CHEMISTRY COMMUNITY

Madison Wong 3H

I think these are related, in Life Science we learned that catalysts work by decreasing the energy of the transition state, which in effect lowers the activation energy of the reaction. This increases the speed of the reaction.

Madison Wong 3H

Kc is the molar equilibrium constant, and Kp is the pressure equilibrium constant. The way of finding both is the same, with products over reactants taking into account coefficients.

Madison Wong 3H

Hi, I found it helpful to make quizlets for equations and going through textbook problems with different equations to gain practice on knowing what equations to use when.

Madison Wong 3H

Enthalpy refers to the transferrals of heat, while entropy relates to the disorder (whether thermal or positional) of a system. While these two are related, they are different concepts!

Madison Wong 3H

Activation energy is important in considering the speed of the reaction. A reaction with a high activation energy requires more energy to complete the reaction and thus is a slower reaction than one with a low activation energy.

Madison Wong 3H

Lavelle sent out an email with the TA and UA review sessions that are throughout this week, I think he sent it out March 4 if that helps!

Madison Wong 3H

We use E naught for the cell, which is found using the reduction potentials of both the anode and cathode.

Madison Wong 3H

For acidic solutions, add H+ to balance the H2O on the other side. For basic solutions, we must use OH- instead of H+, which often requires rebalancing of the hydrogen atoms.

Madison Wong 3H

The average rate is the rate over the duration of the reaction, while the reaction rate is found at specific points. In Lavelle's lecture, the reaction rates were found through finding tangents to the curve, while the average rate was found using a slope technique over a longer period of time.

Madison Wong 3H

The unique rate relates the rates of change in concentration of the reactants and products within a reaction. Using aA-> bB +cC, -1/a(d[A]/dt) = 1/b(d[B]/dt) = 1/c(d[C]/dt) when taking into account the coefficients' relationship to rate of change.

Madison Wong 3H

As oxidizing agents are reduced themselves, the more likely it is to be reduced, the better it oxidizes. Higher reduction potentials suggest stronger oxidizing agents.

Madison Wong 3H

Scand 50, Phil 22, and History 13b were all not too difficult and interesting!

Madison Wong 3H

Yes, exergonic reactions have negative delta G and are thus spontaneous. Exergonic and exothermic are easily confused. Exothermic reactions are not always spontaneous.

Madison Wong 3H

Molar entropy increases as an atom becomes more massive due to more possibilites for degeneracy and disorder within arrangement and positions.

Madison Wong 3H

Catalysts and enzymes work by decreasing the activation energy by lowering the free energy of the transition state. Thus, the reaction has smaller required activation energy and progresses faster.

Madison Wong 3H

Delta G naught is under standard conditions, while G can change as the reaction progresses.

Madison Wong 3H

The textbook problems related to midterm 2 material is under outline 3 and outline 4 of the syllabus posted on his website. Remember to exclude the questions that were covered on midterm 1 in the third outline.

Madison Wong 3H

There are partial credit problems and also two extra credit problems!

Madison Wong 3H

Yes, I believe since it isn't specified on the equations sheet it is just assumed to be the molar heat capacities and not specific heat capacities.

Madison Wong 3H

I'm not sure if there is an error posted in the solution manual, but I think the equation for change in free energy is generally delta G= delta h- T delta s.

Madison Wong 3H

Cp is the heat capacity at constant pressure, and Cv is the heat capacity at constant volume. They are related by the equation Cp = Cv + R.

Madison Wong 3H

Since change of internal energy is dependent on transfers of heat or work being done on the system, neither can occur within an isolated system, and thus, the internal energy change must be zero.

Madison Wong 3H

I usually try to go to UA sessions leading up to exams, but normally focus on reading through the textbook and doing textbook problems, as often there is one or two questions directly from the textbook on exams.

Madison Wong 3H

It will likely cover outline 3, 4, and possibly some of outline 5? im sure it will stop with material covered this week.

Madison Wong 3H

For these problems, it is important to identify what units are given. Sometimes there are conversions involved, but generally you use the gas constant with the units (atm, Torr, J) that match up with what is given.

