CHEMISTRY COMMUNITY

Juwan_Madaki_3K

Yes the scores are additive. Your chemistry community grade should update each week based on the number of times you have posted so far.

Juwan_Madaki_3K

K and Kc are calculated the same way and are sometimes used interchangeably. However, Kc specifically refers to molar concentrations.

Juwan_Madaki_3K

I know that Prof Lavelle mentioned that there would be bonus questions for the final, does anyone know how much those bonus questions are worth?

Juwan_Madaki_3K

I know how to determine which molecules go on the anode and cathode side of a cell diagram, however, I'm struggling with the order in which to write them. For example, Hg(l)|Hg2Cl2(s)|Cl−(aq)||Hg2^2+(aq)|Hg(l), how do you decide which molecule is closest to the salt bride?

Juwan_Madaki_3K

After balancing the oxygens in the half reaction for O3 --> O2, why do you add OH- to the product side and not the reactant side?

Juwan_Madaki_3K

For Chem14A, topics that we spent more time on had more questions pertaining to that content on the final. Does anyone know if Lavelle is doing the same thing for this final?

Juwan_Madaki_3K

I find that the textbook problems are the most important thing you can do. I would also recommended reviewing sapling homework and utilizing office hours/UA sessions.

Juwan_Madaki_3K

I try to do every problem, however, there are instances when there's a lot of different problems that cover the same content. In that case, I start skipping questions that I've already had a lot of practice with.

Juwan_Madaki_3K

Is the slope only equal to negative k(-k) in First Order Reactions or other reactions as well?

Juwan_Madaki_3K

How do you know to reverse the reaction for tin and not for Mercury(I) chloride?

Juwan_Madaki_3K

Does anyone know why we aren't provided with the cell potential values in these problems/aren't directed to a table? Is there a way to find them?

Juwan_Madaki_3K

Since the anode is positively charged in electrolytic cells, does that affect the direction the electrons flow? Will they flow in the opposite direction now (cathode to anode)?

Juwan_Madaki_3K

In lecture 21, Lavelle mentioned how the preferred form for the 2NO2 + 2NO --> O2 reaction would be to divide the reaction rates for NO2 and NO by 2. Why is it better to divide NO2 and NO by 2, instead of just multiplying the reaction rate of O2 by 2?

Juwan_Madaki_3K

Yes, the anode is always on the left and the cathode is always on the right. It also helps to keep the direction the electrons are flowing consistent.

Juwan_Madaki_3K

Will we be asked to draw/label cell diagrams (ex. voltaic, concentration, or porous disk cells) in future exams?

Juwan_Madaki_3K

When calculating standard cell potentials, how do you know which redox reaction to reverse/which E to make negative?

Juwan_Madaki_3K

I think about work in terms of the system. If work is being done ON the system, work is positive. However, if work is being done BY the system, it's negative.

Juwan_Madaki_3K

What is the biggest difference between G,S, and H in standard conditions versus when they aren't in standard conditions? Does this affect calculations?

Juwan_Madaki_3K

I usually look at the units of pressure given and use the R value containing that unit.

Juwan_Madaki_3K

I'm having trouble grasping how to solve question 12. I know that the reaction is spontaneous when the Gibbs free energy is negative, however, I still can't get the correct answers.

Juwan_Madaki_3K

Does anyone know if midterm 2 will have partial credit and to what extent?

Juwan_Madaki_3K

Yeah the midterm is Friday, Feb 19th at the time of your lecture.

Juwan_Madaki_3K

To review your exams, you can go to your TA office hours and possibly in discussion(in a breakout room) if you have extra time.

Juwan_Madaki_3K

I think the step-up sessions will be most useful to you because the chemistry content is explained at a slower pace. Utilizing office hours and forming study groups with peers can also be very beneficial.

Juwan_Madaki_3K

In Sapling week 5/6 question 5, I noticed that we multiplied the cv value by moles to convert to nCV. However, in question 6, the CV value was used for the change in temperature. In what cases, do you use CV and in what cases do you use nCV?

