CHEMISTRY COMMUNITY

SelenaDahabreh1D

Wait, nevermind. I don't think the value changes (or the signs of the value). I just got confused because in today's review session Dr. Lavelle wrote the value as 2.36 and -2.36 so I got confused. I would appreciate it if someone would clarify my understanding.

SelenaDahabreh1D

The only time we alter the standard cell potential is when we either make it negative or positive by flipping the equation, correct?

SelenaDahabreh1D

Is the value of E naught always 0 in a concentration cell?

SelenaDahabreh1D

When H2O(l) is on the reactant side and we have another species on the reactant side, would it be unimolecular or bimolecular because water is not included in the elementary rate law?

SelenaDahabreh1D

I am very confused as to how to go about solving problem 6L.7. Like how do we know how to split up the reactions? Also, how do we use the information provided after the equation to help us solve the problem? This is just an overall very confusing problem for me.

SelenaDahabreh1D

How do we know when to add Pt(s) to our cell diagram?

SelenaDahabreh1D

I believe the trend is that the more negative the standard potential value is, the stronger it is as a reducing agent (thus, more likely to get oxidized); the more positive the standard potential value is, the stronger it is as an oxidizing agent (thus, more likely to get reduced).

SelenaDahabreh1D

Will our final exam include questions from past midterms?

SelenaDahabreh1D

You would have to add up the individual order of the reactants in the formula.

SelenaDahabreh1D

Will the half-reactions be given to us on the exam or will we have to know how to construct them?

SelenaDahabreh1D

How do we determine the value for 'n' in the delta G naught = -nFE?

SelenaDahabreh1D

On the final exam, will we be given the reactions and standard potentials? Such as this website provided by Sapling: https://sites.google.com/site/chempendix/potentials

SelenaDahabreh1D

I would definitely go through each textbook problem more than once and make sure you really understand how to go about answering it if it were asked in a different way or with different wording. I personally enjoy reading the textbook because it helps clarify some topics for me, but if you don't hav...

SelenaDahabreh1D

I was quite pleased with Midterm 2, especially since I now know that my studying habits are paying off. I would say, however, that there were a few more conceptual questions on Midterm 2 than I anticipated, so I expect to spend more time studying these chemical processes conceptually rather than jus...

SelenaDahabreh1D

If we already have 50/50 Chemistry Community Points, are we still allowed to post 5+ posts a week (with the expectation that we are capped at 50 points)?

SelenaDahabreh1D

A state property only takes into account the initial and final states. Heat and work are not considered state properties because they are path dependent.

SelenaDahabreh1D

Definitely take the time to go through every single textbook problem and understand how to do it if it were worded differently. Go to Step-Up, Workshop, and Drop-In sessions if you have time. Dr. Lavelle usually schedules some TA review sessions as well, so go to those too. Read the textbook too, be...

SelenaDahabreh1D

I believe a negative delta G would be more stable because it is spontaneous, and thus favorable. On the other hand, a positive delta G would not be stable because it is non-spontaneous.

SelenaDahabreh1D

You would use the PV=nRT equation to determine the final volume. In part (b) you were asked to determine the limiting reagent. In part (c), it would be helpful to rewrite the chemical equation with respect to the limiting reagent. After doing that, you will calculate the amount of moles to be 0.045....

SelenaDahabreh1D

I don't think there is an explicit relationship between work and entropy, per se. But, it is good to know the relationship between work and delta G, as this is on the outline. To sum it up, w(max)=delta G. This means that the change in Gibbs free energy is equal to the maximum amount of work a syste...

SelenaDahabreh1D

During an irreversible expansion, temperature is not constant. During a reversible expansions, temperature is constant throughout. On Dr. Lavelle's website under the outlines he has a good visual for picturing these types of expansions. For irreversible expansion, you would use w=-PdeltaV, and for r...

SelenaDahabreh1D

Delta U = 0 for isothermal expansions because the temperature is constant in isothermal expansions. When the temperature is constant, no heat could be supplied or released from the process. Thus, delta U = 0. And remember for isothermal (constant temperature) expansions, q=-w, so both q and w would ...

