CHEMISTRY COMMUNITY

Violet Mbela 2B

Thank you so much! And congratulations!

Violet Mbela 2B

If the half-life doesn't change with change in concentration, it's a first order reaction. If an increase in concentration decreases half-life, it's a second order reaction. If an increase in concentration increases half-life, it's a first order reaction. For the one that does not change with conce...

Violet Mbela 2B

Hi,
At lower temperatures, molecules move more slowly and cause the reactions they are participating in to take place at a slower pace as well. Think about it in terms of how cold affects other things, like how when we're cold our muscles are stiffer. It's the same for molecules.

Violet Mbela 2B

Emma Goellner 2I wrote:The Marias, Men I Trust, and Phoebe Bridgers are really nice to work or study to

I love the Marias!

Violet Mbela 2B

Hi,
A zero-order reaction is a reaction that occurs where the rate of the reaction does not change due to a change in concentration. Or basically, it means that the rate of the reaction and the concentration of the reaction are independent of one another.

Violet Mbela 2B

Ashwin Vasudevan 3A wrote:There are a lot of youtube videos that go through certain topics more slowly to help understanding. Aslo, going to the review sessions is helpful.

I second this. The OChem tutor on youtube has saved my grade many a time.

Violet Mbela 2B

Lara Almeida 3D wrote:This form of the Arrhenius Equation is not on the equations sheet, are we expected to know it for the final?

Hi,
I think that even if you can't memorize it, you can derive it from the other form of the Arrhenius Equation so that's why it isn't on the sheet verbatim. Hope that helps!

Violet Mbela 2B

Yes, you need to change your sign.

Violet Mbela 2B

Emmaplant1c wrote:The same equation applies to endothermic and exothermic reactions I believe!

Yes, you are correct!

Violet Mbela 2B

Anne Hogue 2J wrote:What is the slope for a first order reaction again? just want to double check

Hi,
The slope for a first-order reaction is -k, or a decreasing/negative line.

Violet Mbela 2B

Hi,
Honestly I usually just switch between the two depending on how I feel, or how productive I plan on being. As someone else has mentioned, if I'm already down on campuses for something then I'll usually attend in person, but if my mood calls for a more lazy day, then I'll usually stay in.

Violet Mbela 2B

Hi,
The standard unit of time is seconds, but usually, the common rule of thumb is just to make sure that your units match up with the units of the answer/values given.

Violet Mbela 2B

Hi,
A zero-order reaction can be classified as a reaction where the rate is not affected by an increase or decrease in the concentration of a reactant. It also means that the K of the reaction is the same as the reaction rate.

Violet Mbela 2B

Hi,
So with the time conversion, since there are 60 minutes in an hour and you're converting to seconds, you need to multiply by 60, giving you 3600 seconds to use in the equation. Hope this helps.

Violet Mbela 2B

Hi,
Delta U represents the change in the internal energy of a system. So in a problem, the meaning or a negative delta U signifies that the overall change is negative, or a decrease in the overall internal energy.

Violet Mbela 2B

Hi,
It is a bit tricky considering that catalysts are not reactants nor products, so they are not technically consumed, more just utilized to speed up the reaction.

Violet Mbela 2B

Hi,
The plot of a second-order reaction would be a linear (straight line) graph with a positive slope of K+.

Violet Mbela 2B

Hi,
All you need to ensure is that the cathode-anode is > 0. Essentially, you need to ensure that the value is positive.

Violet Mbela 2B

For units, a rule I use is that the rates will always be in M/s (or mol/L*s) so I can use this value to calculate the units for k given the units of the concentrations. For example a 1st order has [A] and the units here are M, so k must be in 1/s to get M/s when you multiply them. This helps me mak...

Violet Mbela 2B

Yes, we can in most cases assume that the constant A is 1. And if it is a special case, I'm sure Lavelle/the problem will state/give us the value of A for that problem.

Violet Mbela 2B

Hi,
The equation for half-life of a second-order reaction is t1/2 = 1/(k*[A]_o), where [A]_o is the initial concentration, which will usually be given.

