CHEMISTRY COMMUNITY

Cole Elsner 2J

In total the rate should be in M/s, but k will have units of 1/M*s

Cole Elsner 2J

Think of the order of the reaction when determining molecularity.

Cole Elsner 2J

E* refers to cell potential at standard conditions, it does NOT change with amount of substance. E is just the potential of the cell under ANY conditions.

Cole Elsner 2J

An example I like to think of is having to reactants, A and B, and a few different experiments changing the concentrations of each, and analyzing the change in the rate. When A is increased, let's say that the reaction shows no change. You do the same for B, still no change. I think of zero order as...

Cole Elsner 2J

Your end goal is to have all units b in M/s. With this, you can figure out what the order of the reaction is and adjust k units to reach that end goal units.

Cole Elsner 2J

It would be in K. Think about the units for R! They all need to cancel out

Cole Elsner 2J

Use the rate law, and add up the exponents of each reactant.

Cole Elsner 2J

We haven't really been taught this yet. We JUST finished our first order work, so we should wait for Dr. Lavelle to actually cover this in lecture.

Cole Elsner 2J

Just stick with kinetics. I do recommend practicing the electrochem problems not included on the test just to stay sharp.

Cole Elsner 2J

In a zero order reaction, the rate constant would just be M*s^-1. With a first order reaction, we'd have just s^-1, as we'd have M from our reactant. In second order we have M^-1*s^-1, and from every unit jump forwards, we have a higher number of M, which is just our order # - 1.

Cole Elsner 2J

If you look over some of the equations in your constants and equations sheet, you can see some overlap with dGnought and dEnought. With these equations you can mix and match in other equations in terms of one or the other.

Cole Elsner 2J

O has a charge of -2, so for of those is 8- charge total. Because the combination of Mn and O4 is -, Mn must be 7+ so when those charges are added together it matches what's given.

Cole Elsner 2J

Does the solutions manual have an error for this problem? It states that the half reaction for In3+ to In2+ is
In3+ + 2e- --> In2+
This causes the Nernst Equation to use 2 for n, when it should just be one right?

Cole Elsner 2J

Also, Fe has no phase change, so Pt is necessary as a solid electrode in the diagram cathode side.

Cole Elsner 2J

I believe n can be the change of moles in the equation or the number of electrons transferred.

Cole Elsner 2J

The salt bridge isn't actually made up of salt itself. It's tubing with gel inside to provide electrical contact between the anode and the cathode.

Cole Elsner 2J

Are you thinking about LEO and GER?

Lose Electron Oxidation

Gain Electron Reduction?

Cole Elsner 2J

Reaction is at physical equilibrium, generally =0 at phase changes!

Cole Elsner 2J

Danny Elias Dis 1E wrote:Can someone explain what is happening on a physical level when deltaG = 0 (the Gibbs free energy is at equilibrium)?

The reaction is at physical equilibrium, and most likely going through a phase change.

Cole Elsner 2J

If it's stated to be in standard conditions. If a temperature is given, use that.

Cole Elsner 2J

Aidan Ryan 1B wrote:What are things we have learned that are not state functions?

Work is NOT a state function because it depends on the path taken to get to the final result.

Cole Elsner 2J

"Test 2 covers all topics on Gibbs free energy and electrochemistry up to but not including the Nernst equation (which is all the new material covered in class Weeks 6 and 7). Test 2 starts Tuesday of Week 8."

Word for word from website. This will 100% be what we're tested on

Cole Elsner 2J

This equation helps us determine how a system behaves at equilibrium at a new temperature. The value of K itself changes, so you can really see if products or reactants are favored more or less than they were before!

Cole Elsner 2J

It's just the difference between standard conditions and specific conditions for a system.

Cole Elsner 2J

These units vary. Always write out your units for calculations, just so you know what R value is needed to solve. In order to get the write answer you need to use the correct R based off of what's asked for and what units are given.

Cole Elsner 2J

Both of these methods work! In the end it's all a state function so your path is up to you. With these problems just try to make the most out of what's GIVEN to you.

Cole Elsner 2J

Yes at constant pressure. If there is no net change in moles, there will be no work done. So there is the potential for deltaU=deltaH.

Cole Elsner 2J

Everything on the constants and equations sheet will be provided. I don't think EVERY formula is on that, so be sure to know them all.

Cole Elsner 2J

Lewis structures ARE helpful for figuring out exactly what is being broken, but it is still possible to solve these problems just by looking at the differences between the reactants and products side.

Cole Elsner 2J

The test will most likely provide these reactions, but I think knowing the general format of a combustion reaction could come in handy!

Cole Elsner 2J

I recommend doing any thermodynamic problems, as that's what was most recently covered.

Cole Elsner 2J

Because there was a certain amount of degenerate states in the initial volume, doubling said volume would double the positions molecules can take. Because there's more volume, there's more space/positions to fill, in fact, it's DOUBLE.

