## Search found 62 matches

Fri Mar 15, 2019 10:27 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Concentration Cells
Replies: 1
Views: 74

### Concentration Cells

What will we be required to know about concentration cells?
Fri Mar 15, 2019 10:25 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: K Constant
Replies: 1
Views: 75

### K Constant

Why does the equilibrium constant K equal the ratio of the forward and reverse rate constants?
Fri Mar 15, 2019 10:23 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Isometric/Isochoric
Replies: 11
Views: 487

### Re: Isometric/Isochoric

Yes, a bomb calorimeter maintains a constant volume (isochoric) for reactions.
Mon Mar 11, 2019 2:16 am
Forum: Second Order Reactions
Topic: 2nd order
Replies: 4
Views: 174

### Re: 2nd order

The y-axis is the inverse of the concentration of A. Thus, the slope shows that as time increases, the inverse of [A] increases (not [A] itself).
Mon Mar 11, 2019 2:14 am
Forum: Zero Order Reactions
Topic: Zero Order Reactions
Replies: 8
Views: 493

### Re: Zero Order Reactions

Different order reactions have different reaction mechanisms, or the number of steps to form the product.
Mon Mar 11, 2019 2:12 am
Forum: General Rate Laws
Topic: Order of rxns and stoichiometric coefficients
Replies: 3
Views: 124

### Re: Order of rxns and stoichiometric coefficients

They are not necessarily the same, but in some occasions they are. It is best not to assume they are the same and to find the order itself.
Sun Mar 03, 2019 8:49 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: pH at 10 C
Replies: 3
Views: 152

### Re: pH at 10 C

I think it depends on the test version you had, but if you used the Van't Hoff equation and used the equilibrium constant equation to then convert [H+] to a pH value, you should get the right answer.
Sun Mar 03, 2019 8:43 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: negative n?
Replies: 2
Views: 116

### Re: negative n?

If you are referring to the exponent n in the rate law, then I do believe it can be a negative value. This would be when the increase of the concentration of a reactant causes the rate of the reaction to decrease.
Sun Mar 03, 2019 8:39 am
Forum: General Rate Laws
Topic: Overall sum
Replies: 7
Views: 255

### Re: Overall sum

The overall order of a reaction is the total sum of the orders of all the reactants.
Sun Feb 24, 2019 1:20 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: test 3
Replies: 10
Views: 366

### Re: test 3

Does anyone know if it will also include entropy and previous thermodynamic concepts?
Sun Feb 24, 2019 1:17 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell diagram
Replies: 3
Views: 146

### Re: Cell diagram

I think it's safe to say the anode is on the left and the cathode is on the right because that's how it was presented in the lectures. The standard reaction potentials are given as reductions, so which ever one is being oxidized in the actual reaction, needs to be reversed.
Sun Feb 24, 2019 1:12 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic Cell Diagram
Replies: 6
Views: 189

### Re: Galvanic Cell Diagram

I think it would be best to have an understanding of how it works. Knowing that, drawing the diagram should come easier.
Mon Feb 18, 2019 9:56 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy vs. Standard Gibbs Free Energy
Replies: 3
Views: 117

### Re: Gibbs Free Energy vs. Standard Gibbs Free Energy

The standard Gibbs Free Energy is fixed for a certain reaction and temperature. It is also under standard conditions and the difference between the Gibbs free energy of pure products and reactants.
Mon Feb 18, 2019 9:51 am
Forum: Calculating Work of Expansion
Topic: Units for R
Replies: 10
Views: 596

### Re: Units for R

There are different values for the constant R depending on the units used in the problem.
Mon Feb 18, 2019 9:50 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: When does delta U equal zero?
Replies: 17
Views: 1924

### Re: When does delta U equal zero?

This is for an isothermal reaction. (We can also infer from this that q=-w)
Sun Feb 10, 2019 12:50 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Delta U
Replies: 8
Views: 280

### Re: Delta U

The internal energy is zero when it is a reversible reaction or if it is at a constant temperature.
Sun Feb 10, 2019 12:47 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Replies: 4
Views: 354

### Re: adding an inert gas

They do not affect the concentrations of other substances in equilibrium because they do not react.
Sun Feb 10, 2019 12:43 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Enthalpy Equations
Replies: 1
Views: 114

### Enthalpy Equations

Can someone explain when and why we use 3/2 R and 5/2 R as the Cv value when finding enthalpy?
Sat Feb 02, 2019 6:04 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Delta U
Replies: 4
Views: 160

### Delta U

If $\Delta$ U is a state function, how is it that we can use work, which is pathway-dependent, to calculate it?
Sat Feb 02, 2019 5:56 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm Review
Replies: 14
Views: 507

