CHEMISTRY COMMUNITY

Lindsey Chheng 1E

The answer for this question is found by substituting -RTlnK for ΔG°in ΔG = ΔG° +RTlnQ, and then plugging in values for the variables. This makes sense to me, but I don't understand why I don't get the same answer if I just plug in -37.2 kJ/mol for ΔG°, which was the value found in Question 5.

Lindsey Chheng 1E

Molecularity refers to the number of molecules that come together to react in an elementary reaction, and is equal to the sum of the coefficients of this elementary reaction. So, if you're talking about an elementary reaction, yes! might seem silly but what do you mean by elementary reaction? An el...

Lindsey Chheng 1E

005162520 wrote:Can we also determine order based on it stoichiometric coefficient ?

yes i think you can!

Lindsey Chheng 1E

Dear Dr. Lavelle, thank you for making chemistry fun with all your jokes, memes, dance moves, cool songs, and poetry! No matter how frustrating chem got, I could never be too frustrated because of how fun of a professor you were. I've learned so much from you, and I will never forget the experiences...

Lindsey Chheng 1E

Hi Lyndon! I'm Johnson's friend, the one from UKS at APIDA Night Market! Thank you for all your help this quarter, you're a big inspiration for the rest of us. I really appreciate all the time you dedicated to help us learn and grow these past two quarters. Good luck with everything, I wish you the ...

Lindsey Chheng 1E

Can someone explain what exactly the bottle neck effect is and how I can remember what it means? I can't picture exactly why the name is "bottle neck".

Lindsey Chheng 1E

Hi! To answer your question, in an electrolytic cell you are trying to precipitate out metal solids from their ionic constituents through input of electrical energy in the solution. In this case we have Nickel (II) Sulfate, so the end goal is to reduce the nickel ion into nickel solid. Because the ...

Lindsey Chheng 1E

Consider the cell Ag(s)|Ag+ (aq, 5.0 mmol/L) ‖ Ag+ (aq, 0.15 mol/L)|Ag(s). Can this cell do work? If so, what is the max work that it can perform (in mole per Ag). The answer for this question is yes; 8.4 kJ per mole of Ag but I keep getting 17 kJ/mol Ag. I calculated Ecell to be +0.18V by using the...

Lindsey Chheng 1E

6N15. 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. I calculated this by assuming it's a concentra...

Lindsey Chheng 1E

alicechien_4F wrote:What sections of the outline can we do for this week's homework? Can we do electrochem since the test is this week, or should it be all kinetics?

I did electrochem, but I'm sure it can be either, or a mix of both!

Lindsey Chheng 1E

We are given 1.0M Ni2+ in one solution, and I have calculated that 6.5 x 10*-12 M of Ni2+ is in the other compartment. How do I determine which is the anode and which is the cathode? Since it's a concentration cell (because the two electrodes are the same metal), I think you would make whichever is...

Lindsey Chheng 1E

Predict the potential of:

Pt(s)|Cl2(g, 250 Torr)|HCl (aq, 1.0 mol/L)‖HCl (aq, 0.85 mol/L)|H2(g, 125 Torr)|Pt(s)

How do I find Q for this question when the gases are in units of Torr and the aqueous ions are in units of mol/L?

Lindsey Chheng 1E

9.a) Write balanced half reactions for the redox reaction of an acidified solution of potassium permanganate and iron (II) chloride. I'm trying to write the overall reaction in order to figure out the half reactions, and I got 2KMnO4 + FeCl2 ⟶ 2KCl + Fe(MnO2)2. Based on this, I know K+ and Cl- will ...

Lindsey Chheng 1E

The cell diagram for this question is Ag(s) I AgBr(s) I Br-(aq) II Ag+(aq) I Ag(s). I'm confused on why there's a single line separating Ag(s) and AgBr(s) when they are both in the same state. Can someone explain?