Juwan_Madaki_3K

The R constant you choose to do your calculations with is based on the units of pressure you're given. If you're given pressure in atm, then use the gas constant that has atm in the units.

Juwan_Madaki_3K

A negative delta H means that the reaction is exothermic and that heat is being released. A positive delta H means that the reaction is endothermic and that heat is required. Q isn't affected by a temperature change because there's no change in concentration. However, increasing temperature for an e...

Juwan_Madaki_3K

I know that a a system is at equilibrium when internal and external pressure are equal. However, does the system being closed, open, or isolated affect the system's equilibrium as well?

Juwan_Madaki_3K

Professor Lavelle moved the due date for homework weeks 3/4 to Sunday, February 6.

Juwan_Madaki_3K

On the 10 point questions, there's partial credit for answers that were close to the correct answers. However, questions lower than 10 points don't have partial credit.

Juwan_Madaki_3K

I find that textbook problems are the most important resource when studying for 14B exams. Additionally, office hours are quite helpful. I usually study over a week so I can give myself time to thoroughly understand the maerial.

Juwan_Madaki_3K

When the equilibrium constant is 10^-4 or smaller, it's safe to just approximate. However, you can run into errors when you're calculating percent ionization. If your percent is greater than 5%, then you're going to have to re-do the calculation without the approximation.

Juwan_Madaki_3K

If we're just given the value of K without specifying Kc or Kp, what units should we use for our calculations? Pressure or molarity?

Juwan_Madaki_3K

Yes, the ice tables are applicable for partial pressure, as well as concentration. They can even be used to calculate just moles.

Juwan_Madaki_3K

Does anyone know how to solve this? Initially I thought it was the sum of product enthalpy minus the sum of reactant enthalpy. However, I can't seem to calculate the correct answer.

Juwan_Madaki_3K

If you're prompted to find total pressure, you need to calculate each equilibrium partial pressure and add them all together. This will give you total pressure and typically, you want your units to be in bars.

Juwan_Madaki_3K

Adding a gas to increase pressure won't affect the system, however, compressing the system to increase pressure will cause equilibrium to shift.

Juwan_Madaki_3K

The most important rule to remember is that K can only be changed by the temperature. When the concentration of products increases/decreases, the concentration of reactants will increase/decrease accordingly to maintain the same ratio of K.

Juwan_Madaki_3K

I know that professor Lavelle has said not to include liquids/solvents in your calculation of the equilibrium constant. However, if your solvent is aqueous, can it be included?

Juwan_Madaki_3K

The solution manual states that compressing the system has no effect because there's an equal number of moles on both sides. However, the equation has 12 moles on the reactant side and 7 on the product side. Can someone explain if I'm missing something?

Juwan_Madaki_3K

I'm having trouble with part A. How do you figure out the coefficients for A,B, and C by looking at the graph?

Juwan_Madaki_3K

In 5J.11 part b X2(g) ⇌ 2X(g), where X is a halogen. The solutions manual states that this reaction is endothermic and that heat is on the reactants side. How can you tell that this reaction is endothermic?

Juwan_Madaki_3K

H2O would still be included as a gas. When it's a liquid/solvent, then we wouldn't include it.

Juwan_Madaki_3K

I think it's especially important to pay attention to the words "equilibrium" and "initial". If only equilibrium concentrations are present, then I think it's safe to assume that the ICE tables aren't necessary. However, if initial concentrations are present, then using an ICE ta...

Juwan_Madaki_3K

Why does PO2/PO3 differ between the two cases and how would you calculate it to verify your answer? I tried calculating the concentration of O2 and computed the equilibrium constant without raising the answer to their respective powers, however, I can't get an answer that verifies the above statement.

Juwan_Madaki_3K

Why do you multiply the equilibrium constants instead of adding them?

Juwan_Madaki_3K

Qc is used for molar concentration, Qp is used for partial pressure, and Q represents the reaction quotient in general. However, Qc, Qp, and Q are all calculated the same as K. The products will be in the numerator and the reactants in the denominator.

