CHEMISTRY COMMUNITY

Hai-Lin Yeh 1J

But because it says it goes from neutral to second oxidation, does that not mean you have to switch the signs?

Hai-Lin Yeh 1J

The rate law of the reaction 2 NO(g) + 2 H2(g) -> N2(g) + 2 H2O(g) is Rate = k[NO]2[H2], and the mechanism that has been proposed is Step 1 NO + NO -> N2O2 Step 2 N2O2 + H2 -> N2O + H2O Step 3 N2O + H2 -> N2 + H2O (a) Which step in the mechanism is likely to be rate determining? Explain your answer....

Hai-Lin Yeh 1J

The hydrolysis of sucrose (C12H22O11) produces fructose and glucose: C12H22O11(aq) + H2O(l) -> C6H12O6(glucose, aq) + C6H12O6(fructose, aq). Two mechanisms are proposed for this reaction: (i) Step 1 C12H22O11 -> C6H12O6 + C6H10O5 (slow) Step 2 C6H10O5 + H2O -> C6H12O6 (fast) (ii) C12H22O11 + H2O -> ...

Hai-Lin Yeh 1J

Rank the following species in order of increasing reducing power going from their neutral to second oxidation state: Pb, Cd, Mn

What is the answer for this question? I got: Mn < Cd < Pb but I got it incorrect so what is the correct answer?

Hai-Lin Yeh 1J

Does anyone know the specific answer to the question regarding Pb, Cd, Mn? I got Mn < Cd < Pb, but I was marked wrong. Why is that?

Hai-Lin Yeh 1J

Can someone explain the effect of T, Ea, and A's effect on K from both a conceptual approach and a mathematical approach using the equation? Also, in the textbook, they state: "the higher the activation energy, the stronger is the temperature dependence of the rate constant". Can someone e...

Hai-Lin Yeh 1J

I know the pattern to organize species in reducing/oxidizing power, but when you do, does the wording or specification matter? For example, on test 2, one of the questions was: "rank the following species (Pb, Cd, Mn) in order of increasing reducing power (so more negative, the stronger) going ...

Hai-Lin Yeh 1J

Does it matter whether our answer is given in mmol or mol? Because for example, in the 6th edition, problem 17, the rate constant and rate answers are given in mmol whereas in problem 19, the rate constant and rate answers are given in mol. Will we get marked off if we give either on the final?

Hai-Lin Yeh 1J

What do you mean by it has lower energy requirements to oxidize?

Hai-Lin Yeh 1J

One stage in the extraction of gold from rocks involves dissolving the metal from the rock with a basic solution of sodium cyanide that has been thoroughly aerated. This stage results in the formation of soluble Au(CN)2- ions. The next stage is to reduce gold to the metal by the addition of zinc dus...

Hai-Lin Yeh 1J

A 1.0 m NiSO4(aq) solution was electrolyzed by using inert electrodes. Write (a) the cathode reaction; (b) the anode reaction. (c) With no overpotential or passivity at the electrodes, what is the minimum potential that must be supplied to the cell for the onset of electrolysis? I'm not sure how the...

Hai-Lin Yeh 1J

Do the units all need to be the same when calculating K for Nernst equation. For example, if one of the reactant was in mol.L-1 and another was atm or bar, do we need to convert one to the other? (See 14.37 as an example)

Hai-Lin Yeh 1J

Determine the potential of each of the following cells: (a) Pt(s) | H2(g, 1.0 bar) | HCl(aq, 0.075 m) || HCl(aq, 1.0 mol.L.-1) | H2(g, 1.0 bar) | Pt(s) In the solutions manual, they got 2H+ + 2e- -> H2 (g) as the equation for the cathode and H2 (g) -> 2H+ (aq) + 2e- as the anode. How did that happen...

Hai-Lin Yeh 1J

Determine the equilibrium constants for the following reactions: (a) Mn(s) + Ti2+ (aq) <-> Mn2+(aq) + Ti(s) In the solutions manual, how did they obtain the equation: at 25C lnK = nE/0.02568 V. Also, is there a way to just plug in numbers into the original formula, lnK = nFE/RT? I'm having trouble b...

