CHEMISTRY COMMUNITY

Nathan Tran 4K

I've seen some chem mods say it is intensive and others say it is extensive. I believe it is extensive because it is not standardized to grams or moles and as such depends on how much "stuff" there is. Is this wrong?

Nathan Tran 4K

Does anyone know what a porous disk is? What is the use?

Nathan Tran 4K

What is an electrolyte in the context of a cell diagram? Can you give an example?

Nathan Tran 4K

Can someone explain how cell potential changes with changes of concentrations of reactants and products? What is the justification behind these changes?

Nathan Tran 4K

How do you find the reverse activation energy for endothermic processes?

Nathan Tran 4K

Yes, that is true. The total rate order involves summing the exponents of each reactant.

Nathan Tran 4K

Oh apologies, I realized the simplification is different so the values probably somehow cancel out. Follow up question, how was this derivation solved?

Nathan Tran 4K

In the constants and equations sheet, there is an equation that simplifies the scalar quantity of ln(Q). However, it changes the ln to log. Can you do this? This seems fundamentally different?

Nathan Tran 4K

I don't think we have to memorize the graphs per se, but it is important that we learn how to derive the relationships for the graphs. We do this by rearranging our dA and dt terms so we can integrate. Then, we change the graph to some form similar to y=mx + b. The graphs allow us to make evaluation...

Nathan Tran 4K

If for example, a reaction is forming something, the reactant would have to be a negative reaction order. We can also see this as the reverse reaction of something that is decomposing--this is why the equilibrium constant has concentration of products in the denominator.

Nathan Tran 4K

The units are different because the reaction order affects the exponent--a first reaction order means an exponent of 1, a second reaction order means an exponent of 2, etc. Because we are raising the concentration (moles/Liter) to a different power, the units change accordingly. For example, by rais...

Nathan Tran 4K

Essentially, because the concentration of one reactant is so high, we can neglect the excess reactant to make the rate law easier to work with. So for a second order reaction involving two concentrations, if one of the concentrations is high, we can ignore it, and say the reaction is a pseudo first ...

Nathan Tran 4K

There are inert electrodes like mercury, but for the purposes of this class, I am sure platinum is the main one we should be concerned with.

Nathan Tran 4K

I am so glad that you have recognized this. I make an active goal to engage in pragmatism, especially in the realm of kinematics. Are you saying you divide the rate of A by the stoichiometric coefficient of A?

Nathan Tran 4K

What does the textbook mean when it asks us to find the unique rate of reaction? What is the process of solving for it?

Nathan Tran 4K

I'm trying to figure out why F/RT equals 1/.02569 V. On number 14.35 of the book, it says this is so. I am confused because I am getting a different value. I plugged in 96485 for F, 8.314 for R, and 298.15 for T. For reference, this is number 14.35 and the solutions manual simplifies F/RT to this va...

Nathan Tran 4K

In terms of the equations, gibbs' free energy sees a relationship with enthalpy and entropy where delta G = Delta H - T * Delta. Heat is a measurement of how much energy is transferred, but in terms of energy that is not able to do work, whereas Gibbs free energy is a measurement of how much work so...

Nathan Tran 4K

We use the third law to identify changes in entropy in systems, surroundings, etc. Applications would be calculating delta s in terms of isothermal, isobaric, and isochoric conditions, calculating S in terms of Boltzmann's equation, and finding relationships in terms of delta s of the system, surrou...

Nathan Tran 4K

Usually, the system is the actual thing we are dealing with in the question. For example, if we are looking at the piston and identifying characteristics like work, heat, etc., the piston is the system, while the surroundings is what is supplying heat or what the system is losing heat to or the surr...

Nathan Tran 4K

I know what the difference between state functions and path dependent functions are. However, how would we rationalize the fact that work and heat are path dependent using our formulas or just conceptually?

Nathan Tran 4K

On 8.57 of the 6th edition, we are given Standard Delta H with a subscript of c. I assumed we could use this value as the standard enthalpy of formation, but the answer manual is using Hess' law. How do you do this? And what does the subscript c mean?

