CHEMISTRY COMMUNITY

AlyssaYeh_1B

Thank you so much for two wonderful quarters of good chemistry! I really can't thank you enough, Dr. Lavelle! It's been a pleasure being in your class, and I wish you the best. Please stay safe and healthy. Take care! High five :D

AlyssaYeh_1B

I was wondering how we'd be able to answer this question without having any data for calculations For which process will deltaH nought and deltaG nought be expected to be most similar? (A) 2Al (s) + Fe 2 O 3(s) --> 2Fe (s) + Al 2 O 3(s) (B) 2Na (s) + 2H 2 O &#...

AlyssaYeh_1B

I believe we discussed in lecture that we should always make the lower concentration the product, so that "it is in solution", which means that the lower concentration will always be on the anode side

AlyssaYeh_1B

For question 11, the van't hoff equation is written like ln(K2/K1) = -(deltaH/R)((1/T2) - (1/T1)). However, in the constants and equations sheet, the T2 and T1 are swapped, which would result in K2=0.0169 instead of 0.0186. I was wondering which form of the equation is correct and which we should us...

AlyssaYeh_1B

How are homogenous catalysts different from heterogeneous catalysts? What's the significance of that difference?

AlyssaYeh_1B

The question provides a table of values, with which we can work out the rate = k r [A][B] 2 [C] 2 (overall order of 5). When I calculate k r , I get the answer 2.85 L 4 *mmol -4 *s -1 . When I calculate the rate with that k, [A] = 3.01 mmol/L, [B] = 1.00 mmol/L, and [C] = 1.15 mmol/L, I get rate = 1...

AlyssaYeh_1B

The example given in class for a different phase was that if the product is a gas, that gas can escape the system and therefore not be returned to reactant

AlyssaYeh_1B

How does one determine which step in a multi-step reaction is the slowest?

AlyssaYeh_1B

How does change in temperature affect k?

AlyssaYeh_1B

In my notes, 'A' is defined as the frequency factor or pre-exponential factor (including # of collisions with correct orientation). What does this mean? Is this what we're trying to calculate with the Arrhenius equation?

AlyssaYeh_1B

Why is water more highly conducting when it has dissolved ions?

AlyssaYeh_1B

If the standard reduction potentials that we are meant to use are -0.23V and -0.83V, how is the minimum potential that must be supplied for the onset of electrolysis +1.46V?

AlyssaYeh_1B

Are we expected to be able to do problems concerning ion-selective electrodes and corrosion on test 2/the final? These topics are included in the reading, but we didn't really explore them much in lecture?

AlyssaYeh_1B

C_(gr) | Cl_{2(g, 1.0 bar)} | Cl^-_{(aq, ?)} || MnO₄^-_{(aq, 0.0010M)}, H⁺_(pH=0.4), Mn²⁺_{(aq, 0.1M)} | Pt_(s) E_cell = -0.30V

What would be the balanced reaction for this cell? I'm having trouble finding the value of Q

AlyssaYeh_1B

How come the value of delta G changes when the chemical equation is multiplied by some factor, but E_cell does not?

AlyssaYeh_1B

Yes it does

AlyssaYeh_1B

What is meant by the terms 'oxidizing agent' and 'reducing agent'?

AlyssaYeh_1B

I also had a question about this. Perhaps it was a typo? Since the solution has Cl^- in the balanced equation, if we supposed that the Cl₂ in the products side was Cl^-, the problem works out. But I'm not exactly sure.

AlyssaYeh_1B

What are the steps we should follow for balancing complicated redox reactions?

AlyssaYeh_1B

The salt bridge allows ion transfer, so the two solutions will remain neutral (prevent charge buildup)

AlyssaYeh_1B

Does anyone have any tips to memorize that the anode is where oxidation occurs, and the cathode is where reduction occurs?

AlyssaYeh_1B

In the Van't Hoff Equation, is the K₁ value supposed to correlate with the T₁ value, and the K₂ with the T₂? Or are they meant to be treated as separate things?

AlyssaYeh_1B

This question asks us to calculate the equilibrium constants for two reactions at 25C and 150C. Can someone walk me through the problem? I'm unsure of where to start. I assume we need to calculate delta G, but which equation would we use to calculate K? These are the reactions: (a) NH 4 Cl (s...

AlyssaYeh_1B

Calculate the equilibrium constant at 25C for each of the following reactions, by using data in Appendix 2A: (a) the combustion of hydrogen: 2H 2(g) + O 2(g) <--> 2H 2 O (g) (b) the oxidation of carbon monoxide: 2CO (g) +O 2(g) <--> 2CO 2 g) (c) the decomp...

