CHEMISTRY COMMUNITY

Eesha Sohail 1D

So this concept is generally used in the gathering of experimental data?

Eesha Sohail 1D

What exactly does temperature define on a molecular level?

Eesha Sohail 1D

Does it matter if the order of the rates? For example if the first step rate is slow and the second step is fast does the slow step control the rate? What happens if the first step is fast and the second step is slow? The slow step is always the one that controls the rate of the reaction. If there ...

Eesha Sohail 1D

Just to make sure I've got this down: for a zero-order reaction the rate doesn't change, for a first-order reaction the rate decreases linearly, and for a second-order reaction it decreases exponentially. Is that correct?

Eesha Sohail 1D

How would you apply this kind of standard rate to a test problem? Arrhenius equation is one thing i can think of, but are there others?

Eesha Sohail 1D

It depends on what you're given. To get from the reactants to the products, bonds must be broken and formed, so an intermediate might be a state where, say, two reactants have joined together before they break into the product forms. It depends on the reaction mechanism of whatever you're studying.

Eesha Sohail 1D

The half life of a reaction is a useful concept for relating time passed to amounts of substance in the real world. Not sure exactly what context may show up on the test, but it is frequently referenced in radioactive dating.

Eesha Sohail 1D

I assume we'd have to be able to correctly interpret general trends in a graph, but I don't really think we'd have to draw accurate graphs on our own; at the most there will likely be a template provided.

Eesha Sohail 1D

Aren't the thermodynamics and kinetics of a reaction connected though, through the relation between K and both k's? Can a change in one predictably affect the other at all?

Eesha Sohail 1D

Is there a way for me to get one-on-one help sometime this week? I'm still shaky on thermodynamics.

Eesha Sohail 1D

Electromotive force refers to the potential difference between the two electrodes in a cell. As the cell goes to equilibrium, the E goes to zero.

Eesha Sohail 1D

An electrolyte is basically a solution of ions, functioning as a medium for current flow. An electrode connects the conducting and nonconducting part of the cell, and directs the flow of electrons.

Eesha Sohail 1D

Since they mean the same thing, it doesn't really matter which you use, but the log equation is easier to translate into useful values for K and pH.

Eesha Sohail 1D

It's not necessarily that it's not the /same/, it's just that since it's a charged value, it's better to make sure you specify that it''s positive. Same deal with oxidation numbers, ion charges, etc.

Eesha Sohail 1D

What is the relationship between current and volts? And what exactly do volts represent contextually?

Eesha Sohail 1D

If the direction is reversed, does G become positive? And what is this reverse case named, if the normal is a battery?

Eesha Sohail 1D

What solutions might I commonly see in a redox problem, in either case? Asking for identification purposes.

Eesha Sohail 1D

Are there any cases where two half reactions cannot be balanced using water, ions, and electrons?

Eesha Sohail 1D

Is reduction generally associated with endergonic or exergonic reactions?

Eesha Sohail 1D

The oxidation number is obtained using a few rules for each of the species in a compound. 1. The cation is written first in a formula, followed by the anion. NaCl - Na is +1, Cl is -1. 2. The oxidation number of an element by itself is always 0. O 2 - O has an oxidation # of 0. 3. The oxidation numb...

Eesha Sohail 1D

Can any real process ever be completely adiabatic? Heat exchange seems like it would be inevitable, in the real world.

Eesha Sohail 1D

The corollary to law #2 is that since no real process is perfectly reversible, change in entropy of the universe is always positive, correct? But why can no real process be completely reversible?

Eesha Sohail 1D

In relation to gases, work is done on the system when compression occurs, and the system does work when expansion occurs. The former is positive and the latter is negative.

Eesha Sohail 1D

Considering equilibrium and K, is the delta H the same for the reaction regardless of the equilibrium concentrations, or does it still change?

Eesha Sohail 1D

Can one actually calculate amounts of G contained in a substance, or only transferred amounts?

Eesha Sohail 1D

Can certain extensive properties be manipulated to produce corresponding intensive values? I'm thinking of heat energy versus temperature here, but I'm not sure how the quantities compare.

Eesha Sohail 1D

It depends on the values/units you are given in the question. If reaction constant is given (which, probably not) then you will most likely use the other equation. However, the G = H-TS equation is definitely the most important one.

Eesha Sohail 1D

What would nonexpansion work entail? Is that essentially just heat transfer?

Eesha Sohail 1D

Physical changes involving a change in state are all reversible. For chemical reactions, I'm not sure exactly what markers you could look for to deem a reaction reversible, but it is useful to remember that reversibility is usually conditional, and reactions deemed irreversible may actually be rever...

Eesha Sohail 1D

Chem Mod, does the A in your equation represent a delta? For change of temperature?