### Re: Midterm Review

For Chem 14A last quarter Lavelle did have review sessions led by TAs and UAs the week leading up to the Midterm, so I would think that would be the case this quarter too?
Sat Feb 02, 2019 5:54 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Problem 8.1 (c) 6th edition
Replies: 2
Views: 154

### Problem 8.1 (c) 6th edition

Why is "coolant in a refrigerator coil" considered an isolated system? I am not familiar with the contraptions inside a refrigerator, so I am just wondering.
Sun Jan 27, 2019 1:30 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: The 3 methods
Replies: 5
Views: 190

### Re: The 3 methods

I believe that it depends on the type of information given in the problem. However, I recall Dr. Lavelle saying that Method 1 would give the most reliable and accurate answer.
Sun Jan 27, 2019 1:27 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Heat vs Enthalpy
Replies: 4
Views: 132

### Heat vs Enthalpy

Are heat and enthalpy considered the same thing, or are there any differences between them?
Sun Jan 27, 2019 1:25 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Work, state property
Replies: 3
Views: 142

### Re: Work, state property

You would need to know the energy expenditure for each step of the reaction to get the total amount of work versus just calculating the net change when finding enthalpy.
Sun Jan 20, 2019 12:50 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium Constant
Replies: 2
Views: 2841

### Re: Equilibrium Constant

If K>1 then there are more products at equilibrium. If K<1 then there are more reactants. If K=1 then there are equal amounts of reactants and products at equilibrium.
Sun Jan 20, 2019 12:35 pm
Forum: Ideal Gases
Topic: ice
Replies: 4
Views: 244

### Re: ice

There is no difference within the ICE table itself, just the type of species that are put into it.
Sun Jan 20, 2019 12:19 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Salt in the Equation
Replies: 1
Views: 104

### Re: Salt in the Equation

In lecture Dr. Lavelle stated that all Group 1 and MOST Group 2 salts do not affect the pH of a solution. However, he did not state specifically which ones do not, so I do not think that is something we are required to know.
Fri Jan 11, 2019 9:00 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Changing Pressure
Replies: 6
Views: 238

### Changing Pressure

Can someone clarify why there needs to be a change in volume for there to be a change in pressure of a reaction in equilibrium?
Fri Jan 11, 2019 8:49 pm
Forum: Ideal Gases
Topic: Ideal Gases
Replies: 7
Views: 192

### Re: Ideal Gases

I believe the general assumption is that a gas acts more "ideal" at higher temperatures and at lower pressures. I think most of the problems we will be given deal with ideal gases unless otherwise stated.
Fri Jan 11, 2019 8:46 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kc and Kp
Replies: 12
Views: 390

### Re: Kc and Kp

We use Kp for gases, and it is calculated by using the partial pressures of those gases, so I don't believe this would apply to solids or liquids.
Thu Dec 06, 2018 7:01 pm
Forum: Lewis Acids & Bases
Topic: Ligands
Replies: 7
Views: 430

### Re: Ligands

A neutral ligand contributes no charge to the coordination compound. An example would be H20 (aqua) or NH3 (ammine).
Thu Dec 06, 2018 6:59 pm
Forum: Naming
Topic: K3[CoF6]
Replies: 2
Views: 179

### Re: K3[CoF6]

I believe this is because Co is the transition metal cation and F is considered the ligand in this case.
Sun Dec 02, 2018 8:35 pm
Forum: Naming
Topic: Polydentate Ligands
Replies: 2
Views: 141

### Re: Polydentate Ligands

A polydentate ligand has multiple binding sites that donate multiple electron pairs. You can look for and count the two dots denoting lone pairs as a sign.
Sun Dec 02, 2018 8:27 pm
Forum: Naming
Topic: water
Replies: 2
Views: 116

### Re: water

The molecules are normally written in an order where the atom with the lone pair is right next to the atom that receives it. Thus, because oxygen has the lone pairs in a H20 molecule, you would write it 0H2 if the atom that receives the electrons is to the left of the water molecule (such as when dr...
Fri Nov 23, 2018 11:45 pm
Forum: Electronegativity
Topic: Nonmetals?
Replies: 6
Views: 371

### Re: Nonmetals?

Yes, generally non-metals tend to be more electronegative than metals, as the non-metals are located on the right side of the periodic table (and from the periodic trends, we know that from left to right electronegativity increases.)
Fri Nov 23, 2018 11:40 pm
Forum: Electronegativity
Topic: Largest Electronegativity
Replies: 4
Views: 177

