CHEMISTRY COMMUNITY

Hannah Lee 2F

I also got that the rate = [HgCl2][C2O4]2, with the the order = 1 with respect to [HgCl2] and order = 2 with respect to [C2O4].

Hannah Lee 2F

If the question gives you a pH of a solution with a certain initial molarity, could you imply that the [H+] you calculate from it is its equilibrium [H+] concentration?

Hannah Lee 2F

By definition, disassociation means that the chemical equation will take the form AB --> A + B. So in this case, we want the net equation for the disassociation of the acid HF to be HF --> H+ + F-, and we need to adjust our anode and cathode half-reactions accordingly. In order for HF to be on the r...

Hannah Lee 2F

Thank you, this helped a lot!

Hannah Lee 2F

(g) half-life against [A] for a reaction that is zeroth order in A; (h) half-life against [A] for a reaction that is second order in A.

Can someone please help me visualize what these graphs would look like? Would [A] essentially be the same as [A]0 (for the half-life equation)?

Hannah Lee 2F

(b) Sketch a reaction profile for the overall reaction, which is known to be exothermic. Label the activation energies of each step and the overall reaction enthalpy. Basically, in the reaction mechanism, there are three steps total: (1) fast, (2) slow (RDS), (3) fast. Does the "steepness"...

Hannah Lee 2F

Calculate (a) the number of half-lives and (b) the time required for the concentration of N2O to fall to one-eighth of its initial value in a first-order decomposition at 1000K. According to Table 7A.1, k = 0.76 1/s for this reaction. However, I keep on getting t = ln8 / k = ln8 / 0.912 s = 2.28 sec...

Hannah Lee 2F

What range (in volts) does a voltmeter need to have to measure pH in the range of 1 to 14 at 25 C if the voltage is zero when pH = 7?

According to solutions manual, [H+] = 1 when pH = 1.
Why would [H+] not equal 0.10 at pH = 1 (because [H+] = 10^-pH = 10^-1 = 0.10?

Hannah Lee 2F

Use the data in Appendix 2B and the fact that, for the half- reaction F2 + 2H+ + 2e- --> 2HF with E = +3.03 V, to calculate the value of Ka for HF. Why do you have to take the square root of K at the end to find Ka? I thought the acid disassociation constant was basically an equilibrium constant, ju...

Hannah Lee 2F

I'm assuming that we won't encounter a problem like this on the test. If we have to order by reducing or oxidizing power, Dr. Lavelle will provide us with the oxidation states or specify them in some way.

Hannah Lee 2F

All components except the concentrations are the same, so we can infer that this is a concentration cell. Thus, E° = 0 (because under standard conditions, concentrations will be the same and so there will be no driving force for change). wmax = deltaG = –nFE, so calculate E using the Nernst equation...

Hannah Lee 2F

Calculate the reaction quotient, Q, for the following cell reactions, given the measured values of the cell potential. Balance the chemical equations by using the smallest whole-number coefficients. https://imgur.com/YgPP9VC E = E° - 0.05916 V/n x logQ -n(E - E°) / 0.05916 V = logQ -2(1.33 - 1.52) /...

Hannah Lee 2F

I am also confused about this. For reference, here is the question: Arrange the following metals in order of increasing strength as reducing agents for species in aqueous solution: (a) Cu, Zn, Cr, Fe; (b) Li, Na, K, Mg; (c) U, V, Ti, Al; (d) Ni, Sn, Au, Ag.

Hannah Lee 2F

At ΔG = 0, the reaction is in equilibrium. What is the difference between ΔG = 0 and ΔG° = 0?

Hannah Lee 2F

6L.7 (c) Write the half-reactions and devise a galvanic cell (write a cell diagram) to study each of the following reactions: Cd(s) + 2 Ni(OH)3 (s) --> Cd(OH)2 (s) + 2 Ni(OH)2 (s), the reaction in the nickel–cadmium cell For the cell diagram, why is there a line instead of a comma between two solid ...

Hannah Lee 2F

How can neutralization of water be considered a redox reaction despite the fact that the oxidation #s haven't changed of either hydrogen or oxygen? And how could you easily identify which half-rxns in the table to use? When I first solved this, I mistakenly used the half-rxns involving H2 instead of...

