CHEMISTRY COMMUNITY

Anil Chaganti 3L

I really hope they don't differ too much from the textbook though. As long as we know the concepts, we will be fine.

Anil Chaganti 3L

Dr. Lavelle went over the plots of the integrated rate laws of first, second, and zero order of reactions. To emphasize, first order reactions are linear when you plot ln[A] vs t (negative slope=-k). This means that when you plot [A] vs t, you will obtain an exponential graph. Second order reactions...

Anil Chaganti 3L

As the galvanic cell proceeds, it uses up its voltage potential because we can think of a galvanic cell as a battery that is using up voltage. Ecell equals zero at equilibrium, and Enaught is the electromotive force or the maximum potential the battery as to start off with.

Anil Chaganti 3L

For reactions that do not favor products, E is less than zero. This means that the reaction is not spontaneous, as deltaG=-nFE shows us that a positive delta G (negative E) produces a value greater than zero. As we know from thermodynamics, this means that the reaction does not favor products.

Anil Chaganti 3L

Yes, I believe that an open system has constant pressure since it is exposed to atmospheric pressure which is rather constant throughout. Any additional pressure is negligent compared to atmospheric pressure, so we can assume that an open system has constant pressure.

Anil Chaganti 3L

I think we can use thermodynamic concepts. For example, if you are forming a product from simple elements usually that means you are releasing energy, so it is exothermic (NH3 formation is exothermic from N2 and H2). Endothermic reactions break bonds, thus requiring energy. I hope this helps!

Anil Chaganti 3L

Yes, you are correct. E0cell is 0 V in a concentration cell because the same substance is being reduced and oxidized in different electrodes so the standard E will be 0. However, Ecell is not 0 because there are differing concentrations, which makes it have a difference in potential.

Anil Chaganti 3L

Cathodic protection is used for large metals, such as ships or pipelines, that simply can't be protected by a paint coating from oxidation. Usually, a cathodic protection is a substance that is more oxidizing (greater reducing agent) than the substance it is required to protect. This is important be...

Anil Chaganti 3L

I don't think any new equations have been added, but I am wondering why the equation using two different temperatures and two different rate constants are on the equations sheet. Do you know if that will be added?

Anil Chaganti 3L

A pseudo first-order reaction is one that has two different molecules colliding to produce a product, but one of them is largely in excess, thus not affecting the rate. For example, if you have a diluted solution of Fe2+, that means that only the Fe2+ concentration will affect the reaction rate, so ...

Anil Chaganti 3L

Solid metal conductors are used to transfer electric currents. However, if you have an ion that is being oxidized or reduced to another ion in the same electrode (ex: Fe3+ to Fe2+ in the cathode), you don't have that solid metal conductor present. Therefore, you must need an inert conductor, which i...

Anil Chaganti 3L

Hey! For this question, I would use the Nernst equation. Remember that in Q, it is always the concentration of anode over the concentration of cathode, thus making the substances in the cathode the reactants of the reaction. When you increase reactant concentration, log Q is decreased (depending on ...

Anil Chaganti 3L

Intermediates are usually produced and then consumed throughout the reaction. For example, let's say it is a product in step 1 of the reaction mechanism. In step 2 (or3), it will appear as a reactant and then will be consumed, thus not appearing in the overall reaction. A catalyst is a substance tha...

Anil Chaganti 3L

For this question, you have to use the Arrhenius equation: ln(k2/k1)= -Ea/R(1/T2-1/T1). You can plug in 4.5k for k2 since k2 is 4.5 times faster than k1 and it will simplify to ln(4.5). Next, for activation energy plug it in terms of J/mol. Plug in the rest of the information and solve for T2. This ...

Anil Chaganti 3L

There is a typo in this section because the other Cl2 on the products should say Cl-. That is why I was confused initially as well. The two half reactions would be Cl2 ---> HClO and Cl2 ----> Cl-. Hope this helps!

Anil Chaganti 3L

I believe what you are asking about applies to a concentration cell, in which case E naught is always zero and E is a different value. You may apply and account the differences in the Nernst Equation. Hope this helps!

