## Search found 59 matches

Wed Mar 13, 2019 1:21 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 7D.7b
Replies: 1
Views: 61

### 7D.7b

How do I determine if this reaction is endothermic or exothermic? It gives the reaction constants of the forward and reverse (so you know the equilibrium constant) and the activation energies for both.
Wed Mar 13, 2019 1:04 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Positive Voltage
Replies: 1
Views: 103

### Positive Voltage

Just want to confirm, is the total cell potential (voltage) always positive for a galvanic cell? Cathode/anode can be positive or negative though right?
Wed Mar 13, 2019 12:59 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Exothermic vs. Endothermic
Replies: 10
Views: 480

### Exothermic vs. Endothermic

If a reaction has activation energy, is it always endothermic? If not, is it because deltaG plus the activation energy is still less than zero? or is there something else?
Sat Mar 09, 2019 10:02 pm
Forum: General Rate Laws
Topic: Unique Rate
Replies: 1
Views: 91

### Re: Unique Rate

The unique rate is a essentially a proportion that gives you the rate of each product/reactant relative to the other. It is the rate of the product or reactant divided by its stoichiometric coefficient. Lavelle gave an example in class that makes a lot of sense. If the equation is 2NO2 ---> 2NO + O2...
Sat Mar 09, 2019 9:46 pm
Forum: Second Order Reactions
Topic: rate constant k
Replies: 3
Views: 128

### rate constant k

Why is the rate constant k not negative for second order reactions?
Wed Mar 06, 2019 6:48 pm
Forum: General Rate Laws
Topic: rate laws
Replies: 3
Views: 130

### Re: rate laws

Ohhh okay thank you so much!!
Wed Mar 06, 2019 6:33 pm
Forum: General Rate Laws
Topic: rate laws
Replies: 3
Views: 130

### Re: rate laws

Also what is/are the underlying key concept(s) that we should take away from the various rate laws?
Wed Mar 06, 2019 6:31 pm
Forum: General Rate Laws
Topic: rate laws
Replies: 3
Views: 130

### rate laws

Are rate laws simply referring to the rate at which a concentration increases or decreases? What's the difference between integrated versus differential?
Tue Feb 26, 2019 12:10 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Anode reaction
Replies: 3
Views: 112

### Re: Anode reaction

So I could be completely wrong as my response is in disagreement with the two answers before me, but I was told that when you have electrons in the reactant side, this is the reduction half of the reaction because it has GAINED electrons. Oxidation half is when the electrons are in the product side ...
Tue Feb 26, 2019 12:05 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram Order
Replies: 3
Views: 169

### Re: Cell Diagram Order

I'm assuming this example was describing the reduction half of the reaction? The form goes as follows oxidation solid (anode) | oxidation gases/liquids | oxidation aqueous solutions || reduction aqueous solutions | reduction gases/liquids | reduction solid (cathode). As you read from outward in, the...
Tue Feb 26, 2019 11:57 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Writing Cell Diagrams
Replies: 2
Views: 92

### Re: Writing Cell Diagrams

First you should write out each half reaction and determine which is the reduction and which is the oxidation components. Oxidation occurs in the anode (left) while reduction occurs in the cathode (right). That being said, your cell diagram corresponds to this order: oxidation on the left and reduct...
Tue Feb 19, 2019 10:04 am
Forum: Administrative Questions and Class Announcements
Topic: 14BL and 14C
Replies: 5
Views: 436

### Re: 14BL and 14C

From what I've heard from friends who've taken BL already is that the labs can be pretty tedious and time-consuming but mostly consist of busywork. If you feel that your other classes are going to be too strenuous to add extra work, then I would hold off on taking it. 14C, 3C and a GE don't seem lik...
Tue Feb 19, 2019 10:00 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Van't Hoff Equation
Replies: 3
Views: 117

### Re: Van't Hoff Equation

K depends on temperature, K being when the system is at equilibrium. When a system is at equilibrium, deltaG equals zero.
Tue Feb 19, 2019 9:53 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: altering gibbs free energy equations
Replies: 2
Views: 123

