CHEMISTRY COMMUNITY

Eliot Kagan 2G

The E should be positive whenever it is considered a galvanic cell. I don't think the E changes with the concentration of the anode/cathode. Since the batteries undergo one reaction at a time, we can determine whether E is positive or negative when we calculate their individual E's.

Eliot Kagan 2G

Yes, it is an error. You can probably just think of it as STP so you have the same calculations as the manual.

Eliot Kagan 2G

Remember that the P in w=-PDeltaV signifies external pressure. When something undergoes a reversible expansion, they change the external pressure and internal pressure with infinitely small intervals. This is why reversible expansions take more work.

Eliot Kagan 2G

Remember that when you break bonds you have a positive enthalpy while when you form bonds you get a negative enthalpy. So the bonds formed should subtract from the bonds broken.

Eliot Kagan 2G

I think you can ignore the 2nd deprotonation when the 2nd deprotonation is less than a factor of 10^3 from the first deprotonation. It says this in 6E.1 if you want to learn more. for example: tartaric acid (weak acid), C2H4O2(COOH)2 ka1= 6.0×10^−4 ka2 = 1.5×10^−5 in this case, you will do the 2nd d...

Eliot Kagan 2G

You can determine it based on the time and concentration it took to do a half-life. Notice that the time increased as the concentration decreased. With this, you can use the half-life equations to figure out which order has this trend.

Eliot Kagan 2G

I think it has to do with the rate flatting out as the reaction goes on in a 2nd order reaction. The 2nd order graph has a decaying exponential line. Correct me if I'm wrong but this is my guess.

Eliot Kagan 2G

We would subtract .006 mols L-1 from 0.015 mols L-1 because that is how many A's are needed to create 0.018 mols L-1 of B. We want to know the [A]t so we would subtract the amount of A needed to create .018 mols L-1 of B from the initial A condition. Note that A is still present in the solution at 3...

Eliot Kagan 2G

I think that for the first, second, and zero-order equations it doesn't matter since we are only considering the reactants. It will likely matter when we consider the whole equation.

Eliot Kagan 2G

Yes. I think it is also due to the fact that the other elements will be so large that their changes will be negligible. If the other two elements are negligible, we can determine that the change in its rate is only based on the element with the small concentration.

Eliot Kagan 2G

I think the section with the closest problems is in 6N but it might be confusing. For this problem, you can start by looking at the info given to you. S.H.E.'s reduction eq= 2H+(aq)+2e−⇀ H2(g) E(nought)= 0 With [H+]=0.46 [MPH2]=4.9 atm, you can find Q (remember [P]^coefficent/[R]^c) With this, you h...

Eliot Kagan 2G

You don't need to multiply the E(c & a) by the coefficients. You should get 3.878 V. Apparently, a standard reduction potential is an intensive property and it does not depend on how many times the reaction occurs. My Work Au3+(aq) + 3e– → Au(s) E=+1.498 (cathode) Mg2+(aq) + 2e– → Mg(s) E=–2.38 ...

Eliot Kagan 2G

The information you should look at is "galvanic cell." Galvanic cells undergo a spontaneous redox reaction so that means that the E should be positive (remember that Delta G = - n*F*E). With this, you can find which combination gives you a positive E. Useful info Au3+(aq) + 3e– → Au(s) +1....

Eliot Kagan 2G

You can also tell by looking at the equations themselves. The anodes will undergo oxidation while the cathodes undergo reduction.

Eliot Kagan 2G

Yeah, it will take billions of years because the energy absorbed from STP is way too low.
According to a study done by a physicist in India, the graphite needed to experience over 100 kbars of pressure and over 2000 C of temperature for it to turn into a diamond.

Eliot Kagan 2G

I think the salt bridge has three main functions: - preventing the accumulation of positive and negative charges around the respective electrodes. in other words, keeping the reaction neutral - allowing a continual flow of electrons between the two sides. - limits/prevents the liquids of each side f...

Eliot Kagan 2G

A salt bridge is used to maintain the charge balance of the reduction and oxidation of the battery. If it is removed, the reaction will likely continue in their respective halves of the cell and will become more negatively/positively charged. This leads the battery to eventually come to equilibrium ...

Eliot Kagan 2G

Just like Anna said, you would be adding the two half-reactions. When deciding on how many moles of an ion there are, I like looking at the number of electrons being exchanged and adjust the moles based on that. In this reaction, since Sn loses 2 electrons, you will need 2 moles of Ags to take up th...

Eliot Kagan 2G

I think as of now, the most important thing to focus on is the number of electrons being exchanged and how to manipulate the electrolytes to be able to do that.

