CHEMISTRY COMMUNITY

Gabriella Bates 2L

By definition, qp = delta H. Therefore, under constant pressure, qp = delta H and w = P(delta V). We can then substitute these into the equation delta U = q + w, yielding delta U = delta H + P(delta V).

Gabriella Bates 2L

A strong acid has a tendancy to dissociate in water, and therefore will have a higher concentration of H+ ions and a lower pH. In contrast, a weak acid will not dissociate as much, and will therefore have a lower concentration of H+ ions and a higher pH.

Gabriella Bates 2L

Since the final is administered through CCLE, it seems as though we will simply submit our answers to each question online. Is there any way that Dr. Lavelle will allow us to submit our work for partial credit? Or will the answers be multiple choice?

Gabriella Bates 2L

"The presence of a catalyst provides a reaction pathway in which the activation energy of a certain reaction is reduced from 125 kJ*mol^−1 to 75 kJ*mol^−1. (a) By what factor does the rate of the reaction increase at 298 K, all other factors being equal? (b) By what factor would the rate change...

Gabriella Bates 2L

Does the presence of a catalyst affect the enthalpy of a reaction? Why or why not?

Gabriella Bates 2L

Lyndon thank you for putting so much effort into every review session and being a terrific UA! I've been going to your sessions since chem 14A and you've been so helpful. I wouldn't have passed without you. I wish you all the best!

Gabriella Bates 2L

"The rate constant of the reaction between CO2 and OH2 in aqueous solution to give the HCO3- ion is 1.5 x 10^10 L*mol^-1*s^-1 at 25 C. Determine the rate constant at human body temperature (37 C), given that the activation energy for the reaction is 38 kJ*mol^-1 Is there an error in the solutio...

Gabriella Bates 2L

You can think about it both ways. If you keep the sign of Eanode as it is, then Ecell = Ecathode - Eanode. However, if you flip the sign of Eanode since it is an oxidation, then Ecell = Ecathode + Eanode. Just be clear which method you use and you will be fine!

Gabriella Bates 2L

The graphs for the different rate laws will all be linear, but what is plotted on the y axis varies. For a 0th order reaction, [A] vs time is linear, and the slop is equal to -k. For a 1st order reaction, ln[A] vs time is linear and the slope is equal to -k. For a 2nd order reaction, 1/[A] vs time w...

Gabriella Bates 2L

For redox reactions in basic solutions, you want to follow the following steps: 1. write the half reactions 2. balance the non O and H atoms 3. Balance O by adding H2O 4. balance H by adding H2O to the side that needs H and OH- to the other side (this step is a little tricky, the reason that we add ...

Gabriella Bates 2L

"A 1.0 m NiSO4(aq) solution was electrolyzed by using inert electrodes. Write (a) the cathode reaction; (b) the anode reaction. (c) With no overpotential at the electrodes, what is the minimum potential that must be supplied to the cell for the onset of electrolysis?" For part b, I underst...

Gabriella Bates 2L

"(a) What is the approximate chemical formula of rust? (b) What is the oxidizing agent in the formation of rust? (c) How does the presence of salt accelerate the rusting process?"

Are we supposed to be able to solve for this mathematically, or should we memorize it form the reading?

Gabriella Bates 2L

"Calculate the potential of a cell constructed with two nickel electrodes. The electrolyte in one compartment is 1.0 m Ni(NO3)2(aq). In the other compartment, NaOH has been added to a Ni(NO3)2 solution until the pH 5 11.0 at 298 K. See Table 6I.1." Can someone explain how to approach this ...

Gabriella Bates 2L

(a) Write balanced half-reactions for the redox reaction of an acidified solution of potassium permanganate and iron(II) chloride. How do we find the half reactions here? I don't understand how this is possible since Mn and Fe have multiple possible oxidation numbers. Do we just chose the most stabl...

Gabriella Bates 2L

So if we start off with an equation: 2KMnO4 + 8FeCl2 --> 2KCl + 2MnCl2 + 8FeO + 5Cl2. Through this equation you would see that your potassium value doesn't change, its charge is still +1. You also notice that the charge of Cl doesn't change and that it is still -1. That means MnO4 and Fe are your c...

