## Search found 51 matches

Sat Mar 17, 2018 12:21 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Homework Problem 14.27
Replies: 2
Views: 318

### Homework Problem 14.27

I'm having some trouble understanding why we can't just add the two standard potentials together from the reactions to get the total. Why exactly do we convert everything to deltaG and back again?
Fri Mar 16, 2018 11:06 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Homework 14.17
Replies: 2
Views: 209

### Homework 14.17

I'm having a little bit of trouble understanding this question. How exactly would we determine the half reactions given only the reactant? We would just look at the table in the back to see which reactions involve that reactant, or is there something I'm missing?
Fri Mar 16, 2018 10:40 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram
Replies: 3
Views: 242

### Cell Diagram

Can someone please walk me through how to put together a cell diagram step-by-step? I know that the reduction half goes on the right and the oxidation half goes on the left, but beyond that, I'm completely lost.
Any help would be really appreciated!
Wed Mar 07, 2018 12:05 am
Forum: Second Order Reactions
Topic: 15.35a
Replies: 3
Views: 351

### Re: 15.35a

I did the same thing and recalculated it with 0.02357 rounded to 0.024 like it does in the answer key, and it gives 744. I think it's just a rounding error on our part.
Tue Mar 06, 2018 11:57 pm
Forum: Zero Order Reactions
Topic: Zero Order Half-Life Calculations
Replies: 2
Views: 519

### Zero Order Half-Life Calculations

Because the half-life for zero order reactions is also dependent on initial concentration, would it be calculated similarly to 15.35 (second order) but using the half-life equation for a zero-order reaction? In other words, do we need to perform the same types of manipulations because initial concen...
Tue Mar 06, 2018 11:49 pm
Forum: General Rate Laws
Topic: Homework Problem 15.5
Replies: 1
Views: 90

### Homework Problem 15.5

Can someone please explain why you multiply by three rather than 1/3 for this problem. I thought that it would be 1/3 of the unique rate because it is 1/a rate[A]. Why do you multiply by 3 instead?
Sat Mar 03, 2018 10:41 pm
Forum: First Order Reactions
Topic: Pseudo-First Order Reaction [ENDORSED]
Replies: 4
Views: 320

### Re: Pseudo-First Order Reaction[ENDORSED]

From what I remember from lecture, K is the rate constant for a normal reaction. K' is the rate constant for the pseudo-reaction where the other reactants are in very high concentrations. In other words, K' is the rate constant for the experimental reaction with just the one reactant. In addition, k...
Sat Mar 03, 2018 10:16 pm
Forum: Second Order Reactions
Topic: K in Rate Laws [ENDORSED]
Replies: 2
Views: 209

### K in Rate Laws[ENDORSED]

I noticed that depending on the reaction order, the slope of the graph can be equal to positive or negative k. For first and zero-order reactions, the slope of the graph is equal to -k, but for second order reactions, the slope is equal to +k. Can someone please explain to me why one is different fr...
Sat Mar 03, 2018 10:12 pm
Forum: Second Order Reactions
Topic: Half Lives [ENDORSED]
Replies: 3
Views: 254

### Re: Half Lives[ENDORSED]

For second and zero-order reactions, I have both half lives depending on the concentration of [A]0 (initial concentration).

For second order: t(1/2)= 1/k*[A]0

For zero-order: t(1/2)= [A]0/2*k
Wed Feb 21, 2018 8:08 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Concentration Cells [ENDORSED]
Replies: 1
Views: 187

### Concentration Cells[ENDORSED]

For problems involving the calculation of an unknown concentration in a concentration cell, is the basic strategy to plug everything into the Nernst equation and solve for the concentration? Are there any unit conflicts that we need to worry about?
Wed Feb 21, 2018 12:35 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagrams
Replies: 3
Views: 212

### Re: Cell Diagrams

Thank you both so much!
Wed Feb 21, 2018 12:06 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagrams
Replies: 3
Views: 212

### Cell Diagrams

Can someone please explain to me how the commas work in cell diagrams? I don't know what they signify and when to use them? Are they similar to the | in the diagram or do they mean something completely different?
Wed Feb 21, 2018 12:04 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: #14.23 finding n [ENDORSED]
Replies: 3
Views: 261

