CHEMISTRY COMMUNITY

SamayaJoshi1A

You have to look at the equation and determine how many electrons are given off. Find this using the charge on each molecule and compare the two sides of the reaction.

SamayaJoshi1A

What is the normal units for the speed of the reaction?

SamayaJoshi1A

I also know that balancing a redox reaction in a basic solution involves and extra step to get rid of the H+ ions. f

SamayaJoshi1A

The higher oxidation the greater reduction potential!

SamayaJoshi1A

How do you go from the pressure equilibrium constant to the molarity constant? Do you use PV=nRT?

SamayaJoshi1A

Does anyone know whether H20 is in liquid or gas form when you add it when balancing redox equations?

SamayaJoshi1A

Gibbs free energy also tells us if the reaction is spontaneous or not based on the sign (positive number or negative number)

SamayaJoshi1A

These are two different things and are not interchangeable.

SamayaJoshi1A

The salt bridge is going to involve a transfer of electrons, causing each side to lose or gain charge.

SamayaJoshi1A

Yes the anode is on the left and the cathode is on the right.

SamayaJoshi1A

In what real-life applications would a reaction not be reversible? I remember in some of the textbook questions the reactions only occurred in the forward direction.

SamayaJoshi1A

This was cool to learn. I did not understand how chargers worked until this lecture.

SamayaJoshi1A

What is the difference between a state function and U/T?

SamayaJoshi1A

Oxidizing just has to do with the addition and subtraction of oxygen right? Can all molecules by oxidized?

SamayaJoshi1A

This is because the larger the molecule (i.e. larger atomic radius) the more disorder aka ways the atoms can be placed exists.

SamayaJoshi1A

Can someone explain why in the textbook they keep coefficients in fractions- isn't this not technically balancing.

SamayaJoshi1A

You should just pour yourself into other work... sounds bad but it helps.

SamayaJoshi1A

How do catalysts affect activation energy?

SamayaJoshi1A

I remember the fine last quarter being brutal. Do the textbook problems again. The nice thing is that Lavelle understands when the finals are too hard and will adjust points for that.

SamayaJoshi1A

I worked all though last quarter. I found splitting my schedule so that my work is spread out throughout the week makes everything more manageable.

SamayaJoshi1A

Yes- also think of it as a one way reaction, where products are being formed and no reactants are being formed. In the graph on Sapling 20, the equation slopes down when Q<K and then it reached the minimum (equilibrium) and the back up to reach Q>K.

SamayaJoshi1A

I just think of temperature and heat/energy as two different things.

SamayaJoshi1A

Kc is just a specification of K. K is an equilibrium constant with no units, while C is in regards to the concentration. If you calculated K using pressure, the constant would be specified as Kp,

SamayaJoshi1A

Entropy and disorder, meaning how much the particles move go hand in hand. This is nice when I think about phase changed because as we know, the higher the temperature, the more mobility. Use the billing point to order them based on entropy.

SamayaJoshi1A

Can someone also explain the relationship between equilibrium and spontaneity. I know this was confusing for me on the last Sapling question.

SamayaJoshi1A

In what condition would we use a number that is not 8.314?

SamayaJoshi1A

In what condition would we use a number that is not 8.314?

SamayaJoshi1A

Can someone explain why q equaled the change in U in the last few questions. I am confused on why they are the same answer but use different notations.

SamayaJoshi1A

This one was kind of difficult. It took a lot of calculations and it seems super easy to mess up with calculations. Does anyone have any specific ways they organize their work? I have trouble with that .

SamayaJoshi1A

I recommend just memorizing strong acids. It really helps.

SamayaJoshi1A

It is 1/K. Also remember that K is going to be different than enthalpy, in enthalpy its a sign change.

SamayaJoshi1A

What I do is i think about where the heat goes. If heat is needed to go from one phase to the other, heat is taken in, therefore it is endothermic. If it also helps, cold blooded animals are endothermic, meaning they take in heat from the sun.

SamayaJoshi1A

Im pretty sure the only one is temperature.

SamayaJoshi1A

Can someone clarify why we have these numbers set as the STP?

SamayaJoshi1A

Normally its the week after.

SamayaJoshi1A

Can someone explain what percent protonation means? I understand how to find this but I am not 100% clear on it conceptually.

SamayaJoshi1A

K is just a value for the equilibrium constant for a reaction. It does not have units. Kp and Kc are specifications of this that tell us how we got to this K value. (using pressure or molar concentrations).

SamayaJoshi1A

If an ICE table is done correctly, Q over K should not have an affect. Im not quite sure what you mean when you did it the reverse way.

