CHEMISTRY COMMUNITY

Alex Nguyen 3I

Why does cyclooctene have more ring strain than cyclohexane? Does it have something to do with the double bond?

Alex Nguyen 3I

Delta G= Delta H - TDeltaS
Not sure, but this is how I thought of it. Delta H is only valid under constant pressure (heat under constant pressure), and temperature in the equation isn't changing (it's not delta T). It's constant.

Alex Nguyen 3I

It's usually just the diatomic molecules H2, N2, F2, O2, I2, Cl2, Br2 in their natural phase (room temp). I think it's gaseous for all and liquid for bromine.

Alex Nguyen 3I

1 gram is about 1 mL

Alex Nguyen 3I

They divide by 4 moles first to get it to be per mole. Then after it's per mole, they multiply by 2 to get it per the reaction.

Alex Nguyen 3I

Constitutional isomers usually just refers to reordering an alkane single bonded chain. Geometric usually has to do with the double bonds or rings.

Alex Nguyen 3I

I don't know the exact details, but equatorial substituents are always the most stable, and if you have two substituents on the same carbon, then the most stable conformation will be the one where the heaver substituent is equatorial.

Alex Nguyen 3I

How could you tell which chair is more stable given that they both have two substituents in the equatorial position, one being cis and the other being trans? I don't have a specific molecule, but would it depend on where the substituents are located (possibly further away being more stable)? Also, I...

Alex Nguyen 3I

Well the change in gas actually negative 2. That's because there's 3 moles of gas on the left side and 1 mole of gas on the right side. Also if you're confused, water is a liquid in this reaction and not a gas because it says the temperature is constant at 25 degrees celsius.

Alex Nguyen 3I

Tert is a substituent that happens to look like a capital T.

Alex Nguyen 3I

Try looking at the electronegativity of the atoms in comparison to the central atom. If the central atom is delta negative then it will probably be a nucleophile and an electrophile is delta positive.

Alex Nguyen 3I

I think the heat cancels the work. I think of it as temperature being the only thing that can change internal energy, and there's no change in temperature in an isothermal process.

Alex Nguyen 3I

How could you tell which chair is more stable given that they both have two substituents in the equatorial position, one being cis and the other being trans? I don't have a specific molecule, but would it depend on where the substituents are located (possibly further away being more stable)?

Alex Nguyen 3I

Only a catalyst can change the activation energy. The change in k could have resulted from a temperature change. However, when Ea changes, k does change but not the other way around.

Alex Nguyen 3I

Using the equation with volume change already accounts for the pressure change because of PV=nRT. Therefore you can use one or the other when finding the entropy. Only when there's a temperature change with a volume/pressure change do you need 2 equations with a combined entropy.

Alex Nguyen 3I

For an irreversible isotherm process, would the work just be -PdeltaV?

Alex Nguyen 3I

Where does E/Z exist besides for double bonds? Would it be on all rings with substituents or only cyclohexane (ring or chair conformation?). If a cyclohexane had 3 substituents for example 1,3,5-trimethylcyclohexane, then what do you do for E/Z?

Alex Nguyen 3I

The oxygens bonded to the carbon are more electronegative making C slightly positive. Therefore, it wants electrons.

Alex Nguyen 3I

Is cis and trans only found on double bonds and cycloalkanes with substituents (or is it only cyclohexane)? Also, how would you designate cis and trans for 3 substituents (if you can)?

Alex Nguyen 3I

Can cis and trans for a chair conformation only exist for 2 and only 2 substituents (what if there's 3 or 4)? Also, does the stability of a cis or trans chair change depending on how close or far they are to each other (all in equatorial position)? Are substituents that are furthest apart most stabl...

Alex Nguyen 3I

Suppose 1.00 mol of methane is combusted irreversibly at constant room temperature (25 degrees C). Calculate the work associated with this process. In the solution, it indicates the process as: CH4(g) + 2O2(g) --> 2H2O(l) + CO2(g) and that delta n(gas) = -2.00 Isn't H2O water vapor (gas) not liquid?...

Alex Nguyen 3I

In the reaction, a double bond between the 1st and 2nd carbon is attacking the hydrogen. In the book, the H from HBr bonds to the first carbon in propene, and the bromide eventually bonds to the 2nd carbon prdocuging 2-Bromopropane as the final product. Could you/should you bond the bromide with the...

Alex Nguyen 3I

How do we know that the electrophiloc addition of HBr to 2-Butene is an exergonic reaction, delta G is negative, and that the reaction is favorable without knowing what the profile looks like.

