CHEMISTRY COMMUNITY

JaesalSoma1E

Like everyone else said organic chemistry tutor is soo helpful, especially for last minute review before the final.

JaesalSoma1E

joules/mol or kilojoules/mol

JaesalSoma1E

In reviewing this problem, I had the same trouble because the solutions manual jumped around! I broke it up like so: 1) subtract 0.27 V from 0.33 V 2) divide 0.06 from the previous step by -0.0129 V 3) take the inverse of ln, meaning calculate e^ 4) take the -log of your answer in step 3 You should...

JaesalSoma1E

Why do you need to add the Pt(s) to the anode in the cell diagram? Why can't I2(s) be the electrode on the anode side? For reference, I attached the problem and the solution from the answer key. My answer was the same as the answer key, except on the left side I didn't include Pt(s) and instead used...

JaesalSoma1E

To clarify, for the textbook problems in 6K they don't tell you whether it is acidic or basic, and those are the ones I'm confused about.

JaesalSoma1E

How can you tell whether you are supposed to balance a reaction using OH- or H+? I understand that you initially can use H2O to balance the oxygens, but after that I am struggling to differentiate when to use OH- or H+. For example, I have correctly balanced reactions using H2O and OH-, but the answ...

JaesalSoma1E

The equations to calculate half life change depending on the order of the reaction, so make sure you use the right one based on the order.

JaesalSoma1E

I'm assuming you are going to be given the rate and order of the reaction and then asked to find the half life.

JaesalSoma1E

The line has a negative slope for first and zero-order reactions which is why you make k negative. For second-order reactions, k is positive because the graph has a positive slope.

JaesalSoma1E

For reactions with multiple reactants that are changing concentration, you have to make one reactant have a really small concentration so it can be the rate-determining reactant, while the rest of the reactants have to be in large excess. You assume that the reactants that are in excess don't change...

JaesalSoma1E

Can someone help me with this question? I used the equation delta G=-nFE and I keep getting the wrong answer. I might just be making a silly mistake somewhere, but I tried -510kj and +510kj and both were wrong.

JaesalSoma1E

I use the acronym OIL RIG, which stands for oxidation is loss and reduction is gain. Then I just look at the equation to see which one is losing electrons and which one is gaining electrons.

JaesalSoma1E

You always have to include the anode and the cathode, so if in your reaction Platinum is one of those two, then you should include it in the cell diagram.

JaesalSoma1E

The salt bridge distributes ions accordingly so that the two solutions in the cell remain neutral.

JaesalSoma1E

Yes, E naught is an intensive property so you don't have to multiply it when you are balancing a chemical reaction. You only have to be concerned with the sign in front of E naught depending on if you flip the half reaction.

JaesalSoma1E

It's not too hard as long as you stay on top of the labs. The lectures on the class planner are actually problem-solving sessions, which are recorded and not mandatory. Those are helpful to watch before doing the lab. Each Sunday, she posts a short lecture video to preview for the week and you only ...

JaesalSoma1E

Delta U, q, and w all equal 0 for an isolated system.

JaesalSoma1E

You only use moles of gas because PV only applies to gases. Solids and liquids don't change enough for PV to be used.

JaesalSoma1E

My trick for remembering is to use 8.314 when solving for energy or joules and using 0.08206 when solving for moles, volume, temperature, or pressure.

JaesalSoma1E

For isobaric processes, delta H=q

JaesalSoma1E

When delta G is negative, it is considered to be thermodynamically favorable.

JaesalSoma1E

It is similar to delta H (enthalpy) and delta H naught. Delta H is the enthalpy for whatever reaction occurring and delta H naught is the standard enthalpy of a reaction.

JaesalSoma1E

You can also try connecting to the VPN before starting the lecture. That has fixed the error message for me a few times!

JaesalSoma1E

+1 Celcius is equal to +1 Kelvin so there is no need to convert. You just have to be mindful of the units when doing calculations because the values for C and K won't be equal.

JaesalSoma1E

While solving a problem, I think having all of the quantities in similar units is a must. So, I like to convert joules to kilojoules or vice-versa before starting the calculations so that it becomes easier to solve the problem without making mistakes. That is a really good idea! I'm definitely goin...

JaesalSoma1E

Just check the units in your problem before deciding which one to use. A general trend however is that 0.0821 is used in PV=nRT problems and 8.314 is used in energy (work and thermodynamics) problems.

