CHEMISTRY COMMUNITY

Joshua Eidam 2A

Look at a molecule and if there is an element such a oxygen that is always a charge of -2, you can determine the oxidation number based on the charge of the overall molecule. For example, NO 2 - , the oxidation number of N would be +3 since the two oxygens will add to a charge of -4, and if the whol...

Joshua Eidam 2A

i understand why adding a catalyst will decrease the activation energy for the forward reaction, but im a bit confused as to why it's the same for the reverse. can someone explain this please? A catalyst will reduce the activation energy for the entire reaction in general, both forward and reverse....

Joshua Eidam 2A

You can think of it as if it were reading a book for example. You go left to right. So the same thing applies to a reaction. The forward reaction will be how it is presented to you and read left to right. The reverse would be the same reaction but from right to left. Additionally, when looking at a ...

Joshua Eidam 2A

If it is not in the overall rate law, it has to be an intermediate.

Joshua Eidam 2A

If you consider how K is represented by the ratio of products to reactants, then yes, as previously stated since increasing temperature in an exothermic reaction will lead to more products being formed, the value of k will decrease accordingly.

Joshua Eidam 2A

Is the reaction "hump" the same as the energy barrier? Yes I believe so. I am not sure if I have heard the term reaction "hump" but it sounds pretty intuitive. The reaction barrier is that little (or big) hill in the reaction profile that the reaction has to get over when beginn...

Joshua Eidam 2A

A clear way to look at the relationship between k and the activation energy, E_a, is through the Arrhenius equation, $k=Ae^{\frac{-E_{a}}{RT}}$ . This equation shows how a decrease in activation energy would ultimately lead to an increase in k and vice versa. Hope this helps!

Joshua Eidam 2A

diangelosoriano wrote:If a catalyst were added, how would this also affect k or activation energy?

Adding a catalyst is going to decrease the activation energy, E_a, which will ultimately lead to an increase in the rate constant k.

Joshua Eidam 2A

Enzymes are proteins used in biological systems that act in the same way as catalysts. In that regard, they are the same thing as a catalyst; however, not all catalysts are enzymes necessarily.

Joshua Eidam 2A

Yes! If you look at the Arrhenius equation, k=Ae^{\frac{-E_{a}}{RT}} , you can clearly see how temperature affects the rate constant. If the temperature of the reaction is higher then the power to which e is multiplied will be a smaller negative number (aka more positive), and therefore the value of...

Joshua Eidam 2A

If you draw out the reaction curve that shows the activation energy and whether it is exothermic or endothermic will be really helpful. Once you determine how the reaction works, you will be able to see how the activation energy, the delta H, and the reverse reaction are related. I believe since the...

Joshua Eidam 2A

It isn't covered in lecture but I know there was a couple Sapling problems as well as textbooks examples that used it so it might be helpful for a problem or two on the final.

Joshua Eidam 2A

It is either kJ/mol or J/mol. Be careful about the units that are being dealt with and possibly the units of answer you are looking for. You may have a problem where you have to convert the given activation energy into either J/mol or kJ/mol

Joshua Eidam 2A

Sorry if this is the wrong section to be posting this question but I am confused as to what the slow step is in a reaction and how to identify it? Why is it called the slow step?

Joshua Eidam 2A

If you know the E a for both the forward and reverse reaction, you could also determine if the reaction is exothermic or endothermic based on this. For example, if the E a for the forward reaction is greater than the E a for the reverse reaction, you would know that the forward reaction is endotherm...

Joshua Eidam 2A

Ultimately, a catalyst simply lowers the activation energy of the reaction. Whether the forward reaction is exothermic or endothermic doesn't matter because the activation energy being lowered is applied to the entire reaction. So if you are looking at the reverse reaction, the activation energy is ...

Joshua Eidam 2A

Like others, this is based on my memory of high school biology class, but the catalyst is ultimately not consumed in a reaction. I believe that is why they are so important. They are able to change a slower reaction into a faster one without changing what products are formed. It is the same reaction...

