## Search found 60 matches

Mon Mar 11, 2019 10:06 pm
Forum: First Order Reactions
Topic: pseudo vs 2nd order
Replies: 4
Views: 188

### Re: pseudo vs 2nd order

You can use the pseudo especially when your rate law is dependent on multiple reactants. If the reaction is first order with respect to any of them it can be rewritten as pseudo-first order.
Mon Mar 11, 2019 9:52 pm
Forum: First Order Reactions
Topic: Doubling the Concentration
Replies: 4
Views: 187

### Re: Doubling the Concentration

No, the order of the reaction is unchanging, but the rate is dependent on the initial concentrations of the reactant. Therefore by doubling the concentration (doubling the physical amount of it, not adding a two to the chemical equation) will double the initial rate.
Mon Mar 11, 2019 9:49 pm
Forum: General Rate Laws
Topic: Avg Rate vs Instantaneous Rate
Replies: 2
Views: 121

### Re: Avg Rate vs Instantaneous Rate

According to the textbook the average rate isn't very important. As far as I know, instantaneous rates are all that is relevant for all of the types of problems we are going to be doing. (unless the problem is "find the average rate")
Fri Mar 08, 2019 10:01 am
Forum: Zero Order Reactions
Topic: initial concentration
Replies: 6
Views: 274

### Re: initial concentration

This can be for a number of reasons. The one that Lavelle specifically mentioned in class is that the reaction is dependent on an enzyme or catalyst rather than on the concentration of reactants.
Fri Mar 08, 2019 10:00 am
Forum: Second Order Reactions
Topic: Final
Replies: 30
Views: 797

### Re: Final

The final is pretty evenly everything that we have covered. I wouldn't expect anything to be more common than other stuff.
Wed Mar 06, 2019 12:39 pm
Forum: First Order Reactions
Topic: Half-Life 1st Order Reaction
Replies: 6
Views: 197

### Re: Half-Life 1st Order Reaction

Yes, that's exactly correct.
Thu Feb 28, 2019 5:28 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Kinetics vs. Thermodynamics
Replies: 3
Views: 139

### Re: Kinetics vs. Thermodynamics

What he meant is that despite the fact that the compound is technically thermodynamically unstable, its kinetic stability trumps that, and the reaction either does not proceed or does so exceedingly slowly.
Thu Feb 28, 2019 5:27 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: speed of reaction based on activation energy
Replies: 6
Views: 208

### Re: speed of reaction based on activation energy

Yes, generally. This is because the reaction will require a greater buildup of heat in order to reach the energy of its transition state.
Mon Feb 25, 2019 12:23 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Using commas in cell diagram
Replies: 3
Views: 126

### Re: Using commas in cell diagram

straight lines indicate that they are in the same phase in the same beaker. A straight line indicates that they are in different phases. (when used to show the different between oxidized and reduced states)
Mon Feb 25, 2019 12:21 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Recharging Batteries [ENDORSED]
Replies: 10
Views: 635

### Re: Recharging Batteries[ENDORSED]

The potential of the reverse reaction is negative, therefore it is not spontaneous and will require a supply of energy to occur.
Mon Feb 25, 2019 12:19 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: E standard
Replies: 3
Views: 146

### Re: E standard

it depends, the half reactions ought to be balanced, otherwise your standard reaction potential will not really make sense/be the right number.
Mon Feb 25, 2019 12:18 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Delta G
Replies: 2
Views: 117

### Re: Delta G

No, n is the number of moles of electrons being transferred.
Thu Feb 14, 2019 10:04 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Statistical and residual entropy
Replies: 3
Views: 138

### Re: Statistical and residual entropy

Statistical entropy is the total amount of entropy for the given amount of micro states, whereas residual entropy is a specific entropy that is left after most of the thermal energy of the system is gone. (i.e. the temp approaches 0K)
Thu Feb 14, 2019 10:00 am
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: Explaining Boltzmann's Equation
Replies: 6
Views: 680

### Re: Explaining Boltzmann's Equation

The actual derivation for Boltzmann's equation is quite complicated and involves a lot of multivariable calc, so I would just take it for granted.
Thu Feb 14, 2019 9:54 am
Forum: Calculating Work of Expansion
Topic: Substituting -nrT for -PΔV
Replies: 4
Views: 179

