Kang 3I wrote:For mini marshmallows 2b, why is the coordination number 4?

Oxalate is a bidentate so it would bind to the central TM in two places making the coordination 4 (2 binding spots for oxalate and 2 from the hydroxide ions).

kim 2I

CaO is considered a base because it acts as a proton acceptor. The oxygen atom in CaO binds to the hydrogen ions from the acid HI to form water, and HI is the acid because it loses its hydrogen atom. Also, since it is know that a neutralization reaction produces a salt and water, knowing that HI is ...

kim 2I

SO3 is a non-metal oxide and non-metal oxides are known to be acidic in nature. It is a Lewis acid in that it accepts electrons, but I'm also a bit confused on how exactly this works.

kim 2I

For Bronsted acids, they can be identified from their formulas by their acidic hydrogen atom, a hydrogen atom that can be released as a proton. They are usually written as the first element for inorganic acids (ie. HCL, HNO3). For organic acids, the acidic hydrogen is usually found at the end of the...

kim 2I

When the litmus paper is turned pink, it shows that the solution is acidic. If the litmus paper turns blue, then the solution is basic.

kim 2I

Since both of the lone pairs belong to oxygen, the TM center could only bind to the one oxygen atom. Also, since the lone pairs are on the same atom and are close together, it would be hard for water to have two binding sites that are available.

kim 2I

You should still draw the Lewis structure with the lowest formal charges since the number of bonds/lone pairs could change and therefore affect the molecular shape. However, you don't need to worry about resonance structures.

kim 2I

Pi-bonds are formed with unhybridized p-orbitalsm, so I'm sure hydridization and double-bonds don't go together. On the other hand, sigma-bonds are usually formed with sp or sp^2 hybrid orbitals.

kim 2I

Fundamentals will definitely be on the final, but probably not nearly as much as other topics and sections we have covered later in the quarter.

kim 2I

Yes. It is possible to have a negative pH. In fact, it is possible to go beyond the known 0 to 14 pH scale.

kim 2I

Yes, if your discussion is on Friday, you'll only have two days before the final to really review it. However, I'm sure if you email your TA, there could be a way to meet up and receive it earlier if you really need it beforehand.

kim 2I

Yep. It doesn't matter. In an example in the textbook, only one of the resonance structures of the carbonate ion was used to figure out what the resulting shape of the molecule is.

kim 2I

London dispersion forces are present in between all molecules, despite the fact that those molecules are nonpolar or polar.

kim 2I

Hybridization further explains the VSEPR model by assuming the mixing of atomic orbitals to help understand why the some bonds have equal lengths when the valence electrons may not be in the same energy level.

kim 2I

A is the central atom. I'm pretty sure it can't have subscripts since there can only be one central atom when we're talking about molecular shape.

kim 2I

Mandeep Garcha 3C wrote:Just to make sure, hybridization is not on the test right?

Yep. There will be no hybridization on Test 2. That will only be on the final.

kim 2I

I'm pretty sure that the topics on test 2 will cover: -VSEPR -dipole moments and shape (non-polar/polar) -identifying intermolecular interations -lone pairs and the reason for their locations -sigma and pi bonds Dr. Lavelle also said that whatever we cover in the Monday lecture will also be on the t...

kim 2I

I'm pretty sure the number of orbitals is based on the orbital angular momentum # (l) so for part a), the orbital associated with l=1 is the p-orbital. 2p has three orbitals (since ml= -1, 0, +1).

kim 2I

I don't think Test 2 topics have been confirmed by any of the TA's nor by Dr. Lavelle just yet. I'm assuming it would cover the rest of Outline 3 (what wasn't on the midterm) and then Outline 4 (Molecular Shape and Structure). Essentially, it should cover everything we go over in lectures that were ...

kim 2I

From rereading the syllabus, Dr. Lavelle doesn't seem to have any extra credit. Your final grade should be based on the weekly homework, the two tests, the weekly chemistry community, the midterm, and the final. I would just focus on getting all the points you can from these catergories!

kim 2I

I don't think Dr. Lavelle will use lecture time to go over the questions on the midterms since we have Test 2 coming up soon. Someone's TA said that the TA's will be handing out the midterms on Wednesday after the lecture.

kim 2I

All molecules have dipole forces. However in class, we will most likely only focus on the electric dipole moment (a partial positive charge next to an equal but opposite partial negatvie charge) that are formed by two atoms in a polar covalent bond.

kim 2I

Ionic bonds are stronger because there is a greater electronegativity difference between the two atoms (greater than 2.0). Also, while covalent bonds share electrons, ionic bonds are formed by the mutual attraction from both of the oppositely charged ions.

kim 2I

You still have discussions on 11/6 Wednesday. The only thing cancelled is lecture.

kim 2I

Another way to think about it is to actually subtract and add 5.0 m/s to the given 5.00 m/s. So then the range would be from 0.00 m/s to 10/00 m/s. Therefore, the deltaV would be 10.00 m/s. There is an error in the solutions manual! (Delta V is NOT 5.00 m/s). Make sure you check the link on the chem...

