Search found 91 matches

by Sanjana K - 2F
Mon Feb 24, 2020 1:07 am
Forum: Administrative Questions and Class Announcements
Topic: Thermo
Replies: 3
Views: 11

Re: Thermo

I feel like it's just a lot of practice with the homework problems he assigned since there's just so much math involved. Also, going through the book and writing down important equations (and when to use them/what conditions) also helps.
by Sanjana K - 2F
Mon Feb 24, 2020 1:04 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: G(not) and G
Replies: 8
Views: 29

Re: G(not) and G

Rafsan Rana 1A wrote:Isn't the equation G = Gnot + RTlnQ ?


Yes, it should be delta G = delta G(naught) + RTlnQ.
by Sanjana K - 2F
Mon Feb 24, 2020 1:00 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst Equation usage
Replies: 6
Views: 11

Re: Nernst Equation usage

You'd use it to relate the reduction potential (under non-standard conditions) to the standard electrode potential. At any point in the reaction, you can find the cell potential using this equation.
by Sanjana K - 2F
Mon Feb 24, 2020 12:57 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic vs. electrolytic
Replies: 4
Views: 10

Re: Galvanic vs. electrolytic

This diagram is pretty helpful too.
by Sanjana K - 2F
Mon Feb 24, 2020 12:51 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: S = 0
Replies: 14
Views: 28

Re: S = 0

S just means entropy, rather than change in entropy that should be denoted as ΔS. Entropy is almost never 0 (the entropies of all perfect crystals approach zero as the absolute temperature approaches zero; "perfect crystal" refers to a substance in which all the atoms are in a perfectly o...
by Sanjana K - 2F
Mon Feb 17, 2020 11:11 pm
Forum: Balancing Redox Reactions
Topic: Electrical energy and Chemical energy
Replies: 2
Views: 12

Re: Electrical energy and Chemical energy

In addition to the answer above, you can also tie this to the first law of thermodynamics (energy is neither created nor destroyed but rather transferred from one form to another). So, this would be an example of the conversion.
by Sanjana K - 2F
Mon Feb 17, 2020 11:05 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Midterm Curve
Replies: 45
Views: 257

Re: Midterm Curve

Individual tests aren't curved :(
by Sanjana K - 2F
Mon Feb 17, 2020 11:02 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Exothermic rxns being spontaneous
Replies: 5
Views: 19

Re: Exothermic rxns being spontaneous

Although reactions being exothermic/endothermic and spontaneous/nonspontaneous are closely related, you should also keep in mind that not all exothermic reactions will be spontaneous. When checking for spontaneity, look at the delta G sign (meaning you need the sign of delta H AND the sign of delta ...
by Sanjana K - 2F
Mon Feb 17, 2020 10:55 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Van't Hoff
Replies: 6
Views: 16

Re: Van't Hoff

Isn't it assumed to be at constant temperature as well as pressure?
by Sanjana K - 2F
Mon Feb 17, 2020 10:50 pm
Forum: Balancing Redox Reactions
Topic: Oxidation numbers [ENDORSED]
Replies: 4
Views: 18

Re: Oxidation numbers [ENDORSED]

For the example in class on Friday ((H+) + (MnO4)- + 5(Fe 2+)) --> Mn2+ + 5(Fe)3+ + 4H20), we know that oxygen always has an oxidation number of -2 so in Mn(O4)-, 4(-2) = -8 so Mn + (-8) = -1 meaning that Mn has to have +7 charge on the reactants side. On the products side, we're told that the overa...
by Sanjana K - 2F
Mon Feb 10, 2020 1:57 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Cv
Replies: 3
Views: 15

Re: Cv

I think they'll be provided on the formula sheet but here are the formulas you'd use anyways:
Ideal gas: Cp = (5/2)R
Ideal gas: Cv = (3/2)R
by Sanjana K - 2F
Mon Feb 10, 2020 1:44 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: q=CΔT
Replies: 5
Views: 23

Re: q=CΔT

Yes, I believe you would use this equation for calorimetry problems. Can someone explain to me why you don't use mass?
by Sanjana K - 2F
Mon Feb 10, 2020 1:40 am
Forum: Administrative Questions and Class Announcements
Topic: Midterm Conversion
Replies: 3
Views: 17

Re: Midterm Conversion

I think you'll be given this value, but just for reference 1 L times atm = 101.325 J.
by Sanjana K - 2F
Mon Feb 10, 2020 1:36 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy Definition
Replies: 2
Views: 10

