CHEMISTRY COMMUNITY

Mingzi Yang 1E

Thank you for all the helpful tips!

Mingzi Yang 1E

The strongest reducing metal is the one that has a lowest reduction potential (meaning that it is more likely to be oxidized) if you are comparing different metals.

Mingzi Yang 1E

Pt(s) is added when there is no conducting metal on any side of the cell.

Mingzi Yang 1E

Yes, the sign of the Eo need to be flipped when reversing rxn. I think E is an intensive property so it stays the same when being multiplied. Please correct me if I am wrong :)

Mingzi Yang 1E

Dr. Lavelle, Thank you so much for these two amazing quarters! I learned a lot and it was a great experience learning chemistry in this remote learning environment!

Mingzi Yang 1E

If you flip the reaction, you should flip the sign of E˚.

Mingzi Yang 1E

The two half reactions should have the same number of electrons so they can get cancel out.

Mingzi Yang 1E

What are some tips for balancing a reaction with acidic or basic conditions? I had a hard time doing this type of question on sapling.

Mingzi Yang 1E

In a few of the sapling questions, they state whether a reaction is in basic or acidic solution so I think that will be the same for other questions.

Mingzi Yang 1E

Yes. Some questions need to take into account the states of matter while some don't.

Mingzi Yang 1E

The oxidizing agent is the one being reduced and the reducing agent is the one being oxidized.

Mingzi Yang 1E

This is what the solution says: Start by writing the reactants on the left side of the arrow and the products on the right side. Fe(s)+O2(g)+H2O(l)⟶Fe2O3∙3H2O(s) Balance the Fe atoms by placing the coefficient 2 in front of Fe. 2Fe(s)+O2(g)+H2O(l)⟶Fe2O3∙3H2O(s) Balance the H2O molecules as a unit b...

Mingzi Yang 1E

Thank you for all the explanations!

Mingzi Yang 1E

For the first one: the phases of each species present should correspond to their phases as originally specified in the equation given in the question: MnO4- is (aq) S2- is (aq) H2O is (l) MnO2 is (s) OH- is (aq) S is (s) For the second one: First begin by writing out the half-reactions. This is in ...

Mingzi Yang 1E

Hi! First we can split the redox reaction into two half reactions. Ag+ + 1e- → Ag since Ag+ gains one e- and is reduced to Ag. NO → NO3- + 3e- since the oxidation state of N in NO is +2 and +5 in NO3-, so NO loses 3e- and is oxidized to NO3-. The Ag reaction is already balanced so we need to balanc...

Mingzi Yang 1E

A closed system is when there is no exchange of matter in and out of the system. For example, when a bottle is sealed. Only energy can be exchanged with the surroundings.

Mingzi Yang 1E

State functions depend on both the initial and the final states. It is applicable to Gibbs free energy, enthalpy and entropy.

Mingzi Yang 1E

Thank you for all the clarifications!

Mingzi Yang 1E

Since volume and pressure are inversely proportional, you can use this equation deltaS = nRln(P1/P2), derived from deltaS = nRln(V2/V1).

Mingzi Yang 1E

I usually look at the unit of the pressure and use the R constant that matches the unit. So if the pressure is in atm, I use the constant that is 0.08206 L*atm*mol^-1*K^1.

Mingzi Yang 1E

Hi! I answered this question for someone else, so I'll paste it here, but I will modify it a bit to fit your specific question. Let's look at the particles inside each container. Container A has a monoatomic ideal gas, which means it's going to be more disorderly than a diatomic one, as there's mor...

Mingzi Yang 1E

I usually look at what unit I need to have for the final answer and then do my calculations. I found myself converting the temperature to Kelvin for most of the time tho!

Mingzi Yang 1E

I converted kPa to bar (1 kPa=0.01 bar) and used this gas constant (8.314x10^-2 L.bar.K^-1.mol^-1). I think it depends on the unit of the pressure. I used "bar" as the unit so I used the corresponding gas constant provided on the constant sheet.

