CHEMISTRY COMMUNITY

KNguyen_1I

i just want to take a moment to appreciate dr. lavelle who is doing his darndest to make sure the rest of this class goes smoothly and fairly. this covid-19 situation is super tough for everyone involved, faculty and student, and i just wanted to take a moment to appreciate how caring prof. lavelle ...

KNguyen_1I

The last two words, bimolecular is just the type of molecularity, and the second is just the kind of reaction it is. It's fast/slow in relation to the other mechanisms proposed and the slowest determines the rate of the overall reaction.

KNguyen_1I

Generally by how fast the individual reaction proceeds. The slow reaction creates a 'bottleneck' and so the previous reaction will have an equilibrium sign as the products oscillate between being reactants and products. They will tell you which mechanism is slow or fast on the test.

KNguyen_1I

Can someone delineate the process to show that the proposed mechanism works for the experimentally determined rate law? I vaguely recall something about intermediates and stuff, but I'm still very confused. Thanks!

KNguyen_1I

What do the integrated vs the differential rate laws represent conceptually and graphically? I read the textbook and the differential was like the rate at the given time or something?

KNguyen_1I

I cannot for the life of me understand what I'm doing wrong here.
For E naught of cell I got 0.79, and I keep getting negative pH values? Can someone walk me thru this?

KNguyen_1I

6N.1 Calculate the equilibrium constants for the following
reactions:
(b) In3+(aq) + U3+(aq) = In2+(aq) + U4+(aq)

I don't know how to do this problem because I can't find the reduction potentials for In 3 to 2+ and the same for Uranium?

KNguyen_1I

6M.3 Predict the standard potential of each of the following galvanic cells: (a) Pt(s)uCr31(aq),Cr21(aq)uuCu21(aq)uCu(s) (b) Ag(s)uAgI(s)uI 2(aq)uuCl2(aq)uAgCl(s)uAg(s) (c) Hg(l)uHg2Cl2(s)uCl2(aq)uuHg2 21(aq)uHg(l) (d) C(gr)uSn41(aq),Sn21(aq)uuPb41(aq),Pb21(aq)uPt(s) Gnarly formatting aside, how do ...

KNguyen_1I

6L.7 Write the half-reactions and devise a galvanic cell (write a cell diagram) to study each of the following reactions: (a) AgBr(s) = Ag+(aq) + Br-(aq), a solubility equilibrium (b) H+(aq) + OH-(aq) = H2O(l), the Brønsted neutralization reaction (c) Cd(s) + 2 Ni(OH)3(s) = Cd(OH)2(s) + 2 Ni(OH)2(s)...

KNguyen_1I

Can someone get into the dynamics and inner workings of the electrolytic cell? I understand that because the E cell is negative so we need an electric current to drive the reaction but otherwise does it functionally stay the same as a galvanic cell, in that the anode erodes and the cathode gets bigg...

KNguyen_1I

I'm trying to reinforce today's lecture materials, can someone explain again ion-selective electrodes, what they do, and what does the glass electrode bit have to do with it?

KNguyen_1I

You should always add H2O's because we need the balance the oxygens if needed. But otherwise say we want to balance an equation in alkalinic conditions. We need to balance it first acidically, and because H+ and OH- neutralize to H2O, we add the corresponding amounts of OH- to both sides of the equa...

KNguyen_1I

You do H+ for in acidic solutions, and OH- for basic/alkalinic conditions.

KNguyen_1I

If you visualize what is going on, there needs to be a physical rapport of some sorts to transfer electrons into the solution. As such, platinum is used often times as said metal to help complete the circuit.

KNguyen_1I

It's not so much between the reactants and products but rather in cell diagrams to denote what species exist in each cell (the anode/cathode). So like it has been said, the single lines denote the different phases they exist in. If they are the same (like aqueous) then they have a comma between them.