Alex Nguyen 3I

How would you name 2,3-dimethylbutane using common names? Would there be 2 iso groups?

Alex Nguyen 3I

2,3-methylbutane looks like it has 2 isohexanes. Is this correct? Also, how would you name 2 iso structures at once.

Alex Nguyen 3I

When using common names, should you just recognize them by structure as opposed to connectivity by formula (i.e. iso-(CH3)2CH)? For 5,
5-Isobutyl-4methylnonane, it looks like the substituent has a CH2 in there which doesn't seem iso from the formula. However, it does look like the isobutyl shape.

Alex Nguyen 3I

Do SN2 reactions always imply 1 transition state, and do SN1 reactions always imply 2 transition states? Also, what would the transition states be for the SN1 reaction between HO- and CH3Br? I think one of the transition states is going to be CH3 with the Br broken off. What would the second transit...

Alex Nguyen 3I

I think that decomposition is the same thing as consumption, just more specific. The orders will therefore not be different as long as you're talking about the initial rates of reactant consumption. Hope this helps.

Alex Nguyen 3I

F_{2}(g)+2H^{+}(aq)+2e^{-}\rightarrow 2HF(aq),E^{o}=+3.03V F_{2}(g)+2e^{-}\rightarrow 2F^{-}(aq),E^{o}=+2.87V Calculate the value of Ka for HF. Can some explain to me the idea behind Ka again as well as why they assumed that potential difference would be nega...

Alex Nguyen 3I

Yeah sure. F_{2}(g)+2H^{+}(aq)+2e^{-}\rightarrow 2HF(aq),E^{o}=+3.03V F_{2}(g)+2e^{-}\rightarrow 2F^{-}(aq),E^{o}=+2.87V Calculate the value of Ka for HF. Can some explain to me the idea behind Ka again as well as why they assumed that potential difference wou...

Alex Nguyen 3I

I'm confused as to why it is assumed that the potential difference of the cell is going to be negative. We are trying to find the Ka for HF. Is it because we need H and F to be products and HF to be a reactant that we flip the half reactions accordingly?

Alex Nguyen 3I

To find K, I used E not=RT/nF(lnK) in order to find K. However, when I used log K=n*E not/0.0592, the answer was different. Is this right? If so, which equation should be used?

Alex Nguyen 3I

Use the bond enthalpies given in the table below to estimate the reaction enthalpy for burning 1 mol of Butane: C4H10 (g) + O2 (g) --> CO2 (g) + H20 (g) The answer was -2186kJ and I got -4372kJ from balancing the equation using whole numbers, which is double the answer. How would you know to use 13/...

Alex Nguyen 3I

It might have to do with the fact that although work is being done and energy is being used, the same energy is put back into the system in order to keep the system at a constant temperature. Hope this helps.

Alex Nguyen 3I

I could be wrong, but I think it might have something to do with the fact that gaseous molecules are much more loose than the rigid molecules in a liquid or solid.

Alex Nguyen 3I

Enthalpy is positive when a bond is broken because an energy input is required to break the bond (i.e. heat energy is added to the system from the surrounding-endothermic). The same logic but opposite process is the reason enthalpy is negative when a bond is formed (exothermic).

Alex Nguyen 3I

Does the amount of heat used to change the volume under constant pressure equal the amount of heat used to change the pressure under constant volume for liquids and solids? Is that why their heat capacity is the same under constant pressure or constant volume?

Alex Nguyen 3I

Would heat be used to raise the pressure under constant volume, like how some of it is used to raise the volume under constant pressure as opposed to the temperature?

Alex Nguyen 3I

The specific heat capacity would not change if you had a different amount of the same substance. It'll still be the amount of heat required to raise a gram/mole of that substance by 1 degree celsius or kelvin. Only changing the substance would change the specific heat capacity. That's why specific h...

Alex Nguyen 3I

Using the HH equation for a weak base titrated with a strong acid, would you just use the ratio of the concentration of base over acid still? Does anyone have an example?

Alex Nguyen 3I

How do you use the equation for a titration before the stoichiometric point? For example finding the pH of .100M HCOOH 25mL titrated with 5 mL of .150M NaOH. The pH turns out to be 3.38, and I tried finding the concentration using the new volumes, but it didn't turn out right.

Alex Nguyen 3I

How come you only calculate the pH using only the amount of H+ that is in excess? Why would you not account for the already slightly acidic solution at the stoichiometric point?