Gabriella Bates 2L

In the solutions manual, the favorable reaction is AgBr --> Ag+ + Br- based off the standard reduction potentials. Therefore, the half reactions are: Ag+(aq) + e- --> Ag(s) (cathode) Ag(s) + Br-(aq) --> AgBr(s) + e- (anode ) This all makes sense to me, but I'm confused about the order they wrote the...

Gabriella Bates 2L

We complete this last step because we want the entropy change at that specific temperature. When we cool the species back down to the original temperature, it completes the cycle, giving up the total entropy required to change the phase at the given temperature. If we don't cool it back down, then w...

Gabriella Bates 2L

b. Ce4+(aq) + I-(aq) --> I2(s) + Ce3+(aq) When writing the cell diagram, the solution writes Pt on the iodine anode side of the cell and says, "An inert electrode such as Pt is necessary when both oxidized and reduced species are in the same solution." Why do do they assume that I is in so...

Gabriella Bates 2L

Calculate the standard reaction Gibbs free energy for the following cell reactions: (a) 2 Ce4+(aq) + 3 I-(aq) --> 2 Ce3+(aq) + I3-(aq), Ecell° 511.08 V How do we find n in this reaction? I tried to find the half reactions and figure out the electron transfer, but I was struggling with the oxidation ...

Gabriella Bates 2L

Balance the following redox reaction in basic solution:
O3 + Br- --> O2 + BrO3-

I know that Br is oxidized and O is reduced. However, why do we balance O3 --> O2 in the reduction reaction? Both have an oxidation number of 0 so I don't understand how to balance it.

Gabriella Bates 2L

Question 6K.3 d asks use to balance the following redox reaction in acidic solution: Cl2(g) --> HClO(aq) + Cl2(g) It doesn't seem possible for there to be two half reactions in this equation, given that Cl2 is on both sides. Is there a typo in this problem? Should Cl2 in the products be Cl-? This wo...

Gabriella Bates 2L

Hydrogen typically has an oxidation number of +1, but has an oxidation number of -1 when bounded to a cation or a metal.

Gabriella Bates 2L

If the voltage is positive, the reaction will occur spontaneously, and therefore creates a working battery. If the voltage is negative, the reaction does no occur spontaneously, and therefore does not create a working battery.

Gabriella Bates 2L

When deriving the Van't Hoff equation in the book, they write, "It is usually reasonable to assume that delta H and delta S are both approximately independent of temperature over the range of temperatures of interest." However, in our other equations they both are dependent of temperature ...

Gabriella Bates 2L

Is the Van't Hoff Equation on the equation sheet, or do we need to derive it? I didn't see it on the sheet but I may just be blind

Gabriella Bates 2L

For 5G.15, I got -2.7 kJ/mol, but the solutions manual said the answer is -27 kJ/mol. I typed it into my calculator multiple times and still go the same thing. Is there an error in the solutions manual? Thanks!

Gabriella Bates 2L

When a compound looses electrons, it undergoes oxidation, and when it gains electrons, it undergoes reduction. You can tell this by looking at the chemical equation and tracking the electron changes

Gabriella Bates 2L

As said above, delta S of the universe will equal zero in a reversible expansion. In addition, delta S of the surroundings will equal zero in an isothermal, reversible, free expansion. This is because isothermal indicates that U = 0, free expansion indicates that w = 0, so q = 0. Since q = 0, then S...

Gabriella Bates 2L

When using S = q/T, does the temperature need to be constant? Thanks in advance!

Gabriella Bates 2L

"Suppose that 50.0 g of water at 20.0 8C is mixed with 65.0 g of water at 50.0 8C at constant atmospheric pressure in a thermally insulated vessel. Calculate DS and DStot for the process." When calculating the final temperature of the water mixture, the book used calorimetry to state that ...

Gabriella Bates 2L

"Container A is filled with 1.0 mol of the atoms of an ideal monatomic gas. Container B has 1.0 mol of atoms bound together as diatomic molecules that are not vibrationally active. Container C has 1.0 mol of atoms bound together as diatomic molecules that are vibrationally active. The container...