### Re: #14.23 finding n[ENDORSED]

For this question, I think you have to figure out the oxidation and reduction half-reactions and those will give you the moles of electrons for the equation.
Wed Feb 14, 2018 4:51 pm
Forum: Van't Hoff Equation
Topic: Van't Hoff
Replies: 9
Views: 691

### Van't Hoff

Can someone give me a situation where you would use the ln(k2/k1) version of this equation? Thanks!
Wed Feb 14, 2018 11:40 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Delta S(tot)
Replies: 5
Views: 590

### Delta S(tot)

Can someone please explain what the difference between delta S, delta S (surroundings), and delta S (tot) is? Also, how do these relate to each other when calculating them?
Wed Feb 14, 2018 11:37 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Cp and Cv
Replies: 2
Views: 231

### Cp and Cv

I am still confused about when to use Cv or Cp when determining the change in entropy for gas that has a change in temperature. Is Cp only used when there is constant pressure? I've heard conflicting things about when to use which, can someone please clarify?
Sun Feb 11, 2018 11:05 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Second Law
Replies: 2
Views: 196

### Second Law

When would we use the equation of the second law delta S=q (rev)/T? I can't seem to find a lot of example problems that use it directly. Is it meant to be used frequently for calculations, or mainly as a means of deriving the other equations we learned in lecture?
Sun Feb 11, 2018 10:51 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: 9.5
Replies: 4
Views: 398

### Re: 9.5

I think that the reason that it is negative is due to the fact that the first reservoir lost heat, and transferred that heat to the second reservoir, meaning that it gained heat. Losing heat is negative, gaining is positive.
Sun Feb 11, 2018 10:44 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy and Spontaneity
Replies: 2
Views: 286

### Gibbs Free Energy and Spontaneity

So I know that when delta G is negative, the forward reaction is spontaneous. Is it then correct to assume that whenever delta G is positive, the reverse reaction is spontaneous?
Sun Feb 04, 2018 10:48 pm
Forum: Van't Hoff Equation
Topic: Entropy and enthalpy
Replies: 2
Views: 300

### Re: Entropy and enthalpy

In my lecture notes, I have written down that it is assumed that entropy and enthalpy are constant when writing the final equation. I would imagine that they would tell us if for some reason we could not make that assumption.
Sun Feb 04, 2018 10:44 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.27 Entropy
Replies: 3
Views: 280

### Re: 9.27 Entropy

Does that mean that every element has a higher entropy than the proceeding element on the periodic table? Or does there need to be a large difference in size for the entropy to differ?
Sun Feb 04, 2018 10:42 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Exothermic and Spontaneous
Replies: 4
Views: 4769

### Re: Exothermic and Spontaneous

I think that the difference between the two is that exothermic means that deltaH is negative, and that spontaneous means that deltaG is negative. So that means that exothermic relates to enthalpy and that spontaneity relates to Gibbs Free Energy. I think that there are some situations that an exothe...
Wed Jan 24, 2018 12:04 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.73 part C
Replies: 3
Views: 235

### Re: 8.73 part C

The enthalpy of the reaction is 0 because the bonds being broken and formed have the exact same energy as one another. For example 4 C-H bonds are broken and 4 Cl-C bonds are broken. Then between the two reactant molecules 4 C-H bonds are formed and 4 Cl-C bonds are formed. The amount of bonds broke...
Tue Jan 23, 2018 11:51 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Homework Problem 8.57
Replies: 1
Views: 115

### Homework Problem 8.57

I have a couple of questions about this homework problem. What exactly is hydrogenation? Also why to the intermediate steps in Hess's Law contain oxygen, or is it part of the hydrogenation process? Any help would be greatly appreciated.
Tue Jan 23, 2018 11:35 pm
Forum: Phase Changes & Related Calculations
Topic: Homework Help on 8.67
Replies: 2
Views: 222

### Re: Homework Help on 8.67

I think the reason that the enthalpy of vaporization is subtracted is due to the fact that changing from a gas to a liquid is an exothermic process, meaning that it would be the negative version of the enthalpy of vaporization. The fact that it is an exothermic process determines that it is subtract...
Sat Jan 20, 2018 10:53 pm
Forum: Phase Changes & Related Calculations
Topic: Heating Curve
Replies: 2
Views: 163

### Re: Heating Curve

If I'm understanding your question correctly, asking if calculations involving transitions between states like solid to liquid, then yes. The enthalpies of fusion and vaporization are given on the constants sheet for the class. I would assume that means they are fair game for the test. Some of the h...
Sat Jan 20, 2018 10:48 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Textbook Sections 8.7 and 8.10
Replies: 1
Views: 117

### Textbook Sections 8.7 and 8.10

I know that both sections 8.7 and 8.10 are included in the reading, and problems appear in the assigned homework. Are we responsible for these topics on the exam? If so, can someone please explain the topics and their related calculations in a way that is a little easier to understand?

