CHEMISTRY COMMUNITY

Mariah

Deena Doan 2F wrote:Are the rest of the discussions going to be on Zoom or are they just canceled?

I saw most TA's posting their notes, so I assume they are just cancelled.

Mariah

Julieta Serobyan4D wrote:I usually listen to music before the exam and try not to think about it. Also, if I know the material well, I am not that nervous. So, yeah practising does help.

Now you can listen to music during!!

Mariah

asannajust_1J wrote:the total order of the reaction is the sum of the exponential coefficients. This can be determined based on graphs, a given rate law, or an integrated rate law.

Would the graphs be given to us?

Mariah

Brandi 2C wrote:** It's not on Sunday anymore. **

He said it was cancelled in the email!

But we are still having a final correct? We just don't have to be on campus.

Mariah

rabiasumar2E wrote:It's zero in an isothermal reversible reaction.

Can you explain how we know whether or not it is isothermal?

Mariah

For concentration cells E of the cell is just zero correct?

Mariah

Ryan Yee 1J wrote:Yes, because of the equation: delta(G) = delta(G0) + RTln(Q) and since we are at equilibrium, Q=K as well as delta(G0) = -RTln(K). So if you plug things back in, you get delta(G) = -RTln(K) + RTln(K) which equals 0

I thought that delta G naught, was just at standard conditions not equilibrium?

Mariah

It just allows electrons to flow I think.

Mariah

The document that Dr. Lavelle shared with us says that the final exam questions will come from the homework. Does this mean all questions will be taken from the homework, or will the format be more like the midterm? I think that says that on every exam file, I don't think ALL questions are homework...

Mariah

Any word on how long it will be ?

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Rosa Munoz 2E wrote:No idea. We're all waiting on Lavelle's email

We won't have to be on campus right?

Mariah

Rebekah Alfred 1J wrote:When E cell is equal to zero, the cell cannot do work.

So can the cell do work whether it is negative or positive?

Mariah

Philip wrote:Whenever we balance the half-reactions, how do we know whether we need to add an H+, OH-, and/or H2O on what side of the reduction or oxidation half-reaction?

Remember it depends on whether it is being balanced in acidic or basic conditions!

Mariah

Clara Cho 2K wrote:When solving an electrolysis problem, do you approach it the same way as a galvanic cell?

I think it is different because E of the cell is 0? Right?

Mariah

I think its easier to think products/reactants.

Mariah

HannahBui 2K wrote:How do you find oxidation numbers?

It might help to look up ionic trend charts on google images.

Mariah

I think that you would have to determine the anode and cathode by looking up the reduction potentials for the half reactions. The more positive value is more likely to be the cathode because it is a better oxidizing agent and the less positive value will be the anode because it is a better reducing...

Mariah

The electrode is a metallic conductor that is in contact with an electrolyte solution. This allows electrons to flow between the cathode and the anode so that the reaction can proceed. Platinum is sometimes used as an electrode because in reactions that only occur with aqueous species, there is no ...

Mariah

annikaying wrote:How would one write the cell diagram of reaction that is in an acidic solution? Is it any different?

The cell diagram would look the same, the half reactions being balanced are where there is a change depending on solutions.

Mariah

Congratulations!!!

Mariah

Aiden Metzner 2C wrote:In lecture it seemed like professor said that k is always the slope of the graph of the rate. Is this true for zero order, first order, and second order reactions. Or is it only true for zero order?

There is a great diagram in the book explaining this, I believe it is on page 608.

Mariah

805312064 wrote:What does it mean when Enaught is negative and why is it always positive for a galvanic cell?

It tells you the spontaneity of the reaction, Galvanic Cells are always spontaneous making them positive.

Mariah

Ghadir Seder 1G wrote:I know that oxidation is the loss of electrons and reduction is the gain of electrons, but how can I tell which one is which by looking at the chemical reaction? Do I use their oxidation states?

I usually use OIL RIG, Oxidation is loss Reduction is gain (of electrons).

Mariah

I dont understand conceptually how the standard Gibbs free energy for pure substances is also zero, like delta H standard. Since the equation for Delta G is H-TdeltaS, why doesnt the TdeltaS part factor in? Why is it still zero? I think since it is a pure substance you assume that delta S is consta...