SelenaDahabreh1D

For an isothermal irreversible expansion, delta S of the surroundings is going to be 0. Thus, you would only need to calculate the delta S of the system and delta S of the system = delta S total.

SelenaDahabreh1D

I think one notable factor that would increase residual entropy is the amount of available positions or orientations a molecule or substance can have. For example, in the book there is a question asking whether cis -MX2Y4 would have higher or lower residual entropy than trans -MX2Y4. Given that a ci...

SelenaDahabreh1D

The question (if I remember correctly) says to use a table that has specific/molar heat capacity values. So, you would use that table to solve q=mCdeltaT for each side. That is: q(copper kettle)=(400.0g)(0.38J/°C*g)(100.0°C-20.0°C) and q(water)=(300.0g)(4.184J/°C*g)(100.0°C-20.0°C). Then you will so...

SelenaDahabreh1D

Entropy is a measure of disorder. I like to think of this in terms of solid, liquid, and gas. In the solid phase, the molecules are tightly packed and are likely to not move around as much (unless they are vibrationally active); thus, the entropy of a solid is likely to be low. Next, molecules in a ...

SelenaDahabreh1D

It is simply a conversion factor to convert L/atm to J. It is on the Constants and Formulas Sheet Dr. Lavelle allows us to use on the exam!

SelenaDahabreh1D

I've seen some questions where when calculating degeneracy, W, the value is put to a power of Avogadro's number. When exactly do we do this?

SelenaDahabreh1D

On Outline 4, one of the objectives is to show how Delta S and Delta H are related for a change at constant temperature and pressure. How would we should this? Would it be using the standard Gibbs free energy equation?

SelenaDahabreh1D

I am still a bit confused on how free energy depends on pressure and the equilibrium constant. Would someone be able to explain this please? :)

SelenaDahabreh1D

I saw this acronym on the internet for memorizing state functions: PVT HUGS. P is for pressure, V is for volume, T is for temperature, H is for enthalpy, U is for internal energy, G is for Gibbs free energy, and S is for entropy. The two path functions are work and heat.

SelenaDahabreh1D

When delta H and delta S are both positive, then delta G would be positive at high temperatures and delta G would be negative at low temperatures.

SelenaDahabreh1D

Container C is vibrationally active, whereas Container C is not. When atoms or molecules are vibrationally active, entropy increases because there is more movement.

SelenaDahabreh1D

Delta G naught is used to signify standard Gibbs Free Energy (meaning under standard conditions such as 25 degrees C or 1 atm). Delta G on the other hand does not need to be under standard conditions.

SelenaDahabreh1D

When do we use this equation: delta U = 3/2nRT?

SelenaDahabreh1D

For reversible processes, delta S total will always be 0. Thus, delta S system = - delta S surroundings. how did you know this was a reversible process? My apologies! I was looking at a different question. Okay, so for this question, you would need to determine changes in entropy of the system and ...

SelenaDahabreh1D

For reversible processes, delta S total will always be 0. Thus, delta S system = - delta S surroundings.

SelenaDahabreh1D

When reviewing the Sapling homework for Week 3-4, I realized that the values for Cv,m were given for question 20. For example, it showed that for atoms, Cv was 3/2R; for linear molecules Cv was 5/2R; and for nonlinear molecules was 3R. Are we expected to memorize these values for the midterm or will...

SelenaDahabreh1D

I definitely agree! I feel like this midterm is covering a lot of topics, and there are many different types of questions to have to know how to answer. I typically like to combat my midterm nerves by just taking a moment every so often to step back and ask myself "At this moment, what do I kno...

SelenaDahabreh1D

When I calculated the delta G value for this problem, I repeatedly got -2.74 kJ * mol^-1, but the answer key says -27 kJ * mol^-1. I've even tried directly plugging in the values in the solutions manual in my calculator and I still get -2.74. Can someone please advise how -27 kJ * mol^-1 is the answ...

SelenaDahabreh1D

I made a table to help me understand: ΔH ΔS ΔG + + at low temp: +, at high temp: - + - at all temp: + - + at all temp: - - - at low temp: -, at hight temp: + Hopefully you can visualize this a bit better!