KNguyen_1I

4F.11 During the test of an internal combustion engine, 3.00 L of nitrogen gas at 18.5 8C was compressed suddenly (and irreversibly) to 0.500 L by driving in a piston. In the process, the temperature of the gas increased to 28.1 8C. Assume ideal behavior. What is the change in entropy of the gas? We...

KNguyen_1I

Why does -w = q at isothermal, reversible conditions? What does this conceptually imply?

KNguyen_1I

Didn't Prof Lavelle say that in class this was 3/2 nRT, and can someone further elaborate on this topic? I sorta missed this part.

KNguyen_1I

What is the conceptual and mathematical difference between Standard Reaction Enthalpies and Standard Enthalpy of Formation?

KNguyen_1I

For isothermal reversible reactions, do we always use the equation w=-nRT ln (v1/v2)?
And so I assume for irreversible equation we can use P delta V?

KNguyen_1I

Today in lecture we started covering the Boltzmann's equation, which involves calculating the number of microstates to calculate entropy. How do you calculate the microstates, even for a simple two state system like the one Dr. Lavelle showed in class? I don't understand the conceptual reasoning nor...

KNguyen_1I

A constant-volume calorimeter was calibrated by carrying out a reaction known to release 3.50 kJ of heat in 0.200 L of solution in the calorimeter (q 5 23.50 kJ), resulting in a temperature rise of 7.32 8C. In a subsequent experiment, 100.0 mL of 0.200 m HBr(aq) and 100.0 mL of 0.200 m KOH(aq) were ...

KNguyen_1I

Why don't we consider the mass of calorimeter?

KNguyen_1I

I'm guessing in most problems we consider water as the surroundings to the system, but in what circumstances do we consider only the calorimeter the surroundings, and when do we consider the water and calorimeter the surroundings?

KNguyen_1I

I know Dr. Lavelle many times relates qp being delta H, what does that mean and why can't qv be delta H either?

KNguyen_1I

How does the concept of equilibrium apply to these systems in thermodynamics? I think Dr. Lavelle mentioned something about fluctuating volume and work stuff and if the external pressure exerted on the piston system thingy is constant then we can use one particular equation to calculate the work don...

KNguyen_1I

In lecture Dr. Lavelle mentioned also something about the external pressure equaling the internal, also some whack equation with mad integrals and delta V's?

KNguyen_1I

Molar heat capacity I think is the heat needed to raise the temperature of one mole of a substance, while specific heat capacity is more of an intrinsic value to identities of substances- like, specific heat capacity is unique to the identity of the substance. So no matter how much you have of it, y...

KNguyen_1I

He said that to further clarify why the bond method is the least accurate as the only bonds we can accurate know are those from diatomic molecules, everything else merely an approximation. It doesn't really have much to do in the way of impeding our ability to math this stuff, it's just a qualitativ...

KNguyen_1I

It's used to calculate the net enthalpy (or energy/heat) change of the reaction. The reason why it's the sigma sign and says the sum because it takes into account not only phase changes (say one reactant goes from a gas to a liquid in the product, that is a phase change and accounts for enthalpy cha...

KNguyen_1I

As opposed to *specific* heat capacity, which is an intensive property; or, no matter how much you have, the amount of energy needed to heat stays the same. Whether you have 1 kg of aluminum or 1 mole, for example,the temperature needed to heat aluminum doesn't change as it's linked to the identity ...

KNguyen_1I

There are a lot of terms being thrown around, and I can't keep all this vocabulary straight. Can someone lay out all the terms we have in the enthalpy unit so far and what they refer to?

KNguyen_1I

6D.13 Rank the following solutions in order of increasing pH:
(a) 1.0 3 1025 m HCl(aq); (b) 0.20 m CH3NH3Cl(aq); (c) 0.20 m
CH3COOH(aq); (d) 0.20 m C6H5NH2(aq). Justify your ranking.

How do you do this?

KNguyen_1I

Find the initial concentration of the weak acid or base in each of the following aqueous solutions: (a) a solution of HClO with pH 4.60; (b) a solution of hydrazine, NH2NH2, with pH 10.20. Just to clarify, wouldn't I need Ka and Kb to solve these problems? And so if we get this question on a test, w...

