CHEMISTRY COMMUNITY

AlyshaP_2B

An intermediate is formed during one step and used up during another, whereas a catalyst does not get used up.

AlyshaP_2B

The 1.8 comes from doing e^(0.59), which you should do to eliminate the ln from the left side!

AlyshaP_2B

Activation energy is the amount of energy needed for a specific reaction to occur. When energy input is needed, the reaction is endergonic, and when energy is released, the reaction is exergonic.

AlyshaP_2B

Catalysis results in lowering the activation energy for a reaction to proceed, thus increasing the rate constant.

AlyshaP_2B

When activation energy decreases, the reaction will proceed faster since there is less energy required for molecules to react upon collision, so the rate constant increases.

AlyshaP_2B

CCLE usually has options for a variety of different formats, so I wouldn't count on the exam being all multiple choice.

AlyshaP_2B

Yes, the step with the slowest rate is the rate determining step for the reaction!

AlyshaP_2B

Water should always be left out of cell diagrams

AlyshaP_2B

I think your best bet would be to go to the Peer Learning Sessions for extra help!

AlyshaP_2B

You mostly will need to use ∆G = -nFE˚and ∆G = -RTlnK, and sometimes a combination of both depending on what the question is asking.

AlyshaP_2B

n is the number of moles of electrons you have in your half reactions

AlyshaP_2B

I'm pretty sure it's 0!

AlyshaP_2B

Most UAs are very helpful in answering questions especially during the drop ins! In the other sessions they usually come with practice questions but are still open to questions from students especially at the end.

AlyshaP_2B

You want the cell to be spontaneous, so you have to check which number being flipped would result in the more positive number.

AlyshaP_2B

A larger value of the standard reduction potentials means it is harder for the element to be reduced.

AlyshaP_2B

No, you just need to include the compound and its state

AlyshaP_2B

Test 2 will cover the last page of the thermodynamics outline and all of the electrochemistry outline!

AlyshaP_2B

As long as your equation is balanced and you have the reactants and products on their respective sides, you should be fine!

AlyshaP_2B

The salt bridge allows ions to move between the two solvents, preventing a stop in the flow of electrons due to too high of a charge accumulating in one solvent.

AlyshaP_2B

Lavelle said that the second method (drawing out the diagram and figuring out which sign needs to be switched) is the better option out of the two we learned.

AlyshaP_2B

The SHE can be used to measure the standard reduction potential of different elements.

AlyshaP_2B

Test 2 is now week 9 and it will cover the rest of outline 4 and all of outline 5

AlyshaP_2B

Concentrations give the molarity, so that would be moles/liter.

AlyshaP_2B

Dina 2k wrote:how soon does he usually have it graded and back to us?

For 14A I think we got our exam back around a week and a half after the day of the midterm!

AlyshaP_2B

I think you should be fine with any topic this week because of the midterm!

AlyshaP_2B

The unit for entropy is J/K

AlyshaP_2B

Office hours during weeks that don't have exams are usually really helpful because you can ask your specific questions!

AlyshaP_2B

I think by the end of this week we will have gone over most of thermodynamics, so the midterm will include outlines 1-4.

AlyshaP_2B

Even though the units are different, an increase of 1 unit Kelvin is equivalent to an increase of 1 unit Celsius. Since this equation uses delta T rather than just T, you can use the same number without having to do any conversions.

AlyshaP_2B

Many of the constants and equations we use will be given, but there are also some that I think we will just be expected to know. I would focus on the ones Lavelle spent the most time on in lecture and also be sure to understand the relationships between all of the different equations.

AlyshaP_2B

Forming a bond releases energy and therefore is exothermic, while breaking a bond requires an input of energy and therefore is endothermic.

AlyshaP_2B

In discussion section for this week, my TA went over 4D and 4E topics.

AlyshaP_2B

The two are interchangeable here because we only look at temperature in terms of how it changes, and one unit kelvin is equivalent to one unit celsius.

AlyshaP_2B

Using bond enthalpies is the least accurate because the values used are averages, so they are not always reliable for the specific molecule in a given question.

AlyshaP_2B

Lavelle seems to be working backwards through this topic. We have covered at least 4D and 4E as of now.

AlyshaP_2B

Your TA will pass back your test during discussion section this week!

AlyshaP_2B

There isn't a practice test posted but going through the assigned homework problems is usually a good way to get practice!

AlyshaP_2B

If H2O is a gas in a given question, you should use it in your calculations for K or Q.

