CHEMISTRY COMMUNITY

Jeffrey Hablewitz 2I

What does this formula represent/what is it used for?
P_n ∝ e(-E_n/k_bT)

Jeffrey Hablewitz 2I

Because HNO 3 dissociates completely in solution, they can be written as aqueous ions in the chemical formula. In balancing the oxidation half-reaction, it becomes clear that NO 3 - is not one of the products of the reaction- the question is somewhat misleading when it suggests that Cu(NO 3 ) is bei...

Jeffrey Hablewitz 2I

Besides changing the temperature or introducing a catalyst, are there any ways to change the rate constant of a reaction?

Jeffrey Hablewitz 2I

I understand how the half-life equation is derived from the integrated rate law, but I was curious if there was a conceptual basis for the half-life being independent of initial concentration. I don't understand why the half-life of a first-order reaction wouldn't be dependent on initial concentrati...

Jeffrey Hablewitz 2I

Why does the cell potential of a galvanic cell decrease as the reaction proceeds? And at what point does the cell potential of a galvanic cell equal 0, assuming that the initial potential was some positive value?

Jeffrey Hablewitz 2I

Problem #13 on Sapling asks to find the overall rate law for a reaction given its elementary steps. I was wondering why OH^-, which seems to be an intermediate, is in the overall rate law.

Jeffrey Hablewitz 2I

I had trouble with this one too! Because the equation is balanced for us, the change in charge in one species will give us the overall number of electrons that moved. In this case, 2 Ce 4+ has a net charge of +8, and 2 Ce 3+ have a net charge of +6. Therefore, 2 electrons must have been transferred ...

Jeffrey Hablewitz 2I

Does this mean that you must balance the half-reactions before you can calculate the n for the overall reaction?

Jeffrey Hablewitz 2I

Textbook problem 6L.9 asks "Write balanced half-reactions for the redox reaction of an acidified solution of potassium permanganate and iron(II) chloride." The correct answer is that MnO 4 - is reduced to Mn 2+ and Fe 2+ is oxidized to Fe 3+ . How do you identify which species are being ox...

Jeffrey Hablewitz 2I

How did you know to make Ag⁺(aq) --> Ag(s) when Ag(s) doesnt appear in the chemical formula?

Jeffrey Hablewitz 2I

Textbook problem 6L.6a is "Write the half-reactions and devise a galvanic cell (write a cell diagram) to study each of the following reactions: AgBr(s) ⇌ Ag + (aq) + Br - (aq), a solubility equilibrium. I'm confused by what "solubility equilibrium" means in this context, and how one c...

Jeffrey Hablewitz 2I

What does n in ΔG = -nFE represent, and how do you find it?

Jeffrey Hablewitz 2I

Yes. By definition, oxidation always occurs at the anode and reduction at the cathode. Therefore, electrons flow from the anode to the cathode.

Jeffrey Hablewitz 2I

A galvanic cell is a chemical system where an electric current is generated through a spontaneous redox reaction. A concentration cell is a type of galvanic cell where the reduction and oxidation half-reactions involve the same species. Different concentrations of the species in the anode and cathod...

Jeffrey Hablewitz 2I

For a visual example: A + B --> C + D D + E --> B + F B would be the catalyst C would be the intermediate is B the catalyst in both? I think that this is showing the two elementary steps of the overall reaction A + E (+B) --> C + F (+B). In this case, B is a catalyst in the overall reaction because...

Jeffrey Hablewitz 2I

If an ion is in an aqueous phase, the equilibrium expression should use the concentration of the ion's constituent cation and anion. The KNO 3 in your example doesn't appear in the equilibrium expression because both K + and NO 3 - are spectator ions and arent involved in the reaction. The reaction ...

Jeffrey Hablewitz 2I

If an isobaric compression is performed on an ideal gas, would the temperature of the gas decrease (assuming the moles of gas remained constant)? The ideal gas law holds that V ∝ T, so it seems like the temperature of the system would decrease, but I'm not sure.

Jeffrey Hablewitz 2I

You are correct! Catalysts (most often enzymes) can increase A by aligning the reactants in the proper orientation for a successful collision.

Jeffrey Hablewitz 2I

Is this formula given on the formula sheet? Or are we just expected to memorize it?

Jeffrey Hablewitz 2I

How do you divide the reaction given in 6K.5a (O₃ + Br^- -> O₂ + BrO₃^-) into reduction and oxidation half-reactions? I understand that the Br is oxidized and the O is reduced, but I don't get how these two processes can be divided as they occur in the same molecule.

