## Search found 51 matches

Tue Mar 13, 2018 9:41 pm
Forum: Balancing Redox Reactions
Topic: Water, oxygen, etc.
Replies: 1
Views: 154

### Water, oxygen, etc.

When we have a balanced equation and we have to split it into its reduction and its oxidation do we always put the oxygens, waters, etc. in the reduction equation and why?
Tue Mar 13, 2018 9:27 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Finding Q
Replies: 2
Views: 190

### Finding Q

Is Q the conc of the anode over the conc of the cathode? what does it depend on?
Tue Mar 13, 2018 9:24 pm
Forum: *Alkanes
Topic: Naming compounds
Replies: 3
Views: 2876

### Naming compounds

Will naming organic compounds, not just alkanes, be on the final? Also, in how much detail are we expected to know the functional groups etc.?
Wed Mar 07, 2018 12:24 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.29
Replies: 2
Views: 174

### 15.29

Although I get the working out, I don't get which equation is being used in part (a) where we're asked to find the rate constant for the reaction given
Wed Mar 07, 2018 12:22 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.27
Replies: 2
Views: 337

### 15.27

part (c) says: How much time must elapse for the concentration of A to decrease to 15% of its initial concentration? How do we use the 15% in our calculations? I looked at the answers and sort of got what they've done but I'm still a bit confused
Wed Mar 07, 2018 12:06 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.23
Replies: 1
Views: 152

### 15.23

a) A -> B, given that the concentration of A decreases to one-half its initial value in 1000s determine the rate constant expressed for the rate loss of A ... I feel like this is simpler than the question is making it seem but I'm getting confused, can someone tell me how to go about this?
Thu Mar 01, 2018 1:08 am
Forum: Zero Order Reactions
Topic: slope
Replies: 9
Views: 1324

### slope

How is it that the slope for both zero and first order reactions is -k but for second order reactions its k?
Thu Mar 01, 2018 12:56 am
Forum: General Rate Laws
Topic: half life vs rate
Replies: 2
Views: 195

### half life vs rate

I'm not sure I understand how half-life is related to rate of reaction. Can someone please clarify?
Thanks!
Thu Mar 01, 2018 12:13 am
Forum: General Rate Laws
Topic: Deriving integrated rate laws
Replies: 4
Views: 280

### Deriving integrated rate laws

Do we need to know how to derive the rate laws in the y=mx+c form or do we only need to know the integrated form of the equation?
Thu Feb 22, 2018 7:30 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: swapping signs of E values
Replies: 8
Views: 931

### swapping signs of E values

When we are trying to find the Ecell how do we know which one of the two equations we swap the sign of?
Thu Feb 22, 2018 7:28 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst Equation to find pH
Replies: 6
Views: 2838

### Nernst Equation to find pH

I read through the book but I still don't understand how we use the Nernst Equation to find pH. Can someone please explain?
Thu Feb 22, 2018 7:26 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Ion-Selective Electrodes
Replies: 1
Views: 136

### Ion-Selective Electrodes

I don't get what we need to know about ion-selective electrodes. I don't think they've come up in homework problems either so I'm not sure in how much depth we need to know what they are and how they're used.
Sun Feb 18, 2018 5:35 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: E equations
Replies: 3
Views: 276

### E equations

What’s difference between the two equations for E? (E = E° - (RT/nF)lnQ and E = E° - (.05916 V/n)logQ).
Sun Feb 18, 2018 5:27 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Conc. Cells
Replies: 2
Views: 237

### Conc. Cells

In a concentration cell, why does the product concentration need to be lower than the reactants?
Sun Feb 18, 2018 3:55 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Electrolyis
Replies: 3
Views: 344

### Electrolyis

In how much detail do we need to know the process of electrolysis?
Thu Feb 08, 2018 12:10 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: interpretation of galvanic cell diagram
Replies: 2
Views: 130

### interpretation of galvanic cell diagram

How would we interpret a cell diagram such as: Ag(s) ; AgI(s) ; I- (aq) ;; Cl- (aq) ; AgCl(s) ; Ag(s) ?

where ; represents one line and ;; represents two
Thu Feb 08, 2018 12:06 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Standard Hydrogen Electrode
Replies: 1
Views: 111

### Standard Hydrogen Electrode

I get that we need to know how to draw a galvanic cell but do we need to distinguish between that and a standard hydrogen electrode? I mean do we need to know how to draw both or just to understand the concept behind the standard hydrogen electrode?
Thu Feb 08, 2018 12:05 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: DG = -nFE
Replies: 3
Views: 307

### DG = -nFE

Can someone please explain which compound's number of moles we put when using this equation?
Mon Feb 05, 2018 1:19 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: DS= q/T for surroundings or system?
Replies: 2
Views: 193

### DS= q/T for surroundings or system?

Can we use the equation DS = q/T for both the surroundings and the system?
Mon Feb 05, 2018 1:16 am
Forum: Van't Hoff Equation
Topic: Which version do we use in calcs? [ENDORSED]
Replies: 1
Views: 265