JaesalSoma1E

In the scope of our class, heat capacity can't be negative because it is the amount of heat required to raise the temperature of a substance. You can't apply a negative amount of heat to something and cause a rise in temperature. There are some systems in space, like stars, that can have a negative ...

JaesalSoma1E

This is a good diagram to help determine whether a reaction is spontaneous or not, using entropy and enthalpy.

JaesalSoma1E

Enthalpy refers to a change in heat for a system, while entropy is a change in disorder for a system.

JaesalSoma1E

Lorena_Morales_1K wrote:I believe he explained this in lecture but can someone explain why entropy is a maximum at equilibrium?

It is because of the second law of thermodynamics.

JaesalSoma1E

Yes they would have more degeneracy because there are more states for each atom to be in.

JaesalSoma1E

How do you determine when to ignore the second Ka in polyprotic acids when calculating pH?

JaesalSoma1E

Yes you can, I've heard of people taking 14D with 14BL

JaesalSoma1E

In a question like 6D.15 (posted below) are we supposed to know the Ka/Kb value or is it implied that we should be looking it up?

Calculate the pH of (a) 0.19 m NH4Cl(aq); (b) 0.055 m AlCl3(aq)

JaesalSoma1E

I think they will be provided. It would be really hard to memorize considering they are different for every acid/base and they change with temperature.

JaesalSoma1E

There isn't a lecture. Under media resources, it is already posted as a blank day with a note that the lecture is canceled because of the midterm.

JaesalSoma1E

I used a TI-84 graphing calculator last quarter with Lavelle, so I don't think it really matters what calculator you use.

JaesalSoma1E

The tests last quarter had questions straight out of the textbook, so I think you'd be better off if you studied using the textbook.

JaesalSoma1E

The tests are based off of homework questions from the outlines, so I'd recommend doing all the problems from outline 1, 2, and the parts of 3 that we have covered.

JaesalSoma1E

Whichever direction the reaction is going would have a positive change in equilibrium. So if the reaction was proceeding to the right, the products would get the +x. But if the reaction was proceeding to the left, the reactants would get the +x.

JaesalSoma1E

The C row is for the change in equilibrium, which is denoted by x. Then, you would multiply x by the stoichiometric coefficient.

JaesalSoma1E

You'll probably get the units from the question and if not, you can just convert to the correct one at the end of the question.

JaesalSoma1E

It means it can only donate one proton. Usually, these acids only have one H atom or have an H that is part of a functional group.

JaesalSoma1E

I use the outlines to study for the midterm, so I normally do a couple of the problems as we are learning the material but the majority of them leading up to the midterm to help review previous topics.

JaesalSoma1E

There's only a handful of strong acids and bases, so it's probably easiest if you memorize those. Then any other acid/base you encounter would be considered a weak acid or base.

JaesalSoma1E

I understand how to do part A and B, but I was wondering how you determine which reaction is more thermodynamically stable. I'll paste the question below for your reference. I got [Cl]=1x10^-4 mol/L and [F]=0.0032 mol/L for parts A and B. (a) In an experiment, 2.0 mmol Cl2(g) was sealed into a reac-...

JaesalSoma1E

You have to use the value that is a positive number because it represents concentration, which can't be negative.

JaesalSoma1E

I think catalysts are written above the arrow because they aren't taking part in the reaction but they are still present. So in this case, Fe would be the catalyst if I'm not wrong.

JaesalSoma1E

They're going to be during lecture and I'm assuming he'll add like 5 minutes, which he did last quarter, so the test will be open for around 55 minutes.

JaesalSoma1E

Kc refers to the equilibrium constant in concentration problems and Kp refers to the equilibrium constant in pressure problems

JaesalSoma1E

I found this question in the first audiovisual focus topic and I was confused about what the answer was even after watching the video. I'd appreciate the help! Determine whether the following statements are true or false: a. When chemical equilibrium is reached, the composition of the reaction mixtu...

JaesalSoma1E

I approached this problem by giving the initial solution an arbitrary molar concentration (for example, 0.5M). Then to get the diluted solution's concentration I took 12% of the initial solution's concentration. To get pH, you have to do the -log of the molar concentration. The answer would be the d...

JaesalSoma1E

I think he means for all topics, not just quantum.

JaesalSoma1E

HI is more acidic than HCl because Cl- is more electronegative. My sapling #11 was comparing oxoacids HClO, HBrO, and HIO, and in this case, you would compare the stabilities of the anions after the proton is donated, so ClO-, BrO-, and IO-, not the electronegativities of the halogens within these a...

