CHEMISTRY COMMUNITY

Lucy Wang 2J

Hi! My understanding is that electromotive force and cell potential are the same! Hope this helps!

Lucy Wang 2J

Hey, I think they function relatively the same. With a salt bridge, the reduction and oxidation reaction need to be in separate cells. However, a cell with a porous disk can contain both the oxidation and reduction reactions in the same cell, and the salts simply pass through the disk

Lucy Wang 2J

The more negative the standard reduction potential, the stronger the metal is as a reducing agent. So the standard reduction potential of Cu is greater, or more positive than that of Cr.

Lucy Wang 2J

2 H2O + Cl2 --> 2 HOCl + 2 H+ + 2e-
2 H2O + 2Cl2 + 2e- --> 2HOCl + 2H+ + 2Cl- + 2e-

so Cl2 is both the oxidizing and the reducing agent

Lucy Wang 2J

First use the equation for half-life of a first order reaction to determine k. Then use the first order reaction equation ln([A]/[Ao]) = -kt to determine the ratio of the current concentration of the drug to the initial concentration. You should get 0.735. Then multiply this by the initial amount of...

Lucy Wang 2J

You should use platinum when there is no solid metal conductor. There may be aqueous metal however this would still need a platinum conductor.

Lucy Wang 2J

A particular reactant decomposes with a half‑life of 129 s when its initial concentration is 0.322 M. The same reactant decomposes with a half‑life of 213 s when its initial concentration is 0.195 M. I'm a bit confused how you would approach this problem to determine what the reaction order is.

Lucy Wang 2J

The mechanism proposed for the oxidation of iodide ion, I−, by the hypochlorite ion, ClO−, in aqueous solution is shown. ClO−(aq)+H2O(l)⇌HClO(aq)+OH−(aq)fast in both directions I−(aq)+HClO(aq)→HIO(aq)+Cl−(aq) slow HIO(aq)+OH−(aq)→IO−(aq)+H2O(l) fast Complete the rate law for the formation of IO− imp...

Lucy Wang 2J

The rate constant of a reaction is temperature dependent. Raising the temperature will increase the rate constant of the reaction with the greater activation energy more than that of the reaction with the lower activation energy. In this case, the forward reaction has the higher activation energy, s...

Lucy Wang 2J

this is because the slope for these lines equals -Ea/R. So a higher activation energy will have a steeper slope than a low activation energy.

Lucy Wang 2J

Because it is the slowest step, you can think of it kinda as the one that holds up the line or the limiting reactant. The reaction can only occur as fast as its slowest step so that is why the slow step is so important for rate.

Lucy Wang 2J

To calculate ΔG∘, you must first calculate ΔH∘ and ΔS∘ of A+B-->2C.(multiply the second equation values by -2). After converting ΔS∘ to kJ/K, use the equation ΔG = ΔH∘ - TΔS∘ to solve.

Lucy Wang 2J

A negatively charged electrolyte flows from the cathode to the anode.

Lucy Wang 2J

Second order means that when you plot 1/[A] vs time, you will get a straight line. Second order also means it requires two molecules to react/collide for the reaction to occur.

Lucy Wang 2J

The answer would be neither. As long as the redox equation is correctly balanced, it makes no difference to Ecell* and Ecell what the stoichiometric coefficients are.

Lucy Wang 2J

I think the solutions can be different, but in the lecture he had a solution of Zinc (Zn --> Zn 2+ + 2e-) on the left side where the negative anode is. And a solution of copper (Cu+2 + 2e- --> Cu) on the right side where the positive cathode is. I think the only significant part is that the solution...

Lucy Wang 2J

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 = -23.50 kJ), resulting in a temperature rise of 7.32 C. In a subsequent experiment, 100.0 mL of 0.200 m HBr(aq) and 100.0 mL of 0.200 m KOH(aq) were ...

Lucy Wang 2J

Container A is filled with 1.0 mol of the atoms of an ideal monatomic gas. Container B has 1.0 mol of atoms bound together as diatomic molecules that are not vibrationally active. Container C has 1.0 mol of atoms bound together as diatomic molecules that are vibrationally active. The containers all ...