Juwan_Madaki_3K

I understand the steps needed to solve these kinds of questions, however, we weren't given the equilibrium constant in the question description. How would you go about solving this particular question?

Juwan_Madaki_3K

I've been having trouble with converting bars to mol/L. Does bar have to be converted to another unit first or can it just be immediately plugged into the ideal gas law equation?

Juwan_Madaki_3K

Professor Lavelle provides TONS of live resources to assist you in this course and is always willing to help. I would utilize officer hours, UA sessions, step-up sessions, and etc. for any areas of confusion. In my opinion, doing the textbook problems is the most important thing you can do to succeed.

Juwan_Madaki_3K

When using the ideal gas law, which units should the temperature be in? Kelvins or Celsius?

Juwan_Madaki_3K

He states earlier that the final is cumulative and the subjects we spent more time on will have more questions in the final. For example, we spent the most time of the quantum section, so you can expect to have more questions about that topic.

Juwan_Madaki_3K

I think he meant that he will draw some questions from the book outline, but not all. However, redoing book problems can still be valuable and beneficial. I wouldn't rely on the idea that he will ONLY pull from homework problems, but expect some.

Juwan_Madaki_3K

Electron geometry focuses on all regions of electron density(including lone pairs). However, molecular shape just looks at the regions of electron density occupied by atoms. For example, NH3 has a tetrahedral electron geometry, but a trigonal pyramidal molecular shape because only 3/4 regions of e- ...

Juwan_Madaki_3K

In what case do you use OH2 and in what case do you use H2O?

Juwan_Madaki_3K

Why is H2O referred to as dihydrate instead of diaqaua in this coordination compound? Is it because H2O is not directly bonded to Co?

Juwan_Madaki_3K

I've been struggling to grasp ligand classification. I understand the definition of monodentate, bidentate, tridentate, and hexadentate, however, I don't understand how to determine if an ion or molecule is one of those types. I need some strategies to help with determining what type of ligand the i...

Juwan_Madaki_3K

Q: Why does hamburger yield lower energy than steak?
A: Because it's in the ground state.

Juwan_Madaki_3K

I know that Professor Lavelle said we wouldn't be drawing vectors, but I still use them to determine if something is polar or nonpolar. A polar molecule's vectors/dipoles DON'T cancel and a non polar molecule's dipoles/vectors DO cancel. I also look at the electronegativity values to help. Typically...

Juwan_Madaki_3K

I noticed that the textbook made a mistake and drew the Lewis structure for SCl4 instead of SF4. However, I was wondering if SF4 would still be polar because the molecule still has the same shape and since F is more electronegative than S.

Juwan_Madaki_3K

For 2E.25 part A, how do you know to draw the Cl's on the same side and the H's on the same side. If you draw them opposite each other, then the vectors will cancel out. However, I'm unsure how to determine where you place the atoms.

Juwan_Madaki_3K

For question 2E.21 Part D, how can we determine the bond angle without looking it up online. N2H4 has a trigonal pyramidal shape, and a bond angle of 107 degrees. I know how to determine if the angle is above/below 120/109.5, but I'm unsure how to find the exact angle for shapes that aren't tetrahed...

Juwan_Madaki_3K

I think we will have to memorize the bond angels for shapes that have a consistent bond angles such as tetrahedral, trigonal planar, and linear. For other shapes, we most likely just need to know if it's above or below 120 degrees or 109.5 degrees.

Juwan_Madaki_3K

You want to look at how many regions of electron density are around the central atom. Regions of electron density can be lone pairs or bonding pairs, but it's also important to note that a single bond, double bond, and a triple bond are each one region of electron density. When drawing NH3, N had 3 ...

Juwan_Madaki_3K

When dealing with shapes like tetrahedral(109.5 degrees) and trigonal planar(120 degrees), those shapes have consistent bond angles, so I feel that it's best to memorize those. However, for shapes like trigonal pyramidal, seesaw, bent, etc., knowing if they're above/below 109.5 or above/below 120 is...

