## Search found 54 matches

Wed Mar 14, 2018 8:09 am
Forum: Phase Changes & Related Calculations
Topic: Midterm, Question 4B
Replies: 2
Views: 206

### Re: Midterm, Question 4B

Hey,
The midterm solutions are posted on Dr. Lavelle's website.
Here's the link: https://lavelle.chem.ucla.edu/wp-conten ... am_ans.pdf

Hope this helps.
Wed Mar 14, 2018 8:04 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test 2 Question 5
Replies: 2
Views: 186

### Re: Test 2 Question 5

Hey, so the potential you've written for Cr should be -0.91 V, the one you've written is the potential for Cr^3+ going to Cr, you need to use the potential from Cr^2+ to Cr. Hope this helps.
Tue Mar 13, 2018 3:31 pm
Forum: Phase Changes & Related Calculations
Topic: Test #1 question
Replies: 2
Views: 187

### Re: Test #1 question

Hey,
viewtopic.php?f=130&t=26787
Sat Mar 10, 2018 11:47 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test 2, Question #5
Replies: 1
Views: 179

### Re: Test 2, Question #5

Hey, so the potential you've written for Cr should be -0.91 V, the one you've written is the potential for Cr^3+ going to Cr, you need to use the potential from Cr^2+ to Cr. Hope this helps.
Sat Mar 10, 2018 11:38 am
Forum: *Enzyme Kinetics
Topic: Chapter 15 [ENDORSED]
Replies: 3
Views: 288

### Re: Chapter 15[ENDORSED]

Yes, the syllabus says to omit 15.9; therefore, we should know all material from the other sections.
Sat Mar 10, 2018 11:36 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Calculating potentials for reactions that have only reduction or only oxidation
Replies: 1
Views: 315

### Re: Calculating potentials for reactions that have only reduction or only oxidation

The way you'd do this problem is similar to how you'd problem number 27 from chapter 14. I have a picture of my work for this specific problem, so I've attached it. Hope it helps.
Sun Mar 04, 2018 6:02 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Rate Constant K
Replies: 4
Views: 300

### Re: Rate Constant K

Units of K change depending on the overall order of the reaction. The units of k change so the concentration x rate constant always yields the same units for the rate. Here is a table from the book.
Sun Mar 04, 2018 3:47 pm
Forum: General Rate Laws
Topic: Rate Law and Initial concentration of Reactant
Replies: 5
Views: 305

### Re: Rate Law and Initial concentration of Reactant

The advantage of examining the initial rate is that the presence of products later in the reaction may affect the rate; the interpretation of the rate is then quite complicated.
Sun Mar 04, 2018 3:45 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Stopped Flow Technique
Replies: 3
Views: 263

### Re: Stopped Flow Technique

Reactions that are initiated by mixing the reagents can be studied by the stopped-flow technique, in which solutions of the reactants are forced into a mixing chamber very rapidly and, within a few milliseconds, the formation of products is observed spectroscopically. This procedure is commonly used...
Sun Feb 25, 2018 6:00 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: 14.55
Replies: 3
Views: 439

### Re: 14.55

viewtopic.php?f=143&t=11404&p=28252&hilit=
Sat Feb 24, 2018 9:14 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: When do you need to include Pt? [ENDORSED]
Replies: 5
Views: 313

### Re: When do you need to include Pt?[ENDORSED]

Platinum is needed when there isn't a metallic conductor. Just because there is a solid it doesn't mean it is a metallic conductor, such as I2(s).
Sat Feb 24, 2018 9:08 pm
Forum: Balancing Redox Reactions
Topic: 14.25
Replies: 3
Views: 230

### Re: 14.25

Here's a link to a previous post, hope it helps.
viewtopic.php?f=140&t=28301&p=86401&hilit=
Sun Feb 18, 2018 4:35 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Nernst equation
Replies: 4
Views: 352

### Re: Nernst equation

Nernst Equation:
Sun Feb 18, 2018 4:01 pm
Forum: Balancing Redox Reactions
Topic: Balancing Redox reactions
Replies: 3
Views: 249

### Re: Balancing Redox reactions

Generally you balance the O first. In acidic solution, balance O by using H2O and then balance H by using H^+ . In basic solution, balance O by using H2O; then balance H by adding H2O to the side of each half- reaction that needs H and adding OH^- to the other side.
Sun Feb 18, 2018 3:53 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Standard Reduction Potential Values
Replies: 2
Views: 143

