CHEMISTRY COMMUNITY

Ariel Fern 2B

How exactly are equilibrium and kinetics connected, and why do we do this? How does a higher equilibrium constant relate to a rate constant?

Ariel Fern 2B

Yes, essentially, a catalyst will be consumed as a reactant but reproduced again as a product in the final step. Thus, it cancels out and does not show up in the overall reaction. Just look at the products and reactants between steps; if a substance is consumed but reappears, then it is a catalyst! ...

Ariel Fern 2B

What exactly is an elementary reaction, and what makes it different from other chemical reactions? Thank you so much!

Ariel Fern 2B

When is the stoichiometric coefficient of a reactant also the order of that reactant? Is that only for elementary reactions? Why is this so? Thanks for any help!

Ariel Fern 2B

Can someone give a brief rundown of the difference between unique, differential, and integral rate laws, and under what conditions each are helpful? I think I'm still trying to process all of the information and put it into categories in my head.

Ariel Fern 2B

What exactly is microscopic reversibility, and how is it related to intermediates and kinetics in general? Thanks for any help!

Ariel Fern 2B

Since it is a Galvanic cell, the E°Cell had to be positive; thus, based on the equation E°Cell = E°Cathode (Reduction) - E°Anode (Oxidation), the Reduction Half Rxn. was the half Rxn. with the more positive E°, and the Oxidation Half Rxn. was the one with the least (most negative) E°. Hope this helps!

Ariel Fern 2B

How do you conceptually determine the units of the rate constants of different orders of reactions, as asked in 7A.7? Is there any equation that you guys use to base this off of? Thanks for any help!

Ariel Fern 2B

I am honestly just as confused as you are; I had all the answers reversed as well because I thought the question was based on electrolysis rather than galvanic cells. I guess others have said that the higher reduction potentials still are more favorable in the solution, but like you said, I thought ...

Ariel Fern 2B

For 6N.7 B, why is the amount of moles (n) only 1 when the half reactions involving H₂ into 2H⁺ have 2 moles of electrons? Any help is appreciated!

Ariel Fern 2B

The answer in the book is a typo! In the solutions manual, they put that n = 2 moles even though it should only be 1 mole of electrons. By using 1 mole, you get the correct answer of K = 1 x 10² rather than K = 1 x 10⁴! Hope this helps!

Ariel Fern 2B

Is it fine to include the stoichiometric coefficients when writing the cell diagram? Also, when do we need to include H⁺ in the cell diagram? Any help is appreciated!

Ariel Fern 2B

Why doesn't Hg(l) need a solid inert electrode even though its half reaction to Hg₂²⁺ doesn't include a solid? This is seen in 6M.3 and 6M.5. Thanks for any help!

Ariel Fern 2B

In 6L.3 D, how did you guys approach writing the half reactions? How did you go from H⁺ or OH^- to the half reactions with H₂O and O₂? Thanks so much!

Ariel Fern 2B

When using an inert electrode, is there any difference between using graphite or platinum? Is there a case where one is better than the other? Thanks so much!

Ariel Fern 2B

Since the pK_a of acetic acid (4.75) is lower than the pH of the specified condition (6), the acetic acid will be able to dissociate into CH₃COO^-, which has a negative one charge. Hope this helps!!

Ariel Fern 2B

What is the best method to calculating oxidation numbers? What should I look for first? Any tips to calculate it faster? Thanks for any help!

Ariel Fern 2B

Solid platinum is used as a conductor when certain half reactions do not have a conducting solid within their species. For example, the reduction of Fe 3+ to Fe 2+ can occur with both species still being aqueous and dissolved in solution. In order for this to happen though, electrons must flow to th...

Ariel Fern 2B

Yes, a porous disk does the same function as the salt bridge: keep the current flowing by preventing charge imbalance. Furthermore, a porous disk does not have the anode and cathode in separate solutions; the ions are in the same solution and the ions are intermixed to prevent the charge imbalance. ...