Violet Mbela 2B

Hi, TS stands for the transition state of the reaction. It is basically the maximum amount of energy needed to take the reactants in an equation over to products. It's essentially like a conversion quota. The reaction needs a certain amount of energy to carry out a transition, and the TS is that max...

Violet Mbela 2B

Hi,
A zero order reaction is a reaction in which the concentration decreases at a constant rate over time. Simply put, the rate does not depend on how much reactant there is, nor the concentration of said reactants.

Violet Mbela 2B

Yup, the coefficients have no effect on the overall rate law of the reaction.

Violet Mbela 2B

Hi,
Q is the ratio of products to reactants when a system is not at equilibrium. So, when Q=K, this states that the system is at equilibrium. And opposed to Q, K is a ratio of products to reactants when a system is at equilibrium. So you only really see K at equilibrium.

Violet Mbela 2B

Daniel Li 3C wrote:I think that Dr. Lavelle stated that they were very rare because they are independent of the concentration of the reactant which is very uncommon.

Yeah I'm pretty sure that's what he said in lecture. So yes, they are the rarest type of reaction.

Violet Mbela 2B

Yes, rate constants will always be positive because they involve concentrations which cannot be negative under the circumstances we deal with rate constants.

Violet Mbela 2B

In class we used an example of diamond reverting to graphite, which was favorable in thermodynamics but unfavorable in kinetics. Kinetics only dictates the speed of a reaction, so does this mean a diamond would slowly revert back to graphite given enough time? Or would kinetically stable mean that ...

Violet Mbela 2B

Hi,
Since catalysts speed up a reaction, the activation energy is lowered. So graphically, the addition of a catalyst lowers the overall curve.

Violet Mbela 2B

Hi,
A is the frequency of collisions. It's usually 1, but it represents the factor or essentially the chance of collision in a system space.

Violet Mbela 2B

Yes, as everyone else is saying, I highly doubt we will come across the third-order reactions graphically in this course.

Violet Mbela 2B

Kinetics tells you the rate of the reaction, while thermodynamics is more about if a reaction will occur at all. Thermodynamics can tell you if a reaction is favored to occur in the forward or reverse direction, but it cannot tell you how fast it will occur -- kinetics tells you the rate. In the ex...

Violet Mbela 2B

Hi,
Basically, you need to think about what is being used up and what is being produced. So if the reactants are being used, they're decreasing while the product is increasing since it is produced. So the products will be positive and with a positive slope while the reactants will be negative.

Violet Mbela 2B

Hi,
I made the same mistake on that problem. But what you need to do is ignore C because its order is 0, so it is ignored in the problem.

Violet Mbela 2B

Hi,
Kinetic stability is affected by the speed of the reaction. So a very fast reaction won't be very stable but a slow one will.

Violet Mbela 2B

Hi,
You would find the overall order of the reaction as a whole by adding up the orders of the individual components of the reaction.

Violet Mbela 2B

14b_student 2E wrote:The focus is on thermodynamics and kinetics

Yeah, I've the same thing from my TA. The material will be proportional to what we covered in most in lectures/spent the most time on.

Violet Mbela 2B

Thank you so much!

Violet Mbela 2B

Hi, For #11, I cannot get the section that asks: "How much time, in minutes, will elapse before the N2O5 concentration decreases from 0.0705 mol⋅L−1 to 0.0274 mol⋅L−1?" The problem states that it's a first-order reaction, so I've been using that equation, but I still cannot get the correct...

Violet Mbela 2B

So for #7, I've correctly found the orders of each reactant, A=1, B=2, and C=0, but when I try to do the rate law with the general concentrations, I keep getting it wrong despite having all of the components. I've been getting k[A]^1[B]^2[C]^0 incorrect and I don't know what else it could be since I...

Violet Mbela 2B

My favorite food is pasta, so I definitely go to Epicuria often, haha.

Violet Mbela 2B

Amy Kalteis 2F wrote:I like the Trader Joe's version of Takis or Scandinavian swimmers!

I 100% second the Trader Joe's Takis! They're so good!

Violet Mbela 2B

I think the corner bakery is a great place to study! It hasn't been open recently, but once it does I think that would be a great place to try out!

