CHEMISTRY COMMUNITY

Alejandra Hernandez 2A

Thank you so much for everything!! These are always so useful :)

Alejandra Hernandez 2A

If you can manipulate the endothermic process so that you end up with a negative deltaG (either by changing the temperature or coupling it) then the process can be spontaneous.

Alejandra Hernandez 2A

ΔGº is the free energy available from a reaction at standard temperature and pressure which is 25ºC/298ºK and 1atm. ΔG is the free energy under current conditions. If ΔG-ΔGº=0 it means that the two are equal and therefore ΔG is under standard conditions. I was also confused about what the differenc...

Alejandra Hernandez 2A

It shows up in the numerator for this problem because the time is measured in seconds. Hope this helped! :)

Alejandra Hernandez 2A

Hi! In simple terms, catalysts tend to increase the forward rate, and they also reduce the reverse rate. Hope this helped! :)

Alejandra Hernandez 2A

Thank you so much Kate!! Congratulations on your graduation and best of luck in the future!! :)

Alejandra Hernandez 2A

Hi! Yes, that is correct! If the system is doing work, the work will be negative and if work is being done on the system, the work will be positive. Hope this helped! :)

Alejandra Hernandez 2A

Hi!! A reaction that's zero-order has the integrated rate law of A=-kt+A0, this law mimics the linear equation y=mx+b (or uses it as a model). This means that -k acts as the 'm' aka the slope. Hope this helped!! :)

Alejandra Hernandez 2A

Hello! The 6 H2O came from the fact that this reaction is taking place in a basic solution. As a result, after balancing oxygens the only way to balance hydrogens is through he use of OH-. However, since OH- also has hydrogen in it, you add OH- to the side that has the H2O at double the amount and ...

Alejandra Hernandez 2A

Delta U can only be 0 when you have reversible expansion and it is also only used for isothermal reactions, or isolated systems. Hope this helped! :)

Alejandra Hernandez 2A

Hello, So basically, the pre equilibrium approach is mainly used when our rate equations include an intermediate (which we do not want), so in order to get rid of it we use this approach. This (intermediate in the rate equation) will occur if the first/early step is fast and the later/next step is ...

Alejandra Hernandez 2A

Hi!! Entropy is heat transferred to and from the system to the surroundings, entropy is a measure of disorder between reactants and products, and Gibb's free energy is the energy available to do work in a chemical reaction! These values are used in the formula ΔG = ΔH - T * ΔS. Hope this helped!! :)

Alejandra Hernandez 2A

Thank you for these!! And thank you for everything you did this past quarter (and past three years!) Best of luck :)

Alejandra Hernandez 2A

The units of A are dependent on the units of k which are dependent on the equation itself! Hope this helped :)

Alejandra Hernandez 2A

We will not be asked to propose mechanisms (like writing out the elementary steps given the net reaction). However, we could be given a mechanism and not be told what the slow step is (there is only ever one). In this case you would determine the rate law however many times as there are elementary ...

Alejandra Hernandez 2A

While there will be a bit of a focus on kinetics since we haven't been tested on it, I believe that the content will be proportionate to how much time we spent on a certain topic in class. Hope that helped! :)

Alejandra Hernandez 2A

If we are to look at potential the one with the highest reduction potential will be what you want to select as the reduction half-reaction. Thus making it also our cathode. While our other will be our anode or the one with the lower potential. But if it is simply based on the diagram the anode is w...

Alejandra Hernandez 2A

Kinetics and thermodynamics both tell us different things about a reaction, so which one is more important depends on what information you're after. Kinetics will tell you about the speed of a reaction based on the pathway it takes to occur, while thermodynamics tells you about the spontaneity of a...

Alejandra Hernandez 2A

One of the reasons why it is important is because it lets us know which units of k to use! Hope this helped :)

Alejandra Hernandez 2A

Units for k are dependent on the order of the reaction. For a zero-order reaction, the units are M/s; for a first-order reaction, it would be 1/s, and for a second-order reaction the units are 1/(M x s). Hope this helped!! :)

Alejandra Hernandez 2A

Hi! To determine the overall reaction order, you have to add the reaction order for each reactant together. For example, a to find the reaction order of A + B -> C, First, find how the initial reaction rate changes if we change the concentration of ONLY reactant A (for example, the new concentratio...