Mingzi Yang 1E

Yes, you are correct that for fusion and vaporization, both the change in enthalpy and the change in entropy are positive. The same is true for sublimation (solid to gas) since it is simply the sum of fusion and vaporization. For the opposite processes, both the change in enthalpy and the change in...

Mingzi Yang 1E

Thank you for all the explanations! They are helpful!

Mingzi Yang 1E

I saw it on sapling that a negative value for work means a system does work on the surroundings.

Mingzi Yang 1E

I have the same question too! All the explanations clarified my question!

Mingzi Yang 1E

I think the system is an isolated system.

Mingzi Yang 1E

Phase change occurs when a substance of one form changes to another form. For example, liquid water becomes a solid (ice).

Mingzi Yang 1E

The difference between the two equations is that in the first one, you use mass in grams, but in the second one you use number of moles. The equation you choose will depend on what the problem is asking. how do you determine which equation to use? I believe it depends on whether you're trying to fi...

Mingzi Yang 1E

I have the same question too! I only know that most diatomic gases are in their stable form.

Mingzi Yang 1E

Yes, you can rearrange the equations so that the number of moles of reactants or products matches the ones you need. Make sure to keep track of the changes to the enthalpy values when you make these rearrangements.

Mingzi Yang 1E

You can determine bond enthalpy values from standard enthalpy of formation values by writing out the equations for the standard enthalpy of formation for the molecule the value is given about. For example, if you are given the standard enthalpy of formation of Cl (g), you can write out the equation...

Mingzi Yang 1E

Thank you for all the responses. These clarified my question!

Mingzi Yang 1E

Ellison Gonzales 1H wrote:Could someone clarify how we check our “x” after using the 5 percent rule? Also, is the 5 percent rule a part of Le chatelier’s principle? Thanks

I don't think the 5% rule is a part of Le Chatelier's principle.

Mingzi Yang 1E

If a reaction is endothermic, then it will favor product formation because more reactant is added. If a reaction is exothermic, then it will favor reactant formation because more product is added.

Mingzi Yang 1E

How much do we need to know about Le Chatelier's Principle for the upcoming midterm?

Mingzi Yang 1E

Changes in pressure affect reactions with gases.

Mingzi Yang 1E

Heat is denoted with q. H / delta H is for enthalpy.

Mingzi Yang 1E

Endothermic reactions have a positive delta H and exothermic reactions have a negative delta H.

Mingzi Yang 1E

Yes, they mean the same thing. The term "shifting" always confuses me too.

Mingzi Yang 1E

I remember in a workshop with Michael, he mentioned that there is a trick: if K>Q, the reaction proceeds right, since the arrow is pointing to the right, and if K<Q, the reaction proceeds left, since the arrow is pointing to the left. This trick only works if K is written before the Q. Thank you fo...

Mingzi Yang 1E

K in general is the equilibrium constant. The subscript a (Ka) is for acids and b (Kb) is for bases.

Mingzi Yang 1E

If Q equals K, the reaction is at equilibrium. Q is calculated the same way as K when the reaction is not at equilibrium.

Mingzi Yang 1E

If H2O is a gas, it should be included in the ICE table. If it is a liquid, we don't include it.

Mingzi Yang 1E

Grace_Remphrey_2J wrote:Here's a table I find super helpful when looking at the difference between real and ideal gas. Hope this helps!
Screen Shot 2021-01-10 at 3.26.10 PM.png

This table is helpful! Thank you!

Mingzi Yang 1E

P=pressure (in atm)
V=volume of gas (in L)
n= number of moles
R= gas constant
T= temperature (in Kelvin)

n/V = concentration

Mingzi Yang 1E

There is a very small difference between the two values, so we would approximate 1 bar = 1 atm as the unit of pressure.

Mingzi Yang 1E

Kelvin should be used as the unit of temperature in this case.

Mingzi Yang 1E

You use Kp when all the reactants and products are gases. If the reactants and products are given in molar concentration, then you should use Kc.

Mingzi Yang 1E

Thank you for sharing this quizlet!

Mingzi Yang 1E

Thank you Dr. Lavelle for this great quarter despite that it is online. Everything is helpful and super organized!

