CHEMISTRY COMMUNITY

Jason Wu 1E

Dear Dr. Lavelle, Thank you for being a great professor for Chem 14A and 14B! I really enjoyed your lectures over these past two quarters, and I feel like I was able to learn the most not just content-wise in your class, but also more personal skills in becoming a better student as I transitioned in...

Jason Wu 1E

I think it doesn't matter if the reaction is exothermic or endothermic because those are the final states while Kinetics focuses on the transition between reactants to products. Increasing the temperature will then increase the rate constant!

Jason Wu 1E

Is there a relationship between k and k'? similar to how Kc of the reverse reaction is Kc^-1?

Jason Wu 1E

Catalysts will still increase the rate of the reverse reaction. This is because a Catalyst will lower the activation energy of a reaction. Thus it will still be a decrease in Ea going in reverse. Delta H will have no change

Jason Wu 1E

I was wondering how the ln(k') - ln(k) = Ea/R ((1/T)-(1/T')) is derived? What was the starting equation for this? I'm curious because this equation is not on the equation sheet.

Jason Wu 1E

The rate constant of the first-order reaction 2 N2O(g) -> 2 N2(g) + O2(g) is 0.76 s^-1 at 1000. K and 0.87 s^-1 at 1030. K. Calculate the activation energy of the reaction. How do we approach this question? are we supposed to substitute for k and T into Arrhenius's Equation to create a system of equ...

Jason Wu 1E

What's the difference between a zeroth, 1st and 2nd order reaction? Is it that they occur based on the number of reactants present? Also when having more than one reaction why does the overall reaction number the sum of all individual order reactions?

Jason Wu 1E

The half-life of a reaction is the amount of time it takes for the initial concentration of half. It is related to kinetics with the equation t(1/2)=ln(2)/k where k is the reaction rate constant within a first order reaction.

Jason Wu 1E

I think the half-reaction when written in the form of reduction and has the most positive cell potential, will be placed at the Cathode to be Reduced. Thus the other reaction which is either negative or less than the reduction reaction will be flipped, placed at the Anode and then oxidized. In summa...

Jason Wu 1E

I got the same result as you... I'm not sure but based on previous posts for the same question they have said there is an error in the solutions manual. However, the answer that they got was also different which confuses me even more :/

Jason Wu 1E

Hi Guys, I'm currently really sick and do not feel well enough to attend lecture in person. Can someone please send me the slides from today? Thanks!

Jason Wu 1E

Salt Bridges are essentially needed to create a complete circuit for electrons to flow and create a complete circuit so that E can be maximized. Usually, a salt bridge consists of a high concentration of easily dissolvable ions like NaNO3 to create Na+ and NO3-. Na+ will then flow to the Cathode whe...

Jason Wu 1E

Balance each of the following skeletal equations by using oxidation and reduction half-reactions. All the reactions take place in a basic solution. Identify the oxidizing agent and reducing agent in each reaction. P4(s) --> H2PO2-(aq) + PH3(aq) for this redox reaction, how do we start the question b...

Jason Wu 1E

How do we determine whether the electrode of a galvanic cell is going to be a metal element or Platinum? Is it safe to assume all solid forms within redox reactions serve as the electrode?

Jason Wu 1E

Balance each of the following skeletal equations by using oxidation and reduction half-reactions. All the reactions take place in basic solution. Identify the oxidizing agent and reducing agent in each reaction. O3(aq) + Br-(aq) --> O2(g) + BrO3-(aq) I understand that Br is being oxidized, however, ...

Jason Wu 1E

Predict the potential of each of the following cells: Pt(s) | H2(g, 1.0 bar) | HCl(aq, 0.075 mol*L^-1) || HCl(aq, 1.0 mol*L^-1) | H2(g, 1.0 bar) | Pt(s) When using the Nernst Equation, I understand that E knot is zero, however, how do you find a value to plug into N for the equation above? On the eq...

Jason Wu 1E

Within a redox reaction, when is it applicable to add water molecules? Why can we do this? and is there any other type of compound we can just add into our redox reaction?