SelenaDahabreh1D

When you have a negative ΔS, then the second part of the Gibbs free energy equation will automatically become positive because the minus sign and the negative ΔS become positive. Let me draw it out to help you visualize it better: ΔG = ΔH - TΔS (This is the standard equation for Gibbs free energy). ...

SelenaDahabreh1D

During lecture, I think Dr. Lavelle was trying to portray that when entropy is at it's maximum when the system is at equilibrium.

SelenaDahabreh1D

Most of the textbook problems I've encountered have specified whether it will be constant pressure or volume, so I assume (and hope!) the same will be for the midterm.

SelenaDahabreh1D

ΔG° is called 'delta G naught' and it is referring to change in free energy at standard conditions, such as 1 atm or 25 C or 298 K.

SelenaDahabreh1D

The questions asks which substance has the higher molar entropy in multiple parts and part (a) states CO2(g) at 25 C and 1 bar or CO2(g) at 25 C and 3 bar. The answer says CO2(G) at 1 bar because disorder increases with volume. So, does that mean that the greater the pressure, the smaller the volume?

SelenaDahabreh1D

When calculating work for a system that is being compressed, is the final value always going to be positive? Comparably, when calculating work for a system that is being expanded, is the final value always going to be negative?

SelenaDahabreh1D

Tikva Cohen 1K wrote:wait so even if we want to review our midterm we can go to any TA?

Yes, I believe so. In Chem 14A, I think we were also able to go to any TAs office hours to review our midterm.

SelenaDahabreh1D

Try using the Pomodoro Technique! It is hard for me to sit down and start studying for an exam, but once I started using the Pomodoro Technique I found myself getting more motivated to study. I use this website to keep track of my timing: https://pomofocus.io/

Hope this helps!

SelenaDahabreh1D

Dr. Lavelle sent out an email last night saying that all grades would be updated sometime today. He said "late Wednesday" so I wouldn't expect the grades to be out until later on this evening.

SelenaDahabreh1D

This was my work for this problem: E = q + w q = E - w We are given that E = +6265 because there was an increase in internal energy. We are also know that w = -346 because work was done by the system. Thus: q = (+6265) - (-346) = +6611 Then, we will use the q=m * c * delta T We want c, so we will re...

SelenaDahabreh1D

You input the initial volume of 4.35 L into the PV=nRT equation.

SelenaDahabreh1D

I think we use the standard enthalpies of formation to determine the standard reaction enthalpy. So, essentially, they are complementary. You'd need to standard enthalpies of formation to calculate the standard reaction enthalpy.

SelenaDahabreh1D

I know that bond enthalpies are the least accurate. But I'm not too sure which one is the most accurate.

SelenaDahabreh1D

Can someone specify what we need to know about these two objectives on Outline 1 and 2 for Midterm 1? - Biological examples. For example: ATP hydrolysis; osmotic pressure (on Outline 1) - Calculate the pH in these industrial, environmental, and biological examples: Carbon dioxide reacts with water t...

SelenaDahabreh1D

Can someone explain how to go about solving part (a) for 4.31? Thank you!

SelenaDahabreh1D

Are we expected to know the equations for calculating reaction enthalpies, as in exercise 4D.15?

SelenaDahabreh1D

If K>1, does that mean that the products are more stable and if K<1 does that mean that the reactants are more stable?
And, the larger the K, the more soluble it is?

SelenaDahabreh1D

I just wanted to double check my understanding of the concentrations of strong acids. So, since strong acids fully dissociate, the initial equilibrium concentration would be the same for the acid and the products, correct? For example, let's say that the initial concentration for HCl is 0.01M for th...

SelenaDahabreh1D

Will we be joining the Zoom proctoring link from our cell phones, as we did in 14A?

SelenaDahabreh1D

I am a bit confused as to how AlCl3 becomes Al(H2O) 3+. Could someone explain this? Thank you!

SelenaDahabreh1D

What makes Cl2 thermodynamically more stable than F2? The explanation in the solutions manual is a bit unclear.