### Which version do we use in calcs?[ENDORSED]

Which one of the equations shown in lecture is the one we will most likely be asked to use? Will we have to show how to get from one equation to the other?
Mon Feb 05, 2018 1:10 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: DG = 0 [ENDORSED]
Replies: 3
Views: 427

### DG = 0[ENDORSED]

Why is it that at equilibrium we say that DG is equal to zero? Do we have to know why or just that we use that in our calculations?
Sun Jan 28, 2018 10:17 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: entropy and spontaneity
Replies: 1
Views: 161

### entropy and spontaneity

In the book it says "A process is spontaneous if it is accompanied by an increase in the total entropy of the system and the surroundings" I know it sounds stupid but I don't get this, can someone explain what exactly is meant by this?
Sun Jan 28, 2018 10:05 pm
Forum: Phase Changes & Related Calculations
Topic: degeneracy [ENDORSED]
Replies: 7
Views: 397

### Re: degeneracy[ENDORSED]

Degeneracy is basically the number of different ways energy can exist and the higher the entropy then the more the ways that energy can exist (proportional).
Sun Jan 28, 2018 10:00 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Boltzmann equation: positional entropy or thermal entropy?
Replies: 3
Views: 198

### Re: Boltzmann equation: positional entropy or thermal entropy?

I also read somewhere that it "quantifies the entropy of a system", what exactly does that mean in terms of types of entropy?
Sun Jan 21, 2018 6:20 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Discussion 1J worksheet- Question 8
Replies: 1
Views: 250

### Discussion 1J worksheet- Question 8

The question is: A cylinder fitted with a frictionless piston contains 3.00 mol of He gas at P=1.00 atm and is in a large constant -temperature bath at 400 K. The pressure is reversibly increased to 5.00 atm. Find w, q, and U for this process?

Can someone help?!
Sun Jan 21, 2018 6:07 pm
Forum: Administrative Questions and Class Announcements
Topic: Week 3 Test Topic is endorsed
Replies: 37
Views: 2941

### Re: Week 3 Test Topic is endorsed

For the test do we need to know how to derive the work equation? I know Dr. Lavelle said work and DU won't be on the test but this seems like a conceptual thing to me so I'm not entirely sure.
Sun Jan 21, 2018 5:50 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Cv vs. Cp [ENDORSED]
Replies: 13
Views: 3910

### Cv vs. Cp[ENDORSED]

Can someone please explain when we use Cv and when we use Cp and how we would know which one to use? Also, what's the difference between DH= nCpDT and DH= gCspDT? Does it matter which one we use?

Thanks!
Sat Jan 13, 2018 9:31 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Homework Question 8.63 (c)
Replies: 2
Views: 170

### Re: Homework Question 8.63 (c)

you do DH= [(2DHf K2S)+(2DHf H2O)] - [(DHf H2S)+(2DHf KOH)] this should be =[-417.5 kJ/mol + 2(-285.83 kJ/mol)] - [-39.7 kJ/mol + 2(-482.37 kJ/mol)] = +15.28 kJ/mol

Hope that makes sense
Sat Jan 13, 2018 9:25 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.51
Replies: 1
Views: 142

### 8.51

Can someone please explain this problem to me? I'm super confused! Are we just supposed to use enthalpies of formation and if so what do we do next?

Thanks!
Sat Jan 13, 2018 9:17 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Delta values
Replies: 3
Views: 152

### Re: Delta values

DU is the total energy of the system whereas DH is the heat addition to the system at a specific temperature.
Thu Dec 07, 2017 3:35 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Identifying if a molecule is monodentate, bidentate, etc.
Replies: 1
Views: 157

### Identifying if a molecule is monodentate, bidentate, etc.

What is the key thing to look at when determining if a molecule is monodentate, bidentate, etc.?
Thu Dec 07, 2017 3:22 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE table
Replies: 7
Views: 607

### ICE table

When doing ICE table problems how do we know when to assume that x is 0?
Fri Dec 01, 2017 5:30 pm
Forum: Naming
Topic: Finding Coordination Number
Replies: 6
Views: 458

### Re: Finding Coordination Number

So if we have a compound with two ligands, and three of each are attached to the metal (6 bonds in total), would the coordination number be that of each individual ligand (3) or that of both ligands added together (6)?
Fri Dec 01, 2017 5:18 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Kw= [H30+]*[OH-]
Replies: 4
Views: 307

### Re: Kw= [H30+]*[OH-]

I think what Dr. Lavelle meant by the water being in large excess was that so little of it is ionized at any one time, that its concentration remains virtually unchanged, so essentially just another constant in the equation.
Wed Nov 22, 2017 12:14 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K and Kc
Replies: 7
Views: 472

### Re: K and Kc

Do we only use the reaction quotient, Q, when the reaction only goes in the forward direction?
Wed Nov 22, 2017 12:12 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Chapter 11, Question 7
Replies: 1
Views: 188

