CHEMISTRY COMMUNITY

Natalie 3k

A tip that I found useful for basic solutions is to find however many Oxygens you need on one side, and add double that many OH- to the same side. Then to balance it, add that number of H2O to the other side. (so for ex, if the left side has 2 oxygens and the right has 1 oxygen, you would add 2 oh- ...

Natalie 3k

Hi! So basically a porous disc is just a membrane that allows the anions of a cell to transfer directly between solutions, whereas a salt bridge uses a salt. For example, a porous disc allows the direct transference of Cl- ions, while a salt bridge requires NaCl to transfer the Cl-. As far as I can...

Natalie 3k

I believe that as long as the anode is on the left and the cathode is on the right, and the electrodes are on the outsides it should be correct :)

Natalie 3k

Hi! Can someone please explain the difference between a porous disc and a salt bridge and what differences they have on the cell?

Natalie 3k

Can someone explain the textbook q 6.53 part c? I'm confused as to why adding NaOH to the cathode compartment would decrease the cell potential. Is it because the NaOH reacts with some of the Cr+3 making the concentration less?

Natalie 3k

Hi! I was just curious as to what topics everyone had a hard time with, and what hints or tips you found that helped you out. Goodluck on all your finals!

Natalie 3k

I believe this is because enthalpy is a state function and depends on the bonds in products and reactants, whereas activation energy is how much energy is needed for the reaction to occur, which can change. Even with a change in activation energy, the reactants and products remain the same, so the e...

Natalie 3k

I'm not fully sure if this is what you're asking, but to find the direction of the reaction we have to compare the Q value to K. If Q is bigger than K then it shifts to the left (because it is measured by products/reactants, and a number bigger than K would mean there are more products), and if Q is...

Natalie 3k

Because it's in a basic environment you can have OH- left over but not H+. You can add OH- to both sides to make the H+ into water and then just have OH- on the other side which is ok because it's in a basic solution!

Natalie 3k

I was wondering this too. I read somewhere that as you read it from left to right your eyes move in the direction of electron flow, so I was thinking this might have something to do with it because the electrons move into the aqueous solution to the other aqueous solution. Not sure if this is right ...

Natalie 3k

It has been extremely difficult for me to stay motivated as well, which is pretty normal during times like these. I've noticed something that helps me is not being too hard on myself when I don't get as much work done as I hoped, because when I am it discourages me from working again and puts me in ...

Natalie 3k

I remember it by Oxidation occurs at the Anode (they both start with vowels) and Reduction occurs at the Cathode (both start with consonants)

Natalie 3k

This one took me a while too, and it was a lot of trial and error for me. First I used the trick that says whatever side needs more oxygen atoms, add two times that number of OH- molecules, and then on the other side, add 1x that number of H2O molecules. Then I split it into the half reactions and b...

Natalie 3k

One thing that helped me with this problem is the hint that said something along the lines of take the number of oxygen molecules you need on the one side, and add 2x that number of OH- molecules to that side, then add 1x that number of H2O molecules to the other side. Then write out the half reacti...

Natalie 3k

I was confused on that too and initially thought the same thing, but I think it's whichever one is most electronegative is the best oxidizing agent.

Natalie 3k

First you have to find E°cell using the table (Ecathode-Eanode), and with that value you have to use the Nernst equation and plug in the values and that should give you the answer

Natalie 3k

I saw something to remember some of them which is PVT HUGS (pressure volume temp, enthalpy, internal energy, Gibbs energy, and entropy), might not be all of them but the hugs part helps me remember.

Natalie 3k

When reactants go from higher energy states to lower energy states, they are more stable, so it is favorable and doesn't require an input of energy. Those that are unfavorable require energy to put the products at a higher energy state than the reactants.

Natalie 3k

I think I remember my hs chem teacher saying something like the Cathode is the (paw)sitive side of the salt bridge because cats have paws :)

Natalie 3k

I just try to see which side the electricity moves into, and that's the anode, also usually the positive side, and which side the electricity moves out of which is the cathode. Wherever the metal loses electrons is the anode side.

