CHEMISTRY COMMUNITY

Michael Torres 4I

When dealing with a problem that has a redox reaction, you should illustrate the individual reduction and oxidation reactions that combine to create the overall redox reaction. If the individual reactions are unclear, it can be helpful to look in the appendix to view individual reduction reactions, ...

Michael Torres 4I

To get vaporized, a substance must undergo some enthalpy of vaporization at the boiling point. Therefore, simply being at the boiling point is not enough to vaporize a substance.

Michael Torres 4I

Question 5N.15 in the seventh edition incorporates solubility products from table GI.1. What are these? Could you explain how to incorporate them into a problem such as 5N.15 in order to solve it?

Michael Torres 4I

Ions or any other species that partake in redox reactions will be included in the cell diagram. The only species which would not be included from the redox reactions making up the overall reaction would be liquid water.

Michael Torres 4I

Yes, you are correct. The reaction is perceived to be occurring faster in other steps relative to the rate determining step. Therefore, the rate determining step will determine how quickly the reaction will proceed since it is the slowest. The effect of the other steps on the rate of the reaction is...

Michael Torres 4I

Yes, chemical equilibria will be on the final exam.

Yes, the final exam is cumulative.

Michael Torres 4I

If you turn the concentrations given in mmol units to mole units, you will get the right answer. For example, on the top row turn each of the 1.25 mmol to 1.25*10^-3 mol. The reaction is of the fifth order. (1.25*10^3)^5 is equal to about 3.05*10^-15. When you set up the equality k(3.05*10^-15)=8.7*...

Michael Torres 4I

To solve this problem, you need to use the equation ln(k2/k1)=((activation energy)/R)((1/T1)-(1/T2)). The problem gives you the values for two different rate constants and their respective temperatures. Therefore, you can plug 0.76 s^-1 into k2 and 1000. K into T2. After that, you can plug 0.87 s^-1...

Michael Torres 4I

I suggest specifically asking or emailing your TA about this. Because your TA is responsible for collecting your homework, they are likely the best resource to address for this question.

Michael Torres 4I

I personally enjoy attending the drop in sessions. Often my questions go unanswered in large workshops, so I like talking to people one-on-one. From my experience, drop in sessions have generally been a pretty good way to do that.

Michael Torres 4I

The order in which you listed them with aqueous in the middle and solids on the outside seems correct. Apart from what you have already mentioned, the book also mentions placing reactants before products when constructing cell diagrams. After you have arranged the phases as you did here, I recommend...

Michael Torres 4I

Some of the self test questions in the seventh edition ask for the products of electrolysis of certain compounds. Can some explain how one would find the products of electrolysis of any compound? Thank you.

Michael Torres 4I

Electrolytic cells generally have their own spontaneous reaction that would occur if an external voltage were not applied to them. However, when a voltage is applied that provides a greater potential difference in what was previously the non-spontaneous direction, electrolysis occurs and what was pr...

Michael Torres 4I

You will often need to balance out the oxygen atoms and hydrogen atoms in a half reaction. When you need to do this, you involve H+ and H2O. Specifically, these would be involved in a half reaction within an acidic medium so that OH- might not be included. An appropriate amount of H2O would be added...

Michael Torres 4I

The molecule featured possesses an octahedral geometry. Consider X1, X2, X3, and X4 to span horizontally across the molecule, with odd numbers being positioned opposite from each other and even numbers being positioned opposite from each other. Now, consider Y1 and Y2 to be the points on the opposit...

Michael Torres 4I

I think you should generally use kJ/mol, especially when some particular reaction is involved. That way you know that you are referring to how much energy is released or absorbed each time that reaction is performed. Other than that, look at the context of the question and the units of the values gi...

Michael Torres 4I

Yes, I believe so. The solutions manual states this when explaining problem 6L.7 from the seventh edition.

Michael Torres 4I

Free radicals have revolutionized chemistry.

Michael Torres 4I

The anode will generally be on the left, and the cathode will generally be on the right.

If standard reduction potentials are given, you would reverse the oxidation reaction, namely that of the anode.

