## Search found 69 matches

Sat Jan 23, 2021 8:53 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Textbook Problem 4D.15
Replies: 2
Views: 34

### Re: Textbook Problem 4D.15

Hi Joey! I was confused at first too, but I think it's because enthalpy of combustion is different from enthalpy of formation. We have to realize that combustion is the formation of CO2 and H2O, which makes combustion extremely different from formation, which uses stable elements. So here, the final...
Sat Jan 23, 2021 8:09 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Textbook Problem 4D.21
Replies: 2
Views: 21

### Re: Textbook Problem 4D.21

Hi Austin! I'm getting the exact same answer as you no matter how many times I look at it. Possibly a textbook error?
Thu Jan 21, 2021 7:24 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Textbook 6.B.3
Replies: 3
Views: 14

### Re: Textbook 6.B.3

Hello! Strong acids completely ionize in solution, so in the desired solution amount of 200.0 mL, [H+] = 0.025. Then, the pH = 1.6 (desired solution). Then, we can find the number of moles of HCl in the solution by doing 0.025M HCl = (x moles HCl)/(0.2L). We find that there are 0.005 moles of HCl. M...
Thu Jan 21, 2021 6:01 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Textbook Problem 6D.3 Part A
Replies: 2
Views: 11

### Re: Textbook Problem 6D.3 Part A

Hello! I also got the same answer as you, with Ka = 0.108 and pKa = 0.967. I'm hoping that it's a textbook error, but I could possibly be wrong as well.
Thu Jan 21, 2021 5:37 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Polyprotic Acids
Replies: 8
Views: 38

### Re: Polyprotic Acids

I also agree; I think if Ka2 is extremely small, we can disregard this because most of the ionization has occured from Ka1. But based on the lectures, it doesn't look like we know much about polyprotic acids yet.
Thu Jan 21, 2021 5:30 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Percent protonated vs percent ionization
Replies: 6
Views: 16

### Re: Percent protonated vs percent ionization

Hello! I think it's basically the same concept except being ionized isn't the same as being protonated. I think for protonated the question would probably ask for a weak base that is protonated into its conjugate weak acid (percent protonated = concentration of conj weak acids/initial concentration ...
Thu Jan 21, 2021 5:24 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Textbook 6B.9
Replies: 4
Views: 21

### Re: Textbook 6B.9

Hello! I also got the same answer for that first row, but I think we were supposed to skip it because the solution manual errors on Dr. Lavelle's site mentions that 6B.9 has errors.
Wed Jan 13, 2021 10:14 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Ka and Weak Acids
Replies: 3
Views: 21

### Re: Ka and Weak Acids

Hi Isis! So we have to memorize some of the common strong acids/bases vs weak acids/bases. Strong acids/bases completely dissociate/ionize, so we don't need very complex calculations to get their pH or pOH. But for all weak acids/bases, we don't know how strong or weak they are relative to all the o...
Wed Jan 13, 2021 9:59 pm
Forum: Phase Changes & Related Calculations
Topic: equilibrium when taking away product
Replies: 3
Views: 38

### Re: equilibrium when taking away product

Hi Mary, When taking away product to make more product, we are basically only changing the concentration of product, not the temperature (unless directly stated). The reason why this reaction doesn't have to undergo a temperature change to create product is because the taking away of product itself ...
Wed Jan 13, 2021 9:52 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5I.13 Part C
Replies: 2
Views: 14

### Re: 5I.13 Part C

Hello! For C, I looked at the equilibrium constant Kc itself to see whether F2 or Cl2 was more stable. The smaller Kc was, the more stable the diatomic element. Because Kc was smaller for the Cl reaction than the F reaction, it meant that the reactants were more favored in the Cl reaction than the F...
Wed Jan 13, 2021 3:31 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Weak Bases without N, O, or F
Replies: 2
Views: 22

### Re: Weak Bases without N, O, or F

Hi Sunny, I also think that an H-bond doesn't really determine whether something is a weak/strong acid/base. I also believe it is the electronegativity and polarity. But because the definition of an acid/base pertains to [OH-] and [H3O+], I think it is a bit inevitable to see a lot of H bonds, as we...
Wed Jan 13, 2021 3:25 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Conjugate Seesaw
Replies: 3
Views: 37