Joshua Eidam 2A

Yes both increasing the temperature of a reaction and adding a catalyst will increase the rate constant. You can use the Arrhenius equation to determine that both factors would increase the rate constant. The Arrhenius equation, k=Ae^{\frac{-E_{a}}{RT}} , shows the relationship between the rate cons...

Joshua Eidam 2A

Hello I am super confused as to what Lavelle was talking about in his lecture 24 when talking about intermediates. I understand that 2NO 2 cannot form an NO and a CO 2 but I don't understand how in the steps he was showing, the NO and NO 2 just turn into CO and CO 2 . Can someone please clarify this...

Joshua Eidam 2A

You need to look at how the elements that make up the rate constant. For example, when trying to find the units for the rate constant of the 3rd Order Reaction, look at the units of the rate(M/s) and the units of the concentration term(M 3 ).The unit of the rate constant is obtained by dividing the ...

Joshua Eidam 2A

I am confused about what constitutes a reaction to be a first order reaction? Can there only be one reactant since the order is the value of the exponents added up? Additionally, how is it possible for there to be a zeroth reaction?

Joshua Eidam 2A

I was a little confused when Lavelle brought up how gases leave the solution so therefore they are not included in the reverse reaction. Is this assuming that the system is open? Even if the system was closed would that even make a difference since it technically may still leave the solution even if...

Joshua Eidam 2A

When the reaction is reversible, then the ΔS_universe= 0

Joshua Eidam 2A

The diamond to graphite example is perfect for representing what "controlling a reaction" really means. Although the thermodynamic aspect of the reaction would suggest that the reaction of diamond to graphite should take place rather easily, there is a huge energy barrier in the way due to...

Joshua Eidam 2A

Yes, the reaction would take place eventually. Unfortunately since diamond is so kinetically stable, it would take a VERY long time, meaning it likely would not be observable, and it and would definitely not be very exciting.

Joshua Eidam 2A

Saying a reaction is either kinetically or thermodynamically controlled means that the kinetic or thermodynamic factors of the reaction are ultimately determining if and how the reaction is going to take place. In this case, it can be helpful to look at what each term means. Thermodynamics looks at ...

Joshua Eidam 2A

The average rate of the reaction is measured over a wide range of time. Although this average is useful, it becomes a more and more inaccurate representation of the reaction rate as the time range increases. This is where Lavelle introduced the instantaneous rate of change. The difference between th...

Joshua Eidam 2A

When considering that a reaction is beginning with a high concentration of reactants, the initial instantaneous rate will be very high as there are lots of reactants available; however, as the reaction continues as this high rate, the concentration of reactants will quickly decrease. With fewer reac...

Joshua Eidam 2A

These two equations will yield the same results if the concentration of each is the same and the stoichiometric coefficients are the same as well. The main difference will be the negative sign to indicate a difference in direction, but if you disregard the negative sign you could say the two rates a...

Joshua Eidam 2A

I like Kinetics so far! My favorite would probably have to be chemical equilibrium though.

Joshua Eidam 2A

An example that Lavelle gave in lecture was how carbon in the form of a diamond is not as thermodynamically favored as carbon in the form of graphite; however, because of the large energy barrier between the two forms of carbon, the carbon will likely stay in diamond form as becoming graphite would ...

Joshua Eidam 2A

As previously mentioned, the unique reaction rate would decrease by a factor of 2. In general, you can apply this same relationship (double coefficients ===> decrease by factor of 2) which any other change that could be made to the coefficients. For example, tripling the coefficients would decrease ...

Joshua Eidam 2A

The difference is that rechargeable batteries utilize reversible chemical reactions that can be "fueled" by the power you can get from a power outlet for example. This allows for energy to be transferred back into the battery.

Joshua Eidam 2A

Introducing Le Chatlier's Principle was meant to demonstrate how increasing certain elements of a reaction will ultimately favor the increase of products or reactants, therefore changing the value of E cell . For example (same example given in lecture): 2Al (s) + 3Mn 2+ (aq) ===> 2Al...