SelenaDahabreh1D

I had a bit of trouble working out 4D.15. I tried looking at the solutions manual but I was confused as to where the balanced equations come from? Are we expected to memorize those? I would appreciate it if someone could walk me through solving this.

SelenaDahabreh1D

I found this website particularly helpful at explaining Hess's law in great detail: https://chem.libretexts.org/Bookshelves ... _Chemistry)/Thermodynamics/Thermodynamic_Cycles/Hesss_Law

SelenaDahabreh1D

Attend as many UA sessions as you can. Do the homework problems listed in the syllabus. Review sapling homework problems. Read the textbook! Also, chemistry community is a great resource, so just by exploring the different questions you can have questions answered that you didn't even know you had. ...

SelenaDahabreh1D

I also had a difficult time figuring this out. But it helps to look at what the problem is sharing. When the problem gives the concentration of the initial reactant only, you use -x for the second row of the reactants because reactants are being used up to make the products in the reaction. When giv...

SelenaDahabreh1D

pKa = -log[Ka] and vice versa Ka = 10 ^ (-pKa). Same thing goes for pKb.

SelenaDahabreh1D

Strong acids and bases deprotonate completely, but weak acids and bases do not. Thus, we must use the ICE table method to determine the concentration of each compound in the chemical equation, and then we can determine the pH and pOH using the -log[] equation.

SelenaDahabreh1D

Sorry I couldn't find the 'Acids and Bases' section on the board index, so I'm posting this here! For 6D.5 part (a), the solution manual says that the Kb value is 1.8*10^-5. Can someone help me get to this value?

SelenaDahabreh1D

Kc is used when determining the molar concentrations, whereas Kp is used when determining the partial pressures. Kp is only applicable to gases, though.

SelenaDahabreh1D

I find ICE boxes to be the best way to determine concentrations, regardless of the strength of the acids. And it is always reliable, so that is a plus!

SelenaDahabreh1D

I think I actually may have found your mistake, as well as mine. After watching today's lecture, I realized that the denominator for the percentage ionization equation is supposed to be the initial concentration of the acid. Once I acknowledged this, I was able to get the correct answer.

SelenaDahabreh1D

I was wondering the same thing! I am assuming that Dr. Lavelle may include some thermochemistry on midterm 1 because we start that next week, but that is just a guess.

SelenaDahabreh1D

I had trouble with this problem too! I found it helpful to write out the equation for the deprotonation of an acid. HA -> A- + H+. From this step, I used an ICE table to determine the x-value, and thus the concentrations of each element. From then, I plugged those values into the equation for percen...

SelenaDahabreh1D

On that note, does anyone know if we will join a Zoom with our TA during the exam time for the proctoring session?

SelenaDahabreh1D

How do we know whether the change in the ICE tables are +x or -x? I have seen examples and homework problems where it might be +x but I have also seen examples where it might be -x. I am referring to the reactants in the ICE table, by the way.

SelenaDahabreh1D

I kind of like to draw it out and physically visualize a seesaw. When a stronger acid is present, then that means that the acid's conjugate base will be weaker. Vice versa for a stronger base. When a stronger base is present, then that means that the base's conjugate acid will be weaker.

SelenaDahabreh1D

I would re-do your ICE table because when I did it I got x=0.05429. When filling out your ICE table, be sure that for SO3 the change in equilibrium is -2x, and for SO2 it is +2x and for O2 it is +x.

SelenaDahabreh1D

Yes, because equilibrium favors the most stable aspect of the reaction I believe it would favor resonance because resonance also favors the more stable drawing.

SelenaDahabreh1D

The answer to self-test 5G.1A includes water into the equilibrium constant. My TA went over this, but I just wanted to ensure that I fully understand. Water is included into the equilibrium constant because water is in its gaseous phase. I would appreciate it if someone could confirm this.

SelenaDahabreh1D

For anyone trying to get into Michael's UA Workshop, do you know the passcode? When I try to join the Zoom link it asks me to input a Meeting Passcode.

SelenaDahabreh1D

I recommend attending as many as you can! They were super helpful for me last quarter, especially since I was exposed to many different practice problems.