Michael Torres 4I

When you have a certain amount of moles present in some equilibrium reaction per the different reactants and products involved, you will have a certain equilibrium constant. Because of PV=nRT, this also applies to gas pressure under ideal conditions. What this means is that if the number of units of...

Michael Torres 4I

An extensive property is one which depends on how much of something there is. An example of an extensive property is heat capacity. Heat capacity either consists of molar heat capacity times the amount of moles present or specific heat capacity times the amount of grams present per the substance in ...

Michael Torres 4I

I haven't come across problems incorporating what you mentioned. Since the value of W is yielded by (number of available positions)^(number of particles), then I think it's fair to assume that you will be using the value of k rather than R. W is in terms of individual particles and so is k, so I thi...

Michael Torres 4I

If such problem were to arise, you would need to be given specific values for enthalpy, temperature, and entropy in order to find the sign of Gibbs Free Energy. Either that, or you would need to be given some means to find those values. Without that information you would be unable to determine the s...

Michael Torres 4I

It's a good idea to learn to draw basic Lewis structures for these types of problems. The structures for these problems are generally pretty basic, but having the image available to you can make adding and subtracting bonds much easier, even if it is rather simplistic. You don't really need to know ...

Michael Torres 4I

OMG

Did you hear that Oxygen and Magnesium are a couple?

Michael Torres 4I

The book mentions that a state function does not need to be composed of state functions itself to be a state function. Therefore, the fact that internal energy is composed of work and heat, neither of which are state functions, does not stop internal energy from being a state function. Thus, the cha...

Michael Torres 4I

This equation would be most applicable when calculating the change in entropy from a pressure change.

Michael Torres 4I

The class will consist of Lavelle reviewing material through the means of past exam questions.

Michael Torres 4I

It might be useful to keep in mind that an adiabatic system will have a constant heat. As such, temperature will also be unchanging due to the insulation provided. I did not see any problems relating to this concept, but it might be useful to know what the term means, especially since both the book ...

Michael Torres 4I

Gibbs free energy starts at 4J. Lavelle said in lecture that Gibbs free energy would not be covered on the midterm. The topic before Gibbs free energy is global changes in free entropy. Therefore, I would probably just do all the homework exercises up through 4I (Global Changes in Entropy) without d...

Michael Torres 4I

Internal energy is composed of kinetic and potential energy. Specifically, the translational and rotational energy components of internal energy are fully composed of kinetic energy, while the vibrational component is composed of both kinetic and potential energy. U(m) = 3/2nRT because the internal ...

Michael Torres 4I

If the question requires you to use moles, it will give you that information or the information necessary to find the number of moles. Is there a specific question which you may be referencing?

Michael Torres 4I

Delta U can be calculated by adding q and w. Since we are just finding the change in internal energy, delta U can be understood as a state function regardless of what its components might be because we are just concerned with finding the differences between final and initial conditions.

Michael Torres 4I

You will know to use this based on whether you are dealing with ideal gas conditions and based on what kind of information you are given relating to heat capacity.

The information given in terms of constant volume or constant pressure should also help determine what you need.

Michael Torres 4I

Since the midterm will cover entropy, I think at least some, if not all, of the material within the sections of 2nd and 3rd laws of thermodynamics will be covered. However, I recommend just going to lecture to listen to specific things Lavelle goes over to get a solid grasp of exactly what you will ...

Michael Torres 4I

What this means is that you have to take into account intermediate steps when accounting for the total work performed rather than the total change between the initial and final states.

Michael Torres 4I

Adding on to the previous explanation, something that is not a state function would be work. Going from one place to another may done differently, and therefore different amounts of work may be required to get from one place to another. On the other hand, enthalpy has no such possibilities for alter...

Michael Torres 4I

Changing pressure by adding inert gas does not affect the reaction. It may slow down the reaction's rate somewhat, but it will not affect the equilibrium constant or the reaction quotient. On the other hand, changing pressure by altering volume does alter the reaction quotient. Concentration in term...