### Chapter 11, Question 7

I'm not really sure how to go about this question: The following flasks (page 456) show the dissociation of a diatomic molecule, X2, over time. a) Which flask represents the point in time at which the reaction has reached equilibrium? b) What percentage of the X2 molecules have decomposed at equilib...
Sun Nov 19, 2017 8:00 pm
Forum: Sigma & Pi Bonds
Topic: drawing sigma/pi bonds
Replies: 6
Views: 426

### Re: drawing sigma/pi bonds

All bonds contain a sigma bond and double and triple bonds contain a single bond each and 1 & 2 pi bonds respectively. The sigma bond is formed by the head-on overlap of two sp orbitals while the pi bonds are formed by the side-on overlap of the p unhybridized orbitals.
Sun Nov 19, 2017 7:57 pm
Forum: Hybridization
Topic: How to tell the hybridization [ENDORSED]
Replies: 4
Views: 335

### Re: How to tell the hybridization[ENDORSED]

You just look at how many electron domains are around the central C. If you have more than 1 C then you look at the hybridization around each one of them separately.
Sun Nov 12, 2017 11:31 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone Pair Placement
Replies: 3
Views: 238

### Re: Lone Pair Placement

You should always put lone pairs as far away from each other as possible. I don't think it matters where you put the first pair as long as the second one is the furthest away it can be.
Sun Nov 12, 2017 11:28 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Book Questions 4.1&4.2
Replies: 4
Views: 253

### Book Questions 4.1&4.2

I'm not sure how we would go about these two questions in the book which basically show two shapes and give a bond angle and ask whether there must be, may be, or cannot be one of more lone pairs of electrons on the central atom. If we don't know what the molecule is, how can we determine how many e...
Sun Nov 05, 2017 6:41 pm
Forum: Lewis Structures
Topic: 3.41 part c
Replies: 2
Views: 213

### Re: 3.41 part c

you would draw the lewis structure the same way the atoms are presented in the formula
Sun Nov 05, 2017 6:39 pm
Forum: Lewis Structures
Topic: Are there any exceptions to carbon?
Replies: 3
Views: 261

### Re: Are there any exceptions to carbon?

Remember that Hydrogen is never the central atom
Sun Nov 05, 2017 6:39 pm
Forum: Lewis Structures
Topic: Are there any exceptions to carbon?
Replies: 3
Views: 261

### Re: Are there any exceptions to carbon?

The central atom will always be the one with the lowest electronegativity. When you have carbon compounds, carbon is typically the central atom.
Sun Oct 29, 2017 11:53 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Subshells [ENDORSED]
Replies: 2
Views: 295

### Re: Subshells[ENDORSED]

P is the subshell and the x,y,z are the orbitals within that subshell.
Sun Oct 29, 2017 11:51 pm
Forum: Lewis Structures
Topic: Homework 3.71 [ENDORSED]
Replies: 3
Views: 321

### Re: Homework 3.71[ENDORSED]

In such cases you would try to find which structure has a formal charge closest to zero, indicating a more stable molecule (0 being the most stable).
Sun Oct 22, 2017 10:38 pm
Forum: Photoelectric Effect
Topic: Exam Question Clarification [ENDORSED]
Replies: 3
Views: 274

### Re: Exam Question Clarification[ENDORSED]

I think it meant increasing the amount of the same-sized light waves hitting the surface of the metal.
Sun Oct 22, 2017 10:36 pm
Forum: Quantum Numbers and The H-Atom
Topic: Abbreviating e- configurations [ENDORSED]
Replies: 7
Views: 612

### Re: Abbreviating e- configurations[ENDORSED]

That's just a way of writing the short-hand e- configuration. If you're asked to write the full electron configuration then you don't shorten it from the last noble gas before it, you do it all starting from the 1s subshell.
Sun Oct 15, 2017 8:12 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Heisenberg's Uncertainty Principle - test
Replies: 1
Views: 157

### Heisenberg's Uncertainty Principle - test

I know we haven't discussed this in class yet but I read somewhere on the chemistry page that we should go through the modules and video for this topic during week 2. Does anyone know whether it will be on this week's test or not?
Sun Oct 15, 2017 7:59 pm
Forum: Properties of Electrons
Topic: Hydrogen series
Replies: 5
Views: 459

### Re: Hydrogen series

I think the Lyman and Balmer series are the only two you should remember, seeing as they were the only two mentioned in lecture. But even for them all you need to know is that for Lyman series (UV) n=1 and for the Balmer series (visible region) n=2.
Sun Oct 08, 2017 8:12 pm
Forum: Balancing Chemical Reactions
Topic: Combustion [ENDORSED]
Replies: 3
Views: 351

### Re: Combustion[ENDORSED]

All (complete) combustion questions are the same. For your equation you always start off with what you are burning (in this case butane) and you react it with oxygen. This always gives you carbon dioxide and water as products. If you had an incomplete combustion question then you'd have to add carbo...
Thu Oct 05, 2017 9:46 pm
Forum: Empirical & Molecular Formulas
Topic: Combustion Analysis
Replies: 5
Views: 415

### Combustion Analysis

In a combustion analysis of an unknown compound do we always assume it only contains C, H, O ? How would we know if it contained something else too?