Alex Nguyen 3I

After the stoichiometric point, when you are overshooting the weak base sample with acid, what reaction is taking place? Is the salt/acidic anion still being made, or is the strong acid just protonating water at this point?

Alex Nguyen 3I

If you had to make a pH curve for a titration, how would you know when the buffer region ends?

Alex Nguyen 3I

Where on the pH curve is the solution at equilibrium? Is it when the curve levels out? Why is the halfway point to the stoichiometric point where pH=pKa? Also, can someone explain again why when the concentrations of the weak acid and conjugate base are the same, it is an optimum buffer?

Alex Nguyen 3I

Well in the case of water, the same type means the same molecule. Water reacts with water in order to form OH- and H3O+ in very small concentrations of neutral water.

Alex Nguyen 3I

Yeah. A high Ka or high Kb values indicates that more product (conjugate base or acid) is formed, which means closer to complete dissociation. Conversely, a low pKa and low pKb indicate the same thing.

Alex Nguyen 3I

Can someone explain to me how the reaction between sodium hydroxide, sodium hydroxide, and water works? I know that aluminum oxide is acting as an acidic oxide here. It's reacting with a base, so shouldn't salt and a water form? Does this have anything to do with the water being involved as a reacta...

Alex Nguyen 3I

Can anyone explain why formic acid is stronger than acetic acid? I don't fully understand what the solution means when it states that the CH3 group in acetic acid has electron-donating properties.

Alex Nguyen 3I

Can anyone explain why using exponentiation on a pKa2 value for an ion will still give you its Ka value?

Alex Nguyen 3I

I actually wrote the equation down wrong. It's $2NaOH(aq) + Al_{2}O_{3}(s)+3H_{2}O(l)\rightarrow 2Na[Al(OH)_{4}](aq)$ , which is balanced, but I'm not sure if the transition metal complex is a salt or not.

Alex Nguyen 3I

For the reaction $MgO(s) + 2HCl(aq)\rightarrow MgCl_{2}(aq) + H_{2}O(l)$ , the base $O^{2-}$ accepts two protons from the hydronium ions present in the hydrochloric acid solution. Is it assumed that all acidic solutions have $H_{3}O^{+}$ ions that can be used?

Alex Nguyen 3I

Can someone explain to me how the reaction between sodium hydroxide, sodium hydroxide, and water works? 2 NaOH(aq)+Al_{2}O_{3}(s)\rightarrow 2Na[Al(OH)_{4}](aq) I know that aluminum oxide is acting as an acidic oxide here. It's reacting with a base, so shouldn't salt ...

Alex Nguyen 3I

It's kind of like how the way ionization energy works. IE gets much higher after removing the first electron. The negatively charged ion is most stable being neutral, taking an H+ would just make it even more negative. Hope this helps.

Alex Nguyen 3I

Not really sure, but I'm just going to take a guess. Is BrO- the stronger base? Less oxygens means less electronegativity to pull protons. Therefore, BrO- is a weaker acid, and weaker acids are stronger bases? Does this sound right? Hope it helps you out.

Alex Nguyen 3I

Nonmetal oxides are acidic, metal oxides are basic, and I'm not 100% sure, but I think that metalloid oxides (or metal oxides close to the metalloid line) are amphoteric. However, the reactions for amphoteric oxides could be written out in order to determine its character.

Alex Nguyen 3I

Is carbonato a chelating ligand if it is bidentate? If so, can someone explain why? Carbonato can either be mono or bidentate. Is it not listed in the book as bidentate because it is more unstable/strained in this position?

Alex Nguyen 3I

Does it matter if we use the old or new convention for naming anionic ligands? If it doesn't matter, is one preferred over the other on quizzes/tests?

Alex Nguyen 3I

Does the number of atoms with lone pairs determine the maximum number of attachment sites on the ligand? I'm confused about carbonate. The solutions manual says it can either be mono or bidentate, but it has 3 oxygens with lone pairs. Does resonance affect this at all?

Alex Nguyen 3I

Chelating ligands have to be polydentate I think, but how can you tell if the polydentate ligand is chelating by just using the formula?

Alex Nguyen 3I

Does anyone know why a complex with a coordination number of 4 would take on a square-planar shape over a tetrahedral shape or vice versa?

Alex Nguyen 3I

Is cyanido interchangeable with cyano when naming the ligand CN- in coordination compounds or complexes?