Re: Enthalpy Definition

Yes, enthalpy will only equal heat of a reaction at constant pressure.
by Sanjana K - 2F
Mon Feb 10, 2020 1:32 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: irreversible vs reversible
Replies: 3
Views: 17

Re: irreversible vs reversible

Here's a graphical representation of both. One thing to note is that the work done under a reversible process will always be greater than that done under irreversible, as you can see.
by Sanjana K - 2F
Mon Feb 03, 2020 2:16 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: state functions
Replies: 10
Views: 29

Re: state functions

Examples: energy, pressure, volume, temperature, density, heat capacity
Non-examples: work, heat
by Sanjana K - 2F
Mon Feb 03, 2020 2:12 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: taking phase change into account
Replies: 5
Views: 15

Re: taking phase change into account

Also, in addition to what is being said above, something to remember: whenever you're dealing with phase changes, you have to calculate the heat required in 2 different steps. For example, if you're trying to go from a block of ice at 0 degrees to water at 50 degrees, you first need to find the heat...
by Sanjana K - 2F
Mon Feb 03, 2020 2:09 am
Forum: Student Social/Study Group
Topic: Test 1 Solution
Replies: 6
Views: 48

Re: Test 1 Solution

I don't think it'll be posted online because only the midterm answers were posted for Chem 14A last quarter, but you can ask your TA to go over it with you. Or you can post a specific question here.
by Sanjana K - 2F
Mon Feb 03, 2020 2:05 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: kinetics
Replies: 8
Views: 25

Re: kinetics

We haven't gone over kinetics yesterday but he mentioned it a little in class to emphasize that delta G could tell us about a reaction's spontaneity (but a spontaneous reaction isn't necessarily a fast one because to find out about a reaction's speed/rate you'd have to consider kinetics and not ther...
by Sanjana K - 2F
Mon Feb 03, 2020 2:01 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: States of a system
Replies: 3
Views: 18

Re: States of a system

For the example he gave us in class, we had 2 possible states (represented by the two circular ends) and 2 particles (A and B), so we do (# of states)^(# of particles) = 2^2 = 4 microstates possible.
by Sanjana K - 2F
Mon Jan 27, 2020 2:43 pm
Forum: Student Social/Study Group
Topic: midterm/final
Replies: 12
Views: 67

Re: midterm/final

I feel like I studied for the tests, midterm, and final the same way though. Even if they are structured a little differently, they're basically all word problems so doing the book problems and going over notes is still the best way to study.
by Sanjana K - 2F
Mon Jan 27, 2020 2:38 pm
Forum: Phase Changes & Related Calculations
Topic: State Property
Replies: 6
Views: 20

Re: State Property

Could someone also explain why heat is not a state property? Thanks! If it's heat given off under constant pressure, then it's basically enthalpy so yes, it would be a state property because the path DOES matter as you take into account what intermediate steps where needed to get to the final tempe...
by Sanjana K - 2F
Mon Jan 27, 2020 2:34 pm
Forum: Student Social/Study Group
Topic: Chemical Bonding Recording
Replies: 1
Views: 20

Re: Chemical Bonding Recording

That's really cool! I like how you can see the rhenium atoms travelling around and then coming into the carbon nanotubes -- makes the concept of bond formation and breaking easier to visualize on a microscopic level.
by Sanjana K - 2F
Mon Jan 27, 2020 2:27 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Extensive vs intensive propeties
Replies: 5
Views: 13

Re: Extensive vs intensive propeties

Also, what is the difference between intensive properties and state properties? State properties don't really take into account the "path" of how the substance was prepared (like altitude, pressure, volume, temperature). I think you mean to ask about the difference between intensive and e...
by Sanjana K - 2F
Mon Jan 27, 2020 2:21 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Units for temperature?
Replies: 11
Views: 27

Re: Units for temperature?

