CHEMISTRY COMMUNITY

Jamie Wang 3C

are you refering to reaction order?

Jamie Wang 3C

I've been doing the textbook problems that have you write the cell diagrams, and for some of them I'm not sure why they wrote it in that particular format. For example: 6L.5.c. The Equation was Cl2(g) + H2(g) --> HCl(aq) and the cell diagram was: Pt(s) | H2 (g) | H+ (aq) || Cl- (aq) | Cl2 (g) | Pt(...

Jamie Wang 3C

intermediates appear in the equations, but are cancelled out in the final equation, catalysts dont

Jamie Wang 3C

yep! exergonic refers to the fact that the gibbs free energy is being released. We can't say that it is exothermic it relies only on enthaply while gibbs free energy relies on both enthalpy and entropy

Jamie Wang 3C

For the reversible, one‑step reaction: A+A⥫⥬ B+C the rate constant for the forward reaction, k1, is 285 L⋅mol−1⋅min−1 and the rate constant for the reverse reaction, k1', is 377 L⋅mol−1⋅min−1 at a given temperature. The activation energy for the forward reaction is 44.6 kJ⋅mol−1, whereas the activa...

Jamie Wang 3C

Hello, Riya here Sorry for the inconvenience and thank you so much for a great quarter! Here is the answer key for the Week 10 worksheet. Please let your peers know. for number 6b, why do we take the -log(Kb) instead of -log(OH-) to find pOH? it was in the work in the answer sheet. please quote me!...

Jamie Wang 3C

for the question about reacting nitric oxide with bromine, it has 2 elementary reaction steps STEP 1: NO + Br2 --> NoBr2 (slow) STEP 2: NOBr2 + NO --> NOBr + NOBr (fast) it asks for the rate law of the overall reaction I understand that the reaction is determined by the slow step, therefore the fast...

Jamie Wang 3C

for the outline question "Know the definition of the electromotive force (emf, ℰ) and why it represents the maximum potential difference" I thought that the electromotive force is different from potential difference and only when no energy is passing through is maximum potential difference...

Jamie Wang 3C

for the question, Co²⁺ + 2e⁻ → CO Estandard = -.28V Au³⁺ + 3e⁻ → Au Estandard = 1.50V What is the equilibrium constant? I calculated Estandard = 1.78V, deltaGstandard = -1030.5 KJ For the equilibrium constant, E = Estandard - (0.0592/n)logK # since at equilibrium, E = 0, I set the equation to zero #...

Jamie Wang 3C

to add on, you also don't need to have the coefficients in the diagram

Jamie Wang 3C

can someone list the steps to calculate the order of each reaction?
I understand how it works for first order, but how do we generalize?

Jamie Wang 3C

given the fact that it is in standard conditions, we can assume that the pressure, temp are the same for both so they would cancel. R constant will cance N and v are left for both.

Jamie Wang 3C

which question is that? I think it might be because we put anode on left side and cathode on right.

Jamie Wang 3C

I know that electron flows from low concentration solution to higher concentration solution. Can someone explain why it does that?

Jamie Wang 3C

you would look for the element with the Ered that is higher than the one oxidized, but lower than the one that isn't

Jamie Wang 3C

I also had the same question because wouldn't the ratios be off?

Jamie Wang 3C

Hi!
you find the element that has a higher Estandard than the one that is oxidized, but lower than the one that isn't

for example, if Zn is oxidized but not Sn.
Zn E= -0.76, Sn E= -0.14
Co2+ E = -0.28
so Co2+ would be the reagent

Jamie Wang 3C

the oxidizing agent is the one that is reduced. Solve this by using half equations and see how electrons are transfered

Jamie Wang 3C

you will need to mulptiply HNO3 reaction by three in order to cancel the 3H out in the Au reaction

Jamie Wang 3C

How do we go about solving this?
"Which of the reagents would oxidize Zn to Zn2+ , but not Sn to Sn2+?"
Is there a faster way than finding the potential for each and seeing if it makes it spontaneous?

Jamie Wang 3C

How do we calculate for this? because doesn't q1 and q3 cancel each other out?

