## Search found 58 matches

Sat Jan 16, 2021 3:20 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: hw question #3
Replies: 10
Views: 41

### Re: hw question #3

For this specific K equation, you can actually take the square root of both sides. It would simplify to square root of 53.3 = 2x/(0.7-x) and then you would solve for x from there by rearranging the equation.
Sat Jan 16, 2021 3:16 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kw constant
Replies: 25
Views: 50

### Re: Kw constant

I agree with the post above. The autoprotolysis of water is really small so it's almost negligible, and the H2O molecules remain in excess.
Sat Jan 16, 2021 3:11 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sapling Week One #9
Replies: 2
Views: 23

### Re: Sapling Week One #9

For this problem, you would calculate Q and see that when the concentration of NO is changed to 0.700M, the reverse reaction would take place. This means that the equilibrium concentrations for N2 and O2 would be (0.100-x) and for NO it would be (0.700-2x). Once you plug these into the K equation, y...
Sat Jan 16, 2021 2:41 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Textbook Problem 5.61
Replies: 2
Views: 11

### Re: Textbook Problem 5.61

I think you're correct that compressing the system means a change in volume. However, pressure and volume changes relate to gases. It's true that when volume decreases the system will shift to the side with less moles, but since there are an equal amount of moles of gases on each side of the reactio...
Sat Jan 16, 2021 2:27 pm
Forum: Ideal Gases
Topic: Sapling Question #4
Replies: 11
Views: 70

### Re: Sapling Question #4

The first thing to do it set up an ICE box for the equation and solve for the equilibrium pressures. It's always best to solve for Q just to find out which way the reaction is proceeding. After setting up the equilibrium constant equation, you would solve for x (using the quadratic equation). Since ...
Sun Jan 10, 2021 8:52 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Pressure and Volume
Replies: 16
Views: 38

### Re: Pressure and Volume

They are inversely proportional, meaning if you increase one the other will decrease. Let's say there's a box(of some volume) full of gas particles that are constantly moving and hitting the walls of the box. If you were to shrink the size of the box, the gas particles would hit the box more frequen...
Sun Jan 10, 2021 8:42 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: H20 and K constant
Replies: 4
Views: 12

### Re: H20 and K constant

We usually emit water in a liquid state from the K equation. So in this case, I'm pretty sure gaseous H2O would be considered in the calculating this K value.
Sat Jan 09, 2021 9:45 pm
Forum: Ideal Gases
Topic: Inert Gas
Replies: 20
Views: 69

### Re: Inert Gas

Basically, an inert gas is any of the noble gases. It's considered "inert" because most of the noble gases do not react.
Sat Jan 09, 2021 9:08 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Calculating concentration using the quadratic formula
Replies: 6
Views: 29

### Re: Calculating concentration using the quadratic formula

It depends on the initial concentrations of the reactants and products. There's no such thing as negative concentration/partial pressure; the lowest it would be is zero. When finding the x value using the quadratic formula, it's important to plug the values into the equilibrium equations for each re...
Sat Jan 09, 2021 8:58 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: K Constant
Replies: 3
Views: 19

### Re: K Constant

I agree with the posts above, assuming that the temperature stays the same. If the temperature were to change, then the value of K would also change.
Sun Dec 06, 2020 7:59 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Coordination Number
Replies: 13
Views: 91

### Re: Coordination Number

Coordination number is essentially the number of bonding sites that a TM will form with ligands. It's important to know the denticity of the ligands since they will affect the coordination number. For example, a bidentate ligand counts as 2 bonds, a tridentate ligand forms 3, and so on. I'm not comp...
Sun Dec 06, 2020 7:52 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Sapling 5
Replies: 6
Views: 41

### Re: Sapling 5

Hi! En refers to the ethylenediamine ligand, C2H4(NH2)2, and is a bidentate ligand. This means that it will bond to the cobalt ion at two sites. Using this information, the two en ligands will make 4 bonds. Add the two CO bonds and you'll get a total of 6 bonds, or a coordination number of 6.
Fri Dec 04, 2020 1:21 am
Forum: Coordinate Covalent Bonds
Topic: H3O+ explanation
Replies: 4
Views: 24

### Re: H3O+ explanation

I'm pretty sure you would still write the (aq). The reaction is still occurring in water, so the H3O+ would be denoted as aqueous.
When in doubt, I don't think writing a state of matter in reaction equations will do any harm (unless its incorrectly identified).
Fri Dec 04, 2020 1:16 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Sapling Week 9 #5
Replies: 3
Views: 45