The change in heat per celsius is the same as the change in heat per kelvin, so you could use either.
by Sanjana K - 2F
Mon Jan 20, 2020 3:26 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Identifying endothermic vs exothermic
Replies: 7
Views: 17

Re: Identifying endothermic vs exothermic

You can also look at bond enthalpies or use Hess's Law to figure out the total energy on the reactants and products side or the energy needed to form/break the bonds and if delta H < 0, it's exothermic and if delta H > 0, it's endothermic.
by Sanjana K - 2F
Mon Jan 20, 2020 3:21 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Effect of Increasing Temperature on an Equilibrium System
Replies: 4
Views: 14

Re: Effect of Increasing Temperature on an Equilibrium System

It might help if you view heat as another reactant (for an endothermic reaction) or as another product (for an exothermic reaction). If you add more of a reactant, according to Le Chatelier's, the effect of the change will need to be minimized so the reaction will proceed to the right. So in an endo...
by Sanjana K - 2F
Mon Jan 20, 2020 3:14 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: ice table
Replies: 5
Views: 18

Re: ice table

The ICE table is just supposed to help you write your equilibrium constant expression and to track changes in the concentrations of the reactants and products. Your final Kc expression won't include solids and liquids, so you wouldn't have any values for them in your ICE table.
by Sanjana K - 2F
Mon Jan 20, 2020 3:11 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Pressure changes
Replies: 7
Views: 23

Re: Pressure changes

The easy way to tell what changes will occur is to see how the moles of gas on the reactants and products sides differ. If the volume (moles of gas) is lower on the products side, then the reaction shifts to the right but if the volume (moles of gas) is higher on the products side, the reaction shif...
by Sanjana K - 2F
Mon Jan 20, 2020 3:06 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: 6B.11
Replies: 2
Views: 16

Re: 6B.11

Yes, Na2O (s) + H2O (l) ⇌ 2Na+ (aq) + 2OH- (aq) is the correct reaction
by Sanjana K - 2F
Thu Jan 16, 2020 9:38 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Percent Ionization
Replies: 11
Views: 55

Re: Percent Ionization

If you don't use the quadratic equation, you still want to justify your reason for ignoring the "-x" terms in your equilibrium by saying that since x is less than 5% of the initial concentration, its change is negligible.
by Sanjana K - 2F
Thu Jan 16, 2020 9:33 am
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: kA and kB
Replies: 3
Views: 18

Re: kA and kB

Yes, and you observe the same thing with H+ concentration and pH as well. The higher the H+ concentration, the lower the pH and the stronger the acid. It's just in the nature of natural logarithms.
by Sanjana K - 2F
Thu Jan 16, 2020 9:29 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Today's lecture
Replies: 5
Views: 44

Re: Today's lecture

pKa is dependent on Ka so if the Ka is greater than 10^-7, then the pKa would be less than 7 but if Ka is less than 10^-7, then the pKa would be greater than 7.
Matt Sanruk 2H wrote:Wouldn't pKa give an integer thats less than 7?
by Sanjana K - 2F
Thu Jan 16, 2020 9:21 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Approximation
Replies: 6
Views: 23

Re: Approximation

In class, he also said that if your Ka is less than 10^(-3), then you can generally approximate by ignoring the "-x" term but you might want to justify it on the test by explaining that since x is less than 5% of the initial concentration, it's considered a negligible difference so it can ...
by Sanjana K - 2F
Thu Jan 16, 2020 9:18 am
Forum: Ideal Gases
Topic: R constant
Replies: 6
Views: 25

Re: R constant

It generally won't tell you exactly what R value to use, but all the constants are given in the formula sheet so depending on whether pressure is reported in atm or kilopascals, you'll know which R-value to use. Lavelle gives you 4 different values for the R constant on his formula sheet during test...
by Sanjana K - 2F
Thu Jan 09, 2020 12:29 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5G.1C
Replies: 3
Views: 30

Re: 5G.1C

If you start with a higher reactant pressure, you'll have a lower reactant volume (because increasing pressure tends to compress volume) so the equilibrium will actually shift left to make up for that loss in volume, according to Le Chatelier's Principle. So, with the reaction shifting left, the equ...
by Sanjana K - 2F
Thu Jan 09, 2020 12:23 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5I.29
Replies: 2
Views: 17

Re: 5I.29

5% Rule: If x/(initial concentration) < 5%, then you can ignore the "-2x" term but if not, then you'd need to use the quadratic formula. Make sure you write out the rule to justify ignoring the "-x" terms whenever you have this type of problem
by Sanjana K - 2F
Thu Jan 09, 2020 12:17 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K of Ionic Compounds in Solution
Replies: 4
Views: 25

Re: K of Ionic Compounds in Solution

Basically, it's telling you to ignore spectator ions like Li+, Na+, K+, Rb+, Sr2+, Ba2+, Cl-, Br-, I-, NO3-, ClO4-, SO4(2-), etc. because these ions occur in the same form on the left and right side of the chemical equation. So when you're writing your equilibrium constant expression they'd cancel a...
by Sanjana K - 2F
Thu Jan 09, 2020 12:07 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE tables
Replies: 1
Views: 20