Jamie Wang 3C

For the equation C6H12O6 (s) + 6O2 (g) → 6CO2 (g) + 6H2O (l), it asks for Suppose a researcher finds that ∆Hrxn = -2756 kJ for the reaction at 200. C. Assuming all heat capacities are constant, calculate ∆Hrxn at the temperature of the human body, 37 C. Hint: Since enthalpy is a state function, the ...

Jamie Wang 3C

when do we use w = -(Pex)(deltaV) and w = -nRTln(V2/V1) ?
I know in a practice problem from Michael's section, we used w = -(Pex)(deltaV) for isobaric compression and w = -nRTln(V2/V1) for isothermal reversible reactions. Is it always this way?

Jamie Wang 3C

I think we would use the molar heat capacity under constant volume, but would it be diatomic or monotonic?

Jamie Wang 3C

How would we know that the C value is?

Jamie Wang 3C

Hi! Could anyone help me calculate K at 150 C? Calculate the equilibrium constant at 25 °C and at 150 °C for each of the following reactions, using data available in Appendix 2A: (a) NH 4 Cl (s ) ⇌ NH 3 (g ) + HCl (g ) (b) H 2 (g ) + D 2 O (l ) ⇌ D 2 (g ) + H 2 O (l ) I figured out how to calculate ...

Jamie Wang 3C

Hi! I was able to calculate the reversible expansion. But for irreversible, I used w = -PexdeltaV and got -2.23 J instead of the answer 226 J Calculate the work for each of the following processes beginning with a gas sample in a piston assembly with T = 305 K , P = 1.79 atm , and V = 4.29 L : (a) i...

Jamie Wang 3C

probably the way your calculator does PEMDAS. use () to avoid confusion for the calculator. I also write out each step and calculate that so the end is just simple addition

Jamie Wang 3C

I drink the same tea while studying and taking the test. It helps calm me down and jog my memory. I also use the same pencil

Jamie Wang 3C

basically showing change of one interms of another. The same equation is on our equation sheet but with delta instead of derivative d

Jamie Wang 3C

I think all of termochem that we weren't tested on last time and all of thermo dynamics

Jamie Wang 3C

I plan on taking it next quarter or else im never gonna be able to finish my req classes

Jamie Wang 3C

For the question which asks us to calculate K, why is delta G needed? Calculate the equilibrium constant, K , at 25.0°C for each of the reactions. Use the thermodynamic information provided in the table. The first step in the synthesis of trichloromethane (chloroform) from natural gas (methane). CH4...

Jamie Wang 3C

Hi! can anyone help me with the problem below? I converted the Wats to energy and got 136800 J. and also converted the initial and final masses to mols ''Three liquid samples of known masses are heated to their boiling points with the use of a heater rated at 475.0 W . Once the boiling points of eac...

Jamie Wang 3C

Hi! I watched the lecture twice but am still kind of confused in general about expansion. Could anyone summarize for me?

Jamie Wang 3C

I literally feel you. I think thermo is something people have to learn multiple times to completely get!

Jamie Wang 3C

Hi! I worked about 20 hrs a week throughout high school and honestly the biggest trick is to write everything down. I have a planner where I write down what I plan to do at each time. Or, when I spend a day spontaneously doing many different homework assignments or even take it easy and have fun, I ...

Jamie Wang 3C

imagine you have a water bottle that is sealed closed, you could put the water bottle in another tub of hot water to heat the water inside, but cannot change the volume of the water inside without taking off the lid

Jamie Wang 3C

im pretty sure delta u = zero when it is an isolated system

Jamie Wang 3C

I think so? since in the lecture he used the example of BF3 then BF2Cl and said that BF2Cl could have 3 possible lewis structures

Jamie Wang 3C

Hi! I think sapling gives out different numbers in the questions, here is mine [A 0.721 mol sample of SO2(g), initially at 298 K and 1.00 atm, is held at constant pressure while enough heat is applied to raise the temperature of the gas by 15.5 K. Calculate the amount of heat required to bring about...