Madison Wong 3H

Usually in calculating the heat capacity for the calorimeter, it is delta H divided by the change in temperature.

Madison Wong 3H

Not sure about the amount of questions, but it will probably be similar to midterm 1 since it is still only 50 minutes. I think midterm 2 just covers material from week 4 to 7, but I'm sure he will release info later.

Madison Wong 3H

Heat is negative when the system loses heat and when the system itself does work. Heat is positive when the system absorbs heat due to work being done by its surroundings.

Madison Wong 3H

I think it would be generally helpful to make distinctions between types of calorimeters and how measurements from calorimeters can help in various calculations.

Madison Wong 3H

The homework is due Sunday week 5, but I think the grade uploads to CClE automatically as you complete it.

Madison Wong 3H

I will be taking 14c in spring!

Madison Wong 3H

Similarly, since water is neutral, the concentrations of H3O+ and OH- are equal, and in autoprotolysis of water, both concentrations are equal to 1x10^-7.

Madison Wong 3H

You still include the coefficient in calculation for the equilibrium constant. I think this is because the ()^2 accounts for the coefficient in the equilibrium constant calculation while the -2x matters in relation to the molar ratios of other reactants and products.

Madison Wong 3H

The kb values for these problems are either given in the basicicity constant table of the textbook or are derived from the Ka value, as it is a conjugate of this. To find Kb from Ka, you divide 10^-14 by the Ka.

Madison Wong 3H

Similar to amphoterism, water being amphiprotic suggests that it can act as both a proton donor or a proton acceptor.

Madison Wong 3H

It's easier for me to think about in terms of heating ice or heating liquid, it is breaking bonds to allow for particle movement. Atoms are most fluid in gases while in solids are largely locked.

Madison Wong 3H

Yes, Ka1 is the value deemed significant, as the second deprotonation is so small that it becomes insignificant when compared to the first.

Madison Wong 3H

It's helpful to consider heat as a reactant or product when considering the impact of changing temperature on a reaction. Whether it is endothermic or exothermic changes the direction of the reaction.

Madison Wong 3H

I saw this in a textbook problem for the chemical equilibrium of acids and bases and was also confused.. The answer key seemed to suggest that the first deprotonation's concentrations are much larger than the second deprotonation, so you just focus on the first. I also want some clarification though.

Madison Wong 3H

alebenavides wrote:does anyone know what time the midterm is ?

The midterm is the same time as your lecture for the day. But it's still a 50 minute period.

Madison Wong 3H

I use moles, because it makes it easier when writing it in the Ka equation to use molarity rather than moles as there is an extra step of considering volume that is missing.

Madison Wong 3H

Since pKA is just the negative log base 10 of Ka, it helps to write out what the equation of Ka is: products over reactants. As stronger acids and bases dissociate more, creating more product, higher Ka values indicate stronger acids and bases. Once you take the negative log base 10, higher Ka value...

Madison Wong 3H

since Ba(OH)2 is a strong base, it deprotonates and creates OH- instead of H3O+. Acidic substances would result in protonation and thus production of H3O+.

Madison Wong 3H

the first midterm is january 29 during your lecture time, but it's still 50 minutes. Before it was discussions, but now everyone takes it on the same day during their lecture time.

Madison Wong 3H

In one of the modules, Lavelle mentioned that solids and liquids (including water) are not included in finding K constants, and sometimes water isn't even written into equations because it is often present in excess.

Madison Wong 3H

I'd recommend Ink Master as background and The undoing on HBO for a bit more focused murder mystery vibes

Madison Wong 3H

Robots and aquamarine!

Madison Wong 3H

I was wondering the same thing, mine doesn't show up on CCLE either.

Madison Wong 3H

I'm a bit confused on how we use the ideal gas law to convert between the pressures of gas and concentrations of gas. What do all of the constants in Pv=nRT stand for?

Madison Wong 3H

Do we have to change our username to our new discussion section in order to get points for chem community? If so, how?