Anil Chaganti 3L

I had a bit of trouble with this one, but I realized that O2 and H+ (or OH-) are both the reactants since they combine to form water. Water is not included in the cell diagram as the aqueous phases of the reactants compensates for the necessity to include water. Use both as necessary. Hope this helps!

Anil Chaganti 3L

Adding more onto what the previous person stated, for acidic solutions you may have H+ left over since there is a greater H+ concentrations for acidic solutions and for basic solutions, you may have OH- left over as there are more OH- ions in basic solutions. However, this may not always be the case...

Anil Chaganti 3L

How come there was a single line between copper 2+ and copper (solid) in the cell diagram but no single line between iron 3+ and iron 2+? Could someone please clarify this? I understand that is is a porous disc but I am a bit confused.

Anil Chaganti 3L

To calculate Ecell, the formula is Ecathode minus Eanode. if that is the case, how come Dr. Lavelle simply did .77V-0.34V for the reaction between copper and iron? How come he didn't do .77V-(-0.34V) for the Ecell? Could someone explain this please?

Anil Chaganti 3L

Since the problem is asking for the entropy of the surroundings, which is -delta H system over temperature, wouldn't the answer be -.341J/K times S and not positive? Can someone please explain this?

Anil Chaganti 3L

I would remember how vibrational energy correlates to more entropy in a diatomic gas compared to a diatomic gas with no vibrational energy. At least according to the textbook problems, that seemed to be the only moment when we applied this. I am not exactly sure though.

Anil Chaganti 3L

Hey, are you sure you are referring to the correct problem? The answer for 5G.13 seems to be .83kJ/mol. You solve this by setting delta G equal to delta G naught plus RTlnQ. You can substitute -RTlnK for delta G naught. Then, plug in all the information given and solve. Hope this helps.

Anil Chaganti 3L

According to the 2nd law of thermodynamics, when delta G is less than zero (spontaneous), the entropy of the universe (or the total entropy) cannot be zero or less than zero and must always continue to increase. However, we cannot predict the sign of delta S system or surroundings just based on the ...

Anil Chaganti 3L

What is the relationship between ideal gas and a real gas? Does an ideal gas occupy more or less volume at higher pressures compared to real gases? Is the relevant to our midterm and can we expect to see it?

Anil Chaganti 3L

Are we allowed to use this on the exam or is it only the equations sheet on your website?

Anil Chaganti 3L

On Sapling, they explained that the greater the molar entropy of a liquid, the more ordered it is. However, I thought entropy indicated disorder. How come a larger molar entropy for liquids indicate higher order? Can someone please explain this? Also, could someone rephrase how to determine which mo...

Anil Chaganti 3L

Since isobaric indicates a constant pressure, would w equal 0? In this case does delta U equal q? How does delta S change according to isobaric conditions? Could someone please explain this?

Anil Chaganti 3L

Why is internal energy under isothermal, reversible conditions zero and q is the opposite sign of work? If there is no temperature change, then wouldn't q be 0. I understand that w will have a value since there will be work being performed. Then wouldn't delta U just equal the value of work and q is...

Anil Chaganti 3L

Hey! At Kate's workshop yesterday, she explained that we set delta G equal to 0 to find the minimum/ maximum value at which temperature the reaction reaches equilibrium. If you recall, at equilibrium delta G equals 0. Therefore, if we find the temperature at equilibrium, we can essentially determine...

Anil Chaganti 3L

I believe delta H and q are interchangeable at constant pressure. This is because the heat transfer will directly correspond to a change in enthalpy.

Anil Chaganti 3L

C6H12O6(s) + 6 O2(g) → 6 CO2(g) + 6 H2O(l) Suppose a researcher finds that ΔHorxn = -2756 kJ for the reaction at 200. C. Assuming all heat capacities are constant at different temperatures, calculate ΔHrxn at the temperature of the human body (37 C). (C values were given in a table) Hint: Since enth...

Anil Chaganti 3L

I don't think we are expected to memorize them because we have been given the charts on the worksheets and in the textbook. If given, just substitute them into C. I would just check the learning concepts too just to make sure.

Anil Chaganti 3L

Hi,
You could calculate work by applying the formula w=-nRT since you are given moles and temperature. Then, you can calculate q by using ncdeltaT by using 4(8.314) for C, 18.7, and use the number of moles given. Then add the two values together to get delta U.
Hope this helps.