Gabriella Bates 2L

The equation pH = -log[H30+] assumes that the concentration of H30+ in an acid ranges between 1 and 10^-14. If the concentration is greater than 1, the acid is extremely strong, and therefore has a negative pH.

Gabriella Bates 2L

Julia Holsinger_1A wrote:For constant pressure the equation is W= -P(delta)V , what is the equation for constant volume?

This is the equation for work, not Cv or Cp. However since (delta)V = 0 at constant volume, then w = 0. Therefore, the system does no work

Gabriella Bates 2L

Benzene is more stable and less reactive than would be predicted from its Kekulé structures. Use the data in Table 4E.3 to calculate the lowering in molar energy when resonance is allowed between the Kekulé structures of benzene. When we calculate the molar energy without resonance, we get 2880 kJ, ...

Gabriella Bates 2L

In the solution for 4D.9, the enthalpy density (enthalpy change per liter) of the reaction of TNT and oxygen is positive. However, delta H for the reaction is negative. Why is the enthalpy density positive but delta H is negative? Thanks in advance

Gabriella Bates 2L

Calculate the final temperature and the change in enthalpy when 765 J of energy is transferred as heat to 0.820 mol Kr(g) at 298 K and 1.00 atm (b) at constant volume. Treat the gas as ideal. In the book, it gives us the the enthalpy change at constant pressure is equal to the heat absorbed or lost,...

Gabriella Bates 2L

Yes. The car releases exhaust, so gasoline is leaving the system. Therefore, it is open

Gabriella Bates 2L

This means that values of enthalpy can be added/subtracted to find the change in enthalpy, as we do in Hess's law. This is because enthalpy is a state function, so the path to get there does not matter.

Gabriella Bates 2L

Most questions will require you to convert to Kelvin, since this is the S.I. unit. However, if the question asks for the change in temperature, delta T, then it's unnecessary to change the units. This is because Celsius and kelvin have the same magnitude, so the change in temperature will be the same.

Gabriella Bates 2L

Do we need to know how to find the heat capacities of ideal gases? For example, in the book it covers that the heat capacity of a monotonic ideal gas under constant volume is equal to (3/2)R. This was covered in the book but not in lecture, so I was wondering if it's important? Thanks!

Gabriella Bates 2L

A piston confines 0.200 mol Ne(g) in 1.20 L at 25 8C. Two experiments are performed. (a) The gas is allowed to expand through an additional 1.20 L against a constant pressure of 1.00 atm. (b) The gas is allowed to expand reversibly and isothermally to the same final volume. Which process does more w...

Gabriella Bates 2L

Prioritization occurs when a base gains an H+ molecule in a chemical reaction, therefore gaining a proton. Ionization is when an acid looses an H+ molecule in a chemical reaction, and therefore becomes negatively charged.

Gabriella Bates 2L

A state property is a property that is not dependent on the path taken to get to that state. Therefore, it's value is only determined by it's current state. For example, volume is a state property because it doesn't matter how that volume was obtained, so it's value is only determined by it's curren...

Gabriella Bates 2L

To draw the Lewis structure of a compound, count the number of valence electrons present in each atom. Then chose the atom with lowest ionization energy as the central atom, and arrange the atoms symmetrically around the central atom. Then arrange the electrons so that each atom has a full octet, ad...

Gabriella Bates 2L

Calculate the pH of (b) 0.055 m AlCl3(aq).

In the solutions manual, the chemical equation they used was
Al(H2O)63+ +H2O <--> H3O+ + Al(H2O)5OH2+

Can someone explain how they got this equation? I'm confused.

Gabriella Bates 2L

Rank the following solutions in order of increasing pH: (a) 1.0 x 10^-5 m HCl(aq); (b) 0.20 m CH3NH3Cl(aq); (c) 0.20 m CH3COOH(aq); (d) 0.20 m C6H5NH2(aq). Justify your ranking.

Is there a way to do this problem without doing an ice table for each one, or is that the best way to do this?

Gabriella Bates 2L

Changing the temperature affects the value of K because it affects whether the reaction favors reactants or products. If the reaction is endothermic, it absorbs heat. Therefore, increasing the temperature means that it will favor the formation of products to use up the additional heat, increasing th...