Ariel Fern 2B

The salt bridge prevents charge buildup/imbalance on the sides of the galvanic cell. If electrons keep flowing to the positive source, the positive charge would soon decrease and become neutral, which would stop the electron flow. Thus, the salt bridge contains spectator ions that keep this from hap...

Ariel Fern 2B

What equation do you use to calculate ΔS for an irreversible expansion? I know that pressure is constant and that work = -PΔV for irreversible expansion, so how does that translate into calculating ΔS? Thanks so much!

Ariel Fern 2B

Yes, as stated above, the easiest way to check for oxidation/reduction is to look at the charges of the ions and see if there is a change in charge! If it has become more negative, then it is being reduced as it has gained electrons, but if it has become more positive, then it has been oxidized beca...

Ariel Fern 2B

According to Dr. Lavelle's email, grading of midterms will be finished Tuesday and then, handed back after class on Wednesday! Hope this helps, and best of luck!!

Ariel Fern 2B

When a question asks to calculate the entropy of a phase change at a certain temperature, why do we bring the temperature back down to the specified temperature? Does it stay in that phase when you bring the temperature back down? For example, for calculating the ΔS of vaporization of water at 85°C,...

Ariel Fern 2B

Hi! I knew previously that the standard enthalpy of formation of an element in its most stable form is zero, but does this carry to Gibbs Free Energy? I heard that H 2 had a Gibbs Free Energy of 0 kJ/mol, but doesn't it have an entropy that you would use in the ΔG = ΔH - TΔS equation? Thanks for the...

Ariel Fern 2B

An equation was brought up for an ideal gas that states:

U = 3/2 nRT

Where did this equation come from, and what should it be used for? Thanks so much!

Ariel Fern 2B

I would play it safe and always stick to entropy's usual units of Joules/Kelvin. Most of the time when you use the gas constant for entropy problems, you'll be using 8.314 J/K*mol, so it would be better to keep using Kelvin for entropy! I think it's only with Calorimetry and specific heat capacities...

Ariel Fern 2B

Can someone clarify what the Second and Third Law of Thermodynamics are, and how they are different? They both have to do with entropy, so I think I just need to see the different applications of both! Thanks!

Ariel Fern 2B

Can someone explain the reasoning as to why the heat capacity of an ideal gas at constant pressure (C_p) is 5/2 R, and why at constant volume (C_v) it is 3/2 R? I got these values from the equation sheet, but I'm unsure of the derivation of the values!

Ariel Fern 2B

I know that a bomb calorimeter reaction occurs at a constant volume, but what difference does it make in calculation problems? E.g. What exactly is the difference between Constant Pressure Calorimetry and Constant Volume Calorimetry in terms of the equations or methods to use? Thanks so much!

Ariel Fern 2B

How do we find the heat capacity of the Kr gas in 4C.3? I know it has to do with ideal gases and constant volume/pressure, but can someone help me understand this concept? Any help is appreciated!

Ariel Fern 2B

Yes, as the others have stated, you use the integral to account for the infinitesimally small changes in volume. In an irreversible expansion, the integral simplifies into just ΔV because the external pressure is constant and can be pulled out of the integral. However, in a reversible expansion, pre...

Ariel Fern 2B

Just to clarify: An irreversible expansion refers to constant external pressure, and we can use -PΔV to calculate the work done. However, a reversible expansion involves changes in pressure, and the integral must be taken, which leads to the following equation: w = -nRT*ln(V2/V1). Are these the righ...

Ariel Fern 2B

What is the difference between isothermic and reversible expansion, and which does more work? In 4A.5, it asks whether allowing the gas to expand reversibly or isothermally to the same volume causes more work to be done. Any help is appreciated!

Ariel Fern 2B

Hey Chloe! Yes, you'll want to use W = -PΔV to find the work, but finding ΔV is definitely the hardest part! To do this, you have to find the area of the pump and multiply it by the distance the pump is depressed. This will be πr 2 times d (distance), which will be (π)(1.5cm) 2 (20.cm). And then, yo...