Re: ICE tables

Yes, so for example if you have 2NO2 in equilibrium with N2O4, your left hand side of the ICE table would be (initial concentration of 2NO2) - 2x and your right hand side would be (initial concentration of N2O4) + x.
by Sanjana K - 2F
Thu Jan 09, 2020 12:00 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5I.23
Replies: 1
Views: 10

Re: 5I.23

Whenever you make an ICE table, you should be listing the concentration values, not the number of moles.
by Sanjana K - 2F
Tue Dec 03, 2019 2:21 pm
Forum: Naming
Topic: Oxidation Number
Replies: 3
Views: 25

Re: Oxidation Number

Here's an example:
K2CrO4
we know that K has a charge of +1 so 2(+1) = +2 and O has a charge of -2 so -2(4) = -8. The molecule is neutral and we're trying to find the oxidation number of the transition metal so (+2) + Cr - 8 = 0 so Cr = +6.
by Sanjana K - 2F
Tue Dec 03, 2019 2:10 pm
Forum: Hybridization
Topic: Conceptual meaning of hybridization
Replies: 3
Views: 31

Re: Conceptual meaning of hybridization

In hybridization, you basically have atomic orbitals mixing into new hybrid orbitals in order to better pair electrons to form chemical bonds in VSEPR (affecting molecular geometry and bonding properties). And yes, this does lower the energy of the molecule, so hybridized molecules are more stable.
by Sanjana K - 2F
Tue Dec 03, 2019 2:01 pm
Forum: Identifying Acidic & Basic Salts
Topic: deciding whether the solution of a salt is basic, acidic, or neutral
Replies: 5
Views: 49

Re: deciding whether the solution of a salt is basic, acidic, or neutral

If, in the presence of water, a salt gains an H+ (becoming an acid) and produces OH- ions, the solution will be basic. If, in the presence of water, a salt loses an H+ (becoming a base) and produces H+ ions, the solution will be basic. ex: C2H3O2 (-) (aq) + H2O (l) ---> HC2H3O2 (aq) + OH- (aq) so ba...
by Sanjana K - 2F
Tue Dec 03, 2019 1:31 pm
Forum: Lewis Acids & Bases
Topic: diff b/w lewis acid and base
Replies: 12
Views: 82

Re: diff b/w lewis acid and base

Also, generally speaking, anions will act as Lewis bases (donate an electron pair) while cations act as Lewis acids (accept an electron pair)
by Sanjana K - 2F
Tue Dec 03, 2019 1:29 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: pKa vs Ka
Replies: 6
Views: 32

Re: pKa vs Ka

For a very weak acid, the Ka can be an extremely small number, so to deal with such numbers, we use the pKa, which converts the Ka values to larger numbers we're more familiar with. It also allows for convenience with graphing.
by Sanjana K - 2F
Tue Nov 26, 2019 2:51 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Oxidation Number vs. Coordination Number
Replies: 8
Views: 43

Re: Oxidation Number vs. Coordination Number

Here's an example of a problem involving coordination numbers: In Co(NH3)6, the coordination number is 6 because you have 6 ligands attached to the central atom Co. CO3 (2-) has a coordination number of 3 because of the 3 oxygens surrounding the carbon atom. You can relate coordination numbers to mo...
by Sanjana K - 2F
Tue Nov 26, 2019 2:43 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Oxidation state
Replies: 3
Views: 22

Re: Oxidation state

For example, if you want to find the oxidation number for Cr in CrCl3, you have to start off by figuring out the charges you DO know (the charges of the non-TM ions). Group 17 elements have an oxidation number of -1 so 3(-1) = -3. The charge of the overall molecule is 0 and we only have one Cr atom,...
by Sanjana K - 2F
Tue Nov 26, 2019 2:38 pm
Forum: Bronsted Acids & Bases
Topic: Memorizing the Bronsted Acids and Bases
Replies: 4
Views: 40

Re: Memorizing the Bronsted Acids and Bases

It will be helpful (later on, in Chem 14B) to know all the strong acids because there are only 7 and any acid that isn't one of those 7 will automatically be weak. So when we do more acid-base equilibria that involve math, it'll be pretty useful. Here they are: 1) HClO4 - perchloric acid 2) HClO3 - ...
by Sanjana K - 2F
Tue Nov 26, 2019 2:27 pm
Forum: Lewis Acids & Bases
Topic: Lewis vs Bronsted Acids and Bases
Replies: 3
Views: 19

