CHEMISTRY COMMUNITY

Yichen Fan 3A

Wait is it cumulative or...? Based on a weekly basis? Will I be able to get my points back even if I didn't post for a week but I still already posted over 50? I'm pretty sure it is cumulative for 50 posts total because Dr. Lavelle said people can still make up for the points before tomorrow 9:00 am.

Yichen Fan 3A

You can still make up for it before 9:00 am Tuesday. As long as you have over 50 posts total for this class you will be fine. Also you can check how many points have been rewarded through your ccle at the grade category.

Yichen Fan 3A

Yeah, for the reverse reaction you will just have negative deltaH and deltaS which if you put into deltaG = deltaH - TdeltaS, it will be a spantaneous reaction below certain temperature.

Yichen Fan 3A

Like you said in the question, we will use E = Eº - (RT/nF) lnQ in all the cases and E = Eº - 0.0592/n logQ at standard condition because basically in the second equation they calculated out all the constant for you. For problem of ln and log, you can always convert between them using: log10(x) = ln...

Yichen Fan 3A

I think it is most likely to be a rounding problem because there are 3 sig figs in the problem but you rounded to 1 sig fig in your answer which is too vague.

Yichen Fan 3A

I think it will depend on which experimental data you have. If you conduct multiple experiments using different initial concentration, you can use method of initial rate to find the order of the reactant and k. If you choose to measure multiple concentrations at different time during a single reacti...

Yichen Fan 3A

I haven't done the question but I think you can take the natural log of the Arrhenius equation to get this: lnk = lnA - Ea/RT, if you graph lnk on the y-axis and 1/T on the x-axis, the slope of that line will be -Ea/R which allows you to find Ea.

Yichen Fan 3A

To test the intermediate species we proposed in a mechanism we can conduct further experiment to look for that species during the reaction. For example, we can go test for existence of NO3 when NO2 reacts with CO. But again even if we do find NO3 we can still not prove our mechanism is the complete ...

Yichen Fan 3A

Yeah like the previous posts have said, you can treat 1/a as a constant through integration and even just pull it out of the integration and multiply it to the final equation afterward. The integrated rate law will just be like 1/a*ln[A] = -kt + ln[A]o.

Yichen Fan 3A

Yeah, pseudo rate law k' exists because in a reaction involving three reactants, we assume two of them as constant. In real case they will be concentration with their own order of reaction, therefore k' is very different from the actual k. You can use k = k'/([B]^m*[C]^l) to find k from k', but make...

Yichen Fan 3A

can someone please remind me what exactly molecularity is used for again? i understand how to find it (i think) but im still a bit confused on what to do after that. Molecularity is the number of molecules that collides to from one molecule of product. For example, if 2 molecules are involved in ma...

Yichen Fan 3A

The k' will not be the same for each reactant. For a reaction A + B + C ---> P, if we are conducting an experiment with excess B and C, we can find the actual rate constant k using k = k'/([B]^m*[C]^l). If we are conducting an experiment with excess A and C, k = k'/([A]^n*[C]^l). Since the concentra...

Yichen Fan 3A

No, they are not the same. If you use ln, the Nernst Equation is E = E°- (RT/nF)lnQ; if you use log, the Nernst Equation is E = E°- (2.303RT/nF)logQ. You can pick either form of the Nernst Equation, but don't mix them together. I think they developed a log form because log is easier to calculate tha...

Yichen Fan 3A

Unlike average rate and the instantaneous rate which can change depend on what time you choose to measure them, a unique rate is the same for each reactant and product in the same reaction. It's a better indicator telling you how fast the reaction goes by showing the rate of reactants disappearing a...

Yichen Fan 3A

Austin Aldujaili 2D wrote:Also, you do not need to convert the H2 from a pressure into a concentration, you can find Q by using the given values for [H+] and PH2

Why can you just get Q from two different units? I think we can get concentration of H2 using PV=nRT, and n/V will be the concentration in molarity.

Yichen Fan 3A

I think metals rarely form anions, therefore they always have priority on a positive oxidation number. Oxygen is always 2- unless it sometimes forms H2O2 with hydrogen. Oxidation number for nonmetals like Cl, N, P, and S varies a lot, so usually we deal with them at last in a compound.