Joshua Eidam 2A

The naught represents the variable (in this case E or cell potential) under standard conditions! These standard conditions are 1atm, 298 K and 1M. The Ecell represents the cell potential under the current conditions which are going to be different from the standard conditions in some way.

Joshua Eidam 2A

Here is how Lavelle put it in lecture:
when a reaction is at equilibrium $\Delta Gcell$ = 0
and since $\Delta Gcell= -nF*Ecell$
then Ecell has to equal 0 in order for $\Delta Gcell$ to equal 0 because n and F are both going to be positive constants.
Hope this helps!

Joshua Eidam 2A

E° represents the cell potential at standard conditions. The naught (°) symbol attached to any other variables (H, G, S, etc.) means that it is that specific variable but at standard conditions (just as a rule of thumb for future reference :) ). As previously mentioned, these standard conditions are...

Joshua Eidam 2A

When looking at the equation w(max)= $\Delta G^{\circ} +RT(lnQ)$ , I was confused as to what Q is? I understand it is the reaction quotient but how exactly do you calculate that?

Joshua Eidam 2A

In outline 4, there is a bullet saying we should know how to "show how ∆S is related to ∆H for a change at constant temperature and pressure and explain the relationship". I am confused as to which equation this is referring to and wanted to make sure I understand the right connection I sh...

Joshua Eidam 2A

Could someone explain how to apply the 1st and 2nd laws of thermodynamics to calculate the change in energy and entropy of a
system? I am confused about what this is asking in specific, in terms of the equations and laws in place.

Joshua Eidam 2A

Just to clarify, the direction of a molecule also falls under the category of position? Meaning it could be in the same exact spot but facing a different direction and still count as a separate position?

Joshua Eidam 2A

Would a mass of some sort also be required for me to find the amount of heat released? I say this thinking that I would need to use the equation q=m*c*(delta)t

Joshua Eidam 2A

I am confused about the wording of one of the bullets in outline 3. It says "Determine the heat output of a reaction, given the temperature change of a calorimeter". What does this mean?

Joshua Eidam 2A

Hi this is a pretty simple question but I am becoming a little confused about this as I watch lectures. When Lavelle is writing certain equations, he's been writing d(something), for example dS= dq(rev)/T. Does d represent delta or is it something else?

Joshua Eidam 2A

Hello I found this link that talks about some of the basics of enthalpy:
https://www.thoughtco.com/definition-of ... d%20as%20h.
hope this helps!

Joshua Eidam 2A

Your problem is coming from the calculated difference in the masses. Switch the order of subtraction so that your value is positive and you should get the right answer.

Joshua Eidam 2A

I am confused about how to identify microstates. In Lavelle's lecture, he consistently used 2 for the value of microstates but I am assuming that is not always the case. In a given problem or example, what are you looking for when trying to identify the number of microstates?

Joshua Eidam 2A

Base it off of the units given/ the units you want for your answer. This will determine which R value you should use.

Joshua Eidam 2A

I am super confused on this problem because even after setting up my ice box, and calculating for x in multiple ways, I keep getting the same answer (0.0375). Subtracting this from 0.900 gets me 0.8625. I have tried changing the sig figs and everything but it is still telling me I am wrong. Am I doi...

Joshua Eidam 2A

Just adding on, and I am not entirely certain if this is what the original question is asking for, but in the context of bonds, the boiling and melting points are heavily affected by the strength of the bond. Specifically, the stronger the bond length is, the higher both the melting and boiling poin...

Joshua Eidam 2A

What exactly is a ligand in the context of chemistry? Sorry if this is a simple question I just have the biological definition of a ligand stuck in my head and it's confusing me. They're somewhat similar right?

Joshua Eidam 2A

Yes, as previously stated when you are being asked for the charge of a transition metal, it should almost be within the context of the TM in a compound, otherwise it is hard to determine since their charges can vary. Use any element in the compound that you know the given charge of, as well as the o...