Madison Wong 3H

Lewis focuses on electrons while Bronsted focuses on protons

Madison Wong 3H

Polydentate ligands are ligands that bond in more than one area, as opposed to a monodentate ligand. For polydentate ligands, to find the coordination number it is the same process, just paying attention to how many bonds each polydentate ligand can make. ethylenediamine for example is a bidentate, ...

Madison Wong 3H

I think the heisenberg uncertainty principle reinforces the idea that the measurement process influences the outcome. With the example that Lavelle gave of the measurement of an electron passing through motion detectors, it shows that photons scattered from an electron within measurement with affect...

Madison Wong 3H

I think it has something to do with Chlorine not reacting with water, and thus it won't make a substance more acidic or basic by donating or accepting protons.

Madison Wong 3H

Amphoteric substances can act as either acids or bases, I think lavelle also said that the amphoteric substances often align with the diagonal band of metalloids, but that it doesn't match up perfectly.

Madison Wong 3H

Noting that the bond angle of an sp3 hybridized atom is 109.5° and that of an sp2 hybridized atom is 120°, do you expect the bond angle between two hybrid orbitals to increase or decrease as the s-character of the hybrids is increased?

Madison Wong 3H

Thanks so much!

Madison Wong 3H

I just count the regions of electron density and find the corresponding number. sp would be two areas, sp2 would be three areas, sp3 would be four areas, etc .

Madison Wong 3H

A delocalized pi bond is similar to the concept of delocalized electrons that occur within resonance structures. When a molecule has different resonant structures, the pi bond can be blended to different areas.

Madison Wong 3H

I think when considering regions of electron density, the type of bond doesn't matter, as there is electron density regardless if it is a lone pair, single bond, double bond, etc.

Madison Wong 3H

I think it was especially common because sp3 is the hybridization for carbon, and tetrahedrals as it suggests four regions of electron density

Madison Wong 3H

I think since the pi bonds are overlapping side by side and have rigid geometry, the bonds can't rotate and thus are all on the same plane.

Madison Wong 3H

Hybridization is also related to the regions of electron density, since the regions of electron density is equal to the number of hybrid orbitals.

Madison Wong 3H

Yes, you consider lone pairs and bonding pairs as regions of electron density. You only count double and triple bonds as one region however, because you're only considering the regions of electron density not the bond types themselves.

Madison Wong 3H

An easy way I remember is that particles with mass cannot be traveling at the speed of light, so you can only use the debroglie equation when considering photons and particles without mass.

Madison Wong 3H

I think so, in his lecture from today he suggested that expanded octets would be in the dsp3 or d2sp3 hybridizations.

Madison Wong 3H

I use this as a reference for VSEPR and the shape/bond angles. Hope this helps!
https://ds055uzetaobb.cloudfront.net/im ... 091b2c.png

Madison Wong 3H

I recommend Community if you want an alternative to parks and rec or the office!

Madison Wong 3H

I think just formal charge and maybe the equation for potential energy in london dispersion forces which involves the polarizability of the two molecules divided by the distance between them^6.

Madison Wong 3H

I think it has to do with formal charge, but it could also depend on electronegativity.

Madison Wong 3H

I think that for intermolecular, and in particular the london forces for induced dipoles are dependent on polarizability for the potential energy. Since larger atoms have electrons that are farther from the nucleus or less tightly held they are more polarizable and thus have stronger london bonds.

Madison Wong 3H

The UA sessions are really helpful, in one of the linked groupme's there is a google drive with shared worksheets from the sessions if you want to access them!

Madison Wong 3H

awesome!

Madison Wong 3H

I think if you email your TA they can tell you which problems you got wrong and which you received partial credit for!

Madison Wong 3H

I'm not positive, but basing it on quantum numbers, I think atoms in the d block have quantum number l=2 and thus can have 10 electrons since Ml can be 2,1,0,-1,-2 and 2 electrons can accompany each of those, which would be an expanded octet. I'm still a bit confused myself though.