Hannah Lee 2F

Why do we tend to measure reduction potential instead of oxidation potential? Is there ever a situation in which we would use oxidation potentials?

Hannah Lee 2F

Write the half-reactions and devise a galvanic cell (write a cell diagram) to study each of the following reactions:
(a) AgBr(s) --> <-- Ag1(aq) 1 Br2(aq), a solubility equilibrium

How can you tell which one is the anode and the cathode since the oxidation states are the same for both species?

Hannah Lee 2F

Balance each of the following skeletal equations by using oxidation and reduction half-reactions. All the reactions take place in basic solution. Identify the oxidizing agent and reducing agent in each reaction. Reaction of ozone with bromide ions: O3(aq) + Br-(aq) --> O2(g) + BrO3-(aq) I'm confused...

Hannah Lee 2F

When balancing redox reactions, I thought that the # of e- transferred should correspond to the change in the oxidation number. In 6K.3(a), S is oxidized from 2+ --> 3+, which means each S atom "lost" an e-; however, in the balanced oxidation half-reaction, it says that S2O3^2- actually lo...

Hannah Lee 2F

https://i.postimg.cc/PfQm5rdv/Screen-Shot-2020-02-19-at-5-42-09-PM.png According to the solutions manual, why do we have to calculate for the limiting reactant? Wouldn't graphite be automatically excluded from the equilibrium constant because it's a solid? If graphite was found to be the limiting r...

Hannah Lee 2F

ΔG, Gibbs free energy, is the energy associated with a given chemical rxn and released from a spontaneous process (negative value) that can be used to do work. The relationship between ΔG and ΔG°is shown via the equation: ΔG = ΔG°+ RTlnQ. ΔG° is the free energy of reaction at fixed, STANDARD STATE c...

Hannah Lee 2F

Can someone conceptually explain the relationship between free energy G and cell potential?

Hannah Lee 2F

The Arrhenius equation shows the temperature dependence of reaction rates: https://www.gstatic.com/education/formulas/images_long_sheet/arrhenius_equation.svg The textbook is showing how to derive van't Hoff equation from the Arrhenius equation by relating the temperature dependence of reaction rate...

Hannah Lee 2F

Depict the progress of the reaction graphically (as in Fig. 5G.1) for the reaction in Exercise 5G.13. (The question for 5G.13 is:(a) Calculate the reaction Gibbs free energy of I2(g) S 2 I(g) at 1200. K (K 5 6.8) when the partial pressures of I2 and I are 0.13 bar and 0.98 bar, respectively.) Can so...

Hannah Lee 2F

4.45 Potassium nitrate dissolves readily in water, and its enthalpy of solution is 34.9 kJ/mol. (a) Does the enthalpy of solution favor the dissolving process? b) Is the entropy change of the system likely to be positive or negative when the salt dissolves? (c) Is the entropy change of the system pr...

Hannah Lee 2F

Are the units for standard free energy kJ or kJ/mol? I thought it was given in kJ unless the question specifically asked for the molar Gibbs free energy but the solutions manual gives them all in kJ/mol. I also assumed the "mol" would cancel out of the units. Or is the solutions manual ref...

Hannah Lee 2F

How would you calculate the entropy of an irreversible expansion of an ideal gas at constant temperature? Could that occur at changing temperatures?

Hannah Lee 2F

In the question, a piece of zinc metal (8.5 g) is dropped into 800.0 mL of 0.500 M HCl solution, and the reaction that occurs between HCl and Zn changes the temperature of the solution. Based on the info given, the first thing you should probably do is write out the balanced chemical equation for th...

Hannah Lee 2F

Calculate the molar kinetic energy (in joules per mole) of Kr(g) at (a) 55.85 8C and (b) 54.85 8C. (c) The difference between the answers to parts (a) and (b) is the energy per mole that it takes to raise the temperature of Kr(g) by 1.00 8C. What is the value of the molar heat capacity of Kr(g)? I u...

Hannah Lee 2F

Hydrochloric acid oxidizes zinc metal in a reaction that produces hydrogen gas and chloride ions. A piece of zinc metal of mass 8.5 g is dropped into an apparatus containing 800.0 mL of 0.500 m HCl(aq). If the initial temperature of the hydrochloric acid solution is 25 8C, what is the final temperat...