Natalie 3k

My first thought is that you would assume T=25 degrees celsius, because as someone mentioned earlier, it's for the standard state, but I'm not entirely sure.

Natalie 3k

The part that I mess up on is forgetting negatives, and what helps me with this is using a lot of parentheses. This helps me group things together and helps when having to divide to isolate a variable.

Natalie 3k

Hi! First you would solve for Q using the pressures given, taking the coefficients into consideration. Then you would use the equation delta G = delta G (standard state) +RT In (Q) and then solve for delta G, hope this helps!

Natalie 3k

First you have to find Q, by using the pressures given, and remember to take the constant into consideration. Then you use the equation Delta G = delta g (standard state) + RT In(Q) and solve for delta G.

Natalie 3k

I was confused about this too, but the way that I thought about it was that if something goes to a higher energy state, like liquid to gas, it takes energy so H is positive. Delta S also increases because at higher energy levels, it can occupy more possible arrangements, meaning a higher delta S.

Natalie 3k

Hi, I thought I understood how to do this problem, but I can’t get the right answer for delta S and delta G. Can someone explain the steps or discuss possible mistakes? Calculate the standard enthalpy, entropy, and Gibbs free energy at 298 K for the given reaction, using the data in the table of the...

Natalie 3k

Celsius and Kelvin both change at the same rate, because Kelvin is just Celsius+273. So a +1 change in celsius corresponds to a +1 change in Kelvin.

Natalie 3k

Can someone explain how to do this problem please? The molar heat capacity for carbon monoxide at constant volume is CV, m=20.17 J/(K·mol). A 13.00 L fixed-volume flask contains CO(g) at a pressure of 7.00kPa and a temperature of 25.0 °C. Assuming that carbon monoxide acts as an ideal gas and that i...

Natalie 3k

I have a very hard time concentrating during tests, but it helps me to write down the problems I'm having a hard time with and go back to them later, eat a good meal before starting, and most importantly take a break from studying 30 mins to an hour before. I also had a hard time remaining focused w...

Natalie 3k

Cp is the molar specific heat capacity at a constant pressure for an ideal gas, and Cv is the molar specific heat capacity at a constant volume so when you set the equations equal to each other I believe you get Cp= Cv+R

Natalie 3k

I don't believe that there is any difference between the two, or at least I haven't found any.

Natalie 3k

Standard enthalpies of formation are most accurate, then Hess's Law, and then bond enthalpies. I think it's because it's just based on averages, but I'm not fully sure.

Natalie 3k

I'm not sure of exactly what we need to know, but bomb calorimeters keep the system at a constant volume, and don't let it expand even if more moles of gas are produced.

Natalie 3k

Can someone please review the steps for this problem? Just want to make sure I'm doing it right.
Calculate the standard enthalpy change for the reaction at 25 degrees C.
MgCl2(s)+H2O(l)⟶MgO(s)+2HCl(g)

Natalie 3k

I believe you would use the q=c*m*delta T equation, but hopefully someone can confirm.

Natalie 3k

Hi, to calculate bond enthalpies you take the enthalpy of formation of reactants - the enthalpies of formation of the products. It's important to keep track of any negatives so maybe a problem is arising because of that; I sometimes have issues with these problems as well.

Natalie 3k

If it's structured similar to how 14A was last quarter, there should be an extra 5 or so minutes to check our setups and equation sheets, and to take any technology errors into consideration. Additionally last quarter some TA's opened the zoom a few minutes early to make sure everything worked right...

Natalie 3k

Hi, I've been kind of confused about this too. I was just thinking that they give us the temperature so we can assume the phases of the given substances are gasses so we can include them in the calculation, but I'm not 100% sure. Hopefully someone else known for sure!

Natalie 3k

I just memorized the list of strong acids and bases and anything that is not on that list I consider to be weak and that has worked best for me.

