Search found 69 matches

Sun Jan 24, 2021 7:46 pm
Forum: Phase Changes & Related Calculations
Topic: Define Phase Change
Replies: 30
Views: 64

Re: Define Phase Change

A phase change is simply when matter changes from one state to another (i.e. solid to liquid aka melting).
Sun Jan 24, 2021 7:41 pm
Forum: Phase Changes & Related Calculations
Topic: Salt
Replies: 8
Views: 20

Re: Salt

Salts can be either acidic, basic, or even neutral (e.g. NaCl) depending on their cations and anions.
Sun Jan 24, 2021 7:38 pm
Forum: Phase Changes & Related Calculations
Topic: State Property
Replies: 3
Views: 20

Re: State Property

Heat is not a state function because it doesn't depend only on the final and the initial state of the system. For instance, recall the hiking example Dr. Lavelle provided in class. The change in altitude is the same no matter the route taken but the heat that leaves your body (in order to do work) d...
Sun Jan 24, 2021 7:28 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: pH of weak acid
Replies: 9
Views: 33

Re: pH of weak acid

We can assume that X is insignificant when Ka < 10-4. Alternatively if the inital concentration of the acid/base is 1000 times greater than the equilibrium constant, you can assume that the X is insignificant.
Sun Jan 24, 2021 7:22 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: approximating
Replies: 10
Views: 34

Re: approximating

X is not a valid apprxoimation for X 2 . If you take out one of the X's in the products (numerator), then you're ignoring the concentration of that product completely.X ≠ X 2 . For the demoninator, you can approximate because a large value minus a very small value is still approximately that large v...
Sun Jan 17, 2021 10:33 pm
Forum: Ideal Gases
Topic: Inverse Kc
Replies: 34
Views: 85

Re: Inverse Kc

Inverse Kc is for the reverse reaction where it's reactants over products.
Sun Jan 17, 2021 10:28 pm
Forum: Ideal Gases
Topic: Bars to atm [ENDORSED]
Replies: 35
Views: 173

Re: Bars to atm[ENDORSED]

1 bar is approximately 1 atm. Bar is the SI unit while atm is more traditionally used in chemistry.
Sun Jan 17, 2021 10:23 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Total pressure calculation
Replies: 8
Views: 27

Re: Total pressure calculation

When you find the equilbrium partial pressures from your ICE table, you can add them all up to obtain the total pressure.
Sun Jan 17, 2021 10:18 pm
Forum: Ideal Gases
Topic: n/V = concentration
Replies: 19
Views: 75

Re: n/V = concentration

so let's say there is a problem where they provide the mols and they are in a certain number of L in a container you would have to find the concentration with is basically mol/L in order to then proceed with the problem? That depends on the problem but mol/L is a common measurement of concentration...
Sun Jan 17, 2021 10:11 pm
Forum: Ideal Gases
Topic: Kp?
Replies: 22
Views: 53

Re: Kp?

Partial pressure only applies to gases because you cannot change the pressure of liquids and solids significantly.
Sun Jan 10, 2021 2:26 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: H2O
Replies: 44
Views: 289

Re: H2O

You would only include H2O when it is in a gaseous phase.
Sun Jan 10, 2021 2:20 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Units
Replies: 27
Views: 100

Re: Units

1 bar is very close to 1 atm so either will work. In lecture, Lavelle mentioned we will be using atm mostly.
Sun Jan 10, 2021 2:19 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: I in ICE Chart
Replies: 11
Views: 37

Re: I in ICE Chart

In the case of a reverse reaction, you will be given the initial concentration of the products instead.
Sun Jan 10, 2021 2:16 pm
Forum: Ideal Gases
Topic: value of R
Replies: 24
Views: 77

Re: value of R

The value of R will be provided on the constants and equations sheet. In lecture, Lavelle stated we will be using atm primarily so I would use the R value of 8.206 x 10^-2.
Sun Jan 10, 2021 2:13 pm
Forum: Ideal Gases
Topic: Inert Gas
Replies: 20
Views: 84

Re: Inert Gas

An inert gas is a non-reactive gas. In other words, they are noble gases.
Tue Dec 15, 2020 10:51 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Bond Angles
Replies: 8
Views: 74

