CHEMISTRY COMMUNITY

Benjamin Chen 1H

1. Identify half reactions; balance all the elements except Hydrogen and Oxygen. Reduction: Br2 -> 2Br- Oxidation: Br2 -> 2(BrO3-) 2. Balance Hydrogen and Oxygens in both half reactions, but in this case only for Br2 -> 2(BrO3-) a. There are 6 extra Oxygens in the product's side. - add 6 H2O to the ...

Benjamin Chen 1H

Jeffrey Hablewitz 2I wrote:Does this mean that you must balance the half-reactions before you can calculate the n for the overall reaction?

Yes, you need to balance the number of electrons gained in the reduction half reaction and the number of electrons lost in the oxidation half reaction.

Benjamin Chen 1H

I don't think you need need to find the number of moles since the question is asking for ∆S/n not ∆S.

Benjamin Chen 1H

Just to add, k is attributed to kinetics as a rate constant while K is usually attributed to equilibrium as the equilibrium constant, and K is related to k in that K = forward k / reverse k.

Benjamin Chen 1H

∆S surr = 0 when the process is an Isothermal and Irreversible Free Expansion. No work is being done on or by the surroundings and no net heat is transferred.

Benjamin Chen 1H

If it gained an electron(s) then it was reduced. If it lost an electron(s) then it was oxidized.

Benjamin Chen 1H

n represents the number of moles of electrons transferred in a balanced redox reaction. The 2 is specific to one half reaction and the 6 is specific to the other reaction.

Benjamin Chen 1H

He was just giving an example where you would see zeroth order. A cell with limited enzymes or a reaction with limited concentration of catalysts would become "saturated" when all the enzymes/catalysts were occupied and performing its function at a capped rate. Zeroth order comes into play...

Benjamin Chen 1H

There's the qualitative reasoning by Le Chatelier's Principle where increasing a reactant's concentration above standards would result in a shift in favor of the forward reaction, thus increasing the cell potential. Increasing the a product's concentration above standards would result in a shift in ...

Benjamin Chen 1H

On page 623, it says that the higher the activation energy, the stronger the temperature dependence of the rate constant. Since the forward reaction of this problem has a higher activation energy, the increase in temperature will have a greater impact on it. When you plot ln k vs 1/Temp, higher acti...

Benjamin Chen 1H

Based off of lecture, the order of the reaction and their graphs (and we are only talking about 1 reactant) seems to solely come from calculus. The reason behind each graph is that we prefer lines rather than curves, so it just happens that the math works out so each order of the reaction has a uniq...

Benjamin Chen 1H

Same, I was pretty confused about this. The only thing I can think of is that the pressure of the Hydrogen gas and the molarity of the H+ ions are actually in the unitless activity notation.

Benjamin Chen 1H

I found a post on this from a while ago, hope it helps.

viewtopic.php?t=5141

Benjamin Chen 1H

I have a feeling there is a typo here (but it's not on the Error Manual pdf) because I don't think Chlorine gas reacting with water will produce Chlorine gas again. I think the product was supposed to say Cl- (aq). Just a hunch.

Benjamin Chen 1H

A reversible process (from the thermodynamics section in 4A) is one that can be reversed by an infinitely small change in a variable. Additionally, electrical work is defined as the charge times the potential difference (Q*deltaV) (Table 4A.1) Such systems however are ideal because they are practica...

Benjamin Chen 1H

I feel like the textbook is really great at providing a solid conceptual understanding especially when they use diagrams/pictures to describe a process.

Benjamin Chen 1H

I would think that they would give us the chemical equation, though it might not be balanced.

Benjamin Chen 1H

Something can have residual entropy because it inherently has positional entropy. When T approaches absolute 0, we say that thermal entropy is 0 too. Based on the Thermodynamics outline, it doesn't seem like we need to know how to calculate it.

Benjamin Chen 1H

You would probably use this when there is 1 mole of molecules. For instance if you have 2 state possible for every molecule and you have 2 molecules, then W = 2^2. When you have 1 mole of the molecules, W = 2^(6.022x10^23).

Benjamin Chen 1H

To add, whenever you have standard changes in entropy or enthalpy, those refer to 1 mole of substance being made which in this case is H20.

Benjamin Chen 1H

Heat of fusion is the enthalpy needed when going from Solid to Liquid (melting). Going from Liquid to Solid (freezing) would be the opposite of the Heat of Fusion, thus needing the negative sign. Conceptually it makes sense because melting something requires an input of energy while freezing somethi...