Hai-Lin Yeh 1J

a) The standard Gibbs free energy of formation of Tl3+(aq) is +215 kJ.mol-1 at 25C. Calculate the standard potential of the Tl3+/Tl couple. (b) Will Tl+ disproportionate in aqueous solution Can someone explain how a redox couple works and for b) I found delta G in the end, but how does delta G for T...

Hai-Lin Yeh 1J

(a) Write balanced half-reactions for the redox reaction of an acidified solution of potassium permanganate and iron(II) chloride.

How would we start off this question? I'm not sure where they got Fe2+ -> Fe3+ from and MnO4- -> Mn2+

Hai-Lin Yeh 1J

Write the half-reactions and devise a galvanic cell (write a cell diagram) to study each of the following reactions: (b) H+ (aq) + OH-(aq) -> H2O(l), the Brønsted neutralization reaction Why can we not use the equations: 2 H+ + 2 e- -> H2 , H2 + 2 OH- -> 2 H2O + 2 e- to get the redox reaction? Also,...

Hai-Lin Yeh 1J

Balance each of the following skeletal equations by using oxidation and reduction half-reactions. All the reactions take place in basic solution. Identify the oxidizing agent and reducing agent in each reaction. (d) Reaction of elemental phosphorus to form phosphine, PH3, a poisonous gas with the od...

Hai-Lin Yeh 1J

Balance each of the following skeletal equations by using oxidation and reduction half-reactions. All the reactions take place in acidic solution. Identify the oxidizing agent and reducing agent in each reaction. (a) Reaction of thiosulfate ion with chlorine gas: Cl2 (g) + S2O3 2- (aq) -> Cl- (aq) +...

Hai-Lin Yeh 1J

The following redox reaction is used in acidic solution in the Breathalyzer test to determine the level of alcohol in the blood: H+ (aq) + Cr2O7 2- (aq) + C2H5OH (aq) -> Cr3+ (aq) + C2H4O (aq) + H2O (l) (a) Identify the elements undergoing changes in oxidation state and indicate the initial and fina...

Hai-Lin Yeh 1J

Note that the equation contains q(rev), where the subscript "rev" on q signified that the energy must be transferred reversibly and in a reversible reaction, temperature is constant. You can also use this equation to work out how to calculate the entropy of vaporization or the entropy of f...

Hai-Lin Yeh 1J

Why does a negative ∆G correlate with a spontaneous reaction? I thought that ∆G was the change in gibbs free energy so why is the reaction spontaneous when the change is negative?

Hai-Lin Yeh 1J

What is the difference between Gibbs Free Energy and entropy and why is gibbs free energy so important??

Hai-Lin Yeh 1J

Does the entire reaction have to contain all gases to be significant and vice versa? So if the reaction have gas as reactants and solid as products, is PdeltaV significant or nonsignificant?

Hai-Lin Yeh 1J

For the first law of thermodynamics in our notes, there is this part about constant volume and constant pressure. For constant pressure, can someone explain the significance of "for a reaction at constant pressure that involves changes in the number of moles of gas, then PdeltaV is significant ...

Hai-Lin Yeh 1J

Use exponential rules and bring Avogadro's number down in front of ln. Also, is this the wrong question? I don't think you need to use Avogadro's number in 9.75.

Hai-Lin Yeh 1J

You have to set it to the power of avogadro's number: 6^(6.023 x 10^23). If you put this into the calculator, it will give you an error, but you can manipulate it with exponent rules and move it down in front of ln.

Hai-Lin Yeh 1J

I believe that the units for entropy/entropy change are always in J.K-1 so the units should be in Kelvin. I haven't seen entropy in Celsius yet.

Hai-Lin Yeh 1J

Hydrochloric acid oxidizes zinc metal in a reaction that produces hydrogen gas and chloride ions. A piece of zinc metal of mass 8.5 g is dropped into an apparatus containing 800.0 mL of 0.500 m HCl(aq). If the initial temperature of the hydrochloric acid solution is 25 C, what is the final temperatu...