Anil Chaganti 3L

For work, when is it negative and when is it positive in terms of a reaction? If temperature increases, does that mean work is negative? I understand the overall concept that work is negative when volume is expanding and positive when volume is compressing but I am a bit confused about how to apply ...

Anil Chaganti 3L

Hi,
Right now, I have a 21/25 for Chemistry Community posts. However, shouldn't we have a minimum of 20 posts since we have not completed week 5 yet? I am just making sure I didn't miss anything.

Anil Chaganti 3L

Last year, Dr. Lavelle needed to take his time in ensuring that the tests were graded fairly and that there were no errors. Therefore, I believe they should be updated in about 1.5 weeks, as last time was approximately around that time. Hopefully it is soon though!

Anil Chaganti 3L

I often find it extremely hard to maintain a solid work-life balance and exercise my mind and body, as Dr. Lavelle advises us to do. I struggle with this because of the amount of work and anxiety I constantly have with being home and going to several zoom sessions. What do you guys recommend to do t...

Anil Chaganti 3L

If you are solving for the standard enthalpy of formation of a molecule using Hess's law, are you allowed to rearrange the equation to be solving for the enthalpy of formation for the reactant molecule or the product molecule since Hess's law is a state function?

Anil Chaganti 3L

Could someone please explain to me how this problem would work since it involves several phase changes?
What amount of energy is required to change a 90 gram ice cube at -10 degrees Celsius to vapor at 110 degrees Celsius? Do I add the heat of sublimation or vaporization? How would this work?

Anil Chaganti 3L

I know this was not a problem assigned, but I was doing some extra problems and had a question about how the internal energy and work work for this question: Each of the four cylinders of a new type of combustion engine has a displacement of 3.60 L. (The volume of the cylinder expands by 3.60 L each...

Anil Chaganti 3L

I was wondering about* the same question. Please excuse my grammar haha.

Anil Chaganti 3L

Hi, I was wondering the same question. However, when I researched this question, I found that electronegativity plays a role in bond enthalpy, As the electronegativity (or the pull) increases between atoms, bond enthalpy also increases as the bond is now stronger and requires a greater amount of ene...

Anil Chaganti 3L

Hi, I was doing sapling and it asked me to identify whether going from a liquid to gas was endothermic or exothermic. Could someone in their own words explain why this process would be endothermic. I assumed that heat is being released so it would be exothermic. Also, if this phase change is endothe...

Anil Chaganti 3L

Hi, so going from a weaker bond to a stronger bond is endothermic because you are gaining heat when you are forming a stronger bond. Additionally, it takes more energy to break a stronger bond than a weaker bond so the enthalpy change (products minus reactants) would be positive because the enthalpy...

Anil Chaganti 3L

I was wondering the same thing. However, I asked the UAs and remember from lecture that the standard enthalpy of formation for the most standard state of an element is 0. So, when looking at the tables related to standard enthalpies, just remember that the phase with the 0 standard enthalpy of forma...

Anil Chaganti 3L

Hi! I went to a UA's drop-in hours and was told that standard enthalpy of formation refers to any reaction at 1 mol and standard pressure. This can be endothermic or exothermic. For example, the reaction between carbon (as graphite) and hydrogen gas forms CH3CH2OH (unbalanced); this uses standard en...

Anil Chaganti 3L

Hi, Essentially, having either the hydronium ion or the conjugate base would be the same thing since they tend to have the same stoichiometric concentrations. However, I would go with Dr. Lavelle's method of having the conjugate base in the numerator as ionization refers to how much the acid has ion...

Anil Chaganti 3L

I understand how Le Chatelier's principle works for regular chemical reactions. However, can someone explains how they would affect pH and pOH? Is there any quantifiable relationship that we can identify? Additionally, for weak acids and weak bases, do pKa or pKb change because I assumed the K const...

Anil Chaganti 3L

I know Dr. Lavelle went over this in lecture, but to find the pH of salts, for example in 6D 17 (Calculate the pH of (a) 0.63 m NaCH3CO2(aq)), would you use the Kb value as CH3CO2 would be a proton acceptor and generate OH- ions in the solutions when dissociating? And Na is negligible as it is the i...