JaesalSoma1E

Outline 5, which is for coordination compounds, says to read sections 9C.1 and 9C.2, and included in the first section there is a table with all the common ligand names, so I'm assuming that means we should know at least those ones.

JaesalSoma1E

H+ is just a proton. A neutral H atom is one proton and one electron, so by removing the electron and creating H+, all you are left with is one proton.

JaesalSoma1E

Ba[FeBr4]2 would have a coordination compound of 4 since there are four ligands bonded to the transition metal. Similarly, K3[CoF6] would have a coordination number of 6, coming from the 6 fluorines bonded to the cobalt. The K3 doesn't affect coordination number because it isn't a ligand and not ins...

JaesalSoma1E

If you are going with the Bronsted definition of acids and bases, they are defined using protons, whereas electronegativity has to do with electrons, so I don't think there is a causal relationship, but there might be some correlation between acidity to electronegativity.

JaesalSoma1E

It would still be an acid before it is turned into an aqueous solution because the definition of a Bronsted acid is that it can donate protons. This doesn't mean that it has to be currently donating protons for it to be considered an acid, just that it has that ability.

JaesalSoma1E

To add on, the -ate ending isn't common, so when it does occur just keep in mind that there would be a cation that bonds with it, not an anion.

JaesalSoma1E

Like the others said, it is probably enough to just know a few examples of each a strong acid, weak acid, strong base, and weak base from the kitchen or household. The chart at the beginning of the lecture on 12/2/20 has some examples of these.

JaesalSoma1E

Delocalized pi bonds form in compounds that have resonance structures since they are delocalized electrons.

JaesalSoma1E

I'm going to go over the textbook problems, reread the text, and look at old UA worksheets.

JaesalSoma1E

Resonance structures have delocalized pi bonds since the electrons are delocalized as well.

JaesalSoma1E

I agree with Lea said. To add on, there is a sigma bond in every single, double and triple bond, and you have one pi bond in a double and two pi bonds in a triple.

JaesalSoma1E

Trigonal planar has 120 degree bond angles and has 3 atoms bonded to the central atom. The VSEPR notation would be AX3. Trigonal pyramidal has 3 bonds and one lone pair and the bond angle is less than 109.5 degrees. This notation would be AX3E.

JaesalSoma1E

Yes, the sulfur will have a -2 charge on it. If you look at the group sulfur is in, you'll notice that all those elements also from -2 charges when they complete their octets.

JaesalSoma1E

I think the "di" refers to two sides of an individual molecule, where one side is a partial positive and the other is a partial negative. In your example, tetrachloromethane would be nonpolar because the negative charges all cancel out. Polarity comes from the symmetry of the molecule, and...

JaesalSoma1E

You can estimate the electronegativity differences based on the atom's location in the periodic table, since electronegativity increases as you move to the top right of the periodic table. High electronegativity means an atom's tendency to attract electrons, so yes this means that sometimes highly e...

JaesalSoma1E

Lewis acids accept electron and lewis bases donate electrons. I remember by saying Acid=Accept.

JaesalSoma1E

It would be fluorine. You don't consider the inert gases because those elements won't take on another electron.

JaesalSoma1E

I haven't heard anything yet, but it would be great if there was another study session. The review for midterm 1 was really helpful!

JaesalSoma1E

Ionic bonding is within one compound, like the bonding of Na+ and Cl-. Ion-ion interactions would be the attractive force felt between two oppositely charged ions, that aren't bonded together yet.

JaesalSoma1E

Lindsey Su 3E wrote:Will 14B have the same format? Like asynchronous learning and everything?

I saw in a different post that Dr. Lavelle will most likely keep the same format with asynchronous lectures and other synchronous hours in the form of office hours and UA sessions since that seems to be working this quarter.

JaesalSoma1E

The lewis structure wouldn't change whether it was aqueous or solid. It is just important to note that in an aqueous solution, the solute has dissolved into the individual ions, but as a solid, the ionic bond is still intact.

JaesalSoma1E

Molecular shapes is on outline 4 so it won't be on this midterm.

JaesalSoma1E

I think they might be loosely interchangeable, but I determine the central atom by looking at their electronegativities, not the ionization energies. The least electronegative atom should be the central atom because it is the most likely to share electrons with the other bonded atoms. If a highly el...