Alex Nguyen 3I

I know that most coordination compounds are either square planar, tetrahedral, or octahedral. I don't think we went too much over why since that goes into crystal field theory. The ligand (en)_{3} is polydentate, and I think it forms an octahedral coordination complex. Can anyone explain the...

Alex Nguyen 3I

Can anyone explain to me why the oxidation of cobalt in [CoBr(NH3)5]SO4 is 2? I thought it would have to be 3 for the compound to be neutral since Br has a 1-charge and sulfate has a 2- charge.

Alex Nguyen 3I

Are Lewis structures necessary in determining whether or not a ligand is polydentate? Also, what is the reasoning behind the idea of lone pairs and shape when it comes to whether a ligand is bidentate, tridentate, etc?

Alex Nguyen 3I

I think that's okay. The formal charge doesn't really change the shape of a molecule. Only regions of electron density will contribute to the overall shape. Also I think you mean a charge of 0 not +0. Hope this helps you out.

Alex Nguyen 3I

Dipole moments are just vectors that point towards the more electronegative atom. It would help a lot if you knew the shape of the molecule as well. For example, if you wrote H2O as a linear lewis structure, then the vectors would pull with equal and opposite magnitude towards the oxygens on both si...

Alex Nguyen 3I

From the MO diagram, you could just look at bond order. The higher the bond order, the more stable the molecule (meaning higher Ionization Energy). The lower the bond order, and the opposite is true. Bond order just tells you the number of bonds between the atoms basically. If there are more bonds, ...

Alex Nguyen 3I

Can anyone explain why the shape of a $I_{3}^{-}$ ion is linear? Does it have anything to do with the opposing repulsion of the lone pairs? I believe there are 3 on the central Iodine atom.

Alex Nguyen 3I

Can anyone explain to me what the number of debyes tells you about the atoms/charges/polarity involved? I know that the electric dipole moment tells you polarity/separation of charges in Coulomb meters.

Alex Nguyen 3I

Well, reactivity is typically from atoms without a full valence shell. Therefore in the case of both covalent and ionic bonding, if an octet or another desired number of E is satisfied, the atom will be less likely to react in order to achieve this completeness. For ionic bonds, I know a large amoun...

Alex Nguyen 3I

Just adding on, copper is more stable with a full 3d orbital than with an incomplete 3d orbital and a full 4s orbital. This is experimentally determined data, and it has something to do with the symmetry of the electrons. Same goes for chromium, it is more stable with a half full 3d orbital (i.e. on...

Alex Nguyen 3I

Can someone explain again the reasoning behind 4s being a higher energy state only when the 3d state is being or has been filled?

Alex Nguyen 3I

Logically it would make sense that the uncertainty in the position of a proton would be higher than the uncertainty in the position of an electron because protons have more mass and are confined to the nucleus; whereas, the electron has less mass and can take a position within the atomic radius. How...

Alex Nguyen 3I

So does the 3d state a higher energy level than 4s until it is "occupied" or does the 4s state always have more energy?

Alex Nguyen 3I

Is there any particular reason why the ground state configuration of both $Co^{2+} and Fe^{2+}$ are designated at [Ar] 3d7 and [3d6] respectively? Is it appropriate to leave out the 4s orbital?

Alex Nguyen 3I

I don't necessarily think you can't use the equation (not sure about exams), but the fundamental equation for the energy of an electron at a certain quantum number n, $E=\frac{-hR}{n^{2}}$ , details the transition/direction of an electron much more.

Alex Nguyen 3I

The Indeterminacy Equation is \Delta p\Delta x\geq \frac{h}{4\pi } . Therefore, if you're given the uncertainty or indeterminacy of position, you would use the full range (+/-) since the position can take on any value within the spread right (i.e. 2x the indeterminacy of position)? Would the same id...

Alex Nguyen 3I

Does it have something to do with the idea that the p state has the potential to hold more electrons than s and so on?

Alex Nguyen 3I

I'm having a bit of a hard time imagining the 3 dimensional structure of the atom and its orbitals. So here's what I know/think: The nucleus is in the center, and as n increases so does the distance from the radius. At these distances n=1, n=2, and so on, there are certain shapes/orbitals that get i...

Alex Nguyen 3I

I think that single electron systems only have degenerate energy levels for orbitals/wavefunctions with the same principal quantum number. Therefore for multi-electron systems, different subshells have different energy levels. If this comes from the quantum number l, how does angular momentum affect...