Lucy Wang 2J

Calculate the standard entropy of vaporization of water at 85 C, given that its standard entropy of vaporization at 100 C is 109.0 J/K*mol and the molar heat capacities at constant pressure of liquid water and water vapor are 75.3 J/K*mol and 33.6 J/K*mol, respectively, in this range. Why is that wh...

Lucy Wang 2J

A calorimeter was calibrated with an electric heater, which supplied 22.5 kJ of energy as heat to the calorimeter and increased the temperature of the calorimeter and its water bath from 22.45 8C to 23.97 8C. What is the heat capacity of the calorimeter? What does heat capacity of the calorimeter me...

Lucy Wang 2J

to solve this you will use the equation ΔG = ΔH* - TΔS*. We set ΔG to zero because the boiling point is when the equation (s) --> (l) is at equilibrium. then plug everything into the equation and solve for T. This is your boiling point.

Lucy Wang 2J

Isolated systems are almost impossible to make because there will always be some sort of inefficiency and it is impossible to create a perfect system.

Lucy Wang 2J

the equation you want to use is ΔG = ΔG* + RT ln(Q).First solve for Q= [products]/[reactants]=[0.8]^2/[0.2][0.1]. Then plug everything else in and solve for ΔG.

Lucy Wang 2J

when a substance changes from solid-> liquid-> gas, the delta H will be + and delta S will also be +.
when a substance changes from gas -> liquid-> solid, the delta H will be - and delta S will also be -.

Lucy Wang 2J

yes i think the two terms can be can be used interchangeably

Lucy Wang 2J

could someone pls explain how to approach this problem? I'm not quite sure where to even start. A 0.617 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 16.5 K. Calculate the amount of heat q requi...

Lucy Wang 2J

hi could someone explain what the heat capacity of a calorimeter is? when would we use this value? is it specific to different calorimeters?

Lucy Wang 2J

Hi could someone please explain how to do this problem? I'm not quite sure where to even start. An 80.0 g sample of a gas was heated from 25 ∘C to 225 ∘C. During this process, 346 J of work was done by the system and its internal energy increased by 6665 J. What is the specific heat of the gas?

Lucy Wang 2J

hi, could someone pls explain why work reactions that happen at a constant external pressure are irreversible?

Lucy Wang 2J

hi, i was wondering if anyone had a good way to remember when work and heat are positive or negative. I kinda get confused often.

Lucy Wang 2J

A sample of an ideal gas in a cylinder of volume 3.98 L at 298 K and 2.94 atm expands to 8.16 L by two different pathways. Path A is an isothermal, reversible expansion. Path B has two steps. In the first step, the gas is cooled at constant volume to 1.34 atm . In the second step, the gas is heated ...

Lucy Wang 2J

one side must be negative to show that an equal amount of heat is being released from one substance and absorbed by the other.

Lucy Wang 2J

the equation for work is w=−PΔV and work is being done when w is negative. That means in order for work to be done ΔV must be a positive value. So we know work is being done with the volume increases in a chemical equation. You can figure this out by looking at the moles in the reactants versus the ...

Lucy Wang 2J

At constant pressure, which of these systems do work on the surroundings? Why is 2A(g)+B(s)⟶3C(g) a correct answer? I understand the equation for work is w=−PΔV and work is being done when w is negative. But since the moles stay the same, doesn't that mean there is no volume change so w would equal ...

Lucy Wang 2J

At constant volume, the heat of combustion of a particular compound, compound A, is −3101.0 kJ/mol. When 1.147 g of compound A (molar mass =115.87 g/mol) is burned in a bomb calorimeter, the temperature of the calorimeter (including its contents) rose by 6.169 ∘C. What is the heat capacity (calorime...

Lucy Wang 2J

An acid equilibrium is the equilibrium constant/chemical equilibrium of an acid.

Lucy Wang 2J

Salt can be acidic, basic or neutral. If the salt contains the cation of a strong base, and the anion of a weak acid, then it will pull H+ from the water and make it basic. If the salt contains the anion of a strong acid, and the cation of a weak base, then it will pull OH- from the water and make i...

Lucy Wang 2J

for the sapling from this week, #9 and #10 focused on the relationship between pH and pKa. Can someone pls explain how the values of pH and pKa can affect the predominant species? Or maybe point to when Professor Lavelle went over it in the lecture/textbook.

