CHEMISTRY COMMUNITY

Aayushi Jani 3A

In order to get the desired equation, 2NH3(g)+3I2(g)↽−−⇀N2(g)+6HI(g), you have to add two of the equations that are given. From the four equations given, we can see that adding the first and third one will get us our desired equation. However, realize that the first equation must be multiplied by 3 ...

Aayushi Jani 3A

pKa & pKb tells you how strong a particular acid/base is, while pH and pOH simply tell you the concentration of OH- and H3O+. However, both are used to describe acids and bases.

Aayushi Jani 3A

Yes, the stronger the base, the larger the Kb value and lower the pKb value.

Aayushi Jani 3A

I would look at outlines 1 & 2 on his website because those are the ones we've done/are doing so far. The bullet points on the outlines tell you all the material you need to know.

Aayushi Jani 3A

Q is the reaction quotient (taken at any time during the reaction). If you let the reaction go until it reaches equilibrium, Q should equal K (since K is the equilibrium constant).

Aayushi Jani 3A

Yes, as others stated above, you would need to know whether the reaction is endothermic or exothermic (given by delta h).

Aayushi Jani 3A

I think that these values are just chosen as they are both clearly very small or large values, so if the value of K was greater/less than that, it would definitely imply that it sits to the left/right.

Aayushi Jani 3A

I think that that is possible looking at it mathematically (for example if the equation is 2R --> P where [R] = 2 mol/L and [P] = 4 mol/L, then K = 2^2/4 = 1). However, I think it is still rare for this to occur, but feel free to correct me if I'm wrong.

Aayushi Jani 3A

If you have two positive values, chances are one of them is larger than the initial concentrations. If x is larger than the initial concentration, then the equilibrium concentration value becomes negative, which is impossible.

Aayushi Jani 3A

We use Kelvin.

Aayushi Jani 3A

There would be no change as the moles on both side are equal (the reaction is not favored to go to any side).

Aayushi Jani 3A

They will be updating the points in a few days (since we were given an extension).

Aayushi Jani 3A

Yes, as Dr. Lavelle mentioned in the lecture, the most common prefixes are mono-, di-, tri-, tetra-, penta-, hexa-.

Aayushi Jani 3A

HF is not a strong acid as F is so electronegative, which means that HF does not easily dissociate into H+ and F- easily in water. This is why, as atomic radius increases, the acids become stronger as they are able to dissociate much easier.

Aayushi Jani 3A

Bronsted Acids are proton donors (donate H+) while Bronsted Bases are proton acceptors (accept H+). Typically, Bronsted Acids have hydrogen (for example: HCl) which dissociates into H+ ions in water to form H3O+.

Aayushi Jani 3A

You would first find the pOH = -log[OH-]. Then, using the value for pOH, you can find the pH by doing 14-pOH = pH. Once you've converted all of your values to pH, you can see which is more acidic and which is more basic (acids have pH < 7, bases have pH > 7).

Aayushi Jani 3A

I think that an amphoteric compound tends to be a weak acid/base as it can be either acid or base. I would imagine that it would be difficult for a strong acid to behave as a base and vice versa.

Aayushi Jani 3A

I think that the pH scale goes from 0-14 (as it is found by finding -log[H+]). In order for the pH to be negative, the concentration of H+ would have to be greater than 1M.

Aayushi Jani 3A

Yes, the pOH scale also goes from 1-14, where 7 is neutral. Also, pOH + pH = 14.

Aayushi Jani 3A

Organic compounds (or at least most of them) contain C-H bonds (an example is C6H12O6 which is glucose). Inorganic compounds do not have C-H bonds.

Aayushi Jani 3A

There are four regions of electron density (three single bonds and one lone pair). Thus, the hybridized orbital that corresponds to four regions of electron density is sp3 (as there are four orbitals, one for each region of electron density).

Aayushi Jani 3A

I agree with the answer given above. The Cl2 that is outside of the brackets is not a part of the coordination sphere, so you would write it separately instead of grouping it with the chlorine inside the brackets. Thus, instead of it being trichloro, it would be simply chloro to represent the chlori...

Aayushi Jani 3A

A Bronsted Acid is a proton donor while a Bronsted Base is a proton acceptor. It is just another way to define/distinguish between acids and bases (another way acids and bases are described is Lewis Acid (electron pair acceptor) and Lewis Base (electron pair donor).

Aayushi Jani 3A

I think we would need to memorize it. However, it is pretty simple to remember (<7 is an acid, >7 is a base, 7 is neutral).