Mariah

Kaylee Clarke 1G wrote:when do you include an inert gas in the cell diagram? and why is it only for one side (cathode or anode) or on both the cathode and anode?

I think you would only include it if it is participating in the reaction, otherwise you wouldn't.

Mariah

Anthony Hatashita 4H wrote:What's the difference between these two?

Whenever you see the not symbol, it means that it is under standard conditions.

Mariah

Honestly, the method that has helped me the most when I am faced with problems I am unsure of how to start (aka many of those on the midterm) is writing down every equation related to what you think the question is asking. Thus, if the question mentions or wants you to find entropy, write down ever...

Mariah

Prasanna Padmanabham 4I wrote:When the Gibbs Free Energy is negative it means that the forward reaction is spontaneous while if it is positive, it means that the reverse reaction is spontaneous.

Spontaneous means that it will occur on its own correct?

Mariah

When is test 2?

Mariah

If delta G is negative, that means that the forward reaction is favored and that the products will be favored because K>1. (You could then say that the reaction shifts to the right.) If the delta G is positive, that means that the forward reaction is not favored (the backwards reaction is favored) ...

Mariah

Ellen Amico 2L wrote:During a phase change, all the added heat energy is going towards breaking the bonds rather than increasing the temperature. Therefore, the temperature won't change.

So once the phase is reached will the temperature then change?

Mariah

Basically, this is because steam has undergone a phase change from liquid to water vapor (vaporization). Vaporization requires a lot of energy. When steam touches your skin, it will release a lot of energy as it cools to form liquid water. Water, while at the same energy, does not have the same lat...

Mariah

Hello, I took 7A last quarter and I remember mention of delta H, or enthalpy in the Gibbs Free Energy Equation. Is this the same as what we are learning now?

Mariah

Eileen Si 1G wrote:Is it possible to calculate K for an unbalanced equation? Or can you only calculate Q?

An equation must be balanced and at equilibrium to determine K. You must balance the equation before determining either K or Q.

Mariah

I think enthalpy is more of the change occurring with heat during a rxn.

Mariah

It just depends on what is given at the beginning and what is being asked for.

Mariah

It does not change because it is being used to uphold its phase instead of actually heating it up.

Mariah

Hui Qiao Wu 1I wrote:He said that buffers help resist change. Our body is only equipped to function under a limited range of conditions. The buffers help our mechanisms stay in that optimal range.

So do buffers just help Chautliers principle ?

Mariah

ALegala_2I wrote:Does this mean that cooling an exothermic reaction will favor the products?

I think this would be correct. Can someone explain why?

Mariah

No all constants are given, just know how to use them.

Mariah

Abhi Vempati 2H wrote:Adding on to what @Hui Qiao Wu 1I mentioned, the lower the pk_a of an acid, the higher the pK_b of its conjugate base. This is because of the equation pk_a + pK_b = 14. Hope this helps!

14 is the same as p[sub]w right?

Mariah

I hope they will be, but I doubt it.

Mariah

the only reason you need to pay attention to the units is when choosing which R variable to use when using the gas law.

Mariah

IT has to be measured at a constant pressure because as pressure increases, so does enthalpy.

Mariah

Its basically how rxs will react to change to minimize actual change that occurs.

Mariah

805097738 wrote:This principle tries to minimize the effect of change by shifting the direction of the reaction in order to maintain equilibrium

Just to clarify, it can shift either way right?

Mariah

Hannah Romeo 1J wrote:Solids and liquids are not included in the K expression as they do not change their concentrations in a reaction as they are pure substances. Essentially, their value is 1 resulting in the K expression only including aqueous solutions.

As well as gases!!

Mariah

It helps us to know the ratio of products and reactants when a rx is at equilibrium.

Mariah

Its basically omitted because it only changes slightly.

Mariah

There is actually a Khan Academy section that has some video lessons and practice problems related to Le Chatlier's Principle https://www.khanacademy.org/science/chemistry/chemical-equilibrium/factors-that-affect-chemical-equilibrium/v/le-chatelier-s-principle This is actually a really good khan ac...

Mariah

You use them when referring to what information is given or asked for. Yes, we use the ideal gas law to switch between the two if needed.

Mariah

He is not going to make it worth less, but he will curve the class at the end depending on how everyone does out of 500 points.