### Re: Substituting -nrT for -PΔV

You have to balance the chemical equation to see if the number of moles of gas will change. For the temperature the problem will tell you.
Sun Feb 10, 2019 1:54 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: 4.15 7th edition
Replies: 1
Views: 100

### Re: 4.15 7th edition

The density of water is 1g/mL and the question states that there are 800mL of solution. You can assume the contribution to density from dissolved solids is negligible and therefore that the weight of the water in question is 800g.
Tue Feb 05, 2019 11:04 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: U total - 3/2nRT
Replies: 3
Views: 162

### Re: U total - 3/2nRT

This equation is derived from the equipartition theorem. This is the form that is for the translational energy of a monatomic gas, and the form can change as you change the molecular structure of the gas in question. (i.e. you have diatomic or polyatomic gases) The equipartition theorem gives us the...
Mon Feb 04, 2019 10:04 pm
Forum: Calculating Work of Expansion
Topic: Converting between units?
Replies: 2
Views: 72

### Converting between units?

How do we convert between (units of pressure x liters) to joules? I know that for (atm x liters) you multiply by 101.325, but I am not sure about other units of pressure, or conceptually why this works.
Wed Jan 30, 2019 12:20 pm
Forum: Calculating Work of Expansion
Topic: 4A.3 7th Ed
Replies: 6
Views: 196

### Re: 4A.3 7th Ed

Change in volume is (pi)(r^2)(change in d) because r is a constant and does not change in between the final and initial volumes. (at least in this example, it could potentially change but that would be a rather more complicated) So in order to calculate change in volume you just need to replace the ...
Tue Jan 29, 2019 11:40 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Isolated systems
Replies: 10
Views: 256

### Re: Isolated systems

An isolated system does not necessarily have constant volume, but it could. Isolated just means that there is no exchange of heat or matter with the surroundings.
Tue Jan 29, 2019 11:37 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat and work
Replies: 4
Views: 197

### Re: Heat and work

Heat and work both contribute to change in internal energy by the equation (delta)U = heat + work. When you have heat exiting the system you subtract from internal energy. Heat into a system adds to internal energy. Work done on a system adds to internal energy, work done by a system subtracts inter...
Fri Jan 25, 2019 1:48 pm
Forum: Phase Changes & Related Calculations
Topic: Reverse fusion
Replies: 3
Views: 156

### Re: Reverse fusion

Fusion is an endothermic process because you put in heat to the system to change the phase, but the temp of the substance does not change. Solidification, or the reverse reaction, is exothermic because the heat that was input to liquify the substance (the enthalpy of fusion) is being released in ord...
Fri Jan 25, 2019 1:44 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 3 Methods
Replies: 3
Views: 107

### Re: 3 Methods

For bonds that are not from diatomic molecules, (molecules with 2 atoms) it is practically impossible to get a constant value for a bond that is found in many different molecules. For example, the carbon-carbon double bond is present in tons of different molecules and has a very slightly different b...
Wed Jan 23, 2019 1:02 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: autoprotolysis
Replies: 5
Views: 269

### Re: autoprotolysis

While I can't confirm what is on the test, you just take the negative log of both sides and then use the formula log(ab) = loga + logb to derive the final equation.
Fri Jan 18, 2019 12:20 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Initial Concentrations of ICE Box and 12.79 (6th Edition)
Replies: 3
Views: 1063

### Re: Initial Concentrations of ICE Box and 12.79 (6th Edition)

If you have a reaction with a polyprotic acid, (acid capable of donating more than one proton, of which H2SO4 is an example) then you can express it as two equilibrium reactions in which the second one the concentration of H3O+ is more than 0. For the vast majority of polyprotic acids the second or ...
Fri Jan 18, 2019 12:17 pm
Forum: Ideal Gases
Topic: Percentage protonated
Replies: 2
Views: 160

### Re: Percentage protonated

The percentage protonated is just another way of indicating the power of a base. If the percent protonated was close to 100, that would mean that you have a strong base because all, or almost all, of the base has received a proton from water and become the conjugate acid. A low percent protonation i...
Wed Jan 16, 2019 12:17 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Acids
Replies: 6
Views: 207