Jeffrey Hablewitz 2I

Is the water that is produced in combustion generally in the liquid or gaseous phase? Does the Δn of gaseous molecules in a combustion reaction = (mol H₂O + CO₂) - (moles of gaseous reactants)?

Jeffrey Hablewitz 2I

How is the entropy of vaporization of a liquid calculated? In Michael's workshop worksheet #6, he states that one can calculate the entropy of vaporization for water at room temp. I was curious how this is computed.

Jeffrey Hablewitz 2I

Thanks so much!

Jeffrey Hablewitz 2I

What is the relationship between the rate constant of the forward and reverse reaction? Is the rate constant of the reverse reaction the inverse of the forward reaction?

Jeffrey Hablewitz 2I

I was really confused about these too. I find it helpful to draw a picture of the reaction before I try to write the cell diagram notation because it helps me orient what is reacting with what.

Jeffrey Hablewitz 2I

I would definitely recommend the guides on how to balance the reactions in acidic and basic conditions.

Jeffrey Hablewitz 2I

Im pretty sure that only Lavelle's current students can post on chemistry community. I don't think we will be able to post after this quarter.

Jeffrey Hablewitz 2I

I am confused by this statement:
"When pOH is less than pK_b, the acid is deprotonated."
What does it mean for a base to be deprotonated?

Jeffrey Hablewitz 2I

I really enjoyed chemical equilibrium because I thought it was very intuitive.

Jeffrey Hablewitz 2I

The change in internal energy of an ideal gas is dependent on the temperature, pressure, and volume. If one of these is constant, the change in internal energy will be different than if a different aspect was held constant.

Jeffrey Hablewitz 2I

I must have misread the assigned problems. Thanks for the response.

Jeffrey Hablewitz 2I

Thank you for all the responses!

Jeffrey Hablewitz 2I

Delta S total represents the entropy of the system and the surroundings. According to the 2nd law of thermodynamics, spontaneous processes always increase the total entropy of the system and its surroundings, even if the entropy of the system decreases.

Jeffrey Hablewitz 2I

Thanks! All your responses were very helpful.

Jeffrey Hablewitz 2I

Thanks! That was very helpful.

Jeffrey Hablewitz 2I

What is the difference between ΔS and ΔS_total? And why is ΔS_total always greater than 0 in a spontaneous process if ΔS is necessarily positive in a spontaneous reaction?

Jeffrey Hablewitz 2I

4C.5: Predict the contribution of each type of molecular motion to the heat capacity and their total for each of the following atoms and molecules: (a) HCN; (b) C 2 H 6 ; (c) Ar; (d) HBr. Ignore vibrations. I don't remember the types of molecular motion and was wondering if anyone knew which lecture...

Jeffrey Hablewitz 2I

What is the difference between ΔH and ΔH°?

Jeffrey Hablewitz 2I

Does the formula ∆S = nRln(V1/V2) only work for reversible expansion? If so, is there a formula that relates the change in volume in an irreversible expansion to ∆S?

Jeffrey Hablewitz 2I

The equation for the ΔH of the reaction is :

ΔH = (ΔH_H2 + ΔH_Zn²⁺ + 2*ΔH_Cl^-) - (2*ΔH_HCl)

(2*-167.16) appears twice in the ΔH equation because the ΔH of formation for Cl^- is the same as ΔH of formation for HCl. (ΔH of Cl- = -167.16, and ΔH of HCl(aq) = -167.16).

Hope this helps!

Jeffrey Hablewitz 2I

I wonder if the lab skills that would normally be taught in person for 14bl are important for 14cl. If so, it might be a good idea to wait to take 14bl in person fall 2021

Jeffrey Hablewitz 2I

You are right that breaking to bonds of the reactants is an endothermic process. But combustion is always exothermic because the formation of O-H bonds in H 2 O and C=O bonds in CO 2 always releases more energy than required to break the O=O bonds in O 2 and the C-C/C-H bonds in the material being c...

Jeffrey Hablewitz 2I

If the glucose solution was sufficiently concentrated, adding water would cause the equilibrium to shift right, as it would decrease the concentration of glucose (a product). However, in this reaction, the glucose solution is so dilute that changing the volume of solvent would not appreciably change...

Jeffrey Hablewitz 2I

Reversible reactions are almost always isothermal and systems that expand without increasing T are normally the product of a reversible process. Systems that change volume as the result of temperature change are generally irreversible. Also, if the problem states that the pressure of the system is d...

Jeffrey Hablewitz 2I

You are right! Diamond has a relatively low specific heat capacity because of its molecular structure. The carbon molecules in the crystal lattice of a diamond are strongly coupled, so motion in one molecule transmits the kinetic energy to surrounding molecules very efficiently. This decreases the t...