### Re: Conjugate Seesaw

Hi Abril, Dr. Lavelle used NH3, a weak base, in his example. Because NH3 is a weak base, it should mean that conjugate acid is stronger (NH4+) and the same if there was a weak acid, then there would be a stronger conjugate base. I think the word "conjugate" might make it confusing, but I t...
Mon Jan 04, 2021 4:51 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sapling hw #4
Replies: 4
Views: 48

### Re: Sapling hw #4

Hi Jazlyn, The reason why the signs of the xs in the change part of the ICE table is because we are inputting PCl5 into the container with no Cl2 or PCl3, so Cl2 and PCl3 are our products in this case while PCl5 is the reactant. However, Kp is actually only used when trying to find the relative pres...
Mon Jan 04, 2021 4:44 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Finding Concentrations at Equilibrium
Replies: 5
Views: 37

### Re: Finding Concentrations at Equilibrium

Hello! I also agree with Akshata; if you look in the first few modules that Dr.Lavelle wanted us to do, you'll see that most problems give us the concentrations of the products and reactants at equilibrium so that we can plug them directly to find Kc. However, in about Module Part 2 I believe, we ar...
Mon Jan 04, 2021 4:40 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kp (pressure used as concentration?)
Replies: 3
Views: 25

### Re: Kp (pressure used as concentration?)

The ideal gas law, PV=nRT is usually used to find P, V, n, n/V for one type of gas molecule. For example, we would use the ideal gas law if we wanted to find the concentration of a particular gas like H2. However, the equilibrium constant using pressure, Kp, is used to see the relative pressures of ...
Mon Jan 04, 2021 3:07 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Liquids and Equilibrium Constants
Replies: 2
Views: 18

### Re: Liquids and Equilibrium Constants

Hello! I think that pure liquids like water are omitted from the equilibrium constant, as well as solids. I think this applies for both Kc and Kp. The ones that are included are aqueous and gaseous substances.

Hope this helps!
Mon Jan 04, 2021 3:04 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Module Question
Replies: 2
Views: 34

### Re: Module Question

Hi Emily! I think for this question, K is in Kp because the units of NO2 and N2O4 are in partial pressures (atm). When asking for whether these conditions are at equilibrium, use Kp = (PNO2)^2/(PN2O4), plug in the numbers of PNO2 and PN2O4 (which in this case are 0.5 atm), and check to see if this i...
Mon Dec 07, 2020 4:58 pm
Forum: Identifying Acidic & Basic Salts
Topic: Difference between pH, pKa, and Ka
Replies: 3
Views: 36

### Re: Difference between pH, pKa, and Ka

Hello! - pH is a scale that uses the concentration of H+ (or H3O+) ions to measure the acidity of a solution on a scale of 0-14. - Ka is an equilibrium constant that are used for determining where the equilibrium lies (if the equilibrium lies to the right it means that the concentrations of the prod...
Mon Dec 07, 2020 4:47 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Chelating Complexes
Replies: 2
Views: 34

### Re: Chelating Complexes

Hi Raashi! The definition that Dr. Lavelle gave us for chelate is a complex containing a ligand that forms a ring of atoms that includes the central metal atom. Basically, if you have a polydentate ligand, the several bonds forms a ring around the TM, and so this whole complex would be a chelating c...
Mon Dec 07, 2020 4:43 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: HClO2 stronger acid than HbrO2?
Replies: 4
Views: 45

### Re: HClO2 stronger acid than HbrO2?

Adding on, the reason why Cl's greater electronegativity makes HClO2 more acidic than HBrO2 is because of the criteria that acids that result in a stable conjugate base will be more acidic. Because of Cl's greater electronegativity, it stabilizes the negative charge of the oxygens and makes the anio...
Mon Dec 07, 2020 4:28 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: coord number and oxidation number
Replies: 3
Views: 30

### Re: coord number and oxidation number

Hello! I believe that oxidation numbers are basically the same as the typical charge of the atom. For example, for oxygen, the typical charge and oxidation number is -2. As for the coordination number, Dr. Lavelle defined it as the number of bonds made by the central atom. So, because it is the numb...
Mon Dec 07, 2020 4:21 pm
Forum: Identifying Acidic & Basic Salts
Topic: Ions as acids
Replies: 2
Views: 31

