## Search found 61 matches

Sun Jan 17, 2021 12:09 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE table and Molarity units
Replies: 16
Views: 34

### Re: ICE table and Molarity units

As long as you are consistent with units throughout your ice table you should be fine! I prefer to convert (if needed) to mol/L at the beginning to ensure that I do not forget to do so at the end!
Sun Jan 17, 2021 12:04 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: quadratic equations to solve for X
Replies: 7
Views: 16

### Re: quadratic equations to solve for X

Usually, when I find two roots that are positive, the best way for me to determine which is the correct one is by actually plugging them in for x. In all of the cases I have encountered, one of the values will result in a negative equilibrium concentration for either the product or reactant (or both...
Sun Jan 17, 2021 11:56 am
Forum: Ideal Gases
Topic: Gas for equilibrium equation
Replies: 8
Views: 31

### Re: Gas for equilibrium equation

"P" is used instead of brackets to indicate that the measurement is using partial pressure as opposed to concentration when calculating the equilibrium constant. This is also a key difference between Kp and Kc.
Sun Jan 17, 2021 10:23 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Using the ICE table
Replies: 32
Views: 79

### Re: Using the ICE table

Yes! ICE tables can be used with partial pressures or concentrations!
Sun Jan 17, 2021 10:18 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sapling WK 1, #4
Replies: 3
Views: 23

### Re: Sapling WK 1, #4

The first thing you will want to do is create an ICE table. You are given the initial pressure of 0.0750 bar for PCl5. The initial pressure will be 0 for PCl3 and PCl2. The change in pressure will be +x for both PCl3 and PCl2 and -x for PCl5 since there is a 1:1 molar ratio for each of the reactants...
Sun Jan 10, 2021 6:59 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Concentration
Replies: 12
Views: 43

### Re: Concentration

A concentration or Molarity is the number of moles per Liter. It is not possible to have a concentration that is less than zero because this would imply that it is possible to have a negative number of moles or liters.
Sun Jan 10, 2021 6:51 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Homogeneous and Heterogeneous Equilibrium
Replies: 13
Views: 58

### Re: Homogeneous and Heterogeneous Equilibrium

The overall reaction would be used in determining if a system has heterogeneous or homogeneous equilibrium. Despite solids and liquids not being included in the expression of the equilibrium constant, these phases are still present and do not change concentration or pressure in reactions. Because th...
Sun Jan 10, 2021 6:31 pm
Forum: Ideal Gases
Topic: Units of Temperature
Replies: 82
Views: 287

### Re: Units of Temperature

Kelvin is the correct unit to use. Using dimensional analysis, you will see that the units of Kelvin cancel out in calculations with ideal gas law! If provided Celsius, you can calculate the temperature in Kelvin by adding 273.15 to this value!
Sun Jan 10, 2021 6:21 pm
Forum: Ideal Gases
Topic: PV=nRT and concentration
Replies: 27
Views: 111

### Re: PV=nRT and concentration

Molarity is measured in moles/Liter. In the expression n/V, n represents moles, and volume (V) is measured in liters. Dividing moles by liters provides the units of Molarity or concentration!
Sun Jan 10, 2021 6:16 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Left vs. Right
Replies: 29
Views: 93

### Re: Left vs. Right

These both can be used interchangeably; however, it is important to understand that physical "shifting" does not actually occur in a system at equilibrium.
Sat Dec 12, 2020 2:18 pm
Forum: Bronsted Acids & Bases
Topic: lewis vs bronsted
Replies: 8
Views: 35

### Re: lewis vs bronsted

Lewis Acids/Bases deal with the transfer of electron pairs where:
-A Lewis Acid accepts a lone pair of electrons
-A Lewis Base donates a pair of electron

Bronsted Acids/Bases deal with the transfer of protons:
-A Bronsted Acid donates a H+
-A Bronsted Base accepts a H+
Sat Dec 12, 2020 2:13 pm
Forum: Hybridization
Topic: Hybridization and Shape
Replies: 6
Views: 51

### Re: Hybridization and Shape

The number of regions of electron density is equal to the number of hybrid orbitals. We can determine the shape and number of regions on electron density from as VSEPR Formula. Keep in mind lone pairs and bonded atoms both count as regions of electron density. I found this quizlet which provides a n...
Sat Dec 12, 2020 1:58 pm
Forum: Administrative Questions and Class Announcements
Topic: Final Content-Naming Acids
Replies: 2
Views: 28