Cole Elsner 2J

The integral equation applies to reversible work, where P is not a constant. Use it if stated to be reversible. Use w=-PdeltaV if it's irreversible.

Cole Elsner 2J

I believe the schedule carries out as normal, unless there's a conflict of timing.

Cole Elsner 2J

Work is a lower case w and degeneracy is a capital W. They appear to be separate from each other, and not have much influence on one another. (I may be wrong about that, but w and W are still different)

Cole Elsner 2J

Delta U and delta H do not fully describe the system without entropy. Entropy is the likelihood (probability) a system will be in a particular start. The combination of delta U delta h and entropy can give more information as to how the system will change.

Cole Elsner 2J

I believe we'll learn how to do this in an upcoming lecture. Don't stress yourself out over it just yet! I'm certain we'll be taught how to do this, if not the book and chemistry community will surely help!

Cole Elsner 2J

This honestly depends on the question being asked. Given units and a period table, you should be able to know whether to convert or not to match the question. Just read carefully and fully understand what's being asked for and how you will get there.

Cole Elsner 2J

Diatomic bond enthalpies tend to be accurate, however every other molecule/bond in a chemical reaction has bond enthalpies made up of an average of thousands of different measurements. This averaging makes it inaccurate.

Cole Elsner 2J

I recommend drawing all lewis structures out and observe what has changed. Visually seeing it helps a lot.

Cole Elsner 2J

It will most likely be made clear whether or not it's constant pressure or constant volume. I believe the type of calorimeter will be said two, so know how to distinguish them.

Cole Elsner 2J

I don't think we learned this in class yet. Would be best to not stress and put it aside until we're taught what to do.

Cole Elsner 2J

I recall in lecture that a problem arises when calculating PH for a small amount of a weak acid that's smaller than 10^-7. I was wondering what I should do if this ever happens. Thanks!

Cole Elsner 2J

Maybe review autoprotolysis and ATP hydrolysis as well. These were 2 things included in lecture that may be important or asked about.

Cole Elsner 2J

This applies to pKa and pKb as well because a log is being taken. If you try to use 10^-pKa/b, you will not get the concentration you initially had, so this rule remains.

Cole Elsner 2J

I believe partial pressure can only be used for homogeneous gaseous reactions. Using Kp and Kc also depends of what information you've been given, like whether or not the problem lists things in M or atm.

Cole Elsner 2J

I believe ICE charts only take concentrations. Like mol/L or partial pressures for gasses.

Cole Elsner 2J

If there are concentrations of both products and reactants, try to figure out Q and determine if the reaction needs to go to the left or the right. This is so you know whether or not to subtract x or add x to both sides. If only given one initial concentration on one side, assume x is subtracted fro...

Cole Elsner 2J

I'm a bit confused as to how I can calculate K for the combination of 2 reactions on table 5G.2. This question asks for the value of K at 300 K for
2BrCl+H2 <-->Br2 +HCl. I don't believe this was taught in lecture, but it is on outline 1 so I'm looking for some tips.

Thanks!

Cole Elsner 2J

Both reactions occur under the same conditions, just with a different amount of O3 to begin with. More of this reactant will produce more of the product, but both reactions will have the SAME equilibrium constants. Because the concentration (or pressure) of O3 increases in the second experiment, the...

Cole Elsner 2J

I believe that equilibrium concentrations should be used when solving for K. In our lecture examples that's what we used, the concentrations of molecules at equilibrium.

Cole Elsner 2J

For this question I put that "The forward reaction rate is the same as the reverse reaction rate" was false, but it was marked wrong.
I thought the reverse reaction rate was 1/Kc, so I'm confused as to why this was incorrect. Thanks!

Cole Elsner 2J

It does have two lone pairs, but only one of them can attach to a center atom instead of a both. Because only oxygen attaches with one of its lone pairs, it's monodentate.

Cole Elsner 2J

Sulfur can have more than an octet, as added electrons can "fill" the 3d orbital. I think both structures are correct, but SO2 with 2 double bonds is more stable, as all atoms have a formal charge of 0.

Cole Elsner 2J

OH2 and H2O are the same! Oxygen has the lone pairs, so that's where the coordinate covalent bond forms in every situation. Some put O first to show Oxygen is the bonding site, however both OH2 and H2O are the same thing

Cole Elsner 2J

Typically more complex acids/bases will have names and formulas provided, but it's always nice to know more common ones and review the table in the book, just to stay sharp.

Cole Elsner 2J

The formulas don't have a charge because the combination of K3 and [Cr(CN)6] combine with no net charge

I don't think order matters much when writing in the brackets, as long as your anions are correct. However, order does matter when naming!

Cole Elsner 2J

AlyssaBei_1B wrote:For polarizability, would the trend decrease across a period from right to left because the atoms are getting smaller from right to left?