Jason Wu 1E

I'm not sure if this is a rule that is always applicable. When we see either a visual diagram or simplified galvanic cell in terms of compounds (i.e. Ni | Ni2+ || Ag+ | Ag ), is it safe to assume the cathode will always be placed on the right? If so, are we expected to do the same at all times?

Jason Wu 1E

I hit "quick links" on the top left, then select "Your Posts", the number of posts you have made will appear on the top right below your user name and notifications tab!

Jason Wu 1E

Based on previous threads, on the product is supposed to yield Cl- and not Cl2. I don't know if this is right but the reduction half reaction was Cl2 to 2Cl- plus 2 e- since the oxidation state of Cl2 goes from 0 to -1

Jason Wu 1E

Balance each of the following skeletal equations by using oxidation and reduction half-reactions. All the reactions take place in acidic solution

d) Cl2(g) -> HClO(aq) + Cl2(g)

How exactly do you solve this question? I'm stuck on identifying what is oxidized and what is reduced?

Jason Wu 1E

Dr. Lavelle picks up the ice cream that he has just heated up (-2.8 Celsius) and accidentally drops it on the ground and can’t eat it. Tears streaming down his face, he watches as half of it melts away when he realizes that from the moment he dropped the ice cream until now, it has received exactly ...

Jason Wu 1E

Through practice problems, I have come across various types of Entropies including S, Delta S, Delta S total, and Delta S surroundings. What do each one of them mean and how do they relate to each other? Thanks!

Jason Wu 1E

What is the C represent? I thought it was a heat capacity but why is it capitalized? is it a constant? or does it depend on the compound at hand? Also when is it applicable for us to use the equation?

Jason Wu 1E

Suppose that 50.0 g of water at 20.0 Celcius is mixed with 65.0 g of water at 50.0 Celcius at constant atmospheric pressure in a thermally insulated vessel. Calculate Delta S and Delta Stot for the process. How do you start this question? What is the difference between Delta S and Delta S total? and...

Jason Wu 1E

A constant-volume calorimeter was calibrated by carrying out a reaction known to release 3.50 kJ of heat in 0.200 L of a solution in the calorimeter (q = -23.50 kJ), resulting in a temperature rise of 7.32 Celcius. In a subsequent experiment, 100.0 mL of 0.200 m HBr(aq) and 100.0 mL of 0.200 m KOH(a...

Jason Wu 1E

Delta U is the change in internal energy and Delta H is the change in Enthalpy. Enthalpy is only accounting for the heat entering or leaving a system while internal energy accounts for all types of energy. The two relate because the change in internal energy equals the change in enthalpy plus the wo...

Jason Wu 1E

In the Chemical Equilibrium unit, I believe that we discussed this. Basically all reactions are reversible but it may be in very VERY small quantities. If the Kc of the reaction is between 10^-3 and 10^3, then it does not favor the products or reactants. Therefore, it is can be running in the revers...

Jason Wu 1E

A human body generates heat at a rate of about 100. W (1 W=1J*s^-1). (a) At what rate does your body heat generate entropy in your surroundings, taken to be at 20 degrees C? (b) How much entropy do you generate each day? (c) Would the entropy generated be greater or less if you were in a room kept a...

Jason Wu 1E

W is positive because in the question it states that "work is done on the system". Furthermore, if you do use W = -P delta V, the final volume minus the initial volume will be a negative number since it is compressed into a smaller volume. Thus delta V will be negative and that cancels out...

Jason Wu 1E

Can someone help explain the diagram of the isothermal reversible expansion Dr. Lavelle explained in class today? How is temperature considered constant when heat (noted by the red arrows) get added into the system, and I'm also confused about why the pressure gets doubled. Thanks!

Jason Wu 1E

Think about an exothermic reaction as heat produced on the products side of the reactants. If you increase the amount of heat in the system, then the reaction will be driven to the other way in favor of the reactants because in order to remove heat from the system by Le Chatelier's Principle, the re...