kim 2I

You're right about the kinetic energy being 0. Since you are looking for the minimum frequency needed for the photoejection of an election, there wouldn't be (excess energy) kinetic energy for the ejected eletron. However, the work function would be set equal to hV in order to find the frequency.

kim 2I

I'm in the 2:00 pm lecture and Dr. Lavelle mentioned that there is no class that day. Since you're in one of the earlier lecture, he probably forgot to let your lecture know.

kim 2I

Hybridization should be on Test 2, but not on the midterm!

kim 2I

Dr. Lavelle said that he will keep us posted on the location. In terms of the date, he said there could be possible changes if he is unable to reserve a large enough room for all of us.

kim 2I

Usually beyond period 3, there are lewis structure exceptions but Boron (in period 2) can also have only 6 electrons bonded to it.

kim 2I

Another thing to be aware of is that homework grades are out of 50 points and should be updated weekly by your TA, so don't worry if it seems like full credit was not received.

kim 2I

The basic periodic trends would not be provided for us on the tests, but just knowing that electronegativity increases as the elements are closer to the upper right-hand corner of the table should be enough.

kim 2I

I don't think it would necessarily be considered wrong, but having a lower formal charge means greater stability, so drawing the Lewis Structure accordingly would be the best answer. Probably if the test specifically asks for the Lewis Structure with the lowest formal charge, then drawing out each o...

kim 2I

Valence electrons in the d block are usually determined by their group number, or the number of electrons in their valence shell. In general, the transitional metals have 2 valence electrons.

kim 2I

It is important to consider light as photon packets of energy where a single photon interacts with a single electron. Therefore, each individual photon must have enough energy to remove each electron. Increasing the intensity only increased the number of photons that are hitting the surface of the m...

kim 2I

The spin magnetic quantum number is important because it describes the direction in which the electron spins. There are only two spin states that can be represented with an up or down arrow. A +1/2 is indicated with an up arrow, while -1/2 is indicated with a down arrow. The arrow pointing up can be...

kim 2I

The correct answer in this case is E=hv since the question is solely asking about the energy of the light and its frequency. Since the question has nothing to do with the energy required to remove an electron from the metal, the only equation you would focus on is the equation of the incoming light ...

kim 2I

Electron affinity of an element is the energy released when an electron is added to a gas-phase atom. In terms of the periodic table, the highest electron affinities can be found toward the right side of the periodic table (especially the upper right near oxygen, sulfur, and the halogens).

kim 2I

An atomic radius is defined as half the distance between the centers of neighboring atoms. This inclues both ionic and covalent radii as well. A covalent radius is specifically referring to two atoms joined by a chemical bond while an ionic radius refers to the distance between neighboring ions in a...

kim 2I

I would rely more on what Dr. Lavelle has used in class/has provided for us on the constants sheet (R = 3.28984 × 10^15 Hz or 1/s). The Rydberg's constant on Google has a different unit (1/m) and would possibly interfere with the calculations Dr. Lavelle has taught us.

kim 2I

The equation E=hv has the basic units of Joules, but if you think back to the photoelectric effect and the incoming light, the units also refer to the amount of energy per photon. Keeping this in the back of your mind will help you make any conversions that are necessary to figure out how many photo...

kim 2I

De Brogile's wave equation can be used for any particle with momentum that has wave-like properties with a wavelength. The equation wavelength=h(planck's constant)/(momentum, or the particle's mass times speed) is usually used to find the wavelength of a traveling particle or electron.

kim 2I

I don't think it's necessary to memorize every specific wavelength and its regions for the exams, but I would recommend knowing just in general that infrared radiation has the longest wavelengths and that UV radiation has the shortest wavelengths. Also, since Lavelle mentioned that visible light is ...

kim 2I

The Heisenberg uncertainty principle states that if the location of a particle is known with an uncertainty (delta X), then the momentum of the particle (p) can be also known within the uncertainty of delta p. The equation is usually used to find the minimum uncertainty in the speed (delta v) or the...

kim 2I

Are you referring to the molar mass of a compound that is given to you in the problem, or are you referring to the molar masses you use for calculations off the periodic table? If it's the molar mass of a compound that is given in the problem, then I would think you'd take its sig figs into account ...

kim 2I

From what I know, formula units can be interchangably used with the number of molecules or atoms, so using Avogadro's number should work for any question asking for a compound's formula units. Something to keep in mind is that formula units usually refer to ionic compounds while molecules refer to m...

kim 2I

For extra practice, you could do the examples that are embedded in the readings of the fundamental chapters. However, the listed problems on Outline 1 should be sufficient to prepare you for the test. My TA said that there will be around 7 calculation-based problems for us to answer, so concepts mig...

kim 2I

For week 2, Lavelle gives us the option to complete 5 homework problems from Outline 1 (Fundamentals) or from Outline 2 (The Quantum World). Since the quiz is on Fundamentals/Review material, he told us that doing 5 different homework problems from Outline 1 is acceptable to assist us in studying. H...

kim 2I

By definition, molarity is the moles of solute divided by the total volume of the solution in liters, so on the test, converting all mL to L before any calculation would be the right thing to do. If the problem gives the a volume in mL, then it would be okay to convert the volume answer found in L b...

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