Jeffrey Hablewitz 2I

What is the difference between equilibrium expansion and reversible expansion?

Jeffrey Hablewitz 2I

Are we allowed to take 14C before we take 14BL? If so, do you think it would be worth it to take 14C in the spring and then take 14BL fall of 2021?

Jeffrey Hablewitz 2I

Concentration is moles of solute per volume, represented mathematically as n/V. Pressure is related to concentration but also factors in the temperature of the system. This relationship is seen in the ideal gas law, where P ∝ T*(n/V).

Jeffrey Hablewitz 2I

Concentration is moles of solute per volume, represented mathematically as n/V. Pressure is related to concentration but also factors in the temperature of the system. This relationship is seen in the ideal gas law, where P ∝ T*(n/V).

Jeffrey Hablewitz 2I

The bond between a ligand and a TM in a coordination compound is a coordinate covalent bond. Coordinate covalent bonds form when a lewis base donates a pair of electrons to a lewis acid. Unlike an ionic bond, the electrons are shared between the two atoms and the bond is often very polar. Remember t...

Jeffrey Hablewitz 2I

You are right that ionization energy generally increases from left to right. However, there are two inconsistencies in the ionization energy of period 2 elements: boron and oxygen. Boron has a lower ionization energy than beryllium because boron has one unpaired electron in the 2p subshell, which is...

Jeffrey Hablewitz 2I

The hydrogen is bonded to the oxygen in each oxoacid, so atomic radius is not really considered when comparing the strengths of these acids (the O-H distance is similar in each acid). Like you said, chlorine has the highest electronegativity (and therefore the strongest electron-withdrawing effect) ...

Jeffrey Hablewitz 2I

Thanks for all the responses! I checked with a TA who confirmed that hard water is alkaline.

Jeffrey Hablewitz 2I

Is hard water acidic or alkaline? I think Lavelle said that hard water is acidic, but a UA and a few other online resources state that it is generally alkaline. It seems like it would make more sense if hard water is alkaline because it contains CO 3 2- ions which would deprotonate H 2 O, but I'm no...

Jeffrey Hablewitz 2I

K a is the dissociation constant of an acid (a measure of how strong an acid is). As its name implies, K a is an intrinsic property of an acid. pK a is just the -log of K a . pH is a measure of the H 3 O + concentration in a solution. If you add an acid to a solution with a pH that is greater than t...

Jeffrey Hablewitz 2I

Here is a list of common ions: https://wps.prenhall.com/wps/media/objects/3079/3153869/tools/common.gif In addition to group one elements, there are three examples of +1 cations: NH 4 +, Cu+, and Ag+ You could figure out that NH 4 is a +1 cation based on the formal charges of the possible lewis stru...

Jeffrey Hablewitz 2I

Because all strong bases completely ionize in solution, it only makes sense to compare the strength of weak bases. This is what I was able to find on how to determine the comparative strength of weak bases: Weak bases do not provide OH- ions by dissociation. Instead, they react with water to generat...

Jeffrey Hablewitz 2I

The fact that pi bonds cant rotate affects the shape, and therefore reactivity, of some molecules. It is particularly important in the shape of organic molecules. This website has a pretty good description : https://chem.libretexts.org/Courses/Sacramento_City_College/SCC%3A_Chem_420_-_Organic_Chemis...

Jeffrey Hablewitz 2I

Is it possible to determine the comparative length of bonds? Did you have to look up the bond lengths for C-N and C-O, or is there some way you can tell which is shorter using trends in the periodic table?

Jeffrey Hablewitz 2I

How can you determine the comparative strength of single bonds? For example, how would you determine if a single bond between a carbon and nitrogen is stronger than a single bond between a carbon and oxygen? Does it have something to do with the difference in electronegativity?

Jeffrey Hablewitz 2I

I find it helpful to use examples to understand delocalized pi bonding. Let's use ozone (O 3 ). The lewis structures for ozone are O=O-O and O-O=O. We know that the real structure of ozone is a combination of the two resonance structures - the oxygens are bound by two bonds of equal length that are ...

Jeffrey Hablewitz 2I

Hybridization accounts for equal orbitals in the same plane. Single bonds occur when one of these planar (and hybridized) orbitals sigma-bonds with an orbital on a nearby atom. Double bonds occur when a sigma bond forms (like a single bond), but also requires that one orthogonal orbital bond to an o...