Mariah

Malia Shitabata 3H wrote:Do we have to memorize the mass of an electron since it's a constant or will it be given on the reference sheet?

Its on the reference sheet.

Mariah

905174774 wrote:Is what considered a base or acid? Or does it just depends on what the problem is?

It is amphoteric which means it can act as both.

Mariah

An H-bond must be bonding to an NOF, but it would already be connected to an NOF within itself.

Mariah

Yes, this is safe to say.

Mariah

You are supposed to compare the compound as is.

Mariah

For the purpose of the chelating ligands, we are using you can see on Lavelles website that certain ligands have a set number of bonding sites. You have to memorize it.

Mariah

chari_maya 3B wrote:I don't understand part b... I know that N is more electronegative than Zn so Zn(OH) must be the bronsted base, but I don't understand why it is Zn(OH)2.

It has to be that because zinc has a +2 charge and OH has a -1 charge.

Mariah

Would our coordination number be raised by just counting the chelating ligand, or how many times it is chelated to the metal?

Mariah

Andrea_3F wrote:9C.7 Which of the following isomers of diaminobenzene can form chelating complexes? Explain your reasoning.

How do you know which isomers can form chelating complexes?

You can tell by remembering the main shapes of coordination compounds and which would fit without straining the bonds.

Mariah

Zoya Mulji 1F wrote:What are some examples of coordination compounds used as chemotherapy drugs?

I think we only need to know about cisplatin.

Mariah

Chloe Alviz 3F wrote:In the textbook, it says that all single covalent bonds are sigma bonds. If this is the case, how would we define the bond for an ionic compound such as NaCl?

Sigma and Pi bonds are only present in covalent bonds, as you said above.

Mariah

What do we need to know about these coordination compounds??

Mariah

Isabel Day 1D wrote:You can identify an amphoteric compound by seeing if it would be able to both accept and donate hydrogen atoms.

So in this case, would water be amphoteric?

Mariah

I believe it has something to do with the three unpaired electrons in the p orbital, and the fact that energy would be needed to add an electron to nitrogen. In the contrary, energy is released when added to oxygen.

Mariah

005388369 wrote:Is memorizing the only way to know the ionic charges in the periodic table?

I know that if you look uo ionic charge trends it shows it on the periodic table, this was the easiest way for me to do it.

Mariah

This type of inter-molecular force is the same thing as a Van der Wall force and can occur with any molecule and is the weakest form of inter-molecular force. Well an example for this is basically any molecule because even if it doesn't happen as often, there will be a point in time where two eleme...

Mariah

According to the solution manual of E15, a seesaw would have an approximate angle of 90 and 120 degrees. Wouldn't the angles be less than 90 and 120 due to the lone pair causing a smaller angle than the typical angles of an electron arrangement of a trigonal bipyramidal? It is less than 120 or 90 b...

Mariah

Omar Selim 3H wrote:sigma bonds are harder to break than pi bonds because the former are a result of end-to-end bonding while the latter consist of side-to-side bonds

So then why are double bonds stronger than single bonds? If they contain a sigma and pi versus just one sigma?

Mariah

The oxidation numbers are determined based off the charge of the ion itself. For example if the compound was C2H6, the oxidation number of the H would be +1 and the C is -3 so when you add the total together it would be (1x6)+ (-3x2) which would make the oxidation number of the whole molecule 0. So...

Mariah

Is this the only case that doesn't follow the ionization trend?

Mariah

I was a bit confused about this too because of the midterm but I am assuming still Chemical Bonds.

Mariah

Tiffany Dong_4e wrote:The central atom is typically determined by whichever atom has the lowest electronegativity. Aside from this, the atom which is alone or has the lowest quantity is usually in the center.

This is probably the best rule to follow! Try not to over complicate it because it may confuse you more.

Mariah

They occur with all molecules because all molecules have electrons floating around the cloud that sometimes create momentary charges. We learned about it in LS7A and they showed us a video about Geckos. I think if you look up Van der Waals Gecko it might help you understand the concept.

Mariah

BaBr2 is more ionic compare to BeBr2 and BBr3 because the electronegativity difference between Ba-Br is the greatest compares to electronegativity difference between Be-Br and B-Br. Electronegativity increases across the period and decreases down the group. Therefore the electronegativity differenc...