KNguyen_1I

For strong acids and bases, 14 = pH + pOH but for weak acids and bases we relate it with the equation that 14 = pKa + pKb just for clarification right?

KNguyen_1I

Can someone explain again the quantitative reasoning Prof. Lavelle presented today in class? Why do we add the two expressions together? In real life application, how would we model this? Why do we relate everything to Kw? My understanding is that this is essentially a neutralization reaction betwee...

KNguyen_1I

5J.5 State whether reactants or products will be favored by an increase in the total pressure (resulting from compression) on each of the following equilibria. If there is no change, explain why that is so. (a) 2 O3(g) = 3 O2(g) (b) H2O(g) + C(s) = H2(g) + CO(g) (c) 4 NH3(g) + 5 O2(g) = 4 NO(g) + 6 ...

KNguyen_1I

Part c of the question asks for the equilibrium composition of the reaction system, what does that term mean? Equilibrium composition, and what am I supposed to calculate?

KNguyen_1I

5I.25 A reaction mixture is prepared by mixing 0.100 mol SO2, 0.200 mol NO2, 0.100 mol NO, and 0.150 mol SO3 in a reaction vessel of volume 5.00 L. The reaction SO2(g) + NO2(g) <=> NO(g) + SO3(g) is allowed to reach equilibrium at 460 C, when Kc = 85.0. What is the equilibrium concentration of each ...

KNguyen_1I

5I.23 A reaction mixture consisting of 2.00 mol CO and 3.00 mol H2 is placed in a reaction vessel of volume 10.0 L and heated to 1200. K. At equilibrium, 0.478 mol CH4 was present in the system. Determine the value of Kc for the reaction CO(g) 1 3 H2(g) ∆ CH4(g) 1 H2O(g) at 1200. K. I'm super confus...

KNguyen_1I

Madeline Phan 1J wrote:when writing the expression for k, how do you know when to use brackets or to write p in front?

I know that P is for partial pressure and brackets are used for concentration so Kc.

KNguyen_1I

What it says on the tin ^

KNguyen_1I

Given that Prof. Lavelle today in lecture covered how we can convert partial pressure to concentration and vice versa, would it be possible to then calculate the Kp for an aqueous solution and therefore also the Kc of a gaseous solution? And would the resulting answers still be valid methods of dete...

KNguyen_1I

What if the K is very small, then would calculating the LR even be possible? What is, in general, the relationship between LR and K? We've only ever done either LR or K problems, and I'm wondering if we'll ever encounter problems that include both the K and ask us to find LR. And, in general, I'm cu...

KNguyen_1I

"A sample of ozone, O3, amounting to 0.10 mol, is placed in a sealed container of volume 1.0 L and the reaction 2 O3(g) S 3 O2(g) is allowed to reach equilibrium. Then 0.50 mol O3 is placed in a second container of volume 1.0 L at the same temperature and allowed to reach equilibrium. Without d...

KNguyen_1I

In today's lecture review, why do we consider the size of the nucleus (the 1.7 x 10^-15 or something) as the delta x? I don't conceptually understand why we plug that value in for the uncertainty in position. Are we saying that within that value or less is where the electron could be located? And so...

KNguyen_1I

I know from lectures and the course outline we need to know about cisplatin, EDTA which is hexadentate, and porphyrin which is bidentate and involved in the heme complex, and what else?

KNguyen_1I

6A.15 Draw the Lewis structure or symbol of each reactant,
identify the Lewis acid and the Lewis base, and then draw the
Lewis structure of the product (a complex) for the following
Lewis acid–base reactions:
PF5 + F- ---->
Cl2 + SO2 ---->

How do you do this problem?

KNguyen_1I

Are all cations Lewis acids (because they accept the e- pair) and are all anions Lewis bases (because they donate the e- pair)?