### Re: Final Content-Naming Acids

I do think it would be beneficial to know the acids and bases discussed in lecture. Can gives a good list of these. Another example I can think of off the top of my head is acetic acid, CH3COOH and the deprotonated conjugate base acetate, CH3COO-
Mon Dec 07, 2020 10:38 am
Forum: Student Social/Study Group
Topic: Chem Website
Replies: 4
Views: 34

### Re: Chem Website

The password was included in one of the first emails we received from Dr. Lavelle. It is LL14A20
Sun Dec 06, 2020 5:38 pm
Forum: Trends in The Periodic Table
Topic: Focus 1 Exercise 13
Replies: 3
Views: 30

### Re: Focus 1 Exercise 13

Ionization energy is the amount of energy required to remove an electron from an atom. Oxygen is the first element in the p-block to have a paired electron. It is slightly easier to remove an electron from oxygen than it is in nitrogen and fluorine because this one paired electron is subject to a gr...
Sun Dec 06, 2020 5:06 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone Pair Locations
Replies: 6
Views: 55

### Re: Lone Pair Locations

It is most energetically favorable for lone pairs to be the furthest distance away from bonded atoms due to their relatively high magnitude of repulsion. Essentially, they will exist where the least amount of atoms are present. Tatyana uses a great example of this with the see-saw in which the lone ...
Sun Dec 06, 2020 4:43 pm
Forum: Hybridization
Topic: Pi Bonds Cannot Rotate
Replies: 23
Views: 162

### Re: Pi Bonds Cannot Rotate

I remember in Dr. Lavelle's lecture on types of bonds he held a marker in his hands parallel to demonstrate how pi bonds do not allow for rotation. If rotation were to occur, the bond would have to be broken which was represented by the marker falling from his hands. I am totally visual as well and ...
Sun Dec 06, 2020 4:36 pm
Forum: Lewis Structures
Topic: Most Stable Structure
Replies: 23
Views: 117

### Re: Most Stable Structure

When drawing your Lewis structure, to get the most stable structure, you should choose the structure that minimizes formal charge for each atom in the structure. Formal charge can be calculated by subtracting the sum of the number of nonbonding valence electrons and half the number of bonding electr...
Sun Dec 06, 2020 4:29 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles
Replies: 13
Views: 100

### Re: Bond Angles

Lone pairs exert a slightly greater magnitude of repulsion than another bonded atom (take for example AX 3 E compared to AX 4 ), which would result in two molecules with the same electron geometry (tetrahedral) and different molecular geometry (trigonal pyramidal vs tetrahedral) with slighlty differ...
Sun Dec 06, 2020 4:19 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Coordination Number Question
Replies: 12
Views: 119

### Re: Coordination Number Question

The coordination number is a value representing the number of atoms, molecules, or ions that are held by a central transition metal atom. It is important to note that denticity can vary and you count only the number of atoms inside brackets held by the transition metal!
Tue Dec 01, 2020 8:55 am
Forum: Naming
Topic: Order of Molecules
Replies: 6
Views: 64

### Re: Order of Molecules

I believe that the textbook mentions that the ligands should be written in alphabetical order when there is more than one; however, I do not know that this is necessary. As already said, I think it is more important that the cation comes before the ligands.
Sun Nov 29, 2020 2:05 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: polar vs non-polar
Replies: 7
Views: 52

### Re: polar vs non-polar

It is also to consider the shape of the molecule. For example, polar bonds arising from differing electronegativities of central and bonded atoms may form on a molecule with a trigonal planar shape; however, this molecule will be nonpolar given the fact that electrons are evenly distributed about th...
Sun Nov 29, 2020 2:00 pm
Forum: Hybridization
Topic: hybridization of phosphorus (Sapling Q.11)
Replies: 21
Views: 96

### Re: hybridization of phosphorus (Sapling Q.11)

There are only four regions of electron density which results in the hybridization of sp 3 . It is important to note that we only consider bonding electron pairs and lone pairs as regions of electron density. This molecule would have the VSEPR formula AX 4 , meaning that there are four regions of el...
Mon Nov 23, 2020 11:07 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles
Replies: 25
Views: 133

