CHEMISTRY COMMUNITY

BKoh_2E

Molecularity just shows us how many molecules are participating in the rate determining step of a mechanism.

BKoh_2E

I highly recommend Rosa and Wesley. They've been super helpful for 14A & 14B.

BKoh_2E

Since the textbook and sapling problems tell you what type of solution it is in, Professor Lavelle will likely tell us on a final question.

BKoh_2E

A straight line represents the order based on one of the three formulas. A first order reaction is a straight line when graphing ln[A], a second order reaction is a straight line when graphing 1/[A], and a zero order reaction is a straight line when graphing [A].

BKoh_2E

Thank you for the reminder! This is really important not to forget.

BKoh_2E

I really enjoyed the quantum unit!

BKoh_2E

I'm looking forward to meeting new people and making friends! Hopefully I will be able to get involved with in-person research as well.

BKoh_2E

I always make sure to get enough sleep two nights before the exam. Usually I plan my studying so that I do not need to cram the information the day before the test. Right before the exam, I wash my face with cold water and take a nice deep breath.

BKoh_2E

I was surprised at how many conceptual problems there were on midterm 2. Although I didn't do as well as I hoped, the test was definitely fair. Hopefully we will finish the new content soon so that we will have more time to review for the final!

BKoh_2E

I've heard that 14C isn't as bad as people make it out to be. My friend told me its a lot of memorization, but not very difficult conceptually.

BKoh_2E

It is highly likely the final will be divided equally. He will probably send an email soon telling us what to expect!

BKoh_2E

I highly recommend Rosa and Wesleys' review sections. They're really good at explaining the conceptual parts of the class

BKoh_2E

You are correct. This concept was a little bit confusing for me in the beginning. Just remember that the oxidizing agent is NOT getting oxidized, and the reducing agent is NOT getting reduced.

BKoh_2E

I think its important to remember that charge is measured in coulombs, while potential is measured in volts.

BKoh_2E

Conceptually, what does it mean when an E value is negative? I'm having a hard time understanding the concept and how it relates to E∘.

BKoh_2E

This problem was tricky because I didn't remember learning how the dot symbol affects balancing the equation. I believe the dot combines the two molecules into "one unit." Any coefficient you put in front of the first part will affect the second half. If you try to balance them individuall...

BKoh_2E

The max is 5 posts weekly for 50 points total. Some TAs don't calculate the points weekly, so just check with yours what they prefer.

BKoh_2E

It is also good to know the difference between adiabatic and isothermal. Isothermal processes have no change in temperature. In an adiabatic process, the heat transferred is zero, but the change in internal energy will depend on if there is work.

BKoh_2E

Chem_Mod replied in another post "In Chem 14B we'll keep it simple. Whenever a conducting electrode is needed, use Pt."

BKoh_2E

The way I like to remember anodes and cathodes is by relating them to anions and cations. Anions are negatively charged, while cations are positively charged (because CATs are awesome). Electrons are released at the anode during oxidation (LEO the lion, loss of electron to the CAThode) and goes to t...

BKoh_2E

Can somebody explain how a chemical reaction produces electrical energy?

BKoh_2E

I ate ice cream and a slice of cheesecake to reward myself :)

BKoh_2E

Can somebody explain under what circumstances the enthalpy ΔH is the same as q?

BKoh_2E

Since there are so many formulas for this midterm, I recommend writing them down and making sure you know when to use them for different problems. Also, like the others have said, the step-up and review sessions are very helpful.

BKoh_2E

The change will be insignificant. I wouldn't worry about using it because the 5 digit isn't on the constants sheet. On the midterm you would just pick the closest answer if there is a slight decimal difference.

BKoh_2E

That is correct. It is also good to understand that if ΔS_univis positive, then ΔG_rxn is negative. Therefore, the reaction would be spontaneous.

BKoh_2E

It sounds like you're on the right track for the first part of the problem. Here is my equation: 2Al(s)+3Cl2(g)⟶2AlCl3(s)ΔH∘=−1408.4 kJ The change in entropy of the system is given by ΔS∘sys=∑S∘(products)−∑S∘(reactants), so you plug in the standard entropy values for this equation, multiply by their...

BKoh_2E

Entropy is also a state function that shows the number of microstates possible for the system through degeneracy. I think it'll be one of the key concepts to know for the next midterm because it relates to the second law of thermodynamics & there are several formulas relating to it on the consta...