### Re: Acids

A strong acid dissociates completely in water, or at least so much that it is practically completely. Mathematically, this means that the Ka (acidity constant) is infinitely large. For weak acids the acidity constant will be less that 10^-3. This means that not all of the acid is dissociating in wat...
Thu Jan 10, 2019 3:57 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kc, Kp, K
Replies: 3
Views: 438

### Re: Kc, Kp, K

K is the general term for an equilibrium constant, which the textbook defines in terms of activities. (which Dr. Lavelle said was more accurate, but unnecessary for an undergraduate-level class) Kp is the equilibrium constant in terms of partial pressures, which applies only to homogenous gas reacti...
Thu Jan 10, 2019 3:49 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Pure solids and liquids in eq. constants [ENDORSED]
Replies: 4
Views: 403

### Pure solids and liquids in eq. constants[ENDORSED]

Why is it that we don't include pure solids and liquids in equilibrium constants?
Sun Dec 02, 2018 10:47 am
Forum: Amphoteric Compounds
Topic: acidic, basic, and amphoteric oxides
Replies: 2
Views: 202

### Re: acidic, basic, and amphoteric oxides

Acidic and basic oxides are just that, oxides that act as acids or bases. Acidic oxides are usually covalent compounds whereas basic oxides are typically metal oxides. The ones that fall in between, the metalloids, (with a bit of overlap and exceptions) are the amphoteric oxides that can act as eith...
Sun Dec 02, 2018 10:40 am
Forum: Bronsted Acids & Bases
Topic: Bronsted, Arrhenious, or Lewis?
Replies: 2
Views: 121

### Re: Bronsted, Arrhenious, or Lewis?

Lewis and Bronsted, Arrhenius is a pretty outdated definition that was superseded by the Lewis and Bronsted-Lowry theories.
Sun Dec 02, 2018 10:31 am
Forum: Conjugate Acids & Bases
Topic: Strong and Weak Acids and Bases in Relations with H2O
Replies: 3
Views: 126

### Re: Strong and Weak Acids and Bases in Relations with H2O

Strong acids totally dissociate in water forming as many hydronium ions as there are acid molecules in the solution. (for monoprotic acids, for acids that donate more than one proton it can be two or three times as many) Weak acids will have incomplete dissociations.
Mon Nov 26, 2018 2:22 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Oxidation Numbers
Replies: 1
Views: 353

### Re: Oxidation Numbers

An oxidation number is pretty much the positive charge on an element if it is positive, or the negative charge if it is negative. It represents the number of electrons lost (positive) or gained. (negative) An oxidation reaction in general refers to the loss of electrons, which is why positive oxidat...
Mon Nov 26, 2018 2:00 pm
Forum: Hybridization
Topic: Hybridization
Replies: 2
Views: 90

### Re: Hybridization

We will have to be able to list the orbitals that are present in a hybrid orbital but I do not believe that he will have us actually draw the hybrid orbitals.
Mon Nov 26, 2018 1:57 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Chelating Ligands
Replies: 1
Views: 54

### Re: Chelating Ligands

The reason for the tighter bond is because multiple coordinate bonds are formed due to the presence of several lone pairs on the chelate. This means that instead of a lone ligand which would only form one bond, the chelate compound can form several, increasing the overall strength.
Sun Nov 18, 2018 12:16 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: AXE
Replies: 7
Views: 304

### Re: AXE

If you memorize which molecules are the ones without lone pairs, then it is fairly easy to intuit which molecules are the ones with one less atom and a lone pair instead. (identical electron arrangement, different molecular shape) This is the method that I usually use.
Sun Nov 18, 2018 12:14 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Sigma and Pi Bonds
Replies: 5
Views: 265

### Re: Sigma and Pi Bonds

Pi bonds are weaker because due to the parallel overlap, the total area of overlap is smaller. This can be derived from quantum mechanical representations of the bonding models.
Sun Nov 18, 2018 12:12 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Geometry and Lone Pairs
Replies: 1
Views: 29

### Re: Geometry and Lone Pairs

Yes, this results in a t-shape molcule with a VSEPR configuration of AX4E1. If you were to change that to AX3E2, then the resultant geometry would be t-shaped, not see-saw.
Sun Nov 11, 2018 11:20 am
Forum: Dipole Moments
Topic: Dipole Moments [ENDORSED]
Replies: 10
Views: 436