Jason Wu 1E

A Negative Delta H is an exothermic reaction where heat leaves the system and enters the surroundings.

Jason Wu 1E

To determine which side has more moles to calculate which direction Le Chatelier's principle deviates yo, you just need the compare the total of the coefficient of the products to that of the reactants AFTER you balance the chemical equation. The reaction will favor the side with lesser moles if you...

Jason Wu 1E

Why is Cpm and Cvm different from each other on the molecular? and why do they equal 5/2*R and 3/2*R respectively? Is it possible to keep both pressure and volume constant?

Jason Wu 1E

When calculating work, how do you determine the sign? What does negative work mean and how is work different from heat? (The only work definition I really know is the Physics definition where W=Fd).

Jason Wu 1E

Ka2 will be insignificant in terms of being able to round your denominator when solving for x. Because Ka2 is always smaller than Ka1, then if Ka1 can be rounded, you could also round Ka2. However, I would suggest you to always calculate Ka2 as it could have a significant effect on the pH of the sol...

Jason Wu 1E

You would need to calculate it twice I believe and then add the concentration of [H+] together. This is because the equilibrium constant is different for the removal of the first proton compared to the second one. Thus Ka1 will be greater than Ka2.

Jason Wu 1E

To find the molarity it is the same way for single coefficient compounds and multiple. What is different is that those with multiple coefficient compounds you would need to power them when calculating the K constant. In your example, Q = [(12/0.6)(3/0.6)]/[(3/0.6)(6/0.6)^3]= 0.02. Thus the reaction ...

Jason Wu 1E

Full Question decpicted here: https://imgur.com/a/8JCAUbw For part B, when I calcultated the equilibrium constant K = (Pc)^2 * (Pb)/(Pa)^2 and plugged in values from the graph, I get 100* 5/(17.5)^2 which equals 1.6326 The answer key says the correct answer is 1.54 * 10^-2. Where is the error I made...

Jason Wu 1E

The answer should be B. In this question, you are simply asked to convert concentrations at equilibrium to partial pressures at equilibrium. To do so, the partial pressure always equals the concentration in moles per liter times the R value times the temperature in Kelvin. Doing all the steps above ...

Jason Wu 1E

K is the equilibrium constant to show the ratio of products to reactants at equilibrium. There are various types of equilibrium constants such as kc, kp, ka, and kb but all that changes is what is compared to one another. For example, kc is the ratio of the concentrations of products to the concentr...

Jason Wu 1E

I believe pH + pOH = 14 could be used for Strong and Weak acids and bases because you can calculate the pH of a weak acid. for pKa + pKb = 14, that equation should only apply to weak acids and bases because ions completely dissociate in strong acids and bases.

Jason Wu 1E

As Lavelle said in today's lecture, a change is insignificant when the K constant is less than 1 * 10^-3 or 0.001. I would assume the same thing will apply if the K constant is greater than 10^3 or 1,000.

Jason Wu 1E

The only other significant autoprolysis examples I could think of are 2NH3 (ammonia) forming NH2- and NH4+ as well as 2CH3COOH (acetic acid) forming CH3COO- and CH3COOH2+. In both examples, a hydrogen atom is removed from one molecule and given to the other same molecule. In the examples however, am...

Jason Wu 1E

ATP Hydrolysis is when an ATP Molecule is broken down to release energy and ADP. My understanding is that this relates to Chemical Equilibrium in the case that the body will convert excess energy to ATP so that it could be used later and start the breakdown of ATP if there is not enough energy. It i...

Jason Wu 1E

For the scope of the class, I'm don't believe that we need to figure out which reagent is the limiting reactant in an equilibrium system because limiting reactants will only be a factor if a reaction drives to completion. If there is an equilibrium constant, then there will always be a certain conce...

Jason Wu 1E

Because the value of K is constant from the ratio of the concentration of products over reactants. By increasing the equilibrium concentration of reactants, it will then increase the equilibrium concentration of the products in order to drive the reaction forward. This will then decrease the concent...