Anil Chaganti 3L

Hi, I was a bit confused how to calculate the final concentrations and pH of polyprotic acids. For example, in 6E1, we are required to find the pH of 0.15 m H2SO4. Since this is a strong acid, do you just take the negative log of this or do you have to do an ICE table? Can someone explain this proce...

Anil Chaganti 3L

I believe protonation is when there is an addition of a proton and an ionization is when the molecule dissociates into ions. In terms of the problems, you essentially do the same math but I am pretty sure bases use percent protonation (because bases can accept a proton) and ionization is when the ac...

Anil Chaganti 3L

I know we have discussed how increasing the temperature affects the reaction and the equilibrium constant for both endothermic and exothermic reactions. But for decreasing temperature, is it the exact opposite, or would it proceed the same way as it is still a change in temperature. For example, wou...

Anil Chaganti 3L

On Sapling, I was provided this question and was a bit confused: At equilibrium, the concentrations in this system were found to be [N2]=[O2]=0.300 M and [NO]=0.400 M. N2(g)+O2(g)↽−−⇀2NO(g) If more NO is added, bringing its concentration to 0.700 M, what will the final concentration of NO be after e...

Anil Chaganti 3L

Hi, On sapling, I was provided with several equilibrium constants to several chemical reactions. Then, the question asked me to find the eqm constant of a reaction that used multiple chemical reactions and told me to use the equilibrium constants to find the whole eqm constant for the bigger chemica...

Anil Chaganti 3L

Adding onto that question, are bars and atm the same thing? Would you use P_species for those expressed in bars and atm too? What are all the unit conversions we have to know for pressure? Is there a conversion factor between Kp and Kc?

Anil Chaganti 3L

Hi Kushaal, In this case, c would be zero since that is the initial concentration. Since the change is very small (thus negligible), we can calculate 2x by eliminating the (-x) from .522 and .633 and set up the equation the same way you would to solve any equilibrium problem: Kc= (2x)^2/ (.522)^2(.6...

Anil Chaganti 3L

At first, I would think of this as being more amphoteric, but I guess it's an acid because it is more likely to give up its charge and form hydronium ions in an aqueous solutions. This is because NH2NH3+ would not accept another hydrogen to make an even stronger cation, but use its polarizing power ...

Anil Chaganti 3L

Hi, In Professor Lavelle's lecture, he discussed that we can decide whether or not a salt is acidic or basic by analyzing its whole reaction to see whether the reaction would generate OH- ions or H3O+ ions. However, I decided to find a quicker way to do it and was wondering if this could work; my ap...

Anil Chaganti 3L

Hi, I came across this question where it asked to find the pH of a solution and provided the grams of two reactants (HCl and CaO) and the volume of the solution. How would you go about solving this? I understand how to find the pH of the HCl but how do you find the pH of CaO? Can you add two separat...

Anil Chaganti 3L

Hi, the conjugate base is the one that has accepts protons. To form the conjugate base, we must lose the proton on HSO4- so that it can accept protons. Therefore, the conjugate base would be SO4 2- and the conjugate acid would be H2SO4 as acids tend to be proton acceptors.

Anil Chaganti 3L

Hi, I believe that utilizes Chemistry 14B concepts as Lavelle stated that we did not have to know the direction of the equilibrium just yet. I believe that all we need to know is that HF is the conjugate acid of F- and CO3 2- is the conjugate base of HCO3-.

Anil Chaganti 3L

Basically as the title states: How do we identify when the compound is structured as a tetrahedral or a square planar? I can identify when it is an octahedral or either a square planar or tetrahedral, but I am having a trouble in distinguishing when the structure is a tetrahedral or a square planar....

Anil Chaganti 3L

As far as I can remember back to my knowledge from biology, I believe bases have lipids and characteristics that create that soapy feel. I believe this is why we use basic compounds like soap to remove oils and bacteria from our body parts as they are the most effective. I'm not entirely sure about ...

Anil Chaganti 3L

How come the carbonate ion is both a mono and bidentate ligand? When is it a monodentate ligand and when is it a bidentate ligand?

Anil Chaganti 3L

For the conjugate acid of CH3NH2, why is the conjugate acid CH3NH3+ and not CH4NH2+? I thought it would be more inclined to form methane. Can someone please clarify this?