Lindsey Chheng 1E

How do you get the half reactions for AgBr(s) ⇌ Ag+(aq) + Br-(aq)
The anode is supposed to be Ag(s) + Br- ⟶ AgBr(s) + e- and the cathode is supposed to be Ag+(aq) + e- ⟶ Ag(s). Am I supposed to get these on my own or am I supposed to just look in appendix 2a in the back of the book?

Lindsey Chheng 1E

How do you find n from an equation for a reaction? n is the total number of electrons that's being transferred from the anode to the cathode, which you can find after balancing the two half reactions. In the equation ΔG = -nFE, n is in mol e-/mol rxn. For example, if an equation had a total of 2 e-...

Lindsey Chheng 1E

annikaying wrote:What does it mean for a reaction if it is first order versus second order or any other order?

0 order: Rate = k
k = mol/L x min
1st order: Rate = k[A]
k = 1/min
2nd order: Rate = k[A][B] or k[A]^2
k = L/mol x min

Lindsey Chheng 1E

Balance P4 → H2PO2- + PH3 in basic solution. I know that the half reactions are: 3 x (P4 + 8OH- → 4H2PO2- + 4e-) 12H2O + P4 + 12e- → 4PH3 + 12OH- and the answer is 3OH- + P4 → 3H2PO2- + PH3 My question is how was the second half reaction found? I know that H2O and OH- have to be added for basic solu...

Lindsey Chheng 1E

Balance Br2 → BrO3 + Br- in basic solution. Answer: 3Br2 + 6OH- → 5Br- + BrO3- + 3H2O I know that Br2 is both the reducing and oxidizing agent, but I can't get the two half reactions right. These are the ones I got: 2 x (12OH- + Br2 → 2BrO3- + 12H + 6H2O + 5e-) 5 x (Br2 + 2e- → 2Br-) Can someone ple...

Lindsey Chheng 1E

5a) Balance O3 + Br- → O2 + BrO3- taking place in basic solution. Answer: 3O3 + Br- →3O2 + BrO3- In order to get this answer, the two half reactions were: 3 x (H2O + O3 + 2e- → O2 + 2OH-) 6OH- + 3H2O + Br- → BrO3- + 6e- + 6H2O I thought that no electrons were being transferred from O3 to O2, but the...

Lindsey Chheng 1E

how can you tell when a metal can be dissolved in solution? If you're talking about a galvanic cell, then the anode electrode will shrink (metal ionized/dissolved) over time. For example, if the anode was Zn, then the oxidation half reaction would be Zn → Zn2+ + 2e-. As you can see, the metal elect...

Lindsey Chheng 1E

vpena_1I wrote:In ∆G*=-nFE*, is n the number of moles of the species that is being reduced?

n is the mols of electrons involved in the total reaction after you balance both half reactions and make sure the charges are balanced as well.

Lindsey Chheng 1E

I know a salt bridge is there to keep both solutions neutral, but what exactly is going on inside the salt bridge that allows it to contribute to the galvanic cell?

Lindsey Chheng 1E

Is the reason we're able to add and subtract E°cathode and anode because it's a state function?

Lindsey Chheng 1E

in the notes for the galvanic cell, it says that max potential is when "very little current flows". What does this mean?

Lindsey Chheng 1E

I feel a little lost. I felt like I had a decent understanding of the concepts for the midterm, and I could provide an answer to every statement on the learning outcome outlines. I went to Step-Ups weekly, I did the homework, I went to multiple review sessions, and I made sure I could do every Pizz...

Lindsey Chheng 1E

Since some of the energy released in chemical reactions is lost as heat, then is the term "maximum work" technically a theoretical explanation for an ideal situation where all the energy released from a reaction is used for work and none is lost as heat?

Lindsey Chheng 1E

When you use w=P_{ex}\Delta V , external pressure is 0 because free expansion means the system isn't pushing against a pressure. It is freely expanding without any use of energy. This means w=0. For isothermal processes, ∆U = 0 = q + w, so q and w = 0 in this case. I'm not sure why the ∆S is the sa...