Gabriella Bates 2L

It's important to remember that the actual value of K does not change unless the temperature of the reaction is changed. Therefore, when you change the pressure, the K value does not change. However, changes in pressure mean that the system at that point in time will not be at equilibrium partial pr...

Gabriella Bates 2L

The autoprotolysis of water occurs when water molecules react with each other to form OH- and H3O+. The equation is 2H2O(l) <--> OH- + H3O+. Since water is a pure liquid, the equilibrium expression for this reaction is Kw = [OH-] [H3O+]. In order to calculate the value of Kw, we must remember that w...

Gabriella Bates 2L

5.61 The overall photosynthesis reaction is 6 CO2(g) + 6 H2O(l) -- C6H12O6(aq) + 6 O2(g), and H = 12802 kJ. Suppose that the reaction is at equilibrium. State the effect that each of the following changes will have on the equilibrium composition: tends to shift toward the formation of reactants, ten...

Gabriella Bates 2L

State whether reactants or products will be favored by an increase in the total pressure (resulting from compression) on each of the following equilibria. If there is no change, explain why that is so. (d) 2 HD(g) ∆ H2(g) 1 D2(g) In the solutions manual, they explain that there is not change in whet...

Gabriella Bates 2L

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. The Kc for Cl2 was 1.2 x 10^-7 and the Kc for F2 was 1.2 x 10^-4. Why is Cl2 more stable than F2? Does stability just mean that the reactants (either Cl2 or F2 in ...

Gabriella Bates 2L

Can someone explain the different between K and Q? How can Q be used to tell us the direction the reaction will proceed? Thanks in advance!

Gabriella Bates 2L

The equilibrium constant is not affected by the initial partial pressures of the reactant due to Le Chatlier's principle. This principle states that when stress is placed on the system (such as increasing the partial pressure of a reactant), then the equilibrium will shift in order to counteract tha...

Gabriella Bates 2L

When K is less than 10^-3, we can say with certainty that the reaction strongly favors reactants. However when K is between 10^-3 and 1, the concentration of the reactants will be slightly higher than the concentration of the products. Therefore, I would assume that the reaction slightly favors the ...

Gabriella Bates 2L

Kc is used when calculating the equilibrium constant using concentration, whereas Kp is used for calculating the equilibrium constant using partial pressure. However, as Dr. Lavelle explained in lecture, K can be used as an abbreviation to represent either Kc or Kp, depending on the context of the p...

Gabriella Bates 2L

In the solutions for 5G.9, the book writes the equilibrium constants using the concentrations opposed to the partial pressures. However, since the products and reactants are gasses, wouldn't it be more correct to use the partial pressure? Thanks in advance

Gabriella Bates 2L

How do transition metal cations function as enzymes? Is this important for the exam?

Gabriella Bates 2L

What is the structure of Vitamin B12? I know that Co is the transition metal that makes up the central atom, but what is the ligand? Also, what is its biological significance and how does the structure enable vitamin B12 to perform its function? Thanks in advance

Gabriella Bates 2L

In the marshmallow problems,it asks what the oxidation state of Fe in the heme complex is. How do we find this? it also asks about the porphryn ligand. What is this? Is it mono or poly dentate? Is this something we need to memorize?

Gabriella Bates 2L

Suggest an explanation for the different strengths of (b) acetic acid and formic acid.

Can someone explain why formic acid is a stronger acid than acetic acid? Is it because is looses protons more easily? Thank you

Gabriella Bates 2L

Which is the stronger base, the hypobromite ion, BrO2, or morphine, C17H19O3N? Justify your answer.

How would you answer this question? Thank you

Gabriella Bates 2L

How do sig figs work on logarithmic functions when doing pH calculations?

Gabriella Bates 2L

You need to look at the chemical formula and see if the molecule is more likely to accept or donate an H+ ion. Since NH3 has a lone pair on the N, it is more likely to accept a proton and is therefore considered a weak base. However, it's also good to memorize common acids and bases.

Gabriella Bates 2L

Jorge Ramirez_4H wrote:Is there a good way of memorizing this?

