CHEMISTRY COMMUNITY

Anthony_3C

I think you misunderstood the question. Each of these mechanisms are hypothetical sets of elementary reactions. One of the 3 could be the actual elementary reactions for the overall reaction: NO2(g) + CO(g) -> CO2(g) + NO(g). You are absolutely right that intermediates cannot be included in the over...

Anthony_3C

Actually, balancing the half equations is the easiest part because you don't even need to balance them! First of all, since the question tells you this is a cell reaction, identify the anode and cathode reaction. Next, because the skeletal equation has only one reactant, you know there's one reactan...

Anthony_3C

I would like a add that the factors that influence the reaction rate constant k are the following: (which I learned from my brilliant high school chemistry teacher) 1. Activity (of the reactants themselves) - for example, in the Alkali metal series, due to electronegativity differences, Fr>Cs>Rb>K>N...

Anthony_3C

I would suggest to use the equilibrium constant to understand better how to find a substitution for the intermediate molecule. However, at equilibrium, the concept that the forward and reverse rate are the same is correct. In this case, the K (equilibrium constant) for the first equation "ClO−(...

Anthony_3C

If you want a more detailed explanation, here is a great website:
https://chemistry.stackexchange.com/questions/5520/why-do-liquids-and-solids-have-constant-concentrations

Anthony_3C

Hello! I'm Anthony, a first year Neuroscience major. I really appreciate your story and I love people who are trying to help young aspiring people learn and grow.

Anthony_3C

According to the U of monoatomic and diatomic gas, which are 3/2RT and 5/2RT respectively, we know that Cv for them respectively is 3/2R and 5/2R because Cv is the derivative of U. What about Cp? Do we need to know Cp for MIdterm 2?

Anthony_3C

I think I know how to explain this. For (b), when the volume is constant ΔU = q because w = 0. This is why the correction puts 765J in place of ΔU. First problem solved. Next, since ΔH = ΔU + PΔV, if V is constant, then according to PV = nRT, pressure must have changed since temperature increased. H...

Anthony_3C

Ok, I can explain this annoying problem. So the reaction releases heat, which can be calculated from the Enthalpy of formation values from Appendix 2 in the textbook. This heat is given off by the reaction(the system) and absorbed by the solution(the surrouding), so although the calculated value for...

Anthony_3C

I found this really good answer on Quora. Please take look. So in thermodynamics, why do we only care about the external pressure when calculating the work done on a system? The key word here is the system ... it includes the piston itself as well. Work done by the system implies a transfer of energ...

Anthony_3C

such a great explanation!

Anthony_3C

It is useful to see whether a reaction is at equilibrium or not if we don't know K for the reaction.

Anthony_3C

I don't know for sure but I think both has a measured value, which can be found using the formulas: the Boltzmann equation for positional entropy and S = Cpln(t2/t1) for thermal entropy. IF you can measure them, you can tell which is larger.

Anthony_3C

In Dr. Lavelle's February 3rd lecture, he said that the Boltzmann equation is used to calculate positional entropy and ignores thermal entropy because it is more practical to do so.

Anthony_3C

multiple J/(mol*K) by the number of moles, which is 4.63

Anthony_3C

Basically, these types of questions require you finding out the total number of possible combinations, similar to the probabilities section in math. After all, entropy is a tool to explain the spontaneity of a change due to possibilities. Take this question as an example. We could reframe it as &quo...

Anthony_3C

Thank you so much Dr. Lavelle!

Anthony_3C

Why does a reversible process do maximum work? Since a reversible process undergoes when the internal and external pressures are equal, is the work done through slight fluctuations of the pressures? And is this why we use the integral to calculate the equation of work for a reversible process equals...

Anthony_3C

The question is as follows: Automobile airbags contain solid sodium azide, NaN3, that reacts to produce nitrogen gas when heated, thus inflating the bag. 2NaN3(s)⟶2Na(s)+3N2(g) Calculate the value of work, w, for the system if 24.9 g NaN3 reacts completely at 1.00 atm and 22 ∘ C. How am I supposed t...