Madison Wong 3H

In order to have the most stable molecule, with the least energy you use a double bond to have the formal charge of -1 for O and 1 for Xe, leading to a stable molecule with low energy.

Madison Wong 3H

The central atom should be the least electronegative atom. A TA also suggested that somethings Lavelle will place the central atom in the middle of the molecular compound, for example in ClCCn, C is the central atom. But in general just pay attention to the electronegativity.

Madison Wong 3H

Hi!
in the same way you put the most electronegative atom in the center, you also choose resonant structures that don't place charge on the central atom as it is the least electronegative.

Madison Wong 3H

Also make sure that you place parentheses in the right places when combining multiple steps of an equation, to make sure there aren't PEMDAS issues that could result in a wrong answer!

Madison Wong 3H

I'm pretty sure they are still considered resonant, as his definition was structures with the same arrangement of atoms, but different arrangement of electrons, so even mirror images would be considered different and resonant.

Madison Wong 3H

I think so, along with the new material that we're learning now! He will probably post another outline of covered topics for midterm 2.

Madison Wong 3H

The number of spectral lines that appears is n-1, so 5-1, and thus four spectral lines. Hope this helps!

Madison Wong 3H

I know that it has something with being in the third period of the periodic table and thus part of the d block, which can have more bonds. I think there is a more in depth way of explaining but this is what he mentioned quickly during the lecture.

Madison Wong 3H

1) The midterm is during your discussion. 2) This is different depending on your TA, but for mine I can use my phone for zoom positioned towards my work space, and use my computer for taking the test itself. I would ask your TA to make sure what their policy is. 3) Multiple choice, it hasn't been co...

Madison Wong 3H

Since we aren't able to un randomize our questions for sapling, does anyone know the questions that cover topics that will be included on the midterm? Thank you

Madison Wong 3H

I think just knowing the general concept, he derived it during lecture it has to do with the equation E=mc^2 and E=H(frequency). You equate them both and then change the speed of light for velocity.

Madison Wong 3H

During Lavelle's lecture on Friday, he kept referring to Px, Py, Pz and other x,y,z orbitals. I was confused on how he determines this, and what the symbols mean. Thanks!

Madison Wong 3H

In general, the amount of spectral lines is n-1.

Madison Wong 3H

Hi, if anyone could help me with this problem, its 8 on the sapling assignment! A violet line is observed at 434.0 nm in the spectrum of atomic hydrogen. Determine the values of n for the beginning and ending energy levels of the electron during the emission of energy that leads to this spectral line.

Madison Wong 3H

I was a bit confused on this too. Does increasing the number of photons increase the energy, or does it not affect the energy since changing the intensity of light didn't result in more emitted electrons?

Madison Wong 3H

Yes, I think diffraction also has to do with the interference of waves- constructive and destructively. From the interaction of waves comes the same properties of waves from electrons, which encourages the idea of electrons having particle like and wavelike qualities!

Madison Wong 3H

It's not open note, it's multiple choice, and not curved. Apparently some questions are weighted more heavily than others. I'm still not sure about partial credit.

Madison Wong 3H

How do we know that n1=2? Is it characteristic of visible light in general or did it require solving?

Madison Wong 3H

I just got one off amazon for 15$ with free shipping before my discussion next week!

Madison Wong 3H

I usually just use all the saved values in my calculator and don't round anything until the last step, I think this helps in multi-step problems!

Madison Wong 3H

I think so but I'm not positive.. I think this relates to the emission spectrum for each element being like a fingerprint of every element and each element absorbs and emits light differently.

Madison Wong 3H

I'm confused on the difference between electrons being ejected and excited.. What is the difference?

Madison Wong 3H

I think multiple electrons are ejected, but each photon must have enough energy to eject each electron. Since there are multiple photons within the light it results in multiple electrons ejected.

Madison Wong 3H

Hi, if anyone could explain the work for this question
"In the ultraviolet spectrum of atomic hydrogen, a line is observed at 102.6 nm. Determine the values of n for the initial and final energy levels of the electron during the emission of energy that leads to this spectral line."

Madison Wong 3H

Thanks!

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