### Re: Dipole Moments[ENDORSED]

He said that we definitely won't have to, but knowing the equation for the sake of conceptual questions is probably a good idea.
Sun Nov 11, 2018 11:19 am
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Dipole-Induced Dipole [ENDORSED]
Replies: 2
Views: 103

### Re: Dipole-Induced Dipole[ENDORSED]

It is when you have one molecules that already has a dipole (polar) and you bring it into proximity of another non-charged molecule, particularly one that has lone pairs. When you bring them together, the dipole's net charge will distort the electrons of the otherwise uncharged molecule, thus induci...
Sun Nov 11, 2018 11:13 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Molecular Shape
Replies: 4
Views: 162

### Re: Molecular Shape

The types of atoms do not affect it, rather the number of atoms and electrons. Indirectly the type of atom affects shape by determining the number of electrons available.
Sun Nov 04, 2018 12:58 pm
Forum: Trends in The Periodic Table
Topic: Rank C,N,O,F on Ionization Energy
Replies: 2
Views: 105

### Re: Rank C,N,O,F on Ionization Energy

The reason that nitrogen has a higher ionization energy than oxygen is because oxygen has an orbital with 2 electrons in it, which results in some electron-electron repulsion. Whereas nitrogen has just one electron in each of its 2p orbitals and therefore lacks that same electron-electron repulsion.
Sun Nov 04, 2018 12:53 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge Exceptions
Replies: 2
Views: 76

### Re: Formal Charge Exceptions

There are also exceptions based on what the central atom is and such. For example, if resonance is possible, then the structure will always have resonance because resonance structures are lower energy than non-resonance structures.
Sun Nov 04, 2018 12:51 pm
Forum: Electronegativity
Topic: How much can you round down for empirical formulas?
Replies: 2
Views: 304

### Re: How much can you round down for empirical formulas?

8.5 to 8 is a pretty big jump. I would check your calculations up to that point, its possible that you rounded too early. The rule, according to my TA, for empirical formulas, is that you can round up or down if the value is within 5% of that rounded value.
Sun Oct 28, 2018 12:32 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Configurations Full or Abbreviated
Replies: 2
Views: 110

### Re: Electron Configurations Full or Abbreviated

In lecture Dr. Lavelle said that we can pretty much always use the abbreviated form unless specifically stated to do otherwise.
Sun Oct 28, 2018 12:31 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Copper exception
Replies: 4
Views: 207

### Re: Copper exception

This is because it is more stable for the entire 3d subshell to be filled than to have the 4s subshell with 2 and the 3d with 9. This is pretty much just how the math happens to work out and what is experimentally observed. A parallel to this is the electronic structure of Chromium, from the same su...
Sun Oct 28, 2018 12:28 pm
Forum: Lewis Structures
Topic: Losing Valence Electrons to Form Ions
Replies: 1
Views: 83

### Re: Losing Valence Electrons to Form Ions

It is usually on a case-by-case basis. For example, CuCl2 is more stable than CuCl, but CuI is more stable than CuI2. This is due to the specific physics of the electrons in the 3d subshell.
Fri Oct 19, 2018 5:05 pm
Forum: DeBroglie Equation
Topic: Momentum of protons
Replies: 2
Views: 130

### Re: Momentum of protons

I assume you meant photons, not protons. (because protons do indeed have mass) The reason that photons have momentum is related to the equation E = mc^2. Since c is the velocity of a photon, this equation can also be written as E = mv^2. Since momentum is equal to mv, this can be rewritten as E = pc...
Fri Oct 19, 2018 5:00 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Spectral Lines vs. Diffraction Pattern
Replies: 1
Views: 51

### Re: Spectral Lines vs. Diffraction Pattern

Spectral lines are the patterns created from the light absorbed or emitted by a hydrogen atom. Diffraction patterns are the patterns created when two light waves interact with each other creating patterns of constructive or destructive interference. These are not necessarily related in the context o...
Fri Oct 19, 2018 4:56 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: orientation of the lobes
Replies: 2
Views: 76

