CHEMISTRY COMMUNITY

Mike Vinci 2B

Hi all,
I recall Doctor Lavelle talking about keynotes and aldehydes location on a molecule, but I'm confused about which one is only found on the end of molecules, and which one cannot be found on the end of a molecule chain.

Mike Vinci 2B

In class the other day (I believe it was the 03/12/2018 lecture), professor level made it a point to emphasize that things like sponges "ABSORB" water, whereas catalysts adsorb reactants. What this means is that the reactant isn't absorbed into the catalyst, but instead rests upon it (adso...

Mike Vinci 2B

Could someone explain why a catalyst is not consumed in a reaction, and how it can effect the reaction while also being reused over time. Also, do certain reactions require specific catalysts, or can catalysts effect many different types of catalysts?

Mike.

Mike Vinci 2B

Hi Sarah, When I did this problem myself, I determined the rate law to be k=[A][B]^2[C]^2. Given this, you can solve part c in two ways, by applying this equation to both the values of concentrations and initial rates for experiment 3 and experiment 4. Knowing that the rate constant is not dependent...

Mike Vinci 2B

Looking into topics for 15.11 that I believe we will cover before the final, is the collision cross-section value an experimentally determined value. And out of general curiosity, with particles like atoms being extremely small, how do scientists determine the value of the surface area actually coll...

Mike Vinci 2B

I agree with the comment above. If you want to conceptualize it I considered limiting reagents from earlier this year, where the limiting reagent determined the overall amount of product created. Similar to reaction rates, the overall reaction is depended on the slowest elementary step, and so we fo...

Mike Vinci 2B

In class, I remember Doctor Lavelle speaking about the units of k, the rate constant, however I wanted to clarify if the units of k can be different depending on the problem we are solving, or if they remain the same across all the problems in the chapter.

Mike

Mike Vinci 2B

Could someone elaborate on half-life and its significance in this chapter? I have the equations to find half-life, but I'm confused about its relevance and application in the chapter.

Thanks,
Mike

Mike Vinci 2B

Hi Ava, When I found information on Arrhenius behavior in 15.11. The book describes it as "reactants that give a straight line when ln k is plotted against 1/T. I'm not exactly sure what questions Professor Lavelle will ask, however the Arrhenius equation is ln k= ln A -Ea/RT or k=Ae^-Ea/RT. Ea...

Mike Vinci 2B

It is important to note that, the oxidation state of oxygen in its compounds is -2, except for peroxides like H2O2, and Na2O2, in which the oxidation state for O is -1. However, since O2 is neutral it's oxidation state is 0.

Mike Vinci 2B

For the first part of your question, I watched this video yesterday https://www.youtube.com/watch?v=XgHUk7apOMA and when the individual speaking balanced the reactions with H+s and H20s, he included H+ in the appropriate side of the cell diagram. However, he did not include water because the other r...

Mike Vinci 2B

In the Nernst equaiton, why do we only use the ratios of the concentrations of aqueous products and not solid or liquids? Also, would we include gases in the ratio, as well? I recall seeing Q include aqueous concentrations by atms/bars, so I am guessing that gases are included? If someone could clar...

Mike Vinci 2B

When you balance the two equations for the number of electrons, would you multiply the E standard of the two equations by the factor you used to balance the equation, or do they remain the same?

Mike Vinci 2B

Hello, When working through the problem 8.31, it uses the calculation q=n*Cp*delta T and q=n*Cv*delta T for the second part. Given that Kr(g) is monatomic, I know that I can replace Cp and Cv with 3/2R and 5/2R respectively, however I'm confused about if I were given a diatomic model, Kr2(g). In the...

Mike Vinci 2B

As we know, a negative delta g correlates with spontaneity. While it seems logical to assume the more spontaneity means more randomness and therefor less stability of the compound, however when the free energy is more spontaneous then there reactants will change into more products that are essential...

Mike Vinci 2B

For the Standard Reaction entropies, the equation includes the sum of the products with n moles subtracted by the sum of n moles of reactants. In regards to the term n, is this value the sum of the stoichiometric coefficients of all the products, and then all the reactants, or do you only take the m...

Mike Vinci 2B

I was wondering if we will be given a molecule and will have to determine the amount of orientations it could have to find W in the Blotzmann formula. If so, are there any tricks to making sure you've identified all the orientations you could get?