Thanks!
Sat Jan 20, 2018 10:34 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess's Law
Replies: 2
Views: 84

### Hess's Law

I have a couple of questions relating to calculation's using Hess's Law. First, why is it ok to use fractions in the chemical equations? I read the explanation in the textbook, but it didn't really help. Second, when should I use fractions as stoichiometric coefficients in Hess's Law calculations? T...
Thu Jan 11, 2018 2:33 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess's Law vs. Using Bond Enthalpies
Replies: 3
Views: 367

### Re: Hess's Law vs. Using Bond Enthalpies

Hess's law and using bond enthalpies are different ways of accomplishing the same task. Both will give the change in enthalpy. I think that we are supposed to select either one method or the other based on the information provided in the problem. In the examples we did in class, we were given the ch...
Thu Jan 11, 2018 2:28 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Homework Problem 8.19
Replies: 3
Views: 263

### Re: Homework Problem 8.19

For this problem, you would calculate the q values for raising the copper to 100 degrees and the water to 100 degrees separately, and then add the q values together to get the final answer.
Thu Jan 11, 2018 2:14 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: #39 from Chapter 8
Replies: 3
Views: 228

### Re: #39 from Chapter 8

I learned in discussion that the formula for this kind of problem is q= m*C*deltaT or q=n*C*deltaT.
m= mass
n=moles
C= heat capacity
deltaT= change in temperature (final- initial)

Sometimes the heat capacity will be specific heat capacity (in grams) or molar heat capacity (moles).
Sat Dec 09, 2017 10:55 pm
Forum: Biological Examples
Topic: #22 on Practice Test
Replies: 1
Views: 273

### Re: #22 on Practice Test

We know from lecture that transition metal complexes typically form tetrahedral, square planar, or octahedral shapes. This means that the transition metal cation can form at most 6 bonds with other atoms or molecules. The iron metal in the diagram is shown bonded to 4 Nitrogen atoms. This leaves 2 b...
Sat Dec 09, 2017 10:45 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Mono/poly Dentates
Replies: 1
Views: 185

### Mono/poly Dentates

I was wondering if there were any common groupings of atoms that could help determine whether a molecule was mono or polydentate. I know COO was mentioned as one in a review session, are there any other common ones?
Tue Nov 28, 2017 8:51 pm
Forum: Hybridization
Topic: 4.43
Replies: 2
Views: 309

### Re: 4.43

I think that when they say "s character" they mean the proportion of the hybridized orbital that the single s orbital makes up. For example as p and d orbitals get added (sp, sp^2, sp^3, sp^3d...etc), the s character of the hybridized orbital goes down because it makes up a smaller part of...
Tue Nov 28, 2017 8:47 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: 17.29C
Replies: 1
Views: 151

### Re: 17.29C

You know it has the -ate at the end of the transition metal name when the overall charge of the complex is negative, as indicated by the 2- after the brackets.
Sat Nov 25, 2017 8:27 pm
Forum: Ideal Gases
Topic: Ideal Gas Law
Replies: 3
Views: 227

### Ideal Gas Law

I never went over the ideal gas law in high school, what is exactly is it used for, and where did it come from?
Sat Nov 25, 2017 8:13 pm
Forum: Naming
Topic: Finding Coordination Number
Replies: 6
Views: 497

### Finding Coordination Number

I know that the textbook explains how to find the coordination number for the complex, but I also know that Professor Lavelle explained it in lecture in a much simpler way. Does anyone remember how he explained it in lecture, and/or an easier way than the textbook describes?
Thu Nov 16, 2017 10:48 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Figure 4.7
Replies: 1
Views: 136

### Figure 4.7

Can someone explain, in figure 4.7 in the textbook, why some of the shapes can be both polar and non polar, especially when there are no lone pairs in the shape depicted?
Thu Nov 16, 2017 10:46 pm
Forum: Hybridization
Topic: Linear Combination of Orbitals
Replies: 1
Views: 113