Lindsey Chheng 1E

"Initially an ideal gas at 323 K occupies 1.67 L at 4.95 atm. The gas is allowed to expand to 7.33 L by two pathways: (a) isothermal, reversible expansion; (b) isothermal, irreversible free expansion. Calculate ΔStot, ΔS, and ΔSsurr for each pathway." For part b, why is the ΔS of the irre...

Lindsey Chheng 1E

Can someone please help me solve this question? An ice cube of mass 50.0g at 0.0 Celsius is added to a glass containing 400.0 g of water at 45.0 Celsius. What is the final temperature of the system? Assume no heat is lost to the surroundings. I know that ice is going through a phase change at 0.0 Ce...

Lindsey Chheng 1E

In the notes after the Boltzmann Equation, it says "Thermodynamic Property ('small' error in S)" and "Statistical ('large' error in W)". What does this mean?

Lindsey Chheng 1E

In the notes, it says "For an isolated system (constant energy) at equilibrium: W is a maximum, therefore entropy is a maximum at equilibrium".
What does maximum mean here?

Lindsey Chheng 1E

In the notes about microstates, it says For 1 mol, W = 2^NA, which means that S = kBlnW = kBln2^NA = NAkBln2 = Rln2.
In the last step, why does NAkB = R? What is R?

Lindsey Chheng 1E

Is the Boltzmann Equation relating Degeneracy (W) and Entropy (S)?

Lindsey Chheng 1E

Deena Doan 2F wrote:Knowing both delta u or delta h and delta s of a system provides info on how the system will change

thank you!

Lindsey Chheng 1E

There was a part of the "Thermodynamics: Second and Third Laws" notes that I missed, if anyone could help tell me what it was, I'd greatly appreciate it! It was at the beginning of his introduction to the term Entropy. --> "Knowing both deltaU (or deltaH) and deltaS of a system provid...

Lindsey Chheng 1E

Very random question, but I'm wondering what happens regarding temperature and phase changes if an ice cube is applied to the skin immediately after a steam burn?

Lindsey Chheng 1E

Why can the units for this chapter be either Kelvin or Celsius? Why are they interchangeable?

Lindsey Chheng 1E

why does the temperature remain constant during a phase change?

Lindsey Chheng 1E

Why does an endothermic reaction have a -delta T and an exothermic reaction have a +delta T?

Lindsey Chheng 1E

Can someone help to explain the difference between standard enthalpy of reaction and standard enthalpy of formation?

Lindsey Chheng 1E

how come when pressure doubles, volume halves?

Lindsey Chheng 1E

why does a smaller pKa or pKb correspond to a stronger acid and strong base?

Lindsey Chheng 1E

Why does the addition of an inert gas not affect the equilibrium position?

Lindsey Chheng 1E

Find the initial concentration of the weak acid or base in the following aqueous solutions. a) solution of HClO with pH = 4.60. I know how to find the concentration of H3O+ using the given pH but I don't know what to do after this. Am I supposed to look up the Ka and set up a Ka expression with the ...

Lindsey Chheng 1E

A student added solid Na2O to a volumetric flask of volume 200.0 mL, which was then filled with water, resulting in 200.0 mL of NaOH solution. Then 5.00 mL of the solution was transferred to another volumetric flask and diluted to 500.0 mL. The pH of the diluted solution is 13.25. (a) What is the mo...

Lindsey Chheng 1E

During lecture, Lavelle said that K does not change when an acid or base is added and that even though [H3O+] > [OH-] or vice versa, the product of them would still be equal to 1.0 x 10^-14. Why is this? I understand that Kw = 1.0 x 10^-14, but if an acid or base is added to water, wouldn't it not b...

Lindsey Chheng 1E

Are all acid and base reactions at equilibrium? For weak acids and bases, we usually write their reactions with equilibrium arrows, but for strong acids and bases we usually write their equations with a single arrow pointing forward to indicate that the strong acid completely dissociates. However, ...

Lindsey Chheng 1E

thank you!

Lindsey Chheng 1E

Will we have to know how to work with acids and bases at equilibrium? If so, is there anything that makes them different when it comes to ICE tables and other calculations we have been doing with regular equations? According to the syllabus, we're going to have to know how to solve problems with ac...