Alejandra Hernandez 2A

Hii! From what I understand, pH measures acidity and basicity in a specific given solution, the lower the pH the more acidic the solution is, and the higher the pH the more basic. The pKa measures the strength of the acid!! Hope this helped! :)

Alejandra Hernandez 2A

You can look at the value of the equilibrium constant for the dissociation of Cl2 and F2. Using the table given in the textbook, the value of k for the dissociation of Cl2 to Cl is equal to 1.2 x 10^-7. The value of k for the dissociation of F2 is 1.2 x 10^-4. If you consider the equilibrium consta...

Alejandra Hernandez 2A

If A does not equal 1, it will always be given. Hope this helped! :)

Alejandra Hernandez 2A

hi!! yes, the final is going to be cumulative, and the material we are tested on should be proportional to how much time we spent talking about it in class although I do know that there will be a specific emphasis on kinetics since we have not been tested on that topic yet! Hope this helped!! :) &am...

Alejandra Hernandez 2A

The sign for work being done on a system is positive. When work is being done to a system, the sign will always be positive! Hope this helped :)

Alejandra Hernandez 2A

I think that the reverse rate of the reaction also increases because when a reaction at equilibrium happens there are both the forward and reverse reactions at the same rate. Hope this helped! :)

Alejandra Hernandez 2A

I was also wondering this myself so I looked it up and found that whatever direction you take, activation energy will always be higher than the enthalpy change. Hope this helps! :)

Alejandra Hernandez 2A

When working with the ideal gas law, I use the R=8.314 with problems that involve the energy of a gas. To solve for values in the ideal gas law like the number of moles or the value, I use R=.0821. Hope this helped! :)

Alejandra Hernandez 2A

Probably the easiest way to describe it is as a measure of the energy that is free to do nonexpansion work in a system. Hope this helped! :)

Alejandra Hernandez 2A

One of my favorite Trader Joe's snacks are the mini peanut butter cups! They're just the perfect size to snack on and they are inexpensive but still so good :) I hope you try them! I decided to give these a try and I did not regret it one bit! These are so so good, thank you for recommending! omg y...

Alejandra Hernandez 2A

The third law of thermodynamics states that in closed systems that are in thermodynamic equilibrium, the entropy of the system approaches a constant value when its temperature approaches absolute zero. Hope this helped! :)

Alejandra Hernandez 2A

The first Law of Thermodynamics states that in any isolated system, energy can be transformed from one form to another, but can be neither created nor destroyed. Hope this helped! :)

Alejandra Hernandez 2A

I also had this question! I'm pretty sure it'll be posted today, so maybe just check in once in a while and refresh the website :)

Alejandra Hernandez 2A

Hi! Here is the link for the Constants and Equations Sheet! [url]https://lavelle.chem.ucla.edu/wp-content/supporting-files/Chem14B/Constants_Equations.pdf
[/url]You can print it out in the lobby of your building or you can use the free printers at the Student Resource Center on campus.

Alejandra Hernandez 2A

If the system is absorbing heat or is being worked on, the appropriate sign to use is the positive sign; however, if the system is emitting heat or is putting in work, then the sign should be negative. Hope this helped! :)

Alejandra Hernandez 2A

My favorite show right now is Daredevil!! It is really good and has a lot of plot twists! I really recommend it :)

Alejandra Hernandez 2A

Happy late Valentines!!!! <3

Alejandra Hernandez 2A

In this context, ΔH° is the change in enthalpy when conducted under standard conditions. And ΔH is just the change in enthalpy with no specifications.

Alejandra Hernandez 2A

Delta u can be zero if and when there is no change in work or heat in the system. However, is true for isolated systems, so it doesn't work all the time.

Alejandra Hernandez 2A

Violet Mbela 2B wrote:Hi!
I think going to Griffith's observatory is one of the best museums and also the closest. It also has an amazing view for hiking and other stuff!