SelenaDahabreh1D

You should be able to choose a free trial on Sapling. I was able to use that option as well.

SelenaDahabreh1D

are we supposed to know how to do problems like J17a (in the textbook) on the final? I am very confused about how this would be solved :/ In each of the following salts, either the cation or the anion is a weak acid or a weak base in water. Write the chemical equation for the proton transfer reacti...

SelenaDahabreh1D

I believe the pi bond composition would just be (C2p, O2p) because p-orbitals are the ones able to take part in pi bonds.

SelenaDahabreh1D

I think if you memorize the trends on the periodic table, then you would be able to decipher which ones are amphoteric compounds.

SelenaDahabreh1D

I think NaCl has a higher boiling point because there is a bigger difference in electronegativity, making the NaCl molecule more ionic than the LiCl molecule. Thus, resulting it NaCl having a higher boiling point.

SelenaDahabreh1D

If you look on Dr. Lavelle's website, there is a file titled "Solution Manual Errors 7th Edition," and there is an error in which one of these chemical reactions is written. So if you were having trouble balancing it, I think this may have contributed to that struggle. Here is the error: i...

SelenaDahabreh1D

This means that strong acids fully deprotonate (meaning they give away a proton) and strong bases protonate (meaning they accept a proton).

SelenaDahabreh1D

I think it is because strong acids and bases fully dissociate in aqueous solutions. So, these strong acids and bases will not be accounted for in equilibrium.

SelenaDahabreh1D

Take a breather. If you are anxious with regards to the final (as I am sure most of us are), I would recommend taking a few moments to write down what you do know and what you don't know. I personally like to take the time to go through each learning objective on all of the outlines and make note of...

SelenaDahabreh1D

I think some questions will come directly from the textbook, but I assume that most of the questions on the final exam will simply be derived from textbook problems.

SelenaDahabreh1D

Darlene Lien 1B wrote:Hi, I think you're supposed to look at Table 6C.2 to get the kB values!

Ahh, okay! Thanks so much!! Do you, by any chance, know if those values will be provided to us on the final exam if we encounter a question similar to this one?

SelenaDahabreh1D

For 6C.17, the question asks us to identify which is the stronger base: BrO- (hypobromite ion) or C17H19O3N (morphine). When I consulted the answer key, it came about answering this question by calculating the pKb values, but the question doesn't offer the Kb values. Are we expected to know the Kb v...

SelenaDahabreh1D

The methyl group (-CH3) in acetic acid inductively donates electron density to the COOH. This makes the O-H bond less likely to break. Formic acid does not have an electron donating group, so its O-H bond is slightly more acidic. So would it be a good rule of thumb that when a methly group (-CH3) i...

SelenaDahabreh1D

Acetic acid is CH3COOH, and formic acid is HCOOH. Comparing these two acids, formic acid would be the stronger acid because it can more easily lose its Hydrogen (H+) to a base. This is because in acetic acid, the CH3 in acetic acid is an electron-donating group, meaning that CH3 inductively donates ...

SelenaDahabreh1D

On almost every UA sheet from Week 9, there was a question about cisplatin. I think Dr. Lavelle spent a significant amount of time explaining cisplatin (and transplatin), so I would expect it to show up on the final in one way or another. On almost every UA sheet from Week 9, there was a question a...

SelenaDahabreh1D

I heard that some of the questions will come from the final, but I believe most (if not, all) will be derived from the textbook problems. I would recommend working through every single textbook problem and ensuring that you understand how to go about answering it, and I think you will be set for the...

SelenaDahabreh1D

I think it would be helpful to know these biological applications:
Cr - assist insulin in control of blood sugar
Fe - hemoglobin, myoglobin, electron transfer in the oxidation of carbohydrates, proteins, and fats (respiratory chain)
Co - vitamin b12
Mn, Ni, Cu, Zn - enzymatic functions

SelenaDahabreh1D

Joshua Eidam 3D wrote:Does anyone know what the format of the test is going to be like as well as how long the test is going to be?

It is going to follow the same format of the previous midterms. It will be 30 multiple choice questions, and it will be 1 hour and 30 minutes (plus 5 extra minutes).

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