CHEMISTRY COMMUNITY

Ziyan Peng 3A

this equation is only used for irreversible processes and that would also mean that these processes are constant pressure

Ziyan Peng 3A

catalysts are used and produced again so that you see it both at the beginning and at the end of reactions where as intermediates are produced and consumed.

Ziyan Peng 3A

delta H doesn't change in the presence of a catalyst. the catalyst just gives the reaction an alternate pathway with a lower activation energy. It's like going through a tunnel vs climbing the mountain to get to the other side.

Ziyan Peng 3A

n is the number of electrons in the balanced equation.

Ziyan Peng 3A

I went to a paperless high school and have been using OneNote since. I really like that I still get to handwrite my notes and my notes on the iPad and have it be sync'ed to my laptop as well.

Ziyan Peng 3A

Talking to & hanging out with friends (safely) and just taking my mind aside from what's causing the burnout for a second to recollect my energy have really been helping me. I've found that exercising makes such a difference, although it might be hard to incorporate that into your routine at fir...

Ziyan Peng 3A

I'm a freshman and attending UCLA 16 hours ahead from Shanghai, so I'm just really looking forward to moving to LA, exploring, and being in the same time zone as the school in general :')

Ziyan Peng 3A

make sure you keep in mind what units are in the question and use the correct value in the context :)

Ziyan Peng 3A

wow I am loving this topic and how y'all are connecting chemistry to real life. it's so interesting to think about haha

Ziyan Peng 3A

Yes, I believe you are correct about it being due to equilibrium :)

Ziyan Peng 3A

Dr. Lavelle mentioned during Wednesday W7's lecture that the salt bridge is where anions leave and e- enter, so to prevent e- transfer from one beaker to another from halting because of charge buildup.

Ziyan Peng 3A

k (lower case) is taken as 1.38x10^-23 J/K and can be found in the top right corner of the constants sheet

Ziyan Peng 3A

I'm assuming that the values we need for a question would be provided in the question (like the previous exams in this course). Someone please correct me if I'm wrong :)

Ziyan Peng 3A

I don't think order really matters as long as you have all the reactants, products, and states written correctly :)

Ziyan Peng 3A

Meet Joe Black is suuuuch a good movie :,)

Ziyan Peng 3A

The Alchemist by Paulo Coelho is hands down my favourite!

Ziyan Peng 3A

n refers to the number of moles of electrons transferred in the reaction.
so just look for the coefficient in front of e- in the half reactions after you have balanced them!

Ziyan Peng 3A

º means "under standard conditions," which indicates 1atm, 1 mol, and 25ºc (298K)
so Eº refers to potential difference specifically under these conditions, while E does not specify the conditions.

Ziyan Peng 3A

Besides H2O(l) and OH-(aq), most will be the same as those given in the question.

Ziyan Peng 3A

I love salt & vinegar goldfish crackers

Ziyan Peng 3A

A state function does not depend on the path taken while properties like work and heat describe the path taken.

Ziyan Peng 3A

In the example that Dr. Lavelle gave at the end of the lecture on Tuesday of Week 6, he mentions as water is melting, H2O(l) occupies more positions and thus have a higher degeneracy and entropy than H2O(s). I am having a harder time to digest - isn't ice less dense than water thus giving it a highe...

Ziyan Peng 3A

since degeneracy is defined as the number of ways of achieving given energy of the state, as stated in lecture, and the isolated system has the greatest amount of possible states at equilibrium, thus the degeneracy is at maximum. Thinking about the gas expanding in the container which Dr. Lavelle ta...

Ziyan Peng 3A

an intensive property is not related to the amount of matter (e.g. specific heat capacity, which is already adjusted to per unit of mass and temperature, with its unit being kJ ºC g^-1), versus extensive properties which depend on amount of particles (e.g. entropy, and therefore we take into account...

Ziyan Peng 3A

qrev stands for heat in reversible processes (which we use for isothermal reversible expansion of ideal gas), as opposed to q in general which can refer to both irreversible and reversible processes

Ziyan Peng 3A

I echo what everyone and especially what Megan is saying! Kp is always for pressure and Kc for molar, and K is just the general concept of the equilibrium constant

Ziyan Peng 3A

one thing that's really helped me is looking at the units! in this case 8.314 :)

Ziyan Peng 3A

Isolated system because as far as we know matter and energy in our universe are contained in here.

Ziyan Peng 3A

Yes they are the same. Think about how water vapour is just another way of saying H2O(s), or the gas form of water.

Ziyan Peng 3A

A phase change is when the state of the matter (solid/liquid/gas) is changed. For example it could be ice melting, which is from solid to liquid.

Ziyan Peng 3A

I agree with what everyone here is saying! Notice how the units for the two units as seen on the equation sheet are different. What R value to use depends on what other units (e.g. for pressure) we are using in the specific question.