Yichen Fan 3A

Based on how I did the sapling questions, you add H+ on either side if you need extra hydrogen atoms and if the solution is acidic, you're done. If the solution is basic, add equal amount of OH- to neutralize that H+ and you will get one side with H2O and the other side with OH-. If you need extra x...

Yichen Fan 3A

Oxidizing agents oxidize other molecules, so they take away electrons from other molecules. Reducing agents reduces other molecules, so they give the electrons away. Whenever I think of the agents, I just associate them with the compounds that initiate the process.

Yichen Fan 3A

I don't think there is a difference between them because they have the same purpose of allowing the flow of ions. And they definitely won't affect the calculation for standard cell potential. I would assume that people use porous disc because they get tired of the cumbersome of two beakers and a sal...

Yichen Fan 3A

If there is no salt bridge, the imbalance in concentration graduate due to the entering or the leaving of metal ion will counter the electro potential. As a result, the electrons will stop following very soon.

Yichen Fan 3A

A free element is an element forming a compound on its own. The overall charge of a compound should be 0, therefore any compound with one element will make the oxidation number of that element 0. Oxidation number is a charge we assume on the atoms if the bonds between them are completely ionic(no sh...

Yichen Fan 3A

For me it is helpful just to remember that cathode is the positive end, and because electron is negatively charged it will flow toward cathode. Cathode gains electrons as a result, therefore it is reduced. On the other hand, anode loses electrons so it is oxidized.

Yichen Fan 3A

Yeah they are the same equation. Dr. Lavelle factored out the negative sign in the lecture while the textbook didn't and switch the 1/T2 and 1/T1, it might be a little bit hard to see the negative sign on the lecture slide due to the quality of the video.

Yichen Fan 3A

∆G has to equal to 0 when a reaction is at equilibrium because if ∆G is not equal to 0, the reaction will favor either the product side or the reactant side, causing a net change in concentration of product or reactant. The definition of equilibrium is that there is no net change in concentration of...

Yichen Fan 3A

Adding on to other comments, because your ΔG is a quite large negative number, the reaction will strongly favor the product side, therefore you should expect to get a very large K value. If your answer is very large, I will check the scientific notation; if you get a small number, I will suggest che...

Yichen Fan 3A

K = [Product]/[Reactant], if K < 1 then it means there is more reactant at equilibrium, so the forming of reactant will be favored and deltaG0 will be positive(forming reactant is spontaneous). On the other hand, if K > 1 then there is more product at equilibrium, the forming of product is favored, ...

Yichen Fan 3A

ΔS refers to the difference of entropy between the liquid and the gas, the smaller this ΔS means there is a smaller difference in entropy between the liquid phase and the gas phase of that substance. If a liquid has a closer entropy value to its gas then it must be really disordered with a high S. O...

Yichen Fan 3A

I agree with the previous post that the position is relative to each other. If you have two atoms in a molecule, you only have two spots for them to go in. As a result, they either go to the "left spot" or the "right spot", or you can use a different term "top spot" or ...

Yichen Fan 3A

Cp is the molar specific heat for gas at constant pressure, if the pressure is kept the constant then the volume must have changed, therefore the q you calculate is in fact ΔU - w. Cv is the molar specific heat for gas at constant volume, if the volume is kept constant then no work can be done, the ...

Yichen Fan 3A

Thank you so much for listing out the unit conversion step! I keep using the R for L*atm and cannot figure out the answer until I saw you multiplying the answer with 101.325.

Yichen Fan 3A

If the question is talking about the work done by the reaction, then it is asking for change in gas volume(ΔV in nongas reactants is negligible). And yes, you will use w=-PΔV to calculate the work. Find the amount of gas produced by the reaction in moles, use the ideal gas law to find the volume cha...

Yichen Fan 3A

Just like the equation q=-w, it is impossible for all the heat being converted into work; the "reversible equilibrium" also cannot happen in real world, but like we calculate heat transfer without considering the heat lost, we calculate the maximum work assuming that reversible equilibrium...

