CHEMISTRY COMMUNITY

Andrew Sun 3F

A is the frequency factor, which basically is how frequent, with a value (probability) between 0 and 1, will the particles be in the correct orientation with enough energy to collide, overcome the activation energy barrier, and react. The value of A will be given to us.

Andrew Sun 3F

Kinetic control predominates at lower temperatures since there is not enough energy to overcome the higher activation energy associated with a thermodynamically favored product.

Andrew Sun 3F

on question 7.21, the plots of "(f) initial rate against [A] for a reaction that is first order in A; (g) half-life against [A] for a reaction that is zeroth order in A; " are linear. How come they are linear?

Andrew Sun 3F

question 7.17 says "A catalyst is added that accelerates the third step only. What effect, if any, will the catalyst have on the rate of the overall reaction?" and the answer key says there is no effect. How come there is no affect?

Andrew Sun 3F

Why does kinetic control predominate at lower temperatures in comparison to higher temperaturess?

Andrew Sun 3F

Yes they are! but when u add the oxidation and reduction portions, they should cancel out. just remember the reduction reactions gain electrons so the electrons should be on the left, and for oxidation half reactions they should be on the right.

Andrew Sun 3F

Id balance the charges by adding electrons at the very end, after balancing ur elements!

Andrew Sun 3F

What is the procedure for balancing a redox reaction in a basic solution? I only know how to do acidic, not sure what to do.

Andrew Sun 3F

Can someone explain how the function with two T's and two K's works? Also, what is the intuition behind the relationship?

Andrew Sun 3F

Can someone explain how entropy works for irreversible and reversible systems? I know that total entropy of a reversible system is 0 but how does that work? Why is that not the case for an irreversible system?

Andrew Sun 3F

Can someone explain the purpose of comparing standard reduction potentials to hydrogen reduction potentials and how it works?

Andrew Sun 3F

How do I know when to include an extra metal conductor in a cell diagram?

Andrew Sun 3F

how does residual entropy work, especially in the context of symmetrical molecules?

Andrew Sun 3F

Can someone explain what this concept is, and how it related to standard reduction cell potential?

Andrew Sun 3F

Does anyone have a good pneumonic to remember how to memorize oxidation and reduction reactions as well as how they're related in a battery?

Andrew Sun 3F

What is the purpose of comparing e- transfer of all cells to a hydrogen electrode? And why does doing this achieve its purpose?

Andrew Sun 3F

In class we calculated Eo in two ways, by writing half reactions and flipping the sign of the anode, or taking E(cathode)-E(anode). In terms of the standard reduction values given, are they always going to be positive?

Andrew Sun 3F

What does it mean that reduction potentials are intensive? How does this affect the way we calculate cell potential?

Andrew Sun 3F

If platinum is the solid, where are the Fe2+/3+ ions coming from? how do they get into the solution?

Andrew Sun 3F

Why do we need platinum on the cathode side instead of just the metal being reduced itself?

Andrew Sun 3F

does anyone have a link to a list of acids and bases we need to memorize for the test? Also, any tips on memorizing these?

Andrew Sun 3F

since acids and bases are fully dissociated, no bonds are broken. however, bonds are formed between H+ and OH-, which is an exothermic process.

Andrew Sun 3F

Why does water vapor produce more severe burns than boiling water at the same temperature?

Andrew Sun 3F

multiply heat capacity by the number of moles and the change in temperature

Andrew Sun 3F

Hi Vanessa!

Heat is an extensive property because all we measure is the initial and final temperatures. What occurs in the middle is irrelevant. Other extensive properties are altitude.

Hope this helps!

Best,
Andrew Sun

Andrew Sun 3F

In achieve 18, the equation Cv=Cp-R was used. Did we ever go over this in class? Also, why does this relationship exist, and how? Why are we using R?

Andrew Sun 3F

Can someone explain how the relationship of Qcal+Qreaction=0?

Andrew Sun 3F

I know for irreversible processes, we use w=-pdelta(v) and for reversible processes we take an integral. However, what about constant pressure makes a process irreversible? I'm struggling conceptually how to piece it together, especially in terms of why we use an integral for one but not the other.

Andrew Sun 3F

When can I use PV=nRT? I thought that since it's called the ideal gas law the conditions had to be ideal (pressure and temperature).

Andrew Sun 3F

For Qcal, how come its Ccal*delta(t)? where did the mass go or do we not have to account for ir?

Andrew Sun 3F

was the equation for achieve #14 in the thermo questions discussed in class? entirely sure how to use it, any guidance would be greatly appreciated!