Eesha Sohail 1D

How is change in entropy calculated? What are its units?

Eesha Sohail 1D

For right now, with energy transfer and stuff, kinetics isn't really relevant, right? I don't believe we've really talked about rates.

Eesha Sohail 1D

How does an isothermic process differ from an adiabatic one?

Eesha Sohail 1D

In an adiabatic process, heat does not enter or leave the system. Energy transfer happens only through work, so Q=0.

Eesha Sohail 1D

Could there be any situation where matter-energy transfer occurs in a closed system? As in, converted into each other.

Eesha Sohail 1D

A state function means that the pathway doesn't matter, only the start and endpoints do. An analogy can be drawn to displacement; between two points there is only one displacement even though there's a multitude of various distances one could take to get there.

Eesha Sohail 1D

Negative enthalpy would indicate that through a reaction, heat was lost. A reaction with negative enthalpy is the same as an exothermic reaction.

Eesha Sohail 1D

I always conceptualized heat as a Thing that is passed around, while enthalpy is the net change in it. How accurate/inaccurate would that assessment be for the purpose of this class?

Eesha Sohail 1D

In general, are there any trends with the bond enthalpies of substances in different states?

Eesha Sohail 1D

On the heating curve, one axis is temperature, but can someone explain what exactly temperature means on a molecular level vs heat?

Eesha Sohail 1D

I don't particularly understand the distinction between the K calculated through pressure of a gas and K from concentration. How are they different, and can they be converted into each other in any case?

Eesha Sohail 1D

Liquids and solids are not part of the equilibrium constant expression, so they will not affect the concentration of the reactants or products.

Eesha Sohail 1D

I understand the logic of the excess analogy, but how does the concept of chemical "activities" factor into this concept?

Eesha Sohail 1D

Would the product NaOH be counted as a solid or as separate ions in solution in the net ionic equation?

Eesha Sohail 1D

As far as I've seen, the ideal gas law is taught in high school chemistry classes more than physics classes, but that's a bit of a moot point. That said, could we possibly use other variants of the law to figure things out as well, such as P(mm) = dRT (where mm = molar mass and d = density)?

Eesha Sohail 1D

The partial pressures in such a case are solely regarded if they are relevant to the occurring reaction; the partial pressures of the reactants/products don't change /in relation to/ each other, because the ratio is what is important. According to the ideal gas law, pressure varies directly with con...

Eesha Sohail 1D

For our purposes at the moment, I think we can apply it to all the situations given to us in classwork. With low temperature and high pressure, the actual results will deviate from the ones given by the law. Doesn't necessary mean it's not applicable, it would just be more complicated to get a more ...

Eesha Sohail 1D

For vapor pressure, what environmental factors can influence how much of a substance will vaporize? Does pressurizing the gas affect that in any way?

Eesha Sohail 1D

The ideal gas law is meant to approximate the behavior of gases excluding potential intermolecular interactions. The more interactions between particles, the more deviation from the law. So, interestingly, noble gases are some of the most ideal gases out there, as far as I know - particularly helium...

Eesha Sohail 1D

Yes, since K represents a ratio of similar quantities, it is unitless. (concentration divided by concentration)

Eesha Sohail 1D

How do hemoglobin complexes create myoglobin; do they bind together, and in what way? I know there are four hemoglobin subunits, but I don't understand how they fit together.

Eesha Sohail 1D

I believe this is correct. Here I don't think iso- counts as a prefix, it's part of the ligand's original name. Would you happen to know whether this alphabetical system is the same for writing out formulas? Or can we just write the ligands randomly?

Eesha Sohail 1D

For this question, they specifically wanted you to look at the provided table, understanding that if pK b is lower then the substance is a stronger base. The given values are pretty close, so I don't think they'll give us a problem like that without giving us the K value. For the questions dealing w...

Eesha Sohail 1D

The reply is showing hydrogen bonding, not a Bronsted acid-base reaction. That said, I'm wondering the same thing; the solution says only N can accept protons that way, but I'm wondering why the double bonded O's don't do it as well.

Eesha Sohail 1D

I'm having trouble figuring out whether different oxides are acidic, basic, or amphoteric. Can someone help me figure out what to look for to decide each case?

Eesha Sohail 1D

Will we have to deal with any questions about Q vs K and le Chatelier's principle on the final?

Eesha Sohail 1D

Can a compound act as both a Bronsted and Lewis acid or base, or must it be one or the other? And if you have one, an example would be helpful.... Lewis acids/bases are a tad confusing to me still.

Eesha Sohail 1D

Wouldn't this work for any solution, essentially? Not just a strong acid? And if not, what different cases might we encounter?

Eesha Sohail 1D

The seven strong acids are: HCl, HBr, HI, HNO₃, H₂SO₄, HClO₄, and HClO₃.