### Re: Ions as acids

Hi Anya! Dr. Lavelle did not include Cl- because, yes, it does not affect the pH of the solution. As seen in his drawing of Na+ and Cl-, both did not create attractions strong enough to actually break the bonds of H2O/ change H2O's structure. Thus, Cl- was excluded from the equation because only the...
Wed Dec 02, 2020 4:00 pm
Forum: Naming
Topic: Naming [Ni(CN)4]2-
Replies: 2
Views: 30

### Re: Naming [Ni(CN)4]2-

Hi Crystal! Like Ashlen stated, in the name, it is 1. ligands (in alphabetical order, and includes anions that are directly bounded to the TM metal because this anion is also a ligand but someone might need to check up on this part) 2. TM metal ion 3. anions or molecules outside that are not directl...
Wed Dec 02, 2020 3:44 pm
Forum: Biological Examples
Topic: Coordination compounds having too many oxidation states
Replies: 2
Views: 44

### Re: Coordination compounds having too many oxidation states

Hi Crystal! I think that Dr.Lavelle mentioned that having many oxidation states was good for e- transfer, because for example, if a transition metal like Fe does not hold on to its electron tightly, it can give or accept electrons fairly easily (the e- transfer), and thus create many oxidation state...
Wed Dec 02, 2020 3:36 pm
Forum: Bronsted Acids & Bases
Topic: Bronsted Acids vs Strong Acids
Replies: 4
Views: 43

### Re: Bronsted Acids vs Strong Acids

I think a bronsted acid is a general definition of an acid. Bronsted acids and lewis acids are the same thing, just that the bronsted acid definition focuses on the protons and the lewis acid definition focuses on the lone pair of electrons. As for strong and weak acids, they are all acids, so they ...
Wed Dec 02, 2020 3:32 pm
Forum: Bronsted Acids & Bases
Topic: Lecture 12/2/20 Weak Bases Clarification
Replies: 2
Views: 25

### Re: Lecture 12/2/20 Weak Bases Clarification

Hi Sofia! Yes, I think he actually explicitly stated that toward the end of his lecture. It is most likely because a molecule with Nitrogen (and some other atom(s) bonded at its lone pair) will not easily dissociate in water to create an OH-.
Wed Dec 02, 2020 3:27 pm
Forum: Bronsted Acids & Bases
Topic: Molarity and Strong Acid Ionization
Replies: 3
Views: 34

### Re: Molarity and Strong Acid Ionization

Hi Sofia! In that example, the strong acid, HCl, was 100% ionized, which means that all HCl (aq) molecules dissociated into H+ and Cl-. However, H+ is just a shorthand for H3O+, because the H+ bonded with the water (hence why HCl is denoted aqueous). So, you can just see HCl (aq) --> H3O+ + Cl-. You...
Tue Nov 24, 2020 10:25 am
Forum: Determining Molecular Shape (VSEPR)
Topic: VSEPR formula
Replies: 4
Views: 41

### Re: VSEPR formula

I think that an E represents lone pairs of electrons present; for example if the molecular shape formula is AX4E, it would represent a central atom bonded to 4 atoms and having one lone pair electron (means that there are 2 electrons, thus 1 lone pair of electrons, on the central atom). Thus in resp...
Tue Nov 24, 2020 10:17 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Why is CH2Cl2 polar?
Replies: 6
Views: 78

### Re: Why is CH2Cl2 polar?

Hi Nane! For CH2CL2, its shape is tetrahedral. Because Cl and Cl are always next to each other anyways, Cl and Cl will create a negative dipole to its side compared to the side with the hydrogens. Although it's tricky to visualize, CH2CL2 is polar. Thus one thing to keep in mind is that the lewis st...
Tue Nov 24, 2020 10:02 am
Forum: Determining Molecular Shape (VSEPR)
Topic: lone pair e-
Replies: 3
Views: 37

### Re: lone pair e-

Hello! Yes, lone pair e-s do play a role in determining if a molecule is polar or not. The only reason why this example, XeF2, is not polar is because the lone pairs actually create the two F molecules to be 180 degrees to each other, which creates the linear shape. Because the F molecules' dipoles ...
Mon Nov 23, 2020 7:46 pm
Forum: Sigma & Pi Bonds
Topic: sp3 orbitals
Replies: 1
Views: 63