Thanks.

Mike Vinci 2B

Hi all, Throughout the book I have noticed that at times we talk about standard enthalpy entropy of reactions at a constant 1 atm, yet other questions in the book might use bars or tours to represent the pressure. While I understand the importance of moles, kelvins, Celsius, and liters, which units ...

Mike Vinci 2B

Hey Mike, So generally when we increase the temperature there is a shift will be a shift towards the reactants in an exothermic reaction, and a shift towards the products in an endothermic reaction. With X2(g)-->2X(g), we must evidently break the bond between X--X, which requires an endothermic proc...

Mike Vinci 2B

Hi all, Could someone elaborate on the difference between the equilibrium constant, K, and the reaction quotient, Q? Also, if you could remind me of what it means if Q>K, Q=K, and so on in terms of the chemical reaction, and if these concepts are important for the subject we're studying now.

Mike Vinci 2B

In the first paragraph of chapter 9, the text book mentions that O2 gas and H2 gas can coexist separately, but need a "spark" of energy in order to combine into water. I was wondering how this process can occur naturally in our environment. I thought of the possibility of lightning providi...

Mike Vinci 2B

For W=-nRTln v2/v1, we account for the infinitesimal and consistent change in expansion of the system. In class, we saw the curve Professor Lavelle drew whose shape was that of exponential decay. This comes from the use of the natural log. However, the important aspect to understand is that such a c...

Mike Vinci 2B

I'm also a little confused with exactly why this occurs, however I did look at the formula for delta G=0, and found that delta S= delta H/ T. If we maximize delta H, and considering that delta S is proportional to it, wouldn't that also maximize delta S? I could be analyzing the wrong equation, but ...

Mike Vinci 2B

The bomb calorimeter is a closed system that can exchange energy with the surroundings and is isochloric (no volume change). The coffee cup calorimeter is isolated, meaning pressure is constant and no energy can be exchanged with the surroundings, known as adiabatic conditions

Mike Vinci 2B

Hey Chemistry Community, Professor Lavelle mentioned that bonds absorb energy as a positive value, however I always that that bonds held some form of energy (could be minuscule). With this being said, when you add energy and break bonds (especially double and triple bonds), wouldn't energy be given ...

Mike Vinci 2B

What's going on Hannah! Molar specific heat is usually shown in Joules per mol or KJ per mole depending on how you want to express it. It represents the amount of heat needed (in Joules or KJ) to raise the temperature of 1 mole of something, by 1 Kelvin. I remember reading that this idea might depen...

Mike Vinci 2B

Hey Chemistry Community, I understand that the bonds between atoms and molecules give off and absorb energy during phase changes, however I was also wondering if such intramolecular forces like van Der wall forces, dipole-dipole forces, or hydrogen bonds give off or receive energy due to phase chang...

Mike Vinci 2B

Hey Chemistry Community, I was just thinking about the nature of chemical reactions, and found myself considering the effect of catalysts on enthalpy change in a reaction. As we know, catalysts help speed up the reaction, thus in our discussion of enthalpy change this would make the reactants underg...

Mike Vinci 2B

Hey Michelle, With the reaction in general it would be kJ/mol, yet if the question asks to find the enthalpy change associated with only one mole of a certain reactant then you just multiply delta H by moles and get units of only kJ. It is helpful to look at the stoichiometric coefficients to see wh...

Mike Vinci 2B

Hey guys,
So I thought I heard that in class something like HS04- would have a formal charge of -1 on the central atom. Is this how you confirm you have the right Lewis structure with an ion?

Mike Vinci 2B

I would say that if no conjugate acid or bases exist, then this was not the dissociation of some acid or base on the reactants side. Given that a conjugate acid or base does exist on the product side, then they must have disassociated from some original acid or base in water where the acid or base e...

Mike Vinci 2B

A weak acid dissociates incompletely, releasing some of its hydrogen atoms into a solution. It isn't as likely to donate protons. A strong acid will fully dissociate in water to form H+ ions. Strong bases dissociate fully into OH-, but weak bases only partially dissociate into OH-.Strong acids inclu...

Mike Vinci 2B

Hey Chemistry Community, I'm reviewing my notes for the final on Sunday, and I was wondering about the effect of cis and trans structures on polarity. I recall that cis usually has two atoms on same sides with similar electronegativity which I assume creates the polarity, and trans has the similar e...