Mingzi Yang 1E

Ariel Guan 1G wrote:pH = -log[H+]
[H+] = 10^(-pH)
pOH = -log[OH-]
[OH-] = 10^(-pOH)
14 = pH + pOH

This is helpful! Thank you.

Mingzi Yang 1E

Thank you for all your responses. They are helpful for me to distinguish some strong acids.

Mingzi Yang 1E

All questions are multiple choices, similar to the format of the two midterms.

Mingzi Yang 1E

To provide a more technical and detailed answer: Water (H2O) is able to release a proton (H+) to form hydroxide ions. Water can also accept a proton to form hydronium (H3O+). Thus, water can act as both a Bronsted acid and a Bronsted base, making it amphoteric/amphiprotic. I found a diagram which a...

Mingzi Yang 1E

Water is amphoteric, which can act as either acid or base depending on the reaction.

Mingzi Yang 1E

What are some common strong acids that I should memorize???

Mingzi Yang 1E

In one of the sapling homework problems (question 5 for me), the feedback includes a table (chempendix) of ligands. You can check it out to see some common ligand names and their denticity.

Mingzi Yang 1E

If there are multiple ligands, name them based on their alphabetical order.

Mingzi Yang 1E

I think either way is fine although Prof. Lavelle used dsp^3 in his lecture.

Mingzi Yang 1E

Hi! This is another part of Sapling Q.11. I understood how your answers applied to the other diagram, but this diagram threw me for a loop. If any of you have advice on how to better understand and complete these questions it would be much appreciated! Thank you! P have three bonding pairs and one ...

Mingzi Yang 1E

The shape of H2O is bent.

Mingzi Yang 1E

Thank you for all responses. It was the problem of the browser that I was using. It got it work using firefox.

Mingzi Yang 1E

When I tried to watch the lecture videos, it shows a green screen instead of the actual video itself (the audio works normally). Is it because of my laptop or does anymore have the same problem accessing the lectures? I had no trouble accessing the videos before.

Mingzi Yang 1E

All three have the same trend on the periodic table, which they increase across a period and decreases down a group.

Mingzi Yang 1E

Anions that are bigger and less electronegative are more polarizable. So nitrogen with a 3- charge is more polarized than oxygen with a 2- charge.

Mingzi Yang 1E

Stephen Min 2K wrote:
isha dis1k wrote:So just to clarify, as the bond numbers increase (etc. single to triple), the number of sigma bonds stay the same and pi and delta increase?

Yes, sigma bonds stay the same while pi bonds would increase, as bond order increases.

That makes sense. Thank you for clarifying.

Mingzi Yang 1E

Sigma and Pi bonds are discussed in lecture 22.

Mingzi Yang 1E

An ionic molecule displays the most covalent character when the two atoms have the least electronegativity difference when compared to the other ionic molecules.

Mingzi Yang 1E

What exactly is the dipole moment? What are some examples that can help me understand the concept of dipole moment? I have a hard time understanding what it is.

Mingzi Yang 1E

Thank you for all the explanations. They really clarify and help me understand this concept!

Mingzi Yang 1E

Generally, polarizability increases as the volume occupied by electrons increases. On rows of the periodic table, polarizability decreases from left to right (larger molecules are more polarizable than smaller ones). Polarizability increases down on columns of the periodic table. I hope this helps!...

Mingzi Yang 1E

The maximum number of water molecules should be 8 because the two oxygen and nitrogen atoms of the urea molecule can form hydrogen bonds with the hydrogen atoms of the water molecule. The four slightly positive hydrogen atoms of the urea molecule can each form a hydrogen bond with the slightly negat...

Mingzi Yang 1E

Since radicals are one of the exceptions to the octet rule, how much should we know about radicals in this context and for the midterm?

Mingzi Yang 1E

I don't think the atomic size of an element is directly affected by its electronegativity. In terms of their trends in the periodic table, they have opposite trends.

Mingzi Yang 1E

They are not the same. Electron affinity is the energy released when electrons are added to the atom and electronegativity is the electron pulling power of an atom.