Natalie 3k

I've found Justins (Thursdays at 12 I believe) to be very helpful!

Natalie 3k

Hi, I was confused about this too, but I remember Dr. Lavelle saying that if the equilibrium constant is under 1x10^-3 then you can assume that the change is insignificant, but I've read that 1x10^-4 is more accurate. It can be assumed to be insignificant if it is less than this and doesn't change t...

Natalie 3k

Hi! Because the question gives you the number in moles/liter (written as mol/L^-1) it already tells you the molarity, so you can just use the values they give.

Natalie 3k

It's important to remember that if a reaction is reversed, the k value will be the inverse of the value shown, and if it is multiplied by a certain value (like 3 of one equation) then that k value is raised to that power. Once you get those values you multiply them together and that should give you ...

Natalie 3k

The important thing for this problem is to remember that if the reaction goes backwards then the k value is the inverse, and if it is multiplied by a certain number, then the value is raised to the power of that number. Other than that it's pretty much just matching up the equations to where the rea...

Natalie 3k

I had trouble with this one too, and ended up with a negative value at first as well. First you have to find the Kc values based on the values they gave you at equilibrium, but when you set up the ice chart the initial value for the NO is the new value they gave, not the one at equilibrium. The chan...

Natalie 3k

Does anyone have any tips for using ice tables? I know all the steps and what to put under each category, but I find myself making mistakes sometimes and any help would be appreciated!

Natalie 3k

This just means that the products are lower in energy than the reactants, so it makes it more favorable for there to be more products than reactants.

Natalie 3k

Yes, that's correct. Q can be used to see which direction the reaction will go to reach equilibrium. If Q<K it will proceed forward, but if Q>K it will go backwards and form more reactants.

Natalie 3k

I believe concentrations can't be negative because they measure how much of a substance is present. So if there was none of something, then the concentration would just be 0, not anything in the negatives.

Natalie 3k

That's what I have written too, with delta n being the sum of the coefficients of the product minus the sum of the coefficients of the reactants.

Natalie 3k

When the pressure changes, this usually affects the volume as well, and as Dr. Lavelle said, it's not necessarily the pressure that changes the concentration, it's the change in volume. Concentration can be written as moles over volume, so if the volume increases (and pressure decreases), the concen...

Natalie 3k

Next quarter I'm definitely going to go to more of the UA sessions because those were super helpful. The hardest part about online learning for me is just staying on top of my work, so I'd try to do the textbook problems more ahead of time to prevent getting behind.

Natalie 3k

For memorizing the angles, shapes that have 4 regions like tetrahedral and trigonal pyramidal are going to have angles of 109.5 or similar, because of the 4 regions, so I just remember that 4 means 109.5. Shapes that have 3 regions on the same plane like trigonal planar are going to be 120 because 3...

Natalie 3k

I believe after removing all the p orbital electrons you remove the s orbital electrons next and then the d orbital but I'm not fully sure, hopefully someone else can confirm.

Natalie 3k

I had this question too. I was thinking that it was a strong acid but that note confused me so I'm not 100% sure.

Natalie 3k

When naming hybrid orbitals do we have to put the orbital number before it? Like does we have to specify that it's 2sp^3 or is it just sp^3 for example.

Natalie 3k

I also have a hard time naming the compounds, but I've heard that just practicing a lot and memorizing as well as you can can help in becoming faster at it.

Natalie 3k

If I'm understanding it correctly, the coordination number is roughly how many attachments can be found on the central atom. So if the coordination number is 4, the geometries that include 4 attachments would be most commonly used.

Natalie 3k

To simplify it, I just think of the coordination number as how many atoms or other molecules are connected to the central atom. In this case the 5 NH3 molecules are connected and the 1 SO4 molecule is connected, so total there are 6, making the coordination number 6.

Natalie 3k

He mentioned this in lecture, but I believe we don't need to memorize the exact number, just that it's slightly less than 109.5.

Natalie 3k

This might be oversimplifying it, but I just remember that each en contributes 2 to the coordination number and each edta contributes 6 to the coordination number. I think we just have to memorize it but correct me if I'm wrong!

