Search found 55 matches

by Emilie Hoffman 1E
Sat Mar 17, 2018 9:14 pm
Forum: Calculating Work of Expansion
Topic: Work with changeP and constant V
Replies: 4
Views: 276

Work with changeP and constant V

Why is there no work done when a systems pressure changes but its volume does not?
by Emilie Hoffman 1E
Sat Mar 17, 2018 1:45 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: First Law Thermo
Replies: 4
Views: 237

First Law Thermo

Is q(system) + q(surroundings) = 0 another iteration of the first law, because that's what I have written in my notes. And if so, can someone explain how?
by Emilie Hoffman 1E
Wed Mar 14, 2018 11:16 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 16.65
Replies: 1
Views: 78

16.65

In this problem, they are asking us to determine whether or not a reaction is exothermic or endothermic. Can someone explain how you can use activation energies to indicate whether a reaction is endothermic or exothermic?
by Emilie Hoffman 1E
Wed Mar 14, 2018 10:45 pm
Forum: First Order Reactions
Topic: Exam question 3
Replies: 4
Views: 232

Re: Exam question 3

I would assume, but honestly I'm unsure. We're not accounting for the ability for the reverse reaction to run in this problem, so I don't know if you would need this information to solve this problem.
by Emilie Hoffman 1E
Wed Mar 14, 2018 10:40 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.63
Replies: 3
Views: 170

15.63

I tried to solve this problem the slope way, with the activation energy over R being equal to (lnk1 - lnk2)/(1/T1 - 1/T2). Is this the correct way to set up this relationship, because I'm not getting the answer listed in the solutions manual. Here is the problem for reference: The rate constant of t...
by Emilie Hoffman 1E
Wed Mar 14, 2018 9:42 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 15.49
Replies: 4
Views: 175

15.49

For this question, they ask you to make rate laws for each elementary step of a two step reaction, the first slow and the second fast. The solution manual keeps the intermediate in the rate law for the second step. Is this done because you can't assume anything is in excess because there isn't a bui...
by Emilie Hoffman 1E
Wed Mar 14, 2018 8:49 pm
Forum: First Order Reactions
Topic: Exam question 3
Replies: 4
Views: 232

Re: Exam question 3

Also, when you balance the equation, A2 has a 1:2 ratio to AC, so you can multiply the unique rate of the reaction (aka the consumption rate of A2 because it has a coefficient of 1) by 2 and then use that to evaluate the change in molarity of the AC.
by Emilie Hoffman 1E
Wed Mar 14, 2018 8:46 pm
Forum: First Order Reactions
Topic: Exam question 3
Replies: 4
Views: 232

Re: Exam question 3

Because the rate is constant, you can assume that this rate is zero order, which mean that the rate will just equal the reaction constant. Since the rate is in units of M/s, you can set the rate equal to an amount of change in the molarity over a time interval. Then you can plug in the change in mol...
by Emilie Hoffman 1E
Sun Mar 11, 2018 3:30 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.37(a)
Replies: 2
Views: 114

Re: 14.37(a)

Sorry, the problem asked us to find the cell potential, just to clarify.
by Emilie Hoffman 1E
Sun Mar 11, 2018 3:29 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.37(a)
Replies: 2
Views: 114

14.37(a)

In this problem, they give us a galvanic cell: Pt(s) / H2(g, 1.0 bar) / HCl(aq, 0.075 M) // HCl(aq, 1.0 M) / H2(g, 1.0 bar) / Pt(s), that indicates that the cathode should be the 1M HCl based on this cell. But, in the answer, we use the .075 M as the cathode. Should we just assume that, regardless o...
by Emilie Hoffman 1E
Sat Mar 10, 2018 11:57 pm
Forum: Calculating Work of Expansion
Topic: Work in Irreversible Process
Replies: 1
Views: 88

Re: Work in Irreversible Process

If by potential, you mean internal energy/potential energy, then you can use the equation deltaU=q+w to conclude that if deltaU isn't at a maximum, then work can't be either.
by Emilie Hoffman 1E
Sat Mar 10, 2018 11:53 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: change in internal energy
Replies: 3
Views: 213

Re: change in internal energy

Because we don't have a way of calculating that kind of energy change at the same time because both of our equations deal with either a change in one or another.
by Emilie Hoffman 1E
Sat Mar 10, 2018 11:51 pm
Forum: Calculating Work of Expansion
Topic: different types of work
Replies: 4
Views: 142

Re: different types of work

*for sorry about that
by Emilie Hoffman 1E
Sat Mar 10, 2018 11:51 pm
Forum: Calculating Work of Expansion
Topic: different types of work
Replies: 4
Views: 142

Re: different types of work

No I don't think so. There would be no actual way fro us to tell unless the process was described to us and it wasn't something we focused on as being important in class or discussion.
by Emilie Hoffman 1E
Sat Mar 10, 2018 11:49 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Finding n
Replies: 4
Views: 248

Re: Finding n

Then it might not be the actual n of the specific concentration you're looking for. My TA said that is should always be close enough to a whole number for you to easily round it, even if it's off a little. Also, I'm confused as to how you're directly calculating n because we usually compare the rati...
by Emilie Hoffman 1E
Sat Mar 10, 2018 11:43 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: equipartition theorem
Replies: 1
Views: 96

Re: equipartition theorem

No I don't think so.
by Emilie Hoffman 1E
Sat Mar 10, 2018 11:42 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: molar heat capacity
Replies: 1
Views: 84

Re: molar heat capacity

I believe it has to do with the overall internal energy with constant volume versus constant pressure. In the book, they derive and compare both of these equations using deltaU= q + w and with constant volume, the work variable drops out, leaving only the heat of the system to determine the change i...
by Emilie Hoffman 1E
Sat Mar 10, 2018 11:37 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Elements Acting as Electrodes
Replies: 2
Views: 121