### Re: altering gibbs free energy equations

The standard conditions for measuring Gibbs Free Energy are constant pressure and constant temperature. A negative deltaG reflects a spontaneous, exergonic reaction because it releases energy while a positive deltaG reflects a non-spontaneous, endergonic reaction as it requires energy.
Fri Feb 15, 2019 2:12 pm
Forum: Calculating Work of Expansion
Topic: S=0
Replies: 12
Views: 695

### Re: S=0

Jason Ye 2I wrote:Entropy is equal to zero in a perfect crystal at T= 0K

This is for residual entropy (3rd Law of Thermodynamics) but if you are asking for when delta S = 0, that's entirely different and occurs when the system is reversible and returns to its original state.
Fri Feb 15, 2019 2:09 pm
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: n in degeneracy
Replies: 8
Views: 881

### Re: n in degeneracy

In the equation for degeneracy, W=(number of potential positions)^(n) in which n represents the number of molecules. This is because the base (number of positions possible) already accounts for the atoms and their positions so n dictates how many molecules there are that you need to take into consid...
Fri Feb 15, 2019 1:58 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Replies: 35
Views: 1178

When do we get our midterm scores back?
Wed Feb 06, 2019 3:53 pm
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: S equation
Replies: 2
Views: 97

### S equation

Does kb equal nR??? Also what is capital W representing and what is kb?
Wed Feb 06, 2019 3:49 pm
Forum: Calculating Work of Expansion
Topic: +/- work values
Replies: 5
Views: 221

### Re: +/- work values

kamalkolluri wrote:w = -P(deltaV) by definition. So an increase in volume (expansion), makes dV positive, so the work done is negative. However, if deltaV is negative (compression), then work is going to be positive (compression).

THANK YOU this immensely cleared things up for my friend and I.
Tue Feb 05, 2019 10:20 pm
Forum: Calculating Work of Expansion
Topic: +/- work values
Replies: 5
Views: 221

### +/- work values

For 4A.3 in the seventh edition, why is work a positive value? like what value in the work equation is negative to make cancel out the negative that's already there? And also, how do I determine logically (without an equation) if work is a positive or negative value? eq. w = -(2atm)*(pi)*(2cm)*(1.5c...
Sat Feb 02, 2019 3:53 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Test Question
Replies: 4
Views: 214

### Re: Test Question

As stated above, Kp is designated for gases because it is the equilibrium constant for partial pressure, hence the p. On the other hand, Kc can be used for both aqueous solutions and gases as it is a measurement of concentrations, usually mol/L.
Sat Feb 02, 2019 3:49 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Calorimeter
Replies: 2
Views: 105

### Calorimeter

How much detail do we need to know about bomb calorimeters and such?
Sat Feb 02, 2019 3:46 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Current Place in Class
Replies: 3
Views: 145

### Current Place in Class

I just wanted to confirm that we've learned everything from the "Thermochemistry" section right? And just began the "thermodynamics" section?
Tue Jan 22, 2019 12:02 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Including mol/L in K calculations
Replies: 2
Views: 82

### Re: Including mol/L in K calculations

To add to the previous reply, the brackets used when writing out the K equation indicate concentration so in doing that represents mol/L.
Tue Jan 22, 2019 11:57 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Rounding within the Problem
Replies: 2
Views: 129

### Rounding within the Problem

In the 6D section of 7th edition book, for calculating pKa/pKb and Ka/Kb, I didn't round until the end and got a number close to what the answer was. I tried it again by rounding after every calculation then got the answer the book indicated. The book has been incorrect time and time again in regard...
Tue Jan 22, 2019 11:53 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Sig Figs of pKa
Replies: 2
Views: 1593

### Sig Figs of pKa

The number of significant figures in pH is equal to the number of digits after the decimal point, I was just wondering if this was the same rule for pKa? I didn't think so but my book solutions keep following that rule. Then again, my 7th edition tends to use the wrong sig figs frequently.
Tue Jan 15, 2019 3:09 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Ionization Constant
Replies: 2
Views: 109