Eesha Sohail 1D

At first I thought HF would be a stronger acid because of the electronegativity of the F atom. Where do you look at the size/polarizability of the anion, and where does electronegativity matter more?

Eesha Sohail 1D

The octahedral geometry's etymology is confusing me a bit; why is it "octa" if there's six? Is it because the shape forms two square pyramids attached base to base?

Eesha Sohail 1D

The "d" actually stood for the word "diffuse" in the beginning, a word that described the spectral lines of these atoms. The d-block elements are all transition metals.

Eesha Sohail 1D

Does it have something to do with the electrons used for the bond being from d-orbitals, the fact that it’s only transition metals? I had OP’s question as well.

Eesha Sohail 1D

Does the oxidation number have any bearing on how electrically positive or negative an atom is in a compound, such as in relation to a dipole?

Eesha Sohail 1D

Why is six the maximum coordination number? (I vaguely remember this from lecture but I’m not sure whether it’s accurate. Is it some simple rule of geometry that dictates it, or is there something I’m missing here?

Eesha Sohail 1D

It would most likely be linear, because the bonded atoms would be as far apart as possible. The lone pairs would be arrayed perpendicularly around the central atom in a triangle. One example of this scenario is XeF 2 , xenon difluoride. The electron pair geometry is actually trigonal bipyramidal, bu...

Eesha Sohail 1D

What name is usually given to molecules like water, with sp4 hybridization but only 2 bonding atoms around the central atom? I used to say "bent" in high school, but the book is calling it "angular." Which name should I use?

Eesha Sohail 1D

When molecules are created, the way they share electrons messes with the shape of each atom's orbitals, and what ends up happening is that the orbitals "hybridize" to create molecular orbitals, rather than behaving the way they do with unbonded atoms. However, since we haven't really talke...

Eesha Sohail 1D

Does that mean that an induced dipole on one atom can be caused by an instantaneous dipole on another? And (just to clarify) the interaction that arises from this would be the dipole moment, a van der Waals interaction?

Eesha Sohail 1D

Dipole moments can be figured out based on electronegativity differences, and electronegativity has a strong correlation to the atom's position on the periodic table. So, yes, @ Leslie; but it's worth it to remember that the periodic table was based on periodic trends and not the other way around.

Eesha Sohail 1D

Since the oxygen atom is actually smaller than the nitrogen, would it be less electronegative than the latter? Meaning, do these two not follow the "general" trend?

Eesha Sohail 1D

Aren't van der Waals interactions still technically dipoles, just not permanent ones? I've seen them referred to as instantaneous dipoles. Also just to clarify, would the C=O bond be able to produce a dipole moment?

Eesha Sohail 1D

I don't exactly understand radicals; how do they form, and why? I was under the impression atoms usually have electrons in pairs. I do understand why they're so reactive comparatively, and why that would be harmful.

Eesha Sohail 1D

I think it helps to think of energy as power to do something, rather than something tangible. It takes energy to break a bond, but energy is released when a bond is formed. That's because a bonded state is typically less energetic or "powerful" than an unbonded one, and therefore more stab...

Eesha Sohail 1D

Double bonds are stronger than single bonds because the extra bonding electrons attract the positive nuclei more strongly than if there were only two. This also pulls them in closer together, making the bond shorter.

Eesha Sohail 1D

I don't quite understand why chlorine has an expanded octet. Doesn't it have seven atoms in its outermost shell only?

Eesha Sohail 1D

If they can't all be zero, then the next course of action is to find the configuration that allows for the lowest possible charge, whatever that might be.

Eesha Sohail 1D

How do you guys decide whether or not a value for formal charge is too egregious? Usually I consider +/- 1 or 2 valid, and anything above that is sketch, but it's not really a set rule.

Eesha Sohail 1D

Feel free to correct my understanding if this is wrong, but resonance structures are less of an absolute reality and more of a graphic representation of what happens. The "usual" arrangement of atoms will average out somewhat between the possible resonance structures, but the representatio...

Eesha Sohail 1D

Can you elaborate on what that would look like? Maybe with a link. It sounds fine to me, but doesn't hurt to check.

Eesha Sohail 1D

For the formal charge on each atom, I usually count up every lone pair electron and bond, and subtract the sum from the neutral number of electrons. I find understanding this conceptually an easier thing to do, as opposed to consulting the equation. After a while, doing this just became second nature.

Eesha Sohail 1D

Is there a particular order the dots are written for each atom? Like, if I had an atom with 6 valence electrons, is there a specific way I must draw the electrons around the nucleus?

Eesha Sohail 1D

This goes slightly outside the scope of the question, but do all elements follow the same pattern of removal of electrons? Like, would removing an electron from Ag work the same way as one from Cu save for being at one higher energy level?