Jamie Wang 3C

I wonder if Sapling gives out slightly different questions for each student. The one I got that was similar was [ A 0.617 mol sample of N2(g) initially at 298 K and 1.00 atm is held at constant volume while enough heat is applied to raise the temperature of the gas by 10.5 K. Assuming ideal gas beha...

Jamie Wang 3C

for the first one, I just talked about how the equation of ADP and free energy is used to creat ATP which is used by the cells. And because of that, we need to eat to give ADP molecules energy to form ATP. Osmotic pressure basically means that solvent basses between membranes until equilibrium is re...

Jamie Wang 3C

Yep the UA worksheets have been extremely helpful! They also go over questions really well.

Jamie Wang 3C

Does anyone know which bullet points in the thermochem outline we should focus on?

Jamie Wang 3C

for percentage ionization I know that it is [H3O+]/[HAinitial] *100%. However, I've been using [A-] instead and getting the same answer. do they both work?

Jamie Wang 3C

can someone explain to me why an increase in volume means that Q>K and a decrease in volume means Q<K? I know that when volume is increased the reaction shifts to the side with more moles of gas and when volume is decreased reaction shifts to less moles of gas, but how does that affect the Q value?

Jamie Wang 3C

K<Q reaction goes to reactants (K <-- Q )
K>Q reaction goes to products (K --> Q)

Jamie Wang 3C

Hi! Could someone please walk me through how they solved this problem? 6D.9 The percentage deprotonation of benzoic acid in a 0.110 m solution is 2.4%. What is the pH of the solution and the Ka of benzoic acid? deprotonation is [A-]/[initial HA] * 100% = % [x]/[0.110M] * 100% = 2.4% x = [A-] [H3O+]...

Jamie Wang 3C

Qp is the ratio that is similar to Kp when you don't know if the reaction is at equilibrium yet

Jamie Wang 3C

Ka2 is the constant of the second chemical equation where another proton is donated.

Jamie Wang 3C

^^ its important to remember that p X and X have an inverse relationship so when one is higher, the other must be lower. This applies to pKa, pKb, pH, etc.

Jamie Wang 3C

is the [H3O+] always the same as the conjugate base?

Jamie Wang 3C

also,
high Ka = increased acidity
high pka = decreased acidity
high Kb = increased basicity
high pkb = decreased basicity

Jamie Wang 3C

Yep! inverse is true. if you remember 14A acids and bases, we used the weak acid/base to determine if the solution when added to water would be acidic or basic

Jamie Wang 3C

Was there a typo in question 21 of chapter 6a?

it states that Kw =2.1*10^-14 at 37degrees C and asks for the H3O+ and OH- concentrations. I thought that each would be half the Kw value = 1.05*10^-7 however, the answer key says that it is 1.4*10^-7

Jamie Wang 3C

Hi, so from lecture, Dr. Lavelle talks about how we use the quadratic formula to solve for the x change value in ICE tables, and then proceeds to show how we omit the negative x value and use the positive one. What happens when we get two positive x values? Would we test both x values into the ICE ...

Jamie Wang 3C

for the reaction 6CO2(g) + 6H20(g) <=> C6H12O6(aq) + 6O2(g) why would there be little to no change if the system was compressed. I thought that when a system is compressed, it shifts in the direction with less moles of non solid or liquid compounds. Wouldn't it be 6:7? or does aqueous moles not count?

Jamie Wang 3C

For the question, we are given a graph of A decomposing into B and C based on partial pressure and time It first asks for the chemical equation. How would we be able to figure it out with just the graph? After looking at the answer key, I used the balanced equation but got a very different value fro...

Jamie Wang 3C

This reaction is taking place presumably at standard temperature and pressure, so the pressure is 1 atm and the temperature is 0 degrees Celsius. Assuming the gas has ideal behavior, we can use PV= nRT to find the moles of gas. The pressure is at 1 atm, and the problem provides the volume, You can ...

Jamie Wang 3C

reverse is 1/K and when multiplied by a constant(n), K^n

Jamie Wang 3C

I didn't attend the UA sessions last quarter, but did pretty well on midterms. During finals week, I went to all of the afternoon workshops, and OMG it changed my life. Even if you know the material, the UAs are REALLY good at making sure u have a wide range of knowledge.