Yichen Fan 3A

The difference between specific heat capacity and specific enthalpy is essentially the difference of heat capacity and enthalpy. Heat is the energy we refer to during a process of transfer and heat capacity is just heat divide by temperature change, enthalpy is the energy contained within the system...

Yichen Fan 3A

When you increase temperature of a gas, it will try to expand in volume. If you keep the volume constant during that process(doesn't allow piston to move) you will use Cv in calculation. On the other hand, if you allow the piston to be pushed back by gas, the pressure remains the same as before, the...

Yichen Fan 3A

I think you need to memorize them. If we encounter a less common element in a question, the actual reaction for the enthalpies of formation needs to be given anyway if we want to do calculation about it.

Yichen Fan 3A

We learned about heat transfer and specific heat capacity(c) in Monday's lecture(at 20 minute), that calculation is also briefly mentioned in it. However, I don't think Dr. Larvelle went over a specific question about that formula.

Yichen Fan 3A

The ice must go through phase change before its temperature can be raised, that is where the standard enthalpy of fusion is needed. You can set the final temperature as x and set up an equation which one side is the amount of heat required for ice to reach x and the other side is the amount of heat ...

Yichen Fan 3A

Yes to both questions. Any number provided in form other than constant contributes to the sig figs, and you want to round to the one with least accurate measurement.

Yichen Fan 3A

Formation of bond release energy, therefore formation of C-H bond will give off energy from the system to the surrounding. On the perspective of the system, it is losing energy so the formation of this compound will have negative enthalpy.

Yichen Fan 3A

Heat q is not an intrinsic property of the system. If there is a glass of water, you can find out its mass, volume, enthalpy but you don't know the answer to what's the heat of this glass of water. Heat is only used to describe a flow of energy either into or out from the system not the amount of co...

Yichen Fan 3A

In the first method of using Hess's law, the delta H that is given is for the NO reaction. It doesn't specify that all the reactants and products are in the standard condition; therefore, it is possible that delta H of that given reaction is different from the standard enthalpy of formation for NO. ...

Yichen Fan 3A

Yes I believe they will all be 0, since there are only 7 diatomic elements (H, N, F, O, I, Cl, Br) and according to the lecture these are their most stable state in standard condition.

Yichen Fan 3A

pKa of a weak acid is the negative log of Ka = [H3O+][A-]/[HA] which [A-] is the conjugate base of that acid after losing the proton. pH is the negative log of [H3O+]. If pKa equals to pH then Ka = [H3O+], therefore [A-]/[HA] = 1. There are equal amount of HA, the neural form of that weak acid, and ...

Yichen Fan 3A

You can think of heat as a product of an exothermic reaction. Increasing temperature is equal to adding heat to the reaction therefore according to the le Chatelier's Principle the equilibrium will favor the other side which is the reactant.

Yichen Fan 3A

Hi, you can first calculate the Kc value base on the given concentration because it is already at the equilibrium. When you are setting up the ice table for every 2 mols of NO used, you gain 1 mol of N2 and 1 mol of O2 so it will be: [NO]=0.8-2x; [N2]=0.3+x; [O2]=0.3+x.

Yichen Fan 3A

Like the previous posts have said, ionization refers to the lost of proton which can also be considered as how much it dissociates in water, therefore it refers to the acid; protonation is the addition of proton and it refers to the base. The calculation process is the same, and you just need to kee...

Yichen Fan 3A

Yes, Ka of an acid multiplies with the Kb of its conjugate base is equal to Kw and vice versa. Ka and Kb can be calculated through that relationship between a pair of acid and its conjugate base but the naming is remained unique to its chemical properties as an acid or base.

Yichen Fan 3A

Like most posts have mentioned Q compares to K in a reaction does not tell you the stability of reactant or product. However, the value of K does tell you which side of the reaction is favored(large K favors product and small K favors reactant) and when we talk about favored side it is generally mor...

Yichen Fan 3A

Bar is the SI unit for the gas pressure and 1 bar is very close to 1 atm so we can use either of them, when the gas is presented in mols per liter it is showing its concentration and can be converted to pressure through ideal gas law.