Alex Nguyen 3I

If that's the only value you're given in the problem, then I'd use 1 sig fig. I don't think there should be a problem with 1 sig fig as long as you use scientific notation.

Alex Nguyen 3I

I think both are the same (i.e. an electron is removed from the atom). I know ionization energy is with regards to gases, and threshold energy was associated with the photoelectric effect on a solid metal. Concepts seems pretty similar to me though.

Alex Nguyen 3I

It's really easy to convert from the standard meters to another prefix and vice versa when the value is not in scientific notation. You just need to look at the chart in the course reader. There are 10^{-9} meters in a nanometer. So if you have 10, 20, or 30 meters, you would just say 10*10^{9}, 20*...

Alex Nguyen 3I

Shielding just means that in a multi-electron system/atom the electrons further away from the nucleus have a weaker attraction to the nucleus. The nucleus has less of a pull because other electrons closer to the nucleus repel the outer electrons (i.e. electron-electron repulsion). Valence electrons ...

Alex Nguyen 3I

By model, I mean mathematical model.

Alex Nguyen 3I

I'm not 100% sure, but I think the wave functions model the orbitals that we know about. I don't know too much about Schrodinger's Equation, but the wave functions that do model the orbitals happen to be solutions to the equation.

Alex Nguyen 3I

You might've already figured out that the answer is the photoelectric effect. So in the experiment, a certain light (i.e. EM radiation) was used to attempt to eject an electron from a metal. If light were a wave, then simply increasing the intensity would increase the energy. However, increasing the...

Alex Nguyen 3I

You would look at the atomic number. The higher the atomic number, the higher the nuclear charge. This means that the nucleus will pull on the electrons more, making the atom/ion smaller because of the tightness.

Alex Nguyen 3I

Also, these electron configurations were experimentally determined. The explanation was that the symmetry/balance resulted in more stability, and stability should be the ground state. So technically if the electron configuration of chromium and copper didn't exist this way I suppose they wouldn't tr...

Alex Nguyen 3I

It turns out that both of these atoms are more stable when the electrons "occupy" each orbital for 3d state (i.e. one electron for each of the three orbitals for chromium I think). For copper, it is more stable when the 3d state is fully occupied (i.e. two electrons for the three orbitals)...

Alex Nguyen 3I

Well actually, you could just solve the Fundamental Energy Difference Equation for n2. Change in E= \frac{-hR}{n^{2}}+\frac{hR}{n^{2}} . Just remember that it's Final Level- Initial Level. We know that the final level is 1 because it's in the Lyman Series for UV EM radiation. You're given the wavele...

Alex Nguyen 3I

I actually incorrectly stated "Rydberg Formula" in the place of the fundamental equation $E=\frac{-hR}{n^{2}}$ . I overlooked the placement of the final and initial E levels. It makes much more sense now. Thank you for the replies.

Alex Nguyen 3I

According to the Rydberg Formula, n1 is actually the final energy level I guess you could say. Therefore solving will only work if you designate n1 as being equal to 1. That's just the way the formula is set up. I'm pretty sure n=1 is still the final energy level though.

Alex Nguyen 3I

"In the ultraviolet spectrum of atomic hydrogen, a line is observed at 102.6 nm. Determine the values of n for the initial and final energy levels of the electron during the emission of energy that leads to this spectral line." I know you can do this by solving for frequency (nu) and solvi...

Alex Nguyen 3I

Spectral lines in the same series always end with the same n2 or final energy level. The Lyman series happens to contain all energy transitions that end with n=1. The initial energy level could be any energy level greater than 1 though. For the hydrogen atom, the electron that drops to n=1 will emit...

Alex Nguyen 3I

Can someone explain why the negative sign is a part of the Rydberg Formula again. I think the formula calculates the energy of an electron at a certain level. So why does a negative change result from a lower to higher energy level? I thought that the electron absorbs energy. Conversely, why is the ...

Alex Nguyen 3I

Do the spectral lines on an emission spectrum represent all the different combinations of electrons of a certain atom moving from a higher to a lower energy level? What does the absorption spectrum show, and what do the spectral lines show on that scale. Lastly, is there any significance in the freq...

Alex Nguyen 3I

How is the energy that energizes an electron related to the photon that is emitted if it is ejected. How is the incoming energy related to the energy of an electron if it is not ejected but moves from an energy level to another?

Alex Nguyen 3I

Can anyone explain by the extent of the change in the electrical field at a given point decreases when the frequency decreases? Is the "extent of the change" referring to the slope of the display of the wave?

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