Juwan_Madaki_3K

When looking at the lecture notes and book problems, I saw that the Seesaw molecular shape can have multiple bond angles, however, I'm not sure why that is. I was wondering if someone could further explain that. Lastly, when does the Seesaw shape have the bond angles 90 and 120 and when does it have...

Juwan_Madaki_3K

I'm still having trouble grasping hybridization. I know that we can look at the number of regions of electron density that are present and determine hybridization from there. However, I want to learn how to do it past memorization. Does anyone have any techniques they have used to increase their und...

Juwan_Madaki_3K

Professor Lavelle recently mentioned that lone pairs are usually drawn farther or opposite from each other due to repulsion. However, I was wondering why the lone pairs are H2O are drawn next to each other. Why aren't they drawn opposite each other on opposite sides of the Oxygen?

Juwan_Madaki_3K

I know that our midterms have been during our discussion time, however, it may be difficult to test us on the whole/or most of the course's content in 50 mins. On MyUCLA for Lecture 2, it says our final is on December 13th from 11:30AM to 2:30PM. Will we have to take the exam at that exact time or w...

Juwan_Madaki_3K

When two different compounds are both experiencing ONLY London Dispersion Forces, how can you determine which one is experiencing greater London Dispersion Forces? What criteria are we supposed to look at?

Juwan_Madaki_3K

When drawing Lewis structures that have more than 4 atoms that are different, how to you ensure that you are placing the atoms in the correct place. I always make sure I have the right amount of electrons, and that each atom is satisfied with the octet rule, but I still run into some trouble. For ex...

Juwan_Madaki_3K

The final answer for this textbook problem was that SO3^2- had the longest S-O bond length and SO2 and SO3 had equal S-O bond lengths. In these problems, should we always try to draw oxygen with a double bond because it has a lower Formal Charge? Initially, I had drawn the SO2 and SO3 structure with...

Juwan_Madaki_3K

Br 2- would be two to the right of the periodic table. Anions like to form noble gas configuration to gain stability, so you will add e- and move to the right.

Juwan_Madaki_3K

I don't think we need to worry about the f-block for the exam, however, I think it's good to have a basic understanding of it to enhance your performance on the exam. By general understand, I mean how many orbitals it has, where it begins on the periodic table, etc.

Juwan_Madaki_3K

When drawing a Lewis structure like COCl2, how do you decide if the CL or O gets the double bond? Is it usually the element with the higher ionization energy?

Juwan_Madaki_3K

When drawing Lewis structures, when are elements allowed to have more than 8 electrons? In other words, when is the octet expansion allowed? I know Professor Lavelle has touched on the reason in lecture, but I'm still a little confused.

Juwan_Madaki_3K

For question 2c.15 part b, I noticed that the book might have made a mistake when drawing the Lewis Structure. When drawing HSO4^-1, the structure on the right has an unsatisfied single bonded O. It only has 2 lone pairs, 1 bonding pair, and doesn't follow the octet rule. However, in the answer key,...

Juwan_Madaki_3K

Another technique that I find best for myself is by being confident and giving myself positive affirmations. If I come into an exam convinced I'm going to perform badly, then I most likely will. Avoid worrying about worst-case scenarios and remain optimistic!

Juwan_Madaki_3K

I don't think we will be tested on f orbitals or required to know about configurations with them. However, I think he would just like for us to know that they're there and some general information about the f orbitals.

Juwan_Madaki_3K

By looking at both options, they do make sense. However, just putting [Ar] may be a little vague or confusing. I think you should stick with starting from [Ne] and writing the remaining configurations.

Juwan_Madaki_3K

In order for 3d to come before 4s, the 4s orbitals must be completely filled(4s2). At this point, 3d is lower in energy than 4s. However, this doesn't apply to exceptions like Copper and Chromium.

Juwan_Madaki_3K

I know that quantum number ml corresponds to a specific orbital. However, I was wondering how you know that when n =2 l= 1ml= -1, it's 2px. Specifically, how does the coefficient and charge of ml help you determine whether it's x, y or z or even x^2...?