Benjamin Chen 1H

Yes, it was the mathematical "step" where at a certain temperature, there would be small change in q and small change in S to where dS = dq/T and when you sum up an infinitesimal amount of these you for the integral with the bonds T2 and T1.

Benjamin Chen 1H

Cp,m is much more clear but I do believe Professor meant Molar Heat Capacity at Constant Pressure since Cp was being multiplied by n (which has the units moles). I think he did mention that the book likes to differentiate Cp,m and Cp.

Benjamin Chen 1H

I can only imagine using mass times deltaH when deltaH is either in the units of J/grams or some other variant like kJ/kg, etc.

Benjamin Chen 1H

I think it relates back to PV=nRT. This system has constant pressure at that instance but doesn't have constant temperature. As the volume of the gas expands, the only other variable that is not constant is T, so T must change. So as V increases, T decreases.

Benjamin Chen 1H

Based on the table from page 266 in the textbook, those would be the equations you would use. As for determining which one, you will need to determine the gas's Lewis Dot Structure and then the 3D structure for that structure.

Benjamin Chen 1H

q is negative when:
-heat is released
q is positive when:
-heat is absorbed

w is negative when:
-the system does work on the surrounding
w is positive when:
-the surrounding does work on the system

Benjamin Chen 1H

The textbook references to an isothermal expansion of an ideal gas as a reversible process and theses systems are at constant pressure, but when you say reaction, do you mean a reaction doing work or a chemical reaction that has a forward reaction and a backward reaction?

Benjamin Chen 1H

You would probably need to know the two temperatures (T1 and T2) and maybe one of the Equilibrium constants (K1 or K2). Also you might want to know the conceptual understanding of what the equation would look like when the reaction is exothermic or endothermic. Reference to page 433 in the Textbook.

Benjamin Chen 1H

Start by calculating the heat capacity of the calorimeter. Ccal=qcalc \Delta T The heat lost by the reaction, q , is gained by the calorimeter, so −q=qcal . −(−0.882 kJ)=0.882 kJ Ccal=0.882 kJ / 2.43 K = 0.363 kJ/K The heat lost by the reaction and the heat gained by the calorimeter is equal to zero...

Benjamin Chen 1H

Although you are given Cp, you want to use Cv because you are solving for ΔU. In the textbook on page 264, Cp is related to ΔH while Cv is related to ΔU. When you have constant volume, you can't preform work but heat transfer is possible, so only ΔU is related. When you have constant pressure, you c...

Benjamin Chen 1H

You want to use the gas constant 62.364 L Torr/K mol. Using this constant in PV=nRT allows you not to convert from Torr to atm (you can if you want 760 Torr = 1 atm, just use the other gas constant) and you get n which is 4.744 moles. Since everything is in 1 to 1 molar ratios, you don't need to wor...

Benjamin Chen 1H

When you mention "released" you are acknowledging that the system is losing energy as a result of the reaction and thus implying a negative when talking about that system.
You can report it as "the reaction released 1107 kJ" or "the change in enthalpy is -1107 kJ"

Benjamin Chen 1H

When something is considered in it's "standard state" it can be: Gas at 1 atm Solution at 1 Molar at 1 atm Pure liquid or pure solid (they are already in their standard states) Elements at their most stable phases at 1 atm Common Standard States Mentioned in Lecture: N2(g), H2(g), O2(g), F...

Benjamin Chen 1H

I found it on Table 6D.1 page 478 of the book or page 615 of the pdf.

Benjamin Chen 1H

I'm not sure, but I would like to say that this problem was not assigned. The 4E problems are 5, 7, and 9, so I don't think you need to worry about this one.

Benjamin Chen 1H

You would end up with:
Heat Absorbed by RXN = - Heat Given Off by Solution
Heat Absorbed by RXN = - (-#) = +#

The Heat Given Off by Solution would be negative since the temperature change would be negative.

Benjamin Chen 1H

You take into consideration this concept (yes, represented by weak acids or bases) by using the ICE Table and Ka or Kb ratios to determine how much H3O+ was made or OH-. Say if we had a 1 M weak acid (HA) and we add it to a solution of water, the weak acid will not completely dissociate into H+ and ...

Benjamin Chen 1H

Well, it depends on the molecule. I think phase changes include all intermolecular forces present between the molecules of interest. For water, I would agree to also think of London Dispersion Forces, but I don't think it plays much of a role as Hydrogen bonding does.

Benjamin Chen 1H

You will want to start with an ICE table with Lactic Acid (0.1173 M) deprotonating into H+ (initially 0 M) and CH3CH(OH)COO- (initially 0 M). Using the Equilibrium Concentrations plug them into the Acidity Constant ratio with products over reactants. You can assume x is small for (0.1173 M - x) Then...