Re: Lewis vs Bronsted Acids and Bases

So the Bronsted acid/base theory deals with PROTON transfer (Bronsted acids donate a proton while Bronsted bases accept a proton). The Lewis acid/base theory deals with ELECTRON PAIR transfer (Lewis acids accept an electron pair while Lewis bases donate an electron pair). Generally, all Bronsted aci...
by Sanjana K - 2F
Tue Nov 26, 2019 2:19 pm
Forum: Bronsted Acids & Bases
Topic: Definition
Replies: 5
Views: 43

Re: Definition

In addition to the previous answer, you can look at the following examples: - Acetic acid (CH3COOH) is a Bronsted acid because it donates a hydrogen atom to water -- it's a proton donor basically, so you're left with CH3COO- (the conjugate base). And in this case, water would be the Bronsted base be...
by Sanjana K - 2F
Thu Nov 21, 2019 12:11 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angle of bent
Replies: 17
Views: 88

Re: Bond Angle of bent

Also, if you're dealing with water, the shape is also bent but the bond angle would be 104 degrees due to the presence of 2 lone pairs, which pushes the bonded atoms even closer together, further reducing the bond angle.
by Sanjana K - 2F
Thu Nov 21, 2019 12:08 am
Forum: Dipole Moments
Topic: Intermolecular forces
Replies: 2
Views: 46

Re: Intermolecular forces

SBr4 is a nonpolar molecule because the central atom (S) is surrounded by 4 identical (Br) molecules that are equivalent in their electronegativity, so the dipoles cancel each other out, and as a result, there is no dipole-dipole interaction. The individual bonds can still be polar but the whole mol...
by Sanjana K - 2F
Thu Nov 21, 2019 12:03 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles
Replies: 6
Views: 38

Re: Bond Angles

The presence of lone pairs causes a higher repulsion since in terms of repulsion, lone pair---lone pair > lone pair---bonded atom > bonded atom---bonded atom, so the lone pair will take the place of a bonded atom and essentially exert greater repelling force against the other atoms, pushing them clo...
by Sanjana K - 2F
Wed Nov 20, 2019 11:56 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Name confusion
Replies: 4
Views: 33

Re: Name confusion

You'll only be expected to name the shape molecularly (not electronically). So in your case, you'd name the molecules as T-shaped because trigonal bipyramidal only tells you that there are 5 regions of electron density (assuming that atoms also count as electron-rich areas). 5 regions of electron de...
by Sanjana K - 2F
Wed Nov 20, 2019 11:51 pm
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Strengths of forces
Replies: 4
Views: 32

Re: Strengths of forces

Hydrogen bonds will always be stronger than other dipole-dipole interactions because hydrogen bonds occur between a partially positive hydrogen atom and a highly electronegative atom (N, O, F), so the dipole will automatically be at one of its strongest in a hydrogen bond, and therefore, the polarit...
by Sanjana K - 2F
Thu Nov 14, 2019 3:13 am
Forum: Electronegativity
Topic: oxygen vs nitrogen electronegativity
Replies: 3
Views: 43

Re: oxygen vs nitrogen electronegativity

Oxygen's ionization energy is lower than that of nitrogen because nitrogen has 3 electrons in the p-shell so it's half-full but oxygen has 4 electrons so there will be one set of paired electrons and 2 unbonded electrons, making it less stable. To be more stable, we're more likely to pull out the ex...
by Sanjana K - 2F
Thu Nov 14, 2019 3:05 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Difference between molecular shape
Replies: 3
Views: 36

Re: Difference between molecular shape

Seesaws: 1 LP, seesaw molecular shape, trigonal bipyramidal electron arrangement, bond angles of 90 and 120 degrees Tetrahedral: 0 LP, tetrahedral molecular shape, tetrahedral electron arrangement, bond angles of 109.5 degrees Trigonal pyramidal: 1 LP, trigonal pyramidal molecular shape, tetrahedral...
by Sanjana K - 2F
Thu Nov 14, 2019 2:46 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles Exceptions
Replies: 6
Views: 38

Re: Bond Angles Exceptions

Adding on to those answers above, since Cl is a larger atom than H (larger radius) and its electron density is also higher, it'll tend to push the H atom inward more, reducing the angle further (so it's less than 109.5 degrees). You can observe the same with CH3F too.
by Sanjana K - 2F
Thu Nov 14, 2019 2:34 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Axial vs Equatorial Lone Pairs
Replies: 2
Views: 39

