CHEMISTRY COMMUNITY

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I have not heard anything from Lavelle, hopefully he makes an announcement soon!

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Yes can anyone say whether or not the final will be online? If so, how will that work with showing work for partial credit.

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Has anyone received an email or heard word from Prof Lavelle concerning class cancellations? I don't know if the remaining lectures, discussions, peer learning sessions and review sessions are cancelled or not.

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The higher Enaught value is the the cathode

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Yes you do not change the sign. Leave the values as is and plug them into Ecell= Ecathode-Eanode

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the strongest reducing agent will be whatever is most likely to be oxidized. Therefore it will be the lowest Ecell value because the lower the value, the more it favors oxidation. The higher the number, the more it favors reduction.

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My TA told me the order shouldnt matter

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week 10 in discussion

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After you balance oxygen's with H2O, you balance out the H with H+

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The reducing agent is the element being oxidized. Now that it has given up its electrons, they can be given to another element and allow it to be reduced. That is why the thing getting oxidized is called a "reducing agent" The oxidizing agent is the element being reduced. Now that it has t...

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I have been having the same issue. However, counting is not too bad as long as you distinguish where you ended your posts last quarter. Counting can be tedious so I also keep track in my notes on my phone and update it every time I post on here. I recommend this if you don't want to count every time.

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From my experience with Lavelle last quarter, he does not curve the tests individually. However, he does curve the final grade of the class with 50% as a C-. This highly elevates your chances of passing the class.

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They represent the same thing and can be used interchangeably. They both represent the change in internal energy of a system.

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Yes, you can use STP (standard temperature and pressure) to solve PV=nRT. STP is measured at 1 atmosphere of pressure at 273.15 degrees Kelvin and you can plug these numbers into the equation.

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unfortunately he did not hand out any worksheets ): today we worked on problems from a worksheet he compiled and shared with us. however it is not on Chemistry Community, your best bet is asking for photos!

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Sue Bin Park 2I wrote:
AMahadi wrote:Do we have to know this info for the midterm?

it was in his topic outline

the midterm will likely cover everything through outline 4: The 2nd and 3rd Law of Thermodynamics. Be familiar with all the topics in this section and in the sections previous to outline 4.

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The easiest trick is to compare expansion verus compression. Expansion will cause work to be negative because the system has to do work in order to expand. Compression will cause work to be a positive value because work is being put into the system to compress it.

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internal energy is the total energy of a closed system. Because the closed system doesn't get energy from its surroundings, internal energy is made up of the potential and kinetic energy the closed system has.

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No because it cannot exchange energy with the surrounding environment because it is closed off.

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pKa is -logKa and pKb is -logKb. If you are familiar with the equation Kw= Ka x Kb and the equation Kw= 1.0x 10^-14, you can make the equation Ka x Kb= Kw= 1.0x 10^-14. Then, you can fill multiply the equation by -log and convert it to Kb and pKa. When you do this, you get the equation pKb + pKa = 14.

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Karina Kong 2H wrote:An example of a closed system is a pot with a lid on top of a stove.

to elaborate further, an example of an open system is an open pot with boiling water. The system becomes closed when you put a lid over the top of the boiling water.

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w represents work. When w is negative, the system is doing work such as expanding. However, when w is positive the system is having work done to it. For example compression of an object by an outside force.

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The sign of delta H depends on whether or not the reaction is exothermic or endothermic. If it is exothermic, delta H will be negative. If the reaction is endothermic delta H will be positive because heat will be added.

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It's usually dependent on your TA how strictly they grade sig figs so always make sure to double check them!

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You should always make sure a chemical reaction is balanced before proceeding to make any calculations. Always.

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will steam be on the midterm? and if so what should we know about it??? All I know is man that stuff burns lol

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Force is pressure multiplied by area
F=PxA

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KBELTRAMI_1E wrote:
Emily Lo 1J wrote:How can you change the energy in a closed system? And does it differ with isolated systems?

Quoting this because I want to see the replies that it gets :)

I would assume you would add heat to change energy since the system is isolated.

