CHEMISTRY COMMUNITY

Shirley Liu 2I

If a reaction is already in equilibrium what will occur if a catalyst is added to the system? Will the reaction proceed forward or reverse or not at all?

Shirley Liu 2I

Ecell = Eocell - (RT/nF) ln Q and Ecell = Eocell - (0.0592/n) log Q both give Ecell. However, why are both given? Why couldn't you just use one or another? What's the point of having both?

Shirley Liu 2I

Are the k' of pseudo reactions and the k' of reverse reactions in rate laws are related or do they just happen to have to same notation?

Shirley Liu 2I

Will the order of a reaction with respect to a single reactant ever be the stoichiometric coefficient of that reaction in the balanced chemical equation?

Shirley Liu 2I

We know that the slow step is the rate determining step, so if the first step is the slow step then the rate law is of that step is the overall rate law. However if the second or third step is the slow step would the overall rate law be just the rate law of that step or do we also take into account ...

Shirley Liu 2I

Is it possible/ how do you solve for the rate order with respect to a reactant if within the data the other reactions aren't constant within two experiments?

Shirley Liu 2I

In lecture on Friday we were given the reaction 2NO2 -> 2NO + O2, where [NO2] decreases at the same rate [NO] increases but [O2] increases half as fast. Therefore, -(d[NO2]/dt) = (d[NO]/dt) = 2(d[O2]/dt). Why is there a 2 in front of the [O2] rate equation if it only increases HALF as fast?

Shirley Liu 2I

The Unique Rate is = (-(1/a)*(d[A]/dt)) = ((1/b)*(d[B]/dt)) = ((1/a)*(d[C]/dt)) and the Unique Rate os the same for all reactants and products on that "unique" reaction. What is meant by a "unique" reaction?

Shirley Liu 2I

How would you be able to tell if there's an inert conductor in a cell diagram if you're only given a redox reaction? (since inert conductors aren't included in the redox reaction)

Shirley Liu 2I

Is electrode material that always written on the outsides of the cell diagrams always solids? or can they be liquids too?

Shirley Liu 2I

For balancing redox reactions, is the procedure for doing so the same in both acidic and basic solutions(balancing elements, adding H2O's,etc.) except in acidic solution you add H+'s and in basic you add OH-'s?

Shirley Liu 2I

How do you know when a redox reaction takes place in an acidic or basic solution (for balancing half rxn purposes)? Would the question have to specify?

Shirley Liu 2I

In writing formation reactions, for delta S how do we know what phases the reaction elements are in (e.g. how would we know C is graphite and not diamond in forming CO(g)) ?

Shirley Liu 2I

DeltaS= nCln(T2/T1) is used to calculate entropy change when the temperature changes. However how would we know when to use Cv or Cp for C??

Shirley Liu 2I

S=qrev/T is one of the various equations for entropy/change in entropy. it’s used when temp is constant but how would we know if the reaction is reversible for qrev? would the question have to specify or are there “key words/phrases” that implies that?

Shirley Liu 2I

what is the difference between the two energies and do they have the same units? Internal energy is energy in a system that can do work but doesn’t gibbs free energy do work too? what is exactly meant by “free energy”?

Shirley Liu 2I

I know that Cv=(3/2)R for when volume is constant and that Cp=(5/2)R for when pressure is constant when theres a temp change for a monatomic ideal gas. However how would we know if the pressure or volume is constant? Also, why do we use Cv=(5/2)R for diatomic ideal gases (I think that is used?)?

Shirley Liu 2I

In this context, "most stable form" is regarding most stable elemental form. Most elements are monatomic and thus are most stable as is. However the diatomic molecules, as its name implies, is most stable when there are two atoms of it. (ex: O2)

Shirley Liu 2I

Yes, you can switch them and will get the same answer as long as you remember that with volume its V2/V1 and pressure is P1/P2 (which is opposite). This is possible because pressure and volume are inversely related due to PV=nRT. Also, the units of your answer will be the same bc the liters and atm'...

Shirley Liu 2I

We don't ever find bond enthalpies. Bond enthalpies are always given are averages of the amount of energy required to break a bond between two atoms. It isn't related to Hess' law. Hess' law allows us to add up individual change in enthalpies (delta H's) in steps to get the net change in enthalpy in...

Shirley Liu 2I

In lecture on Wednesday, the notes said that "w=FD since F=PA then w=PAD = pdeltaV." Can someone please explain how AxD is equal to the change in volume?

Shirley Liu 2I

How are delta H and q related? Are they the same thing and can be used interchangeably? In what contexts do you use each one?