Jamie Wang 3C

I think that if it is not strongly associated with either, there may be other test methods we can use.

Jamie Wang 3C

You should use the net ionic equation if the reaction involves ionic compounds that fully dissociate. You can read more about this on page 401 in your textbook. I took notes on that, but how would you know that the ionic compounds fully dissasociate? Would the problem tell us or is there specific m...

Jamie Wang 3C

The values are different because one is talking about the concentration (mol/L) of each component, while the other is talking about the pressure.

To convert use PV=nRT

P = (n/V)RT

n/V = concentration because it is amount over volume (ex: mols/liters)

Jamie Wang 3C

Hi! In one of the UA sessions, the UA told us that when calculating the equilibrium constant, we should use the NET IONIC equation, not the whole equation. However, in another UA session, they just used the original equation. Ex: Pb(NO3)2 (aq) + 2KCL (aq) <=> PbCl2 (s) + 2KNO3 (aq) UA1: Pb^2+ + 2NO3...

Jamie Wang 3C

Why does the pi bonds not use hybrids?

Jamie Wang 3C

Initially, I thought they were the same, but after looking on google, it turns out that multiplicity refers to possible orientations? Can someone explain?

Jamie Wang 3C

Hi!
I am kind of confused about the question in outline 6 that asks "explain why Salts of weak bases produce acidic solutions and salts of weak acids produce basic solutions"

it would be great if someone could explain it to me with examples!

Jamie Wang 3C

I just saw in his lecture that we can only have a calculator, periodic table, and our formula sheet. Does that mean we have to memorize all the ligands on the Naming Coordination Compound sheet? if so, does anyone have any memorization tricks?

Thanks!

Jamie Wang 3C

The question was: "Noting that the bond angle of an sp^3 hybridized atom is 109.5 degrees and that of an sp^2 hybridized atom is 102 degrees, do you expect the bond angle between two hybrid orbitals to increase or decrease as the s-character of the hybrids is increased? How would you solve thi...

Jamie Wang 3C

I am sort of confused about pH and pKa. I get that when pH>pKa, it means that the acid is charged, and will get deprotonated because it is more acidic than its environment. However in question 14, it shows a weak base ionizing to form conjugate acid (B+H20 <--> BH+ OH-) where pKa= 8.83 and pH = 6.92...

Jamie Wang 3C

The lone pairs react with the bonding pairs at an angle of 90 degrees. In the T-shape, there will be 4 lp/bp interactions, but in the case of a trigonal planar shape, when the lone pairs are placed at the top and bottom, the lone pairs will result in 6 lp/bp interactions, which causes more repulsio...

Jamie Wang 3C

In 6C #17 asks for the stronger base between BrO- and C17H19O3N. After solving, I got that BrO- is stronger. (through realizing that it is the conjugate base of a relatively weak acid). Because C17H19O3N is basic because of a lone pair on the N and doesn't have an OH, the type of molecule is automat...

Jamie Wang 3C

Stephen Min 2K wrote:I think we do need to memorize en since it is a common ligand that we will probably use going forward. Its also on the common ligand table.

Where can we find the common ligand table used for this class?

Jamie Wang 3C

Really excited to start new classes! Our first finals are kind of scaring me though.

Jamie Wang 3C

Why would AX3E2 be t shaped if lone pairs want to be as far away from each other as possible? Shouldn't the LP be axial and the shape be trigonal planar?

Jamie Wang 3C

In outline 4 it asks us to "Use shape and polar or non-polar properties, identify different intermolecular interactions/forces" does this just mean that shape and polar forces makes some intermolecular interactions possible? For example, dipole-dipole would be difficult to occur if electro...

Jamie Wang 3C

Just to clarify, This means that AsF3 would have a hybridization of sp3 and is in the hybrid orbital of 4sp3?

Jamie Wang 3C

The question asks for the Lewis Structure, VSEPR, shape, and bond angles of IO3-. I drew my structure with Iodine having one lone pair, connected to two double bonds to 2 Oxygens and a single bond to 1 Oxygen (a more stable structure). However, the back of the book shows all single bonds to oxygen (...