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If the acid or base isn't completely dissociated then it's probably weak. Be careful using this trick because the strong acid H2SO4. It appears that since it has 2 H that it doesn't fully dissociate in water. The other strong acids all only have one H. However, if you memorize the list you find tha...

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The midterm will take place during week 6 on Wednesday, February 12 from 6-8pm. The room the test is taken in depends on your lecture time and your last name.
For my lecture, the 14B 11am, if you have a last name A-L you are in Moore 100. If your last name is M-Z your test is in Dodd 147.

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If you increase the pressure of a system, the reaction will shift to the side with less moles of gas. For example if you have 2 moles of reactant on the left and 3 moles of product on the right, the reaction will shift to the left under increased pressure because it has less moles.

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Expansion is when the volume of a system increases. It is often used in examples with gases that are compressed or expanded in a system.

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Delta U represents the change in the internal energy of a system

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From my experience, I went to one of each topic just to see where I was at in understanding. From there, I could really tell what other sessions I needed to go to based off how much I remembered/could do at each topics review. Then I would attend the sessions I felt I needed the most help in. For La...

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Delta U = q + w
q is heat
w is work
*the answer to this equation is typically given in Joules (J).

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How do I gain access to the emails of PLF instructors to join? I could use some help with chemistry and math /:

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Renee Grange 1I wrote:What is enthalpy?

Enthalpy is the heat entering or exiting the system. If the change in enthalpy (delta H) is negative then the reaction is exothermic. If the change in enthalpy is positive, then the reaction is gaining heat and therefore endothermic.

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sarahforman_Dis2I wrote:
905373636 wrote:Is W2/W1 always equal to V2/V1?

The proportion between W2/W1 and V2/V1 will always be equal, although the value of W2 and V2 will be different.

How can the proportions be the same but the values be different? Can someone please elaborate or give an example so I can further understand? (:

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Thank you for opening up to us! Do you use chemistry in your medical training at all? I am curious how much chemistry a medical student will use after Lavelle's classes are over. Please let me know how much you use it, if at all! Same with calculus or statistics. Do you see those subjects in your da...

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"w" represents work: the energy that exits or enters a system. Because it is referring to energy, work is measured in Joules (J).

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Heat and energy are required to break bonds. Therefore, breaking bonds is an endothermic reaction and delta H would be positive (+) because heat is being added to the system to break the bonds.

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No review sheet yet): I am sure he will make an announcement during one of lavelle's lectures about it or send out an email. Good luck!

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That is not enough information. To determine the sign of delta H, we need to know what whether its under constant heat or temperature, how much heat is released or added and how much work has been done. The amount of energy alone will not tell us much about the change in enthalpy of the entire system.

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The negative in front of delta H indicates an exothermic reaction. This is because the reaction is releasing/losing heat, hence the negative sign in front of the change in enthalpy (H).

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I would say we need to know that its a coordination compound and the structure (why its cis vs trans). Then I would also know its biological significance as a chemotherapy drug. It is used to stop DNA replication of cancerous cells. The chlorines in cisplatin bind to the guanines in the DNA strand, ...

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Hydrogen only has 1s orbital and can only make one bond, therefore it cannot undergo hybridization.

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It is different depending on whether you are talking about Lewis or Bronsted Acids and Bases Lewis Acids accept electrons. Lewis Bases donate electrons, inversely: Bronsted Acids donate protons. Bronsted Bases accept protons. Acids and bases are also used when referring to the pH scale. A pH of 7 is...

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Yes. A Bronsted Base receives a donated proton. A Bronsted Acid donates the proton to the Bronsted Base. It works oppositely of Lewis Acids and Bases. For Lewis structures, acids accept electrons and bases donate them.

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Ionization energy increases as you go up the periodic table and to the right of the table. As you travel up the periodic table, the atomic radius of a molecule gets smaller. This places electrons much closer to the nucleus than in a larger molecule making the electrons harder to remove from the smal...

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It is cumulative and accounts for everything listed in all 6 outlines on the syllabus. I would practice problems from each section and redo problems on the tests we have taken this quarter, especially problems you missed. The final is also on a Sunday don't forget!