### Re: Sapling Week 9 #5

I got this question wrong at first but then I realized it is super important to look at the denticity of the ligand, not just the number of ligands! Because en, or ethylenediamine, is a bidentate ligand, it will bond to the cobalt cation at two sites. For the two en ligands, that's a total of 4 bond...
Fri Dec 04, 2020 1:03 am
Forum: Bronsted Acids & Bases
Topic: Question about net ionic equation for neutralization of weak acids/bases
Replies: 2
Views: 31

### Re: Question about net ionic equation for neutralization of weak acids/bases

I agree with the statement above! To kind of explain why this happens though, the reason we keep the weak acid/base in its molecular formula is that it has very little dissociation. It dissociates so little that we essentially say "it doesn't happen," and we continue with the net ionic equ...
Sun Nov 29, 2020 9:47 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Nonpolar bonds
Replies: 7
Views: 31

### Re: Nonpolar bonds

A non polar bond would have to be a bond between atoms whose electronegativity difference is essentially zero. There wouldn't be any uneven distribution of electron density. This is why non polar bonds are usually between two atoms of the same element.
Sun Nov 29, 2020 9:37 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: trigonal bipyramidal
Replies: 5
Views: 29

### Re: trigonal bipyramidal

It depends on the atoms you're comparing. You can think of the equatorial atoms as a circle divided by the three atoms, so every angle between the equatorial atoms would be 120 degrees. For the axial and equatorial atoms, when I see a picture of them I usually envision a right angle between them. Th...
Sun Nov 29, 2020 9:32 pm
Forum: Octet Exceptions
Topic: PCl5 expanded octet question
Replies: 6
Views: 44

### Re: PCl5 expanded octet question

Phosphorus is a period 3 element and has d orbitals that electrons can fill, which allows them to have expanded octets.
Sun Nov 29, 2020 9:27 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond angles
Replies: 8
Views: 70

### Re: Bond angles

I don't think we'll have to know the specific angles. Those are usually determined experimentally. It's more about predicting a smaller/bigger bond angle relative to its VSEPR structure. (For example, NH3 has slightly smaller bond angles than 109.5 since the lone pair exerts a higher repulsion than ...
Fri Nov 27, 2020 7:40 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: lone pairs on H2O
Replies: 4
Views: 51

### Re: lone pairs on H2O

I think it has to do with the fact that the regions of electron density create a tetrahedral structure (the molecule is bent but the electron geometry is tetrahedral). If you switch any of the positions of the atoms/lone pairs, the structure will essentially be the same thing again. Dr. Lavelle desc...
Fri Nov 27, 2020 7:33 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: trigonal planar vs trigonal pyramidal
Replies: 9
Views: 62

### Re: trigonal planar vs trigonal pyramidal

The deciding factor between the two structures is a lone pair! Keep in mind that a trigonal planar structure has 3 regions of electron density around the central atom while a trigonal pyramidal structure has 4. The extra region of electron density on a trigonal pyramidal structure is a lone pair, no...
Sun Nov 22, 2020 9:27 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Seesaw Shape
Replies: 8
Views: 39

### Re: Seesaw Shape

The lone pair has to be one of equatorial positions because it creates a lower energy/more stable structure for the molecule. Essentially, the regions of electron density would be farther apart if the lone pair is in one of the equatorial positions, which would minimize repulsion and create a favora...
Wed Nov 18, 2020 10:42 pm
Forum: Student Social/Study Group
Topic: Lewis Structure
Replies: 4
Views: 19

### Re: Lewis Structure

If the element is in energy levels n = 3 or higher, it can have expanded valence shells. This is because they have other orbitals.
A period 3 element in the p-block, for example, has d-orbitals that can accommodate for the extra electrons.
Wed Nov 18, 2020 10:35 pm
Forum: Trends in The Periodic Table
Topic: Trend for effective nuclear charge
Replies: 3
Views: 34

### Re: Trend for effective nuclear charge

The periodic trend is that effective nuclear charge increases across a period (left to right) and up a group. So generally the elements towards the top right have the most effective nuclear charge.
Wed Nov 18, 2020 10:30 pm
Forum: Bond Lengths & Energies
Topic: Boiling/Melting Point
Replies: 20
Views: 142