Shirley Liu 2I

If we can choose our object of interest as the system and "everything else" becomes the surrounding, then can the water in a bomb calorimeter be chosen as the system and then the bomb/oxygen part and the outside surrounding the calorimeter would be the "surrounding"?

Shirley Liu 2I

Why is it that when you calculate delta Hrxn with enthalpy of formation you subtract sum of products from sum of reactants but with bond enthalpy its reversed and you subtract bonds of reactants from bonds of products? What is the conceptual meaning behind it, because I feel like products-reactants ...

Shirley Liu 2I

In lecture notes, it says "by definition, the standard enthalpy of formation of an element in its most stable form is zero" and an example is given: O2(g) -> O2(g). What does this mean? Wouldn't an element in its most stable form not undergo any changes so there wouldn't need to even have ...

Shirley Liu 2I

If "method 2" uses bond enthalpies to calculate the change in enthalpy of the rxn and "method 3" uses the standard enthalpy of formation, what individual "enthalpies" are used in "method 1" with Hess's Law?

Shirley Liu 2I

Several questions in the homework ask for the pH of a weak acid given its initial concentration, so we would have to find the "x" value, which equals [H3O] and then find the negative log of that to find pH. However, I noticed that in the solutions and Dr.Lavelle's examples we round/do sig ...

Shirley Liu 2I

When given a compound, how do we know if it will gain or lose H+ just from looking at its formula?

Shirley Liu 2I

Are ionization and deprotonation the same thing, and are "% ionization" and "% deprotonation" calculated the same way? The two terms seem to be used interchangeably

Shirley Liu 2I

For rxn N2 + 3 H2 = 2 NH3, K=41. If we half the coefficients, then we square root K (sq root 41), and if we double the coefficients we square K (41^2). However, what is the rule for when you triple, quadruple, etc. the coefficients of the chemical rxn?

Shirley Liu 2I

A change in concentraion does not affect K because a chemical reaction at equilibrium represents a fixed P/R ratio, so does this mean that if the concentration of one changes then the other one has to too but in the opposite direction? For example if products increase then reactants' concentration h...

Shirley Liu 2I

Kp is used for when all the products and reactants are in gas phase. However, could we also use Kc for reactions where everything is in gas phase? Would you use PV=nRT to convert between pressure and concentration then?

Shirley Liu 2I

Why would only cisplatin only work for chemotherapy drugs in stopping DNA transcription? would transplatin not work for DNA transcription? does it have to do with the position of the atoms and which atoms do the stopping of DNA transcription?

Shirley Liu 2I

Are all amphiprotic compounds also amphoteric? since amiphiprotic acids can accept and donate H+ wouldn’t that also make them able to be both acids and bases, which is what amphoteric compounds are defined as?

Shirley Liu 2I

How do we know if a complex's ligands can be polydentates from just looking at the formula? Or how do we know at all? There aren't really any examples in the textbook or notes, so I'm not sure how to find out

Shirley Liu 2I

Are oxidation states when naming coordination compounds always positive for the central metal atom/ion? The Roman numeral is always positive, so is the oxidation state always positive? Or how would the parenthesis "()" in the name look if the oxidation state was negative?

Shirley Liu 2I

We know that strong vs weak acid-base reactions is complete vs incomplete ionization of the acid, but can you differentiate them in reaction equations? In other words, how would we know if the acid is weak or strong just by looking at the reaction?

Shirley Liu 2I

On test 3, should we draw dipole moment arrows pointing toward the positive or negative dipoles? In lecture, Dr. Lavelle has them pointing toward the negative dipoles while the textbook has them pointing toward the positive dipoles

Shirley Liu 2I

How do we know if lone pairs should occupy an equatorial or axial position to maximize their bond angles? For example, how do we know to "take off an atom" off the equatorial axis on a trigonal bipyramidal molecule to get a see saw shape instead of "taking off the atom" from the ...

Shirley Liu 2I

When finding the polarity of a molecule, we have to first draw the Lewis Structure of the molecule and then draw dipoles depending on the electronegativity difference between the central and outer atoms. However, wouldn't the position of the outer atoms matter, especially if they are different from ...

Shirley Liu 2I

Why is a double and triple bond considered the same region of electron density for VSEPR? Wouldn't there be electrons in the that area then and thus would have greater repulsion, which should be taken into account for shape and bond angles?

Shirley Liu 2I

On Friday's lecture (11/16/18), we went over polar and non polar molecules, and Dichloroethene was used as an example of both. In one the dipole moments canceled, making it non polar, and in the other it didn't, making it polar. However, I don't understand why and how the same molecule can be both p...