Violet Mbela 2B

Alejandra Hernandez 2A wrote: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 :)

Yes! This always clears my head and allows me to restart my mindset!

Violet Mbela 2B

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!

Violet Mbela 2B

Hi Bailey, my favorite candy is most definitely Reese's!

Violet Mbela 2B

Yes, if the chlorine is outside, it is -ide.

Violet Mbela 2B

Intra is within itself, inter is between one or more.

Violet Mbela 2B

[OH] is hydroxide and [H] is hydronium. Hope that helps!

Violet Mbela 2B

Hello. Note that you have 2 moles of OH from Ca(OH)2. This molecule is a base. Therefore, if you are doing -log([OH-]), you are calculating for pOH. Since you have 2 moles of OH, multiply 2 x 2.5 to get 5M OH- pOH = -log(5) = -7e-1 pH = 14-(-7e-1) = 14.7 Note that values outside the pH range of 0 a...

Violet Mbela 2B

Basically, the conjugate acid or base is the acid or the base after it gets what it wants: so either accepts a donated electron or removes and unwanted electron.

Violet Mbela 2B

Hi, the work function is the minimum amount of work needed to remove an electron.

Violet Mbela 2B

Yes, as the others have said, ionic bonds most likely occur with metals and nonmetals. They are also the strongest IMFs.

Violet Mbela 2B

I try to think of it as angular, so sharp, geometric, and radial as round/circular.

Violet Mbela 2B

In a multiple-choice question, do you think it would be expressed as sp^3 or 2sp^3?

Violet Mbela 2B

Do you expect we'll have to calculate these on the final? Or just use pKA in conjunction with pH and finding acids and bases?

Violet Mbela 2B

I think it's always better to just look at what is making up the compound, including the ions. The general rule of thumb is that an acid is going to donate an H+ ion while a base is going to accept it. For acids: if the compound starts with H or ends in COOH, it's probably an acid. Strong acids are...

Violet Mbela 2B

So the periodic trend is up and to the right?

Violet Mbela 2B

Generally you will be given either the name or the formula. If you are given the name, you can use the ligand naming conventions to find what the charge should be. If the compound has a charge, it will be called an ion. Conversely, if you are given a compound that is shown to be charged , you will ...

Violet Mbela 2B

You have to make sure that you pay attention to what orbital the element is in, because that determines how many e- it can hold.

Violet Mbela 2B

But even if you don't completely have a grasp on it, it will be multiple choice so you can probably figure it out.

Violet Mbela 2B

Would we ever have to classify different coordination compounds?

Violet Mbela 2B

Would that be the same for induced dipole moments and other IMFs?

Violet Mbela 2B

Devika Nair 2G wrote:In Chem 14A, we do not need to know how to calculate PKa or Ka.

Will we need to know in the future?

Violet Mbela 2B

Monse Mata 3D wrote:Yes, you can! I attached an image with the formulas and I hope it helps :)

Thank you so much! This image is super helpful!

Violet Mbela 2B

Yes, as they mentioned you need more than one orbital to form the hybrid bonds. I see it as hybrid= a mix/both, so it's a mix of orbitals.

Violet Mbela 2B

For me, I kinda look at it like what's on the outside and the inside. It's best seen in triple bonds, but in double bonds, I see it as one outside and one inside.

Violet Mbela 2B

Yes, you are likely going to get in.

Violet Mbela 2B

Thank you so much for sharing!

Violet Mbela 2B

I'm a bit confused, doesn't the size influence the intermolecular force? Like with London dispersion forces?

Violet Mbela 2B

Hello,
What causes the formation of a dipole, and how is it different from an induced dipole?

Violet Mbela 2B

I think it's helpful to acknowledge your progress and allow yourself some type of positive reinforcement for what you've done correctly/well. Always harping on the negative can be seriously detrimental to your progress!

Violet Mbela 2B

Hello,
Can someone please explain the circumstances in which you would assign a certain IMF to a molecule? How do you know what is present, and what conditions are needed for each?

Violet Mbela 2B

Helen Ringley 2E wrote:Remember that ions can make elements have different amounts of valence electrons, you can't always assume it is a neutral atom.