### Re: Bond Angles

Adding on to my last response, it would be impossible to know the bond angles for every molecule given that bonding atoms will have different properties that make their properties slightly different from the general bond angles; however, these values listed above give a great idea of understanding t...
Mon Nov 23, 2020 11:02 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles
Replies: 25
Views: 133

### Re: Bond Angles

I think Alexa put this very nicely. Knowing that bond angles 109.5° for tetrahedral shape, 120° for trigonal planar, and 180° for linear will definitely help in comparing molecules. I feel like these might be used as a reference for different molecules. For example, comparing an AX 4 to an AX 3 E wo...
Mon Nov 23, 2020 10:54 am
Forum: Ionic & Covalent Bonds
Topic: C-H bond polarity
Replies: 10
Views: 88

### Re: C-H bond polarity

Since the electronegativity difference between Carbon and Hydrogen is relatively small (approximately 0.35), the electrons will be more likely to be evenly distributed between the two atoms. In response to Joanna, the properties of hydrogen are unique in that hydrogen is likely to attract the one el...
Sun Nov 22, 2020 10:24 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Tips for memorizing different molecular shapes
Replies: 9
Views: 76

### Re: Tips for memorizing different molecular shapes

In terms of memorizing, it helped me a lot to be able to visualize each of the molecular shapes. I really like the PHET simulator I linked because it allows you to experiment with a variety of molecules and observe both molecular and electron geometry for each! https://phet.colorado.edu/en/simulatio...
Sun Nov 15, 2020 6:24 pm
Forum: Ionic & Covalent Bonds
Topic: Electronegativity
Replies: 18
Views: 104

### Re: Electronegativity

I think that we are more expected to know periodic trends relating to electronegativity. For example, electronegativity increases across a period and decreases as you go down a group or column.
Sun Nov 15, 2020 6:20 pm
Forum: Lewis Structures
Topic: Nitrite vs Nitrate
Replies: 17
Views: 141

### Re: Nitrite vs Nitrate

I believe that any polyatomic ion ending with "ite" will always have one less Oxygen than those ending with "ate".
Sun Nov 15, 2020 6:04 pm
Forum: Bond Lengths & Energies
Topic: Hydrogen Bonding
Replies: 13
Views: 68

### Re: Hydrogen Bonding

I think by definition hydrogen bonds only occur with N, O, and F so there shouldn't be any exceptions!
Sun Nov 15, 2020 5:55 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: PCL5 Trigonal planar
Replies: 3
Views: 20

### Re: PCL5 Trigonal planar

For a trigonal bipyramidal structure like PCl5, it is most energetically favorable for three of these electrons in one plane and the other two domains will be 90 degrees to this plane to allow for the most distance between repelling valence electrons of each atom.
Sun Nov 15, 2020 5:47 pm
Forum: Resonance Structures
Topic: bond length
Replies: 37
Views: 152

### Re: bond length

From everything I have seen so far, the bond length is usually given. I think it would be more beneficial to know what factors contribute to bond length. For example, size of an atom may increase the bond length. Also know that the greater the bond length, the weaker the bond will be.
Sun Nov 08, 2020 7:44 pm
Forum: General Science Questions
Replies: 22
Views: 284

You can also check through myUCLA! Click on the classes tab and it will be under the grades and homework section as "exam and homework grades" :)
Sun Nov 08, 2020 7:20 pm
Forum: Coordinate Covalent Bonds
Topic: Definition
Replies: 17
Views: 232

### Re: Definition

Coordinate covalent bonds exist when one atom shares two of its own valence electrons with another atom to form a covalent bond.
Sun Nov 08, 2020 7:19 pm
Forum: Coordinate Covalent Bonds
Topic: Definition
Replies: 17
Views: 232

### Re: Definition

Coordinate covalent bonds exist when one atom shares two of its own valence electrons with another atom to form a covalent bond.
Sun Nov 08, 2020 7:09 pm
Forum: Ionic & Covalent Bonds
Topic: Chemical Bonds
Replies: 12
Views: 65

### Re: Chemical Bonds

There is a stronger attraction that arises from a greater number of electrons and attractive force exerted by the nuclei which would in turn decrease the bond length.
Sun Nov 08, 2020 6:23 pm
Forum: Trends in The Periodic Table
Topic: Octet Rule
Replies: 6
Views: 42

### Re: Octet Rule

For hydrogen, the octet rule does not apply since the atom can only have a maximum of two electrons in its outermost/valence shell! All successive levels can have a maximum of 8 with the exceptions you listed.
Sun Nov 08, 2020 6:19 pm
Forum: Lewis Structures
Topic: Lone Pairs Question
Replies: 22
Views: 119