### Re: orientation of the lobes

The names of each of the orbitals correspond to one of the axes of the three-dimensional cartesian coordinate plane. For example, the Px orbital lies along the x-axis of the plane, whereas the Py orbital lies along the y-axis of the plane and the Pz along the z-axis. This is the way to differentiate...
Mon Oct 15, 2018 4:59 pm
Forum: Administrative Questions and Class Announcements
Topic: Audio Visual Focus Modules
Replies: 1
Views: 48

### Audio Visual Focus Modules

Will there be audio-visual focus modules available for the other topics in the quantum world section? Right now I can only seem to find ones up to Heisenberg's uncertainty principle.
Mon Oct 15, 2018 4:18 pm
Forum: DeBroglie Equation
Topic: 1B19 Edition 7
Replies: 2
Views: 60

### Re: 1B19 Edition 7

They have extremely similar masses. Given the number of significant figures in the problem they have identical wavelengths, and this is the answer that they are looking for. However, if you hypothetically had more sig figs, you could indeed find a percent difference (tiny) between the two wavelengths.
Mon Oct 15, 2018 4:15 pm
Forum: Properties of Electrons
Topic: Rydberg formula
Replies: 5
Views: 217

### Re: Rydberg formula

If you want to use the Rydberg Equation, use the final energy level = n1, the initial energy level is =n2. Then you simply plug in to a calculator and solve. As mentioned in lecture though, the other method is somewhat less susceptible to errors.
Mon Oct 15, 2018 4:12 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: 7th Edition, 1B.27
Replies: 3
Views: 121

### 7th Edition, 1B.27

The question asks us to find the minimum uncertainty in a bowling ball. In lecture Dr. Lavelle said when you are given a velocity + or - a certain value you use the entire range of values as your uncertainty. (i.e. the velocity is 1 m/s +/- 3 m/s, therefore your uncertainty is 6 m/s) The solution ma...
Mon Oct 08, 2018 4:08 pm
Forum: Properties of Light
Topic: Quanta & Photons
Replies: 5
Views: 202

### Re: Quanta & Photons

It is meant to draw notice to the fact that numbers in quantum equations cannot be "anything" like in a lot of classical mechanics situations. In lecture he used the example F= ma can have pretty much any number for each of those values, whereas in a quantum equation some variables will on...
Mon Oct 08, 2018 4:06 pm
Forum: Properties of Light
Topic: Chapter 1 Homework
Replies: 6
Views: 322

### Re: Chapter 1 Homework

I believe you are supposed to do the ones from the unit on the syllabus that we are in right now. So for this week it would be anything from the "Quantum World" section
Mon Oct 08, 2018 4:03 pm
Forum: Properties of Light
Topic: Homework Question 1A.3 C, Seventh Edition Page 9
Replies: 1
Views: 67

### Re: Homework Question 1A.3 C, Seventh Edition Page 9

Extent of change is just a weird way to refer to the slope of the wave. The wave's amplitude is the electric field, so the changes to the slop would represent the extent of change to the electric field.
Wed Oct 03, 2018 5:00 pm
Forum: Limiting Reactant Calculations
Topic: finding grams of product
Replies: 2
Views: 153

### Re: finding grams of product

If you have .3 moles of a substance (and you have verified that this is your limiting reactant) and the equation states that there is a 1:3 ratio between that particular reactant and the product in question, then you will produce .9 moles of the product. (1 mole of the reactant becomes 3 moles of th...
Wed Oct 03, 2018 4:55 pm
Forum: Balancing Chemical Reactions
Topic: Stoichiometric coefficients
Replies: 3
Views: 82

### Stoichiometric coefficients

Is it acceptable to write the number 1 as a stoichiometric coefficient in a balanced chemical equation instead of just leaving the reactant/product with nothing in front of it? I ask only because I keep doing this out of habit and am not sure whether or not this is the proper notation.
Tue Oct 02, 2018 11:00 am
Forum: Balancing Chemical Reactions
Topic: States of Atoms
Replies: 7
Views: 165

### Re: States of Atoms

He did mention that he wants us to use the proper states of atoms. I would recommend memorizing some of the basic ones and looking for the trends in the periodic table. (i.e. the diatomic elements are usually gasses, etc.)