KNguyen_1I

The reason why water is monodentate is because no atom can donate two lone pairs at once, therefore it is a monodentate?

KNguyen_1I

How do bonding angles affect whether a ligand is mono or polydentate?

KNguyen_1I

Can someone explain the conceptual relationship between pH and pKa and pOH and pKb? As well as explaining the reasoning behind each formula. I don't get why we plug Ka/Kb into the -log formula, what does the resulting value mean conceptually and why does it matter? How does it relate to pH which is ...

KNguyen_1I

pKa and pKb are the pH of each weak acid/base at their ideal buffer point, and therefore what we consider the baseline pH/pOH of an acid or base? Which is why a higher Ka/Kb yields a lower pKa or pKb, and therefore we consider it stronger than others with lower Ka's/Kb's and therefore higher pKa/pKb...

KNguyen_1I

A ligand is polydentate if has more than one lone pair of e-, because that means multiple bonding sites and therefore polydentate?

KNguyen_1I

9C.1 Name each of the following complex ions and identify the
oxidation number of the metal:
(a) [Fe(CN)6]4-
(b) [Co(NH3)6]3+
(c) [Co(CN)5(OH2)]2-
(d) [Co(NH3)5(SO4)]+

How do you do name these compounds? I've been trying but there's just so much going on I don't know where to begin.

KNguyen_1I

So regardless of the nature of the elements involved (metal, metalloid, nonmental) if two e-/one e- lone pair is exchanged in order to form the bond, we classify it as a coordinate covalent bond and therefore a compound with covalent properties?

KNguyen_1I

Does the central atom of a coordination compound *have* to be a transition metal or can they include alkali/alkali-earth metals as well?
Also, what are the formal stipulations for a compound to be considered a coordination compound and are the ligands always ionically bonded to a metal central atom?

KNguyen_1I

So no matter what there are always four orbitals in order to indicate the four possible bonds but the hybridization varies?
Also thank u btw your microsoft paint skills are legendary

KNguyen_1I

When determining the VSEPR model for a molecule with lone pairs (such as in the case of SF4 where there exists a lone pair, the reason why we chose to put the lone pair on the equatorial position axes than the other one is because it repels less? Therefore is most stable. So essentially, we place th...

KNguyen_1I

2.57 Acetonitrile, CH 3 CN, is used as a solvent in the pharmaceutical industry. Describe the structure of the CH 3 CN molecule in terms of hybrid orbitals, bond angles, and s - and p -bonds. The N atom is a terminal atom. How would you describe the hybridization of the triple bond? How would you dr...

KNguyen_1I

2.52 Molecules and ions, like atoms, can be isoelectronic. That is, they can have the same number of electrons. For example, CH4 and NH4 +1 re isoelectronic. Therefore, they have the same molecular shape. Identify a molecule or ion that is isoelectronic with each of the following species and verify ...

KNguyen_1I

So, extrapolating from today's lecture example, what would the hybridization of a triple bond look like? Say we have a compound like HC2H, where a triple bond exists between the two carbons.

KNguyen_1I

TL;DR version: VSEPR and Lewis structures, compare domains and kinds of bonds and from there determine your hybridizations. :) (Dr. Lavelle covered this in lecture today.)

KNguyen_1I

Another way to think about it is the fewer regions of electron density, the greater the bond angle because there are just simply less things to repel. And this checks out with what was already said with that as you have fewer hybridized orbitals, there is greater s-character in each orbital. So the ...

KNguyen_1I

So it doesn't necessarily mean that it goes 'up' to 2p. What this means is that okay, so we have three domains so therefore 3 hybridized orbitals. However, between the C atoms there exists a second bond right? And we have 1 s orbital and 3 p orbitals. So let's pair two of p orbitals with the s orbit...

KNguyen_1I

What is the conceptual relationship between VSEPR and hybridization and Lewis structures? From my understanding, we can derive the VSEPR model from Lewis structures, and from there we use both to examine how many domains each central atom has (giving you the number of sp-hybridized orbitals) and whe...