Hai-Lin Yeh 1J

Can you explain why you want to find the limiting reactant? What's different about this problem from others where you don't have to find the limiting reactant?

Hai-Lin Yeh 1J

In 1750 Joseph Black performed an experiment that eventually led to the discovery of enthalpies of fusion. He placed two 150.-g samples of water at 0.00 C (one ice and one liquid) in a room kept at a constant temperature of 5.00 C. He then observed how long it took for each sample to warm to its fin...

Hai-Lin Yeh 1J

But in the answer key, they only used 1.40 g. It never mentions 1.00 mol CO. So why do we disregard 1.00 mol?

Hai-Lin Yeh 1J

8;53 The reaction of 1.40 g of carbon monoxide with excess water vapor to produce carbon dioxide and hydrogen gases in a bomb calorimeter causes the temperature of the calorimeter assembly to rise from 22.113 C to 22.799 C. The calorimeter assembly is known to have a total heat capacity of 3.00 kJ·(...

Hai-Lin Yeh 1J

In the example he used in class, what does he mean by "2 particles both in one of two states, W = 4 (or 2^2)" and "1 particle in one of two states, W = 2 (or 2^1)". Was there 4 microstates or 2?

Hai-Lin Yeh 1J

In Monday's Lecture Notes, after talking about entropy, the slide moved onto deriving the equation for isothermal, reversible expansion. There were a bunch of equations after "need to know". Can someone explain the importance of those equations, especially ∆U = 3/2nR∆T = 0. Also, what does...

Hai-Lin Yeh 1J

Is degeneracy and microstates the same thing since degeneracy is W and microstates is also represented by W. Also, I know that W = (number of possible positions/orientations)^(number of particles), but how do you determine the base, which is the number of possible positions/orientations? Can someone...

Hai-Lin Yeh 1J

Is Pa.m^3 the only expanded "unit" that is equivalent to Joules? Are there other units we should know about??

Hai-Lin Yeh 1J

What is the common preference for the units for ΔHvap, ΔHfus, ΔHsub? Is it joules or kilojoules? Because in problem 8.37, the answer is in kilojoules, but would we be incorrect if we answered in joules?

Hai-Lin Yeh 1J

Can someone explain how the method of using bond enthalpies work in a calculation?

Hai-Lin Yeh 1J

Are we supposed to know the relationship between work and internal energy already? It doesn't seem like we have gone over work, internal energy, or the first law of thermodynamics much in lecture. For example, on 8.3 in the 6th edition, it asks to calculate the work done in the compression and inter...

Hai-Lin Yeh 1J

Determine the reaction enthalpy for the hydrogenation of ethyne to ethane, C2H2(g) + 2 H2(g) -> C2H6(g), from the following data: ΔHc(C2H2, g) = -1300. kJ·mol-1, ΔHc(C2H6, g) = -1560. kJ·mol-1, ΔHc(H2, g) = -286 kJ·mol-1. Can someone explain how to do this?

Hai-Lin Yeh 1J

The difference in pH can be explained by the type of bond and strength of that bond between the oxygen and hydrogen. Since double bonds are stronger than single bonds, these acids would be less likely to give up a hydrogen, which means there's a smaller concentration of hydronium ions, thus, a great...

Hai-Lin Yeh 1J

Le Chatelier's Principle states: chemical reactions adjust so as to minimize the effect of any changes. Adding or Removing Reagents: [CONCENTRATION] -Adding reactants: there is more reactants than products so in order to reach equilibrium again, the reaction will proceed towards the right and more p...

Hai-Lin Yeh 1J

a) Muscles work hard -> no oxygen -> produces lactic acid. If you think about what happens when the concentration of oxygen decreases, based on what we learned on the response to change of concentration, more oxygen will be produced to replace the oxygen that has been decreased. If more oxygen is pr...

Hai-Lin Yeh 1J

There is no error in the solutions manual. If you have calculated correctly, the Ka values for the acids should be: (7.6 x 10^-3) for H3PO4, (1.0 x 10^-2) for H3PO3, (3.5 x 10^-3) for H2SeO3, and (1.2 x 10^-2) for HSeO4-. As you have stated, the larger the Ka value, the stronger the acid. This also ...