Eesha Sohail 1D

In addition to the above, generally a difference in electronegativity between 0 and 0.5 will be regarded as a nonpolar bond, while a difference between 0.5 and 2.0 will be seen as polar, hence why it is seen more as a sliding scale than a set distinction.

Eesha Sohail 1D

So just to clarify, alkali metals and alkaline earth metals cannot make use of an expanded octet? Is it because their outermost shells are on a different energy shell than the rest of their electrons, and there's only 2 electrons max in that shell?

Eesha Sohail 1D

Can something still be emitted with zero KE? It seems as though that would cause it to not move at all, and therefore not break free of the metal surface. However, it's possible I'm ascribing expectations of regular matter to the quantum level where they don't really apply.

Eesha Sohail 1D

The reason why Scandium is written as [Ar] 3d1 4s2 is because after the 20th element in the periodic table (Calcium), the 3d orbitals have a slightly lower energy than the 4s orbitals. Therefore, you would start filling the 3d orbitals until it is full. The 4s orbital is filled first because it is ...

Eesha Sohail 1D

I understand this is a very broad question, but I was wondering if someone could explain the concept of spin to me. Is it an intrinsic value ascribed to one electron, and can it change? How does it practically affect the atom? And, say, if an electron were to be added to an atom's outermost shell, w...

Eesha Sohail 1D

For chromium, the electron configuration would have looked like the following if it followed "normal" conventions: [Ar]4s 2 3d 4 And for copper: [Ar]4s 2 3d 9 However, the atom finds more stability when the d-subshells are half-filled or fully filled: Cr: [Ar]4s 1 3d 5 Cu: [Ar]4s 1 3d 10 T...

Eesha Sohail 1D

The equation is used when referring to the energy of light/electromagnetic radiation, not with matter. v refers to the frequency of the light; if the problem gives you wavelength, you can use v=c/\lambda to find that frequency. Then you can use Planck's constant to find the energy of the particle. A...

Eesha Sohail 1D

Hi, thanks for the reply! Does that mean the electron actually follows that "trajectory," or is it a representation of the highest probability area of finding the particle? And since it's a standing wave, are those oscillations meant to represent oscillations in the electric field? I think...

Eesha Sohail 1D

I think the original poster was asking "why" the wavelike properties exist- which is actually a good question, because a lot of people (myself included) have been parroting the words "wavelike properties" since lecture with no idea what that actually means. The evidence for parti...

Eesha Sohail 1D

I can see how the dash in the second question might be offputting, but it looks like a misprint. Otherwise, this looks like a standard c = \lambda v problem to me. Was there something specific that was confusing in this question? It seems like the procedure is to find wavelength by isolating lambda ...

Eesha Sohail 1D

Also I believe wavelike properties are only demonstrated by objects that are extremely small. While light does exhibit wavelike properties, the equation cannot be applied towards it. So... does this mean objects with wavelike properties move in a wave? or what? That's the part I'm having trouble wi...

Eesha Sohail 1D

From the last lecture, I did not exactly understand what Dr. Lavelle meant by electrons existing as a "circular standing wave." I understand that electron clouds are described in terms of "shells" of orbitals that have integral energy levels, but need help understanding the appli...

Eesha Sohail 1D

I keep on seeing sig figs throughout this discussion. I am not knowledgeable about that term. Can someone explain to me what it means and how it helps with rounding? "Sig figs" is a shorthand term for "significant figures," a term in chemistry used to help gauge level of accurac...

Eesha Sohail 1D

If I recall correctly, incomplete combustion occurs in the presence of inadequate oxygen, but I'd appreciate if someone could check me on that. An example equation I found for the process, ft. methane: 4CH_{4} + 5O_{2} \rightarrow 2CO + 8H_{2}O + 2C Would this also possibly count as a side reaction?...

Eesha Sohail 1D

In what instances would a molecule be liquid as opposed to aqueous? What are some examples of molecules besides water that are in the state of pure liquid and not aqueous? An ionic compound will usually react in solution, so those are, for the most part, written as aqueous; NaCl, CuSO4, etc. Off th...

Eesha Sohail 1D

If anyone is looking for a good list of inorganic naming conventions, I found this one very helpful, as it organizes ions by charge and groups together similar polyatomic ions, including the oxyanions: http://msmcraesscience.weebly.com/uploads/5/1/4/4/5144948/ap_chemistry_ion_sheet_--_chemical_nomen...

Eesha Sohail 1D

In terms of the original question you asked - the relationship between velocity and wavelength for light is given by this equation: V = f\lambda Where V is the velocity of the wave in meters per second, \lambda (lambda) is the wavelength in meters, and f is the frequency, or cycles per second. I bel...

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