### Re: Boiling/Melting Point

We would look at intermolecular forces since those are the attractions between the molecules. For example, if the IMFs are stronger in one compound, they would "stick together" more than the other compound and have a higher boiling point(more energy would be needed to break those intermole...
Wed Nov 18, 2020 10:28 pm
Forum: Ionic & Covalent Bonds
Topic: Nonpolar vs Polar covalent
Replies: 1
Views: 11

### Re: Nonpolar vs Polar covalent

I think a difference of 0.4 or less leads to nonpolar covalent bonding. Following that rule, a C-H bond would be nonpolar.
Sat Nov 14, 2020 11:14 pm
Forum: Dipole Moments
Topic: Dipoles vs Ions
Replies: 5
Views: 29

### Re: Dipoles vs Ions

An ionic bond essentially involves the transfer of an electron, usually from a metal to nonmetal, to achieve a lower energy. A dipole moment is a separation of charge due to differences in electronegativity. There is a momentary unequal distribution of electrons that leads to a dipole moment.
Thu Nov 12, 2020 7:50 pm
Forum: Ionic & Covalent Bonds
Topic: Intramolecular force vs Intermolecular force
Replies: 3
Views: 30

### Re: Intramolecular force vs Intermolecular force

Intramolecular forces are attractive forces that occur within a molecule. For example, atoms within a molecule are attracted to one another by the sharing of electrons(bonding). Intermolecular forces are attractive forces between molecules. Hydrogen bonding would be an example of this since the hydr...
Thu Nov 12, 2020 7:45 pm
Forum: Bond Lengths & Energies
Topic: Sapling HW Bond Length
Replies: 7
Views: 55

### Re: Sapling HW Bond Length

The periodic trend for atomic radii is that it increases down a group! Since S is one period below O on the periodic table, it has a larger atomic radius and that's why the bond length would be larger.
Wed Nov 11, 2020 5:44 pm
Forum: Ionic & Covalent Bonds
Topic: Ions
Replies: 6
Views: 34

### Re: Ions

Yeah I don't think its required but its really useful to know some polyatomic ions. For the question above, there are 18 electrons to account for in NO2-. When you go through the general steps of drawing a lewis structure for NO2-, you'll see that the oxygens single bonded to the nitrogen will fill ...
Wed Nov 11, 2020 5:35 pm
Forum: Electronegativity
Topic: Sapling #14
Replies: 10
Views: 73

### Re: Sapling #14

Hydrogen bonds usually only form between H and fluorine, oxygen, or nitrogen. In the context of the problem, that's why there must be an O on either side of the H in the H-bond.
Thu Nov 05, 2020 2:58 pm
Forum: Octet Exceptions
Topic: Lewis Acid and Lewis Base
Replies: 7
Views: 60

### Re: Lewis Acid and Lewis Base

A Lewis acid is a substance that will accept electrons whereas a Lewis base is one that will donate electrons. So using the example that Professor Lavelle gave in lecture, BF3 would be a Lewis acid since the boron atom, whose octet is not filled, can accept more electrons from an F- atom. The F- ato...
Thu Nov 05, 2020 2:54 pm
Forum: Ionic & Covalent Bonds
Topic: Ionic Charge
Replies: 3
Views: 20

### Re: Ionic Charge

We can usually look at the periodic table to find the ionic charges of elements. Elements in group 1 and 2 have a charge of +1 and +2, respectively, and group 13 has a charge of +3. The turning point is group 14, which has a charge of +4 or -4, and from there on, as you move to the right the ionic c...
Thu Nov 05, 2020 2:45 pm
Forum: Ionic & Covalent Bonds
Topic: Formal Charge
Replies: 3
Views: 18

### Re: Formal Charge

Formal charge is essentially how many electrons an atom in a molecule "holds." I'm pretty sure it's the amount of electrons that are associated with the atom in terms of its bonding characteristics within the molecule.
Tue Nov 03, 2020 10:58 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Sapling 1E.23
Replies: 3
Views: 25

### Re: Sapling 1E.23

The way you wrote it is correct in terms of which levels are filled first (electrons fill the 4s orbital before the 3d orbital) but electron configurations are often written in order of increasing energy levels. I think that's just a general rule that we follow. That's why the answer in the book is ...
Mon Nov 02, 2020 10:20 pm
Forum: Trends in The Periodic Table
Topic: # of electrons
Replies: 23
Views: 118