### Re: Ionization Constant

Do you remember the Lewis structure diagrams Lavelle drew in class? They are depicting the formation of H3O+ and OH- ions (ionizations). The ionization constant of water refers to level at which H3O+ and OH- are equal. 10^-14 is the equilibrium constant of the chemical reaction so 10^-14 = [H3O+][OH...
Tue Jan 15, 2019 12:12 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Test 1
Replies: 2
Views: 103

### Re: Test 1

Definitely everything on Chemical Equilibrium will be on there and I'm pretty sure it will also all of Acid & Bases. You should check the class website outlines for more details on the two. I'm assuming it will cover Acids & Bases because we've already learned to do just about everything on ...
Tue Jan 15, 2019 11:49 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: 5I.35 7th edition
Replies: 1
Views: 62

### Re: 5I.35 7th edition

It is squared because the equilibrium equation is [N2][O2]/[NO2]^2. The change in concentration is denoted as p. Because N2 and O2 began with zero initial concentration, you simply use 0+p to get p as the equilibrium concentrations for both. The problem simplified it further by substituting the p in...
Fri Jan 11, 2019 11:41 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Solids and Liquids in K Expression
Replies: 2
Views: 96

### Re: Solids and Liquids in K Expression

They are exclude because the equilibrium constant describes concentrations/partial pressures whereas solid has neither. Liquids have a concentration but act as a solvent so they aren't included. Aqueous solutions on the other hand, are the solute so they are included because they are a by-product.
Fri Jan 11, 2019 11:07 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kp
Replies: 9
Views: 304

### Re: Kp

As you probably know, K represents the equilibrium constant. The subscripts specify what the equilibrium constant consists of. Kc means the equilibrium constant of concentrations whereas Kp means the equilibrium constant of the partial pressures. You use Kp when the equation includes just gases just...
Wed Jan 09, 2019 12:14 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 7th Edition 5G.3
Replies: 1
Views: 18

### 7th Edition 5G.3

This is a basic equilibrium constant question, but I'm confused on why the answer for this has a "P" then the chemical formula whereas in class we didn't do that. Do we need the "P" and what does it even mean?
Sat Dec 08, 2018 4:34 pm
Forum: Naming
Topic: polydentate?
Replies: 2
Views: 100

### Re: polydentate?

If given a figure, you can tell if the ligand is bound to the TM in more than one spot and then count the number of bonds. If not given a figure, you just have to memorize it (this is what a TA just told us in a review session). The ones we need to know are ox (2), edta (6), en (2), and dien (4).
Sat Dec 08, 2018 4:18 pm
Forum: Amphoteric Compounds
Topic: amphoteric
Replies: 2
Views: 250

### Re: amphoteric

Amphoteric means to display both acidic and basic characteristics. They can act as an acid or a base. An example is water.
Sat Dec 08, 2018 4:14 pm
Forum: Properties & Structures of Inorganic & Organic Bases
Topic: oxoacids
Replies: 1
Views: 271

### Re: oxoacids

We don't need to know this for our final but I believe they are inorganic.
Fri Nov 30, 2018 2:23 pm
Forum: Electronegativity
Topic: SO2
Replies: 1
Views: 318

### Re: SO2

So when determining polarity and dipole, you need to look at the atoms' electronegativities. Oxygen is more electronegative than sulfur so electrons are pulled towards the oxygen atoms. When considering the lone pair electrons, they are negatively charged and actually contribute to electron repulsio...
Fri Nov 30, 2018 2:13 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: sigma composition
Replies: 2
Views: 358

### Re: sigma composition

Keep in mind that when determining the orbital hybridization, you are focusing on the number of electron densities. This where the d oribital will come into play (for octahedrons and square pyramidals). If this is the case, then the composition will be (ELEMENT 2sp3d2, ...).
Tue Nov 27, 2018 11:02 am
Forum: Hybridization
Topic: How to Write Second Pi Bond in Triple Bond
Replies: 3
Views: 150