Yichen Fan 3A

You can think of heat as a product of an exothermic reaction, therefore when you increase temperature, it is the same as adding heat to the product side of the reaction therefore more reactants will be produced. Same with endothermic reaction, you can think heat as a reactant required for the reacti...

Yichen Fan 3A

Yes because when you solve for x in the equation you usually multiply the K constant and the x together to form one term in the quadratic formula, if x itself cannot be larger than the initial concentration(in your case 0.1) and K is very small <1*10^-4 their product will be less then 1*10^-5 which ...

Yichen Fan 3A

It is possible that when you suddenly add a lot of N2, all the H2 in the system will react with those N2 and become the limiting reactant. However, if you wait for the equilibrium to be reestablished some of the newly formed NH3 will eventually break down back to N2 and H2, since the concentration o...

Yichen Fan 3A

On my ccle site although I can see all the names of TAs, only one of them has its name connected to a link to the zoom meeting. I think whoever's name you are able to click on and join the meeting, that is your TA for discussion.

Yichen Fan 3A

Metal oxides contain ionic bonds so they will split into ions in water BaO into Ba2+ and O2-, and that O2- causes water to be basic. Nonmetal oxides mostly stays in water as a single molecule, you don't see SO3 splits into S6+ and O2-, and SO3 can accept more electrons, therefore it makes an acid.

Yichen Fan 3A

Claire_Kim_2F wrote:What happens if it is anionic is it still aqua or would it be aquate?

It will still be aqua, -ate is only added to the end of metal name if the complex is an anion.

Yichen Fan 3A

It's always the final energy state minus the starting energy state. If the electron is raised to a higher energy level, n1 will be greater than n2; if the electron emits light and falls back to a lower energy level, n1 will be smaller than n2.

Yichen Fan 3A

I still don't quite understand why the molecule will form T-shape instead of trigonal planar. I know that if there is one lone pair it will form seesaw because the electrons don't want to be at axial forming three 90 degree bonds with atoms, but when there are two lone pairs won't they try to stay f...

Yichen Fan 3A

The lectures are working for me now but not before 11am. I guess it's due to some problems of ccle and we just need to watch the lectures when we can :)

Yichen Fan 3A

Is the acid itself being more electronegative make it a stronger acid or is it the conjugate base ? This is where equilibrium comes into play, a more electronegative atom means the proton will more likely to break off, and whether that proton stays with water or bind back to the atom is also up to ...

Yichen Fan 3A

It is possible if the molarity of hydrogen ion is greater than 1. If you have 5M HCl solution, -log(5)=-0.7

Yichen Fan 3A

Coordination numbers are numbers of bounds the central metal formed in a coordination compound; regions of electron density is different, it is used while determining the molecule shape therefore electron lone pairs also count as regions of density.

Yichen Fan 3A

The lectures was working for me around 5:30pm but suddenly stopped loading. Now it is just showing error code.

Yichen Fan 3A

A tip if you are thinking about switching into a different life science major. I am currently in biology major and my department counselor strongly suggested me to think about changing major after taking LS7ABC. LS7 series was basically an intro class to biology which corresponds to different topics...

Yichen Fan 3A

Thank you Silvi, that is an excellent visual aid and it helps a lot for me to imagine the interaction!

Yichen Fan 3A

Dr Lavelle mentioned in the lecture that a common structure for bidentate molecules is a lone pair + two spacing atoms + another lone pair. In the example of EDTA4-, if you choose lone pair on nitrogen as the first lone pair, then tracing the structure with spacing atoms(2 carbon), you will find ano...

Yichen Fan 3A

Yes, the electrons in unhybridized 2p orbitals are delocalized; those delocalized electrons form delocalized pi bonds perpendicular to the molecule. Essentially delocalized pi bonds will only appear when there are resonance structures for molecules which involves double or triple bonds.

Yichen Fan 3A

it depends on its ground state electron configuration. Since C ends at 2p. the hybridization orbital is 2sp Is the hybridization of ground state C 2sp because of the 2 electrons in the 2p shell? If it is could someone explain why because I thought the other valence electrons of C could still contri...