AlyshaP_2B

The free response questions are usually similar to the homework questions assigned and examples done in class!

AlyshaP_2B

Calculating Q requires molarity, not moles, so you need to divide by the volume to get the correct values!

AlyshaP_2B

I don't think you will need to do that, you should just use it in whatever form it is given to you and as long as you stay consistent it should get you the correct answer!

AlyshaP_2B

Rosa Munoz 2E wrote:I am confused as well on why you can use the Kb value for NH3

You can use the Kb value for NH3 to find the Ka value of NH4Cl because they are a conjugate acid/base pair

AlyshaP_2B

Test 1 will probably cover Outlines 1 and 2 on his website!

AlyshaP_2B

Autoprotolysis is the naturally occurring transfer of protons between the same type of molecule.

AlyshaP_2B

If the percent protonation is less than 5%, you can assume that your approximation was appropriate.

AlyshaP_2B

I would say it's always better to show extra work rather than not enough!

AlyshaP_2B

I don't think so, but the outlines are good resources to use while studying!

AlyshaP_2B

When the reaction is dealing with gases, I believe you should use Kp.

AlyshaP_2B

During lecture, Lavelle said solids are excluded because they don't have molar concentrations, and liquids are excluded because the solvent concentration stays the same.

AlyshaP_2B

Yes, there are discussion sections during Week 1.

AlyshaP_2B

I think the gas constant will be given to us either in the question or on an equation sheet!

AlyshaP_2B

Since some sections are earlier in the week, week 1 homework is due to your ta at the end of lecture on Friday.

AlyshaP_2B

I think this is because the conjugate base of HCl is more stable than that of HClO.

AlyshaP_2B

Nawal Dandachi 3G wrote:Acetic acid is a stronger acid because it is stabilized by resonance.

So for this question you would have to draw out the lewis structure to determine if there is resonance and if there is then that one is stronger?

AlyshaP_2B

305416361 wrote:CaO is a strong base because it fully dissociates into its constituent components

Is this just something we would have to memorize? How do we know if it will completely dissociate in water?

AlyshaP_2B

I think overall it would be a good idea to understand the details of specific biological examples from class because he spent a good amount of time going into some of those examples pretty thoroughly.

AlyshaP_2B

He might go over some previous test questions like he did for the midterm, but other than that I think review sessions for the final will be similar to how they were for the midterm.

AlyshaP_2B

I think different TAs do it differently, but by the end of the quarter all of your points should be added in.

AlyshaP_2B

I'm pretty sure we'll need our calculators during the final, especially for pre-midterm concepts that were very calculation heavy.

AlyshaP_2B

The exam is cumulative, but may focus more on topics post midterm since we've already been tested on previous concepts on the midterm.

AlyshaP_2B

I think it's possible, but it isn't very common.

AlyshaP_2B

I think we are supposed to consider a radical the same as a lone pair, it's one region of electron density.

AlyshaP_2B

The bracket signifies a coordination sphere.

AlyshaP_2B

I believe we need to know how do do it because one of the objectives on Outline 5 is "Be familiar with the rules for naming coordination compounds."

AlyshaP_2B

205150314 wrote:Does anyone know if we will get some sort of study tools again?

I'm sure Lavelle will be coordinating review sessions like he did for the midterm.

AlyshaP_2B

Dipole dipole is the strongest, followed by dipole induced dipole. London dispersion forces are the weakest, but if you have a lot of them they can add up and be strong.

AlyshaP_2B

Oxygen is more electronegative than carbon, so there will be a dipole moment there which should make this molecule polar.

AlyshaP_2B

Any time the central atom is surrounded by two or more different atoms in a tetrahedral, there will be dipole dipole forces.

AlyshaP_2B

No, hybridization will not be on test 2!

AlyshaP_2B

Knowing this formula will help you identify the shape and geometry more easily than trying to do individual molecules!

AlyshaP_2B

Lavelle touched on this very very briefly so I don't think we are expected to know any details about this concept.

AlyshaP_2B

Many different ions may have the same charge, so at that point you can use the size to determine polarizing power. Smaller = more polarizing power.

AlyshaP_2B

Both have similar periodic table trends, increasing as you move to the top right corner.

AlyshaP_2B

I think questions from the end of the Chemical Bonds outline should be fine. However, it might be more beneficial to do questions on the next outline.

AlyshaP_2B

I think problems from the last sections of the Chemical Bonds outline should be fine for this week!