Hai-Lin Yeh 1J

What if the acid was a strong acid (x is greater than 10^-7) instead of a weak acid? Would you still add it to 10^-7?

Hai-Lin Yeh 1J

Is this correct: The smaller the value of Ka, the weaker the ability of the acid to donate a proton, but the greater the value of pKa. This also means the acid is very weak. Similarly, the smaller the value of Kb, the weaker the ability of the base to accept a proton, but the greater value of pKb. T...

Hai-Lin Yeh 1J

To calculate the initial molarity of Ba(OH)2, [remember molarity= mol/volume (L)], convert 0.43g into mol and divide by 0.100 because that's the volume: 0.43g (1mol/171.344g)(1/100) = 0.025 M Ba(OH)2 Then, if you know that it's in an aqueous solution, Ba(OH)2 will just dissociate and become ions: Ba...

Hai-Lin Yeh 1J

I did do that, but the answer in the answer key is: (5/100)(10/100)^2/(18/100)^2. Can someone explain why this is?

Hai-Lin Yeh 1J

The following plot shows how the partial pressures of reactant and products vary with time for the decomposition of compound A into compounds B and C. All three compounds are gases. Use this plot to do the following: (a) Write a balanced chemical equation for the reaction. (b) Calculate the equilibr...

Hai-Lin Yeh 1J

If you have already calculated the concentration of H2 at equilibrium, which should be 0.053, then you know that the change in concentration of H2 should be 0.08. Note that how I got 0.08 was 60% (.60) of the gas reacted so .60 x 0.400 which equals .24 and to find concentration, divide by 3, getting...

Hai-Lin Yeh 1J

So for part B, the equation should be: F2(g) -> 2(F) BUT, the equilibrium constant (Kc) is 1.2 x 10^-4 Essentially, your ICE table for part B should be very similar to your ICE table for part A. Looks something like this: F2 F I 0.001 0 C -x +x E 0.001-x x Kc= [F]^2 /[F2] = (2X)^2/(0.001-X) = 4X^2/0...

Hai-Lin Yeh 1J

Thank you! But as a follow up question, in the 6th edition, number 11.13 part a, it asks to write the reaction quotient for: 2 BCl3(g) + 2 Hg(l) -> B2Cl4(s) + Hg2Cl2(s) and in the answer key, the answer is given as: 1/ P BCl3 ^2. There was no "partial pressure" or "concentration"...

Hai-Lin Yeh 1J

In an equilibrium constant expression (to find the equilibrium constant), it's [products]/ [reactants] (the concentration of products over the concentration of reactants), but if something is aqueous, do we use the brackets and if something is a gas, then we use partial pressure? For example, P4S10(...

Hai-Lin Yeh 1J

How did you get 1 in the numerator? I know that the molar concentration of a pure substance (solid or liquid) does not change in a reaction so they are not included, but where did you get the 1 from?

Hai-Lin Yeh 1J

So, does that mean if you wrote it like this:
Kc = [C2H4Cl2]^2 [H2O]^2 / [C2H4]^2 [O2] [HCl]^4
is this still correct because you wouldn't have to write P (partial pressure)?

Hai-Lin Yeh 1J

You are transferring the NH to CH3COOH to make CH3CONH2 and O to NH3 to make H2O together, not necessarily a H+ so it wouldn't count.

Hai-Lin Yeh 1J

Why is S2- < P3-? and why is Mg2+ < Li+?

Hai-Lin Yeh 1J

Oxalate is bidentate because there are 2 places that can bond to the metal, M. In oxalate, the formula is C2O4 and two of the oxygens will bind to the metal, which makes it bidentate, unlike monodentate, where only one atom will bond with the metal. In the pictures below, M- metal, and you can see t...

Hai-Lin Yeh 1J

Order these anions in order from least to most polarizable: Br-, S2-, O2-, P3-

Order these cations in order from least to most polarizing power: Li+, Mg2+, Na+, Be2+

Hai-Lin Yeh 1J

For Question J.7. b, I got the answer:
HNO2(aq) + ZnOH (aq) -> H2O (l) +ZnNO2, but it does not match the answer in the solutions manual. Can someone explain why this is wrong?