AlyssaYeh_1B

There is also no expansion work if there's a vacuum

AlyssaYeh_1B

Is there an easy way to remember all the state functions? What about all the intensive/extensive properties we've looked at? I always end up confusing myself when I try to memorize them

AlyssaYeh_1B

For the example we looked at in class today (permanganate and iron), how come the oxidation numbers of hydrogen and oxygen don't change? How do we tell which ones were oxidized/reduced?

AlyssaYeh_1B

The Van't Hoff equation can be used to calculate K at a different temperature, but only if delta S nought and delta H nought are assumed to be constant. Will that always be the case in reality, though? Will delta S nought and delta H nought always be constant in the problems that we're asked to do?

AlyssaYeh_1B

How come delta S of surroundings is 0 when a system undergoes irreversible expansion?

AlyssaYeh_1B

When would we use the Boltzmann equation? How does it relate to entropy?

AlyssaYeh_1B

From the data the question gives, I did the calculation: -1500 - (-1300 + 2(-286)) = 312kJ/mol. However, the answer key shows that it's -312kJ/mol. What did I do wrong?

AlyssaYeh_1B

How come heat capacity is not an intensive property, but specific heat/molar heat capacity is?

AlyssaYeh_1B

Where can I find the standard enthalpies of formation for different molecules in the textbook?

AlyssaYeh_1B

"Oxygen difluoride is a colorless, very poisonous gas that reacts rapidly and exothermically with water vapor to produce O 2 and HF: OF 2 (g) + H 2 O (g) ----> O 2 (g) + 2HF (g) delta H = -318kJ What is the change in internal energy for the reaction of 1.00 mol O...

AlyssaYeh_1B

An ice cube of mass 50.0g at 0.0ºC is added to a glass containing 400.0g of water at 45.0ºC. What is the final temperature of the system? Assume that no heat is lost to the surroundings. How would this problem be solved? I understand that we need to use the enthalpy of fusion and the specific heat o...

AlyssaYeh_1B

Is this reading section mandatory? It includes content that we have not covered in class, such as translational, rotational, and vibrational energy.

AlyssaYeh_1B

Calculate the work for each of the following processes beginning with a gas sample in a piston assembly with T = 305K, P = 1.79 atm, and V = 4.29L: (a) irreversible expansion against a constant external pressure of 1.00 atm to a final volume of 6.52L; (b) isothermal, reversible expansion to a final ...

AlyssaYeh_1B

The question is assuming that only work is done, so heat is not a component of the change of the internal energy. In this case, delta U = w. Your answer for (c) should therefore be the same as (a)

AlyssaYeh_1B

The question is asking for the heat capacity of the calorimeter. Notice that it's not asking for the specific heat capacity or the molar heat capacity. In general, the equation for calculating heat capacity is C = q/delta T (where C = heat capacity, q = heat supplied, and delta T = temperature rise ...

AlyssaYeh_1B

What does it mean for a process to be reversible? I read the section in the textbook (4A.3), but it still doesn't make sense to me.

AlyssaYeh_1B

Among the 4 methods to calculate delta H, is there one that is the most accurate?

AlyssaYeh_1B

Is there a correlation between bond enthalpy and bond length?

AlyssaYeh_1B

Why is the standard enthalpy of formation of O₂ 0? Why does this only apply to diatomic molecules?

AlyssaYeh_1B

Can someone provide a summary for all the methods we learned to calculate delta H? What are the notable differences between each one?

AlyssaYeh_1B

How is a steam burn worse than a liquid burn? Is it because steam condenses on the skin, which releases a lot of energy?

AlyssaYeh_1B

Al 3+ is a metal cation that can act as a bronsted acid and thus be hydrated by water molecules. Therefore, Al 3+ will produce acidic solutions. AlCl 3 is the substance that provides this metal cation in the solution; Cl - can be disregarded since it's the conjugate base of a strong acid. Metal cati...

AlyssaYeh_1B

Why is it that we only look at the moles of gas? I thought it was only solid and liquids that were not included in the equilibrium constant

AlyssaYeh_1B

The given values are in kPa, so you have to convert them to bar. 1 Pa = 1x10^-5 bar, OR this can be written as 100 kPa = 1 bar. That's why you have to divide the values by 100 when you're plugging into the equilibrium constant :)

AlyssaYeh_1B

For the reaction: N₂(g) + O₂(g) <==> 2NO(g), which direction would be favored if the system was compressed?

AlyssaYeh_1B

(a) In an experiment, 2.0mmol Cl 2 (g) was sealed into a reaction vessel of volume 2.0L and heated to 1000. K to study its dissociation into Cl atoms. Use the information in Table 5G.2 to calculate the equilibrium composition of the mixture. (b) If 2.0mmol F 2 was placed into the reaction vessel ins...