Aayushi Jani 3A

It can be written either way, they both work and represent the same thing.

Aayushi Jani 3A

Yes, I agree with the other answers given. OH2 and H2O are the same compound, however, it was written as OH2 to show the bonding order.

Aayushi Jani 3A

Yes, I think that we're expected to have the molecular shapes & bond angles memorized. However, there are many great infographics & charts online that concisely explain everything and I think Dr. Lavelle also does a really good job going in depth in his lectures.

Aayushi Jani 3A

Yes, I think that might have been an error since I also think that ethene has two sp2 hybridization orbitals.

Aayushi Jani 3A

With lone pairs, they are more delocalized than bonding electrons. As a result, lone pairs have greater electron-electron repulsion compared to bonding electrons, so they would want to be farther away.

Aayushi Jani 3A

Yes, all single bonds are sigma bonds while double bonds have 1 sigma and 1 pi bond and triple bonds have 1 sigma and 2 pi bonds.

Aayushi Jani 3A

Yes, I agree with the others. Sigma and pi bonds occur with all covalent bonds. However, single bonds only have a sigma bond while double & triple bonds have sigma & pi bonds.

Aayushi Jani 3A

Technically electronegativity is quantifiable (each element has a specific electronegativity number) so if those numbers were given to you, you would be able to find the exact difference. However, for now, we just need to know the trend that electronegativity follows and we don't need to do exact ca...

Aayushi Jani 3A

Helium is a noble gas, so it does not want more electrons as its valence shell is already full. Fluorine, on the other hand, is a halogen, and only needs one more electron to form an octet. Thus, it has the higher electronegativity.

Aayushi Jani 3A

Yes, LDF are found in all molecules and they are the weakest of all the intermolecular forces.

Aayushi Jani 3A

Yes, it is called bent as there are two lone pairs of electrons and two pairs of bonded electrons.

Aayushi Jani 3A

I think that we can expect it to take around the same time as last time (I'm guessing we'll get our scores sometime next week, after everyone has taken the midterm this week).

Aayushi Jani 3A

So for all of these questions, you would have to use the expected charges. For a, we know that magnesium has a +2 charge in order to be stable and arsenic has a -3 charge to be stable. To form the chemical formula, you would use the charges to decide how many of each ion is needed to make a stable c...

Aayushi Jani 3A

Some species have an odd number of valence electrons, and therefore cannot form a full octet, and may have an unpaired electron (known as a radical). For this problem, I would draw each Lewis structure to see which structures have an unpaired electron.

Aayushi Jani 3A

Radicals have one unpaired electron (for example, in NO). Radicals form when species have an odd number of valence electrons (for example, N has 5 valence electrons).

Aayushi Jani 3A

For this problem, I first determined the number/moles of each atom/molecule. So for example, for part a, which is ammonium chloride, you know that ammonium is NH4 and chloride (chlorine) is just Cl. In order for both of them to be stable, NH4 needs to get rid of one electron and Cl needs to gain an ...

Aayushi Jani 3A

In the lecture, it was mentioned that high polarizability means higher attractive force. The greater the number of electrons, the more polarizable it is. When there is high polarizability, and therefore more attraction, instead of it being a liquid, it would form a more waxy solid (as seen in the le...

Aayushi Jani 3A

London dispersion forces occur between all molecules and are also known as Van der Waals forces and induced dipole-induced dipole forces in the lecture. In this question, you would look at only nonpolar molecules as they would only exhibit London dispersion forces (others would exhibit London disper...

Aayushi Jani 3A

Yes this is true as the Lewis base is the one donating electrons while the Lewis acid gains the electrons.

Aayushi Jani 3A

Yes, I believe that is correct. You would have one electron in each of the px, py, and pz orbitals to have the lowest energy.

Aayushi Jani 3A

A stable structure is one that has a formal charge of 0. This is because it would have the lowest energy.

Aayushi Jani 3A

I think that finding the formal charge is a good way to check that your Lewis structure is the most stable. I agree, I think that it is mostly used for structures with resonance as they have multiple Lewis structures for the molecule.

Aayushi Jani 3A

This is also a double bond related question. How do we exactly know when there has to be a double bond when creating the Lewis Structure? We know what bonds to use based on the amount of available valence electrons and the octet rule. For example, in NO3-, if you try to use only single bonds, you w...

Aayushi Jani 3A

Yes, the charge represents the charge of the polyatomic ion/molecule. NO3 has a -1 charge, hence the -1 sign at the top right. This is because the Lewis structure drawing itself cannot showcase the specific charge of the molecule, so it is shown in this way.