Lucy Wang 2J

In today's lecture, Professor Lavelle pointed out that the standard state of Bromine is I2 and that it is a liquid. what does i2 mean? did he mean to say Br2 or is there some other meaning?

Lucy Wang 2J

A reaction vessel of volume 0.500 L at 700. K contains 1.20 mmol SO2(g), 0.50 mmol O2(g), and 0.10 mmol SO3(g). At 700. K, Kc 5 1.7 3 106 for the equilibrium 2 SO2(g) 1 O2(g) ∆ 2 SO3(g). (a) Calculate the reaction quotient Qc. I calculated Qc=(.1)^2/[(.5)(1.2)^2]=.0139, however the answer key says t...

Lucy Wang 2J

when a reaction is endothermic, meaning energy is required for the reactants to go to products, if a reaction is heated this will favor the forward reaction/the formation of products so Kc will increase. when a reaction is exothermic, meaning energy is released when the reactants go to products, if ...

Lucy Wang 2J

To solve for the equilibrium constant, Kc, you do [products]/[reactants]. So for this it would be (2.28)^2/(0.463)

Lucy Wang 2J

not necessarily, the composition of a reaction mixture is the reaction quotient, Q, which gives the concentration values for an expression that may not necessarily be at equilibrium yet.

Lucy Wang 2J

I think you need to factor the equation to be a quadratic so it will be Ax^2 + Bx + C = 0 and then use the quadratic formula x=[B +/- sqrt(B^2-4AC)]/2A. From this, you will get two answers and you need to eliminate the one that would give you a negative concentration value. Then you will have your x...

Lucy Wang 2J

Hi!

I think Professor Lavelle said that in order for x to negligible, the value must be smaller that 10^-3 but to be safe under 10^-4.

Lucy Wang 2J

you would raise it to the power of that coefficient

Lucy Wang 2J

yes when enthalpy is positive it's an endothermic reaction and when it is negative the reaction is exothermic

Lucy Wang 2J

you can use ICE tables to figure out the molar concentration of the products and reactants at equilibrium and the change in the molar concentration

Lucy Wang 2J

during lecture 2, Professor Lavelle said that if Q<K during a reaction, then [R]>[P] and the forward reaction is favored. however, isn't it possible for Q<K but for [P] to be greater than [R]?

Lucy Wang 2J

an inert gas is just a gas that does not react in the reaction

Lucy Wang 2J

There will be 30 questions on the final, each worth 6 points. I think quantum will be covered the most on the final since we spent the most time on it. The distribution is based on how long we spent on each topic.

Lucy Wang 2J

If a species is more predominant that means that is the majority in the solution. For an acidic solution, the predominant species will be charged and for a basic solution, the predominant species is neutral.

Lucy Wang 2J

first you list the ligand names in alphabetical order with (Greek Prefix), then the transition metal cation name (Roman Numeral) and then if there are anions, then you put the anion name, with a Greek Prefix and then the hydrate

Lucy Wang 2J

In aqueous solution, classify these compounds as strong acids, weak acids, strong bases or weak bases.

How do you tell if an acid is strong or not?

Lucy Wang 2J

I was wondering if someone could explain the difference between a bronsted and a lewis acid. What's the difference between them? Is it possible for an acid to be both a bronsted and lewis acid?

Lucy Wang 2J

The seesaw shape applies to when there are 5 areas of electron density. One area is a lone pair and the other 4 are bonds. When this happens, it leads to a seesaw structure.

Lucy Wang 2J

Yes the electrons are delocalized and a pi bond is formed above and below the ring.

Lucy Wang 2J

In lecture #24, Professor Lavelle mentioned that to form salts, KCN or NaCl or NH3 would replace water's position in the ligand. Is there a reason water is so easily replaceable in a ligand solution?

Lucy Wang 2J

it depends on its ground state electron configuration. Since C ends at 2p. the hybridization orbital is 2sp

Lucy Wang 2J

Select the correct statement about the relative positions of the hydrogen atoms in the three structures. ->The hydrogen atoms of H2CCH2 and H2CCCCH2 lie in the same plane. The hydrogen atoms of H2CCCH2 and H2CCCCH2 lie in the same plane. The hydrogen atoms of H2CCH2 and H2CCCH2 lie in the same plane...