Michael Torres 4I

A changes from about 27.5 to about 17.5. C changes from 0 to 10. B changes from 0 to 5. If the change in values is understood as X, then X = 5. B's value increased by X, whereas the values of A and C both changed by 2X. Therefore, K = ([2X]^2[X])/[27.5-2X]^2 in the form of ([C]^c[B]^b)/[A]^a. As see...

Michael Torres 4I

Because the question asks for the percentage protonation of the following solutes, then you can assume that the solutes that are given are bases. Bases can become protonated whereas acids become deprotonated.

Michael Torres 4I

I think what this means is that pressure is decreasing through an increase in volume.

In response to such an increase of volume, the concentration or partial pressure values of the gasses your reaction depends on would decrease.

Michael Torres 4I

Yes, you would assume that the concentration of the hydronium ions equals that of hydroxide ions.

Michael Torres 4I

I was also confused about this. I assumed this may have just been an error in the book.

Michael Torres 4I

I believe you are free to make the approximation you mentioned both in quadratics and cubics. The source for my answer is question 5I.29. The equation would have ended up being a quadratic, but the solutions manual displayed usage of the aforementioned approximation.

Michael Torres 4I

The Kc of the reverse reaction is related to the Kc of the forward reaction because these two values are reciprocals of each other.

If the Kc of the forward reaction is X, then the Kc of the reverse reaction is 1/X.

Michael Torres 4I

Q is the reaction quotient. You can find Q just as you would find K by finding the ratio aA<>bB as [B]^b/[A]^a. Q can give you a ratio of products to reactants, which you can then compare to K in order to see where the reaction will head in order to reach equilibrium, expressed as the value of K. If...

Michael Torres 4I

I think the flasks are displayed in chronological order from left to right. Therefore, the reaction is at equilibrium in both flasks 3 and 4. However, because flask 3 occurs first, it displays the point in time when the reaction first reached equilibrium. By the time the reaction reached the state d...

Michael Torres 4I

I think it depends on what the question gives you. For example, take a look at 5H.3 in the seventh edition. It specifically asks you to take into consideration the equilibrium constants for reactions occurring at 300K, despite the fact that all the products and reactants in the reactions are gases. ...

Michael Torres 4I

I believe Lavelle mentioned in one of the modules that the temperature will be given to you. You will not have to assume which is correct.

Michael Torres 4I

If there had been initial values for ADP or Pi, you would have added those values to the change each individual value underwent in order to find their equilibrium values. When finding the equilibrium value for the molarity of a particular substance, add the change in molarity to the initial value of...

Michael Torres 4I

I think it would be a good idea to memorize the more common acids that show up. However, my TA said that Lavelle told her we should not have to worry too much about memorization. Regardless, I recommend you do some memorizing just to be safe.

Michael Torres 4I

If something is a strong acid, then it will be a weaker base. Weaker acids will also be stronger bases.

Michael Torres 4I

When comparing the strengths of acids such HOI and HOCl, the electronegativities of the Cl or I ions is important because these atoms pull electrons away from the HO bond toward themselves. This weakens the bond between the O and H atoms. The weaker the bond is, the stronger the acid will be since i...

Michael Torres 4I

When Boron accepts lone pairs from water in the form of OH-, it is acting as a Lewis acid. After all, a Lewis acid is defined as an acid which accepts lone pairs.

Rather than being a Bronsted acid which donates protons, it is a Lewis acid that accepts electron pairs.

Michael Torres 4I

You add an -ate at the end if the coordination complex as a whole has a negative charge.

Michael Torres 4I

Bond angles in a tetrahedral structure are approximately 109.5 degrees. Bond length depends on the atoms themselves. Therefore, bonds between different types of atoms can have different lengths. For example, due to the fact atoms with larger atomic radii tend to have longer bonds, a bond between a s...

Michael Torres 4I

The ligand is the molecule which binds to the transition metal in a coordination complex. Therefore, in response to your question, the status of ligand is conditional. It is granted to the molecule based on whether it has bonded to the central metal ion or atom.

Michael Torres 4I

Yes, I believe they do. Finding the hybrid orbitals of an atom can thus be facilitated by knowing beforehand how many regions of electron density are around it.

Michael Torres 4I

I have had no issue using 3.0*10^8 m/s on my exams. I recommend asking your TA about the problem you missed to see what they recommend.