BKoh_2E

Like Kaitlyn said, the textbook is definitely the most important resource. If you really don't have time to do all of the problems, focus on the more difficult ones. If you can do the difficult ones by yourself, the easier ones shouldn't be a problem.

BKoh_2E

Also remember that if work is done on the system or heat is transferred into the system, then it is positive.

BKoh_2E

This happens to me all the time. Before I do any chemistry work I always wash my face with cold water to really wake myself up. It also helps to double check the calculator inputs before pressing enter.

BKoh_2E

If you feel like you aren't learning anything new at the workshops, don't go to too many. Focus on the difficult textbook problems and make sure you can do those.

BKoh_2E

Although this probably won't be tested specifically, it may be useful to know ATP hydrolysis is an exothermic reaction, and thus moves towards the reactants when exposed to heat. I believe this was briefly mentioned in the textbook.

BKoh_2E

When doing calculations, I always make sure to double check the values before moving on. Especially when using the calculator, make sure to check again before pressing the enter button. I've entered the wrong digits and decimal places into my calculator way too many times.

BKoh_2E

Here is the link for the Chem14B Pizza Rolls review !

viewtopic.php?f=160&t=58508&p=224708&hilit=pizza+rolls&sid=297c8e7a86a4e1bca675da3c35540d64#p224708

BKoh_2E

To find delta H using bond enthalpies, you need to know the structure of the molecules. The problem will provide a value for each type of bond (ex: C-C, C=C). Looking at the reaction, see which bonds from the reactants are broken, and which bonds are then formed to make the product. To solve, take t...

BKoh_2E

Dr. Lavelle also mentioned out of the three methods for finding Delta H, bond enthalpies are the least accurate.

BKoh_2E

The way I like to thing of it is that phase changes require energy to occur. As a result, steam will have more energy than liquid water. The extra stored energy that steam has because it is a gas will be released when it touches your skin and changes to a liquid, so it will burn more than liquid wat...

BKoh_2E

I always make sure to exercise when I feel anxious. It might seem like a lot of effort, but I guarantee you'll feel better afterwards.

BKoh_2E

Make sure you understand the conceptual topics. He usually includes a mixture of concept and calculating problems on the midterms. Personally, I re-do all of the homework problems before the exam.

BKoh_2E

The important part to understand is that you would add the enthalpy of the phase change. I don't believe you will need to solve this type of question though because none of the textbook problems he assigned have it.

BKoh_2E

The reaction of 1.40 g of carbon monoxide with excess water vapor to produce carbon dioxide and hydrogen gases in a bomb calorimeter causes the temperature of the calorimeter assembly to rise from 22.113 8C to 22.799 8C. The calorimeter assembly is known to have a total heat capacity (calorimeter co...

BKoh_2E

Monoprotic acids can only give away one proton, while polyprotic acids can donate more than one. I believe it is the same rule for monoprotic bases, where a monoprotic base can only accept one proton.

BKoh_2E

Remember that molarity and concentration are basically the same thing. The formula for molarity is M=mol (n)/volume (L). So for the formula PV=nRT, we can divide both sides by volume and get P=MRT.

BKoh_2E

I think you're applying it correctly. That was my understanding when Dr. Lavelle explained it.

BKoh_2E

There are some guidelines to figure out if an acid or base is weak, but in general you will need to memorize the strong acids. The strong acids are HCl, HBr, HI, H2SO4, HNO3, HClO4, and HClO3. You can assume any other acid is not a strong acid. Additionally, acids with Carbon are usually weak. Stron...

BKoh_2E

It is safest to assume this only when K is less than 10^-4. Remember this is not the same as assuming x is zero in all cases, because we still need to solve x for the problem.

BKoh_2E

If you don't fully understand the topics or just want a review, step-up sessions are good. If you mostly understand the content and want more practice problems, go to the workshop sessions. The drop-in sessions are for when you have either homework or concept questions.

BKoh_2E

Molarity and concentration are the same for the purpose of these problems. Just remember that molarity is mol/volume (L), and "n" refers to moles.

BKoh_2E

They shouldn't expect you to make up for last quarter. Just inform your TA so they are aware when they input the grades.

