## Search found 50 matches

Sun Mar 18, 2018 7:53 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic Cells
Replies: 2
Views: 253

### Re: Galvanic Cells

I believe they are the same thing. They are both electrochemical cells.
Sat Mar 17, 2018 9:35 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Reducing vs Oxidizing Agents
Replies: 4
Views: 394

### Reducing vs Oxidizing Agents

How do we determine what is an oxidizing agent and how do we determine what is a reducing agent?
Sat Mar 17, 2018 9:27 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: Final 2011 1C
Replies: 1
Views: 208

### Final 2011 1C

Which has greater residual entropy at 0K: NO or BF3

Why does NO have a greater residual entropy at 0K?
Sat Mar 17, 2018 8:54 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.61
Replies: 1
Views: 249

### Re: 15.61

k and k' in this case are referring to the rate constants at different temperatures. The k and k' which you are referring to have to deal with forward and reverse reactions. k and k' in this case can also be referred to as k1 and k2 in this instance.
Sat Mar 17, 2018 7:33 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Q5 on the midterm
Replies: 1
Views: 233

### Re: Q5 on the midterm

The delta U is +158J because in step 2 it returns to its original internal energy. So, the work the system had done which was -158J returns back to its original state by saying delta U of the second step is +158J.
Sat Mar 17, 2018 12:56 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Arrhenius Equation 15.61
Replies: 3
Views: 342

### Re: Arrhenius Equation 15.61

This equation is derived from the same reaction at different temperatures where the rate constants are different at separate temperatures so: ln(k 1 )= lnA - Ea/RT 1 ln(k 2 )= lnA - Ea/RT 2 Then we subtract the the equations: lnk 2 -lnk 1 = Ea/R(1/T 1 -1/T 2 ) ln(k 2 /k 1 )= (Ea/R)(1/T 1 -1/T 2 )
Sat Mar 17, 2018 12:10 pm
Forum: General Rate Laws
Topic: Time it takes to reach a certain molarity
Replies: 1
Views: 307

### Re: Time it takes to reach a certain molarity

Well first off you have to balance the equation: AB 4 +2C 2 ->AC2+2B 2 C Then you can set up the rate where: The consumption of AB 4 = deltaAB 4 /deltat= .400M/s Then we can infer that the production of B 2 C= (½) (delta[B 2 4])/delta t which equals .400M/s We plug in the 30M-.15M for delta B 2 4 mu...
Sat Mar 17, 2018 10:39 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Total entropy change determining spontaneity
Replies: 3
Views: 329

### Re: Total entropy change determining spontaneity

If you look at the equation delta G= deltaH-TdeltaS, we can determine why we want entropy to be positive for a spontaneous reaction. For a reaction to be spontaneous we want delta G to be a negative value because a negative value indicates spontaneity. There's a table in the textbook Table 9.5 on pa...
Sat Mar 17, 2018 12:36 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Homework Problem 14.27
Replies: 2
Views: 306

### Re: Homework Problem 14.27

We can't add the standard potentials together because E is not a state function. But, we can make use of delta G as being a state function through the addition of the delta G values of the half reactions and then solving for the desired half reactions standard potential through the equation delta G=...
Fri Mar 16, 2018 10:56 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram
Replies: 3
Views: 216

### Re: Cell Diagram

A double vertical line, || , represents a salt bridge. A single vertical line, | , would represent a phase boundary. Whenever a comma is used that is used to separate substances that are in the same phase. And the phases are included within parentheses And like you said, the reduction goes on the ri...
Fri Mar 16, 2018 10:25 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: What do we use for the axis of reaction profiles?
Replies: 1
Views: 173

### Re: What do we use for the axis of reaction profiles?

From the reaction profiles that I have seen in the textbook, potential energy was used for the y-axis while the progress of the reaction was used for the x-axis.
Fri Mar 16, 2018 10:23 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: What are the units of activation energy?
Replies: 2
Views: 1499

### Re: What are the units of activation energy?

You would use J/mol. The J*mol-1 cancel out with the units of the R constant which has JK-1mol-1
Fri Mar 16, 2018 9:33 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.63
Replies: 2
Views: 185

### Re: 15.63

You can calculate this using another form of the Arrhenius equation where:

ln(k2/k1) = (Ea/R)(1/T1-1/T2)