Hai-Lin Yeh 1J

No, induced-induced dipole is between 2 nonpolar molecules whereas dipole-dipole is between two polar molecules where the partial negative would be attracted with the partial positive charge of the other molecule. In an induced-induced dipole, since the molecule is non-polar, that means one molecule...

Hai-Lin Yeh 1J

When you name the transition metals, you would use the Roman numerals after the name of the transition metal. The Roman numeral matches the charge of the ion, so for example, if your ion was Fe 2+, then you would write it with the Roman numeral two in parenthesis after the name, like Iron (II).

Hai-Lin Yeh 1J

The angles for seesaw is <90 and <120 because for a normal trigonal bipyramidal, the bond angles are 90 and 120 so if you replaced one of the atoms with a lone pair, then it would repel the others, causing the bond angles to become smaller.

Hai-Lin Yeh 1J

What is the purpose of hybridization? I know VSEPR allows us to figure out the actual shape of a molecule accurately, but what does hybridization do and why is it important?

Hai-Lin Yeh 1J

Remember that the bond angles in a tetrahedral is not 90 degrees. The lewis structure is different from the vsepr geometry so, putting the lone pairs opposite each other would not make it linear. You can see, at the picture attached, that there really isn't any "opposite". Also, according ...

Hai-Lin Yeh 1J

The reason to the octet expansion involving d-orbitals is because if n=2, the second row of the periodic table, the electron configuration would only be s2p6, which involves no d-orbitals, therefore, aren't allowed for octet expansion. On the other hand, if n=3, you can recall that l would equal to ...

Hai-Lin Yeh 1J

Can someone explain the definition of a dipole or an electric dipole moment and does this have anything to do with a molecule being polar/non-polar?

Hai-Lin Yeh 1J

For 6 electron pairs:

Octahedral: AX6
Square pyramidal: AX5E
Square planar: AX4E2

Hai-Lin Yeh 1J

What is meant by "single region" is that there is this one area where this bond is happening, whether it be a single, double, or triple bond. Like for example, if you have a double bond, it doesn't mean you have 2 regions were a bond is happening. It's only one region where two atoms are b...

Hai-Lin Yeh 1J

The principal quantum number is n, which can be 1, 2, 3... (all integers from 1) and they represents the size of the orbital and energy. Magnetic is denoted as ml, which is basically -l....0...+l and it ml represents the orbital orientation. Note: l is called angular and can be integers starting fro...

Hai-Lin Yeh 1J

If there is uncertainty in momentum, then there is uncertainty in wavelength because wavelength equal h/(uncertainty of momentum [p]) results in uncertainty in wavelength = h/ (uncertainty in momentum). If the uncertainty in momentum increases, the uncertainty in its wavelength decreases. If uncerta...

Hai-Lin Yeh 1J

Since BeCl2 is linear and the central atom has 2 bonding pair, does that mean H2O is also linear and has 180 degree bond angle? If not, why?

Hai-Lin Yeh 1J

How I looked at these types of problems is I first wrote the electron configuration out. Then, I rearranged it according to the charge and number. For (b), Bi3+: if you look at the periodic table, the noble gas notation is [Xe]. From there, I just list it from left to right: so, first is 6s2. When y...

Hai-Lin Yeh 1J

3.33: Write the Lewis structure of (a)CCl4; (b)COCl2; (c) ONF; (d)NF3 For 3.33 c, Nitrogen is the central atom because it has the lowest electron affinity, but does it matter if Oxygen and Fluorine are placed on the left or right? For example, if Oxygen was on the left versus right, is one more corr...

Hai-Lin Yeh 1J

I think Ag is like an exception, where you remove one electron from the s orbital and it makes the d orbital full, so d10. Cu (copper) and Cr (chromium) follow the same pattern. So, Ag+ is originally [Kr] 5s24d9, but you remove one from 5s2 to make the 4d orbital full, so it becomes 5s1 4d10 and the...