Eliot Kagan 2G

Oxidation numbers are used to find how many electrons are removed/gained in an atom in a given molecule. I wanted to share this website since it really helped me understand how to find these values. https://chem.libretexts.org/Bookshelves/Analytical_Chemistry/Supplemental_Modules_(Analytical_Chemist...

Eliot Kagan 2G

k = 1.381 x 10^-23 J/K
You can find the Boltzmann's constant on the constants and formulas sheet on the top right (it says k but kB and k are the same thing).

Eliot Kagan 2G

ΔU=q+w which comes from the first law of thermodynamics. q = the transfer of the thermal energy. The energy usually goes from an object of high temperature to an object of low temperature. q is negative when the heat is released by the system. (exothermic) q is positive when the heat is absorbed int...

Eliot Kagan 2G

Yes, you would have to use different equations to figure the amount of work done. For irreversible rxns, you would use dw= -p*dV or w =- Sp dV (S = integral). For reversible isothermal gas rxns, you would use w= -nRTln(V1/V2). The difference in these equations arises from the differences in p in the...

Eliot Kagan 2G

Adiabatic compression/expansion of gases is also a reversible pathway. It transfers energy only through work.

Eliot Kagan 2G

They say that because the entropy of the system decreased. Entropy is referred to as the measure of the disorder of a system, so if it is decreased there is more stability in the system. This difference in stability largely arises from the KCl's(s) lower entropy.

Eliot Kagan 2G

Lorena_Morales_1K wrote:What exactly does it mean when work is positive? Thank you in advance for your help :)

Work is positive when done on a system.
Work is negative when done by the system.

I recommend this video for more info.
https://youtu.be/NyOYW07-L5g

Eliot Kagan 2G

It has to do with the pressure value. The isothermal equation is derived from the original w=-PΔV equation. The reason w = -PΔV works is because the P (a constant) can be taken out of the integral in −∫pdV. However, in an isothermal reaction, the external pressure isn't constant so we can't take it ...

Eliot Kagan 2G

To add on, I like to use the "thermal" in isothermal to help myself remember that it is related to temperature. In an isothermal reaction, the temperature is constant. I hope this helps!

Eliot Kagan 2G

Cv = ΔU/ΔT is the heat capacity at a constant volume Cp = ΔH/ΔT is the heat capacity at a constant pressure In order to find the relationship between these heat capacities, we need to dissect the ΔH. ΔH = ΔU + PV PV can be changed to nRΔT bc PV = nRΔT so, ΔH = ΔU + nRΔT is formed. Cp = ΔH/ΔT = (nRΔT...

Eliot Kagan 2G

I think the textbook is wrong. When we went over this in my discussion section, we found that work was 490J.
w= change of U - q = 982J - 492J = 490J.

Eliot Kagan 2G

I think that it has to do with the changing pressure of the external pressure. If we were dealing with one pressure, we can take it out of the integral (since it's a constant) and solve it with the equation given to us in class. That is why we do w= p *change of volume. But now since P is changing, ...

Eliot Kagan 2G

In order to solve this problem, you will need to use this equation. heat required to melt ice + heat required to bring the grams of melted ice to the final temperature=(negative) heat released that cools grams of water to the final temperature For heat required to melt ice - use the standard enthalp...

Eliot Kagan 2G

Like the post above me, you should use the equation ΔU = Q + W. However, I think that the signs of each value (Q, W and U) depend on the problem. For work: w = + when work is done "on the system" w= - when work is done "by the system" for q: when heat is absorbed by the system it...

Eliot Kagan 2G

I think you should watch this video. It has really helped me get a grasp of this concept.
https://youtu.be/LsqKL3pBVMA

Eliot Kagan 2G

You should set up the problem with the equation below to solve for Tf.
heat required to melt ice (by doing what Amanda said) + heat required to bring the 53.6 g of melted ice to the final temperature = (negative) heat released that cools 364 g of water to the final temperature

Eliot Kagan 2G

I think that the standard state for complex molecules will be given to us. If you want to learn about the standard state of the pure elements, I recommend looking at this site and changing the temperature to 25C.
https://ptable.com/#Properties

Eliot Kagan 2G

I think that the Leidenfrost effect happens when an object of extremely hot temperature (the lava in this case) touches a liquid. The extreme temperature difference between the lava and the sweat or water on the skin causes the water to form a vapor layer that shields the skin from direct contact wi...

Eliot Kagan 2G

We'll have access to all of these conversions on the constants and formulas sheet.
Here's a link
https://lavelle.chem.ucla.edu/wp-content/supporting-files/Chem14B/Constants_Equations.pdf

Eliot Kagan 2G

I think that the one-sided arrow just tells us that the reaction is heavily favored to that side. For these questions, I think we can assume that the reactants are completely used. I think that it was done to make the calculations easier.