Mike Vinci 2B

Hi Emma,
Lewis acids are known by nature to accept electron-pairs. The lewis structure of BF3 shows no lone electron pairs on the central boron atom, and it is therefore more inclined to want to accept electron-pairs making it a Lewis acid.

Mike Vinci 2B

Hey Chemistry community,
I understand the idea of both pKa and pH, however I'm having trouble understanding the relationship between the two. Could someone describe if knowing either the pKa or pH helps you describe the other? Is their an inverse relationship or direct relationship?

Mike Vinci 2B

Hi Connie, Kw is the ionic product of water and is a constant. I'm not sure if we're required to memorize it (it could be on the equations and constants sheet), however I'd double check with a moderator on this forum. In regards to your question, the equation of this formula Kw = [H3O+][OH-] can be ...

Mike Vinci 2B

Are acids and bases always aqueous in order to ionize the presence of water, or can acids and bases exist in any state and still ionize into their component ions?

Mike Vinci 2B

Hi Stephanie, In b. there is a proton transfer from NH4 to I making it NH4+ and I-. In this reaction, NH4+ serves as a acid and I- as a base. NH4I is composed of NH4+ and I-, and can therefore both gain and lose a proton making it both an acid and base, know as being amphoteric. This question doesn'...

Mike Vinci 2B

Hey chemistry community, I'm a little confused on how to identify oxidation state of a molecule. On the test we have tribromodicarbonyl (III) nickel and its oxidation state is 3+ which I assume comes from the roman numeral III. However, I'm not sure how this correlation exists. If you could enlighte...

Mike Vinci 2B

In regards to the most recent test we were given, how can you identify delocalization pi bonding? I've researched that delocalized pi bonds can move more freely about a nuclei or atom, but I'm not sure how to identify it on a structure like paroxetine?

Mike Vinci 2B

What's going on Chemistry Community, After going to Dr. Lavelle's lecture today, I found myself wondering about the results of mixing an acid and a base. Consider that you mix an acid and a base in water so that they disassociate into their component parts. What happens to the solution if you mix eq...

Mike Vinci 2B

What's going on Chemistry Community, while doing homework I came across VSEPR formula, and I had to study the dynamics of it to understand how to do it. However, I noticed that some species have the same VSEPR formula. For example, both BeCl2 and CO2 are AX2. I understand they might have similar str...

Mike Vinci 2B

Given that we have 4 regions of electron density around the C atom, and also no loner pairs on the C atom, the shape of the molecule is tetrahedral. Therefore, it appears symmetrical in structure, and many times symmetry means non-polar. However, relating to your question, the difference in electron...

Mike Vinci 2B

I also didn't think of this before you asked, and I'm not sure if Professor Lavelle has touched about the d-orbital and hybridization in class (I'm sure he will.) However, after researching the internet, I found that you DO place the d infront of the s and p orbitals as you would do given the molecu...

Mike Vinci 2B

I see that this has already been answered, but I'd like to expand on hybridization in general for anyone who comes across this topic. When were looking to use the VESPR theory to describe the structure of molecules, the hybridization of an atom is based of the steric number, that is the steric numbe...

Mike Vinci 2B

What's going on Chemistry Community. After looking over 3.63 for homework earlier, the question asked to write the lewis structure for a.)SF6 , B.)XeF2, c.) ASF6[-],and d.) TeCl4. I don't think I'm struggling with drawing the structure. After reviewing Lew structures for the past few years (high sch...

Mike Vinci 2B

Using the VSEPR theory we've been learning in class, we are able to predict the structure of atoms surrounding the central atom. In order to find the structure, we must first determine the structure by identifying regions of electron density. A region of electron density can either be bonding or non...

Mike Vinci 2B

Hey Elizabeth, I was wondering the same thing earlier this week, and I'm glad you asked the question. So after doing some research online and in the book, I've come to the understanding that one may "safely assume" that the greater the electronegativity, the stronger the bond. If you think...

Mike Vinci 2B

Hey Robert, so in chemistry, species are know to be atoms, molecules, ions, and so on. For this specific problem asking about radicals, radicals are species that have an unpaired electron. As a result of this condition, they have an odd number of valence electrons and do not fill their outer valence...

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