Where k1= 1.5 * 1010 L*mol-1s-1, T1= 298K, T2=310K, and Ea= 38kJ/mol and then solve for k2 from there. You get the .59 from the calculations on the right hand side.
Fri Mar 16, 2018 6:20 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: State functions?
Replies: 9
Views: 638

### Re: State functions?

Enthalpy and entropy are both state functions.
Fri Mar 16, 2018 2:42 pm
Forum: Calculating Work of Expansion
Topic: Midterm Q5
Replies: 2
Views: 256

### Re: Midterm Q5

It is +158J because it returns back to the original internal energy. Delta U in step 1 is -158J so in order to return to its original internal energy in step 2 it must be +158J.
Thu Mar 15, 2018 10:18 pm
Forum: First Order Reactions
Topic: Exam 3: Question 6
Replies: 2
Views: 268

### Re: Exam 3: Question 6

If you were to use the integrated rate law for the constant you could determine it by substituting for the concentration at time t with (.719)(initial concentration) and then isolate k from there. ln[A]= -kt + ln[A initial ] ln(.719[A initial ]) - ln[A] = -kt ln[.719[A initial ]/[A]] = -kt -ln[.719]...
Thu Mar 15, 2018 8:04 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat curve
Replies: 1
Views: 233

### Re: Heat curve

https://lavelle.chem.ucla.edu/forum/viewtopic.php?t=3241

This post back from 2013 does a good job explaining what you are asking.
Tue Mar 13, 2018 11:27 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.63
Replies: 6
Views: 291

### Re: 15.63

The derivation for this equation is on page 642 in the textbook but in summary you use the Arrhenius equation at one temperature and at another and subtract the first equation from the second equation getting rid of the lnA. At T1 : lnk1=lnA-Ea/RT1 At T2: lnk2= lnA-Ea/RT2 The subtraction after furth...
Tue Mar 13, 2018 10:49 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.63
Replies: 6
Views: 291

### Re: 15.63

The .59 comes from the Ea/R(1/T1-1/T2) calculation where Ea=38kJ/mol T1=298K and T2=310K while on the other side of the equation ln(k2/k1) where k1=1.5x10^10.
Tue Mar 13, 2018 8:34 pm
Forum: *Enzyme Kinetics
Topic: Collision Theory
Replies: 1
Views: 241

### Re: Collision Theory

Yes you should. It's on the outline for chapter 15 where we have to "Explain how the collision model and activated complex model account for the temperature dependence of reactions".
Tue Mar 13, 2018 5:55 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Relationship between K and k
Replies: 2
Views: 571

### Re: Relationship between K and k

If we were to look at a reaction that reaches equilibrium like A+B<=>C+D then the equilibrium constant would be the concentration of the products over the reactants where: K= [C][D]/[A][B] If we were to write the forward and reverse rate laws for this reaction, they would be: A+B->C+D where the Rate...
Tue Mar 13, 2018 1:33 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Intermediates
Replies: 2
Views: 231

### Re: Intermediates

https://www.chemguide.co.uk/physical/ba ... rofile.gif

Here's an image that shows the location of the intermediates on a reaction profile.
Tue Mar 13, 2018 1:13 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 15.65 c
Replies: 2
Views: 191

### Re: 15.65 c

The rate constant and the equilibrium constant of endothermic reactions are increasing with the raising temperature (as temperature goes up k and K). This is because when temperature increases the equilibrium shifts towards the right.
Wed Feb 21, 2018 12:39 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: appendix 2
Replies: 2
Views: 143

### Re: appendix 2

I'm pretty sure it is a typo in the book. It should be Fe^3+ + e -> Fe^2+ E=.77
Sun Feb 04, 2018 8:50 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Exercise 9.75
Replies: 1
Views: 134

### Re: Exercise 9.75

I believe this is due to the number of different arrangements either molecule can have. If you were to draw out the cis-MX2Y4 molecule there would be about 12 different orientations that it could possibly have whereas with a trans-MX2Y4 molecule there are 3 different orientations.
Sun Jan 28, 2018 4:34 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.11
Replies: 2
Views: 479

### Re: 9.11

You would use the equation delta S= nRln(P1/P2) which turns out to be delta S = (1.5mol)(8.3145 J.K^-1.mol^-1)(ln 15atm/.5atm) which equals 42.4 J.K^-1
Mon Jan 22, 2018 9:21 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.67
Replies: 1
Views: 104