AlyshaP_2B

I don't think we need to know these terms since Lavelle never mentioned them.

AlyshaP_2B

Oxygen has a lower ionization energy than Nitrogen because of the 4th electron joining. Having 2 electrons in the same orbital increases the electron repulsion, making Oxygen more likely to want to give up an electron.

AlyshaP_2B

I'm pretty sure we'll just be asked to draw the dipole moment on a Lewis structure, which is just adding an arrow that points in the direction the electron is moving.

AlyshaP_2B

A lot of the practice questions convert it to J/mol so that's probably your best bet. Just make sure your units cancel out while you're doing the equations and you should be fine.

AlyshaP_2B

The photoelectric effect tells us that light is quantized into packets of energy (photons). De Broglie's equation is the one that supports the idea of electrons being able to have wave like properties!

AlyshaP_2B

Chem_Mod wrote:Here is the key for worksheet on the quantum world.

Is there a different key with the answers to the last two questions on this worksheet? This answer key only has up until question 6 and I wanted to check my answers for number 7 and 8 on the worksheet!

AlyshaP_2B

Schrodinger’s equation uses a wave function to describe an electron because of its wavelike properties and indeterminacy in momentum and position. The wave function represents the orbital (position) that and electron can be found. Do we just have to know the concepts behind Schrodinger's equation? ...

AlyshaP_2B

Electronegativity increases up the periodic table and towards the right. Fluorine is the most electronegative element.

AlyshaP_2B

During lecture, Lavelle said an easy way to remember the direction of the arrow is that it's pointing in the direction that the electron is moving.

AlyshaP_2B

In addition to the previously given definitions, Lavelle also mentioned in class that resonance leads to more stable and less reactive molecules because it results in multiple bond characteristics being spread out throughout a molecule, lowering its energy.

AlyshaP_2B

For ions, it's easiest to first write out the regular electron configuration and then add or take away electrons depending on the charge. Since full and half filled d shells are more stable, those should be filled before the 4s. For Cu, the electron configuration is [Ar] 3d104s1, and when the charge...

AlyshaP_2B

The atomic radius is half the diameter of a neutral atom, measuring across the outer electrons. The ionic radius is half the distance between two gas atoms that are joined by an ionic bond. Both generally have the same periodic table trend: radius decreases moving across a period and increases movin...

AlyshaP_2B

Usually, non-metals with a d-subshell can have expanded octets because there are more spaces for electrons to fill

AlyshaP_2B

I think it would be best to play it safe and draw the structure with the lower formal charge because that is the one that is most stable and most likely to be an accurate representation.

AlyshaP_2B

I think homework questions would be the most efficient way to study because practicing the same types of questions as the exam will have will be a good way to prepare!

AlyshaP_2B

Energy and wavelength are inversely proportional. Radio waves are longer, so they have less energy than UV.

AlyshaP_2B

I believe that saying there is 0 KE means that after the electron has been ejected, there is no excess energy leftover that would be considered Kinetic Energy. When the energies match up, all of it is used to eject the electron so there will be 0 KE.

AlyshaP_2B

In the textbook chapters, I believe this concept only came up when referencing where electrons had 0 density or a "nonzero density." Since there weren't any homework questions assigned, I don't anticipate needing to know too many details about this concept!

AlyshaP_2B

I think most TAs are flexible about what homework you turn in! As long as the material is recent, I think you should be fine.

AlyshaP_2B

I think he will specify! However, when going through them in class he usually defaulted to using the shorthand, so I would expect that to be what's asked of us on the exams unless specified otherwise.

AlyshaP_2B

I believe Dr.Lavelle said it was because at that point in energy levels, electron repulsion comes into play so it's more stable to have parallel spins before filling in the paired spin electrons

AlyshaP_2B

I don't think it will change your answer too much, but if you're rounding at multiple steps during the process then your final answer won't be as accurate as it could. If possible, I would avoid rounding as much as possible until getting to the final step.

AlyshaP_2B

The Step-Up sessions in Covel that I have gone to have had about 15 students and 1 LA leading and going through practice problems. They do a really good job of breaking the questions down so if you're struggling with a topic or just want extra clarification, those would be great resource. However, i...

AlyshaP_2B

I think the units will be clarified in the questions. If they aren't, I would probably stick to one of the more conventional ones such as m or nm!

AlyshaP_2B

I believe the midterm and final are both outside of class/section hours! There is "Test and Exam Schedule" on Lavelle's website with details for both.

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