### sp3 orbitals

1. Why are the lone pair electrons in the sp3 hybrid orbital for NH3 depicted as full orbital? I know that N has 5 valence electrons and thus the remaining electron will fill the first sp3 orbital with a spin down. However, wouldn't this full orbital mean that this lone pair will not form a bond bec...
Mon Nov 23, 2020 7:35 pm
Forum: Sigma & Pi Bonds
Topic: Lecture 11/23/20
Replies: 2
Views: 30

### Lecture 11/23/20

In today's lecture, Dr. Lavelle labeled all the 3 regions of e- density for each Carbon in C2H4, ethylene, as sp3 in his drawing on the whiteboard instead of sp2 hybrid orbitals. Was this a mistake or am I missing something? His lecture notes also seemed to label the 3 regions of e- density as sp2, ...
Wed Nov 18, 2020 11:49 am
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Textbook 3f. 3
Replies: 3
Views: 49

### Re: Textbook 3f. 3

Adding on a bit, options a and e's symmetry allows any dipole moments to be cancelled (the vectors are cancelled). Although c also looks slightly symmetric, I think this molecule also has a dipole-dipole because the tetrahedral shape does not allow the dipole moment vectors of the Cl molecules to ca...
Wed Nov 18, 2020 11:39 am
Forum: Lewis Structures
Topic: Sapling #4
Replies: 3
Views: 39

### Re: Sapling #4

Hello! By contributing substantially to the overall structure, I think that it was asking about which one of the molecules was the one that is most accurate, thus found in reality. By accurate, the molecule with the more likely formal charge would have been the one to contribute substantially to the...
Wed Nov 18, 2020 11:36 am
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: London Dipole
Replies: 3
Views: 38

### Re: London Dipole

Hi Heather, London dispersion forces are temporary dipole moments caused because electrons aren't totally fixed on one spot and are slightly moving about. Because of this slight movement, one side of a nonpolar covalent molecule might become temporarily negative or positive, which then causes anothe...
Wed Nov 18, 2020 8:31 am
Forum: Lewis Structures
Topic: N and Expanded Octet
Replies: 3
Views: 32

### Re: N and Expanded Octet

I agree with Margaret; the d orbitals can accommodate more electrons, and this is possible for 3p elements and below. Thus Nitrogen cannot have an expanded octet, and the octet rule has to be followed.
Wed Nov 18, 2020 8:28 am
Forum: Lewis Structures
Replies: 4
Views: 53

Hello! The textbook actually says that b and c are radicals. Option a would not be a radical, because there are no unpaired lone electrons as seen in its lewis structure. So you are correct that OH is a radical!
Sat Nov 14, 2020 1:22 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Why aren't the bond angles in PCl5 maximized?
Replies: 3
Views: 42

### Re: Why aren't the bond angles in PCl5 maximized?

Hello! The 90 degrees and 120 degrees is the maximal repulsion of PCl5. PCl5 spreads out to create three atoms in a trigonal planar shape (thus the 120 degrees) while one atom is above this trigonal planar and one atom is below the trigonal planar. The 90 degrees is just from these two atoms in comp...
Fri Nov 13, 2020 6:42 pm
Forum: Ionic & Covalent Bonds
Topic: Sapling question
Replies: 3
Views: 53

### Re: Sapling question

In this case, BCl3, Br2, and C2H6 would display only London dispersion forces. BCl3 is symmetric in shape, and its "vectors" (regions of charge) cancel out (pointing in opposite directions), thus is nonpolar and has only london dispersion forces. Although NF3 also looks like a good option,...
Fri Nov 13, 2020 6:34 pm
Forum: Resonance Structures
Topic: plausible perchlorate ion
Replies: 3
Views: 47

### Re: plausible perchlorate ion

Hello! By using the formula for finding formal charge (FC = V - (L + S/2)), you can find the formal charge of each of the atoms in the perchlorate ion. One thing to realize though, is that Cl has a high electronegativity, and thus will not prefer positive charges. The chlorines with a formal charge ...
Fri Nov 13, 2020 6:22 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone-Lone Pair vs Lone Bonding Pair vs Bonding-Bonding Pair?
Replies: 5
Views: 50