Natalie 3k

I have some trouble with this too, but normally I just think of it like an equation! Each atom has its own charge, and the molecule as a whole has a charge, and the sum of the charges of the atoms needs to equal the charge of the molecule. Normally all the atoms except the one you're looking for has...

Natalie 3k

As of what we've learned so far I think the biggest thing to look at is the formal charge if the question doesn't give you any more info. The structure with the least number of formal charges is most stable. I also believe that the structure with the least separation of formal charge is more stable ...

Natalie 3k

Hi, I think that because it's the same element with the same electronegativity that's on all the sides, it cancels out. I was kind of confused on whether or not the charges would affect the polarity too but I don't think it does because then it would seem to be polar.

Natalie 3k

Hi, I sometimes struggle with finding the resonance structures for certain molecules, does anyone have any tricks that help you easily make all the structures?

Natalie 3k

Hi! Does anyone have any tips for better visualizing how pi bonds work? I understand the basics but I'm having a hard time picturing them. Thank you!

Natalie 3k

Does any one have any tips for remembering the bond angles or is it just somethings that needs to be memorized as is?

Natalie 3k

Without doing an experiment, you can compare viscosities by looking at the IMF's of the substances. If a substance has high IMF's they will be closer together and more viscous. If it has low IMF's, the molecules won't be as attracted to each other and farther apart, so it will be less viscous.

Natalie 3k

I have this issue a lot too, but I know that the octet rule can be defied for certain elements. In some cases, the d orbitals can accept electrons as well, which allows some elements like sulfur and chlorine to have more than 8. I'm not sure what the exact rules for this are, but hopefully someone e...

Natalie 3k

I have read that Sb is slightly larger than Sn, but I'm not sure if this is true because I can't seem to find any more information on it

Natalie 3k

If you know how the electron is being shared, or if it's being given up and given to the other atom that's another way to tell if it's polar covalent or ionic, but mostly it's looking at the electronegativities or what kind of elements it's between (like metal or nonmetal).

Natalie 3k

Can someone please explain how we know when an atom will use the expanded octet? I know which atoms can I just get confused on knowing when it will use it if at all. Thank you!

Natalie 3k

I believe that if the electronegativity difference is more than 1.7 it will be an ionic bond and .5-1.7 is a polar bond, so for the lewis structure for an ionic bond you would draw the two ions separate, and for the polar bonds it would be the normal lewis structure. I'm not 100% sure though so hope...

Natalie 3k

First look at whether the bonds are polar or not by looking at electronegativity, and if there are no polar bonds then the molecule is non polar. If there are polar bonds, look at the arrangement of the molecule and if it is not symmetrical, then the molecule is polar. I have a hard time with this t...

Natalie 3k

For formal charge the most probable structures are the ones with the least amount of formal charges on the individual atoms (as long as it still adds up to the total charge), and for bond length, it says that experimentally it was found that the bond length was 144 which is close to 140, the bond le...

Natalie 3k

Hi! Can someone please explain how to find which lewis structure is best based on the oxidation number of the central atom? (like number 9 on sapling) Thank you!

Natalie 3k

I think of it as counting up the number of electrons in an element. The metals on the left side of the periodic table have electrons in the s orbital (1s^1, 1s^2, 2s^1, 2s^2...) and these can only go up to _s^2. The 6 groups on the right side are the p orbital and the exponent can go up to 6 because...

Natalie 3k

Yes, I believe the formal charges should add up the charge of the molecule as a whole. I think certain atoms are more likely to be negative or positive based on their electronegativities, but I don't know if chlorine for example would always have to be negative, even though it usually is because it ...

Natalie 3k

Ionization energy is the amount of energy that is required to remove an electron, and more specifically the least bound electron to the atom. Elements that only have one valence electron have lower ionization energies because removing the one electron would make it have a full outer shell. As you mo...