Jamie Wang 3C

do you think he'll be able to record zoom classes if he isn't able to prerecord the videos? There weren't any other chem spots that wouldn't create an overlap in my schedule.

Jamie Wang 3C

I think it probably has something to do with the types of bonds since pi bonds don't allow rotation, while sigmas do

Jamie Wang 3C

Lavelle has mentioned the importance of exercising our mind and body so I was interested to see what types of exercises everyone was up to! I usually just go for walks/runs with my dog. There are some really good exercise videos on youtube too! I usually do a full body one from Madfit or Pamela Reif.

Jamie Wang 3C

I swear I somehow did worse on this one since math is a little easier for me than conceptual. I guess we'll see :(

Jamie Wang 3C

The larger the anion is, the more easily it is polarized (polarizable). The smaller the cation is, the more polarizing power it has

Jamie Wang 3C

The larger the anion is, the more easily it is polarized (polarizable). The smaller the cation is, the more polarizing power it has

Jamie Wang 3C

London Dipoles are found in all intermolecular bonds. It is the only IMF when the Electronegativity of the two atoms are similar (ex: ch4)

Jamie Wang 3C

Q: The first ionization enthalpy values (in kJ/mol) of group 13 elements are - B (801), Al (577), Ga (579), In (558), Ti (589). Explain the deviation in the general trend. For B --> Al, I understand that ionization energy decreases going down a period due to an increase in electron shielding and rad...

Jamie Wang 3C

could someone explain to me why H2SeO4 has dipole dipole forces? What region is more negative if it is all balanced around the Se?

Jamie Wang 3C

For problem a) [Ar]3d7, I just looked at the table and saw that it is equivalent to Co, however I read somewhere else that we needed to add two electrons to it to see the true state. If I do that, it doesn't line up with the answer at the back of the book, can someone please tell me how to figure ou...

Jamie Wang 3C

I think it is true in nature because aren't resonance structures more stable than having single and double bonds. Since things aren't constantly exploding or having dramatic chemical reactions, I would assume it is because of that.

Jamie Wang 3C

Hydrogen bonds could form when the hydrogen in the compound is attached to N, O, or F. In the diagram, there are 2 Nitrogen atoms each with one lone pair, and 1 Oxygen atom with 2 pairs of lone electrons. Those four lone pairs can each form a hydrogen bond. In addition, for each of the Hydrogens tha...

Jamie Wang 3C

For each, I plugged it into the formal charge equation FC = valence electron - ( (shared electrons in bonds/2 electrons per bond) - number of unpaired electrons) For example for carbon, there are 4 valence electrons (according to the periodic table), 4 electrons that are shared in bonds (2 with H, 2...

Jamie Wang 3C

Does just remembering the number of orbitals for s,p,d, and f always work for the number of orbitals, or should we always double-check with the ml -1,0,1 etc?

Jamie Wang 3C

Hi! Is there a faster way to calculate the formal charge for our structures besides for what we did in class? I find myself taking a long time which is fine for now, but not sure how I'll be able to answer all the questions on the midterm.

Jamie Wang 3C

Hi! Is there a faster way to calculate the formal charge for our structures besides for what we did in class? I find myself taking a long time which is fine for now, but not sure how I'll be able to answer all the questions on the midterm.

Jamie Wang 3C

I don't think you can switch the C and N easily because of electron affinity and ionization energy. However, if you are looking for another structure, take a look at the other oxygen. What I did was I made the double bond bond the C with the OTHER oxygen atom. Hope that helps!

Jamie Wang 3C

We also add and and subtract so we know the total number of electrons to put in our Lewis Structures. Later, I think it also helps to see how reactive an element is.

Jamie Wang 3C

I believe its because Cl only needs to share one electron to get a full octet since it already has 7 valence electrons. On the other hand, oxygen has 6 valence electrons, so it wants to share two electrons to gain a full octet, and to do so you would have to form a double bond with carbon. It makes...

Jamie Wang 3C

Does anyone have any memorization tricks for them? I find myself memorizing them for the semester/year and then completely forgetting about it later.

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