### Re: Standard Reduction Potential Values

Appendix 2B: Standard Potentials at 25 celsius
Sat Feb 10, 2018 8:36 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.15
Replies: 3
Views: 262

### Re: 9.15

The book gives the heat of fusion of water as 6.01 kj.mol^-1, meaning thats how much energy is required to go from solid to liquid water. However, the question is asking you to calculate the entropy for the freezing of water; therefore, you would use negative heat of fusion, because that's how much ...
Fri Feb 09, 2018 10:01 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.85 (a)
Replies: 1
Views: 197

### Re: 9.85 (a)

viewtopic.php?f=135&t=10424&p=25838&hilit
Fri Feb 09, 2018 9:50 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: How to calculate W [ENDORSED]
Replies: 6
Views: 441

### Re: How to calculate W[ENDORSED]

W is the number of ways that the atoms or molecules in the sample can be arranged and yet still give rise to the same total energy, and each arrangement is known as a microstate.
Sun Feb 04, 2018 10:30 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: qrev
Replies: 3
Views: 225

### Re: qrev

Just to add on to what Shawn said, q is the energy transferred as heat, and the subscript rev indicates that the energy must be transferred reversibly.
Sat Feb 03, 2018 7:11 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Test Number 1
Replies: 9
Views: 502

### Re: Test Number 1

Based on what you've said in your post it appears that the system did work; therefore the balloon expanded. Can you post the full question?
Thu Feb 01, 2018 6:45 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Homework 9.13
Replies: 2
Views: 202

### Re: Homework 9.13

Yeah, for problem 13 there is a solutions manual error.
Thu Jan 25, 2018 10:37 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Examples of work being done
Replies: 7
Views: 490

### Re: Examples of work being done

Yes what Shawn said above is true. Just to add on, a system does no expansion work when it expands into a vacuum, because there is no opposing force. Expansion work against zero work is called free expansion.
Mon Jan 22, 2018 6:08 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 8.61 Question
Replies: 2
Views: 86

### Re: 8.61 Question

In the third equation there is already H2 on the reactants side; however, there are four moles of H2 in the third equation and you only want one mole in your final equation. Which is why you flip the second equation to cancel out 3 moles of H2 so you're only left with one mole in your final equation.
Mon Jan 22, 2018 4:41 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: W for BFCl2 in the lecture example
Replies: 1
Views: 180

### Re: W for BFCl2 in the lecture example

It would be 3^4A, because you need to consider the shape of the molecule. It's trigonal planar so there are three different places the atoms can bound to; therefore your equation would be 3^NA. The question states in the beginning that there are 4 moles of this molecule; therefore it's 3^4A. S= Kb l...
Thu Jan 18, 2018 6:42 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 3 Methods
Replies: 2
Views: 95

### Re: 3 Methods

You are calculating the ∆H (change in enthalpy). There are three methods to get this. Method 1: Hess's Law Enthalpy changes are additive. Enthalpy change at each step of a multi-step reaction can be added to give the total enthalpy change. Method 2: Bond Enthalpies Add up all new bonds formed (energ...
Thu Jan 18, 2018 4:36 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Lewis structures for bond enthalpies
Replies: 3
Views: 144

### Re: Lewis structures for bond enthalpies

Just to add on, when bonds are broken (require energy, + ) and when bonds are formed (released energy, -).
Thu Jan 18, 2018 4:30 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Knowing which equation to use when finding q
Replies: 2
Views: 191

### Re: Knowing which equation to use when finding q

When heat capacity is given you don’t need to take number of moles or mass into account. However, when specific heat capacity is given you would use the mass in the equation, and when molar heat capacity is given you would use the number of moles. You are essentially multiplying by the number moles ...
Fri Jan 12, 2018 6:30 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess Law
Replies: 4
Views: 185

### Re: Hess Law

Hess's law states that energy changes are state functions. The enthalpy change at each step of a multi-step step reaction can be added to give the total enthalpy change.
Wed Jan 10, 2018 7:43 pm
Forum: Phase Changes & Related Calculations
Topic: Exothermic Rxn
Replies: 6
Views: 471