Aayushi Jani 3A

Yes I agree, it can be on any side. What matters is that the number of electrons add up to the available valence electrons and that the appropriate bonds are used (single, double, triple).

Aayushi Jani 3A

Ionic bonds form between a metal and a nonmetal atom (an example from the lecture: KCl, potassium chloride). In an ionic bond, the electron transfer results in an an octet of electrons for each atom. The cations lose electrons and the anions gain electrons. In covalent bonds, however, cations cannot...

Aayushi Jani 3A

h-bar is h/2pi. You can use either equation, but personally, I prefer just remembering h and using ∆p ∆x ≥ h/4π.

Aayushi Jani 3A

The uncertainty in position refers to the position of the electron (which is in meters), so it would also be in meters.

Aayushi Jani 3A

En refers to the energy at an energy level, n. The E in E=hv refers to the energy of the incoming photon, while Ek in Ek = 1/2 mv^2 refers to the energy of the electron.

Aayushi Jani 3A

l could be 4, but I think that in this class, we'll only deal with elements up to l=3.

Aayushi Jani 3A

p represents momentum, which can be found by multiplying mass and velocity.

Aayushi Jani 3A

For this question, l refers to the orbital angular momentum, which is found by finding n-1. However, the l values that are possible are everything from 0 up to n-1. Therefore, when n=7, the possible values can be 0, 1, 2, 3, 4, 5, 6 which are 7 total values.

Aayushi Jani 3A

We haven't learned how to utilize it mathematically yet, however, conceptually, it essentially describes the concept that an electron (which has wavelike properties and indeterminacy in momentum) can be described by a wave function.

Aayushi Jani 3A

Electron density refers to the amount of electrons in a specific area (also known as the probability of finding an electron in that area). If there are a lot of electrons in one area, then the probability of finding an electron is high. In s-orbitals, where there are no nodal planes, the electron de...

Aayushi Jani 3A

Yes, technically, nothing can travel faster than the speed of light, and in the example from class, the velocity comes out to be much higher than the speed of light.

Aayushi Jani 3A

Yes, I agree, I think that it was just added as a funny last question in the module.

Aayushi Jani 3A

As frequency and wavelength are inversely proportional, as frequency decreases, wavelength increases. The extent of change refers to the slope of the wave. When the wavelength increases, the slope, or the extent of change, decreases.

Aayushi Jani 3A

I think that an equation sheet with constants is provided.

Aayushi Jani 3A

I also got 1m. I think that the answer at the back of the book just has the wrong units.

Aayushi Jani 3A

Hi! The equation for finding the n level is E = -hR/n^2. In this problem, we have n(initial) and n(final), meaning we would need to find E(initial) and E(final) in order to solve for the corresponding values of n. First, you would have to find delta E (total Energy), which is found by the equation E...

Aayushi Jani 3A

Yes, I agree, I don't think we have to memorize the entire spectrum but knowing the general order (which rays have a higher wavelength, what color corresponds to a lower wavelength, etc.) would definitely help while doing problems.

Aayushi Jani 3A

The electrons will still absorb the energy, but it would not be enough for them to be ejected/excited to a higher energy level.

Aayushi Jani 3A

Stoichiometric coefficients are just used to highlight the ratios of each reactant and product in a chemical equation. They are not measured in moles or any units.

Aayushi Jani 3A

In the problem, it states that 1 meter = 1,650,763.73 wavelengths. That means that in order to find the length of each wavelength, you would need to divide 1 meter by 1,650,763.73 wavelengths = 6.058 x 10 ^-7 meters. Then, using E = hc/lamda, you would plug in Planck's constant for h, the speed of l...

Aayushi Jani 3A

I agree with the others, the mole ratio of CO2 and H2O in the products would vary based on the reaction. You would have to balance the chemical equation just as you would for any other reaction.

Aayushi Jani 3A

To answer both questions, I think that it is pretty unlikely (based on the lectures & problems in the textbook) that there would be more than one limiting reactant (since the only one that is going to limit how much product is produced is the first one that gets "used up.") However, if...

Aayushi Jani 3A

I think that the colon is just there to highlight what the product of the equation is (in the first equation, P4O6 is created). It's not a part of the equation and I do not think it has any other significance other than that!

Aayushi Jani 3A

In the lecture, it was mentioned that stoichiometric coefficients must be in the lowest whole number possible, so I assume it is necessary. Hope this helps!

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