Lindsey Chheng 1E

how do we know which equilibrium constant of the three per equation column (the ones decreasing in value) to use? for example in the Kc column for H2+I2--> 2HI do we use 794, 160, or 54? thanks so much! You would have to look at the given temperature in the problem as well as if the compounds are g...

Lindsey Chheng 1E

Consider the equilibrium CO(g) + H2O(g) ⇌ CO2(g) + H2(g).
a) If the partial pressure of CO2 is increased, what happens to the partial pressure of H2?

I think that the partial pressure of H2 will decrease from the reaction shifting left to re-establish equilibrium. Is this correct?

Lindsey Chheng 1E

what does it mean when K is a very large value and not just simply >1 but more like >>>>>1?

Lindsey Chheng 1E

What exactly is the difference between an equilibrium constant and a reaction quotient? The textbook said that the reaction quotient can be used for any stage of the reaction, and it accounts for free energy, but I am confused as to how exactly it does this. K is a ratio solved with values at equil...

Lindsey Chheng 1E

I think the answer is true because K will always be the same ratio no matter what you start with, as long as the reaction is kept under the same conditions.

Lindsey Chheng 1E

What did Lavelle say was the reason that there are no units for K?

Lindsey Chheng 1E

For a heterogeneous equilibrium, what expression is utilized to find the equilibrium constant? K is always equal to [Products]/[Reactants]. Heterogeneous Equilibria just means that at least one of the components in the reaction, whether it be a reactant or a product, is in a different phase (gas, l...

Lindsey Chheng 1E

what does it mean when an acid is neutral or negatively charged?

Lindsey Chheng 1E

Can someone please explain how resonance, delocalization, and stabilizing of negative charges contribute to the strength of an acid?

Lindsey Chheng 1E

Can someone give examples of how we would change the naming of a ligand that has di, tri, and tetra- or is a polydentate to its name that has bis-, tris-, tetrakis-, or pentakis-?

Lindsey Chheng 1E

Is Mg+2 bigger or smaller than Na+? Is O-2 bigger or smaller than N-3? Arrange the anions Cl- , Br- , N-3, and O-2 in order of increasing polarizability and give reasons for your decisions. Thanks! Mg2+ is smaller than Na+ because two cations have the same amount of electrons but Mg has one more pr...

Lindsey Chheng 1E

how does the difference in electronegativity contribute to the strength of an acid? When comparing the strength of these acids (HF, HCl, HBr, and HI), what difference in electronegativity is crucial in telling us how strong the bond is between Hydrogen and the respective halogen. Since F has the hi...

Lindsey Chheng 1E

Why do Ka and Kb not exist for strong acids/bases?

Lindsey Chheng 1E

Is it possible we will be asked to draw out the lewis structures of equations like HCl + H2O --> H3O+ + Cl- on the test?

Lindsey Chheng 1E

What makes them different The Bronsted-Lowry definition of acids and bases are focused on the proton (H+). Bronsted Acids are proton (H+) donors and Bronsted Bases are the proton (H+) acceptors. My high school chemistry teacher used the phrase "shake and take", where acids "shake&quo...

Lindsey Chheng 1E

Identify each compound as either a Brønsted acid or a Brønsted base: (a) NH3 ; (b) HBr; (c) KOH; (d) H2SO3 ; (e) Ca(OH)2 . Is there a strategy for identifying each compound as a Bronsted acid/base? I think you just have to already know which compounds are acids or bases. The compounds in this quest...

Lindsey Chheng 1E

JChen_3C wrote:Can coordination compounds only be made with transition metals? Or can other metals act as the central metal atom?

aluminum, silver, gold and platinum also form coordination compounds

Lindsey Chheng 1E

What was the alternate way of naming Diethylenetriamine with the prefix bis-?

Lindsey Chheng 1E

Is Fe always at the center of a Heme Complex? I feel like he went into a lot of detail about the Heme Complex today. Will we have to know it in as much depth as he went over?