Ariel Fern 2B

Delta U is the change in internal energy, but what exactly does that mean, and how is it different from enthalpy? Any help is appreciated!

Ariel Fern 2B

What order are you guys doing the Focus 4 problems? Should I start on Focus 4C or 4D for Thermochemistry? There are definitely stuff that I don't recognize yet, like delta u, so I'd love advice to see how you guys are approaching these problems!

Ariel Fern 2B

How would you predict whether one gaseous compound has a higher molar heat capacity? For example, question 4C.1 asks to compare the molar heat capacity of NO to NO₂. Any help would be appreciated! Thanks!

Ariel Fern 2B

As far as I know, a state property/function only depends on the current and initial states to calculate the value; it does not depend on the path it takes to get to the current state. An example outside of chemistry would be driving on a road trip. A state property/function would be just the shortes...

Ariel Fern 2B

Yes, like the others have said, you have to add 273.15 to the Celsius temperature to get Kelvin. This is really important for gas laws because the gas constant has units of Kelvin, so never forget to convert the temperature if it's in Celsius!

Ariel Fern 2B

To find the desired pH you just use the desired concentration 0.025 and you get pH of 1.6. To get the actual solution pH you multiply the molarity by the 0.200 L volume in order to find the desired moles and divide that by 0.250 L to get the new molarity/H3O+ concentration. From there you put that ...

Ariel Fern 2B

Hey Jina! If you're asking about acid/base reactions in the real world sense, then it would make sense that most reactions have reached equilibrium and are in a state where the products and reactants are being formed at a constant rate. But in terms of this class, we're probably going to come across...

Ariel Fern 2B

Also, if you look at the stoichiometric coefficients of the autoprotolysis reaction, both the H₃O⁺ and OH^- have a coefficient of one; thus, in this reaction, both H₃O⁺ and OH^- would have a change + "x" to get to the equilibrium concentration, making them equal.

Ariel Fern 2B

What volumes did you use to get the pH's in this problem? Wouldn't it be 0.200 L and 0.250 L due to the volumetric flasks? I'm not getting the correct pH's using those numbers though, so any help would be appreciated!

Ariel Fern 2B

Can someone give me a refresher of how to identify strong acids & bases and the conjugate ions to look out for in salts based on these? Thanks!

Ariel Fern 2B

Yes, as stated above, a large K a value signifies a strong acid. This is because the equilibrium lies toward the products, which includes the hydronium ion and the conjugate base. Ultimately, this means that the acid is more stable in the dissociated form of the hydronium ion and conjugate base rath...

Ariel Fern 2B

The book says that we can use the approximation technique of making +/- x negligible if the change in composition is less than about 5% of the initial composition. What exactly does this mean in terms of K values? I think I used to remember that if K < 10 -5 that we can use the approximation techniq...

Ariel Fern 2B

Focus 3D covers Graham's Law of Effusion, the Kinetic Model of Gases, and the Maxwell Distribution of Speeds. Do you think we will need to know these concepts in depth, and can anyone give a short summary of these, if possible? Thanks!

Ariel Fern 2B

Under what conditions are most gases considered to be "ideal?" For the most part, can we assume that we can use the ideal gas equation?

Ariel Fern 2B

I didn't cover gas laws that much in depth in high school, so is it fine if I just know the ideal gas law, PV = nRT? Boyle's Law, Charles's Law, Gay-Lussac's Law, and Avogadro's Principle are all put together into the ideal gas law, so do you think we still need to know each individual one, and does...

Ariel Fern 2B

Do you think that we have to know all the different units of pressure and be able to convert between them? I know that R, the gas constant changes depending on each unit (atm, bar, Torr, kPa, etc.), so would it be useful to be familiar with all of these units? Thanks!