Natalie 3k

They represent the different orientations of the electrons in the atom. They are the different orbitals in the p subshell, so basically the three different positions of those electrons.

Natalie 3k

I believe it comes down to the electronegative of the atoms, so it depends on which you're looking at. The more electronegative it is compared to the atoms it is bonded to the more likely it is to follow the trends seen on the periodic table, (like oxygen having a -2 charge).

Natalie 3k

Hi! I believe this is because it would cause nitrogen to have 5 bonds, the two double bonds and a single bond, which wouldn't be very stable.

Natalie 3k

Hi Stella! I had this question too. I've been doing what the UA said and starting from the previous noble gas, but I'm not sure if both are correct or if one is preferred.

Natalie 3k

Usually I just watch tv or workout, (which isn't very relaxing sometimes), but I've been trying to do yoga recently and it's pretty fun!

Natalie 3k

Hi, I come across this problem a lot too, but it helps me to write out each equation with units every step of the way, without skipping steps. Hope it helps!

Natalie 3k

Can someone please explain how to start this problem? The incident radiation had a wavelength of 1064 nm, and the ejected electrons were found to have an energy of 0.137 eV. The electron affinity is the difference in energy between the incident photons and the energy of the ejected electrons. Determ...

Natalie 3k

Can someone please explain how to find the number of electrons in an Atom based on the Quantum number? I'm getting stuck on what the l means and how it factors into how many electrons there are. Thank you!

Natalie 3k

I've been watching Lucifer on Netflix! Really funny, gets interesting and I think another season is coming out soon!

Natalie 3k

This has been confusing me too, but I believe work function is the energy needed to remove an electron from a surface, and this energy must match the energy of the photon for the electron to be removed. I think the problem has to give you the work function if you are supposed to use it, or if you kn...

Natalie 3k

I'm not sure if this is what you're asking, but I believe an electron cannot be in between energy levels, if it doesn't have enough energy it will just remain at the lower energy level. Not too sure about the circular standing wave I was curious about that too.

Natalie 3k

Hydrogen bonds are the weakest, and I believe ionic bonds tend to be stronger than covalent because of the different charges on the ions and the electronegativity differences, except when placed in water or some solution covalent bonds are stronger.

Natalie 3k

Hi! I had a question of one of the problems from sapling which is, suppose the typical work function of the metal is roughly 4.170×10−19 J. Calculate the maximum wavelength in angstroms of the radiation that will eject electrons from the metal. What would be the first step to solve this? I tried loo...

Natalie 3k

Since most of the topics relate to each other in some way, I've just been compiling everything into one document. I make sure I label everything appropriately so it is easy to find later on. The only thing that helps me retain information better is repetition and practice so I go over my notes multi...

Natalie 3k

If I understand your question and the topic correctly, then the energy required to remove an electron would be the lowest the energy of the photon could be. So if the photon is going to remove the electron it must have the same or more energy than the required energy. I'm not sure if you can assume ...

Natalie 3k

Adding onto what everyone else said, because photons have no mass, they get all their energy from their momentum. Which is why light is never at rest if I'm correct.

Natalie 3k

From what I've read as well, intensity is the square of the amplitude so they are proportional but not the same thing. They are both related to the amount of energy a wave has.

Natalie 3k

The gaps become smaller as energy levels increase because the farther away from the nucleus the electrons are the less the pull from the protons is. So the farther away the electron is the less energy is needed, so the gaps decreases.

Natalie 3k

When converting units it makes it easier for me to write them all out as fractions so I can see and make sure the appropriate ones cancel out. That way I can easily see which units go where. I usually convert before calculating but am not sure if it can be done after as well.

Natalie 3k

You have to find the molar mass of the empirical formula and the molar mass of the molecular formula and then find the ratio between them. Then you multiply that by the number of atoms in the empirical formula. So if the molar mass of the molecular formula is 3x as much as the molar mass of the empi...

Natalie 3k

I believe he mentioned that on tests we will be given conversion factors and some formulas but I could be mistaken.

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