Lindsey Chheng 1E

Are the weak acids we talked about in class today (carbonic acid and benzoic acid) also bronsted acids?

Lindsey Chheng 1E

Ligands must fit two criteria:
a. must have a neutral or negative charge
b. must have at least one pair to donate

Lindsey Chheng 1E

NicoJones_1B wrote:When H2O becomes H3O, where does the oxygen pick up a hydrogen? Does it take it from a nearby oxygen?

The reaction we did in class was HCl + H2O --> H3O+ + Cl-
The extra H comes from the HCl since HCl dissociates in H2O.

Lindsey Chheng 1E

Can someone please explain why AsF3 has a boiling point of 63C while AsF5 has a boiling point of -53C? Since AsF3 has a lone pair in its structure, it has a net dipole moment and exhibits polar characteristics. Meanwhile, AsF5 has no net dipole moment and is nonpolar. Therefore, it will take more e...

Lindsey Chheng 1E

KBELTRAMI_4I wrote:does it include the midterm topics?

I think it would be too much for Lavelle to include past midterm topics on the next test; the next time we'll be tested on them will probably be on the final.

Lindsey Chheng 1E

Based on the lewis structure, how are we able to determine the molecular shape since the lewis structure is only 2-D? To determine molecular shape, you have to take into account the steric number (# bonding regions + lone pairs) and the number of lone pairs. Determining the name of the molecular sh...

Lindsey Chheng 1E

How would you calculate the longest wavelength of light that can remove an electron when given the work function? The longest wavelength of light would correlate to the least amount of energy a photon has to be in order to eject an electron from a metal surface, which means it would be equivalent t...

Lindsey Chheng 1E

Why are double and tripe bonding pairs still considered a single region of electron density and not affect the shape/bond angles? I'm confused because I thought if you had more electrons there would be a greater repulsion, so it would affect the shape and the bond angles. Thank you! I think it's be...

Lindsey Chheng 1E

What is the explanation behind why single bonds have longer bond lengths than double and triple bonds? In single bonds, only 1 pair of electrons are shared, so they have less of a pull on the two nucleus's of the atoms they bond. Therefore, they are longer than double of triple bonds, where more el...

Lindsey Chheng 1E

I'm still not understanding the concept of dipole moment too well. Can someone explain how this applies in lewis structures? Dipole moments are the result of differences in electronegativities. An atom with a greater electronegativity, such as the Cl atom in HCl. Since the electronegativity of Cl i...

Lindsey Chheng 1E

aphung1G wrote:Is it better for the central atom to have a +/- charge or have the other atoms take the +/- charge? And if so, why?

Dr Lavelle said that typically, charges are held by the outer atoms in a Lewis structure.

Lindsey Chheng 1E

why does the trend in electronegativity increase when you go up a column and increase when you go to the right in a row? Electronegativity is the ability for an atom to attract an electron. From top to bottom, electronegativity decreases since there is an increase in the distance between the nucleu...

Lindsey Chheng 1E

Can someone please explain how electronegativity determines the dipole moments? Which element gets which partial charge? If Ionization Energy and Electron Affinity are high, then atom will have high Electronegativity and pull shared electrons towards it (resulting in a partial negative charge), the...

Lindsey Chheng 1E

It did! Thanks!

Lindsey Chheng 1E

In his lecture, Dr. Lavelle said that if you know something's position really well, then the uncertainty in the position will go down and the uncertainty in the momentum will go up. I understand why the uncertainty in the position goes down, but can someone explain the other?

Lindsey Chheng 1E

In homework problem 15 from section 1B, part d asks what what kind of electromagnetic radiation was used from a wavelength of 8.8 nm. The answer was x-ray/gamma rays, however, is this something we will have to know for exams? We are probably only expected to know that visible light falls under the ...

Lindsey Chheng 1E

Lauren Haight 1E wrote:Does anyone know the general format of the midterm? As in, how many questions there will be and how many questions there will be on each topic we have gone over? Thanks.

There's going to be 8 questions on the midterm, and I'd assume each question contains its parts of a, b, c, etc.