Mingzi Yang 1E

How much do we need to know about the effective nuclear charge of an element? What does "shielding electrons" refer to in this context?

Mingzi Yang 1E

The number of electrons of an element is the same as the atomic number. If it asks for the valence electron, then the column number of where the element is in, is the number of the valence electron.

Mingzi Yang 1E

I think memorizing the trend (increases down a group and decreases across a period) is beneficial, especially when the test may ask for this type of question.

Mingzi Yang 1E

Generally, the radius size increases down a group and decreases across a period. Besides all the concepts mentioned above that can help in memorizing the trends, I also like to memorize F as the element that has the "smallest" radius size and it helps me visualize the trends.

Mingzi Yang 1E

Generally elements with high electron affinity are in top right of periodic table (group 17). Electron affinity increases across a period and decreases down a group.

Mingzi Yang 1E

The excited-electron in the 3s orbital will return to the 2p orbital when it is in its ground state. So the ground state is 1s2 2s2 2p5 and the element is fluorine (F).

Mingzi Yang 1E

Although n=5 and the general rule is l=n-1, I don't think l automatically equals to 4. l can equal to 1,2,3 or 4 depending on the situation.

Mingzi Yang 1E

Yes. atoms with lone pairs are usually reactive because they would want to become more stable by forming bonds and fulfilling the octet.

Mingzi Yang 1E

What is the main takeaway from the Heisenberg Indeterminacy Equation?? I am still a little confused about this equation after listening to the lecture. Like what is this "uncertainty" that this equation is trying to find?

Mingzi Yang 1E

I think it will be better to keep all decimal places and try not to round it until the end so the final answer can be more accurate. I usually round it only if this number contains too many decimal places that I can't keep track of.

Mingzi Yang 1E

You should convert the wavelength to meters so units can be cancelled out in future calculations for that problem. It will be convenient if you convert all units into SI base units before starting your calculations.

Mingzi Yang 1E

What concepts should we understand from the photoelectric experiment ?? (if we get a conceptual question about it on the midterm)

Mingzi Yang 1E

I thought we have to have a scientific calculator??? So we don't have a restriction on the type of calculator we use??

Mingzi Yang 1E

According to the email Professor Lavelle sent, we can use another device such as an ipad to show our workplace on zoom if we don't have a webcam. In this case, we will need two devices, one for doing the exam and one for showing our workplace.

Mingzi Yang 1E

alebenavides wrote:Does anyone know when we get our access code? I bought the book a few days ago but haven't received it so I had to get the free 10 day trial.

When I ordered mines, it took about 6 days for the code to get delivered. I hope you will get your access code soon.

Mingzi Yang 1E

Is this question asking us to calculate the number of moles of the compound then?? No, the question is asking how many many molecules of the compound are present in 5.15 g of the compound. In order to find that number, you do need to find the number of moles of the compound by using its molecular w...

Mingzi Yang 1E

According to the lecture today, a diffraction pattern results from both constructive and destructive interference.

Mingzi Yang 1E

I think constants and other necessary information will be given for the exams.

Mingzi Yang 1E

I think if the number has many decimals, it will be better not to round it and use the exact number. But for example, if the decimal has four or five places and you want to follow the sig fig rule and round it to two places, it will be fine to do so according to my experience.

Mingzi Yang 1E

I think it is fine to have a fraction as the coefficient. But it will be more convenient if the fractions are converted into whole numbers, especially when you need to do further calculations such as finding the molecular formula etc.

Mingzi Yang 1E

If the molar mass is given in the question, the way I usually would do is not to round it. If the molar mass is not given, then I would write what the molar mass from the periodic table accordingly. But I notice that some molar masses vary (by one decimal, for example) depending on which periodic ta...

Mingzi Yang 1E

7.00 x 10^2 has three significant figures. The way I understand it is that we mainly focus on the number "7.00". Since 7.00 has a decimal in between 7 and the two zeros, the two zeros after the decimal will also be considered to be significant figures.

Mingzi Yang 1E

Is this question asking us to calculate the number of moles of the compound then??

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