### Re: Lone-Lone Pair vs Lone Bonding Pair vs Bonding-Bonding Pair?

I agree with Ryan. You can imagine it like this: If there is a central atom, and there are two lone pairs around it and two bonded atoms around it, the repulsion between the two lone pairs are larger than the repulsion between a lone pair and a bonded atom (if there was a central atom with one lone ...
Wed Nov 11, 2020 11:00 am
Forum: Trends in The Periodic Table
Topic: Textbook Problem Ionization Energy Oxygen
Replies: 3
Views: 34

### Re: Textbook Problem Ionization Energy Oxygen

Hello! The energy needed to remove an e- from Oxygen is an exception because its electron configuration is 1s2 2s2 2p4, and although 2p3 allows all the 3 electrons in the p orbitals to be stable, the extra electron in the 2px orbital causes an electron electron repulsion in the 2px orbital, making i...
Tue Nov 03, 2020 2:27 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: electron con fig
Replies: 2
Views: 27

### Re: electron con fig

This happens only for the d orbitals and s orbitals, and not the p orbitals. As the energy of electrons increase, the space between these orbitals also decreases as seen in Dr. Lavelle's lectures. The d and s orbitals are so close that their energy levels seem to fluctuate. I think that the s and p ...
Tue Nov 03, 2020 2:13 pm
Forum: Resonance Structures
Topic: Limitations of Lewis Structures
Replies: 6
Views: 59

### Re: Limitations of Lewis Structures

I wouldn't say that resonance is the name of a limitation; I would say that resonance (some lewis structures having a blending of their resonance structures) is a characteristic of molecules that just isn't well displayed in a lewis drawing. In lewis structures, we use double, single, etc. bonds bec...
Mon Nov 02, 2020 9:48 pm
Forum: Resonance Structures
Topic: Resonance Structure vs Resonance Hybrid
Replies: 2
Views: 33

### Re: Resonance Structure vs Resonance Hybrid

I also agree that we have to know how to draw resonance structures, but do not have to draw resonance hybrids. I think Dr.Lavelle explained in the lecture that we can draw dotted lines as well but that it would be too complicated, thus why we draw resonance structures instead and can use them to und...
Mon Nov 02, 2020 9:36 pm
Forum: Trends in The Periodic Table
Topic: Sizes of ions vs elements
Replies: 4
Views: 37

### Re: Sizes of ions vs elements

Along with the periodic table trends for atomic radius, you can think of it like this: Cl has more protons than Na, thus has a greater nuclear charge. Although Cl has more electrons, its electrons are still in the same principal energy level (3) as Na, so its greater nuclear charge has a greater imp...
Mon Nov 02, 2020 9:28 pm
Forum: Trends in The Periodic Table
Topic: Covalent Character of Compounds
Replies: 2
Views: 33

### Re: Covalent Character of Compounds

Hi Arezo, I'm thinking that AgF is less covalent because of its bonding compared to BeCl2. Disregarding how far apart these elements are from each other on the periodic table, a covalent character would imply more sharing and an ionic character would imply more of a transfer of electrons. Because Be...
Wed Oct 28, 2020 4:10 pm
Forum: Trends in The Periodic Table
Topic: Electron Affinity
Replies: 10
Views: 69

### Re: Electron Affinity

Just to clarify about this topic, I believe it was mentioned in today's lecture that ionization energy and electron affinity are alike to opposites of each other, yet both increase across a period and decrease down a group? Yes; although this may seem confusing, this is correct. But although the wo...
Wed Oct 28, 2020 3:59 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Lecture 11
Replies: 2
Views: 52

### Re: Lecture 11

I agree with Janelle; I think this is also why electron configurations still go by 3d first, then 4s because they are still lower in energy than 4s when occupied (even though 4s is occupied first).
Wed Oct 28, 2020 3:55 pm
Forum: Photoelectric Effect
Topic: Energy of photon
Replies: 5
Views: 57

### Re: Energy of photon

Hello! In this equation, Ep is the energy of the photon (Joules per photon) and you would use Avogadro's number to find it in Joules/mole or use SI conversion to get it to kJ. However, the threshold energy and kinetic energy is usually just in Joules.
Wed Oct 28, 2020 8:59 am
Forum: SI Units, Unit Conversions
Topic: picometer conversion
Replies: 13
Views: 137