Lucy Wang 2J

i think multidentate ligands are more stable because they have more bonds so its more difficult to break but I'm not sure how easy it is to form multidentate ligands versus unidentate ligands

Lucy Wang 2J

Metallic character is greatest at the bottom left corner of the periodic table. The answer is in increasing order so P has the least metallic character and Na has the most. This follows and makes sense with the trend of metallic character across the periodic table.

Lucy Wang 2J

Hi!
Yes, all molecules that have an odd number of electrons are radicals.

Lucy Wang 2J

if a N, O or F atom has 2 lone pairs, then hypothetically yes it could form two hydrogen bonds, one for each lone pair.

Lucy Wang 2J

I think you should know trends for ionization energy, electronegativity, atomic radius.

i'm not really sure about any others

Lucy Wang 2J

The subshells possible for a certain shell is l=0,1,...n-1.
so for n=2, l=0, 1. However since for l=2 for d, the subshell 2d cannot exist.
Hope this helps!

Lucy Wang 2J

The lewis structure that has more formal charges that are closer to zero are lower energy and more stable.

Lucy Wang 2J

The sum of the oxidation numbers of the atoms in the perchlorate ion must equal the charge on the ion, -1. When oxygen is bonded to a nonmetal other than flourine, it has an oxidation number of -2. Because there are four oxygen atoms in the ion, chlorine must have an oxidation number of +7 to equal ...

Lucy Wang 2J

If a molecule is polar, that means the charge distribution will be unequal. For example, in the molecule HF it would be polar because F is much more electronegative than H and therefore will have a stronger pull on the electrons. Making the F side of the molecule slightly more negative than the H si...

Lucy Wang 2J

Hey! In order for there to be hydrogen bonding, there needs to either be a Hydrogen bonded to a highly electronegative atom (N, O, F) or a lone pair of a highly electronegative atom (N, O, F). So for this problem, theoretically there are 8 sites where hydrogen bonds can be formed with this molecule....

Lucy Wang 2J

Hey!
My understanding is that E=hv is only used for light/photons. However, E=pc is used for these that have mass, like electrons.

Lucy Wang 2J

So my understanding is that valence shells must have 8 electrons. And these are represented by the s2p6. However, what does the d and f orbital represent then? Do these also fill valence shells?

Lucy Wang 2J

I think it has to do with formal charge. If two of the oxygen had a double bond, then the nitrogen would have 5 bonds which is not very stable.

Lucy Wang 2J

how can we tell the difference between a molecule that is an acid or a base? do they react differently in chemical reactions?

Lucy Wang 2J

I would say to do the textbook homework problems and attend the step up learning sessions. Don't wait until the last minute to do these questions, you should try to do these along with the lectures that pertain to the textbook problems. For me, it helps to reinforce my understanding of what Prof.Lav...

Lucy Wang 2J

The question is basically asking how many electrons could have these criteria. so for the first one, n=3 The 3 shell has 3s, 3p, 3d and in each of these subshells they can contain 2, 6, 10 electrons respectively. Then add them together and the answer is 18. For the second question, n=4, l=2 This is ...

Lucy Wang 2J

Hi Brett, I'm not completely sure but my understanding is that in order to conduct electricity, electrons need to be able to to be transferred relatively easily from atom to atom as free electrons. And when the ionization energy for an atom is low, this means that the energy needed to remove an elec...

Lucy Wang 2J

Hi Quinton, So for the first question since n=4 AND l=2, this is referring to electrons that are in the 4d subshell only. The value of l for the electrons from the 4s or 4p subshells do not equal 2 so they don't apply to this question. I think the answer should be 10. For the second question, when n...

Lucy Wang 2J

Identify the reasons why oxygen has a lower first ionization energy than both nitrogen and flourine.

So I understand why oxygen has a lower first ionization energy than oxygen but can someone explain why for nitrogen?

Lucy Wang 2J

can someone explain the point on the Unit 2: Outline that says"with respect to electron transitions that give rise to a UV or visible spectrum: understand the difference between electronic transitions in atomic orbitals and electronic transitions in molecular orbitals" or if u could point ...