You don't need to memorize the coordination number for each coordination compound. Just look at the number of ligands in the square brackets of the chemical formula and you should be able to find it.

Gabriella Bates 2L

Can someone explain what a chelating ligand is and why it's important? Also, how is this related to a ligand being polydentate?

Gabriella Bates 2L

Unfortunately, the only way to know the charge of a common poly atomic ions, such as SO4 2-, is through memorization. I recommend flashcards. And Lavelle won't give us the ligand table for naming coordination compounds, we have to memorize that as well.

Gabriella Bates 2L

Which of the following can be classified as reactions between Brønsted acids and bases? For those that can be so classified, identify the acid and the base. (Hint: It might help to write the net ionic equations.) (a) NH4I(aq) + H2O(l) -> NH3(aq) + H3O1(aq) + I2(aq) Would the acid in this case be NH4...

Gabriella Bates 2L

In lecture, Lavelle mentioned that we should write cyano for CN- in cooridation compounds, but the book says we should write cyanido. Which is correct?

Gabriella Bates 2L

I'm not exactly sure what you mean by regular acids, but if I understand correctly, a Lewis acid is a regular acid. A Lewis acid is simply a way to define chemically what an acid is. By definition, a Lewis acid is an electron acceptor, which provides a visual representation what what an acid does in...

Gabriella Bates 2L

A Bronsted atom is a proton donor, whereas a Lewis acid is an electron acceptor. While the definition of these acids are different, they are complimentary, meaning that if a molecule is a Lewis acid it is also a Bronsted acid. Therefore, both definitions are acceptable.

Gabriella Bates 2L

The suffix -ide is used for the naming of common anions. For example, Cl-1 is named "chloride," and S2- is named "sulfide." However, as Lavelle stated in lecture on Friday, when naming coordination compounds, you drop the -ide from the anion name and add the suffix -o. Therefore,...

Gabriella Bates 2L

The heme complex is an iron ion bound to a porphyrin ligand, which is a cage like molecule consisting of four tetradentate square planar nitrogen molecules. When the heme complex binds to a protein, it creates myglobin. Myglobin is important because the structure of the molecule allows the iron ion ...

Gabriella Bates 2L

The Cl atoms on the clisplatin molecule bind to the exposed N on two nearby (but not necessarily next to each other) guanine nucleotides, forming a coordination compound with the DNA molecule. The bound cisplatin blocks DNA replication machinery, preventing the DNA from replicating and ultimately st...

Gabriella Bates 2L

Should we memorize the approximate strengths of each intermolecular force? Or is it sufficient to know the strengths relative to each other (ie knowing that hydrogen bonding is stronger than dipole-dipole, etc)

Gabriella Bates 2L

IN 2E.21, the answer key says that the bond angle of N2H2 is 107 degrees. Are we expected to be able to predict this, or is saying the angle is less than 109.5 degrees sufficient?

Gabriella Bates 2L

I believe that the example of the cis and trans molecule served as an example of how two molecules with the same molecular formula but different arrangements can be either polar or non polar, depending on whether the dipole moments cancel. Since the cis molecule had the Cl atoms on the same side of ...

Gabriella Bates 2L

A double bond isn't twice as strong as a single bond because there are electron electron repulsions in the double bond that slightly reduce the strength.

Gabriella Bates 2L

In the book, they use the term angular, but does the term bent also apply?Thank you

Gabriella Bates 2L

Identify the arrangement (I, II, or III; all molecules are CH2Cl2) that should possess the strongest intermolecular attractions, and justify your selection. (there's an image in the textbook). How are we supposed to be able to tell the difference in the arrangements of these molecules? I cannot see ...

Gabriella Bates 2L

Which way is the dipole pointing on CHCl2? I don't understand why this molecule experiences dipole-dipole attraction. Thanks

Gabriella Bates 2L

Identify the types of attractive intermolecular interactions that might arise between molecules of each of the following substances: (d) SO2. The solutions manual said this molecule experiences London dispersion forces and dipole-dipole attraction. How does it have dipole-dipole attraction? Which wa...