Eliot Kagan 2G

I think the only distinction we need to make is that bond enthalpy can be inaccurate (except for diatomic elements) because it is the average. The other two seem to be as accurate as each other so the method that you use will largely depend on the information given.

Eliot Kagan 2G

The 2nd deprotonation is when the acid loses another H after the first reaction.
For example, when H2SO4 reacts with water, the 2nd deprotonation will be when HSO4- turns into SO4 2-
Sometimes we are able to ignore the 2nd ka because the change to the pH is so small.

Eliot Kagan 2G

To add on, I think you have to consider the 2nd ka value when doing strong acids like Sulfuric acid H2SO4.

Eliot Kagan 2G

You will typically use the inverse Kc when solving for the reverse equation.
For example in the reaction 2SO3 = 2SO2 +O2.
kc will equal ([SO2]^2[02])/[SO3]^2
The inverse kc will equal [SO3]^2/([SO2]^2[02])

Eliot Kagan 2G

A couple of places you should check:
- whether you changed moles to molar concentration
- whether your kc formula is correct = (SO2)^2*(O2)/SO3^2
- whether the concentrations of the final values are correct
- remember that the change for the ice table will be -2x = 2x x

Eliot Kagan 2G

Since H2SO4 can deprotonate 2 times you will have to make an ice table for the weak acid HSO4-. The ice table should start with .15M of HSO4- and .15M of H3O+.

Eliot Kagan 2G

Yes, I would also assume that the elements above are catalysts of the reaction. They likely affect the reactants in a way that allows the chemical reaction to occur while not being consumed by the reaction.

Eliot Kagan 2G

Every chemical reaction should have the potential to reach equilibrium given that it has the right conditions to reach the reaction's equilibrium constant. This could depend on things like time, since reactions need time to occur and reach that equilibrium constant. I think that there are reactions...

Eliot Kagan 2G

The question will likely tell you when the product is not zero. The examples provided above will also imply that the product isn't zero.

Eliot Kagan 2G

It might be good to consider these inert gases like the solvents in the normal solution. Since the inert gases don't react to anything, when solving for the K constant, we put the inert gas both on the reaction and product part of the equation, thus causing them to cancel each other out.

Eliot Kagan 2G

You should be careful with the liquids. While solvents aren't taken into account for the K value, liquids that are reacted together can be involved in the K concentration.

Eliot Kagan 2G

You could also use -log (3.50 x 10-3 M) to find the pOH and subtract the result from 14 (because pH+pOH = 14). You should get 11.54 pH

Eliot Kagan 2G

Since it is an ionic compound, we don't use the prefixes because we can find out the number by checking their respective charges. We use prefixes in covalent bonds because the number of atoms in the molecule is more ambiguous.

Eliot Kagan 2G

Rather than not interacting, Na+ isn't strong enough to make the water molecules lose a hydrogen like Fe, Cr, Al, Cu, and Ni. A general rule to follow is that the cations in groups 1 and 2 aren't strong enough to affect the pH. For anions, the really strong anions create a more basic solution becaus...

Eliot Kagan 2G

Here is a picture of the amphoteric oxides for convenience.

Eliot Kagan 2G

How do we know that Al 3+ forms a complex with water and that it'll react with more water to form hydronium ions? In one of his classes (I think it's the 12/7 one), our professor went over the small cations that acted as lewis acids when alone in an aqueous solution. (this is why the problem is Ph<...

Eliot Kagan 2G

I actually think the atom with the larger radius is the "stronger" acid because the bonds are more easily broken (longer bonds = weaker bonds). This is why HF is considered a weaker acid than HI. If we look at the group 17 acids, HF<HCl<HBr<HI in terms of acidity. Remember that the weak/st...

Eliot Kagan 2G

My TA gave us this resource to memorize the vespr model. It was a very helpful resource and wanted to share.
http://chem.illinois.edu/chemdoodleweb/table.html

Eliot Kagan 2G

^ Adding onto this, the equation that he has in his lecture Ka = [A-][H+]/[AH] is just the concentrations of the products divided by the concentration of the reactants, but I am not 100% sure if we would have to know this/calculate the equilibrium of the weak acid so if someone could answer that'd ...

Eliot Kagan 2G

For future reference, I think it is also good to memorize the specific charge for the ligands so you can easily find the charge (or oxidation) of the transition metal.