Benjamin Chen 1H

You can find the Ka and Kb values (at 25 degrees Celsius) in table 6C.1 and 6C.2.

Benjamin Chen 1H

In the problem, the question refers to CH3NH3Cl and probably wants to be consistent with what it is providing. Also, it's just making the connection that CH3NH3Cl is the conjugate acid of CH3NH2 in solution. CH3NH3Cl will dissociate into Cl- and CH3NH3+ so when you write out the chemical equation, y...

Benjamin Chen 1H

For equilibrium problems...probably not or else the reaction wouldn't be in equilibrium.

Benjamin Chen 1H

As far as I can tell, the "+" in front of N is indicating that the formal charge of 1+ is on N (and thus the total charge of NH3OH is 1+). Drawing out the Lewis Dot Structure might be helpful. When you do, Nitrogen will have 4 single bonds (3 with H and 1 with O) and thus a formal charge o...

Benjamin Chen 1H

I wouldn't consider the 60% as a "limiting reagent" since that is not an accurate description. Instead it is simply the change in mols (subsequently, molarity) of the H2 as equilibrium is reached. You're main goal then is to fill out the ICE Table. You would use (60% of 0.400 mol) / (3.00 ...

Benjamin Chen 1H

Does this mean that a pH of 7 isn't neutral if the temperature is higher or lower than the temperature that constitutes a pH of 7 as neutral?

Benjamin Chen 1H

You would want to determine the change in A, B, and C. A starts at 27 P/kPa. A changes by -10 P/kPa. B and C start at 0 P/kPa. B changes by +5 P/kPa. C changes by +10 P/kPa. Since these changes also represent the molar ratios, it tells us the coefficients for the equation. Assuming a change of 5 is ...

Benjamin Chen 1H

Following the progression of events, the equilibrium concentrations ([N2]=[O2]=0.100 M and [NO]=0.500 M) will be used to find the equilibrium constant, Kc. [NO] = 0.800 M will be used as the new initial concentration along with [N2]=[O2]=0.100 M, still. ([NO]=0.500 M is replaced with 0.800 M) This i...

Benjamin Chen 1H

Is there a guideline for determining if a change, after equilibrium is reached, is seen as having "no effect" on some reagent's concentration, like in 5I. 17 where the concentrations of O2 and N2 are said to remain essentially the same?
Thanks.

Benjamin Chen 1H

You'll want to use the ICE or Equilibrium table described in Toolbox 5I.1. When the reaction proceeds, [H2] and [I2] will each decrease by a certain change called "x" while [HI] will increase by "2x" since there is a 1:2 molar ratio between reactants and products. The resulting c...

Benjamin Chen 1H

Hello! Although the problem doesn't tell you how much CO(g) you have, you can still find it. Initially there is no H2(g) but at equilibrium there is 0.04 M which means that the change that occurred was +0.04 M. This also means that there was a +0.04 M for CO(g) because when the reaction proceeds, CO...

Benjamin Chen 1H

I don't really get what you are asking..., but for doing this problem I was able to arrive at the answer by noticing that Kc = Kp since the number of moles of gas in the reactants and the products are the same. Then, I converted everything into partial pressures and then solved for x. After finding ...

Benjamin Chen 1H

I would also like to know this. Does this have to do with the fact that equilibrium constants are in terms of "activity" which is something we don't need to worry about?

Benjamin Chen 1H

Yep, Kc = 11.20. When it says they added 1.00 mol of NO2 means that it is in addition to the given amounts in the context of the problem (1.00 mol/L + 2.28 mol/L of NO2 = 3.28 mol/L of NO2) This means you'll need a new ICE table to accommodate for this change. Initial: 0.464 mol/L for N2O4 3.38 mol/...

Benjamin Chen 1H

Can some one explain how O2- in water makes 2 OH-? I'm confused on where the electrons go to. on the O2- and the H20 to make 2 OH-

Benjamin Chen 1H

Would HSO4- and H2PO4- be considered as amphoteric (if the conditions were right like pH>pka or pH<pka)?

Benjamin Chen 1H

To add, I think neutral Transition Metals in row 4 have 2 valence electrons since the outer most shell is 4s2 (unless they are special cases like Cr and Cu who would have 1 probably). But transition metals are unique since they don't have a filled inner shell (ie the d-orbital electrons).

Benjamin Chen 1H

The pH refers to the solution in which the weak acid is placed into (which has its own pKa value).
The terms basic solution and acidic solution refers to the relative comparison between that pH and pKa value.