Re: Bond Angles

The bond angle for AX3E depends on the molecule specifically but they are always less than 109.5 due to electron repulsion from the lone pair.
Tue Dec 15, 2020 10:47 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: [OH-] and pOH difference
Replies: 9
Views: 54

Re: [OH-] and pOH difference

The relationship between [OH-] and pOH is the same as the relationship between [H+] and pH. We use the logarithmic value (p- prefix) for convenience. pOH = -log[OH-] [OH-] = 10 -pOH You might find this image useful. https://www.sciencegeek.net/Chemistry/taters/graphics/pHSchematic.gif
Tue Dec 15, 2020 10:41 pm
Forum: Identifying Acidic & Basic Salts
Topic: Titration Graphs
Replies: 6
Views: 70

Re: Titration Graphs

Understanding the equilibrium point and the shape of the graph should be sufficient.
Tue Dec 15, 2020 10:37 pm
Forum: Air Pollution & Acid Rain
Topic: Acid Rain Formula
Replies: 1
Views: 21

Re: Acid Rain Formula

There are multiple formulas for acid rain because there are several reactions that make rain acidic. Here are some of the common ones: https://4.bp.blogspot.com/-Kf5m0cGVlqc/WwrcJQ71uYI/AAAAAAAAS1s/jlwP3BdDDVcWpJP32lUBq5rT6jrPekXswCLcBGAs/s1600/Screenshot_2018-05-27-21-28-02-069_com.google.android.a...
Sun Dec 13, 2020 1:35 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: pH and pKA
Replies: 6
Views: 74

Re: pH and pKA

Ah okay I see, thanks! I kind of get the relationship between pH and pKa now.
Sun Dec 13, 2020 1:26 pm
Forum: Lewis Acids & Bases
Topic: Water
Replies: 62
Views: 492

Re: Water

Water is amphoteric so it can act as either an acid or base depending on the context of the reaction.
Sun Dec 13, 2020 1:24 pm
Forum: Polyprotic Acids & Bases
Topic: Polyprotic Acids & Bases [ENDORSED]
Replies: 1
Views: 28

Polyprotic Acids & Bases[ENDORSED]

Are there any other common polyprotic acids/bases besides H2SO4, H2CO3, and H3PO4?
Sun Dec 13, 2020 1:14 pm
Forum: Air Pollution & Acid Rain
Topic: Acid Rain
Replies: 23
Views: 1634

Re: Acid Rain

When rain reacts with pollutants in the air (sulfur dioxide or nitrogen oxides), it becomes acidic.
Mon Dec 07, 2020 11:18 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: pH and pKA
Replies: 6
Views: 74

pH and pKA

Can someone explain/clarify the relationship between pH and pKA in terms of determining whether the acid being neutral or negatively charged? i.e. Why is it that when pH is lower than the pKa, the compound will be protonated? I think I'm missing some fundamentals here...
Tue Dec 01, 2020 5:55 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: AX2E3 Bond Angle
Replies: 7
Views: 70

Re: AX2E3 Bond Angle

Yes, the distribution of electron densities would be trigonal bipyamidal. The 3 lone e- pairs would be equatorial, leaving the two atoms opposite of each other (axial). Since the atoms are opposite of each other, the molecular geometry would be linear -> bond angle: 180.
Tue Dec 01, 2020 5:46 pm
Forum: Biological Examples
Topic: Biological Functions of Transition Metals
Replies: 5
Views: 62

Re: Biological Functions of Transition Metals

There is no trend, it is independent of order. Just know that the first row of the d-block transition metals have unique functions in biological systems and some examples covered in lectures.
Tue Dec 01, 2020 5:41 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Ligand
Replies: 4
Views: 57

Re: Ligand

In the context of a coordination compound, the Cl- is an anion inside the coordination sphere with 8 e- so it uses 2e- to form a bond with the TM.
Tue Dec 01, 2020 5:36 pm
Forum: Naming
Topic: Using ido or o
Replies: 24
Views: 140

Re: Using ido or o

In his lecture, Dr. Lavelle stated that either -ido (IUPAC) or -o (traditional) is acceptable.
Tue Dec 01, 2020 5:34 pm
Forum: Naming
Topic: Ferrate vs iron
Replies: 5
Views: 49