With ions, a positive indicates that you take away an electron while a negative indicates you adding an electron, right?

Violet Mbela 2B

Hi,
How do you know whether to use a single, double, or triple bond in a chemical structure?

Violet Mbela 2B

P.S. It would be a big help if what lectures we started at and will stop at can be shared!

Violet Mbela 2B

Hello,
What exactly is going to be covered on midterm 2?

Violet Mbela 2B

Shreyesi Srivastava 2D wrote:Do you have 11 protons?
Cause you sodium fine

Please, someone test that one out!

Violet Mbela 2B

I always just login, go to quick links, and then click on "my posts."

Violet Mbela 2B

Hi,
Will we be going over the results and solutions in class? Or is that for office hours?

Violet Mbela 2B

When I am working on finding molecular formulas, the process makes sense to me up until you divide all of the mols by the smallest value to find the integers. Because I know that you are multiplying to try to find the smallest possible integer, but what doesn't make sense is how you find the number ...

Violet Mbela 2B

Hi,
When I open the lockdown browser it asks me for canvas PROD or canvas TEST. Which one do I choose, or is this an error?

Violet Mbela 2B

Hello,
I think the rounded 3.0 would work just fine, but even if you felt the need to use the other value, I think that since the midterm is multiple choice, whether you rounded or not you would be able to see your answer within the bank.

Violet Mbela 2B

Hey all,
So do we have to do any conversions for the two thresholds, or are they in the same units?

Violet Mbela 2B

Hello,
Since other particles like neutrons have mass, could you use those for the equation? Or is a neutron too big to be considered?

Violet Mbela 2B

Hello,
Since other particles like neutrons have mass, could you use those for the equation? Or is a neutron too big to be considered?

Violet Mbela 2B

Hi!
I'm sure many people have already put this name into the hat but Northern Cafe Dumpling House on Gayley has the best pork potstickers and soup dumplings! And their prices and portions are fair as well.

Violet Mbela 2B

When you melt sugar and water into invert sugar syrup, it is a hydrolysis reaction that can be sped up with catalysts such as cream of tartar or lemon juice. I never thought about it but I do make a lot of syrup so it's interesting to see the chemistry in action and I have this thread to thank for ...

Violet Mbela 2B

Hi,
Does this also tie into diffraction and how light acts as a wave and a particle simultaneously?

Violet Mbela 2B

Hi!
I don't know if you are taking LS30A, but something that I connected to this is thinking of the waves as vectors. So vectors going in the same direction can be added to create a large vector but vectors going in opposite directions take away when you combine them. I'm not sure if that helps.

Violet Mbela 2B

Hello,
Is the midterm only going to be the quantum world? Or what else will be on it?

Violet Mbela 2B

Hi all!
What type of wave is 10^-15? Is is visible light, or like UV or Gamma?

Violet Mbela 2B

No worries, its important to understand the difference. Quanta are a discrete quantity of energy whereas photons are small particles of light. It can be confusing because like someone said above, photons are light quanta. Hi, so when you say that quanta are discrete quantities of energy, does this ...

Violet Mbela 2B

Thank you so much for this post! Since I am a more visual learner, the addition of the model really helped to clear things up for me!

Violet Mbela 2B

For those of you who are knowledgeable on balancing equations, when you are looking at both sides of an equation and deciding on what to multiply, what does it mean when you constantly end up with the coefficients being too large? Does this mean that you should not be multiplying by the least common...

Violet Mbela 2B

Hey All,

I find that Chemistry is my hardest class to keep up with and was wondering if there were any study groups/sessions for people living in Reiber Hall, or any that take place here? If so, please let me know!

Violet Mbela 2B

Thanks for the cool acronym Nico! I was just wondering if this only applies to basic SI units or if it also applies to quantum units and atomical measures?

Violet Mbela 2B

Hi,

After finishing this week's homework, I'm realizing that I don't exactly have as tight of a grip on sig figs as I thought I did. For one, the entire 0 debacle was a challenge for me. Why is it that sometimes trailing zeros can be ignored, but other times they are counted as a significant figure?

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