Andrew Sun 3F

I think about the first law of thermodynamics and how the universe is a perfect system where the heat of the system and heat of the surroundings are always exchanged to each other. When we examine delta H along the lines of your thinking, i think it would be for the entire system, and we know that t...

Andrew Sun 3F

In the problems where we equate mcdeltat=-mcdeltat, why is there a negative sign? Shouldn't the inherent characteristic of temperature decreasing naturally produce a negative answer?

Andrew Sun 3F

Hi,
Will Monday's lecture be a part of midterm 1? Some of the achieve problems utilize equations that we haven't learned. Do we need to know them for the midterm?

Andrew Sun 3F

For week 3/4 achieve problem #12, why do we use c=q/delta(t) instead of c=q/n*delta(t)?

Andrew Sun 3F

Does manipulating equations change delta H the same way that manipulating acid/base equations change K?

Andrew Sun 3F

Why are bond enthalpies of diatomic molecules accurate?

Andrew Sun 3F

Can someone explain to me the concept of state properties and state functions? are they the same thing

Andrew Sun 3F

Can someone explain to me how endothermic and exothermic reactions relate to the formation and breaking of bonds?

Andrew Sun 3F

Can someone explain to me how to use this formula and when I would use it?

Andrew Sun 3F

how come a strong acid is correlated with a weak conjugate base?

Andrew Sun 3F

Can someone explain to me what a buffer is? It seems to be something that makes the pH of the solution less likely to change, but how does it work on a molecular level?

Andrew Sun 3F

I know that Dr. Lavelle said that introducing new gases doesn't shift equilibrium. However, how come it doesn't cause the reaction to shift towards the side with less moles? I think conceptually I am unsure.

Andrew Sun 3F

how do I know if a nitrogen in a molecule will cause the molecule to be basic or acidic?

Andrew Sun 3F

K changes for temperature because when temperature is changed, it is an external factor in which the system must adjust for without additional products or reactants introduced into the mix. Since the amount of products and reactants are held unchanged prior to any changes in temperature, then the on...

Andrew Sun 3F

Those should be provided in the question. Alternatively, you could solve for partial pressures using PV=NRT if you're given concentration and need to convert it.

Andrew Sun 3F

If K is less than 10^-4, can we only approximate for concentrations in which there is an initial concentration given?

ie. in lecture, we only approximated N2 and O2 since they had initial concentrations, but not N20 which we were solving an equilibrium concentration for.

Andrew Sun 3F

Can someone explain why an exothermic reaction favors R formation? How does creating R use up heat?

Andrew Sun 3F

[P]/[R] changes immediately after the change in volume, so it would actually be classified as Q. In lavelles example, K is 100 and Q is 25. However, over time Q will work its way up back to K through the reaction converting from reactants to products to decrease the amount of moles in the container,...

Andrew Sun 3F

Hello Vanessa! Great question, I was wondering the same thing for myself! You use an ice table to find the concentrations at equilibrium for a reaction when you're not given the equilibrium concentrations. Don't forget that if the K value is less than 10^-4 you can approximate x to be zero for items...

Andrew Sun 3F

CH3COOH --> CH3CONH2?

Well, the compound does gain a Hydrogen, and if that is true, then the compound must be a base. However, we also see that the compound loses the OH- and gains a NH2-, further proving that CH3COOH is a base.

Andrew Sun 3F

If you are given a compound, identify the compound that loses an H+. For example, if in the reaction h3o+ becomes h2o, then you know that it lost a H+, or donated that. that compound will be an acid.

Andrew Sun 3F

What is the acid and base in these reactions? a. CH3NH2 (aq) + H30+ (aq) ---> CH3NH3+ (aq) + H20 (l) b. CH3NH2 (aq) + CH3COOH (aq) ---> CH3NH3+ (aq) + CH3CO2- (aq) c. 2 HI (aq) + Ca0 (s) ---> CaI2 (aq) + H20 (l) acids are the compounds that donate an H+, so: 1. acid - H3O+ 2. CH3COOH 3.HI the bases ...

Andrew Sun 3F

when hydrogen bonding exists, dipole dipole exists. However, the vice versa is not true, as if dipole dipole exists, it may not be hydrogen bonding as H needs to be attracted to N,O, or F.

Andrew Sun 3F

if a question asks what is the hybridization around the central atom, does it need a coefficient to specify which energy level?

Andrew Sun 3F

If an acid is an electron acceptor, whilst giving away the H+ (which is essentially a proton), how does it take in another electron? or does the electron already exist to the acid?