Re: Ferrate vs iron

For complex anions, Latin names are used for the following: Silver -> Argenate, Copper -> Cuprate, Lead -> Plumbate, Tin -> Stannate, Gold -> Aurate, and Iron -> Ferrate.
Sun Nov 29, 2020 9:12 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Oxidation State
Replies: 3
Views: 45

Re: Oxidation State

Oxidation number and oxidation state are the same thing. They are used interchangeably. Generally, for the first row of the d-block, the transition metals have a +2 oxidation state (the charge for transition metals is usually a case by case basis). You can determine the charge of a transition metal ...
Sun Nov 29, 2020 9:05 pm
Forum: Hybridization
Topic: hybridization, but very simple
Replies: 9
Views: 53

Re: hybridization, but very simple

Yes its very simple.
2 regions of e- density -> sp
3 regions of e- density -> sp2
4 regions of e- density -> sp3
5 regions of e- density -> sp3d
... etc.
Sun Nov 29, 2020 9:03 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: sigma vs pi bonds
Replies: 33
Views: 185

Re: sigma vs pi bonds

All single bonds are sigma bonds. Consequently, double bonds have one sigma and one pi bonds and triple bonds have one sigma and two pi bonds. (i.e. The bonds in addition to one sigma bond are all pi bonds). Pi bonds are stronger than sigma bonds. You can conceptually verify this because triple bond...
Sun Nov 29, 2020 9:00 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Polar
Replies: 10
Views: 67

Re: Polar

If the dipole moments cancel out, then the molecule is not polar. In other words, if there is no net dipole moment, then the molecule is not polar. Visualizing the 3D structure and symmetry of a molecule might help you in determing whether a molecule is polar.
Sun Nov 29, 2020 8:57 pm
Forum: Hybridization
Topic: delocalized pi bonds
Replies: 15
Views: 73

Re: delocalized pi bonds

Drawing the Lewis structure can help you identify whether a compound has delocalized pi bonds. For a compound that has a resonance structure(s) containing pi bonds (double and triple bonds), then it is said to have delocalized pi bonds because the pi orbitals extend over more than two atoms. An exam...
Sun Nov 22, 2020 12:04 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone Pair E-
Replies: 47
Views: 268

Re: Lone Pair E-

Yes, lone pair electrons are also regions of electron density. If they weren't then, molecular shape would be only determined by bonding electrons.
Sat Nov 21, 2020 11:34 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Shape Names
Replies: 50
Views: 299

Re: Shape Names

The shape is commonly referred to as either bent or angular. Some examples of this are H2O and NO2- (due to their lone pair(s)).
Sat Nov 21, 2020 11:32 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Linear shape
Replies: 7
Views: 54

Re: Linear shape

When you draw the Lewis structure for NO2-, the N has a lone pair which is more repulsive than bonding pairs and pushes the O atoms away from it causing the bent shape.
Sat Nov 21, 2020 11:26 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: H20 Bent Structure
Replies: 14
Views: 107

Re: H20 Bent Structure

The lone pairs are more repulsive than the bonding pairs and thus their electron distribution causes H2O to be bent as the lone pairs "push down" on the H atoms.
Sat Nov 21, 2020 11:24 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Polar or Nonpolar
Replies: 13
Views: 222

Re: Polar or Nonpolar

Are there other factors that affect polarity besides symmetry?
Sun Nov 15, 2020 11:11 pm
Forum: Ionic & Covalent Bonds
Replies: 18
Views: 116

Adding more electrons to an anion would increase the ionic radius because there would be more electron repulsion for the same nuclear charge.
Sun Nov 15, 2020 11:10 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Oxidations Numbers
Replies: 4
Views: 50

Re: Oxidations Numbers

You can find a guide to oxidation numbers on Sapling (https://sites.google.com/site/chempendix/oxidation). He hasn't gone over oxidation numbers in depth yet.
Sun Nov 15, 2020 11:08 pm
Forum: Octet Exceptions
Replies: 6
Views: 56

Radicals are highly reactive because they are unstable due to their unpaired valence electron. I think the question would typically tell you when a radical is involved.
Sun Nov 15, 2020 11:04 pm
Forum: Lewis Structures
Topic: Recognizing lowest formal charge
Replies: 11
Views: 50