Wow that sounds so fun!! I would have to check it out some time! Thanks for sharing :)))

Alejandra Hernandez 2A

My favorite snacks right now are girl scout cookies!!!!

Alejandra Hernandez 2A

Something super fun to do either by yourself or with friends is spend the day at the beach!! You can take a bus there for about a dollar and you could either take a day off and relax or take some work with you and do it at the beach! Hope this helped :)

Alejandra Hernandez 2A

My favorite candy definitely has to be jolly ranchers!! :))

Alejandra Hernandez 2A

ln is log with base e and log is usually base 10 unless the base is specified. Hope this helped :)

Alejandra Hernandez 2A

One of my favorite Trader Joe's snacks are the mini peanut butter cups! They're just the perfect size to snack on and they are inexpensive but still so good :) I hope you try them!

Alejandra Hernandez 2A

One of my favorite ways to get myself moving is to take a walk to Westwood with my friends! It is always really fun because we can just talk and then maybe stop for some lunch :)

Alejandra Hernandez 2A

Honestly, I really love sitting at the tables outside the Starbucks on Weyburn. I would recommend it if you like people watching & don't mind the noise!

Alejandra Hernandez 2A

Hi! The final is going to be pretty similar to the midterms we've had this quarter, it's going to be 140 points with a 90-minute time limit. It will be cumulative so anything we've covered this quarter is fair game. I am sure he will send out more specific information as the date approaches. Hope th...

Alejandra Hernandez 2A

Definitely! I think that the more time we spent on a topic in lecture and the more problems there were on a specific topic on the syllabus, the more we can expect to see of that topic in the final. Hope this helped :)

Alejandra Hernandez 2A

Hi! All elements in the p-black that are in period 3 or higher can have an expanded octet, and the most common ones are sulfur, phosphorus, silicon, and chlorine. Hope this helped :)

Alejandra Hernandez 2A

A general rule that I have found helpful is that if a molecules lewis structure can have multiple bonds in different equivalent locations, then it has resonance. NO3-, which was brought up during lecture, is a good example of this. I definitely think that this is a good rule of thumb, if you can pl...

Alejandra Hernandez 2A

One reason that it is thought to be called "The Milky Way" is because there is Greek myth about the goddess Hera who sprayed milk across the sky, another reason is because it appears as a milky band of light in the sky when you see it in a really dark area. Wow! That is so interesting, I ...

Alejandra Hernandez 2A

The main difference is that Bronsted Acids donates a part of the acid (for ex H+) and Lewis acids accept electrons. Hope this helps :)

Alejandra Hernandez 2A

Hi! My favorite would definitely have to be The Organic Chemistry Tutor! I definitely recommend you check his videos out, he gives very clear explanations and gives a lot of detail. If you want more overview-like videos that are a little more bread but still really informative I would also recommend...

Alejandra Hernandez 2A

I definitely see where you're coming from!! Especially because we are getting so close to the end of the quarter and at this point, we are kind of burned out, it is kind of difficult to stay motivated. Something that always works to keep me motivated is to have things to look forward to, or if you w...

Alejandra Hernandez 2A

Hydrogen, helium, lithium, beryllium, and boron will never have an octet because they are stable with fewer than 8 electrons. Hope this helped! :)

Alejandra Hernandez 2A

Hi :) the x,y, & z subscripts are there to differentiate the different axes if the p orbital. Hope this helped :))

Alejandra Hernandez 2A

14a_student wrote:Does anyone know how many questions are on the final and if it will be multiple choice as well?

I believe the final will be about 30 multiple choice questions, but I am sure Dr. Lavelle will send an email with more information closer to the final date so that should clarify everything :)

Alejandra Hernandez 2A

Congrats! I'm so happy you get to see your hard work pay off! Thanks for posting your methods on here, they seem really efficient so I might have to try them when studying for the final! Keep up the great work :)

Alejandra Hernandez 2A

Yes! The E is only representative of the lone pairs around the central atom :)

Alejandra Hernandez 2A

Midterm 2 scores are up right now! Best of luck to everyone & remember grades don't define you :))) I am especially thankful for my friends & family and for this break coming up!