Ziyan Peng 3A

I was wondering about that too but I think it just has not been updated to include your posts from week 5 yet. I'm pretty sure the 22 posts were just tallied from weeks 1-4 and the 25 posts that it is out of are supposed to be done by the end of week 5 :)

Ziyan Peng 3A

I echo with what everyone has been saying here that because work typically describes the path taken to to get to a state, it is not a state function (which is the same regardless of the path taken).

Ziyan Peng 3A

This chart attached helped me a lot when I was studying! Hope it helps :)

Ziyan Peng 3A

Yea! Think of acid and base reactions we wouldn't get Ka & Kb if we didn't include the aq agents :)

Ziyan Peng 3A

Same as literally everyone here haha I had not been caught up with sleep until after this midterm this week :)) So proud of all of us!

Ziyan Peng 3A

Raising temperature makes K higher in endothermic reactions and lower in exothermic reactions.

Think of it in terms of the reaction curves: raising temperature pushes the reaction towards the products, which are higher energy than reactants, in endothermic reactions, and vice versa.

Ziyan Peng 3A

first you typically look at if K ≤ 10^-4, and if the question satisfies that you go ahead with neglecting x in the denominator, but you double check afterwards to see if x value < 5% of the initial concentration.

Ziyan Peng 3A

Indie rap and alternative R&B, R&B songs with electronic-esque beats really hit different!! Masego, Kali Uchis, Galimatias, Weston Estate, Savannah Ré, Riz La Vie, and of course Jhené Aiko :)) If you use Apple Music like me I highly recommend the Baseline playlist and Northern Vibes playlist...

Ziyan Peng 3A

In a simple analogy, when you are trying to get somewhere and the Maps app on your phone tell you it is 2 kilometres away by straight line distance , but when you start navigation and find out that the actual path to go around the blocks adds up to 2.5 kilometres. The straight line distance 2km is l...

Ziyan Peng 3A

I agree with these responses! Unless you are very determined to hurt yourself, your biological reflexes tell you to pull your hand away from, say a pot of boiling water. With the little amount of vapour whose heat is also partially lost to the air, especially if your hand isn't directly on top of th...

Ziyan Peng 3A

not a movie but The Office is the epitome of comfort shows :))

Ziyan Peng 3A

Coefficients! This is because x in and of itself represents some amount of molarity and in the C part of the ICE chart we are trying to quantify the amount of change. These changes should be proportional to the stoichiometry of the reaction, therefore the coefficients before x.

Ziyan Peng 3A

Yes. You can also make sense of this by thinking about enthalpy being a state property. As long as the amount of heat is greater than the system began with, it is definitely endothermic, and vice versa for exothermic reactions.

Ziyan Peng 3A

Chem_Mod wrote:No class that day due to midterm. :-)

Hello :) Are there any accommodations in place for international students for the midterm like there is for the final? Thanks in advance!

Ziyan Peng 3A

Does anyone know if there is any sort of accommodations for students located in very different time zones? I am 16 hours ahead of LA time and having the exam during lecture time does not seem very friendly with my schedule :(

Ziyan Peng 3A

Ka=10^(-pKa), just like how [H3O+]=10^(-pH) and how [OH-]=10^(-pOH). I find grouping these together easier to remember, especially if you don't want to run the math through your head every time like me :)

Ziyan Peng 3A

Chemistry puts the cation in education.

Ziyan Peng 3A

I was a little confused in the beginning as well but thinking about the equations really helped me differentiate between the two concepts: pKa is equal to the product concentrations (which includes H3O+) multiplied together over reactant concentration, but pH is just the negative log of H3O+ concent...

Ziyan Peng 3A

I agree and a stronger Kb would translate into higher product concentrations in the basicity constant equation, meaning that the equilibrium lies to the right (more dissociation), indicating that it would bee a stronger base. Since pKb is the negative log of Kb (thus Kb=10^(-pKb), this would mean th...

Ziyan Peng 3A

I think it would be helpful to go to the UA sessions earlier because I really only went for the review sessions and I think if I had gone earlier there would have been less stress when it came time for the final Hi! What do we usually do at the UA sessions? I have not taken them with Dr. Lavelle an...

Ziyan Peng 3A

^^! Adding on to that I remember Dr. Lavelle mentioning in the first lecture that he will briefly go over the fundamentals of any new topic that he talks about. I wouldn't worry too much about spending a ton of time reviewing chem 14a material especially if you feel like you digested the content wel...

Ziyan Peng 3A

Hi! Does anyone know when Dr. Lavelle says the Sapling assignments are due midnight Sunday of the week is he referring to Sunday as the first day of the week? Like is the Week 1 Assignment due on 11:59pm on Jan 10th or 17th? Thanks in advance :)

Ziyan Peng 3A

Hi! I thought that this infographic I found was quite clear in explaining this. Hope this is of help to you :)

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