Jason Wu 1E

Yes, when you solve for Reaction Quotient (Q), it is the exact same as solving for The equilibrium Constant (K). The only difference is that the reaction quotient is not the complete reaction at equilibrium and you must use it to be compared with K to determine whether the reaction will continue in ...

Jason Wu 1E

One of my favorite ways to review is to watch various videos from YouTube to get a better grasp of the material. Some awesome channels I will recommend you to check out in learning about ideal gases and other concepts in Chemistry are Crash Course, Bozeman Science, and the Organic Chemistry Tutor. I...

Jason Wu 1E

Changing the equilibrium means that you are taking a system that is in equilibrium and removing a product/reactant so that a reaction could continue to happen. On the other hand, changing the equilibrium constant means that one would need to alter the pressure or temperature of the system as a whole...

Jason Wu 1E

An acid is more corrosive when the pKa is lower (or Ka is higher) or is a strong acid. Corrosion happens when a lewis acid gains electron pairs from metal atoms. This makes the metal atoms positively charged, in order to counteract that the metal cation will be oxidized with surrounding oxygen and u...

Jason Wu 1E

pOH is basically 14 minus the pH of the solution (which also means pH = 14 - pOH)so it would not be difficult to convert between the two. This information is just good to know since pOH is just measuring the concentration of [OH-] in a base.

Jason Wu 1E

When do you know if a polyprotic acid will release a second H+ ion or instead pick another one up to form an HA compound? For example, when do you know if H2PO4- will release H+ to form HPO4 2- or instead back to H3PO4?

Jason Wu 1E

I uploaded my notes onto imgur (since i can't figure out how to post images here. Hope this was helpful!

https://imgur.com/a/Ig3hgqG

Jason Wu 1E

What do you always get with your extra swipes at Rende during Week 10?

5 8 56

*periodictable.jpg

Jason Wu 1E

What is the best way to determine which acid is stronger if you are given two different types of weak acids? Is there a foolproof step you can use to determine it?

Jason Wu 1E

Adding onto Paige's answer, you also need to use the shape of the molecule to determine the denticity of a molecule. If the shape of the molecule does not have lone pairs close enough for the metal cation to bond, then the ligand will differ in Denticity.

Jason Wu 1E

Which is the stronger base BrO-, or C17H19O3N?

How would one approach a problem like this? is there a ranking of steps to determine if a compound is more acidic/basic?

Jason Wu 1E

I didn't understand what makes certain acids stronger than others. Specifically, I don't understand why is it that when a molecule exhibits more of a dipole due to high electronegativity of an element results in it being more of an acid. For this example is it using the Lewis Acid model?

Jason Wu 1E

What is the best way to determine in a reaction on which of the following elements are the acids, conjugate acids, bases, and conjugate bases? Is it possible to find out whether there are more than one of each type if there are more than two reactants/products (ie when the precipitation of a solid o...

Jason Wu 1E

Not sure if we need to know this: but I think when reactions occur and bond breaks, the pi bonds break first before the sigma bonds and sigma bonds form before pi bonds when bonds form.

Jason Wu 1E

May be off-topic, but I feel like I have used this compound before when dissociating cells and transferring them to a new culture. Now I am confused about what the purpose of EDTA is within Cell Passaging after learning that it is used to uptake metals?

Jason Wu 1E

A dentate is how many lone pairs within a ligand that can bind to the metal cation. If there is one, then the ligand is considered a monodentate, if it was two then the ligand is bidentate, three is tri-, four is tetra and so on.

Jason Wu 1E

I'm unsure if there will be more biological concepts but my guess is everything covered in lecture has the possibility to show up on the final!

Jason Wu 1E

When we place ligand names in alphabetical order, are we supposed to use the English names or are we supposed to use the Latin names for elements (ie Mercury vs. Hydrargyrum). If so which ones are we supposed to remember?

Jason Wu 1E

London dispersion forces are present in all atoms because all compounds have electrons and just through random chance electrons may gravitate towards an atom as they are always in motion. Because of this, at any time there will be an atom that is more positive (and one that is more negative), so thu...