Andrew Sun 3F

The pi bond is not the entire double bond, just the single bond on top of the preexisting sigma bond. For example, a double bond consists of one sigma bond (C2sp2) and a pi bond (C2p).

Andrew Sun 3F

A lone pair takes up more space in terms of it's electron cloud or density, so it'll push the other bonds closer together, resulting in a lower bond angle.

Andrew Sun 3F

Is there a way to dictate double bonds in our VSEPR drawings? If we have to draw in lone pairs, is there anything else we need to do as well to closer match the elements depicted by lewis structures?

Andrew Sun 3F

Essentially you want to determine if the molecule is polar or non polar, and this will allow you to figure out if there will be dipoles. Using electronegativity values, if u calculate the difference between values and find that it is 0.5 or greater, then the molecule will be polar and therefore have...

Andrew Sun 3F

CBr4 would have a VSEPR shape that is tetrahedral, and since the difference between carbon and bromine electronegativity values are 0.3 (2.8(br)-2.5(c)), the molecule is non-polar. Therefore, the only IMFs that would be present in a non-polar molecule are london dispersion forces.

Andrew Sun 3F

You find the difference in electronegativity values between the elements, and if the difference is greater than 0.5 than the molecule will be polar towards the more negative atom. However, if all atoms point towards - for example - a central atom, then the molecule is non-polar as there is no overal...

Andrew Sun 3F

To calculate electronegativity, you simply take the difference between the two elements. And using these values, you can see if the compound is polar or nonpolar, as well as having possibly ionic characters or covalent.

Andrew Sun 3F

Hello! Could someone explain why going down a family will increase covalent attributes? I think where I get confused is that since the atomic radius is increasing down a family, so that means it'll hold on to the cation with less force, and therefore act like an ionic compound and be more soluble. t...

Andrew Sun 3F

I would assume no, as they already have filled orbitals.

Andrew Sun 3F

Do the formal charges of each individual element of an ion always add up to the overall charge of the ion?

Andrew Sun 3F

Some elements can have expanded octets, as explained in lecture on 10/29. Those elements that are in the third row can have expanded octets because the now have a d-orbital as well.

Andrew Sun 3F

id just locate the fifth row of the periodic table, and then focus on the l value and which orbital it correlates to. For your example, it would be the p orbital, which means only 6 elements would have n=5 and l=1, those elements in the p block of the 5th row

Andrew Sun 3F

if a question says the speed is 3.24 +/- 0.06 m/s, would delta V be 0.12 m/s?

Andrew Sun 3F

pretty sure the values of frequencies will be given to us in the problem. Most problems state v= blank so i dont see why it wouldnt for those as well.

Andrew Sun 3F

quantum number for l just describes the shape. It isnt necessarily always going to be l=n-1. For example, the third energy level has s, p, and d orbitals, meaning you can have l=0,1 or 2 for which electron you are describing.

Andrew Sun 3F

The equation gives us the probability of finding an electron at a certain location/position, at an orbital or a cloud. I heard we won't be needing to know how to use the formula, just to understand its purpose.

Andrew Sun 3F

It would just be the electron represented on the most right. for example, element (II) would have s2p5 and element(I) would be s2p4.

Andrew Sun 3F

They're interchangeable terms, but i think Lavelle said something about uncertainty being used too often, and that indeterminacy is used because it is less used, if that makes any sense. However, im sure it doesnt make a difference what you use in terms of vocabulary or tests/quizzes.

Andrew Sun 3F

In my 10-11 lecture, he said when the value is x10^-18 or more, someone asked that question too in my class. However, not sure what makes that value suddenly detectable as compared to other values, like if it is a specific threshold or boundary of a value.

Andrew Sun 3F

Yes, when the original calculation gives a negative value it just signifies that there was a negative change overall, but you can't have negative energy. The negative sign is just there for conceptual understanding.

Andrew Sun 3F

I use a TI-30X and it works wonders. Also heard a few of the Casio ones have a fraction button that would help you organize or visualize your work better!

Andrew Sun 3F

the coefficients are 0,4,3,4

Andrew Sun 3F

i think it means you need to mix in 9.8ml (the answer) of the 0.0380M KmNO4 into say a volumetric flask, then fill it up to 0.250L with water, and that will create the 1.50x10^-3M solution of KmNO4. At least I think that is how it can be interpreted, open to other thoughts

Andrew Sun 3F

Currently doing the modules, and for the ones in which topics were covered in class, the problems he does are the same as the ones from class. Seems useful for reviewing for tests or if you miss class, or want to review prior to class though

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