Ariel Fern 2B

We use VSEPR of the central transition metal ion in order to determine the shape of the coordination compound, right? Does it make any difference if one of the ligands is polydentate or chelating?

Ariel Fern 2B

Lewis Acids are electron acceptors, but what is the best way to determine that from a Lewis Structure? I'm having a little trouble visualizing the concept of Lewis Acids in terms of where an electron pair can be added on an atom. For Lewis Bases, I can see where lone pairs could be donated, but I'm ...

Ariel Fern 2B

For this problem, it gives you a [H₃O+] of 1.50 mol/L. When I take the negative log of this, I got a negative pH of -0.176 instead of 0.176. Am I overlooking something with the positive/negative sign? Thanks for the help!

Ariel Fern 2B

If an anion is more stable, then it will want to get rid of any H+ in order to get to the more stable, lower energy state! Thus, stable anions tend to form strong acids, which is why resonance structures and electron delocalization are factors to consider when determining relative acidity. Hope this...

Ariel Fern 2B

How would you explain that HCLO₄ is stronger than H₃PO₄? Do the extra hydrogens in H₃PO₄ play a role in this being the case, or should I just mention Cl's higher electronegativity leads to more electron withdrawal? Thanks!

Ariel Fern 2B

Yes, I agree with the others: Bronsted deals with protons (H⁺), while Lewis deals with electrons. A tip is that Lewis Acids are e(L)ectron (A)cceptors, so just remember the LA, and you can figure out the rest of them! Hope this helps!

Ariel Fern 2B

Jorge Ramirez_4H wrote:How about if there is a cation?

I believe cations are written before the coordination compound if there is one. For example, potassium hexacyanidochromate (III) in 9C. 3a. Anions should be written after the cation.

Ariel Fern 2B

Can you explain how to find the hybridization? I've always struggled with it The way I find hybridization is just counting the amount of electron densities around the atom in question. For example, if there are two electron densities, then you need an s-orbital and a p-orbital, so sp. Four electron...

Ariel Fern 2B

I agree with the others; we haven't really focused on spectroscopy, and there weren't any specific homework problems regarding spectroscopy. I would say that anything on the homework could potentially be on the final, but I don't recall any assigned problems for spectroscopy.

Ariel Fern 2B

A ligand can be polydentate if it has two or more lone pairs that can form a coordinate covalent bond with the transition metal cation. The chloride ion can only be monodentate because it is only one atom and can only donate one electron pair to form a coordinate covalent bond with the cation. Typic...

Ariel Fern 2B

How would one know if a coordination compound has a chelate shape? What is a usual coordinate number for a chelate complex? Thanks!

Ariel Fern 2B

I'm having trouble visualizing what a coordination sphere is. Is it just the shape that the ligands take around the central metal atom? And the coordination sphere isn't a connection between the ligands, right? It's just something to visualize to help see the shape of the compound, right? Thanks!

Ariel Fern 2B

What does exactly polydentate mean? It has something to do with the amount of lone pairs a ligand shares, right? Can you also give examples of a monodentate, bidentate, and a tridentate? Thanks!

Ariel Fern 2B

What exactly is a coordinate covalent bond, and can someone give an example or two? Thanks!

Ariel Fern 2B

What is the Valence Bond (VB) Theory, and what is its relationship to hybridization?

Ariel Fern 2B

Yes they are! The book tends to refer to it as "angular" but Prof. Lavelle referred to it as "bent" in lecture, so they should be interchangeable.

Ariel Fern 2B

Yep! Like others have said, it is a special and specific kind of dipole-dipole intermolecular force; it's good to know that hydrogen bonding is the strongest form of dipole-dipole interaction!

Ariel Fern 2B

He also said there was one slide from Monday that we would cover, which is distinguishing sigma and pi bonds!

Ariel Fern 2B

I know it was mentioned in lecture briefly, but how and why do the bond angles change when an atom is replaced with a more electronegative one? For example, the bond angles in CCl₄ VS. CCl₃F₁. Thanks!