Nathan Tran 4K

Hi, so you know standard enthalpy formation is based off the moles of each reactant and product. Refer to table 8.4 to find the enthalpy of the whole reaction. Remember that diatomic molecules will have an enthalpy of zero, that product enthalpy will be negative and that reactant enthalpy will be po...

Nathan Tran 4K

In 8.49 of the 6th edition, we're asked to find the change in internal energy, knowing the reactions' change in enthalpy, and given the change in moles. We're not given a temperature, but we need a temperature to solve for work, or -p times delta V. We can solve for this using the ideal gas law. The...

Nathan Tran 4K

The application of what people said before comes from the equation, delta U = q + w. If for example, something is isolated, that means that there can be no change in energy or matter, so delta U is zero.

Nathan Tran 4K

I feel like there are a lot of ways to evaluate the change of signs for entropy--heat conventions is one of them, but because there are so many derivations of heat, you could also look at entropy change through different variables (this is good because then if you're not given heat or do not know ho...

Nathan Tran 4K

I would say review notes, read textbook for unfamiliar concepts, do lots of homework problems, and go to review sessions! Lavelle has so many resources!

Nathan Tran 4K

This is a bit of a manipulation of our equation Delta u = q + w. If we know that there is a constant volume, we can assume there is zero work. As such, delta u = qp. We learned that qp is the same as delta H so u = delta H.

Nathan Tran 4K

I might also add that it would be helpful to know the equation Delta U = qp + w, where work can be rearranged. It's helpful to know as many derivations of the same term as possible.

Nathan Tran 4K

Hess's Law allows us to manipulate equations where one constituent appears in one equation's reactants while the same constituent appears in another equation's products. As such, you can cancel out the constituent by adding the equations together. In doing so, you must also add up the enthalpies. In...

Nathan Tran 4K

How do you justify that an increase in temperature for endothermic reactions favors product and vice versa for exothermic reactions? Can we reason this out without just memorizing?

Nathan Tran 4K

If you are given equilibrium partial pressures and an overall volume, can you just ignore the overall volume, assuming you're finding Kp? In other words, would the overall volume just be extraneous information?

Nathan Tran 4K

I have a question regarding sig figs. In 11.61, all the initial concentrations are given in three sig figs, but the Kc is given in two sig figs (the value is 0.56). The question asks to find the equilibrium concentrations of all the reactants and products. Why does the answer manual have the answers...

Nathan Tran 4K

Also, it could depend on what phase your reactants and products are in if you are not given actual values.

Nathan Tran 4K

If the question just asks for K, you can use either, but it is probably better to use what you are given. In this case, I am sure you were given partial pressure which is why you got a Kp value. However, if the question asked for Kc, you would need to convert your partial pressures to concentration ...

Nathan Tran 4K

Is there any change in a reaction if inert gas is added?

Nathan Tran 4K

What value does Kc have to be less than for you to estimate, meaning you can negate the -x term when employing ice method to solving for concentrations of products given initial reactant concentration? Is it less than 10^-3 or something else? Just making sure!

Nathan Tran 4K

The question asks you to find the concentration of H3O+ given the Kw as 2.1(10)^-14. I realized that the concentration of H3O+ would be the same as the concentration of OH- so I made 2.1(10)^-14 equal to x^2. I ended up solving for x and got 1.45(10)^-7, but of course, in interest of sig figs, round...

Nathan Tran 4K

If you calculate Kp and Kc of the same chemical equation with the same conditions, would the values of Kp and Kc be the same? There is the logic that because both Kp and Kc are simply rations of products/reactants, they would be the same. If they are not the same, why not?

Nathan Tran 4K

The reason why only temperature changes the K value is because the other variables e.g. pressure only really change the initial concentration of reaction or product. However, because of this, the Q value changes which will shift the chemical equation.