Michael Torres 4I

You can determine whether a molecule is polar based on its symmetry. For example, if you have a trigonal planar structure with BCl3, then you know it will be nonpolar because the partial negative charges of the Cl atoms will be positioned symmetrically in such a manner that they cancel out. On the o...

Michael Torres 4I

The molecular shape of ICl3 is T-shaped. Therefore, because of the repulsion exerted by the two lone pairs the bond angle of ClICl should be slightly less than 90 degrees between a Cl atom located in the axial position and the Cl atom in the equatorial position.

Michael Torres 4I

You must remember to take into account the area of electron density present due to the lone pair of nitrogen. Nitrogen has 5 valence electrons. It uses 1 to make a covalent bond with fluorine and 2 to make a covalent bond with oxygen. After using 3, it has 2 remaining. These two create a trigonal pl...

Michael Torres 4I

I think it would be good to know the exact angles of the trigonal pyramidal structure. However, saying less than 109.5 should probably suffice if you don't know it since Lavelle already said we don't need to know the specific value.

Michael Torres 4I

You know you would be unable to do C-C because that doesn't have an angle. That's just a bond. Triangles have angles on their corners because there are lines pointing in two different directions from each corner. If you tried to find the angle of the bond between two atoms you would just get 180 deg...

Michael Torres 4I

I recommend asking a TA or Lavelle specifically about this. However, the syllabus itself says we can receive 3 points per week from the weekly online discussion. Therefore, I would assume that the intent behind this is that you are active on a weekly basis. Based on that assumption, I would arrive a...

Michael Torres 4I

Yes, it would be polar since the dipole interactions would not cancel out. Overall, this molecule would experience a net dipole moment, and it would be polar.

Michael Torres 4I

I think finding an average of the given bond values is the best way to find the bond length in the resonance structure. It may not be necessarily exact or equal to the actual observed value, but it should be fairly close.

Michael Torres 4I

Dipole-Dipole interactions, Induced-Dipole Induced-Dipole interactions, hydrogen bonds, etc are responsible for binding molecules of different substances together. The more of these you have and the stronger they are, they more tightly bound this substance will be. For example, because H2S lacks hyd...

Michael Torres 4I

You can know the difference between them by electronegativity difference. If the electronegativity difference between the atoms involved in a bond is 2 or above, you know the bond is ionic. If the difference is 1.5 or below, then you know it's covalent. Professor Lavelle said the area in between 2 a...

Michael Torres 4I

Yes, you are correct. However, if the difference in electronegativity is over 2, you should consider the bond to be ionic.

Michael Torres 4I

Hydrogen bonds can exist between hydrogen and nitrogen, oxygen, or fluorine atoms. Because H2O possesses hydrogen bonds in addition to covalent bonds, it can stick together better than H2S. Therefore, it has a higher melting point.

Michael Torres 4I

For 8b, why can't you use Ek = hc/λ to find the kinetic energy then proceed to solve for frequency using this value + the work function all over h? The variable c incorporates the speed of light into the equation, but ejected electrons cannot travel at the speed of light. Therefore this cannot work...

Michael Torres 4I

My TA said the midterm would be about as difficult as Test 2. I don’t know how this compares to the homework problems, but I suggest you do as many as possible to prepare. The concepts in the homework problems should at least be similar.

Michael Torres 4I

What this means is that in ionic bonds, the cation may distort the electrons on the anion. Although this is an ionic bond in which the anion has pulled the electrons away from the cation, the cation's positive charge still affects the electrons around the anion. Thus, the anion electrons' orbitals m...

Michael Torres 4I

You should count each paired electron as one, and you should also see the bonds as having two electrons. The formula to find the formal charge is the following. Formal charge = valence electrons - (lone electrons + 0.5(bond electrons)) Therefore, although each bond has two electrons, you will be add...

Michael Torres 4I

The possible quantum numbers of a 3p orbital include the following.

n=3
l=1
m(l)=-1, 0, 1
m(s)=-0.5, 0.5

These may be written as the following sets of {n, l, m(l), m(s)}.