Hai-Lin Yeh 1J

I believe it doesn't matter if the dots are left or right, but it DOES matter if you have 2 paired electron. If there is 2 paired electron, you need to make sure that they are shown in your diagram/drawing of your lewis dot structure. For example, Mg has 2 paired electrons. So you wouldn't put one a...

Hai-Lin Yeh 1J

Since wave function squared means the probability of finding an electron, does that mean the wave function of a nodal plane is 0? Since you won't find an electron in a nodal plane?

Hai-Lin Yeh 1J

In the atomic spectra module (video portion), at one point (at 26.04), Professor Lavelle introduces a formula that he derives, which involves the frequency and 2 energy levels. The formula is: V = R [(1/n1^2) - (1/n2^2)]. So, you know that the frequency (v) = 1.14 x 10^14 Hz. The energy level that i...

Hai-Lin Yeh 1J

The answer is E) both C and D because the work function (also called your threshold energy) indicates how much energy is needed to eject an electron. (Think of it like a threshold, you need to reach a certain level for something to occur). Therefore, if you have more than enough, that is E(photon) >...

Hai-Lin Yeh 1J

I believe professor Lavelle said that there will be a cover page full of constants, like the speed of light, etc. on the tests so they will be given to you. It should be the very front page and the constants should be listed, but they won't tell you WHICH constant to use for which problem so you sho...

Hai-Lin Yeh 1J

Wait, can someone elaborate what it means by a close range of wavelengths? These series are different because for the Balmer series, the energized electrons fall down to n=2, whereas the lyman series falls down to n=1 right? Also, in the answer key, it says "in each of these series, the princip...

Hai-Lin Yeh 1J

You know the energy which is 7.807 x 10^-19 J. If you want to find the wavelength, use the formula λ=(hc)/E to find the wavelength: λ=(6.626 x 10^-34 J.s^-1)(3.00 x 10^8 m.s^-1) / (7.807 x 10^-19 J) = 2.54 x 10^-7 m or 254 nm OR you can take the longer step, which is first finding out the frequency,...

Hai-Lin Yeh 1J

Ok, so the molarity of the sodium carbonate is 0.0797 M. For part a, they have given you 2.15 mmol of Na+. That means, you have the number of moles and you have the molarity of the compound. So, you would just use the molarity formula: M (molarity) = n(number of moles) / V. You can plug in the numbe...

Hai-Lin Yeh 1J

As you said, when something is combusted, it reacts with oxygen to produce CO2 and water, H2O, and you aren't sure what elements are in caffeine. But, if you write the chemical equation out: Caffeine (unknown formula) + O2 -> CO2 + H2O + N2. Looking at the chemical equation, the reactants are caffei...

Hai-Lin Yeh 1J

So, you know that in the second reaction, O2 is the limiting reactant. That means in the second reaction, the excess reactant (the one that there is too much of left) is going to P4O6 and they are asking us how much of that will be left. Remember that in reaction one (the first reaction), the produc...

Hai-Lin Yeh 1J

The chemical equation is: 4 C4H10 (g) + 26 O2 (g) -> 16 CO2 (g) + 20 H2O (g) You can find the net number of moles produced by looking at the stoichiometric coefficients. You take the sum of coefficient of product and minus sum of coefficient of reactants to get the net number of moles produced. 4+ 2...

Hai-Lin Yeh 1J

The reason he says that you multiply 1.56 (moles of CaC2) by 2 is because in the balanced chemical equation, it says that 1 mole of CaC2 reacts with 2 mole of H2O. 1 CaC2 (s) + 2 H2O (l) -> Ca(OH)2 (aq) + C2H2 (g) By looking at the stoichiometric coefficients in the chemical equation, we see that fo...

Hai-Lin Yeh 1J

Step 1: Check if the chemical equation is balanced. In this case, it isn't. Thus, the rewritten, correct chemical equation would be: C6H9Cl3 + 3AgNO3 -> 3 AgCl +C6H9(NO3)3. Then, it always helps if you write out what they give you, what they do not give you, and what you are trying to find. In this ...

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