Jeffrey Hablewitz 2I

Hybridization accounts for equal orbitals in the same plane. Single bonds occur when one of these planar (and hybridized) orbitals sigma-bonds with an orbital on a nearby atom. Double bonds occur when a sigma bond forms (like a single bond), but also requires that one orthogonal orbital bond to an o...

Jeffrey Hablewitz 2I

Bond angles are experimentally determined, but generally follow the rules we learned in lecture (trigonal planar molecules have bond angles of 120, tetrahedral have 109.5, etc.) Factors that affect bond angles are lone pairs, which we discussed in class, and the relative size of the peripheral atoms...

Jeffrey Hablewitz 2I

I believe the equations are showing that each hybrid sp 3 orbital is the sum of the wave functions of the component orbitals. Adding together wave functions is essentially measuring wave interference. The signs assigned to each orbital on the right side of the equation represent whether the interfer...

Jeffrey Hablewitz 2I

Thanks for the response! I'm pretty sure ligands can be molecules or atoms as long as they have a lone pair that can be donated to the central transition metal. I was wondering why transition metals sometimes form ionic compounds, as is the case with FeCl 3 , and why they sometimes form coordinate c...

Jeffrey Hablewitz 2I

When do transition metals form coordinate compounds and when do they form traditional ions? For example, is NiCl2 an ionic compound or a coordination compound, and why?

Jeffrey Hablewitz 2I

Thanks, your response was very helpful!

Jeffrey Hablewitz 2I

How does pi bonding occur if the orbitals of bound atoms hybridize to form orbitals based on areas of electron density? For example, it is my understanding that a double bond would result when a p-orbital electron and s-orbital electron from one atom match with a p-orbital electron and an s-orbital ...

Jeffrey Hablewitz 2I

In lecture #22, Dr. Lavelle explains that the geometry of cis-dichloroethene is fixed because the pi-bond between the carbons prevents them from rotating. I understand why the carbons can't rotate, but I was wondering why the chlorine and hydrogen cant rotate around the fixed carbon. The chlorine an...

Jeffrey Hablewitz 2I

VSEPR notation always includes A to represent the central atom, so I think this is a mistake. Hope this helps

Jeffrey Hablewitz 2I

Do all lewis bases have lone pairs on the central atom? Are all molecules with lone pairs on the central atom considered lewis bases?

Jeffrey Hablewitz 2I

The difference in electronegativity between carbon and hydrogen is so small that a H-C bond is nearly nonpolar. It definitely isn't as polar as a H-N bond, which is so polar it exhibits hydrogen bonding. Hope this helps!

Jeffrey Hablewitz 2I

Oxygen almost always has an oxidation number of -2. Because the net charge of the ion equals -1, the sum of the oxidation numbers must equal -1. Therefore, the oxidation number for Cl can be solved algebraically: 4(-2)+x=-1, where x = oxidation number of Cl. In this case, chlorine's oxidation number...

Jeffrey Hablewitz 2I

While you could technically have double bonds between the oxygens and phosphorus, it is far less energetically favorable. Because oxygen is more electronegative than phosphorus the negative formal charges should be placed on the oxygen atoms. In general, when a molecule must have negative formal cha...

Jeffrey Hablewitz 2I

Would ion-dipole attraction occur between an ion and a symmetrical molecule that has bond dipoles? For example, would Na+ ions be attracted to the Cl atoms in CCl₄ ? CCl₄ is a nonpolar molecule, but I believe the Cl atoms still have a ẟ- charge.

Jeffrey Hablewitz 2I

You're right! Hydrogen bonding occurs because the electrostatic attraction between two oppositely oriented dipole moments is very strong. These dipole-dipole interactions are so strong because the atomic radii of nitrogen, oxygen, and fluorine are very small. Electronegativity is related to atomic r...

Jeffrey Hablewitz 2I

I was curious about this too, and this is what I found online: - Percent ionic character/percent covalent character is most relevant in determining the bond character of ionic compounds. - In molecules, where the bonds between atoms are overwhelmingly covalent, % covalent character is less important...

Jeffrey Hablewitz 2I

The way I solved that problem was by comparing the experimentally determined bond length to the expected bond length. If the experimental bond length was somewhere between the expected bond length for a double bond and a single bond, I figured the bond exhibited characteristics of both a single and ...

Jeffrey Hablewitz 2I

What is the difference between the percent ionic character and the electric dipole moment of a bond? Does % ionic character only apply to ions?

Jeffrey Hablewitz 2I

I was curious why the 4s subshell fills before the 3d subshell in ground-state period-4 transition metals. As the 4s subshell is listed after the 3d subshell in the electron configurations, I assumed that the 4s subshell is more energetic. Assuming this is correct, why would the electrons fill the 4...