Alejandra Hernandez 2A

Hi! A very easy way to remember axial and equatorial atoms is by thinking of those terms with respect to Earth. The Earth's axis is vertical, and the equator is horizontal. In a 3D model, the axial atoms are placed in a vertical plane around the central atom, and the equatorial atoms are placed in a...

Alejandra Hernandez 2A

Hi! I believe you have the option to take either Math 3B, Math 31B, or LS 30B. From what I've read, you do have to take one of these in order to be enrolled in 14B but I would recommend reaching out to your academic counselor and seeing if maybe your Calc credit can replace one of those classes. Bes...

Alejandra Hernandez 2A

Hi! Generally, the stronger the IMF is, the higher the boiling point will be. The order from strongest to weakest bond is ion-ion>ion-dipole>hydrogen bond>dipole-dipole> london dispersion forces; this would then also be the order from highest to lowest boiling point. Hope this helped :))

Alejandra Hernandez 2A

Yes! You take them from the highest energy level because they are n the outermost shell and therefore easier to remove. Hope this helped :)

Alejandra Hernandez 2A

If you can, I would recommend going to office hours so you can actually talk to them and explain your situation! Wishing you luck! :))

Alejandra Hernandez 2A

The formal charge is determined by the number of electrons an atom has around it, and the oxidation number is determined by the number of electrons gained or lost by the atoms during the formation of a molecule. Hope this helped! :)

Alejandra Hernandez 2A

Ep is just the energy that is created by a dipole-induced dipole interaction! Hope this helped :)

Alejandra Hernandez 2A

Midterm 2 will only include material starting from where we left off from Midterm 1 so no need to worry about that :) Definitely still review it though so that you won't need to re-learn everything before the final!

Alejandra Hernandez 2A

The most "plausible" Lewis structure is the one that has the formal charge closest to zero, we want atoms to have formal charges of zero or get as close to zero as possible. For example, if there is a lewis structure where N has a +1 FC and another in which N has a FC of zero, the second s...

Alejandra Hernandez 2A

Double bonds are used when there are not enough electrons to fulfill an atom's octet using single bonds, however, they can also be used when creating resonance structures in order to give atoms the most desirable formal charge. Hope this helped :)

Alejandra Hernandez 2A

It is definitely easier to memorize the periodic trends! Since we know that electronegativity increases from left to right and decreases down a group, we can easily figure out which elements are more/less electronegative in comparison to other atoms on the periodic table. Hope this helped :)

Alejandra Hernandez 2A

H and He are exceptions to the octet rule because they are both in the s group meaning that their electron shell can hold a maximum of two valance e-. The reason for Li and Bi also being part of these exceptions is because they are more likely to lose an election, than gain one and complete their oc...

Alejandra Hernandez 2A

It does not matter which atoms you double bond to. Because some compounds have resonance, as long as the double bond is there, it does not matter which O you double bond to :)

Alejandra Hernandez 2A

To figure out the number of valance e- that an element has, you just need to look at its group number. For example, O is in group 6 so it has 6 valance electrons, CL is in group 7 so it has 7 valance e-, etc. Hope that helped :)

Alejandra Hernandez 2A

They are both energy measurements so they can both be used in energy equations as long as all the conversions are done properly. To convert from eV to J you can use 1eV=1.602x10^-19 J :)

Alejandra Hernandez 2A

If you're talking about De Broglie's equation, then yes as velocity increases then wavelength decreases and vice versa. However, if you are referring to speed as a constant then it should not be affected.

Alejandra Hernandez 2A

I believe that the exception of having 5 or 10 electrons in the d orbital and only 1 in the s applies to the entire group from groups 6 through 11.

Alejandra Hernandez 2A

When n=2 you have 4 orbitals because you have the 1 s orbital and then the 3 p orbitals (1s, 3p(x), 3p(y), 3p(z))

Alejandra Hernandez 2A

I think that the amplitude squared is proportional to the wave intensity, however, I would recommend that you go to TA office hours so they can give your more detail on the question and the relationship between wave intensity and amplitude.