JaesalSoma1E

I don't think we have to memorize specific radicals, but it is probably a good idea to know how to recognize them. There are a few practice problems in section 2C that go over radicals a bit more.

JaesalSoma1E

The 1 and 2 are the principal quantum number, n, which tells you what shell the electron is in.

JaesalSoma1E

The second ionization energy is higher because now you are taking an electron away from a positively charged atom, whereas the first time you were taking an electron away from a neutral atom.

JaesalSoma1E

This question in the textbook gave the lewis structure below and we have to identify which element is E (and it is given that the element is in Period 3).

I have no idea how to go about solving this so any and all help is appreciated!

JaesalSoma1E

When you are talking about Potassium and Calcium, it is correct to say that the 3d orbitals have a higher energy than their 4s orbitals. However, I think you run into problems when you try ranking the energies of the elements within the d-block, because it isn't always true to say the 3d orbitals ha...

JaesalSoma1E

I think he mentioned that it is really time consuming for him to make new modules, so he probably won't have any new ones. I hope he does create some though, they are really helpful for studying and learning new material!

JaesalSoma1E

Yes, Rydberg's only works for Hydrogen atoms or other 1 electron atoms.

JaesalSoma1E

I'm planning on taking chem 14b next quarter and I was wondering if I should also take 14bl in the same quarter. I haven't talked to anyone who has taken 14b or 14bl, so I wanted to see if anyone knew what's recommended.

JaesalSoma1E

I think midterm 2 will contain material from the end of outline 2, outline 3 and, outline 4.

JaesalSoma1E

For the midterm, I'm doing all the problems on outlines 1 and 2 (up to 1A.D) and all the audio-visual focus topics as well.

JaesalSoma1E

You can find information about Rydberg's constant and the related equations in section 1A.3, which is part of the assigned reading. There are also a few problems on outline two that involve Rydberg's constant for more practice on the topic.

JaesalSoma1E

In the lecture, Dr. Lavelle also used the example of a baseball to show how the mass of an object can affect indeterminacy. That being said, neutrons and protons are more massive than electrons but not as massive as a baseball, so I think the Heisenberg equation can show what the indeterminacy is fo...

JaesalSoma1E

Professor Lavelle said it will be multiple choice.

JaesalSoma1E

If you are using the De Broglie Wave equation to determine if something has wavelike properties, the cutoff for the wavelength is around 10^-15 m. Anything smaller than that won't have wavelike properties.

JaesalSoma1E

Writing the states of matter in an equation is important when you are writing net ionic equations. This type of equation shows how aqueous ions combine to create a solid precipitate, so it is important to specify which reactants and products are changing in state.

JaesalSoma1E

This has to do with the principle of wave-particle duality. This means that a particle can be described as a wave. Specifically, with electrons, diffraction refers to the behavior of electrons as waves.

JaesalSoma1E

I think you should know the range in wavelength for visible light (~400-700nm). In addition, you should probably know how different types of light compare to each other regarding their wavelengths and frequencies. For example, that infrared light has a larger wavelength than visible light or that UV...

JaesalSoma1E

It is possible to use a nonmetal to demonstrate the photoelectric effect, however it is more difficult. Metals have lower electron affinities than nonmetals, so it is easier for an electron to be ejected from a metal than a nonmetal.

JaesalSoma1E

I believe the n1 = 1 comes from the fact that ultraviolet electromagnetic radiation is in the Lyman series (where n1 = 1). However, I also do not quite understand how we determine what series to use. Is it something that we should have memorized? Yes, this something that you just need to memorize. ...

JaesalSoma1E

They are essentially interchangeable however formula unit is used more often with non-molecular compounds, such as salts, whereas empirical formula is used with molecular compounds, like water.

JaesalSoma1E

idella 1F wrote:It doesn't matter how often/how long we attend these sessions right?

I think they are made so you can drop in whenever you are able to!

JaesalSoma1E

I'm pretty sure it would not matter how many sig figs are on the periodic table because those values are known. Instead you would determine the number of sig figs from any given or measured values in the problem. For example, if it said 1.53 mol of CO2, then you would use 3 sig figs throughout the p...

JaesalSoma1E

Dr. Lavelle mentioned in his lecture on 10/05/2020 that we would mainly be focusing on elements, ions and molecules that are found in living organisms. These are included but not limited to carbon, oxygen, hydrogen, nitrogen, sulfur, etc.

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