Jason Wu 1E

I am having trouble differentiating these two terms. What exactly is the difference between the polarizability of an atom vs. its electronegativity? Right now I just see it as complete opposites where an atom with high polarizability won't be electronegative and vice versa.

Jason Wu 1E

I understand that Lone Pairs have a greater repulsion force than the force of atoms have each other. However why exactly is this the case because generally within larger atoms there are more electrons, so shouldn't the number of electrons make a difference? Will there be a case where the repulsion o...

Jason Wu 1E

Yes, greater repulsion strength between two atoms/lone pairs results in a larger bond angle between the two atoms of the same compound. You can determine which bonding pairs have a greater repulsion by the polarizability of the atom. Generally, atoms with a higher number of electrons are more polari...

Jason Wu 1E

I don't believe that this is possible within the same solution. This is just because a dipole-dipole interaction occurs between two polar molecules, and a dipole induced interaction occurs between a polar molecule and nonpolar molecule. I don't believe you can have a solution that has both polar and...

Jason Wu 1E

I would assume that the next test will be focused on new concepts, however it is likely that you may need to know some basic chemistry fundamentals to be able to solve multi-part problems. So it is best to still review concepts we have learned especially because the Final exam will then be only 1-2 ...

Jason Wu 1E

Not a commuter but because I had to travel to attend events/plans outside of LA so I wasn't able to attend any review sessions the week leading up to the final. I will suggest what helped me the most in studying for this midterm was to still do as many problems posted as possible. Through Chemistry ...

Jason Wu 1E

In the lecture, we have discussed that London Dispersion forces are stronger within larger atoms because they have a larger number of electrons. But why is that the case because aren't there supposed to be more electron repulsion with more electrons? Thanks :)

Jason Wu 1E

Technically, yes, polar molecules can be more polar than another because the net dipole moments of a molecule can have a greater magnitude than another molecule. I don't think we need to calculate which molecule is more polar than another though.

Jason Wu 1E

As you go down in the periodic table for a group, the London dispersion forces of an atom become stronger since there are more electrons present within the atom. As a result of this stronger London dispersion force, the atoms will require more energy placed into the system for it to change phases. T...

Jason Wu 1E

What you have to do in this case is to first figure out the molecular compound from the nomenclature. After doing so, you could try to figure out whether the compound is an ion through its bonds (difference in electronegativity) or dissociation rules. In your example, Sodium Hypochlorite converted t...

Jason Wu 1E

A molecule is considered polar if the net dipole moment yields zero. As in the case of CO2, the dipole moments yield zero because the molecular structure is linear. In the case of H2O, because the molecule is bent by the lone pairs on the Oxygen atom, there is a net dipole moment and thus the molecu...

Jason Wu 1E

I believe when you are minimizing formal charge you are supposed to have all atoms be as close to zero as possible. Meaning that it is best to have a compound with 3 zero charges and one +1 charge rather than two zero charges and one with +1 and one with -1. This is because formal charge relates to ...

Jason Wu 1E

A radical is a compound that has one unpaired electron while a biradical is a compound that has two separate unpaired electrons (not a lone pair), in both situations, the compound is unstable and will not likely remain for a long time within that state.

Jason Wu 1E

I think it really depends on the context of the question and what you are trying to solve. Within the practice midterm kJ per mole is used which may be needed to be converted to Joules per photon with dimensional analysis to solve the problem. However overall, when stating an answer that has energy,...

Jason Wu 1E

Xenon has a maximum of 18 valence electrons because it is able to access the 4d orbital and place up to 10 electrons there. Therefore, Xenon does not follow the octet rule because it could form bonds with more than 4 elements (ie XeF6)

Jason Wu 1E

How does one figure out if a compound has resonance structures or a lone pair at the central atom? Any explanation helps!

Jason Wu 1E

I understand that Boron can have 6 valence electrons to be satisfied, however, why is that the case while Aluminium (same group, one period down) can't (or can it also?!?)? Also why exactly could P, S, and Cl access the d orbital even if the 4s orbital should be filled before then?