Jeffrey Hablewitz 2I

The quantum number ml indicates which orbital the electron belongs to, and there can only be two electrons in the same orbital. Therefore, a maximum of two electrons can occupy the same energy level (n), subshell (l), orbital (ml).

Jeffrey Hablewitz 2I

The way I solved it is : I calculated the energy per photon (3.13 * 10^-19 joules) and multiplied this value by the number of photons produced per second (2.4 * 10^21). This gave me the amount of energy in joules per second (751 J/sec). Because 1joule/sec = 1 watt, the answer is 751 watts. This is r...

Jeffrey Hablewitz 2I

Yes. Dr. Lavelle said at the end of lecture #9 that all material on the midterm had been covered by that point.

Jeffrey Hablewitz 2I

I was curious about this too. conceptually, I don't understand why would the work function be equivalent to the electron affinity conceptually.

Jeffrey Hablewitz 2I

I believe Dr. Lavelle said that everything covered up to the end of lecture #9 will be covered on the midterm. Lecture #9 included information on orbitals in the context of Schrodinger equation, so I assume it will be on the midterm.

Jeffrey Hablewitz 2I

I believe nitrogen has a higher ionization energy than oxygen because it has a half-full P shell, which is more stable than a p-shell with 2 paired electrons as found in oxygen. Oxygen has a lower ie than fluorine because of the periodic trends in atomic radius.

Jeffrey Hablewitz 2I

Thanks for the response. I also realized that the nucleus of a hydrogen atom is usually only one proton, so the measurement Dr. Lavelle used was the diameter of a proton. This might have contributed to the really high uncertainty.

Jeffrey Hablewitz 2I

Because an electron is being emitted, the energy of the electron must be negative. The correct formula is -hv=(-hR/n^2)-(-hR/n^2). Note the negative in front of the first term hv, which denotes the negative energy. When you plug the values into this formula you get n=6. Hope this helps!

Jeffrey Hablewitz 2I

In lecture 9, Dr. Lavelle works an example which shows that the uncertainty in the velocity of an electron contained in the nucleus of an atom exceeds the speed of light. Using this reasoning, I attempted to calculate the uncertainty in the velocity of a proton, which we know is contained in the nuc...

Jeffrey Hablewitz 2I

Waves with different frequencies would still interfere with each other, but the resulting interference pattern would be far more complex. I think the interference pattern could be determined using the superposition principle.

Jeffrey Hablewitz 2I

The Heisenberg uncertainty principle formula requires one to quantify the uncertainty of momentum and position. How do you find the uncertainty of an object? What units is it measured in?

Jeffrey Hablewitz 2I

E=hv defines the energy of a photon (hv = Ephoton). Therefore you can replace Ephoton with hv in any formula, including the one used for the photoelectric effect.

Jeffrey Hablewitz 2I

You begin with the formula v=R(\frac{1}{final level^2}-\frac{1}{initial level^2}) . The problem gives the frequency as 1.14*10^14Hz (v), and the final energy level as 4. Rydberg's constant is 3.29*10^15. You are trying to solve for the intitial level. When you plug those numbers in you will ...

Jeffrey Hablewitz 2I

Photons do not have mass, but experiments confirm they have momentum. This is one of the failings of classical physics.

Jeffrey Hablewitz 2I

The energy of light is directly proportional to frequency as defined in E=h*nu, where h is the Planck constant. Increasing frequency will always result in higher energy light. However, the intensity of light is representative of its amplitude, which is completely independent of the light's energy.

Jeffrey Hablewitz 2I

The .23 grams of 3-methyl-3-hexanol is the actual yield of the reaction. Percent yield = (actual yield)/(theoretical yield), so I believe you can derive the percent yield with the theoretical yield you calculated and the actual yield given in the problem.

Jeffrey Hablewitz 2I

Amplitude is completely independent of wavelength and frequency. Wavelength and frequency are inversely proportional because light moves at a constant velocity, but no such relationship exists between amplitude and wavelength in electromagnetic radiation.

Jeffrey Hablewitz 2I

In a chemical reaction, the amount of products created is always dependent on the amount of reactants consumed during the reaction. The moles of product calculated using the limiting reactant represents a theoretical maximum yield if the reaction goes to completion. It is impossible for more product...

Jeffrey Hablewitz 2I

I believe you can also determine the chemical formula, and therefore molar mass, of the reactants based on their given structures. The reactants and products are shown in bond line notation, which is similar to a Lewis structure. This website has a really brief explanation of bond line structures an...

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