{3, 1, -1, 0.5}
{3, 1, 0, 0.5}
{3, 1, 1, 0.5}
{3, 1, -1, -0.5}
{3, 1, 0, -0.5}
{3, 1, 1, -0.5}

Michael Torres 4I

1. You can check your grades via CCLE. If you are curious about a certain grade that isn't posted, you may want to consider asking your TA about it directly. 2. There is no curve. Rather, grades are assigned based upon the class average out of 500 points. This is not calculated until after all the p...

Michael Torres 4I

Yukta Italia 3I wrote:So are elements with high electron affinity most likely to form anions?

Elements with a high electron affinity are more likely to form anions than elements with a lower electron affinity.

Michael Torres 4I

m(l) refers to the different orbitals in a subshell l. The s-subshell (l = 0) has one orbital, so m(l) has the value of 0. The p-subshell (l = 1) has three orbitals, so m(l) has the values of -1, 0, +1. The d-subshell (l = 2) has five orbitals, so m(l) has the values of -2, -1, 0, +1, +2. This patte...

Michael Torres 4I

In addition to what others have said I also recommend taking into consideration Hund's Rule and the electron configuration exceptions Lavelle mentioned (Cr and Cu) whenever asked anything about electron spin even if you may not know the specific spin of an electron in an orbital.

Michael Torres 4I

I believe most equations that you need will be given. However, I heard from a TA that you should memorize equations utilizing the Rydberg constant.

Michael Torres 4I

(lambda)=c(nu) really only works for photons and electromagnetic radiation because it incorporates the speed of light. Neutrons do not travel at the speed of light. When dealing with objects that have rest mass, you should use DeBroglie's equation.

Michael Torres 4I

Which of these equations you use ultimately depends on the information you are given. However, they should both be used when dealing with the wavelengths of electromagnetic radiation. Therefore, yes, you would specifically use these equations when dealing with photons.

Michael Torres 4I

The problem with using (lambda) = hc/E in this case is that it can only be applied to light or something without rest mass. Because the electron has rest mass, DeBroglie's equation must be used. (lambda) = hc/E can be used to find the wavelengths of electromagnetic radiation, whereas DeBroglie's equ...

Michael Torres 4I

Plasma is defined as being an ionized gas consisting of free electrons and positive ions. Plasma is created when a gas is exposed to high temperatures, or as would occur in this case, an electrical current. Because the current makes the atoms in the gas move very quickly, the electrons get knocked o...

Michael Torres 4I

For the work function, I got 1.506 x 10^5 J, but on the post assessment survey for photoelectric effect, the answer showed up as wrong. Would the frequency be (1.99 x 10^-19)/(6.626 x 10^-34) = 3.01 x 10^-14 Hz? I'm not sure about your first question. However, for your second question consider the ...

Michael Torres 4I

I recommend memorizing whichever constants and formulas you can, but don't stress about it too much. I can recall hearing that a formula sheet would be provided, but you should still play around with all the formulas just to make sure you understand everything before the exam.

Michael Torres 4I

To find the frequency for 2.5 nm use the equation (speed of light)=(wavelength)(frequency). You can start off by converting the wavelength to meters so you're using proper SI units. You need to do this because you're also using the speed of light in meters. Next, arrange the equation as (speed of li...

Michael Torres 4I

Avogadro's constant still applies. For example, in chlorine gas (Cl2), there are 6.022 * 10^23 molecules of Cl2 per mol. Avogadro's constant can refer to the number of atoms, molecules, or formula units depending on the substance in question.

Michael Torres 4I

So this problem was really easy at the beginning, but it quickly turned hard at the end. The question is " G.25 Practitioners of the branch of alternative medicine known as homeopathy claim that very dilute solutions of substances can have an effect. Is the claim plausible? To explore this que...

Michael Torres 4I

Is the conversion between US units and SI units given in the tests? Thanks! In response to your question, I think it would be very likely that these conversions would be given if they are necessary. I cannot say for certain whether or not this is the case, though. I recommend asking during office h...

Michael Torres 4I

I do believe office hours start this week (Week 1), and I think peer learning sessions start next week (Week 2).

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