Gabriella Bates 2L

On outline three, it says we should be able to "Draw line structures of organic compounds." I don't remember Lavelle going over this, should we know it for the midterm?

Gabriella Bates 2L

On outline 2, the seventh bullet point says: "With respect to electron transitions that give rise to a UV or visible spectrum: understand the difference between electronic transitions in atomic orbitals (atomic spectroscopy) and electronic transitions in molecular orbitals (molecular spectrosco...

Gabriella Bates 2L

"Use the covalent radii in Fig. 2D.11 to calculate the bond lengths in the following molecules. Account for the trends in your calculated values: (a) CF 4; (b) SiF 4; (c) SnF 4"

Can someone explain how to do this? Thank you

Gabriella Bates 2L

Does Cl04- not have any resonance structures? I thought it did have resonance, but it makes more sense to me that oxygen has the negative charge because it's more electronegative. It does have resonance structures, since three of the oxygen are double bonded to the Cl and the other has a single bon...

Gabriella Bates 2L

In 2C.3 c, the book asked up to draw the Lewis Structure for chloric acid. The answer gave three structures, two of which had expanded octets. Would all of these be considered resonance structures, or is the final structure they gave (the one with lowest energy charge) technically correct? Thanks

Gabriella Bates 2L

Yes. Since Avogadro's number is in particles/mol, dividing the number of atoms by Avogadro's number will give you the number of mols.

Gabriella Bates 2L

When electrons are delocalized, it means that they aren't associated with a single atom or covalent bond. We can see this in resonance structures, where the Lewis structure can have multiple equivalent locations for a bond, such as a double bond. Here, the observed bond lengths are between the exper...

Gabriella Bates 2L

On Dino Nuggets question 12b, why does ClO4- have three double bonds and not four? I know that with three double bonds the Cl will have a formal charge of zero and the single bonded O will have a formal charge of -1, but why is this more stable than the Cl having four double bonds and a formal charg...

Gabriella Bates 2L

It doesn’t matter if an electron is in the px, py, or pz orbital, but you must follow Hunds rule and ensure that each orbital is filled before electrons are paired.

Gabriella Bates 2L

Yes, this is true. However, you have to remember that going across a period, the number of electrons is increasing, but so is the effective nuclear charge. Therefore, the atomic radius gets smaller across a period, but increases down a group.

Gabriella Bates 2L

The ionization energy is the energy it takes to remove an electron from an atom. Ionization energies are paired with atomic radius. Since atomic radius increases from left to right on the periodic table so does ionization energy. Na is to the left of Mg so this would mean that Na has the smaller at...

Gabriella Bates 2L

Can someone please explain why certain elements can have an expanded octet?

Gabriella Bates 2L

"Give the notation for the valence-shell configuration (including the outermost d-electrons) of (c) Group 5 transition metals."

Can someone please explain this? The answer says it is (n-1)d5ns2, but i thought it was (n-1)d3ns2. Thanks!

Gabriella Bates 2L

Can someone help explain the significance of Coulomb's Law to me? I don't understand why Coulombs Law states that the electrostatic energy is lower at a larger distance, but electrons further from the nucleus have higher energies. These statements seem to contradict each other, so I'm confused. Than...

Gabriella Bates 2L

Linear momentum is the product of the mass and velocity of an object. It is a vector quantity with units of kg*m/s, and is conserved.

Gabriella Bates 2L

If the energy of the light matches the threshold energy, then electrons will be emitted from the surface. If the energy of light is greater than the threshold energy, then the electrons emitted will have increasing kinetic energy.

Gabriella Bates 2L

1.054 457x10^-34 isn't the value for h, but it is actually the value of h bar. H bar is equal to h/(2pi), and is denoted as an h with a line through the top. Although it's used in the uncertainty principle in the book, it's not necessary to know it because it's just a shorthand.

Gabriella Bates 2L

A bowling ball of mass 8.00 kg is rolled down a bowling alley lane at 5.00 +/- 5.0 m/s. What is the minimum uncertainty in its position? In the answer key, they used 5.00 m/s as the uncertainty in velocity (delta v). Why wouldn't the uncertainty be 10.00 m/s? I thought it would be that because 10.00...

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