Re: Recognizing lowest formal charge

There's no way to recognize the formal charge without calculating so I draw Lewis structures by counting the number of electrons, then trying different bonds for the lowest formal charge.
Sun Nov 15, 2020 11:02 pm
Forum: Coordinate Covalent Bonds
Topic: Hydrogen bonding
Replies: 15
Views: 112

Re: Hydrogen bonding

Hydrogen bonding is a intermolecular force unlike coordinate covalent bonds which are intramolecular.
Sun Nov 08, 2020 11:59 pm
Forum: Ionic & Covalent Bonds
Topic: Octet rule exceptions
Replies: 15
Views: 75

Re: Octet rule exceptions

Be and Li tend to lose electrons so they don't form a full octet. H and He only have electron(s) in the 1s orbital (max of 2 e-) so they don't form a full octet.
Sun Nov 08, 2020 11:57 pm
Forum: Ionic & Covalent Bonds
Topic: resources
Replies: 7
Views: 23

Re: resources

If you have time, I'd recommend Organic Chemistry tutor on Youtube. His explanations are pretty easy to understand and follow.
Sun Nov 08, 2020 11:55 pm
Forum: Lewis Structures
Topic: octet rule
Replies: 7
Views: 57

Re: octet rule

The octet rules applies to the first three rows of the periodic table if I remember correctly. (Correct me if I'm wrong please)
Sun Nov 08, 2020 11:53 pm
Forum: Trends in The Periodic Table
Topic: memorizing trends
Replies: 14
Views: 57

Re: memorizing trends

I would try to understand the conceptual reasoning behind the each of the trends. So even if you forget the trends, you can conceptually deduce the trends.
Sun Nov 08, 2020 11:50 pm
Forum: *Shrodinger Equation
Topic: The Hamiltonian
Replies: 8
Views: 126

Re: The Hamiltonian

The Hamiltonian is just a specific word for double derivative in this context.
Sun Nov 01, 2020 6:16 pm
Forum: Ionic & Covalent Bonds
Topic: Is ionic or covalent stronger?
Replies: 31
Views: 393

Re: Is ionic or covalent stronger?

Ionic bonds are stronger than covalent bonds because their difference in electronegativity is greater than that of covalent bonds.
Sun Nov 01, 2020 2:37 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg Equation Confusion
Replies: 9
Views: 77

Re: Rydberg Equation Confusion

n1 is always smaller than n2 because electrons are moving from higher energy state to a lower energy state. Therefore, n1 can be thought of as n final.
Sun Nov 01, 2020 2:30 pm
Forum: Quantum Numbers and The H-Atom
Topic: Nodal planes
Replies: 5
Views: 35

Re: Nodal planes

A nodal plane is where the probability of finding an electron is 0 (i.e. no electrons can exist in the nodal plane). The s orbital has no nodal planes due to its spherical nature.
Tue Oct 27, 2020 1:41 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg Equation Confusion
Replies: 9
Views: 77

Re: Rydberg Equation Confusion

Nevermind, I figured it out (correct me if I'm wrong pls). The Rydberg equation for frequency uses the Rydberg constant Lavelle gave us on the equation sheet which is in Hz. On Sapling, the Rydberg constant (1.0974 x 10^7 m^-1) is for the wavelength equation. Tl;dr: Two different equations with two ...
Tue Oct 27, 2020 1:28 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg Equation Confusion
Replies: 9
Views: 77

Rydberg Equation Confusion

To my understanding, the Rydberg Equation for wavelength is: https://cdn.shopify.com/s/files/1/0093/2298/7617/files/Screen_Shot_2019-08-09_at_2.30.14_PM.png?v=1565325071 so how was the equation for frequency (below) obtained on the Constants and Equations sheet by Lavelle? https://i.imgur.com/RKxSit...
Sun Oct 25, 2020 11:57 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Amplitude
Replies: 16
Views: 85

Re: Amplitude

Increasing the amplitude only increases the intensity. It does not affect wavelength or frequency.
Sun Oct 25, 2020 11:56 pm
Forum: DeBroglie Equation
Topic: Derivation of Equations on Midterm?
Replies: 17
Views: 99

Re: Derivation of Equations on Midterm?