Benjamin Chen 1H

I believe so.
Alkaline solutions refers to a mixture of base solids dissolved in water (from the internet).

Benjamin Chen 1H

-ide goes to -ido
-ate goes to -ato
-ite goes to -ito

(from Toolbox 9C.1)

Benjamin Chen 1H

I'm not familiar with the "coordination number of a metal species" but the coordination number of a coordination compound is the number of points at which ligands are attached to the central metal atom.

Benjamin Chen 1H

I count the total negative charge by the ligands (like Cl- means -1) and if the complex is neutral, that the roman numeral for the transition mental would be the total charge (but positive).

I ignore the neutral ligands when determining the charge (roman numeral) on the transition metal.

Benjamin Chen 1H

Yeah, it seems like H2O is higher on the spectrochemical series than Cl-, though I don't know what role electronegativity plays.

Benjamin Chen 1H

The coordination number is equal to the number of coordinate covalent bonds between the ligands and the central transition metal. You can get a general estimate of the coordination number by counting the number of ligands within the coordination sphere (notated by brackets []). The caveat is that so...

Benjamin Chen 1H

I know these hybridized orbitals won't be our focus, but would the energies of these orbitals be lower than the 3d energy level and above the 3p energy level, or is it a little bit more complex than that?

Benjamin Chen 1H

I start with the Lewis Dot structure Apply the VSEPR Model (each bond [single, double, or triple] and/or lone pair(s) will have their own region of electron density) From the number of electron densities in the VSEPR Model, that tells me the number of hybridized orbitals. We apply the bonding model ...

Benjamin Chen 1H

What was the rational behind having an equatorial lone pair in a trigonal bipyramidal (arrangement) molecule rather than an axial lone pair, resulting in a seesaw shape?

Benjamin Chen 1H

Would we consider the single, unpaired electrons on radicals and biradicals each a single region of electron density?

Benjamin Chen 1H

Does anyone have an example for a molecule with two sp hybridized orbitals?

Benjamin Chen 1H

repulsion strength: lone-lone pair > lone-bonding pair > bonding-bonding pair This refers to the repulsion strength between two regions of electron density. There are 3 types of repulsions that can happen in a molecule: lone pair to lone pair repulsion -Example: the two lone pair electrons on H2O re...

Benjamin Chen 1H

Yes. First consider how many regions of electron density there are (lone pairs and bonds [single, double, triple]) and their arrangement. Then consider the arrangement of the electron densities contributed by the bonds only. This will determine the name used to describe the shape of the molecule Car...

Benjamin Chen 1H

The double bond doesn't change the shape to something other than trigonal planar because in the VSEPR Model since we consider single, double, and triple bonds as a single region of electron density. The Lewis Dot structure does have the limitations of being unable to accurately represent a molecule,...

Benjamin Chen 1H

What are the factors that contribute to an atom's/molecule's polarizability when considering the strength of the Dispersion/London/Induced Dipole-Induced Dipole/Van der Waals Force?

Benjamin Chen 1H

In lecture, we were given the example of Cl- and H2O for the Ion-Dipole IMF and it had -15 kJ/mol while in Hydrogen bonding between 2 water molecules it was -20 kJ/mol. Was it only in this specific case that the Hydrogen Bonding interaction was stronger than the Ion-Dipole interaction or is Hydrogen...

Benjamin Chen 1H

α1 represents the polarizability of an atom/molecule α2 represents the polarizability of another (different or the same) atom/molecule r^6 represent the distance between those two atoms/molecules An atom's/molecule's polarizability is proportional to it's molecular mass (more specifically referring ...

Benjamin Chen 1H

Just to add to this, LDF is an intermolecular force meaning it's between other molecules, so the r^6 refers to the distance between two molecules and not the bond length. When considering the strength of the Intermolecular Forces, the bond strength or bond length shouldn't be a big factor for LDF, r...

Benjamin Chen 1H

Yes, when you consider the system as the Na+ and the Cl-.

Benjamin Chen 1H

Since b and d have the magnetic quantum number (ml) that means the electron is restricted to one certain orbital. If you don't indicated the magnetic quantum number (ml) and only the principle and angular quantum numbers, then the electron can be in any of the orbitals of that angular quantum number...

Benjamin Chen 1H

Count total Valence Electrons N: 5 C: 4 S: 6 Charge: 1 more electron Total: 16 Lowest Ionization Energy is the central atom: C (furthest to the left) Start with a single bond between C and N and a single between C and S (to indicate that N, C, and S are bonded) Add 3 pairs of lone pair electrons to ...