Re: Axial vs Equatorial Lone Pairs

Lone pairs in particular will occupy equatorial positions because that's where they face the least repulsion (more energetically favorable). For example, for a trigonal bipyramidal structure, if you have the lone pair on the axial plane, it'll be 90 degrees away from 3 regions of electron density bu...
by Sanjana K - 2F
Thu Nov 14, 2019 2:17 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Memorization
Replies: 15
Views: 109

Re: Memorization

You might be able to use this table to help you conceptualize the models

https://web.gccaz.edu/~kimld88531/VSEPR%20handout.pdf
by Sanjana K - 2F
Fri Nov 08, 2019 7:03 pm
Forum: Dipole Moments
Topic: Dipole - Dipole vs. Hydrogen Bonding
Replies: 7
Views: 278

Re: Dipole - Dipole vs. Hydrogen Bonding

N,O, and F tend to bond with H in a hydrogen bond and since they're more electronegative, they'll result in a higher polarity with the positive hydrogen so the bond will also be stronger than a normal dipole-dipole.
by Sanjana K - 2F
Fri Nov 08, 2019 6:24 pm
Forum: Dipole Moments
Topic: Hydrogen Bonds
Replies: 6
Views: 45

Re: Hydrogen Bonds

For hydrogen bonds and dipole-dipole bonds, you're looking at the strength of the bond between partially + and partially - atoms. Since N,O, and F usually bond with H in a hydrogen bond and they tend to be more electronegative, they'll result in a higher polarity against the positive hydrogen so the...
by Sanjana K - 2F
Fri Nov 08, 2019 6:15 pm
Forum: Lewis Structures
Topic: Hybridization
Replies: 2
Views: 25

Re: Hybridization

Hybridized orbitals tend to have lower energy states than unhybridized ones, so it's mostly for stability. It also helps predict the molecular geometry better by VSEPR (so bonds are more accurate in distance/angles).
by Sanjana K - 2F
Fri Nov 08, 2019 6:07 pm
Forum: Dipole Moments
Topic: Electric Dipole Moment
Replies: 2
Views: 20

Re: Electric Dipole Moment

It's basically a measure of how polarizable a system is. It'll tell you how the + and - electrical charges are spread with the equation p = q*d where q = magnitude and d = distance between a pair of opposite charges.
by Sanjana K - 2F
Sun Nov 03, 2019 11:57 pm
Forum: Trends in The Periodic Table
Topic: Atomic Radius
Replies: 9
Views: 60

Re: Atomic Radius

The radius increases as you go down a group (because you're adding more shells) and decreases as you go to the right across a period (because electrons are added to the same shell and the electrostatic attraction increases L-->R so the increasing nuclear charge draws them inwards and radii length de...
by Sanjana K - 2F
Sun Nov 03, 2019 11:51 pm
Forum: Properties of Electrons
Topic: Rydberg Constant
Replies: 2
Views: 42

Re: Rydberg Constant

So you'd use it for atomic spectra (since the energy at a specific shell is denoted by -hR/n^2) and you could find the frequency emitted from one level to another by doing E(final) - E(initial). You'd apply En = -hR/n^2 to the two different n values (or shells) and then subtract the two to find the ...
by Sanjana K - 2F
Sun Nov 03, 2019 11:39 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal charge
Replies: 16
Views: 72

Re: Formal charge

If you can't narrow it down, you might want the negative formal charge to be on the more electronegative atom. For example, you can refer to #12 on the Dino Nuggets Midterm, where we ultimately chose our structure to be N --- N - O instead of N -- N -- O because we'd rather have the -1 charge on the...
by Sanjana K - 2F
Sun Nov 03, 2019 11:26 pm
Forum: Trends in The Periodic Table
Topic: ionization energy vs electronegativity
Replies: 4
Views: 23

Re: ionization energy vs electronegativity

Ionization energy is the amount of energy you need to remove an electron from an atom/ion while electronegativity is how likely an atom is to gain/attract an electron.
by Sanjana K - 2F
Sun Nov 03, 2019 2:15 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: paul and hundd rules
Replies: 4
Views: 35

Re: paul and hundd rules

They might ask you to identify which rule is being violated when filling shells (like they did for #9j on the Dino Nuggets practice midterm). So it would help to know that Pauli's Exclusion Principle says you can only have 2 electrons per orbital that must be spin-paired and that Hund's Rule says th...
by Sanjana K - 2F
Sat Oct 26, 2019 6:20 pm
Forum: Ionic & Covalent Bonds
Topic: "Delocalized" Electrons
Replies: 5
Views: 50