We won't have to derive the equations on the midterm since it's multiple choice; I think the test would focus more on how to apply the equations and which equations to apply rather than how to derive them.
Sun Oct 25, 2020 11:52 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Orbitals
Replies: 9
Views: 100

Re: Orbitals

In the lecture, 5s state was an example of a silver atom's electron (5th row on ptable, n = 5) in s-orbital, hence 5s.
Sun Oct 25, 2020 11:50 pm
Forum: *Shrodinger Equation
Topic: Schrodinger on MT
Replies: 7
Views: 89

Re: Schrodinger on MT

The questions will most likely be conceptual so you might want to rewatch the Shrodinger portion of lecture to review.
Sun Oct 25, 2020 11:46 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Midterm 1
Replies: 18
Views: 206

Re: Midterm 1

The Heisenberg Indeterminacy concept will most likely be on the exam since he said anything up till 10/21 lecture would be on exam.
Sun Oct 18, 2020 9:23 pm
Forum: Photoelectric Effect
Topic: Photoelectric experiment vs atomic spectra
Replies: 5
Views: 57

Photoelectric experiment vs atomic spectra

I know Lavelle covered this in the lecture, but what is the difference between the photoelectric experiment and atomic spectra?
Sun Oct 18, 2020 9:16 pm
Forum: Photoelectric Effect
Topic: photoelectric effect
Replies: 17
Views: 135

Re: photoelectric effect

Yes, threshold energy and work function are interchangeable.
Sun Oct 18, 2020 9:10 pm
Forum: Student Social/Study Group
Topic: How are you studying?
Replies: 203
Views: 1296

Re: How are you studying?

I try to study with my friend for one hour each week. It's almost like having a gym buddy in terms of accountability. We both benefit from this by explaining to each other our understanding of the concepts covered and asking questions we previously didn't think of.
Sun Oct 18, 2020 9:00 pm
Forum: Einstein Equation
Topic: m vs nm
Replies: 66
Views: 462

Re: m vs nm

Lavelle mentioned in the lecture that it's acceptable to leave the answer in meters. I'm assuming that this also applies to exams.
Sun Oct 18, 2020 8:59 pm
Forum: Einstein Equation
Topic: What are the units for E
Replies: 16
Views: 124

Re: What are the units for E

Since the units for Planck's constant (h) are Joules second (J.s), the unit for E should Joules (J).
Sat Oct 10, 2020 12:25 am
Forum: Balancing Chemical Reactions
Topic: Order of Balancing Rxns
Replies: 23
Views: 115

Order of Balancing Rxns

Hey, I was just wondering how everyone approaches balancing chemical reactions in terms of which element to balance first (or the order in general). Also, how do you guys keep track of the number of elements on each side of the eqn (a mental note, tallies, etc.)?
Fri Oct 09, 2020 11:59 pm
Forum: Limiting Reactant Calculations
Topic: Actual yield
Replies: 20
Views: 194

Re: Actual yield

If the question asks for percent yield, then actual yield should be given. I hope this answers your question!
Fri Oct 09, 2020 11:52 pm
Forum: Balancing Chemical Reactions
Topic: Periodic Table
Replies: 50
Views: 484

Re: Periodic Table

There is a periodic table provided by Sapling under the Resources Tab on the left side of the dashboard screen. I prefer to use ptable.com. You will end up memorizing the molar masses of biologically essential elements eventually as you take more chemistry classes.
Fri Oct 09, 2020 11:47 pm
Forum: Balancing Chemical Reactions
Topic: WK 1 Sapling #10
Replies: 7
Views: 87

Re: WK 1 Sapling #10

How did you guys obtain the molar mass? I don't remember how to interpret skeleton drawings of organic molecules.
Fri Oct 09, 2020 11:45 pm
Forum: Balancing Chemical Reactions
Topic: Fractions
Replies: 26
Views: 169

Re: Fractions

You should use whole numbers (by convention). Ex: It wouldn't make sense to have 3/2 of a molecule just as it wouldn't make sense to have 3/2 people. So you would multiply both sides of the equation by 2 to obtain a whole number.