Hannah Lee 2F

It is because heat at constant pressure is equal to change in enthalpy: qp = deltaH.

Therefore, heat capacity will be equal to qp / deltaT --> deltaH / deltaT.

Hannah Lee 2F

I also got 490 J, so I think the answer key must be off. But someone feel free to correct me!

Hannah Lee 2F

Cv = 3/2R and Cp = 5/2R. This means that the molar heat capacity of a monoatomic ideal gas at a constant volume is 3/2R, and for constant pressure it is 5/2R. Both Cv and Cp are independent of T and P. You would use this when calculating enthalpy changes related to heating an ideal gas, and replace ...

Hannah Lee 2F

For the isothermal expansion of an ideal gas in which deltaU = 0, is heat energy still being transferred into or out of the system and why?

Hannah Lee 2F

I'm confused about this equation: ΔH = ΔU + nRΔT, which is mentioned in the textbook. I understand how to derive/use ΔH = ΔU + ΔnRT, but how could ΔU = ΔH - nRΔT be possible? I thought that in order to use any variation of ΔU = ΔH - PΔV, pressure had to be constant. However, in the book, it says you...

Hannah Lee 2F

In general, the lower the heat capacity of a substance, the steeper the line (and the greater the slope). This is because it takes less heat energy to raise the temperature of the substance, so temperature would increase at a faster rate relative to those with higher heat capacities. For instance, i...

Hannah Lee 2F

Oxygen difluoride is a colorless, very poisonous gas that reacts rapidly and exothermically with water vapor to produce O2 and HF: OF2 (g) +H20 (g) --> O2 (g) + 2HF (g) with delta H being -318 kJ. What is the change in internal energy for the reaction of 1.00 mol OF2? Do you assume that external pr...

Hannah Lee 2F

I also got -38.72 kJ/mol so I think it may be an error in the answer key, though I'm not completely sure because it's not on the list of solutions manual errors.

Hannah Lee 2F

For 4D.9:

Why is the answer given as a positive instead of negative value? I thought that since the reaction is exothermic and the enthalpy of rxn is negative, the enthalpy density would also be negative?

Hannah Lee 2F

4.184 is the specific heat capacity of water as a liquid. You should be able to find it in the appendix.

Hannah Lee 2F

Does anyone know where to start in the outline/have any recommendations on which problems to go over first, because I know we didn't go over everything yet? I know Dr. Lavelle mentioned starting from the end of the chapter.

Hannah Lee 2F

Are the enthalpy of reaction units kJ or kJ/mol? I thought that because change in enthalpy of rxn = q, the units would be written in kJ. However, the solutions manual writes enthalpy of reaction as kJ/mol when using bond enthalpies to calculate it.

Hannah Lee 2F

Glucose has high potential energy that can be utilized as an energy source. The series of enzymatic reactions that break down glucose into CO2 and H2O (cellular respiration) has an overall negative enthalpy (deltaH < 0) since energy is released. In other words, the enthalpy of the products, CO2 and ...

Hannah Lee 2F

In the case of the lecture problem, I think it was assumed that the reaction would just proceed forward. However, unless you're working with acid-base equilibria related reactions, I think it's always safest to calculate Q to make sure that the direction of the reaction is correct, even if the probl...

Hannah Lee 2F

As a general rule of thumb, can we assume the approximation rule whenever K < 10^-5 or K < 10^-3? Which value of K is it? (assuming that you always check if the approximation is valid after solving for x)

Hannah Lee 2F

I think it depends on the values the problem gives you and on the context of the problem – if the problem gives you atm, for instance, then you would most likely find the equilibrium constant in terms of partial pressure, unless it explicitly states for you to convert it to Kc.

Hannah Lee 2F

Is it possible to find the % ionization/de-protonation (not protonation) of a basic solution, or does it only apply to acids?

Hannah Lee 2F

https://upload.wikimedia.org/wikipedia/commons/thumb/6/6a/Autoprotolyse_eau.svg/330px-Autoprotolyse_eau.svg.png The autoprotolysis of water can be used to link the concentrations of H3O+ and OH- in an aqueous solution via the autoprotolysis constant, Kw. Because Kw is essentially an equilibrium con...