### Re: Largest Electronegativity

Fluorine is the most electronegative atom on the periodic table.
Fri Nov 23, 2018 11:37 pm
Forum: Hybridization
Topic: double bonds
Replies: 14
Views: 408

### Re: double bonds

A double bond consists of one sigma and one pi bond. (Sigma and pi bonds are different because of the different orientation of the orbitals of the bond.)
Sun Nov 18, 2018 6:27 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: molecular shape and bond angles
Replies: 3
Views: 151

### Re: molecular shape and bond angles

I think we just need to know the angles for the basic geometry (electron density geometry) because those values are known and consistent I believe (like 90, 120, 180 degrees). For the electron density geometry, I think we just need to know how the lone pairs affect the bond angles.
Sun Nov 18, 2018 6:19 pm
Forum: Administrative Questions and Class Announcements
Topic: Chem Community Posts
Replies: 3
Views: 170

### Re: Chem Community Posts

My TA told us that posts were cumulative, and thus built up and counted at the end. So, just in case we miss a week or something we could make it up. I am not completely sure if this is the case with all TAs though.
Sun Nov 18, 2018 6:16 pm
Forum: Dipole Moments
Topic: Dipole moments in terms of very electronegative atoms
Replies: 3
Views: 155

### Re: Dipole moments in terms of very electronegative atoms

Because the dipole moments are not symmetrically distributed and are different strengths, there would be a net dipole moment, thus making it polar.
Sun Nov 18, 2018 6:14 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Molecular Geometry
Replies: 6
Views: 249

### Re: Molecular Geometry

The electron density geometry does take into account all the bonding and lone pairs linked to the central atom. Molecular geometry only takes into account of the bonds that are actually attached to other molecules. If there are no lone pairs, these shapes are the same.
Sat Nov 10, 2018 2:44 pm
Forum: Bond Lengths & Energies
Topic: MIDTERM Bond Length Question
Replies: 15
Views: 536

### Re: MIDTERM Bond Length Question

There were resonance structures for the molecule that included single and double bonds, so the actual molecule would have an average of those two bonds. I took the average of the two lengths and got 130pm.
Sat Nov 10, 2018 2:31 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Naming the shape
Replies: 6
Views: 360

### Re: Naming the shape

There are also other names of shapes when there are lone pairs such as bent, T-shaped, see-saw, etc.
Sat Nov 10, 2018 2:23 pm
Forum: Electronegativity
Topic: Electron Affinity
Replies: 3
Views: 260

### Electron Affinity

Would a neutral K atom or K+ ion have a more negative value of electron affinity and why?
Sat Nov 03, 2018 9:33 pm
Forum: Lewis Structures
Topic: Brackets around ions
Replies: 2
Views: 78

### Re: Brackets around ions

I am not sure why that is, but during the TA review sessions, they mentioned that you should put brackets around ions when completing their Lewis structure.
Sat Nov 03, 2018 9:28 pm
Forum: Trends in The Periodic Table
Topic: Exceptions to ionization energy
Replies: 1
Views: 129

### Re: Exceptions to ionization energy

The concept basically follows that having a half or full filled subshell is more stable for an atom. Regarding electron affinity, N would have a lower E.A. than expected because it doesn't want to gain another electron due to the fact that it already has a half filled 2p subshell. Carbon, on the oth...
Sat Nov 03, 2018 9:22 pm
Forum: Ionic & Covalent Bonds
Topic: Ionic character [ENDORSED]
Replies: 5
Views: 216

### Re: Ionic character[ENDORSED]

If you look up the electronegativity values of H, C, and F, they are 2.1, 2.5, and 4.0 respectively. So, the electronegativity values for Carbon and Hydrogen are a lot closer than the value for Fluorine. Just because they appear closer on the periodic table doesn't necessarily mean their values are ...
Sun Oct 28, 2018 2:48 pm
Forum: Trends in The Periodic Table
Topic: Removing 2nd e- [ENDORSED]
Replies: 4
Views: 156

### Re: Removing 2nd e-[ENDORSED]

If you remove an electron, you are creating a cation. This net positive charge creates a stronger electrostatic attraction that holds the electrons tighter to the nucleus, thus requiring more energy to separate.
Sun Oct 28, 2018 2:43 pm
Forum: Ionic & Covalent Bonds
Topic: ionic vs. covalent bonds
Replies: 3
Views: 146

### Re: ionic vs. covalent bonds

This depends on the environment because in an aqueous solution covalent bonds would be stronger as ionic bonds would beak and separate due to the polar characteristics of water. However, ionic bonds out of water would be stronger due to the attraction of opposite charges.
Sun Oct 28, 2018 2:39 pm
Forum: Lewis Structures
Topic: Lewis Structure Drawing
Replies: 6
Views: 189