Nathan Tran 4K

I know the triangle on top of the arrow indicates there is heat involved, so you know that equation can be endothermic or exothermic. However, to determine whether a reaction is exothermic or endothermic, I would assume we would be given delta H or some variation of it.

Nathan Tran 4K

Over lecture and in the textbook, we went over the idea that liquids and solids have concentrations we can ignore in context to finding the equilibrium constant--or in other words, concentrations of 1. Because H20 is a universal solvent, this makes sense. But what if H20 is in the gas phase? During ...

Nathan Tran 4K

It's essentially a constant usually equal to 8.315 JK^-1mol^-1. I am sure it will be on our constant sheet.

Nathan Tran 4K

If I remember correctly, a larger equilibrium constant occurs due to a larger concentration of product than the concentration of reactant. This is because Kc = [Product]/[Reactant]. Alternatively, a smaller equilibrium constant occurs due to a larger concentration of reactant than that of product.

Nathan Tran 4K

This comparison is different because in your first comparison, you are comparing bond lengths, but in your second comparison, you are comparing the electronegativity. The reason why we compare electronegativity in your latter comparison is because H is attached to O in both molecules; thus, comparin...

Nathan Tran 4K

In this question, it is specified that H2Se has a higher boiling point. Normally, we cannot determine which intermolecular force dominates, but in this question, we know that since the LDF and the dipole dipole forces contradict each other, the LDF is more dominant. It's a really weird nuance!

Nathan Tran 4K

The shape is determined by how many ligands are attached. Even more so, we have to consider whether something is polydentate. For example, three bidentate ligands would be octahedral in shape.

Nathan Tran 4K

Did you know that oxygen went for a second date with potassium?

How did it go?

It went OK2!

Nathan Tran 4K

I encountered this problem I 12.127 in the 6th edition book where the question asked how many protons could interact with thymine. My question is how come double bonded O can't accept H. Someone told me that it was because this would make O have a formal charge of +1, but when you add the proton to ...

Nathan Tran 4K

Hi, I need help with question 12.25 with figuring out the concentration of H3O+. I understand how to calculate everything else, but I don't understand why there would even be a concentration of H3O+ if we are just dealing with a Bronsted base. In the solution manual, it mentions Kw. How would you do...

Nathan Tran 4K

You can determine if a molecule is a ligand by first looking for a coordination sphere. If there is a bracket, there is a coordinating covalent compound, which means there are ligands. You can probably also look for them by looking for a transitional metal. Transitional metals can bond with 6 ligand...

Nathan Tran 4K

I believe it's safe to assume that when we name ligands, we can just go left to right because the ligands are already in alphabetical order in the chemical equation. When we write the chemical notation for coordinating compounds, we start with the transitional metal, and then name the compounds base...

Nathan Tran 4K

I noticed when we did pH computations, we used the concentration of specific ions or molecules. When we did this, we used M, which is the unit for molarity of moles/liters. However, I always understood concentration as g/L of Kg/L. What is the difference between molarity and concentration? Is there ...

Nathan Tran 4K

I actually bought an answer solution in the book form, so my solutions manual is a physical copy.

Nathan Tran 4K

On 17.29, in the chapter 6 edition, it says in the answer manual that the CN portion of the coordinating compound will be cyano (not including everything else). However, on page 742 of the book with the chart of common ligands, it says that CN is cyanido. How come the answer solution changed cyanido...

Nathan Tran 4K

As stated before, you will need to find the total sigma and pi bonds in the molecule. This will involve counting the single bonds for sigma bonds and characterizing the excess bonds as pi bonds.

Nathan Tran 4K

I know what you're talking about when you say the textbook and lectures are different when it comes to drawing dipole. I would stick with what Lavelle said though. You are right about how we draw it--the arrow points to the more electronegative atom while the "tail" is near the less electr...

Nathan Tran 4K

No, these shapes cannot be nonpolar because of the inherent asymmetry of the molecules. The lone pair in each shape pushes the other atoms so bond lengths are slightly different than that of their arrangement structure counterparts. Thus, the dipole vectors will not cancel out.