Hannah Lee 2F

I was also confused about this! It was most likely a typo in either the solutions manual or textbook, but I just went with the value in the solutions manual; I don't think we should worry too much about it as long as we know how to do the problem.

Hannah Lee 2F

The equation for (c) is as follows: 4NH3(g)+ 5O2(g) -> 4NO (g) + 6H2O(g) There are 9 moles of gas on the reactant side and 10 moles of gas on the reactant side. Compression implies that pressure (and thus concentration) increases while volume decreases. To counteract this increase in pressure/concen...

Hannah Lee 2F

Yes, I think the test will cover that as it is similar to the ICE box problems we did in class.

Hannah Lee 2F

When considering sig figs for acid/base calculations, do you leave it to the very end to maintain accuracy or cut off digits for sig figs as we go? For instance, for an ICE box problem, if the initial concentration was 6.69 mmol/500mL = 0.01338, would you keep it as 0.01338 or use sig figs which mak...

Hannah Lee 2F

(c) Use your results from parts (a) and (b) to determine which is thermodynamically more stable relative to its atoms at 1000. K, Cl2 or F2.

Can someone please explain this?

Hannah Lee 2F

PV = nRT is the ideal gas law, where P = pressure, V = volume, n = number of moles, R = ideal gas constant, and T = temperature in K. In the context of this unit, we can use it to convert between partial pressures and molar concentrations by rearranging the equation as follows: P = (n/v)RT = (concen...

Hannah Lee 2F

I agree! The equilibrium constant can be defined in terms of either Kp or Kc. You look at the values given to you to determine whether you will be calculating Kp or Kc - for instance, if the problem gives you moles and volumes, you will probably be using Kc, but if the problem gave you partial press...

Hannah Lee 2F

(a) The amount of O2 @ eq will be different in the containers. Because container 2 has a higher amount of initial reactant (0.50 mol O3), it will subsequently have a higher amount of product (mol O2) at equilibrium. This is because K must remain constant across both containers, so if the rxn starts ...

Hannah Lee 2F

State whether the following statements are true or false. If false, explain why. (d) If one starts with higher concentrations of reactants, the equilibrium concentrations of the products will be larger. The answer is true - can someone please explain this? How does higher initial [R] indicate larger...

Hannah Lee 2F

17. If the initial amounts of CO and H2O were both 0.100 M, what will be the amounts of each reactant and product at equilibrium for the following reaction? Keq = 23.2 at 600K CO (g) + H2O (g) ⇌ CO2 (g) + H2 (g) After using ICE, for my quadratic equation, I solved it from: x^2 / (0.100 - x)^2 = 23.2...

Hannah Lee 2F

You would need to be given the pKa or Ka values to make sure, so if this was given on an exam, you would be provided with that information.

Hannah Lee 2F

Why can't NO2- also be bidentate and donate the e- pairs from its adjacent O atoms, similar to CO32- (which can be mono- or bi-dentate)?

Hannah Lee 2F

If you draw out the Lewis structure, the main difference between the two groups is that acetic acid has a methyl group (CH3) where formic acid only has H. Thus, CH3COOH has an e- donating group, CH3, that destabilizes the negative charge of the resulting anion by contributing e- density. This means ...

Hannah Lee 2F

What's the difference between the two terms? Are they normally used interchangeably?

Hannah Lee 2F

BrO- would be the stronger base because it is the conjugate base of a weak acid, HBrO. A weak parent acid always indicates a strong conjugate base that must be a relatively good proton acceptor, which can relatively easily form HBrO molecules when added to water in the rxn: BrO- + H2O --> HBrO + OH-...

Hannah Lee 2F

I also kept on getting answers different from the solutions manual, so the manual itself may be incorrect. It's not on Dr. Lavelle's list of 7th Ed Solution Manual errors though, so I'm not sure. I used the relationship pH = -log[H+] and [H+] x [OH-] = 1.0 x 10^-14 to get the following answers for (...

Hannah Lee 2F

Thank you! It makes sense now :)

And an Arrhenius base is a species that produces hydroxides (OH-) in water. It is restrictive because it does not account for species that produce OH- in solutions other than water, so we normally go with the Bronsted definition.