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It is a covalent bond formed between two molecules. However the 2 electrons in the covalent bond come from the same atom. Typically, a covalent bond is formed between two atoms using one electron from each. However a coordinate covalent bond shows that you can create a covalent bond between two atom...

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The electrons overlap much closer to the nuclei in sigma bonds. This creates a greater pull on them because of the attraction between the positive nucleus and negative electrons. This strong attraction makes them harder to break than pi bonds, that have less electron overlap.

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If a lone pair is present, the angle will be less than 109.5 degrees because the electrons will repel the molecules away from it.

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Lone pairs on the central atom affect molecular shape. Like a bond, they represent a region of electron density on the atom and bend the bonds away from it because of electron repulsion.

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The difference between Bronsted and Lewis acids and bases is that Lewis acids accept electrons while bronsted acids accept protons. Lewis bases give electrons while bronsted bases give electrons away. They are the same thing but with protons instead of electrons.

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Hydrogen bonding sites are represented by and H paired to an N, O or F so it would look something like this O-H N-H F-H. These bonds would in turn bond to an O, N or F with a lone pair on the opposite antiparallel strand of DNA. The partial positive created on the H in the N,O or F-H bond will be at...

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Drake Choi_1I wrote:I think we will have to memorize the basic ones.

yes know the basic ones but familiarizing yourself with all of them won’t hurt.

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I think we'll be asked to draw the lowest energy Lewis structure and then name the shape and what the bond angles are. We should know how to draw the most stable Lewis structure and then identify dipoles within the molecule. Using the dipoles we then know the repulsion and shape of the molecule and...

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Diana A 1G wrote:Hey, I am down for a study group. If anyone wants to form one, email me at dmarut20@gmail.com
And then I'll give you my number:)

I am also struggling and can use some help!! please email me coraf1999@aol.com if you’d like to form a group!

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TanveerDhaliwal3G wrote:How do radicals affect electron arrangement and shape?

Radicals act as electron density in the shape of the molecule. However since it only has one electron instead of a pair, the repulsion is not as strong as it would be in an area with 2 electrons.

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sarahsalama1G wrote:also, are basically LDF in everything?

Yes, basically all molecules demonstrate LDF

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It covers only the material learned after the midterm. Thankfully it’s not too much content!

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Test 1 will only topics covered after the midterm !

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The test is supposed to cover everything from midterm 1 until outline 4. I'm sure he will say in class where the exact cutoff in the outline and notes are. Last time he said specifically in class the stuff that was not going to be on the midterm from that point onward. I am sure he will do the same ...

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oxygen is more likely to lose one electron to get a half-full shell, which is more stable than having 6 valence. Nitrogen is already half full so will likely keep its electrons. This gives O a lower Ionization energy

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although they are strong, hydrogen bonds are not stronger intermolecular forces than covalent or ionic bonds so they are not the strongest overall. It is a permanent dipole of sorts and is stronger than typical dipole-dipole attractions.

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I dont believe we ever calculate electronegativity. We only need to know and understand the electronegativity trends on the periodic table (it increases as you go up and to the right on the table).

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I dont have any tips and could use some as well!! Does anyone have a quizlet or a good method they have found??

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If you can't get all the formal charges to zero, get as many as you can close to zero so that the Formal Charge of the molecule is as low as possible.That will be your most correct answer. It also helps to keep the charge off of the central atom. If the charge is on the outer molecules its easier fo...

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O, N and F have very high electronegativity as well as a small size. These make it easy for hydrogen bonding to occur since they are not strong enough to break the weak H-bond

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Do you need to take 14C in order to take BL? I am confused about that

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'in an ionic bond, one molecule is positive and one is negative. Their opposite charges create an electrostatic attraction between the molecules, holding them together.

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Resonance can be described as the delocalization of electrons in a molecule. The electrons help form bonds within the molecule that can be drawn in Lewis Structures.

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I am not 100% sure but I think it has something to do with the fact that these elements are nonmetals with the presence of a d orbital. This somehow allows then to fill and sometimes expand their octets to stabilize the structure.