Lucy Wang 2J

The reason you must use de Broglie's equation for this problem is because it is talking about an electron. The equation c=wv only applies to photons since c is the speed of light. When you use that equation for an electron, your answer will be incorrect. However, de Broglie's equation can be used fo...

Lucy Wang 2J

For an excited state electron configuration, the electrons won't necessarily be in the "correct" (groundstate) order. For example Carbon has 6 electrons. A ground state configuration would be 1s2, 2s2, 3s2. But if one of the electrons were to be excited, then the excited-state electron con...

Lucy Wang 2J

I asked my TA about this and I think he was just explaining how they got the equation but for this class we won't necessarily need to know how to derive it. I think the wave is to represent the probability that you will find an electron there. So at the peaks, it has the greatest probability and whe...

Lucy Wang 2J

Hey! I'm not 100% sure why it is that they have lower energy but I don't think we need to know why for now, just know that the order of increasing orbitals is s, p, d, f.

Lucy Wang 2J

Hey! I think you are doing it correct but you just need to convert from cm to m before you find Energy (J).

Lucy Wang 2J

Hey! So I don't think the electrons are necessarily lined up right next to each other. We never know the exact location of the electron, we only know that they are located in their orbitals which are high probability areas, like the s-orbital(sphere). Even though we don't know the exact location, th...

Lucy Wang 2J

I solved it by using the equation E=(hc)/wavelength to get 4.73 x 10^-19 Joules/photon. Then in order to get the # of photons, I divided 64J by 4.73 x 10^-19 J/photon to get the number of individual protons (1.35 x 10^20 photons). Then to convert the photons to moles use Avogadro's number to get 2.2...

Lucy Wang 2J

Hey! I posted a reply to this in Lec 7. Question [ENDORESED] but I've attached it below. I hope it helps! The negative sign simply is to show that this is the amount of energy LOST by the electron. We changed it to a positive sign to show the amount of energy being ABSORBED by the photon or turned i...

Lucy Wang 2J

The -1/16 is denoting the energy for when the n=4. In the equation, E = (hR)/n^2, so when n=4, it would be (-1/16)*hR. The -1/4 is showing when n=2.

Lucy Wang 2J

i think the easiest way would just be to plug the equation, as it's written, into your calculator! If you are having trouble figuring out which 10^?, then I would recommend switching to scientific notation rather than flo. It would probably be easiest just to look up how to do this for your specific...

Lucy Wang 2J

electron transition refers to when an electron changes energy levels in an atom/molecule. For example an electron can be excited during a photoelectric experiment and jump from energy level n=1 to n=3

Lucy Wang 2J

The negative sign simply is to show that this is the amount of energy LOST by the electron. We changed it to a positive sign to show the amount of energy being ABSORBED by the photon or turned into light. This works because according to the conservation of energy, energy cannot be created or destroy...

Lucy Wang 2J

I think to find the change in energy, you do the final energy - initial energy.

Lucy Wang 2J

You should be able to calculate the theoretical yield. As for the actual yield, I think this is usually given to you or maybe as a percentage of the theoretical yield, so that you would be able to solve for the actual yield.

Lucy Wang 2J

I think they will all be closed book.

Lucy Wang 2J

E.15 The molar mass of the metal hydroxide M(OH)2 is 74.10g*mol -1. What is the molar mass of the sulfide of this metal?

What does it mean the sulfide of this metal? Am I supposed to convert it to something else?

Lucy Wang 2J

Yes! I agree! We need the music back! It helps to make it feel like a real lecture in the classroom

Lucy Wang 2J

So in the first solution, there are 0.20 moles of NH4NO3. When the florist dilutes it by adding 3.0L of water, the molarity of the solution is .20 mol/ 4 L = .05 Molarity. From there, the florist pours 100ml, or 0.1 L, of this diluted solution into each plant. So the number of moles of NH4NO3 being ...

Lucy Wang 2J

My understanding is that amplitude does not affect wave velocity. However, amplitude has more to do with the energy or intensity of the light? I'm not 100% sure though, anyone can feel free to correct me.

Lucy Wang 2J

hey! could you be more specific about where this problem is from?

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