Anthony_3C

Hi, I believe that entropy is very small because oxygen only has two particles, which means the number of combinations to achieve the state of oxygen is very small. We can tell from the equation with the degeneracy variable, and so all diatomic molecules have very small degeneracy.

Anthony_3C

To add on to Asheley's wonderful explanation, the heat of sublimation is equal to the heat of fusion + the heat of vaporization. So you could combine steps 2 and 4 in Ashley's description by calculating m*(heat of sublimation) = q. Then add this to the rest of the calculations, which will yield the ...

Anthony_3C

Hi,
I just saw in the textbook that there are some questions requiring Calculus, so I'm wondering if there's any class in UCLA that teaches using calculus to approach chemistry.

Anthony_3C

Hi, for your first question, we don't divide c by mass; we divide C by mass. c is the specific heat while C is the heat capacity. They are related by the equation C = c*m. Thus, c = C/m. So, if the question gives you the heat capacity, then divide it by the mass of the substance combusted. For the s...

Anthony_3C

Go check table 6C.1 and 6C.2. lol. It will give you the answer.

Anthony_3C

I believe that the resonance structure has lower energy, and is therefore more stable.

Anthony_3C

I'll just attach these texts and graphs from the textbook to show that: 1. Ka1 for Sulfuric acid is considered so large that it is basically a 100% deprotonation. 2. Accounting for Ka2 of sulfuric acid (and other rare cases) only shifts the pH slightly 3. when Ka2 is less than Ka1/1000 then it does ...

Anthony_3C

You need to calculate [H+] to solve this. First, observe that C6H5NH2 is basic in solution while all others are acidic solutions. Therefore, it has the highest pH. Next, do calculate [H+] for the rest. First, for HCl [H+] is 10^-5, which is the same as the initial concentration. For CH3NH3Cl, use th...

Anthony_3C

I suggest checking a few things before you do the work. 1. which side will the reaction shift towards? (so that the plus and minus signs are placed correctly) 2. the coefficients of each reactant and product (so that the ratio is clear and the power of each item is correct when writing the K) 3. whe...

Anthony_3C

B(aq)+H2O(l)↽⇀BH+(aq)+OH−(aq) It is hard to understand the relationship of pH and pKa if you don't break it down mathematically. Let me give you the magic equation: pH = pKa + log\frac{[A^{-}]}{[HA]} I highly encourage you to calculate this by your self, which requires some simple logarithmic calcul...

Anthony_3C

First, watch this video: [youtube]https://www.youtube.com/watch?v=50tT_jdkINw[/youtube] It helps a lot. But I'll still explain. First calculate the volume(mL) of NaOH needed, which is 50.51082959mols from this: 7.416\cdot10^{-3}\cdot\frac{100}{1.4682\cdot10^{-2}} . So you now have the mols of NaOH a...

Anthony_3C

It is simple. Contruct the ICE table and you get this: CO | 3H_{2} | CH_{4} | H_{2}O 2-x |3-3x | +x | +x 2-x |3-3x | 0.478 | x Since the change in concentration of CH4 is x, and its equilibrium concentration is 0.478, then x = 0.478. And don't forget to divide these numbers by 10L in the end!

Anthony_3C

So first calculate K from the equilibrium concentrations, which is indeed 25. Then, calculate x from your equation = 25. Finally, SUBTRACT 2X from 0.8. You did correctly so I think it may be that you did this final step wrong.

Anthony_3C

Table 5G.2 in the textbook has an error. For the reaction N2O4 ⇌ 2NO2 at 298 K, the Kc value is 6.1 x 10-3. 5.39 Since the reverse reaction is needed the inverse of 6.1 x 10-3 is 1.6 x 102. Which is the correct value used in the solutions manual for 5.39. The solutions manual is correct. This is the...