Benjamin Chen 1H

Sigma bonds are head-on electron orbital overlaps while pi bonds are side-by-side electron orbital overlaps.

We haven't covered this yet. This has to do with VSEPR theory.

Benjamin Chen 1H

The main difference for me is that Electron Affinity is experimentally determined while Electronegativity is calculated from Electron Affinity and Ionization Energy. Electron Affinity is the Energy released when an electron is added to an atom (in gas phase) (Ionization Energy is the Energy needed t...

Benjamin Chen 1H

Hydrogen Bonding isn't a true chemical bond but it's an attraction between a partial positive Hydrogen on one molecule and a partial negative atom on another molecule, so it isn't a coordinate covalent bond.

Benjamin Chen 1H

I think you want to add up all the valence electrons (32 valence electrons) then subtract the amount of valence electrons each known atom has (O provides 6, Cl provides 7), so the remaining should tell us which atom it is that provides 5 valence electrons in period 3 (P).

Benjamin Chen 1H

When you take one electron away from Mn, you get the electron configuration of Cr. Cr is a special configuration because each 4s and 3d orbital has 1 electron instead of 4s having 2 electrons and 3d having 4 unpaired electrons. Since the first configuration is more stable (I think it was because of ...

Benjamin Chen 1H

p state electrons are usually farther out than s state electrons.
You can interpret this as electrons closer to the nucleus are more stable (having less energy) while being farther away from the nucleus means less stable (having more energy).

Benjamin Chen 1H

I think it has something to do with hybridization of atomic orbitals, where the character ratios of p and s tell us why single bonds are longer than double bonds. Maybe this link helps.

sp hybridization | AP Chemistry | Khan Academy:
https://www.youtube.com/watch?v=BRHfy7envyQ

Benjamin Chen 1H

I think it was because of the octet rule.

Or, you can think of the N as N+ so it can form 3 sigma bonds in the sp2 hybridization orbital and 1 pi bond in the remaining p orbital. (this might be completely wrong)

Benjamin Chen 1H

Yeah, I encountered that too.

Benjamin Chen 1H

First, you want to apply the octet rule on each atom. Then, you want to check the formal charges of each atom. Generally, you want to have a Lewis Dot structure that has the least amount of Formal Charges, and you want the more electronegative atoms to have the negative Formal Charges and the less e...

Benjamin Chen 1H

On page 45 of the text book it says: "Note that in the orbital diagram the two 2p-electrons have been drawn with parallel spins, indicating that they have the same spin magnetic quantum numbers. For reasons based in quantum mechanics, electrons with parallel spins tend to avoid each other. Ther...

Benjamin Chen 1H

In the lecture today on resonance, what does it mean when electrons are delocalized, like in the Benzene?

Does it mean that the electrons are shared equally in "partial" bonds?

Benjamin Chen 1H

I thought Pauli's Exclusion Principle says that no two electrons can have the same 4 quantum numbers...not just the first three. Also, the model we were discussing for the different energy levels only modeled Hydrogen, a 1 electron system. It definitely gets a little more complicated with a multi-el...

Benjamin Chen 1H

Z is how many protons are in an atom. I think Z electron is the short hand for saying that the number of electrons is equal to the number of protons. I might be wrong.

Benjamin Chen 1H

What do you mean by "using g/mol"? It seems like you're taking moles and turning it into grams if you're multiplying by g/mol (probably a molar mass?). What would you do if you had gram sample? Like a 1.00 g sample has 0.112 grams of H and 0.888 grams of O, and you wanted to find the empir...

Benjamin Chen 1H

Yes, you're correct.

kilogram x meter/sec x meter = Joule x sec

Benjamin Chen 1H

This problem wants you to count how many possible photons (with different wavelengths and frequencies, or energies) can be emitted if the excited electron starts at n=6. So, the only possible energy levels are the lower ones: n=5, 4, 3, 2, and 1. So there are 5 different spectral lines that will app...

Benjamin Chen 1H

:0000
That makes a lot of sense! Thanks!

Benjamin Chen 1H

Can someone explain what (c) is saying because that's the only option that is true? 1A.3 Which of the following happens when the frequency of electromagnetic radiation decreases? Explain your reasoning. (a) The speed of the radiation decreases. (b) The wavelength of the radiation decreases. (c) The ...

Benjamin Chen 1H

That mass is the rest mass of an electron.

Benjamin Chen 1H

Mass plays a larger role because velocity is capped at the speed of light, which is only around 10^8 and mass is more capable of having a 10^(negative number). Since Planck's Constant is around 10^-34 and the cut off is around 10^-15, mass can have a really small value to create an observable wavele...

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