Yichen Fan 3A

Like most people have mentioned, double bond still counts as one region of electron density in hybridization. Also don't forget lone pairs as region of electron density as well.

Yichen Fan 3A

Yes, if the molecule is symmetrical then it is nonpolar regardless of the difference in electronegativity. However, you do need to make sure that the atoms attached to the central molecule are all the same. CHCl3 is in a tetrahedral shape which is considered symmetrical, but the dipole moments does ...

Yichen Fan 3A

Do the electrons in hybrid orbitals have different properties/characteristics compared to electrons in their normal orbitals? Will hybridized electrons behave differently? Also, does hybridization and the mixing of orbitals affect the shape of an atom or molecule? Electrons are electrons and they d...

Yichen Fan 3A

I'm going to use this answer I provided for a similar question about hybridization. Like Dr. Lavelle mentioned at the very end of the lecture, we find out the shape of the molecule through VSEPR model first and then use hybridization to explain the bond in that shape. In the case for carbon, we foun...

Yichen Fan 3A

Yes, the net vector is the end product of all the vectors combined in a molecule. It is the vector that ultimately matters and will lead an overall effect on the molecule. Just like net weight you see on a bag of chip, the total weight of that bag of chip is 200g, but the bag is 20g, therefore the n...

Yichen Fan 3A

Like Dr. Lavelle mentioned at the very end of the lecture, we find out the shape of the molecule through VSEPR model first and then use hybridization to explain the bond in that shape. In this case for carbon, we found that there needs to be 4 sigma bonds distributed all equally around carbon so we ...

Yichen Fan 3A

The potential energy of london dispersion force is directly proportional to the polarizability of an atom. And the polarizability of an atom is related to the size of the atom. Larger atoms means the outer electrons are more loosely held, therefore they can be polarized more easily to create a tempo...

Yichen Fan 3A

I definitely agree with the explanations that have been posted, oxidation number is usually not a good way to determine the resonance structure because it is treating a bond as if the bond is completely ionic: the more electronegative atom will get a -1 charge, and the less electronegative atom will...

Yichen Fan 3A

We definitely need to consider electron lone pairs while determining the shape of a molecule, the shape of NH3 molecule is actually trigonal pyramidal because the electron lone pair will push the other bond away. 4 electron pairs are distributed as a tetrahedral shape, but since one of them is lone ...

Yichen Fan 3A

You can definitely use all these terms interchangeably and there is nothing special about the hydrocarbons. I think professor prefer induced dipole-induced dipole because it actually describes what is going on to create the attraction, instead of just showing someone's last name :)

Yichen Fan 3A

For intermolecular force, larger size means more electrons can be polarized, leading to a greater induced dipole-induced dipole attraction (At room temperature, I2 is solid, F2 is gas). For intramolecular force, larger size means longer bond length, leading to a weaker bond strength (HF bond is stro...

Yichen Fan 3A

This is a great example of how ionic bond containing characteristic of covalent bond due to polarization since you will expect ionic compound to dissolve in water and covalent compound don't. The result of this experiment is also easily observed as you see obvious difference in solubility in test tu...

Yichen Fan 3A

I totally agree with all the explanations that have been posted, just to make things clearer: London dispersion force is caused by the temporary polarization of the electron in atoms, therefore the more electrons an atom has a stronger London dispersion force it will possess, which means that the bi...

Yichen Fan 3A

Like most people have said the electron spin is not found by the mathematical equation. In fact it was a property that is not confirmed until the experiment of electron beam passing through the magnet. The scientist found that when an beam of electron passes through the magnet it splits into two, on...

Yichen Fan 3A

If you are still unsure, you could compare the formal charge when the atoms are placed differently. what do you mean by comparing the formal charge when the atoms are placed differently? For example if you have a CO2 molecule, putting an O in the middle and forming two double bonds on both sides wi...

Yichen Fan 3A

Yes, ionic bonds are typically formed by elements from two sides of the periodic table. Different types of bonds between atoms are determined by their difference in electronegativity, halogens usually have very high electronegativity so they gain electrons and metals have low electronegativity there...

Yichen Fan 3A

Karen Elrayes 1L wrote:We don't need to do any problems from section topic 1C right?