Anthony_3C

A concentration table would be 0.304-x | +x| +1/2x|
Since 1/2x = 0.13, x = 0.26, so K = $\frac{0.13*0.26}{(0.76-0.13)}$ , which is 0.0.14. Hope this helps!

Anthony_3C

This is really weird. The answers given are 0.0065M for N2O4 and 0.007M for NO2, but if you calculate K from this: 0.0065/(0.007)^2, then K = 132.653, which does not match Table 5G.2. Table 5G.2 gives 0.15 for the reverse reaction, so K should be 1/0.15 = 6.66666667. I can't explain this. However my...

Anthony_3C

You've made a good point. A reaction can actually have two K values: a forward one and reverse one, but scientists define Kp of a reaction written as A+B -> C as equal to [C]/[A][B]. So the Kp given by the problem is equal to [PCL5]/[PCl3][Cl2], which has nothing to do with what is going on in the r...

Anthony_3C

I got 3.909 too. I'm pretty sure it's correct. My calculation was $\frac{0.0478^2}{(0.2-0.0478)*(0.3-3*0.0478)^3}$ .

Anthony_3C

N2O4c -> 2NO2 is allowed to reach equilibrium in a chloroform solution at 25 ∘C . The equilibrium concentrations are 0.487 mol/L N2O4 and 2.34 mol/L NO2 . Calculate the equilibrium constant, Kc , for this reaction. The correct Kc is 11.24. I was stuck on the last question in this problem: Calculate ...

Anthony_3C

(a) HOK + CH_{3}COOH \rightarrow K(CH_{3}COO) (b) 3NH_{3} + H_{3}PO_{4} \rightarrow (NH_{4})_{3}PO_{4} (c) CaOH + 2HBrO_{2} \rightarrow Ca(BrO_{2})_{2} (d) 2NaOH + H_{2}S \rightarrow Na_{2}S So I've typed the equations. The general rule here i...

Anthony_3C

What the textbook is saying is that Ka1 for sulfuric acid is way larger than other polyprotic acids. In fact, sulfuric acid is classified as a strong acid if you remember the list: HCl, HBr, HI, HNO3, HClO3, HClO4, and H2SO4! Since Ka is a tool to measure the degree of deprotonation of weak acids an...

Anthony_3C

Screen Shot 2020-12-07 at 10.37.14 AM.png Hi, I'm pretty sure aqua is incorrect, as well as your own naming, because according to this chart in this website http://www.chemistry.wustl.edu/~edudev/LabTutorials/naming_coord_comp.html , OH as a ligand is called hydroxo while H2O is called aqua, so the...

Anthony_3C

This is the lewis structure from the internet https://www.chemistrylearner.com/wp-content/uploads/2011/10/Acrolein-Pictures.jpg Although the lone pairs are not shown, it is obvious that oxygen has two lone pairs and no other atoms has any. Let's work on the bonds first, though. For the bonds, lets g...

Anthony_3C

The answer for this problem is that the common shapes for coordination number 4 are tetrahedral and square planar but not seesaw. Why is this? Is this because seesaw is not a ring, which coordination compounds look like?

Anthony_3C

I believe that Dr. Lavelle just want us to know about acid rain and its causes, instead of reading the information in 6E.4, which is about composition and pH. However, I think we should be familiar with the major acids involved in acid rain.

Anthony_3C

In class Dr. Lavelle defined organometallic compounds as transition metal cations with organic ligands, which reminds me of the heme groups in hemoglobin of a RBC. However, the wikipedia says that it is an organometallic compound while another website claims that it's not because the ligands are &qu...

Anthony_3C

NiCl2 is an ionic compound. A coordination compound is defined as being surrounded by multiple ligands (large molecules), forming multiple coordination bonds, as shown in the picture below. Although NiCl2 is surrounded by Cl, Cl is not a molecule and it does not form coordination bonds with Ni. http...

Anthony_3C

Hi! The internuclear axis is defined as the straight line connecting the center of the two atoms in a bond. For your first question, the sigma bond does have electron density on both sides of the axis, but the density directly overlaps the axis, as seen in the image below. However, a pi bond is also...