Re: "Delocalized" Electrons

Delocalized electrons are basically the electrons that aren't fixed to any particular atom or covalent bond. They're the ones that you see go back and forth, from one atom to another, resulting in the resonance structures we see for molecules like benzene (where the double bonds constantly change po...
by Sanjana K - 2F
Sat Oct 26, 2019 6:06 pm
Forum: Ionic & Covalent Bonds
Topic: Resonance (all bonds are a hybrid of different bonds)
Replies: 10
Views: 74

Re: Resonance (all bonds are a hybrid of different bonds)

I've noticed that for molecules like carbonate and benzene, they may have you draw out all the resonance forms OR you can use dotted lines to represent the bonds that change from one structure to another. Here's an example.
by Sanjana K - 2F
Sat Oct 26, 2019 5:55 pm
Forum: Ionic & Covalent Bonds
Topic: + and - ions
Replies: 3
Views: 64

Re: + and - ions

1. Fe^+ has the same config as Mn. 2. Fe^- has the same config as Co. 3. Fe^+ means that Fe lost an electron. 4. Fe^- means that Fe gained an electron. You can think of Fe as initially a neutral molecule [Fe]. But by adding a minus sign after it, as [Fe]^-, you're saying that it has one additional e...
by Sanjana K - 2F
Sat Oct 26, 2019 5:28 pm
Forum: Lewis Structures
Topic: Homework 2C #15
Replies: 3
Views: 47

Re: Homework 2C #15

Also, just some general rules for finding the lowest energy resonance structure:
- most atoms with FC = 0
- lower FC in general (negative is good too!)
- resonance forms with opposite sign charge on adjacent atoms
- most electronegative atoms
- most number of octets
by Sanjana K - 2F
Sat Oct 26, 2019 5:01 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge
Replies: 7
Views: 63

Re: Formal Charge

It also helps you keep track of the electrons and can help you predict the reactivity of the molecule. It assumes that all electrons are shared equally so you don't have to worry about bond polarity contributing to differences in potential. It'll help more when we do coordinate covalent complexes la...
by Sanjana K - 2F
Sun Oct 20, 2019 2:27 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Overlapping
Replies: 4
Views: 50

Re: Overlapping

The reason the orbitals overlap more as you move away from the nucleus is because the distance between the shells decreases so as they move closer together, the orbitals overlap more. As a result, the potential energy drops and new electrostatic interactions and bonds between the orbitals form.
by Sanjana K - 2F
Sun Oct 20, 2019 2:20 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Aufbau Principle
Replies: 3
Views: 27

Re: Aufbau Principle

It's basically the "building up" principle, which helps you determine electron configuration. It says electrons with lower energy levels with tend to fill up first. Here's a diagram of the order.
by Sanjana K - 2F
Sun Oct 20, 2019 1:52 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Structure of electrons
Replies: 5
Views: 30

Re: Structure of electrons

This picture might help. Orbitals are arranged into shells and subshells. Shells are orbitals with the same value of n & subshells are orbitals with the same value of n and l. In the picture, you'll notice that anything from energy level "2" is of the same shell (so 2s and 2p belong to...
by Sanjana K - 2F
Sun Oct 20, 2019 1:12 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Short Hand
Replies: 11
Views: 65

Re: Short Hand

So you want to base your shorthand off of the last element in the previous row (the last noble gas before your element). Chromium belongs in period 4 so you'd go to the previous row (period 3) and move to the last element (group 18), which is Argon. The "s" block consists of groups 1-2, th...
by Sanjana K - 2F
Sun Oct 20, 2019 1:10 am
Forum: Quantum Numbers and The H-Atom
Topic: Magnetic Spin
Replies: 4
Views: 50

Re: Magnetic Spin

The magnetic spin is used in the context of the spin magnetic number (the fourth quantum number that you use to describe an electron), so it is somewhat important. We denote the spin with either a +1/2 or a -1/2, which means the electron either spins clockwise or counterclockwise. No 2 electrons in ...
by Sanjana K - 2F
Sun Oct 20, 2019 12:42 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Spin up and spin down
Replies: 13
Views: 111