Yes, polarizablity follows the same trends as atomic radii.

Cole Elsner 2J

The trend in polarizability is similar to the trend of atomic radii. Decreases to the right and increases down the periodic table.

Cole Elsner 2J

CN- has a triple bond, so it's bond is shorter and stronger than the double bond in O2

Cole Elsner 2J

The arrow points towards the more electronegative element. This element has a delta negative, as it's where the dipole moment goes.

Cole Elsner 2J

Just know how to draw the lewis structure and name the shape based off of electron densities, bonds, and lone pairs. Wedges just help with visualization.

Cole Elsner 2J

As long as you do the work and have it all together, you should be fine.

Cole Elsner 2J

Hybridization will most likely be asked. Just know how to mix your valence electrons to understand the concept itself.

Cole Elsner 2J

Dipole moments go towards the more electronegative element in a molecule. To determine polarity, consider the shape of the molecule itself. Take into account the arrows, where they're going, if they cancel out, or if they're different atoms. If everything cancels out, it's nonpolar, but if it's even...

Cole Elsner 2J

Lone Pairs do influence shape, they are still an area of electron concentration, and should be taken into consideration instead of being omitted.

Cole Elsner 2J

Draw everything out first, then find the most electronegative atom (remember trends on the periodic table). This atom becomes delta negative, as it is an acceptor, and the other atom is delta positive.

Cole Elsner 2J

We weren't taught any set formula to calculate any bond angles. I believe the only way for us to really have an idea of what the angle may be is to memorize the shape of a molecule and what bond angles it yields.

Cole Elsner 2J

Yes it works, use whatever formula you're most comfortable with, but understand what the formula presented means.

Cole Elsner 2J

Just carry out the process of drawing the lewis structure and finding formal charge. At the end of it all once it's balanced you'll be able to figure it out

Cole Elsner 2J

yes, as long as it isn't a graphing calculator

Cole Elsner 2J

E represents the energy of the photon. h is Plancks's Constant (6.63*10^-34) and v is the calculated or measured frequency of a light source (typically UV or above for these equations)

Cole Elsner 2J

Typically the atom with the lowest ionization energy ends up in the middle for lewis structure. Remember, ionization energy increases from going up and to the right of the periodic table.

Cole Elsner 2J

They're just the results that he found. There's no specific way we need to know to find these, they're just examples of bond lengths to put things into perspective.

Cole Elsner 2J

I'm a little confused about part C of question 11. For the other answer choices in the same column, their electron affinities are equal. However, for oxygen and sulfur, sulfur has a higher affinity. Why is this so?

Thanks

Cole Elsner 2J

Even if the test isn't concept heavy, it is useful to have a deep understanding of concepts. When you perform all your calculations, you can really understand what they mean and kind of predict what the answer will look like.

Cole Elsner 2J

For part B of question 1E7, the electron configuration for nitrogen is considered to be excited. Is it because 2py is a down spin? I'm a little lost. Thanks!

Cole Elsner 2J

These really help me out a lot! Practice makes perfect, the more to do the better. Thanks!

Cole Elsner 2J

I would recommend waiting until we learn about orbitals in lecture. There's a lot of unnecessary stress involved trying to do problems that haven't been taught yet. For now just practice what we know, and when the time is right, practice orbitals!

Cole Elsner 2J

We're still in the quantum section. It's nice trying to get ahead and understanding things in advance,but I would recommend doing problems pertaining to what is currently being taught in class. This could save you some time and reduce stress!

Cole Elsner 2J

It will be given, but it's always helpful to know the mass of an electron is 9.11*10^-31 off the top of your head! It could save some time during tests so you wouldn't have to search for it!

Cole Elsner 2J

v is used in both lectures and the textbook, so it's probably the safest symbol to use.

Cole Elsner 2J

In the experiment, a detector is used. If it is not performed in a vacuum, then air molecules may get analyzed by the detector and interfere with the process. There is also the risk of air molecules interacting with the electrons in the experiment.

Cole Elsner 2J

This questions observes a line of 102.6nm on the hydrogen spectrum. It then asks to determine the values of n for initial and final energy levels of the electron that lead to this line. Any tips for how to start?

Thanks!

Cole Elsner 2J

Question 1A.3 asks to clarify what happens when the frequency of electromagnetic radiation decreases. It's basically true of false with explanation. The part of the question that confused me was part C, which states: "The extent of the change in the electrical field at a given point decreases.&...

Cole Elsner 2J

The solutions manual has Fe3Br8 listed. That's the only way it works out. I guess it's a typo in the Seventh edition :/

Cole Elsner 2J

Is it mandatory to include state symbols (s, l, aq, g) when writing out chemical equations? I was just wondering.

Thanks!

Cole Elsner 2J

Any advice for writing formulas based off of a given name? In this case, how would one write out Magnesium Sulfate Heptahydrate?

Thanks!

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