### Re: How to Write Second Pi Bond in Triple Bond

I just asked my TA this today and he said it would be (Cp -Cp) because they are the same type of bond. The compositions are the same but there are more than one.
Sun Nov 18, 2018 2:40 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Drawing Molecules
Replies: 5
Views: 163

### Drawing Molecules

When and if we are asked to draw out molecule in their correct molecular shape, it has to be in 3-D right? My concern is that the 3-D figure will look wrong if we draw it poorly.
Sun Nov 18, 2018 2:35 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone Pairs
Replies: 8
Views: 455

### Re: Lone Pairs

When determining the shape of a molecule, all the regions of electron density need to be taken into account. They must be spread as far apart as possible in order to make the structure more stable (close together causes e- repulsion and therefore instability). Since lone pairs are regions of e- dens...
Sun Nov 18, 2018 2:24 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Shape and Polarity? [ENDORSED]
Replies: 4
Views: 198

### Re: Shape and Polarity?[ENDORSED]

In a molecule, the atoms surrounding the central atom have some degree of electronegativity (the "hogging" of electrons when sharing). This creates a dipole moment. If the shape doesn't allow the polarity (pull of the electrons and difference in charge) to cancel each other out, it will be...
Sun Nov 11, 2018 9:49 am
Forum: Electronegativity
Topic: Electronegativity
Replies: 8
Views: 415

### Re: Electronegativity

Yes, the above statement is correct regarding the electronegativity trend. The noble gases, with the exceptions of Xe and Kr that sometimes bond with fluorine and highly reactive elements, do not have electronegativity values. Those two exceptions are not of much importance though.
Sun Nov 11, 2018 9:44 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Angles of Shapes [ENDORSED]
Replies: 4
Views: 300

### Re: Angles of Shapes[ENDORSED]

Dr. Lavelle hasn't gone over this with us yet so this could be a part of Wednesday's lecture or it may not be something we learn how to calculate in this class. For now, I would suggest just memorizing (it will probably be on the formula page though) until further notice from Lavelle.
Sun Nov 11, 2018 9:40 am
Forum: Bond Lengths & Energies
Topic: Bond Length
Replies: 9
Views: 475

### Re: Bond Length

Yes they can be the same length. This would indicate that this Lewis structure is a resonance structure. We all know double bonds and single bonds are not equivalent so if the structure shows they are, this means the electron is delocalized and shifts from one atom to another in the middle.
Sun Nov 04, 2018 8:43 pm
Forum: Ionic & Covalent Bonds
Topic: Test bank?
Replies: 9
Views: 1008

### Re: Test bank?

My friend said she got chem material from the test bank, but I don't think it's from Lavelle's tests. There are several worksheets on here, Chemistry Community, from step ups and such other than the Garlic Bread one.
Sun Nov 04, 2018 8:39 pm
Forum: Administrative Questions and Class Announcements
Topic: MIDTERM PRACTICE - Garlic Bread Review Session [ENDORSED]
Replies: 121
Views: 6915

### Re: MIDTERM PRACTICE - Garlic Bread Review Session[ENDORSED]

For question 12c, why is it better to have a triple bond with the two nitrogen atoms instead of double bonds on nitrogen and oxygen? The charge is both the same.
Sun Nov 04, 2018 12:33 pm
Forum: Electronegativity
Topic: MIDTERM
Replies: 5
Views: 226

### MIDTERM

The midterm is just covering material up to Wednesday's lecture correct? So we don't have to know electronegativity and everything else from Friday's lecture?
Sun Oct 28, 2018 2:14 pm
Forum: Quantum Numbers and The H-Atom
Topic: Magnetic Spin Number
Replies: 5
Views: 198