AlyssaYeh_1B

How come adding inert gas to a reaction vessel would result in no change to the concentrations of the reactants and products? If nothing changes, what's the effect or purpose of adding the gas then (besides increasing pressure)?

AlyssaYeh_1B

When calculating the change in molar concentration with the quadratic equation, and the results are one positive number and one negative number, would there ever be a circumstance where the negative number is also an acceptable answer?

AlyssaYeh_1B

When calculating the equilibrium constant in general, how come the stoichiometric coefficient becomes an exponent for the concentration of the reactant/product?

AlyssaYeh_1B

What is Pa and how do we convert it to bar? Do we always have to do our work in the units of bar?

AlyssaYeh_1B

I understand why solids cannot be included in the equilibrium constant, but how come liquids cannot? It's possible to measure the concentration of liquids right?

AlyssaYeh_1B

For the final, will we be expected to know how to assign hybridization schemes to terminal atoms?

AlyssaYeh_1B

What's the difference between describing something as amphoteric vs. amphiprotic?

AlyssaYeh_1B

Write the chemical equations of the two proton transfer equilibria that demonstrate the amphiprotic character of (a) HCO₃^—; (b) HPO₄^2—. Identify the conjugate acid-base pairs in each case.

What does it mean by amphiprotic character? How exactly would I format the answer for this question?

AlyssaYeh_1B

How do we write the formulas of conjugate acids and bases?

AlyssaYeh_1B

Are we expected to know the names of common acids and bases? Like ammonia or phosphoric acid?

AlyssaYeh_1B

Why is trichloroacetic acid a stronger acid than acetic acid? We went over this in lecture, but I didn't quite understand.

AlyssaYeh_1B

sodium bisoxalato(diaqua)ferrate(III)

formula: Na[Fe(OH₂)₂(C₂O₄)₂]

Does the order matter when writing the formula of the complex? Would it be possible to write the (C₂O₄)₂ in front of the (OH₂)₂?

AlyssaYeh_1B

Dr. Lavelle also has a very helpful table on his website about the ligand names we will cover in this course. Just click on the link that says "Naming Coordination Compounds"

AlyssaYeh_1B

What is a chelating complex?

AlyssaYeh_1B

We don't need to know the exact bond angles for those shapes! Just approximating it by saying it's less than 109.5 degrees, or less than 120 degrees is enough :)

AlyssaYeh_1B

Since a double bond consists of one sigma bond and one pi bond, does that mean a double bond does not allow atoms to rotate?

AlyssaYeh_1B

Since lone pair electrons have stronger repulsion force, bonded atoms will be pushed further from it and gather closer to each other. This is more stable, since atom-atom repulsion is weaker than lone pair-atom repulsion. We don't need to memorize that the particular bond angle is 106 degrees. We on...

AlyssaYeh_1B

Trigonal planar would be the shape when taking into consideration the bonds AND the lone pairs, which the textbook calls the "electron arrangement" around the central atom. However, since we name shapes based only on bonds, the final answer would be bent or "angular."

AlyssaYeh_1B

katrinawong3d wrote:There's still one more slide that he's going to cover on Monday, so maybe he'll cover it then?

I believe Dr. Lavelle will be going over sigma and pi bonds on Monday. I'd recommend familiarizing yourself with all the molecular shapes

AlyssaYeh_1B

Lone pairs have a more strongly repelling effect than elections in bonds because the electron cloud of a lone pair can spread over a larger volume than a bonding pair can. That's why the strengths of repulsions are in the order: lone pair-lone pair > lone pair-atom > atom-atom. This will not change

AlyssaYeh_1B

How come hydrogen bonding occurs with only molecules that have N, O, F? Why can't hydrogen be bonded with other electronegative atoms and become partially positive?

AlyssaYeh_1B

Question 3F.5 is:
Suggest, giving reasons, which substance in each of the following pairs is likely to have the higher normal melting point

(b) C₂H₅OC₂H₅ (diethyl ether) or C₄H₉OH (butanol)

I'm confused why the answer is butanol? Is it because of how the atoms are arranged?

AlyssaYeh_1B

Is hydrogen bonding generally stronger than london forces?

AlyssaYeh_1B

Why is the london interaction considered "universal"?

AlyssaYeh_1B

Why does the polarisability of molecules increase with size?

AlyssaYeh_1B

1) Electronegativity increases across a period and up a group. P<S<Cl<N<O<F 2) Atomic Radius increases down a group and decreases across a period. F<O<N<Cl<S<P 3) Electron Affinity increases across a period and up a group, like electronegativity. P<S<Cl<N<O<F 4) Ionization Energy increases across a ...