### Re: # of electrons

The amount of electrons is the same as the atomic number. If you want to find valence electrons, it would be the number in the ones place for elements in group 1,2, and 13-17. For example, oxygen is in group 16 and it has 6 valence electrons.
Thu Oct 29, 2020 7:25 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: h vs. ħ?
Replies: 11
Views: 119

### Re: h vs. ħ?

h is Planck's constant, which is defined as 6.626x10^-34 J s. ħ is equivalent to Planck's constant(h)/2pi. I'm assuming the second formula should have a ≥ instead of an = sign but the formulas should represent the same thing, just in different notations. The textbook also explains this in section 1B...
Thu Oct 29, 2020 7:17 pm
Forum: Quantum Numbers and The H-Atom
Topic: Effective Nuclear Charge
Replies: 4
Views: 46

### Re: Effective Nuclear Charge

I like to think of effective nuclear charge as " the more protons in an atom, the stronger the pull," where "the pull" is the electrostatic attraction between the nucleus and electrons that Professor Lavelle mentioned. Essentially, it's the positive charge/attraction of the nucle...
Wed Oct 28, 2020 8:05 pm
Forum: Molarity, Solutions, Dilutions
Topic: Dilution module
Replies: 6
Views: 65

### Re: Dilution module

I think I remember Professor Lavelle saying something along the lines of "someone is more likely to say 'I need 6.36mL of solution' instead of 'I need 0.00636 L of solution." and that's why we usually convert to mL. It's not that big of a deal as long as you convert units correctly though.
Wed Oct 28, 2020 5:32 pm
Forum: Properties of Electrons
Topic: Rydeberg's Equation Help
Replies: 3
Views: 56

### Re: Rydeberg's Equation Help

I think you switched the n1 and n2 values in the equation. The final level(n2) is 6 and the initial level(n1) is 2 for this electron transition. This is because the electron is going from n=2 to n=6. This should help you get a positive value.
Wed Oct 28, 2020 5:22 pm
Forum: SI Units, Unit Conversions
Topic: SI Unit for Mass
Replies: 10
Views: 103

### Re: SI Unit for Mass

It's probably easier to use kg instead of grams since Planck's constant is given as 6.626x10^/34 kg m^2 s^-1. Cancelling units is pretty easy from there.
Wed Oct 28, 2020 5:15 pm
Forum: Photoelectric Effect
Topic: Sampling #4
Replies: 3
Views: 39

### Re: Sampling #4

The work function that you found is equivalent to the amount of energy needed to eject an electron. That value is in joules per photon, so to solve for how many electrons are ejected, you would just divide the amount of energy of the photon burst (4.61×10−7 J) by the work function(remember the energ...
Mon Oct 26, 2020 10:13 pm
Forum: Photoelectric Effect
Topic: Moles of atoms/photons
Replies: 3
Views: 39

### Re: Moles of atoms/photons

It really does depend on the question but if you solve for an amount of atoms/photons and you're trying to convert it to moles, you would most likely divide by Avogadro's number.
Mon Oct 26, 2020 10:10 pm
Forum: Properties of Light
Topic: Tips for knowing what equation to use?
Replies: 5
Views: 74

### Re: Tips for knowing what equation to use?

It really depends on the question but the first thing I do when I start a problem is to write down/identify what information is already given to me and what the question is asking me to find. What the question is asking for it the key component because it tells you what equation it relates to. For e...
Fri Oct 23, 2020 1:50 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Sapling 2/3/4 #26
Replies: 2
Views: 43

### Re: Sapling 2/3/4 #26

Hi! I actually kept messing this part up too. This is how I ended up finding the mass of a single Helium atom. The tricky part of dimensional analysis is the units and cancelling them out accordingly. To solve for the uncertainty in the helium atom's velocity, we plug that into the equation h/(4pi)(...
Wed Oct 21, 2020 1:40 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Atomic Spectra
Replies: 2
Views: 27

### Re: Atomic Spectra

When the energy from an electron is being emitted, the energy is "taken away" or "subtracted" from the electron, which results in the negative sign. On the other hand, that is the same energy as the photon emitted. The values are equal and opposite in order to satisfy the law of ...
Wed Oct 21, 2020 1:13 am
Forum: DeBroglie Equation
Topic: Sapling Question 10
Replies: 5
Views: 87