Joshua Eidam 2A

Also I think it is important to notice that other electrons contribute to the shielding effect with the negative repulsion. I found this on a website and I thought it was helpful: "In hydrogen-like atoms, which have just one electron, the net force on the electron is as large as the electric at...

Joshua Eidam 2A

Hi I also found this snippet from this website: "There are four nodes total (5-1=4) and there are two angular nodes (d orbital has a quantum number ℓ=2) on the xz and zy planes. This means there must be two radial nodes. The number of radial and angular nodes can only be calculated if the princ...

Joshua Eidam 2A

Could someone clarify for me what a buffer exactly? I am confused as to both what they are and what their intended purpose is? Also, how do you identify them?
Thanks

Joshua Eidam 2A

Yes I believe stability is the main factor for why hybridization takes place. Without hybridization taking place, I believe the overall energy level would be higher and the likelihood of there being instability increases.

Joshua Eidam 2A

Adding on to this, since O is very electronegative does that mean it shouldn't be the central atom in lewis structures? Neha, the least electronegative atom is in the middle, and since nitrogen is less electronegative, it is the center atom. This is not to say though that oxygen can't be the centra...

Joshua Eidam 2A

Hi, I am a little confused as to where exactly the cutoff is for elements that are able to have more than 8 electrons in their valence shell. Also, I am confused about how to calculate what the central atoms expanded octet is when given a lewis structure or just a formula?

Joshua Eidam 2A

Kelly Singh wrote:KA measures the strength of an acid whereas pKA is the negative log of that value. It's just an easier and more convenient way to refer to the KA value as far as I know. =)

Does a higher Ka value represent a stronger acid or is it not that simple?

Joshua Eidam 2A

I thought the same thing but as previously mentioned, the COOH gives it away to be a weak acid. It dissociates partially into H+ and COO−. Here is a link that explains more about the carboxyl group: http://www.phschool.com/science/biology_place/biocoach/biokit/carboxyl.html#:~:text=Carboxyl%20groups...

Joshua Eidam 2A

I am still a little confused as to what causes delocalization in an atom or molecule? What could change an unstable molecule with uneven electron distribution into a stable one?

Joshua Eidam 2A

So what is the exact equation for Ka? Also if only aqueous samples are used in calculating the Ka, then are any samples in different forms (solid, liquid, gas) just disregarded?

Joshua Eidam 2A

Sukhkiran_Kaur_3F wrote:If there is more than one H in front, it'll be polyprotic.

Is it specifically just in front or is it in general? I am a little confused as to whether or not all the H contribute to it being polyprotic?

Joshua Eidam 2A

For this question, I am confused as to how I am supposed to determine the pH of "the predominant species present at pH 2.70". How do I know what the predominant species is and how do I know what its pH is? How does the given pH and pKa help with that? Please help. Thank you.

Joshua Eidam 2A

I remember hearing about the term amphiprotic. What is the difference between amphiprotic and polyprotic? polyprotic is the ability of an acid to donate multiple protons (H+) while amphiprotic means a substance can act as an acid and a base. Yes, but not to confuse amphiprotic with amphoteric, whic...

Joshua Eidam 2A

What characteristics make a salt acidic or basic or neutral? Is it similar to normal acids and bases or is it different?

Joshua Eidam 2A

I am confused as to how I can identify an amphoteric substance from a list of substances. I know that it means it the substance can act both as a Bronsted Acid or Base but how can I identify that just from looking at a list of substances?

Joshua Eidam 2A

I am confused as to why something that is more electronegative would result in the formation of a weaker acid. Would the H+ not be more attracted to Cl- if it is so electronegative, thus making it harder to break away and therefore an overall weaker acid?

Joshua Eidam 2A

So basically to find the conjugate acid of a molecule, we add a hydrogen to it and give it a positive charge, and to find the conjugate base of a molecule, we take a hydrogen away from the molecule and make it a negative charge? Yes that is one way of looking at it for sure. I think focusing on how...