Hannah Lee 2F

Identify each compound as either a Brønsted acid or a Brønsted base: (c) KOH; (e) Ca(OH)2. It is clear that both KOH and Ca(OH)2 are bases since they are metal hydroxides. However, to align with the Bronsted definition, how would KOH and Ca(OH)2 accept a proton? Do we have to conform to just the Bro...

Hannah Lee 2F

Are all complexes with a polydentate ligand examples of chelation? Are all complexes that include a polydentate ligand considered chelating complexes? Is any ligand that is not monodentate an example of chelation, or is it restricted to complexes with a large coordination number, like EDTA? Similarl...

Hannah Lee 2F

Can ligands be positively charged? If so, how would you name them?

Hannah Lee 2F

How would you name iron in a TM complex? Would it just be iron (Roman numeral), or is there another unique name for it?

Hannah Lee 2F

D-block elements can experience multiple oxidation states since they may have incomplete inner subshells that do not restrict valence e- to the outer shell. They are also a good source of e- due to their ability to form expanded octets, and they can form complexes via coordinate covalent bonds with ...

Hannah Lee 2F

It represents the protein binding to the heme complex, forming myoglobin. This ultimately forms an octahedral complex when Fe binds 1 O2, which is why myoglobin contributes to the transport of O2 in muscle cells.

Hannah Lee 2F

Are terminal atoms hybridized? When can we tell if they are?

For instance, in 2.45, the O double-bonded to the central C atom has sp2 hybridization. How about in the case of CS2 in 2.59(b), would the S atoms be hybridized to sp2 as well? How about terminal atoms that are halogens?

Hannah Lee 2F

Hybridization results from orbital overlap and stabilizes the molecule by lowering the overall energy. It allows orbitals to "blend" into new hybrid orbitals that align with the pairing of electrons in forming covalent bonds according to the VSEPR theory.

Hannah Lee 2F

What's the difference between writing hybridization with the d before sp vs the d after sp? I know both of them mean basically the same thing, but can someone explain to me why Dr. Lavelle chooses to write it so that d comes before sp?

Hannah Lee 2F

I agree! The triple bond will be drawn the same way - 1 sigma, 2 pi bonds, and just label them on the Lewis structure.

Hannah Lee 2F

To determine hybrid orbitals, you count the number of electron densities around the central atom. That should align with the hybridization of the central atom, since the number of hybrid orbitals is always the same as the number of atomic orbitals used in their construction. For instance, PCl5 uses ...

Hannah Lee 2F

In the notes, it says that dipole-dipole, dipole-induced dipole, and induced dipole-induced dipole all typically have around -2 kJ/mol of E. However, I thought that the order of IMF strength went from dipole-dipole > dipole-induced dipole > induced dipole-induced dipole? Can someone clarify this for...

Hannah Lee 2F

O has only one e- less than F, giving it a high nuclear charge and a greater ability to attract e-. On the other hand, Cl is below F with an entirely new shell of valence e- added to it, which decreases the nuclear charge experienced by outer e- and decreases its ability to attract e- compared to th...

Hannah Lee 2F

When there is more than 1 central atom, the bonding about each atom is treated independently, so the same rules for bond angles would apply. For instance, for ethylene (CH2=CH2), there are 3 regions of high e- density around each central atom, with 3 bonding pairs and 0 lone pairs. Therefore, the e-...

Hannah Lee 2F

I'm pretty sure it will be around the same length since we are allowed the same amount of time, but you can double-check with your TA. Dr. Lavelle might also mention the length of the test in tomorrow's lecture.

Hannah Lee 2F

2E.25 Draw the Lewis structure and predict whether each of the following molecules is polar or nonpolar: (a) CH2Cl2; (b) CCl4; (c) CS2; (d) SF4. How can I tell if molecules are polar or nonpolar? To determine whether a molecule is polar or nonpolar, you would determine its molecular shape based on ...

Hannah Lee 2F

What are "axial" and "equatorial" atoms? What do we need to know about them when determining molecular shaping using VSEPR?