Shirley Liu 2I

On Friday's lecture (11/16/18), we went over polar and non polar molecules, and Dichloroethene was used as an example of both. In one the dipole moments canceled, making it non polar, and in the other it didn't, making it polar. However, I don't understand why and how the same molecule can be both p...

Shirley Liu 2I

Why aren't lone pairs on non-central atoms in molecules considered in the VSEPR model? Don't they contribute to repulsion between atoms as well?

Shirley Liu 2I

Why are single, double, and triple bonds all considered one region of electron density for the VSEPR? I understand that all the electrons are clustered in that one region, but wouldn't having more electrons (from double and triple bonds) create greater repulsion and bend angles even more in the VSEPR?

Shirley Liu 2I

Are "polarizability" and "polarizing power" the same thing or are they opposites? Is polarizability the propensity of an atom to be polarized and polarizing power the ability of an atom to do the polarizing? Can someone explain in simple terms? Thank you

Shirley Liu 2I

Polar covalent bonds are covalent bonds in which electrons are not equally shared. As the difference in electronegativity increases the more ionic character the covalent bond has, but if the difference becomes greater than 2, would this "covalent bond" not be covalent at all and now comple...

Shirley Liu 2I

Atoms in molecules have molecular shapes that try to get each atom as far away from each other. However, why are tetrahedral angles 109.5 degrees each instead of 90 degrees if we follow the rationale of 360degrees/4?

Shirley Liu 2I

For elements with diagonal relationships, how would you compare their ionization energies and electron affinities? For example, would oxygen or chlorine have a higher ionization? Oxygen has a smaller shell number but chlorine is further to the right of the periodic table and thus has a higher effect...

Shirley Liu 2I

Biradicals are defined as molecules that have 2 unpaired electrons. However, why can't these two electrons just be paired together? Wouldn't the molecule want to have lower energy and be more stable?

Shirley Liu 2I

I know you can use the De Brogile equation for matter, such as balls, cars, etc., but can you also use the De Brogile equation for finding the wavelengths of electrons and photons or can you only use the c= wavelength x frequency for that ?

Shirley Liu 2I

Why does Boron not have to follow the octet rule in drawing lewis structures? (i.e. why can it just have six electrons in its outermost shell, when all atoms have an affinity for filling up all their shells to gain the most stability?)

Shirley Liu 2I

Is there a convention for ordering the d orbitals, or can you just list the five orbitals in any order? (like how with p orbitals it goes: px, py, pz)

Shirley Liu 2I

As electrons are added to an orbital, the atomic radius gets smaller. However, wouldn't increasing the number of electrons also increase electrostatic repulsion which would lead to the orbital expanding?

Shirley Liu 2I

Does anyone know if we will have to memorize an electron's mass and constants' values for test 2 or will they be given on the formula sheet?

Shirley Liu 2I

Does the absorption spectrum line have the same frequency as the lines in the emission spectra, or are they reversed or negative values instead?

Shirley Liu 2I

Is the variable "v" in the kinetic energy of an ejected electron equation (Ek=1/2 *Me*v^2) and in the speed of light equation (c=λν) the same? Are they both frequency?? I've been having trouble using both those equations to solve for specific values in the end

Shirley Liu 2I

Is there a convention for ordering d orbitals or can it be done in any order?

Shirley Liu 2I

I know that wave-like properties can only be noticed for moving objects with extremely small masses (like electrons), but at what point/value of a wavelength is a moving object considered to have "measurable wave-like properties?" ((in today's lecture (10/12/18), we found the DeBroglie wav...

Shirley Liu 2I

In the equation V=R(1/(n1)^2 - 1/(n2)^2), is n1 always the lower of the two energy levels? Is this because having a larger n2 would make the R(1/(n1)^2 - 1/(n2)^2) negative and subsequently V a negative value as well, and there is no negative value that corresponds to the atomic spectra?

Shirley Liu 2I

If a wavelength value falls exactly in between two values for two colors on the electromagnetic, what would it be classified as? (e.g. if a wavelength is 500 nm, is it considered green or blue?)

Shirley Liu 2I

We should only round up or round down when the value is within about 5% of its closest integer. Values such as and near to 0.25 and 0.75 can be easily multiplied by whole numbers, such as 4, to get or get near integers which you can then round to.

Shirley Liu 2I

I know we shouldn't round off/apply sig figs until the end of all the steps and calculations of a problem, but what should be done if a value in a step has vinculum/a reoccurring number with the bar over it(e.g. 1.333333...) ? At what decimal point should you round off?

Shirley Liu 2I

Can the terms molarity and concentration be used interchangeably/do they mean the same thing?

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