Nothing for 1C, for testing topics and textbook problems related to each topic there is an outline on Dr. Lavelle's Chemistry 14A website under "learning outcomes".

Yichen Fan 3A

Basically 2 things you're looking for in each wave:
1. The frequency and amplitude need to be constant
2. In the given segment of wave it must complete whole number of cycles (each cycle is where it begins to repeat itself)

Yichen Fan 3A

Dimensional analysis is basically writing out all the units for numbers during calculation and trying to cancel them out at the end. It always starts with a "start unit", the unit you are given in problem; and it ends with the "end unit", the unit of the answer you are looking fo...

Yichen Fan 3A

Intramolecular bonds are bonds within a single molecule, in others words it is bond between atoms which forms that one molecule. Intermolecular bonds are attraction forces between two molecules, a classic example will be Hydrogen bond: a hydrogen atom attracting to an electronegative atom from anoth...

Yichen Fan 3A

Whether a bond is polar covalent or nonpolar covalent or iconic can be determined by the difference in electronegativity between the atoms. Typically less than 0.5 is nonpolar, between 0.5 and 2 is polar covalent, greater than 2 is ionic. The electronegativity value of elements can be found easily b...

Yichen Fan 3A

My TA said for concept about the topics just understand everything Dr. Lavelle mentioned in class lecture. If you are reading extra information from the book then it is good for further understanding but they won't be applied to specific question on the exam.

Yichen Fan 3A

Yes, it still stay positive and wavelength is always positive. Think about the problem in this way: electron loses energy while dropping from a higher number of n to a lower one, therefore the energy is negative for electrons; the light that got emitted gains energy from the electron, therefore the ...

Yichen Fan 3A

If you're plugging in the energy to solve for other components then you should use the same sign that is given by the problem. The number n and frequency v is always positive in the answer.

Yichen Fan 3A

Pranav Daggubati 1A wrote:I think that its because the orbital is very similar looking to a hyperbolic functions

My mistake! I do find in other videos that people call it "x square minus y square" orbital, I think you are right about it has something to do with the hyperbolic function.

Yichen Fan 3A

I don't see any reason why the y should be negative in the orbital expression. I'm believe that it is just a dash connecting x^2 and y^2 to indicate them being a term together. dxy orbital locates in-between axis and dx^2-y^2 orbital locates along the x and y axis.

Yichen Fan 3A

I am still confused by electron skipping energy levels. To put in the context of orbital, if an electron is excited from level 1 to level 4, does it travels through p and d orbital and finally enter the f orbital, or it goes straight from s orbital to f orbital.

Yichen Fan 3A

I will assume that as long as the problem does not specify, we can use which ever makes more sense in the context of the problem. For me personally I like to use nm only for wavelength that are in or fairly close to the visible region. Also most of the questions will be online in form of multiple ch...

Yichen Fan 3A

A black body is not really black, in fact you can never see it because it absorbs the lights of all frequencies and nothing will be reflected into your eyes. We call it a "black" body simply because black is the color that absorbs all the visible lights in our daily life which best resembl...

Yichen Fan 3A

Just like you stated in the question, increasing frequency increases energy per photon according to E = hv. Increasing intensity only increases number of photon which does increase the total energy of the light beam. However, as long as individual photon doesn't have enough energy to knock out the e...

Yichen Fan 3A

Yes, the energy required for each element to excite its electron from ground state to the next level is different. There are different numbers of protons in different atom of elements. As the proton number increases, the attraction between proton and its electron also increases which gives each elem...

Yichen Fan 3A

If the calculation is addition in the first case your will round to one decimal place 5.9 + 8.79 = 14.7 because 5.9 has one decimal place, and 8.79 has two decimal places(round to the least decimal number). For multiplication you need to count the total sig fig of each number in the given problem an...

Yichen Fan 3A

Wavelength decreases as you move from color red to color purple(700nm - 400nm). They are all classified as visible light and only takes up a very small part of the EM Spectrum which is between 1 micrometer to 100 nanometer. In the lecture the EM spectrum includes other lights as well and their wavel...

Search found 104 matches