KNguyen_1I

Looking along the periodic table, does hybridization only occur in atoms with more than one subtype of orbital? I'm not sure how to phrase this, but is there ever a situation where the bond is not between hybridized orbitals but just strictly p or s orbitals? Or do we assume that when looking at Lew...

KNguyen_1I

Dipole moments are within mostly covalent compounds where the greater electronegative differences between the elements/atoms int the molecule create a slight polarity between the charges of the atoms and causing slightly ionic properties due to the electronegativity.

KNguyen_1I

Are there any other intramolecular forces besides polar and nonpolar bonds?

KNguyen_1I

Resonance structures arise from the idea of delocalized electrons. They're not bound to exactly one spot. So let's say we have a molecule that has a central atom and two other atoms bonded to it, and a double bond only exists between the central atom and one of the other atoms. However, because of 3...

KNguyen_1I

Let's say a molecule with dipoles and one that does not. Due to the electronegative pull exerted on the nonpolar molecule from the molecule with dipoles, the nonpolar molecule can temporarily develop dipoles in response to the electronegative pull. It's a bit like a magnet and a piece of metal. The ...

KNguyen_1I

So, there are two types of overlapping orbitals to my understanding: sigma and pi bonds. Sigma bonds are formed when the ends of each electron orbital comes together, while pi bonds are where they overlap side by side (think of the p-orbital lobes-- touching tips is a sigma and side by side is a pi ...

KNguyen_1I

Yes, we consider the single electron as a spot of electron density. However, the bond angles would be a little skewed because the single electron in the orbital demands less space and there are less e to e repulsion. So while the shape should stay the same, the bond angles would be different than st...

KNguyen_1I

When considering boiling point, what are the rankings of the intermolecular forces (from weakest to strongest) we should consider to determine highest boiling point?

KNguyen_1I

So due to things in nature wanting to be at a lower state of energy, when we calculate the net interaction potential energy, the greater the magnitude of the negative value the more favorable the interaction is right? For example, LDF has a Ep of -2 kJ/mole but for hydrogen bonding it's like around ...

KNguyen_1I

The larger the molecule means a greater amount of electrons to be polarized, and therefore a stronger induced dipole-dipole moment?

KNguyen_1I

So we consider things like ion-dipole, LDF, dipole-dipole, etc as intermolecular forces right? So what do we call polar and nonpolar bonding between the atoms within the molecule? Or rather, in general, what are the relationships between these things?

KNguyen_1I

The molecule in question is H2SeO4 and it's asking for the intermolecular forces present. That would only be dipole-dipole, due to the electronegativity of the elements, LDF because of its large amount of electrons present, and therefore repulsion due to it have net dipole movements? Is there anythi...

KNguyen_1I

Can you calculate the wavelength of a photon using De Broglie's wavelength, or do you have to use c= frequency x wavelength. Also, I notice in texts wavelengths found using De Broglie's equation often refer to the output as "De Broglie's wavelength" as opposed to just wavelength, is this j...

KNguyen_1I

When do you use the De Broglie equation when opposed to the Einstein equation, and what are the conceptual differences?

KNguyen_1I

So they are conceptually related in that they quantify the energy of electrons within a Hydrogen atom, but the Rhydberg calculates the change in energy as one electron jumps from one energy level to another, while Bohrs calculates the actual energy an electron possesses at nth shell?

KNguyen_1I

2B.20 Using only Lewis structures that obey the octet rule, draw
the Lewis structures and determine the formal charge on each
atom in (a) SO 2 ; (b) SO 3 ; (c) SO 3 -2 .

What does it mean by obey the octet rule? Does it mean that the central atom must have only an octet of valence electrons?

KNguyen_1I

2A.17 Predict the number of valence electrons present for each
of the following ions: (a) Mn 4+ ; (b) Rh 3+ ; (c) Co 3+ ; (d) P 3+ .