### Re: Magnetic Spin Number

Parallel shells are electrons with the same spin (up or down) in different orbitals but the same subshell. As a result, the only differing quantum number is ml. Electrons cannot have the same spin in the same orbital because that would give them identical quantum numbers.
Sun Oct 28, 2018 2:02 pm
Forum: Ionic & Covalent Bonds
Topic: The Stronger Bond [ENDORSED]
Replies: 3
Views: 160

### The Stronger Bond[ENDORSED]

Is a covalent or ionic bond stronger? I've heard people argue both. Also why is it that one?
Sun Oct 28, 2018 1:52 pm
Forum: Lewis Structures
Topic: Electron configuration
Replies: 2
Views: 48

### Re: Electron configuration

This is one of the exceptions Lavelle discussed in lecture. It's called the "Full d^10" exception because usually the 4s has lower energy level (4s before 3d) but this case it does not and the 3d has all elections and is full.
Sat Oct 20, 2018 11:30 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Test 2 Material
Replies: 9
Views: 223

### Test 2 Material

Is everything from The Quantum World going to be on Test 2? If not, which concepts are we NOT going to be tested on?
Sat Oct 20, 2018 11:14 am
Forum: *Shrodinger Equation
Topic: Shrodinger Explained
Replies: 2
Views: 133

### Shrodinger Explained

So I wasn't able to make Friday's lecture and I was looking at my friend's notes, but I'm really confused. Can someone explain the Shrondinger equation and the concepts behind it please!
Sat Oct 20, 2018 11:02 am
Forum: Properties of Electrons
Topic: Heisenberg uncertainty principle
Replies: 1
Views: 104

### Re: Heisenberg uncertainty principle

The probability is psi squared because of the Born Rule. This rule states that "the probability of obtaining any possible measurement outcome is equal to the square of the corresponding amplitude."
Sun Oct 14, 2018 1:36 am
Forum: Properties of Light
Topic: Test #1
Replies: 1
Views: 71

### Test #1

This doesn't apply to "properties of light," but does anyone know when we will receive our results from test 1 and if we will be able to go over our answers?
Sun Oct 14, 2018 1:32 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Empirical Equation for H Atom
Replies: 1
Views: 98

### Empirical Equation for H Atom

Where does the R come from in this equation (En=-hR/n^2)? Since it's Rydberg's constant, does it just have to do with proportionality like Planck's constant?
Sun Oct 14, 2018 1:14 am
Forum: Properties of Light
Topic: Moles in photoelectric effect? [ENDORSED]
Replies: 2
Views: 84

### Re: Moles in photoelectric effect?[ENDORSED]

A mole isn't referring to a specific type of unit; instead, it is a numerical representation of whatever object, unit, etc. is at hand. There are 6.022 x 10^23 objects of whatever your measuring. This could be atoms, molecules, Joules, etc. It's just a measurement similar to how a "dozen" ...
Fri Oct 05, 2018 5:04 pm
Forum: Molarity, Solutions, Dilutions
Topic: Rounding molar mass
Replies: 4
Views: 158

### Re: Rounding molar mass

What I usually do is round the molar mass to the number of sig figs in the initial problem. By initial problem, I mean the number amount given in the question. If there isn't one given, probably stick to the molar mass of the periodic table.
Thu Oct 04, 2018 5:59 pm
Forum: Limiting Reactant Calculations
Topic: Post Assessment 26 [ENDORSED]
Replies: 1
Views: 89

### Re: Post Assessment 26[ENDORSED]

Yes, you just multiply the two because theoretical yield is in grams so by multiplying 81g.mol-1 and 0.20 mol, you get 16.2g. Basically, the student will have 0.2 mols of product, the expected and theoretical results if nothing alters the reaction. If the product has a molar mass of 81g.mol-1 and if...
Wed Oct 03, 2018 4:31 pm
Forum: Limiting Reactant Calculations
Topic: Limiting Reactant Step 5
Replies: 1
Views: 78

### Limiting Reactant Step 5

Can someone explain Step 5 of "Solving a Stoichiometry Problem" more in depth please?