Anthony_3C

Sorry but I don't know what you mean by electon rich, but according to Dr. Lavelle, a ligand is any molecule that interacts with a transition metal, which is usually a cation. So, ligands are usually electron pair donors; they form coordination bonds with the transition metal ion.

Anthony_3C

This problem is about the pattern of H2C(C)xCH2, which starts with H2CCH2 and continues with H2CCCH2 and so on. The pattern is that for even numbers of x, the H atoms are in the same plane, meaning that H2CCCH2, H2CCCCCH2, H2CCCCCCH2 have H atoms on the same plane. Why is this? Is this due to the pi...

Anthony_3C

I don't know what you mean by get closer because is inherently the connection of two atoms so of course they are close. But there is a repelling force between the nuclei of the two atoms, so although the bonding decreases the potential energy of the two atoms involved, allowing them to be stabler, t...

Anthony_3C

In molecules with a steric number of 5 and 6, why are the lone pair electrons placed with different patterns? For example, AX4E1 is a seesaw shape. AX3E2 is a t-shaped. The lone pair electrons are placed first in the center triangle. However for molecules of steric number 6, the lone pairs are place...

Anthony_3C

To further clarify Melody Haratian's points, I want to point out that vapor pressure is a definition for convenience of calculation and comparison. You could tell which substance has higher boiling point by its vapor pressure. The correct definition of vapor pressure is the pressure (N/m^2 = pascal(...

Anthony_3C

I think if it asks about the bond strengths then it is intramolecular forces. By the way, the ranking of intramolecular strengths is metallic bond > ionic bond > polar covalent bond > nonpolar covalent bond. Also, for ionic bonds, there are also stronger ionic bonds, which are less polarized. If the...

Anthony_3C

Thank you Edward! I love how you explained this. since we do not even know exactly where the electron is in even a single atom. Like mixing paint, mixing black and white will yield a color that is much darker than white but slightly brighter than black. So we would say black is a major contribution....

Anthony_3C

In textbook problem 2C.3, when trying to draw the Lewis structure of hydrogen phosphate ion, I can't help but notice that it also has several possible forms, but with the H attached to different oxygens. I googled and found an article with this picture bellow. It didn't explain much besides that &qu...

Anthony_3C

In some Sapling problems, we are asked to identify which resonance structure makes the most contribution to the actual structure. What does this really mean? Suppose a structure with more double bonds make the contribution, does this mean that empirical bond data would find a bond length closer to t...

Anthony_3C

Hello! To add on to previous points, molecules with one unpaired electron are called radicals and those with two unpaired electrons are called biradicals. A picture here for examples: https://upload.wikimedia.org/wikipedia/commons/thumb/d/de/Non-Kekule-Structures.svg/510px-Non-Kekule-Structures.svg....

Anthony_3C

To summarize and simplify, phosphate has one double bond and 3 single bonds and chlorate has two double bonds and 1 single bond. The difference is probably because chlorine is more electronegative than phosphorous. The hydrogen phosphate ion and chloric acid are just phosphate and chlorate with an e...

Anthony_3C

Hi~ For question c, if you look at the electronegativity chart, you'll see that the electronegativity of I is very close to C, but that of F is way larger than C. Thus CHF3 is a much more polar molecule and it would experience stronger dipole-dipole forces. So it has a higher melting point.

Anthony_3C

Can someone explain the vacuum permittivity in plain English? I've been confused by it since high school when we learned about the Coulomb force between charges.

Anthony_3C

This problem is testing your knowledge on intermolecular forces since the stronger this force, the higher the melting point of a molecule. A) The difference in electronegativity is larger for NaCl, meaning a stronger ionic bond, so NaCl has a higher melting point. B) Butanol (an alchohol) has hydrog...