Jason Wu 1E

One easy way I use to calculate the formal charge of an element is to simply take the number of valence electrons of the element and subtract how many lines and dots are surrounding it. This should be faster to compute, to begin with, however it is still important to understand the full concept.

Jason Wu 1E

I believe that the reason the least electronegative atom is in the center of an atom because the element in the center of the atom have to share electrons with all the other surrounding elements. By having the least electronegative atom in the center allows for a more stable bond between the element...

Jason Wu 1E

What are the specifics to using the Noble Gas shortcut? Additionally, for example, to write the electron configuration for Argon, are you allowed to just write [Ar]? or do you have to write [Ne] 3s^2 3p^6?

Jason Wu 1E

Let's talk about spin. What is even going on and how do we know if it's positive or negative? The spin is determined by how many other electrons are in the outermost subshell of the atom. If the subshell is less than half-filled, then electrons with positive spin will fill out the subshell until it...

Jason Wu 1E

I believe you are supposed to remove the electron in the highest energy shell, subshell, and orbital first. Additionally, you are supposed to remove electrons that have negative spin first before you remove ones with a positive spin within the orbital (aka you want to pull from a paired electron fir...

Jason Wu 1E

To determine an electron's configuration, all you need to do is to find where the element is on the periodic table and follow the sequence to get it (sequence will always be 1s^2 2s^2 2p^6 etc.). You could write the shortcut for it by starting with the most recent noble gas that has a smaller atomic...

Jason Wu 1E

I Believe that all equations needed will be given to you on the test (correct me if I'm wrong). You just need to know when to use what equation depending on the givens and modify it for it to solve the unknown!

Jason Wu 1E

It really depends on what you are used to and what you find as most effective through trial and error. I personally will do more practice problems than assigned, go over YouTube videos, modules, and the post assignment quizzes. Still trying to better improve my strategies as times goes on but I thin...

Jason Wu 1E

Because photons are released when an electron returns from an excited energy state to its normal energy state, the energy released has to be positive since it is there will always be excess energy released when going from a higher energy state to a lower state.

Jason Wu 1E

I am having trouble conceptualizing the importance of these two series shown on the light spectrum. Why are those two regions important/highlighted and how does it relate to n? (I'm not completely sure but is n denoted as the energy level of the electron in this case?)

Jason Wu 1E

A Lamp Rated at 32W (1W=Js^-1) emits violet light of wavelength 420 nm, how many photons of violet light can the lamp generate in 2 seconds? How many moles of photons were emitted in 2 seconds? For this question, I first calculated how much energy is released by a single photon through using E=\frac...

Jason Wu 1E

I would say these two models compliment each other. This is becasue in quantum mechanics the unit is so small to the point that it could only be possible to flow one molecule each time. While in classical mechanics, the descrete unit could be also well defined as a value even if water is continuousl...

Jason Wu 1E

If you're a Texas Instrument type of person, I would suggest to get the TI-30XIIS. That was the calculator I used in AP Chem and in my opinion it is the best non-graphing scientific calculator to get. Other than that I use the TI-BAII Plus as of right now, not a huge fan of it because it is mainly u...

Jason Wu 1E

I believe you could always use whatever number is on the denominator to make the equation whole. For example if one reactant after balancing has 7/4 as its coefficient, you could simply multiply the entire equation by 4 to get everything to a whole number. If there are more than one fraction in the ...

Jason Wu 1E

I'm not sure if this would be on the test but i'm curious on how to do these types of questions anyways so i'll ask a hypothetical question here. (Hypothetical Example) Does anyone know how to calculate how much water is needed to dilute a 100mL of 50% glucose to a solution that is 20% glucose? Does...

Jason Wu 1E

I would suggest you to write out the state symbols within Chemical Equations right now just as good practice! You can actually learn alot more about the reaction because of them. Going off the previous comment on aqueous compouds, you could also learn from the state symbols on whether or not a preci...

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