### Linear Combination of Orbitals

I understand that the formulas for linear combinations are the wave functions for the hybrid orbitals, but where do the positive and negative signs in between the s and p orbitals come from?
Sat Nov 11, 2017 12:07 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Determining Electron Density [ENDORSED]
Replies: 1
Views: 133

### Determining Electron Density[ENDORSED]

Why are some types of electron interactions stronger than others? For example why do lone pair-lone pair interactions repel more strongly than bond-bond interactions?
Sat Nov 11, 2017 12:01 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles [ENDORSED]
Replies: 3
Views: 267

### Bond Angles[ENDORSED]

Could someone please explain to me why some atoms have multiple degree values for their bond angles and others only have one?
Tue Oct 31, 2017 9:33 pm
Forum: Trends in The Periodic Table
Replies: 2
Views: 264

For an ionic compound like K+CL-, when potassium transfers its valence electron to chlorine, does the radius for potassium get smaller? If so, are the radii the same for Potassium and Chlorine, or will Potassium's radius become smaller due to its increased nuclear charge?
Tue Oct 31, 2017 9:17 pm
Forum: Trends in The Periodic Table
Topic: Diagonal Relationships- 2.73
Replies: 2
Views: 313

### Diagonal Relationships- 2.73

Does all that a diagonal relationship means that the two elements that share the relationship have similar properties, or does it imply something else as well?
Fri Oct 27, 2017 12:09 am
Forum: Quantum Numbers and The H-Atom
Topic: Electron Probability Calculation
Replies: 1
Views: 180

### Electron Probability Calculation

I know that the textbook provides an explanation of how to calculate the probability of finding an electron in a specific place. Could somebody walk me through it step-by-step, in terms that are a little easier to understand?
Thu Oct 26, 2017 11:52 pm
Forum: *Shrodinger Equation
Topic: Shrodinger Equation Applications [ENDORSED]
Replies: 7
Views: 525

### Shrodinger Equation Applications[ENDORSED]

Two questions in one here, first do we need to know how to use/derive the shrodinger equation for the exam?
Also, I know in class that the professor said that the solutions for the equation are the electron orbitals, is that all the equation is used for?
Wed Oct 18, 2017 9:26 pm
Forum: Quantum Numbers and The H-Atom
Topic: Magnetic Spin Numbers
Replies: 3
Views: 271

### Magnetic Spin Numbers

Can someone explain why the values of (1/2) are positive or negative for the magnetic spin numbers?
In other words, what determines if it is spin up or spin down?
Wed Oct 18, 2017 9:24 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: s-,p-, d-, and f- orbitals
Replies: 7
Views: 509

### s-,p-, d-, and f- orbitals

Can someone please explain to me in a little more detail what each of the orbital letters means, and how that relates to their positions on the x,y,z axes?
He went over them kind of quickly in class, and I didn't learn this in high school.
Thu Oct 12, 2017 11:53 pm
Forum: DeBroglie Equation
Topic: DeBroglie Relation
Replies: 1
Views: 158

### DeBroglie Relation

How did DeBroglie determine that the wavelength of a "matter wave" is inversely related to the its linear momentum?
Thu Oct 12, 2017 11:44 pm
Forum: Properties of Electrons
Topic: Energy Levels
Replies: 6
Views: 523

### Energy Levels

Could someone please the energy levels of electrons to me?
I understand that they are limited to discrete values and that they have to do with spectral lines, but other than that I'm confused.
Thu Oct 05, 2017 8:52 pm
Forum: Limiting Reactant Calculations
Topic: After determining the limiting reactant, how do you find the mass of a product?
Replies: 2
Views: 274

### Re: After determining the limiting reactant, how do you find the mass of a product?

Once you have determined the limiting reactant, you look at the formula and determine how many moles of product can be formed based on the moles of limiting reactant present (the molar ratio of the limiting reactant to the product). Then convert the moles to grams by multiplying by the molar mass.
Thu Oct 05, 2017 8:42 pm
Forum: Empirical & Molecular Formulas
Topic: Problem L.35
Replies: 2
Views: 294

### Re: Problem L.35

Once you have converted the tons to grams, divide by the molar mass of NaBr which will give you the moles of NaBr that need to be produced. Then multiply the by the mole ratio of (1mol Fe(sub3)Br(sub8)/8mol NaBr). Then refer to the previous equation for the mol ratio of (3mol FeBr(sub2)/1mol Fesub3)...