Anthony_3C

In the Sapling Homework week 5&6 quesiton 5, the problem lists three resonance structures of HCNO. However, the bond angles of some bonds in each structure are different, according to VSEPR theory. For example, the carbon in one has no lone pair electrons, another has 1, and another has 2. So in...

Anthony_3C

Adding on to Claire_Latendresse_3J, both the formal charge and oxidation number are rules that are not accurate to describe the real property of bonds. They are simply convenient tools for chemists to calculate. The exact property of atoms or ions bonding with others are not whole numbers like +1 or...

Anthony_3C

Alex is completely correct. Adding on to his point, I want to say that for crystalline solids, Network solids have stronger bonds than Ionic solids, but normal covalent bonds are weaker than ionic bonds. What I'm talking about here is intramolecular forces , the forces acting inside a molecule, not ...

Anthony_3C

The ionic bond is stronger than the covalent bond because electric forces are strong, making ions harder to separate than the atoms sharing electrons in a covalent bond.

Anthony_3C

To clarify, the range only indicates the "possible values" of ml (orbitals) , which is based on the value of l. L indicates the subshells s, p, d, f etc., with l = 0 representing s, 1 representing p, and so on. It would be better to visualize this concept by looking at the periodic table. ...

Anthony_3C

1. n= 4 ℓ=2

This is in the 4d sub-shell, so there are 5 orbitals. Each orbital can only have 2 electrons. So that's a total of 5*2 = 10 electrons.

2. n= 6 ℓ=1 mℓ= -1

This is in the 6p orbtial. There are 3 orbitals and the ml means one of the two electrons in a orbital. So thats 3*1 = 3electrons.

Anthony_3C

I don't think the Uncertainty Principle can explain where the electrons are in different outer shells, when the electrons move up or down energy levels, when electrons are ionized, or when electrons are affected by the shielding effect. You could take a look at page 31 in the text where it explains ...

Anthony_3C

In the Schrodinger equation, I understand the left part (Hamiltonian), but I'm confused about what EΨ actually means. Is it just "one" symbol, so that EΨ means the total energy of an electron, or is it that E means the energy and Ψ just represents the wave function itself, so that EΨ equal...

Anthony_3C

In the Equation that Schrodinger found: $En = -\frac{hR}{n^2}$ , the Rydberg constant according to the text book is 3.29 X 10^15 Hz. However, in the hint section for a question on Sapling, it says R = 10 973 731.6 $m^{-1}$ . Which one should I use??

Anthony_3C

I had problems with this one too! So first you need to open the link to a table with the energy of fusion of solid H2O, which is in units of J/g. So multiply this value by 411grams and you get the total energy(J) needed. Then calculate the energy of one photon, which is h*\frac{3*10^8}{899*10^{-9}} ...

Anthony_3C

I'm confused about the units and the exact value of ∆P and ∆x. Since they are uncertainties i'm assuming the values of these two should be probabilities? In the textbook examples it doesn't really explain how to calculate clearly. Can someone explain?

Anthony_3C

Since in this case the equations E = hv and E = KE + Φ come from quantum physics, they concern only values of one electron, not a mole.

Anthony_3C

The number of orbitals in a subshell is determined by the orbital angular momentum quantum number l. The magnetic quantum number m, represents the number of orbitals, and m ranges from -l to +l. So in this case, l = 1, so m = -1, 0, or 1. Therefore there are three orbitals, and each orbital contains...

Anthony_3C

I understand the uncertainty equation but fail to know how to apply it for calculations. This is the question What is the minimum uncertainty in an electron's velocity (Δvmin) if the position is known within 15 Å. I know the unit means 10^-10 meters, but couldn't understand what the phrase "kno...

Anthony_3C

5 Taiwan

Anthony_3C

Hello Isabel, Ok. So first it gives you the wavelength, 194 nanometers, of the light. Therefore, the frequency of this light is \frac{3*10^8m/s}{194nm} , according to this equation: c = λν And according to a website: For the relationship to hold mathematically, if the speed of light is used in m/s, ...

Anthony_3C

Yes Please!

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