Ariel Fern 2B

In the VSEPR formula, is it fine to put a subscript 1 on the E if there is one lone pair on the central atom? The answers in the book just have E, but I like putting E₁ to let me know there is only one pair. For example, AX₃E₁. Thanks!

Ariel Fern 2B

Fluorine is more electronegative, but that only means that it will have a stronger hold on the electrons in its own bond between its central carbon atom than the other molecule will have. This question is asking about intermolecular forces: the attraction between molecules, not the atoms. The argum...

Ariel Fern 2B

Another trick that helps is checking whether the Lewis Structure is asymmetric or has a bent angle (like in an H 2 O molecule). Typically, looking at the Lewis Structure and seeing elements not in symmetry, especially with lone pairs, helps determine whether or not a molecule will be polar. Hope thi...

Ariel Fern 2B

Is there a difference between London Dispersion Forces (LDF's) and Induced Dipole - Induced Dipole, or are these terms interchangeable? I was much more familiar with using the term LDF's, so I was just want to ensure that I'm using it correctly. LDF's were explained to me as temporary charges on a m...

Ariel Fern 2B

Even though the signs are opposite, is it allowed to compare the strengths of ionic and covalent bonds based on their potential energy and dissociation energy, respectively? For example, if the covalent bond strength between HF is 543 kJ/mol, and the interaction potential energy between Na + and Cl ...

Ariel Fern 2B

Can someone clarify why dissociation energies are always positive in covalent bonds, but interaction potential energy is always negative? What do these signs signify? Thanks!

Ariel Fern 2B

When I think about the trends, I like to think about them conceptually! Going across a row (L to R), the electrons occupy the same shell, so there is less shielding from the nucleus. As a result, they have a greater pull to the nucleus and are much smaller in radius. When you go down a group, the e...

Ariel Fern 2B

Can anybody clarify the connection between polarizability of ions and their covalent character when bonded with another ion? Larger ions have higher polarizing power, right? I am just trying to visualize what it means by covalent character though; any thoughts would be helpful!

Ariel Fern 2B

For larger molecules, what is the best way to go about arranging the atoms? For example in 2B.11, the organic molecules are quite large in terms of number of atoms. I've used trial and error, but is there a better way to determine which order the atoms go in and whether to bond a hydrogen with an ox...

Ariel Fern 2B

I know that atoms in period 3 or higher can potentially accommodate more than 8 electrons due to the d-orbitals, but is there a sure way to know when the octet rule needs to be exceeded? For instance, in BrF 3 , Br exceeds 8 electrons, but in BrO - , Br follows the octet rule. Is there any way I can...

Ariel Fern 2B

Can someone give me a quick and easy way to think about trends? Like tips to remember the arrows of decreasing to increasing without having to look up values? Also, when elements are in a different period and group, how should I think about trends (for example, trying to determine whether chlorine, ...

Ariel Fern 2B

Does anybody have like a "step by step" list in how they draw Lewis Structures? So far I feel like I'm all of over the place in terms of arranging atoms and assigning lone pairs. I always count valence electrons first, but if anybody has tips on the order they do stuff afterwards, that wou...

Ariel Fern 2B

When a question asks to write the electron configuration, it is typically asking for just the subshells and the number of electrons within the subshell. I was wondering under what context would we also have to draw out the orbitals and arrows representing the electron spins: Would the question just ...

Ariel Fern 2B

Since the ionization energy is higher for non-metals, this means that it takes much more energy for an electron to remove an electron from an atom and allow it to become a positive cation. Rather than expend the energy releasing electrons to form a full outer valence shell, the atoms would rather el...

Ariel Fern 2B

Thank you for responding! That definitely makes sense; I wasn't thinking of Aufbau's Principle originally so now it is much more clear!

Ariel Fern 2B

Anybody have any tips to memorizing the Formal Charge equation? Or should I just keep practicing it to become "second nature?" I honestly keep having to reference my notes right now, so if anybody has tips for formal charge calculations or memorizing the equation, that would be great! Than...