BKoh_2E

You are correct that a reaction at equilibrium will not naturally make more products and have a Q value greater than the equilibrium constant. Examples of when Q will be higher are due to external factors (reactants have been removed) or the reaction has not yet reached equilibrium .

BKoh_2E

Number 35 says: The following plot shows how the partial pressures of reactant and products vary with time for the decomposition of compound A into compounds B and C. All three compounds are gases. Use this plot to do the following: (a) Write a balanced chemical equation for the reaction. (b) Calcul...

BKoh_2E

One of the UAs mentioned that most of the metalloid oxides such as Al2O3 are amphoteric.

BKoh_2E

Since he said there will be textbook problems on the final, you should focus on those first. The review sections this week will definitely be helpful as well.

BKoh_2E

Yes! H+ and proton are interchangeable. If you take the LS7 series they also reference H+ as protons.

BKoh_2E

Identify the salt that is produced from the acid–base neutralization reaction between (b) ammonia and phosphoric acid, Write the complete ionic equation for each reaction. I understand how to identify the salt, but I'm not sure how to write the ionic equation. Can anybody go through their thought pr...

BKoh_2E

Select an acid and a base for a neutralization reaction that results in the formation of (a) potassium bromide; (b) zinc nitrite; (c) calcium cyanide, Ca(CN) 2 ; (d) potassium phosphate. Write the balanced equation for each reaction. I understand how to do part A, but I'm stuck on part B. I don't un...

BKoh_2E

In general, strong acids have weaker bonds. Acids with Carbon are also weak. However, we will likely need to memorize the list because these trends are not inclusive of all types of acids.

BKoh_2E

Here is an image that may help you visualize it!

BKoh_2E

HF is a weak acid because the bond between Hydrogen and Fluorine is so short. It is more difficult for the bond to be broken, so it will not completely dissociate in water.

BKoh_2E

I believe weak acids can be characterized as Bronsted acids as well. As long as it donates protons it will be a Bronsted acid.

BKoh_2E

Professor Lavelle mentioned in lecture that HBR is stronger than HCl. I just wanted to confirm that the weaker the bond is the stronger the acid is. So HAt would be a much stronger acid than HCl?

BKoh_2E

All double bonds have one pi bond. Since resonance structures are a blend of the possible structures (delocalized electrons), the pi bonds in a resonance structure would also be delocalized.

BKoh_2E

It is important to know that it would more tightly connected due to multiple bonding sites.

BKoh_2E

They both are correct. You can use either one of them.

BKoh_2E

Since Fluorine has the highest electronegativity, I try to remember the trend as the closer you get to Fluorine (top & right) the more electronegative.

BKoh_2E

Definitely try to go to the UA sessions if you can. They're super helpful.

BKoh_2E

I believe that is correct. One of the LAs informed me that the number of nodes is related to the "l" orbital angular momentum quantum number. Since the d orbital is "l"=2, it will have two nodal planes.

BKoh_2E

In general, polarizability will increase down and to the left because those elements have a larger radius and more electrons; so, Francium would have a high polarizability. Polarizing power increases as the size gets smaller and the charge of the cation increases. For example, an Aluminum 3+ cation ...

BKoh_2E

Copper is one of the exceptions to the standard electron configuration rules. The other exception is chromium. Based on the rules we learned, it would appear copper's electron configuration would be [Ar] 4s^2, 3d^9. However, the d subshell would be very reactive because it only needs one more electr...

BKoh_2E

It is also good to know that resonance structures are indicative of stability because they represent delocalization of electrons. They spread energy over a larger
area rather than keeping it confined to a small area.

BKoh_2E

Why is it when you draw H2O's Lewis structure you draw both lone pairs on the same side pushing down the bonds? I thought you were supposed to put the lone pairs as far away as possible like in XeF4's structure.

BKoh_2E

A good method to stay on track for a class is to make sure you truly understand all the material from one lecture before next class. That way you won't fall behind and feel overwhelmed. Right before starting a test if I feel nervous, I like to close my eyes for a few seconds and take a deep breath. ...

BKoh_2E

Can anybody explain the logic behind induced dipole-induced dipole interactions?

BKoh_2E

How is Hydrogen bonding different than normal bonding? I think he mentioned that Hydrogen can form a bond with a lone pair, but I didn't understand why this is possible.