### Lewis Structure Drawing

In high school I remember being allowed to draw straight lines whenever there were two valence electrons on a Lewis structure diagram, as a kind of shorthand method instead of drawing all dots. However, in lecture we learned to use straight lines only for shared electrons. Is the other way incorrect?
Sun Oct 21, 2018 9:46 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Particle Size
Replies: 3
Views: 145

### Re: Particle Size

It was not said exactly if there have been experiments done on this. However, I would think that anything at the atomic level would be affected by the light source.
Sun Oct 21, 2018 9:33 pm
Forum: Photoelectric Effect
Topic: Visible Light Spectrum
Replies: 6
Views: 218

### Re: Visible Light Spectrum

I believe in lecture Dr. Lavelle said it is safe to assume the visible light spectrum range is from about 400 to 700nm.
Sun Oct 21, 2018 9:19 pm
Forum: Properties of Light
Topic: Using a rounded speed of light in EM problems
Replies: 4
Views: 262

### Re: Using a rounded speed of light in EM problems

If the speed of light was given at 2.998 x 10^8 and you want to round it, I would use 3.000 x 10^8 because it has the same amount of sig figs but would require less digits to input in the calculator. Using that value with 4 sig figs and given a value 2.55 nm with 3 sig figs, your answer should have ...
Sun Oct 21, 2018 9:07 pm
Forum: Quantum Numbers and The H-Atom
Topic: Electron Spin
Replies: 3
Views: 164

### Electron Spin

I know the electron spin, or ms quantum number, is used because every electron had their own unique set of quantum numbers, but why is it +1/2 and -1/2? Was the value of 1/2 arbitrary?
Sun Oct 21, 2018 9:03 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Atomic Orbitals
Replies: 3
Views: 114

### Re: Atomic Orbitals

The s, p,d,and f orbitals correspond to the main types of shapes of the atomic orbitals. For example, the s orbitals are in the shape of a sphere and the p orbitals are two lobes with a nodal plane through the center. The periodic table is also split up in to s, p, d, and f blocks in which the valen...
Sun Oct 14, 2018 12:19 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: n Quantum Number
Replies: 1
Views: 74

### n Quantum Number

In the equations involving n, I know its value has to be a whole integer. In the book, it's followed by an ellipsis, implying that the value continues forever. Is there a certain value of n that becomes unreasonable?
Sun Oct 14, 2018 11:57 am
Forum: Properties of Light
Topic: Speed of Light
Replies: 41
Views: 1418

### Re: Speed of Light

I did some research behind it, and some sources are claiming that recent studies show light doesn't always travel at the speed proposed by Einstein's theory. However, for the purposes of this class the speed of light is assumed to be constant.
Sun Oct 14, 2018 11:52 am
Forum: Photoelectric Effect
Topic: 1B.15 Part C
Replies: 2
Views: 96

### Re: 1B.15 Part C

I don't see a question 1B.15 in the textbook. Is it at the end of the chapter?
Thu Oct 11, 2018 8:44 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: H-Atom Emperical Equation
Replies: 2
Views: 97

### H-Atom Emperical Equation

We learned in class that the equation E{n}= -(hR)/n^2 was only used for Hydrogen atoms because it was based on experimental data, but how different would an empirical equation like this be for other atoms?
Thu Oct 04, 2018 8:46 pm
Forum: Molarity, Solutions, Dilutions
Topic: HW #L 11
Replies: 1
Views: 106

### Re: HW #L 11

When something is neutralized, water is formed. So, taking the reactants of that second equation, Mg(OH)2 and HCl, you would have H2O as a product. This would be formed from the OH- in the Mg(OH)2 and the H+ from the HCl. Then, the remaining Mg2- and Cl- ions would form a compound, MgCl2. Once you h...
Thu Oct 04, 2018 8:20 pm
Forum: Molarity, Solutions, Dilutions
Topic: Homework help G21
Replies: 2
Views: 133

### Re: Homework help G21

43123230_162077154732160_7899198701413859328_n.jpg 43102606_2120414714877915_907926004423458816_n.jpg I did the work for the problem step by step. To solve it you need to know that the compounds given dissolve and break up into ions. The answer was 0.01 off from the textbook solution mostly likely ...
Thu Oct 04, 2018 7:55 pm
Forum: SI Units, Unit Conversions
Topic: HW E9 in textbook
Replies: 3
Views: 164

### Re: HW E9 in textbook

A mole is 6.022 x 10^23 units of something, whether it be particles, atoms, molecules, etc. So, for example, there should be 6.022 x 10^23 separate water molecules in one mole of H20. The characteristic that differentiates moles of different particles would be their mass.