### Re: Exothermic Rxn

The -58KJ means that the reaction is exothermic, indicating that the reaction will release energy.
Wed Dec 06, 2017 10:35 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Drawing the Lewis structure for Coordination Compounds
Replies: 3
Views: 256

### Re: Drawing the Lewis structure for Coordination Compounds

In short: yes, I think so. The charge on the outside lets you know the overall charge of the whole molecule, thus it should be kept into account when drawing a Lewis structure. For your example for instance, [HgF2(OH2))2]1+, I believe the oxidation number of Hg would be (V) since there are 4 negati...
Tue Dec 05, 2017 11:15 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Equilibria shift with temp. increase 11.77
Replies: 2
Views: 244

### Re: Equilibria shift with temp. increase 11.77

Hey, If a reaction requires heat, meaning it's endothermic, then heating it will favor product formation. If a reaction gives off heat, meaning it's exothermic, then heating it will favor reactant formation. If delta h is positive it means the reaction is endothermic, and if it's negative than it's ...
Tue Dec 05, 2017 9:44 pm
Forum: Coordinate Covalent Bonds
Topic: Naming - Prefixes
Replies: 2
Views: 502

### Re: Naming - Prefixes

If a ligand already contains a Greek prefix then the those prefixes are used. For example, if a ligand has a name with -di or -tri in it then you would use those prefixes.
Tue Dec 05, 2017 9:20 pm
Forum: Dipole Moments
Topic: Dipole Moments and Polarity
Replies: 9
Views: 537

### Re: Dipole Moments and Polarity

Patricia Macalalag 3G wrote:Aren't we just supposed to analyze the electronegativity trend on the periodic table? It increases as you go left to right, and as you go up a group.

Yes, electronegativity values tend to increase as you go to the right and up. I
Sat Dec 02, 2017 11:23 pm
Forum: Amphoteric Compounds
Topic: amphoteric properties
Replies: 3
Views: 245

### Re: amphoteric properties

Amphoteric compounds have both acidic and basic character.
Wed Nov 29, 2017 9:39 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Post Assessment Chemical Equilibrium Part 2 #29 [ENDORSED]
Replies: 6
Views: 595

### Re: Post Assessment Chemical Equilibrium Part 2 #29[ENDORSED]

You need the 2x, because that's the ratio of BrCl. You can use x instead of 2x for BrCl, but then you would need to use 1/2x for Br2 and Cl2. The 2x is involved in the equation, because that is the change from initial to equilibrium.

Hope this helps.
Sun Nov 26, 2017 7:58 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Post Assessment Chemical Equilibrium Part 2 #29 [ENDORSED]
Replies: 6
Views: 595

### Re: Post Assessment Chemical Equilibrium Part 2 #29[ENDORSED]

1.84x10^-4 - 2x = 3.36x10^-5

Using this equation you can find X, since you know the initial and equilibrium concentrations.
Sat Nov 25, 2017 11:02 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Chemical Equilibrium module Part 2 #27?
Replies: 2
Views: 155

### Re: Chemical Equilibrium module Part 2 #27?

Hey, The question is asking for the equilibrium concentration of H20. Since you know the initial concentration of H20 and the equilibrium concentration of H2 you can setup an ICE table and find the value of X. The products start off with initial concentration of zero and end up with an equilibrium c...
Sat Nov 25, 2017 10:51 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Post Assessment Chemical Equilibrium Part 2 #29 [ENDORSED]
Replies: 6
Views: 595

### Re: Post Assessment Chemical Equilibrium Part 2 #29[ENDORSED]

Hey, So in this problem you're given the initial concentration of BrCl, 1.84x10-4 mol/L. The question also tells you that at equilibrium the molar concentration is 18.3% of the initial concentration, which would be 1.84x10^-4 mol/L times .183 which gives you 3.36x10^-5. Now that you have the initial...
Sat Nov 18, 2017 6:39 pm
Forum: Hybridization
Topic: Hybridized Orbitals
Replies: 2
Views: 261

### Re: Hybridized Orbitals

I think the questions will ask to predict the hybridization. Like if the questions asks to predict the hybridization for BCl3, you would answer with sp2. I may be wrong, but that's what I think the questions will be like
Sat Nov 18, 2017 6:33 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Lewis Structures and VSEPR Shape
Replies: 4
Views: 310