Joshua Eidam 2A

Does anyone know if we need to understand more than just how acid rain is formed? Or will we have to know more about the biological applications as well like how it negatively affects the environment etc.?

Joshua Eidam 2A

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. Can you clarify more on the "aligning with the diagonal band of metalloids"? Was he su...

Joshua Eidam 2A

Also, when trying to find the concentration of the H+ or OH- from a pH or pOH, how do you do the reverse of -log[ ]?

Joshua Eidam 2A

lwong Dis1L wrote:What is the difference between pH=-log[H3O+] and pH=-log[H+]?

They are the same thing. The H3O+ just represents the H+ bonded with an H2O but the concentration of either of them can be used to find the pH.

Joshua Eidam 2A

Just to clarify, when using the concentration of OH to find the pH, you simply subtract -log[OH-] from 14 and that will equal the pH?

Joshua Eidam 2A

In regards to what the Chem Mod wrote about conjugate bases and acids, when an acid or base dissociates, is the portion that is not the H+ or the OH- the conjugate base and acid respectively? For example, ClO4- is the conjugate base but in the case of NaOH dissociating in H2O, the water is the conju...

Joshua Eidam 2A

What exactly makes an acid or a base a Bronsted acid and base? Are there unique characteristics to them compared to other types of acids and bases?

Joshua Eidam 2A

Does anyone know what the format of the test is going to be like as well as how long the test is going to be?

Joshua Eidam 2A

Just to clarify, the roman numerals only apply to transition metal cations and anions? Also, the way you determine their charge is by looking at the charges of the other elements in the compound, as well as the total charge of the entire compound? Someone please correct me if I am wrong.

Joshua Eidam 2A

I was wondering what are some helpful ways of remembering how to recognize which is a Lewis Acid and Lewis Base when presented with an equation for a reaction. For whatever reason I find it challenging to identify them when I look at an equation. Let me know!

Joshua Eidam 2A

Like the person above mentions, there are a lot of really great graphics that display all the different shapes based on lone pairs and such. Here is a link to a website with a graphic that I find quite helpful: https://courses.lumenlearning.com/boundless-chemistry/chapter/molecular-geometry/ Hope th...

Joshua Eidam 2A

Another question that I am confused about is how LDFs are affected by the molecule's surface area? If I am not mistaken, I believe that greater surface area means strong LDFs but why would that be the case?

Joshua Eidam 2A

I understand that if there are multiple polar bonds present, and their dipole moments are not canceling out, then the molecule is polar. But what exactly makes a certain molecule more polar than another? Does it have to do solely with the strength of the polar bonds or are there other factors that c...

Joshua Eidam 2A

I agree with the previously mentioned equation using dots and lines. By counting each dot and line as 1, there is less confusion (at least for me) in terms of what value do I subtract from the valence electrons.

Joshua Eidam 2A

Is there a specific benefit for hybridization? Why does it occur in the first place?

Joshua Eidam 2A

In a triple bond, is there a way of knowing which specific bond is a sigma or a pi bond? Do we even need to know how to do this?

Joshua Eidam 2A

I believe that overlapping waves will alter one another no matter where each wave is in its respective cycle. The obvious effects can be seen clearly at the peaks and troughs of the waves (when overlapped with other peaks and troughs), but I am sure that different effects can be noted at any point a...

Joshua Eidam 2A

I believe "ejected" electrons are ones that have been removed from the atom due to the high frequency of the light being shone on it. "Excited" electrons are ones that are raised to higher levels of energy in the atom but do not leave. They eventually return to their original ene...

Joshua Eidam 2A

I ordered the textbooks required for Chem 14A from the UCLA bookstore but they are insanely back ordered I think because I still have not been contacted to get them. Does anyone know of another way to access the textbook? I know we are going to be needing it more and more as the quarter continues. T...

Joshua Eidam 2A

Has anyone else ordered a textbook from the campus bookstore and it still hasn't arrived? I am not really sure what to do about it because I already spent the money on it but we are going to be needing the textbooks more and more. Does anyone know of a place online where I can find it? Thanks.

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