### Re: Lone Pairs Question

Lone pairs are valence electrons that exist in pairs and are not shared or bonded with another atom.
Sun Nov 01, 2020 5:56 pm
Forum: Quantum Numbers and The H-Atom
Topic: Ionization energy
Replies: 2
Views: 28

### Re: Ionization energy

The first ionization energy is the amount of energy required to remove the first valence electron. This will vary depending upon the depending on the magnitude of electrostatic attraction towards the nucleus. Oxygen has a greater degree of electron-electron repulsion in its subshell than Nitrogen (2...
Sun Nov 01, 2020 5:47 pm
Forum: Student Social/Study Group
Topic: Favorite TV shows
Replies: 176
Views: 874

### Re: Favorite TV shows

I just finished a show called Biohackers on Netflix and really enjoyed it!
Sun Nov 01, 2020 5:36 pm
Forum: Trends in The Periodic Table
Topic: Electron Shielding Question
Replies: 5
Views: 40

### Re: Electron Shielding Question

The most important thing to understad is that electron shielding is the same as repulsion. For each subsequent shell or period, there is an added ring or shell outside of the inner shells containing electrons. These electrons on the inside will repel the outer valence electrons, resulting in an over...
Sun Nov 01, 2020 5:24 pm
Forum: Trends in The Periodic Table
Topic: Second ionization energy
Replies: 3
Views: 34

### Re: Second ionization energy

The second ionization energy will be greater after the first electron is removed. When there are fewer valence electrons, there is a lesser magnitude of repulsion between these valence electrons which would increase the overall center seeking force resulting in a higher ionization energy or amount o...
Sun Nov 01, 2020 4:27 pm
Forum: Lewis Structures
Topic: ionization energy
Replies: 3
Views: 57

### Re: ionization energy

Adding on to the last response, as you increase energy levels, you also have a greater number of shielding electrons betweeen the outer valence electrons and the nucleus of the atom. This would in turn result in a lower ionization energy as there is a lessened center-seeking force along with an incr...
Sun Nov 01, 2020 3:33 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Ground state electron configuration?
Replies: 9
Views: 47

### Re: Ground state electron configuration?

The "ground state" is the most stable and lowest energy state of an atom. Using the term excited would imply that the electron has been increased in energy level.
Sun Oct 25, 2020 2:04 pm
Forum: Administrative Questions and Class Announcements
Topic: CCLE DOWN
Replies: 6
Views: 74

### Re: CCLE DOWN

Sun Oct 25, 2020 12:02 pm
Forum: Properties of Light
Topic: Sapling Homework Question 7
Replies: 5
Views: 86

### Re: Sapling Homework Question 7

When you click on the provided link, you will see that the enthalpy of fusion of water is 333.6 J/g. You will multiply this number by the provided mass of 445 g to calculate the amount of energy required to melt the ice. You then need to calculate the amount of energy per photon using the equation E...
Sun Oct 25, 2020 11:52 am
Forum: DeBroglie Equation
Topic: Sapling Question #10
Replies: 8
Views: 108

### Re: Sapling Question #10

nayha a 1L wrote:Everyone in this thread is mentioning Avogadro's number, but as I look through my notes, I can't seem to find anything about it. Does anyone know which lecture talked about this?

Avogadro's Constant is referenced near the beginning of the October 2nd Lecture! (Listed in Week 1 I believe)
Fri Oct 23, 2020 11:51 am
Forum: Quantum Numbers and The H-Atom
Topic: Lecture confusion in quantum numbers
Replies: 6
Views: 54

### Re: Lecture confusion in quantum numbers

I believe the 2px state would correspond to n=2,l=1, and ml=-1! If ml were equal to +1 I believe this would be 2pz
Fri Oct 23, 2020 11:45 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Problem 1B.25
Replies: 3
Views: 69

### Re: Problem 1B.25

If we manipulate other equations based on the values given, and we set the two equal to each other, does it matter that the one equation has a greater than or equal to symbol? For example, if we have delta p = m(delta v), and delta p is greater than or equal to h/(delta x)(4pi), can we still substi...
Mon Oct 19, 2020 11:48 am
Forum: Photoelectric Effect
Topic: How to find kinetic energy from velocity
Replies: 6
Views: 74