### Re: picometer conversion

I agree with Geethika. One way you can visualize it is by doing this method: 1.5 x 10^-10 m (1x10^12 pm / 1 m) = 1.5 x 10^2 pm = 150 pm This way, you can see how the units cancel out. You can also check your answer vaguely by knowing that picometers should have a greater number than meters because i...
Wed Oct 28, 2020 8:54 am
Forum: Limiting Reactant Calculations
Topic: Textbook Fund. Problem M11
Replies: 2
Views: 42

### Re: Textbook Fund. Problem M11

Hi Emily! After you've found the limiting reactant, find how much O2 that you could have created with that limiting reactant. For example, you would do ____ moles P4 x (3 moles O2/ 1 mole P4) x (32 g O2/ 1 mole O2) to find how many grams of O2 was used. To find how much O2 is left, do 5.77g (the tot...
Tue Oct 27, 2020 6:02 pm
Forum: Photoelectric Effect
Topic: Photoelectric Effect
Replies: 13
Views: 119

### Re: Photoelectric Effect

I actually thought that if this happened for the photoelectric effect, the electron was excited but not removed. I thought that the part about not being able to absorb the light and the light passing through was for the atomic spectra.

Someone might have to check up on this though!
Mon Oct 19, 2020 7:20 pm
Forum: DeBroglie Equation
Topic: Deriving De Broglie Equation
Replies: 2
Views: 38

### Re: Deriving De Broglie Equation

Hello! So we are given that E=pv. Now from here, I think that we can substitute c into v because we are specifically talking about "electromagnetic radiation" or light. This is why we can use the speed of light (because we are talking about light) as the velocity so that now, E=pc is speci...
Mon Oct 19, 2020 7:10 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Sapling homework Question 8
Replies: 2
Views: 49

### Re: Sapling homework Question 8

I agree with RDove! The only thing I wanted to add is that you also know this is an "emission" of energy from the question, and thus you can further check that your final is n=1 and not n=2. But usually, most questions so far seem to ask for the emission of energy anyway; just wanted to ad...
Mon Oct 19, 2020 7:06 pm
Forum: DeBroglie Equation
Topic: 1B27
Replies: 3
Views: 38

### Re: 1B27

Hello! It's most likely from Planck's constant. Planck's constant is not the exact calculation we use (we usually use 6.626x10^-34 Js), and there is more after the 6.626. We can probably assume that because Planck's constant is actually slightly larger than what we use, it's probably making that sma...
Mon Oct 19, 2020 7:01 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Sapling Week 2/3 Problem 11
Replies: 2
Views: 26

### Re: Sapling Week 2/3 Problem 11

Hi Sameer! I agree with Sarah; I think the bare minimum we should know is that energy levels down to n=1 come from the Lyman series, and levels down to n=2 is from the Balmer series. I think you may be confused about where the initial energy level was for the question (as the lower energy level was ...
Mon Oct 19, 2020 6:52 pm
Forum: Einstein Equation
Topic: Sapling homework Question 9
Replies: 3
Views: 51

### Re: Sapling homework Question 9

Hi Jaclyn! Here is the formula that was used for the photoelectric effect: (E per photon) = (Work Function) + (KE) The work function is the bare minimum you need to eject the electron from the metal surface with 0 kinetic energy. By maximum wavelength, it's asking us for the wavelength needed to mat...
Fri Oct 16, 2020 6:07 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Atomic Spectra Module Question 39
Replies: 2
Views: 38

### Re: Atomic Spectra Module Question 39

I believe that after you have the energy for both energy level n=4 and n=2, you subtract n=4 energy from n=2 energy to get the difference in energy. The positive difference in energy is the energy of the light emitted as well. Thus using E=hv you can find the frequency, the use c=(lambda)(frequency)...
Fri Oct 16, 2020 5:41 pm
Forum: Properties of Electrons
Topic: Electrons Excited or Ejected
Replies: 19
Views: 142

### Re: Electrons Excited or Ejected

I also think that an electron is ejected when it matches its threshold energy (not including any kinetic energy), and that below this threshold energy, electrons can be excited (moving up energy levels). Maybe it could be more interpreted like this: an electron can be excited by electromagnetic radi...
Fri Oct 16, 2020 5:14 pm
Forum: SI Units, Unit Conversions
Topic: Converting from kJ/mol to J
Replies: 2
Views: 28

### Re: Converting from kJ/mol to J

Hi Kaylee!