What would the answers be here and why?

KNguyen_1I

In lecture, Professor Lavelle said that as opposed to other values regarding periodic trends, electronegativity is a calculated value as opposed to an observed value. What does this mean?

KNguyen_1I

Why do s and d orbitals not have electron density?

KNguyen_1I

The problems often give us the data in units where we have to convert. I have trouble keeping track which equations require which units. What are the units for each equation?

KNguyen_1I

In part C, you use that 1/2mv^2 to find the kinetic energy of the electron ejected. But, to find the energy of the incoming photon, you must add that energy to the energy threshold. Why? Conceptually this implies that the energy of the incoming photon was enough to overcome the threshold energy and ...

KNguyen_1I

Use the Bohr frequency condition to explain the origin of the lines in the spectrum of an element.

Is it because we get quantized answers and therefore specific lines in the atomic spectroscopy?

KNguyen_1I

Can someone in layman's terms explain what this equation is, what it's used for, and its connection to Schrodingers wave function?

KNguyen_1I

The velocity of an electron that is emitted from a
metallic surface by a photon is 3.6 x 10^3 km/s.

(a) What is
the wavelength of the ejected electron?

How do you solve this problem? Which equations do you use?

KNguyen_1I

1A.5 Arrange the following types of photons of electromagnetic radiation in order of increasing energy: g -rays, visible light, ultraviolet radiation, microwaves, x-rays. So, just to clarify, energy is proportional to wavelength, so in order to find the answers to this problem I should arrange the t...

KNguyen_1I

So from today's lecture, from my understanding as opposed to normal waves, intensity of a photon merely indicates number of photons bombarding a given object but not necessarily correlative to its energy (which instead relies on frequency/wavelength) which is against the wave model, which usually in...

KNguyen_1I

M.9 Copper(II) nitrate reacts with sodium hydroxide to produce a precipitate of light blue copper(II) hydroxide. (a) Write the net ionic equation for the reaction. (b) Calculate the maximum mass of copper(II) hydroxide that can be formed when 2.00 g of sodium hydroxide is added to 80.0 mL of 0.500 m...

KNguyen_1I

Additionally, what does t as in the mass of 2.5 t mean?

KNguyen_1I

Here is the question: L.35 Sodium bromide, NaBr, which is used to produce AgBr for use in photographic fi lm, can itself be prepared as follows. Fe Br2 ¡ FeBr2 FeBr2 Br2 ¡ Fe3Br8 Fe3Br8 Na2CO3 ¡ NaBr CO2 Fe3O4 What mass of iron, in kilograms, is needed to produce 2.50 t of NaBr? Note that ...

KNguyen_1I

The problem: G.17 (a) Determine the mass of anhydrous copper(II) sulfate that must be used to prepare 250 mL of 0.20 m CuSO4(aq). (b) Determine the mass of CuSO45H2O that must be used to prepare 250 mL of 0.20 m CuSO4(aq). I was able to solve part a) just fine, but in part b) the fact that it's a hy...

KNguyen_1I

Find how many moles of reactant you have. Then, pick a product to convert said moles into to see how many moles of the product are produced by each reactant. Whichever produces the least product is the limiting reactant. You can also kind of cheese this process though by eyeballing molar ratios and ...

KNguyen_1I

They'd just be considered a mixture. Solutions technically are a solute dissolved in a solvent, and as you can't technically dissolve a gas within a gas gaseous mixtures are defined as gaseous mixtures.

KNguyen_1I

So the two equations basically piggy back of each other, so the product produced in the first reaction will go on to be a reactant in the second equation. And, if oxygen is in excess, and we know the already quantifiable amount of the phosphorus product turned reactant (I forgot chemical formula, so...

KNguyen_1I

So if you recall, most metals have more than just one oxidation state. However, most nonmetals have very specific and defined oxidation states we can always remember, like oxygen always being -2 and flourine being -1 for example (this can be corroborated with them having the highest electronegativty...

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