CHEMISTRY COMMUNITY

Jerry_T

A phase change is simply when matter changes from one state to another (i.e. solid to liquid aka melting).

Jerry_T

Salts can be either acidic, basic, or even neutral (e.g. NaCl) depending on their cations and anions.

Jerry_T

Heat is not a state function because it doesn't depend only on the final and the initial state of the system. For instance, recall the hiking example Dr. Lavelle provided in class. The change in altitude is the same no matter the route taken but the heat that leaves your body (in order to do work) d...

Jerry_T

We can assume that X is insignificant when Ka < 10^-4. Alternatively if the inital concentration of the acid/base is 1000 times greater than the equilibrium constant, you can assume that the X is insignificant.

Jerry_T

X is not a valid apprxoimation for X 2 . If you take out one of the X's in the products (numerator), then you're ignoring the concentration of that product completely.X ≠ X 2 . For the demoninator, you can approximate because a large value minus a very small value is still approximately that large v...

Jerry_T

Inverse K_c is for the reverse reaction where it's reactants over products.

Jerry_T

1 bar is approximately 1 atm. Bar is the SI unit while atm is more traditionally used in chemistry.

Jerry_T

When you find the equilbrium partial pressures from your ICE table, you can add them all up to obtain the total pressure.

Jerry_T

so let's say there is a problem where they provide the mols and they are in a certain number of L in a container you would have to find the concentration with is basically mol/L in order to then proceed with the problem? That depends on the problem but mol/L is a common measurement of concentration...

Jerry_T

Partial pressure only applies to gases because you cannot change the pressure of liquids and solids significantly.

Jerry_T

You would only include H₂O when it is in a gaseous phase.

Jerry_T

1 bar is very close to 1 atm so either will work. In lecture, Lavelle mentioned we will be using atm mostly.

Jerry_T

In the case of a reverse reaction, you will be given the initial concentration of the products instead.

Jerry_T

The value of R will be provided on the constants and equations sheet. In lecture, Lavelle stated we will be using atm primarily so I would use the R value of 8.206 x 10^-2.

Jerry_T

An inert gas is a non-reactive gas. In other words, they are noble gases.

Jerry_T

The bond angle for AX3E depends on the molecule specifically but they are always less than 109.5 due to electron repulsion from the lone pair.

Jerry_T

The relationship between [OH-] and pOH is the same as the relationship between [H+] and pH. We use the logarithmic value (p- prefix) for convenience. pOH = -log[OH-] [OH-] = 10 -pOH You might find this image useful. https://www.sciencegeek.net/Chemistry/taters/graphics/pHSchematic.gif

Jerry_T

Understanding the equilibrium point and the shape of the graph should be sufficient.

Jerry_T

There are multiple formulas for acid rain because there are several reactions that make rain acidic. Here are some of the common ones: https://4.bp.blogspot.com/-Kf5m0cGVlqc/WwrcJQ71uYI/AAAAAAAAS1s/jlwP3BdDDVcWpJP32lUBq5rT6jrPekXswCLcBGAs/s1600/Screenshot_2018-05-27-21-28-02-069_com.google.android.a...

Jerry_T

Ah okay I see, thanks! I kind of get the relationship between pH and pKa now.

Jerry_T

Water is amphoteric so it can act as either an acid or base depending on the context of the reaction.

Jerry_T

Are there any other common polyprotic acids/bases besides H2SO4, H2CO3, and H3PO4?

Jerry_T

When rain reacts with pollutants in the air (sulfur dioxide or nitrogen oxides), it becomes acidic.

Jerry_T

Can someone explain/clarify the relationship between pH and pK_A in terms of determining whether the acid being neutral or negatively charged? i.e. Why is it that when pH is lower than the pKa, the compound will be protonated? I think I'm missing some fundamentals here...

Jerry_T

Yes, the distribution of electron densities would be trigonal bipyamidal. The 3 lone e- pairs would be equatorial, leaving the two atoms opposite of each other (axial). Since the atoms are opposite of each other, the molecular geometry would be linear -> bond angle: 180.

Jerry_T

There is no trend, it is independent of order. Just know that the first row of the d-block transition metals have unique functions in biological systems and some examples covered in lectures.

Jerry_T

In the context of a coordination compound, the Cl- is an anion inside the coordination sphere with 8 e- so it uses 2e- to form a bond with the TM.

Jerry_T

In his lecture, Dr. Lavelle stated that either -ido (IUPAC) or -o (traditional) is acceptable.

Jerry_T

For complex anions, Latin names are used for the following: Silver -> Argenate, Copper -> Cuprate, Lead -> Plumbate, Tin -> Stannate, Gold -> Aurate, and Iron -> Ferrate.

Jerry_T

Oxidation number and oxidation state are the same thing. They are used interchangeably. Generally, for the first row of the d-block, the transition metals have a +2 oxidation state (the charge for transition metals is usually a case by case basis). You can determine the charge of a transition metal ...

Jerry_T

Yes its very simple.
2 regions of e- density -> sp
3 regions of e- density -> sp²
4 regions of e- density -> sp³
5 regions of e- density -> sp³d
... etc.

Jerry_T

All single bonds are sigma bonds. Consequently, double bonds have one sigma and one pi bonds and triple bonds have one sigma and two pi bonds. (i.e. The bonds in addition to one sigma bond are all pi bonds). Pi bonds are stronger than sigma bonds. You can conceptually verify this because triple bond...

Jerry_T

If the dipole moments cancel out, then the molecule is not polar. In other words, if there is no net dipole moment, then the molecule is not polar. Visualizing the 3D structure and symmetry of a molecule might help you in determing whether a molecule is polar.