Eliot Kagan 2G

The difference between pH and pOH is that they both measure different things. pH measures the concentration of H3O+ while pOH measures the concentration of OH-. They both add up to 14 so if they give you one of them, you can find the other one easily. However, we usually use pH so be careful not to ...

Eliot Kagan 2G

The carbon usually forms 4 bonds because it wants to fill up it's 4 orbitals (2sp3) to be stable. There are many reasons why carbon can be called "special" - it can form huge chains of carbon that can form macromolecules which are big enough for larger organism to use. - it is very stable ...

Eliot Kagan 2G

I think you can spot delocalized bonds by assessing their resonance structures. For example, in benzene since the combination of the resonance structures will result in single/double bond characteristics in all the bonds. With this, we can tell that there is one sigma bond between each of them and a...

Eliot Kagan 2G

Hello. I think this image does a good job describing how a delocalized pi bond is formed in benzene. It is because the resonance structures all combine to form a molecule with bonds with both double and single bond characteristics. During this process, the pi bonds forms a large e- cloud (which is w...

Eliot Kagan 2G

As Tamara said above, the major difference that you should look out for is that sigma bonds can rotate and the pi bonds are rigid. I also wanted to add a visual to help. https://cdn.shortpixel.ai/client/q_glossy,ret_img,w_596/https://vivadifferences.com/wp-content/uploads/2019/06/Sigma-Vs-Pi-Bond.png

Eliot Kagan 2G

Although they can be considered to have both particle and waves like motions, I think that you shouldn't see them as very similar. The negativity of the electron and the mass-less light greatly differentiate them from each other and have very different implications in chemical reactions.

Eliot Kagan 2G

I don't know if this will help but an easy way to think of vapor pressure is to think of it as the urge to become a vapor. So the higher the vapor pressure, the higher the urge to become a vapor. In terms of boiling point, the lower the vapor pressure, the higher the boiling temperature.

Eliot Kagan 2G

Like those above, the atoms after period 3 can all have expanded octets. The periodic table is always expanding as we find more atoms, so there is likely an 8d that just hasn't been discovered yet. I think for this course we will only need to know that the atoms after neon can have octets because n=3.

Eliot Kagan 2G

I think looking at the forces in terms of vectors may help. Note that the example below works because the atoms surrounding the dipole moments are exactly the same, thus having the same forces acted upon it (just in a different direction). https://www.andrew.cmu.edu/course/09-105/GIFs/DIPOLE.08.GIF

Eliot Kagan 2G

To add on, I think that looking at the general direction of the forces will be helpful in determining whether they are polar or not. The trans-dicholorethene are nonpolar because they point the opposite way while cisdichloroethene is polar because they point towards a general direction. https://www....

Eliot Kagan 2G

I also don't think we need to know it but I think this website is quite informative for learning electrostatic potential maps. link: https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Chemical_Bonding/Fun...

Eliot Kagan 2G

In general intramolecular interactions will require more energy to break than intermolecular interaction since intramolecular bonds are usually a lot stronger.

Eliot Kagan 2G

Catherine Bubser 2C wrote:What is an example of a molecule that exhibits a delta bond?

I don't think we need to know this but apparently Re2Cl8 2- ion has a delta bond .

Eliot Kagan 2G

Hello. Like Emily said, I think you should follow the trends of the periodic table. Think about how many electrons they need or don't need to become stable. As a general trend the atoms on the left side are usually cations while the atoms on the right side are anions. If you need additional help you...

Eliot Kagan 2G

The negative sign represents that the energy is being released outside the system.

Eliot Kagan 2G

To add on to what Edward said, the formal charge exaggerates the covalent character of the bond by assuming that all the bonds are equally shared while the oxidation number exaggerates the ionic character by assuming that the more electronegative gets the e-. So in the scope of this question, since ...

Eliot Kagan 2G

If I remember correctly, in one of the lectures the professor said that we will be focusing on s, p, and d blocks so I don't think the f block is necessary. However, if you want to learn it just incase I recommend watching this video: https://youtu.be/KJLgnAUVALc

Eliot Kagan 2G

The inner core would be the electrons that are already filled in. I like to think of it as the electrons that aren't touched in a reaction so this will usually be the closest noble gas.

Eliot Kagan 2G

The s-electrons have lower energies because they are closer to the nucleus than the p-electrons. This protects the p-electrons from the nucleus's charge (aka shielding). You can probably get a better explanation here: https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textboo...

Eliot Kagan 2G

To add on to those above me, you should focus on how many protons they have to determine their electronegativities and ionization.