Anil Chaganti 3L

The textbook states that Bismuth and Arsenic are amphoteric but yesterday's lecture stated otherwise; which should we follow? Are they acidic or amphoteric?

Anil Chaganti 3L

For textbook #45, the question asked for the composition of the bonds and the hybridization. Does the composition of bonds just mean the difference between sigma and pi bonds? Or do we have to know any specific reaction or something?

Anil Chaganti 3L

(a) Draw a Lewis structure for each of the following species: CH 3+ ; CH 4 ; CH 3- ; CH 2 ; CH 2 (2-) ; CH2(2+) . (b) Identify each as a radical or not. (c) Rank them in order of increasing HCH bond angles. Explain your choices. Why is the bond angle of CH2(2-) less than CH3(-). Shouldn't the presen...

Anil Chaganti 3L

On Sapling #17 (Draw the three possible structures of C3H4), why are the three structures not resonance of one another? Do they not contribute equally to chemical bonding?

Anil Chaganti 3L

Will we be given the names of the organic compounds (en, dien, etc) and their molecular formulas or do we have to memorize their molecular formulas and how many ligands they have?

Anil Chaganti 3L

A chelate is usually if the compound is bidentate or more. Structurally, I recall one of the UAs describing it as there being two spacers (nonbonding sites) and a bonding site.

Anil Chaganti 3L

Hi, I was working on some additional problems from the book and noticed this question: " Given that the atomic orbitals used to form hybrids are normalized to 1 and mutually orthogonal...." What does it mean for hybrids to be normalized or orthogonal. Can someone please explain this? Are w...

Anil Chaganti 3L

Hey Jonathan, I am also a little unsure, but here is how I am visualizing it. I am seeing that sigma bonds are not concerned with position, and it is usually when two atoms are next to each other, allowing for their electron densities themselves to rotate and overlap. Even if they rotated, they woul...

Anil Chaganti 3L

Another way to distinguish the difference is to understand how the transition of a substance works. For example, if we had a solid, the transition from a solid to liquid to gas involves two different things: the melting (which comes first) and the boiling point. Both require energy in the form of he...

Anil Chaganti 3L

Hi, I understand how sigma and pi bonds can be represented for single, double, and triple bonds. However, since it is split between multiple bond lengths, how do we represent sigma and pi bonds for hybrid resonance structures? Do we just represent sigma and pi bonds for each separate resonance struc...

Anil Chaganti 3L

I also had the same question but I'm pretty sure we only have to focus on sigma and pi bonds for single, double, and triple bonds as quadruple bonds are highly rare in nature.

Anil Chaganti 3L

CH4 is not considered having a dipole-dipole moment for two reasons: 1) The dipole moments cancel each other out due to the fact they are distributed equally throughout the molecule (as stated above). 2) The dipole moment is not strong enough due to the lack of a large electronegativity difference, ...

Anil Chaganti 3L

Hi,
How do the trends for nuclear charge and effective nuclear charge differ on the periodic table? How do the trends work among the subshells throughout a period and a group? Could someone please expain how this affects the trend for atomic radius?

Anil Chaganti 3L

Hi, I saw a question while doing some practice online where it listed several ionization energies (first, second, etc) and it told me to guess the element. How would I be able to guess the element just by looking at its ionization energies? What is the general trend for successive ionization energies?

Anil Chaganti 3L

Yes, some shielding is better than no shielding. However, it was worded in a way to state that shielding was "ineffective" as it isn't large enough when compared to the other atoms, therefore reducing ionization energy across a period. Hope this helps!

Anil Chaganti 3L

Hi! So basically for resonance structures, we regularly represent them by drawing multiple structures with different locations of the double bond. However, in reality, the bond length is distributed equally throughout the molecule as no particular atom has a double bond over a single bond. Therefore...

Anil Chaganti 3L

For this question, they provide a Lewis structure and we are required to determine the element in the center. The elements surrounding the unknown element were (3 Cl and 1 oxygen). Do you have any strategies in determining the center element? Are there several answers for this question?