AlyssaYeh_1B

Why is a radical highly reactive?

AlyssaYeh_1B

What exactly does it mean when a bond length is long/short? The distance between nuclei is larger/smaller? How is this related to the electrons the atoms share?

AlyssaYeh_1B

How is the Aufbau principle related to the Pauli Exclusion principle and Hund's rule? Is it like a fusion of the two?

AlyssaYeh_1B

If oxygen has a lower ionization energy than nitrogen, does that apply to all the other elements in group 16? As in, they will all have lower ionization energies compared to their neighbor to the left?

AlyssaYeh_1B

Remember that if a formal charge of 0 is not possible, the atoms on the outside of the central atom generally have the formal charges that are not 0

AlyssaYeh_1B

Part e of this question asks for the ground-state electron configuration for tungsten. The answer is [Xe]4f¹⁴5d⁴6s². Why is the f block included in this electron configuration? And how come 5d⁴6s² isn't written as 5d⁵6s¹ even though it's more stable in the latter configuration?

AlyssaYeh_1B

It's harder to remove a second electron from an atom because removing the first one gives the atom an overall net positive charge. Therefore, the attraction that's exerted on each electron gets larger, making it harder to remove. And yes, there are multiple ionization energies for an element

AlyssaYeh_1B

In a lewis structure, double bonds can be drawn in different equivalent locations to indicate resonance. How come triple bonds are unlikely to do this?

AlyssaYeh_1B

How come P, S, and Cl can accommodate more than 8 valence electrons? I don't understand how they can use d-orbitals to expand their shells

AlyssaYeh_1B

This additional information about the baseball's weight is not necessary at all to do the problem. It's probably just supplemental information given for the context of the problem :)

AlyssaYeh_1B

When doing your calculation, the Δv you should use is 10m/s, which is your maximum uncertainty.

AlyssaYeh_1B

"What is the minimum uncertainty in the speed of an electron confined within a lead atom of diameter 350. pm? Model the atom as a one-dimensional box with a length equal to the diameter of the actual atom. I understood the first part of the question and got the correct answer of Δv = 1.65 x 10 ...

AlyssaYeh_1B

RRahimtoola1G wrote:For ∆x, I got 6.6 x 10^-36m also, but the answer in the back of the book and the solution manual is 1.3 x 10^-36m. Which is the correct answer?

The correct answer would be 6.6 x 10^-37m. There was an error in the solutions manual (Δv = 5m/s when Δv should've been 10m/s)

AlyssaYeh_1B

You can't specify the precise location of a particle if it behaves like a wave, because a wave is not localized at a precise point. Since waves don't have a location, you can't describe the location of a particle that has a precise linear momentum.

AlyssaYeh_1B

The answer is (d) photoelectric effect because during the photoelectric experiment, scientists noticed that increasing the intensity of the light did not eject electrons. This means that the incident light was not acting like a wave. Therefore, they concluded that electromagnetic radiation had prope...

AlyssaYeh_1B

You would first use the wavelength you have and find the energy change using E=(hc)/wavelength. Once you have the energy change, use the equation E=(-hR)/n^2 with n=1 to find the energy of the electron at n=1. Once you have the energy change and the energy of the electron at n=1, you can set up thi...

AlyssaYeh_1B

During lecture, Dr. Lavelle mentioned something about the QM description of an election in a box. What did he mean by that/what exactly is he referring to?

AlyssaYeh_1B

"The y-ray photons emitted by the nuclear decay of a technetium-99 atom used in radiopharmaceuticals have an energy of 140.511 keV. Calculate the wavelength of these y-rays."

What is meant by keV? How should I go about starting this problem?

AlyssaYeh_1B

For part b of this question, it asks for the wavelength of the x-rays. I got my answer of 150pm. However, the answer written at the back of the textbook says 150nm. Is this simply a typo or were my calculations off?

AlyssaYeh_1B

In my high school, my teacher never really went over the different prefixes, names, and meanings for the SI units. How come they ascend and descend in degrees of 3? Would it be good practice to memorize all of them for the tests?

AlyssaYeh_1B

In a question, say it asks me to calculate percent yield of some compound. The given sig fig is 1. If my answer is something like 56%, would I have to round it to 60% to maintain that sig fig of 1? Sig figs in the answer should match the given ones right?

AlyssaYeh_1B

There's an inverse relationship between frequency and wavelength. Do they have any relationship with the amplitude of a wave?

AlyssaYeh_1B

Yes, electrons gain energy by absorbing light. When they jump down energy levels, light is emitted

AlyssaYeh_1B

In lecture, we briefly went over a diagram showing the vectors for electric fields and magnetic fields. What exactly is the significance of these vectors? Is there a reason they're perpendicular to each other?

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