Jerry_T

Drawing the Lewis structure can help you identify whether a compound has delocalized pi bonds. For a compound that has a resonance structure(s) containing pi bonds (double and triple bonds), then it is said to have delocalized pi bonds because the pi orbitals extend over more than two atoms. An exam...

Jerry_T

Yes, lone pair electrons are also regions of electron density. If they weren't then, molecular shape would be only determined by bonding electrons.

Jerry_T

The shape is commonly referred to as either bent or angular. Some examples of this are H2O and NO2- (due to their lone pair(s)).

Jerry_T

When you draw the Lewis structure for NO2-, the N has a lone pair which is more repulsive than bonding pairs and pushes the O atoms away from it causing the bent shape.

Jerry_T

The lone pairs are more repulsive than the bonding pairs and thus their electron distribution causes H2O to be bent as the lone pairs "push down" on the H atoms.

Jerry_T

Are there other factors that affect polarity besides symmetry?

Jerry_T

Adding more electrons to an anion would increase the ionic radius because there would be more electron repulsion for the same nuclear charge.

Jerry_T

You can find a guide to oxidation numbers on Sapling (https://sites.google.com/site/chempendix/oxidation). He hasn't gone over oxidation numbers in depth yet.

Jerry_T

Radicals are highly reactive because they are unstable due to their unpaired valence electron. I think the question would typically tell you when a radical is involved.

Jerry_T

There's no way to recognize the formal charge without calculating so I draw Lewis structures by counting the number of electrons, then trying different bonds for the lowest formal charge.

Jerry_T

Hydrogen bonding is a intermolecular force unlike coordinate covalent bonds which are intramolecular.

Jerry_T

Be and Li tend to lose electrons so they don't form a full octet. H and He only have electron(s) in the 1s orbital (max of 2 e-) so they don't form a full octet.

Jerry_T

If you have time, I'd recommend Organic Chemistry tutor on Youtube. His explanations are pretty easy to understand and follow.

Jerry_T

The octet rules applies to the first three rows of the periodic table if I remember correctly. (Correct me if I'm wrong please)

Jerry_T

I would try to understand the conceptual reasoning behind the each of the trends. So even if you forget the trends, you can conceptually deduce the trends.

Jerry_T

The Hamiltonian is just a specific word for double derivative in this context.

Jerry_T

Ionic bonds are stronger than covalent bonds because their difference in electronegativity is greater than that of covalent bonds.

Jerry_T

n1 is always smaller than n2 because electrons are moving from higher energy state to a lower energy state. Therefore, n1 can be thought of as n final.

Jerry_T

A nodal plane is where the probability of finding an electron is 0 (i.e. no electrons can exist in the nodal plane). The s orbital has no nodal planes due to its spherical nature.

Jerry_T

Nevermind, I figured it out (correct me if I'm wrong pls). The Rydberg equation for frequency uses the Rydberg constant Lavelle gave us on the equation sheet which is in Hz. On Sapling, the Rydberg constant (1.0974 x 10^7 m^-1) is for the wavelength equation. Tl;dr: Two different equations with two ...

Jerry_T

To my understanding, the Rydberg Equation for wavelength is: https://cdn.shopify.com/s/files/1/0093/2298/7617/files/Screen_Shot_2019-08-09_at_2.30.14_PM.png?v=1565325071 so how was the equation for frequency (below) obtained on the Constants and Equations sheet by Lavelle? https://i.imgur.com/RKxSit...

Jerry_T

Increasing the amplitude only increases the intensity. It does not affect wavelength or frequency.

Jerry_T

We won't have to derive the equations on the midterm since it's multiple choice; I think the test would focus more on how to apply the equations and which equations to apply rather than how to derive them.

Jerry_T

In the lecture, 5s state was an example of a silver atom's electron (5th row on ptable, n = 5) in s-orbital, hence 5s.

Jerry_T

The questions will most likely be conceptual so you might want to rewatch the Shrodinger portion of lecture to review.

Jerry_T

The Heisenberg Indeterminacy concept will most likely be on the exam since he said anything up till 10/21 lecture would be on exam.

Jerry_T

I know Lavelle covered this in the lecture, but what is the difference between the photoelectric experiment and atomic spectra?

Jerry_T

Yes, threshold energy and work function are interchangeable.

Jerry_T

I try to study with my friend for one hour each week. It's almost like having a gym buddy in terms of accountability. We both benefit from this by explaining to each other our understanding of the concepts covered and asking questions we previously didn't think of.

Jerry_T

Lavelle mentioned in the lecture that it's acceptable to leave the answer in meters. I'm assuming that this also applies to exams.

Jerry_T

Since the units for Planck's constant (h) are Joules second (J.s), the unit for E should Joules (J).

Jerry_T

Hey, I was just wondering how everyone approaches balancing chemical reactions in terms of which element to balance first (or the order in general). Also, how do you guys keep track of the number of elements on each side of the eqn (a mental note, tallies, etc.)?

Jerry_T

If the question asks for percent yield, then actual yield should be given. I hope this answers your question!

Jerry_T

There is a periodic table provided by Sapling under the Resources Tab on the left side of the dashboard screen. I prefer to use ptable.com. You will end up memorizing the molar masses of biologically essential elements eventually as you take more chemistry classes.

Jerry_T

How did you guys obtain the molar mass? I don't remember how to interpret skeleton drawings of organic molecules.

Jerry_T

You should use whole numbers (by convention). Ex: It wouldn't make sense to have 3/2 of a molecule just as it wouldn't make sense to have 3/2 people. So you would multiply both sides of the equation by 2 to obtain a whole number.

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