Re: Spin up and spin down

You only really need to know about the electron spins in the context of the spin magnetic number (the fourth quantum number that you use to describe an electron). We denote the spin with either a +1/2 or a -1/2, which means the electron either spins clockwise or counterclockwise. No 2 electrons in t...
by Sanjana K - 2F
Thu Oct 10, 2019 10:00 pm
Forum: Properties of Light
Topic: Electromagnetic Spectrum
Replies: 5
Views: 51

Re: Electromagnetic Spectrum

I don't think you'll need to memorize the exact wavelengths, but you should have a good idea of where the different waves lie in relation to one another. It might also help to come up with examples for each. The "types of EM Radiation" picture in this site is pretty nice. https://www.brita...
by Sanjana K - 2F
Thu Oct 10, 2019 9:44 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Rounding with basic calculator
Replies: 7
Views: 113

Re: Rounding with basic calculator

Use the "Ans" key on your calculator whenever possible. We're allowed to use scientific calculators but not graphing calculators, so you should be able to store values. Also, I generally leave at least 5 numbers after each decimal point (for each step) and apply sig figs at the very end.
by Sanjana K - 2F
Thu Oct 10, 2019 9:37 pm
Forum: Balancing Chemical Reactions
Topic: Importance of the State of Molecules
Replies: 6
Views: 106

Re: Importance of the State of Molecules

The state will usually be given to you in the problem (ex: 25ml of precipitate means solid, NaOH dissolved in water means aqueous). When we do acids/bases and solubility equilibria especially, you'll become familiar with which compounds dissociate in water (nitrates, acetates, compounds with group 1...
by Sanjana K - 2F
Thu Oct 10, 2019 9:28 pm
Forum: Balancing Chemical Reactions
Topic: H 1
Replies: 6
Views: 132

Re: H 1

Also, oxygen won't generally be present in a reaction as one oxygen atom alone. Oxygen is a diatomic molecule, so it'll only show up in a reaction as O2. Here's a list of other diatomic molecules (hydrogen, oxygen, fluorine, bromine, iodine, nitrogen, chlorine.. AKA HOFBrINCl).
by Sanjana K - 2F
Thu Oct 10, 2019 9:16 pm
Forum: Significant Figures
Topic: Final Answer
Replies: 4
Views: 68

Re: Final Answer

As Brian was saying, you want to make sure you're using the right number of sig figs first. Generally, if you're doing a lab and you're measuring amounts, it's better to use the whole number because it's easier to conceptualize 25ml than 2.5x10^(-2)L, but when you're answering a problem on paper, le...
by Sanjana K - 2F
Thu Oct 03, 2019 3:04 am
Forum: Significant Figures
Topic: Powers of 10
Replies: 10
Views: 96

Re: Powers of 10

When performing calculations, you generally want to keep the powers (especially if you're dealing with a very small or large number). After calculations, you could express the powers in simpler units (just for convenience or when in a lab setting, where you can't measure negative exponents of 10). S...
by Sanjana K - 2F
Thu Oct 03, 2019 2:56 am
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Fundamental E. 15 Question...
Replies: 3
Views: 43

Re: Fundamental E. 15 Question...

One thing to keep in mind is that when you're trying to find the molecular formula of the sulfide, you shouldn't just add an "S" to the metal. Based on the molar mass of the metal, you should try and identify it so that you can figure out its charge. If you know it's charge, you can then f...
by Sanjana K - 2F
Thu Oct 03, 2019 2:47 am
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Different types of formulas
Replies: 2
Views: 59

Re: Different types of formulas

I think it's more important to distinguish between an empirical formula (which shows you the simplest whole number ratio of atoms of each element in the compound) and a molecular formula (which shows the actual number of atoms of each element in a compound). A lot of sources online are using the ter...
by Sanjana K - 2F
Thu Oct 03, 2019 2:28 am
Forum: Balancing Chemical Reactions
Topic: Unequal coefficients
Replies: 7
Views: 69

Re: Unequal coefficients

Like Junwei was saying, it may seem convenient to use fractions initially when you're balancing but it will quickly get messy. Especially if the coefficients are quite large, you'll want to deal with whole numbers for convenience. But technically yes, you can balance with fractions as long as you mu...
by Sanjana K - 2F
Thu Oct 03, 2019 2:22 am
Forum: Limiting Reactant Calculations
Topic: M.9
Replies: 5
Views: 89

Re: M.9

Your net ionic equation does not include spectator ions (because they're essentially the elements that don't react with water; they just sit there). Spectator ions cancel out on each side of the reaction. I do think it would be a good idea to commit some of these spectator ions to memory because it'...

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