### Re: Sapling Question 10

It seems a little confusing since diatomic means 2 atoms and a particle refers to a single unit. In this case, the entire molecule of oxygen acts as one particle! The unit itself is the diatomic oxygen molecule. So when calculating the molar mass of this particle, you would say it is 2 times the mol...
Wed Oct 21, 2020 1:05 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Sapling week 2-4 HW # 7
Replies: 1
Views: 21

### Re: Sapling week 2-4 HW # 7

The enthalpy of fusion is essentially the amount of energy, usually in the form of heat, needed to change a substance from solid to liquid(melting). Specific heat is related to the amount of energy needed to raise the temperature of the substance by 1 degree Celsius. Since the problem deals with mel...
Wed Oct 21, 2020 12:53 am
Forum: DeBroglie Equation
Topic: Sapling Question 17
Replies: 2
Views: 22

### Re: Sapling Question 17

The steps you took seem correct to me but I think you may have made an error when entering the values into your calculator. I followed the steps you provided and got 1.74x10^-11 m for the wavelength instead.
Sun Oct 18, 2020 10:26 pm
Forum: Significant Figures
Topic: Sig Figs and Scientific Notation
Replies: 10
Views: 97

### Re: Sig Figs and Scientific Notation

Only the first part counts, not the 10^x part.
Fri Oct 16, 2020 11:12 am
Forum: Student Social/Study Group
Topic: High School Chemistry Review/Resources
Replies: 6
Views: 68

### Re: High School Chemistry Review/Resources

My AP chem teacher used notes from the National Math and Science Initiative and I still use them for class today. I think you can just search "NMSI chemistry notes" and they should pop up. Crash course is really helpful too.
Wed Oct 14, 2020 4:40 pm
Forum: Properties of Light
Topic: intensity, photons, and frequency
Replies: 7
Views: 58

### Re: intensity, photons, and frequency

I don't think intensity necessarily refers to frequency since frequency has to do with the wavelength and the energy of the light. In terms of the photoelectric effect, I'm assuming intensity means using more photons of the same wavelength as opposed to a higher/lower energy light to eject the elect...
Wed Oct 14, 2020 4:35 pm
Forum: Photoelectric Effect
Topic: Photoelectric Effect
Replies: 5
Views: 70

### Re: Photoelectric Effect

Hi! Essentially the photoelectric experiment involves shining light at a metal surface to eject electrons from the atoms of the metal. The equation used to calculate energy released is E(photon) - (threshold energy/energy needed to eject the electron) = excess kinetic energy. If the energy of the ph...
Thu Oct 08, 2020 11:30 pm
Forum: Balancing Chemical Reactions
Topic: How moles should be balanced on each side
Replies: 11
Views: 64

### Re: How moles should be balanced on each side

A balanced equation has the same number of atoms of each element on both the reactant side and product side of the equation. So 2Na + 2H2O -> 2NaOH + H2 is the balanced equation. I think the 2 moles + 2 moles -> 2 moles + 1 mole equation is just meant to show the stoichiometric coefficients in the b...
Thu Oct 08, 2020 6:16 pm
Forum: SI Units, Unit Conversions
Topic: Kg to g
Replies: 13
Views: 136

### Re: Kg to g

One kilogram is 1000 grams, so if you're trying to convert grams to kilograms, divide by 1000. If you're converting kilograms to grams multiply by 1000!
Thu Oct 08, 2020 3:44 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Moles vs molecules
Replies: 14
Views: 151

### Re: Moles vs molecules

A mole is a unit of measurement and a molecule is a group of atoms bonded together. Avogadro's number plays into this since a mole is equivalent to 6.022x10^23 particles(or molecules) of an element or compound.
Thu Oct 08, 2020 12:54 pm
Forum: General Science Questions
Topic: Credit for community forum [ENDORSED]
Replies: 7
Views: 92

### Re: Credit for community forum[ENDORSED]

On Dr. Lavelle's website under the Chem 14A Class Website, there is a tab called "Weekly Online Discussion" that outlines how we get our participation points. It says that "Post can be a question, an answer, a comment on a question or answer, general discussion, assisting other studen...
Wed Oct 07, 2020 4:11 pm
Forum: Empirical & Molecular Formulas
Topic: Rounding EF to Integers
Replies: 6
Views: 62

### Re: Rounding EF to Integers

I'm not sure if it's absolutely necessary but I think it's a lot easier to find the molecular formula in the end using whole number integers in the empirical formula. From there it's just a matter of comparing the molar mass of the empirical formula to the given molar mass to determine the molecular...

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