Nathan Tran 4K

I am currently working on number 4.13, question C in the 6th Edition book. When drawing the lewis structure of IO3-, I noticed the solution manuals had three single bonds for each I-O and one lone pair which means I has a formal charge of +2 and each O has a formal charge of -1. Sure, this makes I h...

Nathan Tran 4K

I was reviewing my notes, and saw that increasing electrons increases the distortion, which in turn increases london dispersion force. To me, this seems counterintuitive because I typically attribute the increase in electrons to an increase in atomic radius, which I associate with weaker bonds. Can ...

Nathan Tran 4K

Can someone clarify the point Lavelle made about rotating with pi bonds? I recall he used two pencils to try to rotate the atoms, but I think he said something along the lines of "if there is a pi bond, it means there can be no rotation." Could someone clarify this concept?

Nathan Tran 4K

Hybridization occurs because it rectifies the problem of unequal energy in bonds that unhybridized models imply. Let's look at the molecule CH4. If we were to look at the C-H bonds, we would do so by drawing the valence electrons in the outermost shell of Carbon in its ground state. Thus, we would s...

Nathan Tran 4K

As Ashley said, the systematic approach is to first look if there are any dipole moments. We can look for dipole moments by looking at the symmetry of the molecule and the vectors of the dipoles. If the molecule is asymmetrical, we know there is a dipole dipole force. If it is symmetrical and the di...

Nathan Tran 4K

Electron distortion refers to an interaction between a cation or anion where a cation (because of the positive charge) alters the electron cloud of the anion. In this sense, electron distortion is very important in ionic bonds. The power a cation has to distort the electron cloud of an anion refers ...

Nathan Tran 4K

What is this trend on the periodic table for polarizability and polarizing power and how do you justify these trends using ideas like more shells and greater effective nuclear charge?

Nathan Tran 4K

When we draw the lewis structure for for ClO2, we usually pick the atom with the lowest ionization energy. However, between the two atoms, there is a conflicting trend where Cl gets more rightward and gets more downward in comparison to O. This is counterintuitive because ionization energy increased...

Nathan Tran 4K

In addition, when we are working with VSEPR theory, we might be asked to put the molecule in the form AXnEm. This helps us predict the actual 3d shape of the molecule while a lewis structure really only predicts the molecule in the 2d plane. Also, the lewis structure has things like single bonds, do...

Nathan Tran 4K

Lavelle discussed in lecture that the number of bonds should not affect the regions of electron density. Thus, with the information we have now, it is best to assume that double and triple bonds do not affect shape. However, of course there may be nuances to this, but I think that we can stick to th...

Nathan Tran 4K

Also, to add a quick thing--it's actually VSEPR, not VESPR. This is because VSEPR stands for valence shell, electron pair, repulsion theory. As stated above, the basic formula AXnEm where A represents the central atom with an implicit subscript of 1, X represents a ligand (the atom attached to the c...

Nathan Tran 4K

Another common exception to the octet rule that we don't often talk about is hydrogen just because it's so intuitive to make a single bond without completing its octet. It's one we don't think about often breaking the octet, but one that does nonetheless.

Nathan Tran 4K

Another thing to add that I have down in my notes is that greater force in interactions leads to greater melting points. But as reiterated before, your understanding thus far seems spot on!

Nathan Tran 4K

I noticed what Christopher noticed as well. Could it have something to do with the fact that this decrease tends to cluster more to the right of the transitional metals? I am looking at a periodic table with the actual electronegativities for each element and it seems like this is somewhat of a trend.

Nathan Tran 4K

I recall my TA saying that all molecules undergo London Van Der Waals Forces in some way, and that for example, diploe-dipole forces are just stronger forces of this nature. What exactly are these London Van Der Waals Forces and are they synonymous to dispersion and induced diploe-induced dipole for...

Nathan Tran 4K

During Lavelle's lecture, we learned that higher distortion results in greater interaction potential energy which ultimately leads to higher boiling points. What exactly is distortion though?