Hannah Lee 2F

Use Lewis structures and the VSEPR model to give the VSEPR formula for each of the following species and predict its shape: (d) xenon trioxide. When drawing the Lewis structure for XeO3, does it have to be structured in a tetrahedral arrangement (other than the 1 lone pair)? I thought that the prese...

Hannah Lee 2F

In Problem 3F.5 part c, it says that CHI3 has stronger intermolecular forces than CHF3 and will have a higher melting point. This difference is attributed to the difference in strength of induced dipole-induced dipole forces between the two molecules. I understand why CHI3 has stronger London force...

Hannah Lee 2F

(a) The melting point of solid xenon is -112 C and that of solid argon is 2189 C. (b) The vapor pressure of diethyl ether (C2H5OC2H5) is greater than that of water. (c) The boiling point of pentane, CH3(CH2)3CH3, is 36.1 C, whereas that of 2,2-dimethylpropane (also known as neopentane), C(CH3)4, is...

Hannah Lee 2F

Adding onto the previous answer, both the electronegativity and small sizes of N, O, and F allow it to bond to H. You can think of H-bonding as a stronger version of dipole-dipole bonds.

Hannah Lee 2F

Is it possible to use de Broglie's equation to find frequency, considering we can't use the equations for EM radiation? Do we have to know how to do that for the midterm?

Hannah Lee 2F

Whenever you're dealing with photons and electromagnetic radiation, you use E = hv, c = lambda x frequency, etc. However, when you're dealing with particles WITH mass (like electrons, protons, neutrons, etc), then you'd use de Broglie's equation, λ = h / p --> λ = h / mv. You can't use E = hv or c =...

Hannah Lee 2F

Polarizing power refers to the ability of an atom/ion to "distort" the electron cloud of another atom/ion. In ionic bonds, this can create a covalent character, since the positive charge on the cations will pull the electrons from the anion into the bonding region. Because of this, higher ...

Hannah Lee 2F

What is the relationship, if any, between polarity and polarizability? Can polarizability contribute to nonpolar covalent bonds?

Hannah Lee 2F

For part (a) of 2C.3, it asks: "Draw the Lewis structure, including typical contributions to the resonance structure (where appropriate, allow for the possibility of octet expansion, including double bonds in different positions), for (a) periodate ion." Then for the resonance structures, ...

Hannah Lee 2F

How can Cl form an expanded octet? And can someone please provide an example of a compound in which Cl acts as an expanded octet?

Hannah Lee 2F

I don't recall seeing that structure in my notes, but assuming that carbon is the central atom, the most electronegative atom should carry the negative formal charge. In this case, N should have the negative charge since it's more electronegative than sulfur. So the most stable structure would go: S...

Hannah Lee 2F

The electron configuration of Sb is [Kr]4d105s25p3. Because valence electrons are used in bonding, they are always in the highest-energy, outermost orbitals. In the case of Sb, this would be n = 5, and we would exclude the completely filled 4d-subshell (which would not participate in bonding). 5s2 a...

Hannah Lee 2F

When determining the most stable structure, does symmetry or formal charge come first? For instance, for question 2B15) which asked to draw ClNO2, I mistakenly drew the Cl attached to the oxygen instead of the nitrogen, making an L-shape, because I thought that each atom's formal charge had to amoun...

Hannah Lee 2F

You can find an example of a question dealing with formal charge in Example 2B.4 (page 85)! There's also a short section devoted to formal charge that starts on page 84.

Hannah Lee 2F

Electronegativity refers to the tendency of an atom to attract e-, while ionization energy refers to the amount of energy it takes to remove an e- in the gas phase. Both follow similar trends in the periodic table, increasing from left to right across a period as effective nuclear charge increases a...

Hannah Lee 2F

The lithium photomultiplier basically means that upon absorption of a photon of light to the surface of the lithium cell, electrons are emitted. This implies that we are dealing with the photoelectric effect, and the laser the agents choose has to discharge enough energy/emit a high-enough frequency...

Hannah Lee 2F

Ionization energies usually increase on going from left to right across the periodic table. The ionization energy for oxygen, however, is lower than that of either nitrogen or fluorine. Explain this anomaly. If you look at the filling of e- in the p-subshells for O, N, and F: - N has three unpaired...

Search found 117 matches