BKoh_2E

Can anyone explain the dissociation energy trend in the periodic table? I want to make sure I understand it correctly.

BKoh_2E

Can anybody explain what makes a molecule polar vs. nonpolar and how it relates to dipoles? I know he mentioned it in lecture, but I didn't really understand it.

BKoh_2E

The Rydberg constant (R) should be in the formula. On the online version its in a different font and italicized. It appears very lightly when printed, so maybe that's why it didn't appear on your sheet.

BKoh_2E

Agreed. I'm so glad Professor Lavelle organized these study sessions. The LAs have have been extremely helpful, and they always make great practice worksheets.

BKoh_2E

What type of reactions are acid-base reactions? Do coordinate covalent bonds only occur in Lewis acid-base reactions or can they occur in any molecule?

BKoh_2E

In the Lewis structure for BF₃ , why can't there be a double bond with one of the Fluorine atoms? Is formal charge always more important than having an octet?

BKoh_2E

Can anybody explain which elements can have an expanded octet? In lecture he mentioned something about the d-block, but I didn't really understand.

BKoh_2E

In lecture Professor Lavelle mentioned that the 4s orbitals of Potassium and Calcium were occupied sooner than expected, but I don't really understand what it means when writing their electron configuration. Can anybody clarify?

BKoh_2E

Why do we write electron configurations from lowest energy to highest energy? Wouldn't writing it from highest to lowest give you more information at first glance?

BKoh_2E

Are degenerate orbitals just orbitals with the same energy? Is hydrogen the only atom that will have degenerate orbitals because its a one electron system?

BKoh_2E

Can anybody help explain the relationship the quantum numbers n, l, and m have with each other?

BKoh_2E

Yes, you're correct. Also remember that the Lyman Series corresponds with UV light, while the Balmer Series corresponds with visible light. Sometimes questions online provide the wavelength of the incident light, so memorize the general wavelength range for UV light & visible light.

BKoh_2E

Yes, kg is the SI unit for the formulas. Be careful because a lot of problems give values, especially electron or proton mass, in grams.

BKoh_2E

The mode of the calculator shouldn't matter for this test. Just remember to try and use parentheses so there aren't errors when doing arithmetic with X10^x values.

BKoh_2E

Just think of a nodal plane as a place electrons won't be. You are correct only p, d, and f orbitals have a nodal plane, while the s orbital does not. Nodes are points of zero amplitude along a standing wave, which means there are no electrons present.

BKoh_2E

In general, you should how the wavelengths of each group relate to each other. The important ones to take note of are visible light (red and blue), UV light, microwaves, x-rays, gamma, and infrared. I doubt he would ask for the specific wavelengths without providing extra information.

BKoh_2E

I definitely agree with what everyone else has been saying. Velocity is speed in a given direction, while momentum is the motion of an object. The equation illustrates that momentum is directly proportional to an object's mass and directly proportional to the object's velocity. Just be aware that a ...

BKoh_2E

I was confused by a practice problem from one of the TA's worksheets. An electric current is passed through a tube that contains Hydrogen gas. Light is then passed through the prism and the emission spectrum of Hydrogen gas is recorded. A band was recorded, and it has a frequency of 6.1684E14 hz. Wh...

BKoh_2E

What happens if $\Delta p X \Delta x$ is less than Planck's/4pi? or is that not possible?

BKoh_2E

You probably won't need to know the specific wavelengths, but definitely know the general size of each group compared to the rest. The common ones we will see are UV, X-rays, visible (know red and blue), microwaves, and infrared.

BKoh_2E

What do the Balmer & Lyman Series represent in atomic spectroscopy? Can anyone explain why they are important?

BKoh_2E

Does anyone know if you can only use metals for the photoelectric effect experiment? If so, why don't non-metals work for it?

BKoh_2E

Correct! It is way too small for us to observe. Wavelength is inversely proportional to mass, so the larger the object the smaller the wavelength.

BKoh_2E

The question asks what is (a) the energy of a single photon of blue light of frequency 6.4 X 10^14 Hz; (b) the energy per mole of photons of the same frequency. Once you calculate part a, how do you find the energy per mole of photons? The formula they used is E(per mole of photons) = N(subscript A)...

BKoh_2E

Yes, they are both the same. Be careful not to confuse them as a shortened version of molecule, especially when doing conversions.

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