SamayaJoshi1A

The shift indicates whether more products or reactants are being made in the reaction. Most of teh time, the reaction is heading towards the equilibrium, where a set amount of products and reactants are being formed.

SamayaJoshi1A

I think Kp and Kc is just a specification of K. K also ha son units, while Kp and Kc have implied units.

SamayaJoshi1A

Make sure that you're including the initial values in your Kc equation. For example if the change is 2x, make sure you use #-2x, rather than just 2x. This mistake slipped me up a lot in the Sapling problems.

SamayaJoshi1A

Yes. Make sure to square both sides so you do not have to end up with a messy quadratic. :)

SamayaJoshi1A

There a multiple ways to combine K. When adding two equations you multiply them together, and when you switch an equation you use the inverse. Make sure when you add two equations to multiply not add the K values.

SamayaJoshi1A

First find the Kc using the original values. Next, set up an ICE table with the original values of the reactants and the new valu of the product. Then, find x using the Kc value. Then you can use x to find final equilibrium concentrations.

SamayaJoshi1A

Also remember that total pressure means add all of the individual pressures together! I had that problem with this problem.

SamayaJoshi1A

Can someone explain what the term (aq) means? I know that it is aqueous, but how does that differ from a liquid? Is it because its a solution?

SamayaJoshi1A

Why are inert gases only noble gases? Is there a reason these noble gases are the only type of gases that go through the equations where inert gases are present? I am a bit confused.

SamayaJoshi1A

If you have all the information you can solve for K. It is probably easier to do it at the end as shown by our homework and sapling problems.

SamayaJoshi1A

This is because an inert gas does not contribute to the volume. Because K is calculated in terms of concentration, the inert gas would not contribute to this in the equation.

SamayaJoshi1A

Pretty sure its with 14B students!

SamayaJoshi1A

Why is the gas constant a constant? To me that part is a bit confusing because I would have thought the gas constant differs for each gas.

SamayaJoshi1A

Why is the gas constant a constant? To me that part is a bit confusing because I would have thought the gas constant differs for each gas.

SamayaJoshi1A

Does anyone know why the [OH-] is different from the pOH. Why is it a very small negative number?

Thanks in advance!

SamayaJoshi1A

For bond angles, I know some is a little less than a number, for example <109.5, does anyone know why?

SamayaJoshi1A

I am finally moving to Westwood! Yay

SamayaJoshi1A

How do oxidation states come into play when naming a complex compound?

SamayaJoshi1A

Hi!

You find the number of each moles in the compound and then divide by the smallest mol. From there you have to find a whole integer, and you get the empirical formula.

SamayaJoshi1A

Hi!

You have to find the moles and then see which one produces the least amount of product. That will determine how much of each product is created.

SamayaJoshi1A

Can someone explain the previous post? Why does one talk about protons and why does one talk about electrons?

SamayaJoshi1A

Yes. This also helps in identifying acids and bases. Example- H+ and OH-

SamayaJoshi1A

Hi! The lewis structure for O is biracial because all sides need to be filled before they pair up. For Example, you can't go pair by pair, only electron by electron.

SamayaJoshi1A

I think it might be because of the polar/nonpolarity of the molecule, rather than the angles, but someone could clarify!

SamayaJoshi1A

You can also think of electron density as the probability that an electron resides there. Remember that the electrons are always moving, and that why every molecule is slightly polar.

SamayaJoshi1A

Im pretty sure the answer to your question is yes, but if someone could clarify that that would be great.

SamayaJoshi1A

Remember to look at the formal charges as well. The least amount of formal charges equals the most stable Lewis structure.

SamayaJoshi1A

Theres a really helpful picture if you look up how to recognize acids and bases on google. For example one of the rules you can use from just looking at the formula is that all OH formulas are bases

SamayaJoshi1A

-OH and OH- are the same thing!

SamayaJoshi1A

Check if the Lewis structure is drawn a certain way because of the formal charges. remember that the lewis structure with the lowest amount of formal charges is the most stable structure.

SamayaJoshi1A

Just go backwards and count the valence electrons based on the levels. Make sure to know that s has 2, p has 6, and d has 10. Then you can literally count the squares on the periodic table.

SamayaJoshi1A

The best thing I did in AP chem was to just memorize the chart. Memorizing the chart helps with boiling and melting point problems, poplar vs non polar, and lewis structures. It even helped me on the most recent midterm.

SamayaJoshi1A

2 different atoms almost never have non-polar bonds. They can have a polar shape if there are lone pairs, but not non-polar bonds. C and H will have dipole moments because any molecule has dipole moments due to the uneven electron distribution.

SamayaJoshi1A

It might just be easier memorizing popular non-polar molecules. The ones with no lone pairs are almost always non-polar. The linear ones, one with three and four branches and no lone pairs are non-polar. There is a really helpful graph if you just look up "VSPER chart".