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Yes! If the formal charge of the central atom is zero, the central atom is in a stable state.

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in class the examples of elements with expanded orbitals went up to 10.

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Pauli's exclusion principle limits orbitals to only 2 electrons each (1 pair of electrons per orbital). Hund's rule states that an orbital must be occupied by one electron before it can be occupied by a second.

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making sure you know how to use one equation to fill in missing pieces to another is really important as well. Converting units properly and using the necessary formulas for each problem is really important and should be practiced as well!

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Using the equation given in class, you can find the formal charge of a molecule. When the FC equation equals zero, you have reached the most stable form of the compound. If it does not equal zero, you know some modifications can be made to the electrons or bonds in order to reach a FC of zero and ha...

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This equation along with most we learn in class will be provided (: Lavelle is pretty cool about this, I think he understands there is a lot of equations to keep track of so providing them helps us succeed (:

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Nodal planes have no electrons present in them. The s-nodal plane resembles a sphere while the rest all follow lobe-like shapes and patterns.

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"ground state" represents the lowest energy level possible for a molecule. It is often the state listed on the periodic table, where no electrons have been excited or removed. Just the most basic, low energy state of an element.

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"promoted" is just another way of saying an electron has been excited to a new energy level!

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Going to the review sessions is saving me!! In class I find it hard to fully understand topics sometimes because it's so fast and the class is so big. So being in a smaller review or step-up session really helps me because I get more one-on-one help and feel much less intimidated asking questions. E...

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Going to the review sessions is saving me!! In class I find it hard to fully understand topics sometimes because it's so fast and the class is so big. So being in a smaller review or step-up session really helps me because I get more one-on-one help and feel much less intimidated asking questions. E...

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The numbers present in his diagrams were the lengths of the bonds on the molecule. The double bonds had a lower Angstrom value because they are stronger bonds resulting in a stronger pull between molecules. The stronger pull positions them closer together and requires a smaller bond between the mole...

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Due to the unique properties of water, it was a higher boiling point. The hydrogen bonds are stronger and require more heat to break them and allow the water to boil to steam.

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Bond lengths equal one Angstrom, and will lively be given. However, double bonds will be shorter than single bonds a lot of the time because they have a stronger pull between molecules, likely pulling them closer together and requiring a shorter bond.

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the trends are identical (: both electronegativity and ionization energy increase as you go up the periodic table and increase also as you go right on the periodic table.

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They are very different. Electron affinity is the energy released when an atom gains an electron. Electronegativity is the atom's tendency to attract a electrons from other elements and is based on the elements location on the periodic table.

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According to my notes the center of the Lewis structure is always the element with the lowest ionization energy. I am not 100% sure on the explanation as to why though.

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metals can only give electrons to nonmetals

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Peter Dis1G wrote:I think instantaneous rate is the general but more accurate measure of the rate of change of concentration, and unique rate is like the instantaneous rate of individual species. (so the name 'unique')

unique rate is is the same for all reactants because of its coefficients

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Ziyan Wang 3J wrote:Does anyone know what will be tested tomorrow? Any topics on quantum world?

all review of highschool chem and topics we covered as review in the syllabus!!

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They are only between two nonmetals (:

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IS CAMPUS GETTING EVACUATED???? I keep hearing mixed answers

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classes are cancelled (: I am unsure if the sessions are still on though, likely not because of air quality. I heard there's a possibility they may evacuate the school as well but it could just be a rumor.

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nodal planes are a zone of the atom with no electrons present.

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KHowe_1B wrote:What exactly is the Rydberg equation and how do you know when to use it?

used to measure the wavelength of light emited when an electron moves from one energy level to the next. Energy of the electron changes when it jumps levels so this equation accounts for that.

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Victoria Li 1L wrote:Does anyone know what the Sapling learning thing is? I heard it was extra practice but I was wondering how to access it/what kind of practice it was.

sapling is similar to launchpad for the LS7 series, you practice problems and review concepts. It comes with the textbook lavelle posted on the site!

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