### Re: Lewis Structures and VSEPR Shape

No, you don't need to draw the lewis structure to reflect the shape. However, is could assist you in determining the shape if you do so.
Wed Nov 08, 2017 11:48 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Post Module #18
Replies: 2
Views: 221

### Re: Post Module #18

hope it helps
Wed Nov 08, 2017 11:40 pm
Forum: Lewis Structures
Topic: Exceptions
Replies: 4
Views: 317

### Re: Exceptions

Copper and Chromium
Fri Nov 03, 2017 6:46 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Writing Electron Configurations for ions
Replies: 2
Views: 267

### Re: Writing Electron Configurations for ions

Cu^+ is a cation; therefore, you would remove the outermost electron. The person above me wrote the electron configuration for it.
Fri Nov 03, 2017 6:42 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Quantum Numbers
Replies: 3
Views: 189

### Re: Quantum Numbers

Yeah, as the person above me stated if n = 7 l = 0,1,2,3,4,5,6. But in class we're only working with l=0,1,2,3.
Fri Oct 27, 2017 7:14 pm
Forum: Trends in The Periodic Table
Topic: Periodic Trends
Replies: 2
Views: 189

### Re: Periodic Trends

yes, first ionization energy refers to the energy required to remove one electron, and the second ionization energy refers to energy required to remove another electron. Additionally, the second ionization energy will always be greater than the first ionization energy, because the first electron is ...
Fri Oct 27, 2017 7:04 pm
Forum: Trends in The Periodic Table
Topic: Exceptions [ENDORSED]
Replies: 4
Views: 437

### Re: Exceptions[ENDORSED]

Yeah, you only need to know copper and chromium.
Fri Oct 20, 2017 7:50 pm
Forum: Properties of Light
Topic: Rydberg's Constant
Replies: 4
Views: 522

### Re: Rydberg's Constant

Yeah R = 3.29x10^15 s-1
Fri Oct 20, 2017 7:34 pm
Forum: DeBroglie Equation
Topic: Should velocity always be in m.s. when solving? [ENDORSED]
Replies: 11
Views: 1037

### Re: Should velocity always be in m.s. when solving?[ENDORSED]

Yeah, velocity should be in meters per second.
Fri Oct 20, 2017 7:34 pm
Forum: DeBroglie Equation
Topic: Should velocity always be in m.s. when solving? [ENDORSED]
Replies: 11
Views: 1037

### Re: Should velocity always be in m.s. when solving?[ENDORSED]

Yeah, velocity should be in meters per second.
Fri Oct 13, 2017 7:45 pm
Forum: Properties of Light
Topic: Rydberg's Formula
Replies: 3
Views: 476

### Re: Rydberg's Formula

Yeah the formula used in the video is v = -R((1/n1^2) - (1/n2^2). This is for calculating the energy emitted. For example, if there is a jump from level 4 to level 2, you would used the formula to calculate the frequency.
Fri Oct 13, 2017 7:22 pm
Forum: Photoelectric Effect
Topic: Post-assessment problem
Replies: 3
Views: 249

### Re: Post-assessment problem

Hey,
For part a to calculate the KE you would use the formula KE = 1/2mv^2. You need the mass of the electron which is 9.109 x 10^-31 kg. From this you can just plug in the velocity, and solve to find the answer. Hope this helps.
Thu Oct 05, 2017 9:02 pm
Forum: Molarity, Solutions, Dilutions
Topic: G17
Replies: 2
Views: 305

### Re: G17

Hey, I also noticed that in the solutions manual that the answer rounded up for part A and rounded down for part B. In part B, the answer I got was 12.484 grams, and the solutions manual rounded down to 12 (this was probably done on accident). But yeah, you're typically supposed to do what the perso...
Mon Oct 02, 2017 8:07 pm
Forum: Molarity, Solutions, Dilutions
Topic: Help with G13 Homework Problem
Replies: 2
Views: 247

### Re: Help with G13 Homework Problem

Hey, So you found the number of moles of NH4NO3, but the question is asking how many moles of nitrogen will each plant receive. To get the amount of moles of nitrogen all you would have to do is multiply 5 x 10^-3 mol of NH4NO3 x 2 mol N/1 mol NH4NO3, which gives you the answer 0.01 mol of N. (There...