Ariel Fern 2B

On question 1E.13, it asks for the electron configuration of Tungsten, which has 14 electrons in the 4f subshell. I just had some clarifications about this subshell: it fills up before the 5d subshell, right? And does the 4f subshell always have 14 electrons automatically? It seems like all of the t...

Ariel Fern 2B

I was definitely confused about this too because if you think of the numbers of protons and electrons per atom; it doesn't come out right since electrons are being shared. Like was said, you have to think of the molecule as a whole and consider the valence electrons and how much is needed to have fu...

Ariel Fern 2B

Hi everyone! I was just wondering if the + sign on the magnetic quantum number (m l ) is mandatory or if it is just good practice. The answers in the book have the + sign, so I was just wondering if it was necessary or if writing 2 was fine as opposed to +2. Thanks! I'll probably include the + sign ...

Ariel Fern 2B

Hi Anisha! The Balmer and Lyman Series refers to transitions back to the lower energy levels (n=1 & n=2, respectively). These electrons emit energy because they are going from a higher energy level to a lower one. Therefore, the electron in the H-atom could occupy a space in the n=6 energy level...

Ariel Fern 2B

Hi Matt! It's Ariel!

Which resource are you referring to? I believe the Sapling Learning and Ebook needs an Access Code that you need to pay for, not sure though. But all the tutoring sessions/workshops, office hours, and Chemistry Community are for sure free!

Ariel Fern 2B

The letters themselves represent a word. S represents sharp, p represents principal, f represents fundamental and d represents diffuse.Thi sis from the spectra of the alkali metals. That's interesting to learn! Honestly, I've been looking at the letters for so long but haven't really considered wha...

Ariel Fern 2B

Just wanted to share a clarification on something I used to mix up all the time. Shells refer to the principal quantum number (n); subshells refer to the angular momentum quantum number (l); and orbitals refer to the magnetic quantum number/subshell orientation (m l ). When something is referred to ...

Ariel Fern 2B

Thank you all! That makes more sense; I guess I was just thinking of only transitions from adjacent shells - it makes more sense to consider the transitions from the other shells as well. Thanks!

Ariel Fern 2B

FDeCastro_1B wrote:Yes! E(photon) should always be greater than or equal to the work function in order to eject an electron.

Thank you so much! This gives me peace of mind that I didn't copy down the notes wrong or misunderstand the lecture, haha!

Ariel Fern 2B

It's important to distinguish between equations that are relevant to light (EM radiation) and quantum movement of electrons. For light specifically, you should pay attention to: These two equations are applied to light in the theory that light is a wave: c = λv = 3*10^8 (speed of light = wavelength...

Ariel Fern 2B

Hi everyone! Can somebody help me understand what exactly these series are referring to? I know that generally it's about electrons emitting energy/photons when excited when moving between quantum levels, but I don't understand how all of these series relate to energy levels (n=1, 2, 3, 4...) as the...

Ariel Fern 2B

In the lecture notes, it states that: "(E = hv) - Work Function = (Ek = 1/2 mv^2), UNLESS... E(photon) > E(Energy Remove e-) then e- not emitted even for high intensity light If light had only wave properties, then increasing intensity should eject e-" This E(photon) is referring to a ligh...

Ariel Fern 2B

Hi Ellis! This is Ariel. Here's a general list from my notes: c = λ ν -- Used to calculate wavelength/frequency E(photon) = h ν -- Used to calculate energy per single photon -- Bohr Frequency Condition: v = ∆E/h; used to calculate frequency E(photon) = Work Function/Threshold Energy + EK EK =(1/2)mv...

Ariel Fern 2B

Hi Petrina and Ishaa!

I'm glad to hear that this has helped and is another viable option for you! If the problem gives the quantities in grams, then I convert grams into moles by dividing by molar mass, which then allows me to use the method! Hope that makes sense!

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