Alejandra Hernandez 2A

Phi, or work function, is the minimum energy required to remove an electron from metal, and KE is the energy that an electron carries because of the movement when being removed off the metal.

Alejandra Hernandez 2A

When an element is in an excited state it means that some electrons have moved up orbitals/energy levels which required a higher input of energy.

Alejandra Hernandez 2A

I think for now since we have not really gone into more advanced topics, it's okay to use them interchangeably, However, the difference between them is important so I assume that once we move on into more complex concepts, they will be used properly.

Alejandra Hernandez 2A

I think a very good reference point for the equations that we might need to know would be the 'Constants and Equations' pdf that is on Dr. Lavelle's class website! :)

Alejandra Hernandez 2A

Intensity doesn't affect the ejection of electrons because the wavelength is what will affect it. :)

Alejandra Hernandez 2A

I would say to try and memorize them and especially memorize the mathematical conversions (for ex. you multiply by 10^ -3 to get from mm to m)

Alejandra Hernandez 2A

My personal favorites are Crash Course and The Organic Chemistry Tutor! :)

Alejandra Hernandez 2A

I also find it pretty impressive that we subconsciously learned a few of the very basics of chemistry as children through the process of cooking or watching others cook. (ex: melting solids by adding heat, combustion, etc) Yes! It has been so surprising to see how many chemistry concepts are intert...

Alejandra Hernandez 2A

Actually I learned a while ago that you can un-boil an egg using chemistry and thought it was pretty cool. What!? That seems so cool, I'll definitely have to look up how to do this and maybe even attempt it, this is such an interesting concept I would have never guessed it was possible to 'un-boil'...

Alejandra Hernandez 2A

Something I recently learned was the difference between heat-safe and regular glass. Heat-safe glass (like the kind you can use oven, eg. Pyrex) is made of borosilicate glass, which has a low coefficient of thermal expansion and therefore is less likely to break at high temperatures. I think this i...

Alejandra Hernandez 2A

I have not taken chemistry since my sophomore year so I can definitely relate to feeling a little lost! Something that has really helped me is looking at the textbook, although there are a lot of other amazing ( and certainly more entertaining) resources for refreshing your memory, our textbook has ...

Alejandra Hernandez 2A

I found the Audio-Visual Focus-Topics on Professor Lavelle's site very helpful in reviewing high school chemistry! I definitely agree with you! It has been very helpful to go back and watch the Audio-Visual-Focus-Topics provided by Professor Lavelle because they are basically a review or a preview ...

Alejandra Hernandez 2A

Although I have only been in this class a little over a week, I can already tell that it is going to be one that I will truly enjoy. It is very evident that Professor Lavelle is truly passionate about what he teaches and it makes the class all that more fun and engaging. I am really looking forward ...

Alejandra Hernandez 2A

I would say one thing to make sure you do is make sure you know how to navigate your scientific calculator very well and make sure you know how and why the equations we learn work. Don't just remember the equations and plug things in. :) I agree!!! This is especially helpful because a lot of calcul...

Alejandra Hernandez 2A

Just to add on-- Crash Course on Youtube is great for conceptual chemistry and overarching themes, and really helps with understanding the "greater picture" when it comes to some concepts. If you are looking for more step-by-step instruction with worked out examples, I'd highly recommend ...

Alejandra Hernandez 2A

Hey All! I'm unsure if someone has said this already, or if this even relates, but a trick I do know in the kitchen is when it comes to preparing... (drumroll) ONIONS! It's incredibly easy to prevent the onslaught of tears, all you have to do is place a wet paper towel on your cutting board while y...

Alejandra Hernandez 2A

Bon Appetit has an awesome youtube channel too and they tie in chemistry facts as to why they do certain things while cooking so it's really cool!! My favorite one from their staff is Claire <33 I've seen that show!! I also really enjoyed that you were learning some very interesting chemistry facts...

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