Mariah

You can also see how there is only a double bond between A and T which helps to remember there is only 2 hydrogen bonds, which makes it weaker than G and C pairs that have a triple bond.

Mariah

Count the bonds around the atom as 1 electron and then count each lone pair as 2 electrons (count each dot you drew individually) and you want this to add up to the number of valence of electrons of the actual element. However if this is on a test then you should show the actual calculation. My TA ...

Mariah

Anisha Chandra 4H wrote:Yes, the 4s orbital is lower energy than 3d, but once 4s is filled, it becomes higher energy than 3d, which is why electrons will be removed from 4s before 3d during ionization.

So to clarify, if we need to remove electrons we would go to 4s before 3d, because this confused me.

Mariah

Leila_4E wrote:Will we have to know the actual values of electronegativity to determine the minute differences? I assume probably not..

I was told that we do not, but it might help when trying to figure it out. I think it just depends on your understanding.

Mariah

I think the only time you have to make sure the formal charges are zero is when it asks to draw the most stable version.

Mariah

DarrenKim_3G wrote:I think we would just have to know that electronegativity increases bottom to top in groups and left to right across periods

Electronegativity becomes relevant in drawing lewis structures correct? Or is that a different trend?

Mariah

Alexa Hernandez 3k wrote:The more Bonds means a stronger pull so consequently you also get a smaller length because of the increased attraction.

So the smaller the bond, the stronger it is?

Mariah

How do we know which elements have expanded octets? Do these need to be memorized?

Mariah

Jamie Lee 1D wrote:Any electron configuration can be written in shorthand, so you can write ground-state or excited-state configurations using shorthand.

Thank you! This helps, what are the differences between ground-state and excited-state configurations?

Mariah

This question confused me as it is asking for the chemical formula for Aluminum Hydride. Don't Aluminum and Hydrogen both have positive charges? Are they allowed to bond with each other?

Mariah

Are noble gas electron configurations, or shorthand, the same as ground-state configurations? If a homework problem asks for the ground-state configuration of an element, is a noble gas shorthand allowed to be used?

Mariah

The atomic radius is half the distance between the nuclei of two identical atoms bonded together. For the purpose of this class I don't think we would be calculating the exact value of the radius. During the lecture, a picture was shown that said 2r from both nuclei of atoms bonded together. Do you...

Mariah

I have a question regarding whether it's a cation or anion. Does that affect the ionic radius of the element? In my notes, I wrote "cations are smaller than their parent atoms and anions are larger" I wrote the same, I think they do have an effect on the radius of an element, but I don't ...

Mariah

All of these also increase for a hydrogen atom as well. I think the important part of the question is understanding why these increase in a hydrogen atom versus a lithium atom. For a, b, and c, (all properties that apply to single-electron systems), the reason for the increase is the same between h...

Mariah

Im kind of confused about this, what would cause an electron to transition into a higher energy level in the first place? Do they do this on their own or because of some outside force?

Mariah

So, can we reorganize this equation to find velocity? Would V=(h/wavelength*m) be correct?

Mariah

I am also confused about this, are they grouped by which lower energy level they are moving towards?

Mariah

Qiu Ya Wu 4F wrote:In his lecture today, Lavelle emphasized that the plane the electron is found in is arbitrary and different textbooks associate different l values with different x,y, and z planes.

So, because he said this we can assign the x,y,z variables to the values we have correct? That confused me as well.

Mariah

I just watched a video that described it as wave-packets, which have both the properties of waves and particles. That concept helped me to understand the photoelectric effect, I hope it helps you too.

Mariah

Thank you! This helps a lot. I did not know we could round if it was just a couple hundreths off.

Mariah

Can anyone explain how the units should turn out? Or how they work throughout the problem because I am having trouble with that.

Mariah

What if you cannot multiply to get a whole number? If I have 2.66 for example, could I just round to 3?

Mariah

Try to avoid rounding to how many significant figures you need until the very end or your final answer. If you do it throughout the problem, it makes your answer less accurate.

Mariah

If you are doing the empirical formula, I think that is when you have to worry about making things a whole number. Just remember you can manipulate numbers by multiplying, and dividing by the smallest if needed. Also whatever you do to one number, make sure to do to the others as well. If you fail t...

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