Anil Chaganti 3L

For this question, it asks us to draw the Lewis structure for glycine (H 2 C(NH 2 )COOH). How do we know the order in which to draw this molecule? In the answer key, they drew NH2 first and then the rest and I was just confused on how we are supposed to know the correct order of the elements in the ...

Anil Chaganti 3L

Adding onto what the previous person stated, formal charge refers to the number of valence minus the number of bonds divided by 2 and the number of nonbonding electrons (the dots). Each atom gets its individual charge according to the number of bonds there are and valence electrons there are. Theref...

Anil Chaganti 3L

Hi,
Can someone explain to me how isoelectric atoms work? Do they have the same charge? Are there electronegativities and ionization energies the same? I just feel like I am a little bit confused on that vocabulary word.

Anil Chaganti 3L

Hey! So for this question, I began to draw my typical Lewis structure for Carbon and made sure to make three rings of six carbons bonded together. I then added one hydrogen to each carbon as per the description. To ensure that carbon has an octet (aka 4 bonds), I added alternating double bonds as ne...

Anil Chaganti 3L

After calculating electron affinity using the energy of ejected electrons (convert ev to J by multiplying by 1.602 x 10^-19 J) and the energy of incident light using the wavelength (E=hc/ wavelength in m), you would get your answer in J. Then, convert this answer back to eV using the conversion fact...

Anil Chaganti 3L

Some of my favorite TV shows are Bobs Burgers, Greys Anatomy, New Girl, Friends, and the Office. I know they're a bit basic, but honestly they're so good to just chill to after a long day. Coming to childhood TV shows, I really liked Phineas and Ferb, Good Luck Charlie, and Arthur. They are classics.

Anil Chaganti 3L

Hi, Atomic radius is essentially the radius of an atom and its electrons that accompany it while the ionic radius measures the radius of two ions joined by an ionic bond. Atomic radii increases down by a group as the addition of more subshells makes the distance further from the nucleus and decrease...

Anil Chaganti 3L

Hey!
I heard that you can email UCLA store and they can email you your code directly if you needed it. Apparently there has been a delay and several people did not receive their codes through mail. Try emailing them to send a PDF of your code. Hopefully it works!

Anil Chaganti 3L

In 1E 25, the question was asking for valence shell configurations. How is this different from electron configurations? Does it still adhere to the same principles of electron configurations?

Anil Chaganti 3L

Hi,
I was working on the quantum numbers section and I was confused on this question:
1D.25 Which of the following subshells cannot exist in an atom:
(a) 2d; (b) 4d; (c) 4g; (d) 6f?
When do subshells not exist?

Anil Chaganti 3L

I believe the photon gets absorbed by the metal as it is unable to emit electrons. The opposite of emission is absorption, so I think this is a fair assumption. Edit: I realized that the photon just passes through as there isn't enough energy to get absorbed or emit energy. My bad, I realized my mis...

Anil Chaganti 3L

I saw this on the outline (With respect to electron transitions that give rise to a UV or visible spectrum: understand the difference between electronic transitions in atomic orbitals (atomic spectroscopy) and electronic transitions in molecular orbitals (molecular spectroscopy) and was a bit confus...

Anil Chaganti 3L

Hey, It functions as a way of allowing us to calculate energy by relating both psi since the double derivative returns the same function (sin returns sin). It allows us to relate Hpsi and Epsi together to solve for Energy. It doesn't have any units or anything, just solely an "operator". D...

Anil Chaganti 3L

H (Hamiltonian number) is the double derivative of the wave function which allows for energy to be calculated using the wavefunction as it is the same on both sides. For example, the double derivative of sin is sin again, showing that we can then calculate energy when the wavefunction corresponds to...

Anil Chaganti 3L

Hey, I believe Heisenberg will be there since it was covered on the modules. Things to know related to this: 1) There is an indeterminacy in smaller objects as their momentum and velocity is unknown when interacting with light. For an object like a baseball, we can determine their position and momen...

Anil Chaganti 3L

Hi,
I understand that DeBroglie wavelength is based on mass and velocity. But how come it differs from the wavelength based on the electromagnetic spectrum? Shouldn't they be the same but just determined using different variables?

Anil Chaganti 3L

Electron density corresponds to the probability of finding an electron in an area. We use Schrodinger's wavefunction to determine this but we haven't gone over the math for it yet.

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