### Re: 8.67

Yes it does indicated that methanol is in a liquid phase, but bond enthalpies refer to gaseous substances. So any substance in a chemical reaction that isn't in a gaseous phase has to be converted from their previous phase into the gaseous phase. So what we are actually looking at is: C(g) + 2H2 + ½...
Sun Jan 14, 2018 8:47 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: q and w
Replies: 5
Views: 316

### Re: q and w

Overall, q and w added together make up the internal energy that happens within a system. Q is the energy transferred as heat where a positive q would indicate an absorption of heat while a negative q would indicate a release of heat from the system. A positive w would indicate that work has been do...
Sun Jan 14, 2018 7:49 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: reversible vs irreversible
Replies: 2
Views: 201

### Re: reversible vs irreversible

I think what's also important to note is that a change that is done reversibly does more work than a change carried out irreversibly if you are asked to identify in that instance which is reversible and which is irreversible. This is provided that the initial and final states are the same.
Sun Jan 14, 2018 7:41 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: U=q or U=q+w?
Replies: 3
Views: 221

### Re: U=q or U=q+w?

Yes this is true, the change in U= q + w. The change in internal energy is equal to the heat in the case that there are no other processes taking place except that of transferring energy as heat.
Sat Dec 09, 2017 7:38 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ice box question
Replies: 2
Views: 403

### Re: ice box question

No what the reaction quotient (Q) is supposed to tell you is where the how the reaction will shift to reach equilibrium. If Q>K then equilibrium will shift towards the left. So when you put it into the ice chart you will put +x on the change for the reactants and will put -x for the change in the pr...
Sat Dec 09, 2017 7:14 pm
Forum: Naming
Topic: Cis vs trans
Replies: 3
Views: 374

### Re: Cis vs trans

cis- and trans- are used to indicate the placements of ligands when there are multiple of them. When cis- is used the similar substances will be arranged on the same side while with trans- this indicates that they will be arranged on opposite sides.
Sat Dec 09, 2017 7:09 pm
Forum: Dipole Moments
Topic: Test 4 Question about Dipole
Replies: 1
Views: 202

### Re: Test 4 Question about Dipole

03 has a trigonal planar arrangement but has a lone pair so the actual shape is bent. Because of the lone pair occupying one of regions of high electron density, the dipole moment is not cancelled out and is therefore polar.
Sun Dec 03, 2017 11:28 pm
Forum: Lewis Acids & Bases
Topic: Donating electrons versus protons [ENDORSED]
Replies: 4
Views: 388

### Re: Donating electrons versus protons[ENDORSED]

I think what is important to clarify in this question is that there are two several definitions in the textbook which define both acids and bases. Lewis acids and bases involve the giving and accepting of electron pairs while Bronsted Acids and Bases involve the donation and accepting of a proton (H...
Sun Dec 03, 2017 5:54 pm
Forum: Bronsted Acids & Bases
Topic: 12.1
Replies: 2
Views: 207

### Re: 12.1

I believe when the molecular formula isn't fully condensed as it is not in the conjugate acid of CH3NH2. The way that it is written would be the best representation of the actual formal structure. In this case, CH3NH3+ is most likely the best representation of this structure where Carbon has the 3 H...
Sun Nov 26, 2017 10:15 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Diatomic Molecules
Replies: 2
Views: 275

### Re: Diatomic Molecules

A homonuclear diatomic molecule is a 2 atom molecule made up of the same element. A heteronuclear diatomic molecule is a molecule composed of two atoms of two different elements.

Example of a heteronuclear diatomic molecule: HF
Example of a homonuclear diatomic molecule: O2
Sun Nov 26, 2017 10:10 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Question 4.1 Part B
Replies: 1
Views: 135

### Re: Question 4.1 Part B

There are multiple electron geometries that can produce a linear shape depending on the number of lone pairs a centra atom has. For instance, in the case of a molecule whose central atom has 5 regions of high electron density and and 3 lone pairs it will produce a linear shape. This is the same for ...
Sun Nov 19, 2017 7:16 pm
Forum: DeBroglie Equation
Topic: Midterm Question: wavelike properties
Replies: 6
Views: 425

### Re: Midterm Question: wavelike properties

I believe at one point in Dr. Lavelle's lectures he said that anything smaller than 10^-15m would be out of the range of an object being measurable.
Sun Nov 19, 2017 7:03 pm
Forum: Naming
Topic: Ch. 17 Problem 29a [ENDORSED]
Replies: 4
Views: 282