Eliot Kagan 2G

Hello,
I don't have an acronym to remember the trends but I found this website very helpful in doing so.
Website: https://chem.libretexts.org/Bookshelves ... _Chemistry)/Descriptive_Chemistry/Periodic_Trends_of_Elemental_Properties/Periodic_Trends

Eliot Kagan 2G

To add on to those above me, the high ionization energy of these materials are also the reason why they are bad conductors of electricity.

Eliot Kagan 2G

To add on to those above me, I think there is a correlation between the charge of the electrons and the nucleus. I don't think the charges of the nucleus of these atoms (+1 H, +2 H, +3 Li, +4 B) are strong enough to hold all 8 electrons together.

Eliot Kagan 2G

You will need to find the atom with the lowest electromagnetic and then surround it based on how many valence electrons it needs. For more complex molecules, there are isomers (molecules with same number of molecules but different structures) so we may have to build our structures based on the infor...

Eliot Kagan 2G

You should finish it by 11:59pm on Sunday but I assume that you can still do the problems past the time since he didn't seem to set an "available from date" on the website itself.

Eliot Kagan 2G

To add on, ionic bonds are held together by the charges of the whole atom while covalent bonds are held together by their shared electron.

Eliot Kagan 2G

The LR for this problem would be Mg because the weight of 3 Mg's are greater than the weight of B2O3. The book seems to also use Mg as the LR so you may have done your calculations wrong.

Eliot Kagan 2G

To add onto those ahead of me, if you are having problems with a specific topic, I recommend that you watch The Organic Chemistry Tutor on youtube. I find him really helpful because he goes over each problem step by step.

Eliot Kagan 2G

In order to solve for the delta V, we have to divide each side by M (Delta V= delta P/M). I think it will help if you think of the deltas (delta V and Delta P in this case)as a variable that cannot be split.

Eliot Kagan 2G

The problems will typically be in J/photons unless they tell you to convert to moles. In this problem, instead of changing it to moles, you had to divide 36.14 J by the joules of the photon with the wavelength of 6.18×10−4 cm.

Eliot Kagan 2G

So we're going to be in a zoom call with our whole discussion group? Doesn't that mean that we'll be able to see each other's work? Yes, I'm pretty sure we will be in a zoom call with our group, however I think it will be quite hard to cheat off of each other since the TA will be watching your scre...

Eliot Kagan 2G

Yes, you are correct. Although every object has a wave-like property, for classical objects like baseballs we often consider them as particle-like objects since the lambda is too small to be noticed or have substantial effects.

Eliot Kagan 2G

To add to the post above, while all objects have wave-like properties, we consider classical objects like baseballs to have particle-like properties since the lambda is too small to consider.

Eliot Kagan 2G

Hi. It is 10m/s because you have to consider both the negative and positive uncertainty of the equation. For example, if a ball had a velocity of 7.00 ± 3.0 m/s. The uncertainty will be 6.

Eliot Kagan 2G

The black body radiation is a item that can absorb all frequencies of light and is purely theoretical. Scientist still haven't found any material able to do so. But the reason why black gets hotter than the other colors is because it can absorb more light frequencies than them.

Eliot Kagan 2G

To add onto the posts above, I personally think the Audio-Visual Focus-Topics really straightened-out a lot of topics for me. If you are struggling with some of the topics there, you can re-watch and redo the post-assessment. I plan on redoing the post-assessment test and re-watching the video befor...

Eliot Kagan 2G

You can do either, but I think it is safer to find the moles of the product since it will always consider the moles ratios between the product and reactant unlike the first option.

Eliot Kagan 2G

Yes, you are correct C14H18N205 is the limiting reactant in this case since it has less moles, meaning the reaction runs less. If you are unsure, you can always check your answer by just converting it to the moles of the product. Hope this helps!

Eliot Kagan 2G

No, you don't need to know what 2-butanone or 1-bromopropane are. You can determine their elemental composition by counting the provided Lewis structures. The Hydrogens aren't usually shown in Lewis structures so you will have to add hydrogens based on how many electrons each element needs for a sta...

Eliot Kagan 2G

After changing the 2.5 t into moles of NaBr, you need to convert the moles of NaBr to Fe3Br8 (1mole of Fe3Br8/8 moles of NaBr); then, convert moles of Fe3Br8 to moles of FeBr2 (3 moles of FeBr2/1 mole Fe3Br8); then, FeBr2 to Fe (1 mole of Fe/1 mole of FeBr2). As you're doing this, you should find th...

Eliot Kagan 2G

The question: "the reaction of ammonia gas with oxygen gas at high temperatures in the presence of a copper metal catalyst produces the gases water and nitrogen dioxide." If the copper metal is a catalyst of the formula, is the copper metal included in the chemical equation? If not, how do...

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