### Re: How to find kinetic energy from velocity

The formula for Kinetic Energy is 1/2(m)(v^2). In this problem, the velocity is provided as 6.61x10^5 m/s. Here you would not use molar mass as you are considering the velocity for a sole electron and this would not provide you with the correct units for Kinetic Energy (keep in mind Joules are kgm^2...
Sat Oct 17, 2020 6:27 pm
Forum: Administrative Questions and Class Announcements
Replies: 9
Views: 103

I have been using a printed version of the periodic table provided on the class website. Will this be the same one we are able to use on exams?
Sat Oct 17, 2020 6:15 pm
Forum: Administrative Questions and Class Announcements
Topic: Calculator?
Replies: 9
Views: 104

### Re: Calculator?

I have a TI-nspire cx.. it hadn't occurred to me we might not be able to use certain calculators! Have you heard anything about this calculator or just the rules if there are any for calculators during exams? I have a TI-nspire cx as well! Not sure either if the TI-84 is approved or not, but the TI...
Tue Oct 13, 2020 12:42 pm
Forum: Administrative Questions and Class Announcements
Topic: Webcam for Midterms
Replies: 3
Views: 100

### Re: Webcam for Midterms

Actually was included in the last email sent out! Here is the link! https://lavelle.chem.ucla.edu/wp-conten ... equest.pdf
Tue Oct 13, 2020 12:22 pm
Forum: Administrative Questions and Class Announcements
Topic: Webcam for Midterms
Replies: 3
Views: 100

### Re: Webcam for Midterms

I was told today during my discussion that an email would be sent out later this week addressing the webcam requirements!
Tue Oct 13, 2020 11:58 am
Forum: Photoelectric Effect
Topic: Light Intensity
Replies: 5
Views: 62

### Re: Light Intensity

My understanding is that light intensity is simply how bright a light is, and increasing the intensity increases the amount of photons being emitted by that light source. The wavelength and frequency are independent of the amplitude, and are instead dependent on the length of a wave. So changing th...
Sat Oct 10, 2020 8:41 pm
Forum: Limiting Reactant Calculations
Topic: Double Check my Understanding
Replies: 10
Views: 138

### Re: Double Check my Understanding

You are correct! When you calculate the molar mass of an element or molecule you will not multiply this by the stoichiometric coefficient; however, stoichiometric coefficients are relevant in determining the number of moles of each reactant and product present in a reaction. Take for example the rea...
Sat Oct 10, 2020 8:06 pm
Forum: Limiting Reactant Calculations
Topic: Limiting reactants in all chemical rxns?
Replies: 18
Views: 148

### Re: Limiting reactants in all chemical rxns?

On this same topic, is there a maximum amount of limiting reactants an equation can have? Thanks! It is highly unlikely that there will be more than one limiting reactant since this would require that the moles of two or more different reactants are exactly equal and completely react with each othe...
Sat Oct 10, 2020 7:45 pm
Forum: Empirical & Molecular Formulas
Topic: Ratios for empircal formulas
Replies: 6
Views: 67

### Re: Ratios for empircal formulas

Hope I am answering this question correctly, but I believe you are asking about the process of using the calculated moles of each element in a molecule to determine the empirical formula. If we use the example of being given a mass percent composition, we can first determine the number of grams of e...
Sat Oct 10, 2020 6:57 pm
Forum: Administrative Questions and Class Announcements
Topic: Homework Due Time
Replies: 8
Views: 51

### Re: Homework Due Time

I believe it is safe to assume based on the wording on Sapling that it is due tomorrow night at 11:59 PM.
Fri Oct 09, 2020 12:30 am
Forum: Limiting Reactant Calculations
Topic: Limiting reactants in all chemical rxns?
Replies: 18
Views: 148

### Re: Limiting reactants in all chemical rxns?

From my understanding, to not have a limiting reactant would be nearly impossible even if the number of moles of each reactant and stoichiometric coefficients appeared to be the same. Thinking back to Avogadro's Constant which defines a mole as having 6.022x10^23 particles or "things" woul...
Thu Oct 08, 2020 11:01 pm
Forum: SI Units, Unit Conversions
Topic: Acronym for prefixes
Replies: 7
Views: 86

### Re: Acronym for prefixes

Thank you guys so much for sharing these acronyms! I was definitely in need of these as well and will be using them this year! :))