### Re: Ch. 17 Problem 29a[ENDORSED]

It changes to ferrate because the "ate" indicates that the overall charge of the complex is negative. Fe originally comes from the latin ferrum and that's where the ate is added onto.
Sun Nov 12, 2017 8:08 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Calculating Formal Charge
Replies: 4
Views: 419

### Re: Calculating Formal Charge

Yes so each bond line that you see would count as one electron and each lone pair would have two electrons and you would just subtract that from the usual amount of valence electrons that surround the atom.
Sun Nov 12, 2017 7:50 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: T-shape vs. trigonal
Replies: 2
Views: 373

### Re: T-shape vs. trigonal

Yes the difference is going to be the difference between the arrangement of the electrons and the regions of the high electron density and the number of lone pairs around the central atom. With a molecule with an arrangement of AX3E2 where there are five regions of high electron density and 2 lone p...
Sun Nov 05, 2017 10:24 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 3.9 and 3.11 in the homework? I am confused as to what it is they are asking
Replies: 3
Views: 397

### Re: 3.9 and 3.11 in the homework? I am confused as to what it is they are asking

For "a" on 3.11 if you look at the ground electron state configuration of Co it is [Ar] 3d7 4s2. As we are looking for a 3+ ion, when 3 electrons are taken from a Co atom they are first removed from the s subshell and then they are lost through the d subshell resulting in the [Ar] 3d6 conf...
Sun Nov 05, 2017 10:13 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Regions of Electron Density
Replies: 2
Views: 236

### Re: Regions of Electron Density

Yes lone pairs are considered as one region of high electron density when counting the regions around the central atom.
Sun Oct 29, 2017 4:39 pm
Forum: Trends in The Periodic Table
Topic: Ionization Energy [ENDORSED]
Replies: 5
Views: 407

### Re: Ionization Energy[ENDORSED]

As you go down a group of atoms their radii increases. Thus, there are more levels/ shells shielding the outermost electrons from the pull of the nucleus making it easier for valence electrons to be removed. As you go across a period more electrons are filling the valence shell as that happens the r...
Sun Oct 29, 2017 3:45 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: 2.29
Replies: 2
Views: 268

### Re: 2.29

A) When you're are given the n and l to find the total number of possible electrons you determine the possible ml values and and multiply the number of possible ml values by 2. ml is l, l-1,...-l. n=2; l=1 so the subshell is p. This means that ml can be -1,0,1 and 2 electrons can fill each of those ...
Sun Oct 22, 2017 9:27 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Quantum Number l exception [ENDORSED]
Replies: 4
Views: 390

### Re: Quantum Number l exception[ENDORSED]

Just to clarify I believe that the l quantum number is going to be positive. The ml or the magnetic quantum number is when you will start getting negatives where for example where l=1, ml can be -1, 0, or 1.
Sun Oct 22, 2017 9:15 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: ORBITALS, SHELLS ETC. [ENDORSED]
Replies: 6
Views: 512

### Re: ORBITALS, SHELLS ETC.[ENDORSED]

An atomic orbital is basically the most probable location an electron is going to be located which is based off a wave function. The orbitals are mainly classified by three different quantum numbers the n, l, and ml. The n determines the size and energy of the orbitals this is the defining factor as...
Sun Oct 15, 2017 5:41 pm
Forum: Properties of Electrons
Topic: Problem 1.33
Replies: 2
Views: 285

### Re: Problem 1.33

To add on, I think something important to note is the line " No electrons are emitted from the surface of the metal until the frequency of the radiation reaches 2.50*10^16 Hz." This information gives us what we would call the threshold frequency or the minimum frequency required to eject e...
Mon Oct 09, 2017 3:10 pm
Forum: Limiting Reactant Calculations
Topic: M.15
Replies: 5
Views: 4114

### Re: M.15

(a) The chemical equation before being balanced would be Al + Cl2 -> AlCl3. After it is balanced it would look like 2Al + 3Cl2 -> 2AlCl3 (b) For this one you have to determine the limiting reactant so you need to convert the masses of the reactants to moles and then compare the ratios of the stoichi...
Sun Oct 08, 2017 11:57 pm
Forum: Empirical & Molecular Formulas
Topic: F11 part B [ENDORSED]
Replies: 2
Views: 263

### Re: F11 part B[ENDORSED]

Both ways are correct they only teach it that way so the concept is easier to grasp. Personally, I convert from grams to moles and just divide the smallest from there and you end up with the same thing anyways so its only a matter of preference.