SamayaJoshi1A

Also something to remember is that the effective nuclear charge is never proportional to the number of levels. For example if there is an electron in the second level, it does not have half the strength of the one in the first level. It all depends on other factors.

SamayaJoshi1A

Can someone explain to me Sapling Question 9, specifically the plausibility based on oxidation section. Not sure how the two relate exactly.

SamayaJoshi1A

Im pretty sure it means which one is the most accurate shape, or representation of the molecule. The resonance form with the least amount of formal charges will be the most accurate and stable shape.

SamayaJoshi1A

I don't understand this either! And could someone explain the main differences between these two types of forces? Thanks.

SamayaJoshi1A

Most textbooks say to be polar, it needs to be more than .5.

SamayaJoshi1A

I am pretty sure just the general trends, as there were no sapling problems with the exact electronegativity numbers. Saying that, the trends just follow the numbers.

SamayaJoshi1A

Im pretty sure that the stronger the bonds, the more tightly held the molecules are with each other, meaning it is less fluid.

SamayaJoshi1A

So when you have multiple structures, look at the one with the least amount of formal charges (meaning closer to a stable molecule.) This is how you can determine that. There are also multiple other ways to do this such as oxidation numbers and bond length (as mentioned in the sapling homework. )

SamayaJoshi1A

Hi! I can definitely explain. So quantum numbers have some basic rules you have to know. The oxidation numbers in a neutral compound should add up to zero. For the example where there is a -1 charge, it should add up to that number. Oxygen normally has a O# of -2 (thats just a rule). Then you multip...

SamayaJoshi1A

Pretty sure we will be asked this. The fourth quantum number is probably the easiest. There are only two options because it is referring to the spin. The first electron is going to be -1/2 while the second will be 1/2.

SamayaJoshi1A

Can someone explain that in other words? I know that the bigger the molecule the stronger the forces, but for some reason that still isn't making sense to me. I would have thought that because the valence electrons are further from the nucleus the forces would be weaker, but I know that is not the c...

SamayaJoshi1A

Can someone explain to me what the ML quantum number is referring to and how it related to the spin of the electron.

Thanks!

SamayaJoshi1A

Yes, one of my friends told me that it is the same format as this class.

SamayaJoshi1A

There has been no info about when grades will be out! We are all waiting too don't worry you did not miss any info.

SamayaJoshi1A

I had to watch it offline once on a plane so I screen recorded it on 3x speed while I did other things and then slowed the video down when I had to watch it offline.

SamayaJoshi1A

Ground state also means that there is no energy affecting the electrons energy levels. The electron has not been excited to another energy level.

SamayaJoshi1A

Yes- for me it is generally easier to look at the units and convert them to meters per second and SI units before I begin the problem. Something that always catches me is the meters per hour- make sure it is in seconds!

SamayaJoshi1A

Yes- basically it is saying that there must be an electron in every single orbital/subshell until one orbital/subshell can double up.

SamayaJoshi1A

Different wavelengths look different! For example, humans can see colors and differentiate different wavelengths. So with the spectral lines, each one appears different.

SamayaJoshi1A

I don't think it will update until its due- you're fine :)

SamayaJoshi1A

Hi! I don't think this is a necessary step for any of the questions. Dr. Lavelle just does this to show that there is a ratio and that the percentages should add up to 100 percent.

SamayaJoshi1A

Because it is proportional, it should not matter. But... you should convert to L just to make your life easier and to make sure the correct units are being used throughout the whole problem.

SamayaJoshi1A

Normally, rounding to three sig figs is acceptable. My TA noted that she normally rounds to how many sig figs are used in the question. I will ask again though and Dr. Lavelle should say something about this!

SamayaJoshi1A

You would use the smallest amount of moles found. The reactant with the smallest amount of moles is the limited reactant. The, you can use the molar ratios to see how many moles of the excess reactant you would use per mole of the limiting reactant. Then, by converting moles to grams you can see wha...

SamayaJoshi1A

I have gone to multiple step up sessions and they have been very helpful.

SamayaJoshi1A

Does anyone know if we have asked if webcams can be another device? I don't want to go buy a webcam.

SamayaJoshi1A

Each atom has a molar mass, yes based on the size, number of protons and neutrons, etc. Atomic mass has a pattern on the periodic table. As you go from left to right and top to bottom, the atomic mass of the elements increase. The molar mass is the mass of all the elements in the molecule added toge...

SamayaJoshi1A

Yes, D is density, g/ml. Sometimes because it looks like concentration/molarity, which is mol/L people get mixed up (including me). Be careful!

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