Juwan_Madaki_3K

When using shorthand notation, the [KR] symbolizes the electron configuration of Krypton gas. So all that's left to do is use the building-up principle and write the remaining electron configuration until Iodine. In this case, the remaining configurations that lead to Iodine are 4d10 5s2 5p5. The d ...

Juwan_Madaki_3K

For this textbook problem for part a, we had to write the electron configuration for Ag. The textbook listed it as [Kr] 4d10 5s1. I remember Chromium and Copper were listed as exceptions, but I don't remember Silver. Is this an instance where Silver is an exception or did the book make a mistake?

Juwan_Madaki_3K

I know this is far in the future, but does anyone know if Midterm 2 and the final are cumulative or if they just cover the content we learn in between each exam?

Juwan_Madaki_3K

I know that two electrons can only exist in an orbital if they have an opposite spin. However, I'm still confused about how to determine which electron has a +1/2 or -1/2 spin. Does the first electron in the orbital typically have a +1/2 spin and the second a -1/2 spin?

Juwan_Madaki_3K

Theoretical yield also differs from actual yield because it's the maximum amount of product one can get from a molecule/atom/formula unit in grams based on the limiting reactant. It is always greater than actual yield due to side reactions, reactants not being pure, and product sticking to the beake...

Juwan_Madaki_3K

By knowing which wavelengths each EM region corresponds to, you can also just calculate the frequency using c= wavelength x frequency. This way you won't have to memorize the frequency ranges. Hope this helps! :)

Juwan_Madaki_3K

They're some things such as net equations and organic chemistry formulas that have come up in book problems and previous homework. Will we be expected to use/know these subtopics on the midterm even if we haven't covered them in class?

Juwan_Madaki_3K

Does anyone know if we will have an equation sheet with constants given to us during the midterm or if we have to memorize that information?

Juwan_Madaki_3K

When reading the Balancing Chemical Equations section in the textbook, they refer to NaOH as a formula unit, but H2O as a molecule. What is the difference between those two terms and how do you know how to categorize the compounds in regards to these terms( which are formula units and which are mole...

Juwan_Madaki_3K

Does anyone know how to solve this? I've tried multiple methods, but I can't seem to figure it out.

Juwan_Madaki_3K

I find that writing the state of the molecules helps me visualize and understand how it takes place. Thought at times, it may not be necessary, writing the states may increase your overall understanding of the chemical reaction. I would also get in the habit of listing states so that you aren't mark...

Juwan_Madaki_3K

In question 3 of focus topic IA, I understand why options A,B, and D are wrong. However, I do not understand why C is correct. I am confused about how the extent of change in the electrical field relates to EM radiation. What is the "extent of change" referring to in the question? The word...

Juwan_Madaki_3K

Hello everyone! I hope you all are doing fine. My question is when you balance any equation is there only one correct way of doing it or can there be different approaches and answers? I also find it easier to begin balancing the atom that only shows up in one compound on both sides. For example, wh...

Juwan_Madaki_3K

I am unsure how to begin solving part C of M11. How do you use the formation of P4O6 to solve the problem?

Juwan_Madaki_3K

Chem_Mod wrote:Is there a particular problem you are referring to?

I am referring to question 18 in the Photoelectric effect module. It asks what conditions must occur for an election to be emitted from a metal surface.

Juwan_Madaki_3K

To determine the empirical formula of the substance, we must convert the moles of the compounds to moles of elements within the compounds (ex. finding moles of Hydrogen within moles of H2O). However, when solving the problem, the book multiples the moles of H2O by 1 instead of 2. I am confused about...

Juwan_Madaki_3K

If the energy of the light photon is equal to the energy required to remove the electron, why is the electron still ejected from the surface if its kinetic energy is zero?

Juwan_Madaki_3K

I know that "points" on the diagrams translate to carbon molecules. However, on 3-methyl-3-hexanol, they're two vertical lines pointing upwards. What does that translate to when finding the molecular formula?

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