Energy, E, is in J/photon. Essentially, a mole is 6.022 x 10^23 things, thus a mole is also 6.022x10^23 photons! When we divide by the constant, we convert the J/moles (after converting from kJ to J) to J/photon.

Hope this helps!
Fri Oct 16, 2020 5:11 pm
Forum: Photoelectric Effect
Topic: Excess energy
Replies: 20
Views: 135

### Re: Excess energy

Yes, that equation is the equation to calculate KE (kinetic energy). The energy emitted by the light, E, has to equal the threshold energy (work function) + the kinetic energy of the electron when it is emitted because of the law of conservation of energy. The threshold energy is the energy needed t...
Fri Oct 16, 2020 5:03 pm
Forum: Properties of Light
Topic: Textbook Excercise A1.3
Replies: 3
Views: 38

### Re: Textbook Excercise A1.3

Hello! I also agree that one can use process of elimination to get C, as the other three answers are incorrect. But I think that C is correct because if you imagine light passing through a point, the lower frequency/longer wavelength the light, the less "cycles" or "waves" are pa...
Thu Oct 08, 2020 4:18 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Confidence Interval and Accuracy & Precision
Replies: 5
Views: 62

### Re: Confidence Interval and Accuracy & Precision

Your question got me thinking- if precision is how close your answers are relative to each other, wouldn't 34≤x≤35 and 33≤x≤36 and the 95% and 97% confidence interval only be talking about accuracy (thus making the 97% confidence interval the more accurate one than 95% but 95% not being more precise...
Thu Oct 08, 2020 4:04 pm
Forum: Molarity, Solutions, Dilutions
Topic: Post Assessment Question - Moles
Replies: 3
Views: 30

### Re: Post Assessment Question - Moles

Hi Melanie, I think this one is also a combustion reaction question. 1. Try creating another unbalanced equation so you can see what is happening: 4C4H10 (g) +O2 (g) --> CO2 (g) + H2O (g <-- I think H2O in combustion reactions are actually gas instead of liquid) 2. Then, balance your equation to get...
Thu Oct 08, 2020 3:56 pm
Forum: Administrative Questions and Class Announcements
Topic: All Assignments
Replies: 8
Views: 75

### Re: All Assignments

Jeffrey Fenn 1G wrote:I don't know if this helps but just make sure to do the first four modules this week, as the next four aren't due until the end of week 2!

Thank you! Are the first four due by a certain time this week?
Thu Oct 08, 2020 3:54 pm
Forum: Molarity, Solutions, Dilutions
Topic: Post Assessment Survey Question Help
Replies: 3
Views: 44

### Re: Post Assessment Survey Question Help

Hi Melanie! So this question is a combustion reaction, where a substance reacts with oxygen gas to form carbon dioxide and water vapor. 1. You'll need to create an unbalanced equation to first see what you need to do: 2C6H6+ O2 --> CO2+ H2O 2. Then, balance the equation for CO2 and H2O to get: 2C6H6...
Thu Oct 08, 2020 3:34 pm
Forum: Administrative Questions and Class Announcements
Topic: Accessing the E-textbook [ENDORSED]
Replies: 106
Views: 7184

### Re: Accessing the E-textbook[ENDORSED]

I'm still a bit confused on how we get the E-book. After ordering through the UCLA Store, and getting the access code for Sapling, is the E-book just a link for the pdf file that also comes in the mail (or through email in recent cases) or is it accessible through Sapling?
Thu Oct 08, 2020 3:12 pm
Forum: Administrative Questions and Class Announcements
Topic: All Assignments
Replies: 8
Views: 75

### All Assignments

Hello! I recently joined the class and wanted to clarify whether these were the main things that needed to be done by Week 1:
- Modules on the Chem14A website
- Weekly Homework on Sapling due Sunday midnight
- Chemistry Community: 5 posts

Is there anything that I'm missing?