Lindsey Chheng 1E

romina_4C wrote:Do you only use this equation to find the wavelength or velocity of something that is not light (electrons, atoms, objects, etc.)?

Yes, I believe so since De Broglie is for any moving particle with momentum, p, that has wavelike properties with wavelength.

Lindsey Chheng 1E

In homework problem 9 from section 1B, we are given 2 seconds which eventually needs to be converted to joules. The solution manual says that 2 seconds is equal to 64 J. How do we convert seconds to joules? So in the question we are given 32W, where 1 W = 1 J/s, which means that 32W = 32J/s. Use di...

Lindsey Chheng 1E

What causes a molecule to have an octet exception? Some atoms are stable with fewer electrons, which doesn't meet the octet rule: H, He, Li, Be, B. In class, Dr. Lavelle talked about how B and Al are involved in Lewis Acid-Base reactions, where B in BF3 completes its octet if other atom provides bo...

Lindsey Chheng 1E

Can someone explain what the Balmer and Lyman series are and what the significance of them is? Knowing the Balmer and Lyman series can help us identify whether or not the light is in the visible or UV region. Sometimes a problem will simply state that the light involved is in, say the UV region. Yo...

Lindsey Chheng 1E

how come when the book asks you to give the ground-state electron configuration for Ni^2+, the answer is [Ar]3d^8 and not [Ar]3d^64s^2? You have to remove electrons from the highest energy shell first, which in this case would be n=4. This is because the electrons in the highest energy shell, which...

Lindsey Chheng 1E

some atoms are stable with fewer than electrons: H, B, Be
some atoms are stable with more than 8 electrons: P, S, Cl, As, SE, Br, Kr, Sb, Te, I, Xe

Lindsey Chheng 1E

I believe Threshold Frequency is the amount of energy of a photon required to displace an electron on a metal surface. The photon needs to at least match the threshold, which will result in a kinetic energy of 0. Yes that part makes sense to me but when we're calculating the threshold frequency, is...

Lindsey Chheng 1E

can someone explain to me the electrostatic/coulomb potential energy and its significance? I know it's proportional to (q1)(q2)/r. Coulomb's Law shows the relationship between q1, q2, and r, and their effects on the attractive forces between particles. -if q1 and q2 are opposite charges, then there...

Lindsey Chheng 1E

Level or shell: the level or "ring" that the electron occupies aka the Principal Quantum Number (n) Ex: 1s = 1st shell Ex: 2s and 2p = 2nd shell Sublevel or subshell: the combination of all the types of shapes (s, p, d, f) Ex: 1s = subshell Ex: 2s = subshell Ex: 2p = subshell Orbital: a si...

Lindsey Chheng 1E

505316964 wrote:Is velocity usually in nm or m? does it matter when using the equations if the question doesn't specify units?

velocity is usually in m/s

Lindsey Chheng 1E

In class today, Dr. Lavelle discussed an "exception" in writing electron configurations... He said "Half full d5 and full d10 subshells have lower energy". So in the example of Cr, the configuration is written as [Ar]3d5 4s1. Can anyone explain this to me? Why does the 4s shell ...

Lindsey Chheng 1E

What is the difference between an orbital and a shell? Level or Shell: the level or "ring: that the electron occupies, which is the Principal Quantum Number (n) Orbital: a single shape that can hold up to 2 electrons (ex: px, py, or pz) - for this class, we are expected to know the shapes of s...

Lindsey Chheng 1E

How exactly does Schrodinger's Wave Function equation relate to the orbitals (1s, 2s, 2p... etc.)? I know the orbitals are solutions to the Wave Function, but what exactly does that mean? Like do the orbitals have energies corresponding to the ones calculated by this equation? Atomic orbitals are s...

Lindsey Chheng 1E

Could someone please explain what are constructive interference and destructive interference? Thanks. In phase means to interact with Constructive -two wavelengths are in phase, that is the peak of one wave is in phase with the peak of the other wave -together, the two waves result in a larger wave...

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