Nathan Tran 4K

How does one find the number of nodal planes given principle quantum number and the subshells? So how does the number of nodal planes relate to s-,p-,d-,and,f- and other things like that?

Nathan Tran 4K

For trends like electronegativity, what do we do if the atom we are comparing gets more rightward but more downward in position? Does one of the values (period versus group) affect the electronegativity more significantly?

Nathan Tran 4K

Furthermore, will we be expected to know how to do so on the test?

Nathan Tran 4K

How do you find the number of unpaired electrons?

Nathan Tran 4K

Moreover, to add on to all of these answers, the "true" model for the bonds would be a blend of all the resonance structures, meaning that every bond between nitrogen and oxygen has characteristics of both a single bond and a double bond. Drawing multiple lewis structures of the same molec...

Nathan Tran 4K

Just writing the ground state as [Ar] would be an acceptable answer, as the charge of plus 2 means the Calcium atom lost two electrons, equal in valence electrons to that of the noble gas Argon.

Nathan Tran 4K

Knowing the trend like you mentioned is probably something we need to know, but knowing the actual values will be given, as we are not expected to memorize the values of atomic radii.

Nathan Tran 4K

That makes sense, thank you!

Nathan Tran 4K

(This question requires the solution manual in hand) In the solution manual for 1.55, the way the question is solved is v/c = wavelength. However, this means frequency = speed of light times wavelength which makes no sense. Am I misinterpreting this problem, misinterpreting the solution manual, or i...

Nathan Tran 4K

In question 1.45, the bowling ball is rolling down an alley at 5 plus or minus 5 meters per second. In Lavelle's lecture, I recall the uncertainty in position would be 10 because the maximum value is 10 meters per second while the minimum value is 0 meters per second. However, in the solution manual...

Nathan Tran 4K

I need help with the following question: 18. The hydrogen atom has a radius of approximately 0.05 nm. Assume that we know the position of an electron to an accuracy of 1 % of the hydrogen radius, calculate the uncertainty in the speed of the electron using the Heisenberg uncertainty principle. Comme...

Nathan Tran 4K

Hi, I need help with the following question on the module: 13. In the above experiment if only the absorbed wavelengths of light are detected what is the experiment called? What is the spectrum called? I know this is a question about the definition but why is it not: A. Atomic absorption spectroscop...

Nathan Tran 4K

The fact that they act as particles manifests in the one to one interaction in the photoelectric experiment. However, diffraction is one of the main characteristics that show that they act as waves.

Nathan Tran 4K

On number 1.9, in the 6th edition book, the wavelength of the third type of radiation solves to be 1 meter. Looking at an electromagnetic chart, 1 meter is the approximate wavelength of radio waves (or relatively close to that value). However, on the answer key, the radiation event is supposedly &qu...

Nathan Tran 4K

Doctor Lavelle used a very pertinent example of a water faucet in his discussion of the difference between discrete and quanta variables. Essentially, the holistic view of water exiting a water faucet is comparable to a discrete value because water is seen as continuously flowing. An example of this...

Nathan Tran 4K

This is very helpful! Thank you for this! I'll make sure to study it, and I look forward to seeing you on Sunday!

Nathan Tran 4K

Yes, they are the same notation. Negative powers just indicate that the exponent will appear in the denominator. For example, x^(-1) is simply 1/(x)^1. Another way to think of it is looking at the term as the reciprocal of the absolute value of the exponent. Because the grams are multiplied by (mole...

Nathan Tran 4K

The way I balance equations is I always scan for an element that appears on the reactant side of the equation and product side of the equation once. In doing so, I make sure that there are no other elements affecting the balancing of the element. After this, I look to see if the element I balanced w...

Nathan Tran 4K

The way I solve limiting reactant problems is the way you highlighted in your first description. Converting the grams of reactants to moles allows one to compare the moles of the actual reaction to those in the molecular equation. I understand what you mean about comparing the two values as being co...

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