Elements Acting as Electrodes

Should we assume that when the oxidation state of an element is zero, then they are acting a solid?
by Emilie Hoffman 1E
Sat Feb 24, 2018 4:09 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Finding Standard Potential Through Compiling Half-Reactions
Replies: 2
Views: 119

Finding Standard Potential Through Compiling Half-Reactions

Why can you assume that the deltaG of the final reaction is a composite of the deltaGs of the two other half reactions?
by Emilie Hoffman 1E
Sat Feb 24, 2018 3:47 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Trends in Increasing Reducing Ability
Replies: 5
Views: 250

Re: Trends in Increasing Reducing Ability

So is there any importance in comparing equal oxidation states going to a neutral atom? For example, would Cu2+ ---> Cu and Cr3+ ---> Cr be just as valid a comparison as Cu2+ ---> Cu and Cr2+ ---> Cr?
by Emilie Hoffman 1E
Fri Feb 23, 2018 12:23 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Trends in Increasing Reducing Ability
Replies: 5
Views: 250

Trends in Increasing Reducing Ability

To compare this between different elements, do we need to compare the same increase in oxidation number? For example, if we were comparing Cu and Cr, do we have to use Cu2+ ---> Cu in comparison with Cr2+ ---> Cr, or can we compare between different oxidation state changes?
by Emilie Hoffman 1E
Fri Feb 23, 2018 12:19 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.15c
Replies: 1
Views: 89

Re: 14.15c

This reaction might not be set in basic conditions, as it isn't specifically stated that it is in the problem, and thus the reaction must account for the extra OH- group without insinuating it is in excess because of the solution. I'm not sure why exactly K is paired with it other than the fact that...
by Emilie Hoffman 1E
Fri Feb 23, 2018 12:12 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.23 part a
Replies: 1
Views: 82

14.23 part a

In the solutions manual, there is no listed electrode for the oxidation part of this reaction, while platinum on serves as such on the cathode side. Furthermore, none of the oxidation reactants or products are solids. Can someone clear up what is happening here? Here is the original problem: For eac...
by Emilie Hoffman 1E
Wed Feb 21, 2018 11:15 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.13 Part D
Replies: 2
Views: 157

Re: 14.13 Part D

Okay thank you, the cell diagram was what I didn't understand from the solutions manual.
by Emilie Hoffman 1E
Tue Feb 20, 2018 9:59 pm
Forum: Balancing Redox Reactions
Topic: Determining acidic or basic solution
Replies: 3
Views: 133

Re: Determining acidic or basic solution

We shouldn't have to. This should be given at the beginning of the problem as part of in initial condition.
by Emilie Hoffman 1E
Tue Feb 20, 2018 9:56 pm
Forum: Balancing Redox Reactions
Topic: Acidic Solution vs. Basic Solution
Replies: 2
Views: 96

Re: Acidic Solution vs. Basic Solution

It should always state whether or not the solution the reaction is happening in is acidic or basic because that facilitates the addition of water, H+, or OH-. My TA said that you should always be given this as a part of the initial condition.
by Emilie Hoffman 1E
Tue Feb 20, 2018 9:54 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.13 Part D
Replies: 2
Views: 157

14.13 Part D

Can anyone explain how to do this problem?

Write the half-reactions, the balanced equation for the
cell reaction, and the cell diagram for each of the following
skeletal equations:
(d) Au+(aq) --> Au(s) + Au3+(aq)
by Emilie Hoffman 1E
Sat Feb 10, 2018 9:44 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Molar entropy v standard entropy of formation
Replies: 3
Views: 691

Re: Molar entropy v standard entropy of formation

The entropies that we use in the back of the book (the molar entropies) are inherently standard, which is indicated by the little degree sign. We use standard molar entropies so that we can use the same number to calculate the standard entropy of many reactions.
by Emilie Hoffman 1E
Sat Feb 10, 2018 9:41 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.49 STP vs. SATP
Replies: 2
Views: 131

Re: 8.49 STP vs. SATP

We usually assume that a normal reaction is happening at room temperature (somewhere around 25 degrees Celsius or 298 K) unless temperature is specifically being used to drive the process. So yeah if they don't specify another temperature that the reaction is occurring at, we assume it's room temper...
by Emilie Hoffman 1E
Sat Feb 10, 2018 9:37 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: 9.75
Replies: 1
Views: 92

9.75

Can anyone explain how they got to the conclusion that the cis molecule has more available states than the trans version of the molecule? Considering positional disorder, would you expect a crystal of octahedral cis-MX2Y4 to have the same, higher, or lower residual entropy than the corresponding tra...
by Emilie Hoffman 1E
Sun Feb 04, 2018 3:32 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Using dS vs change in S
Replies: 3
Views: 125

Using dS vs change in S

Can anyone give a clear distinction between when you use dS to solve a problem rather that changeS for calculating the general change in entropy?
by Emilie Hoffman 1E
Sun Feb 04, 2018 3:30 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Question 9.10
Replies: 2
Views: 162

Question 9.10

This isn't an assigned problem, but I just wanted to check if I was doing it correctly as it is another iteration of 9.9.

9.10: Calculate the entropy change associated with the isothermal compression of 4.80 mol of ideal gas atoms from 12.86 L to 4.80 L.
by Emilie Hoffman 1E
Tue Jan 16, 2018 11:56 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.52
Replies: 1
Views: 106

8.52

I know this problem isn't assigned for the homework, but can anyone shed light on how to go about doing it? 8.52 A natural gas mixture is burned in a furnace at a power-generating station at a rate of 13.0 mol per minute. (a) If the fuel consists of 9.3 mol CH4, 3.1 mol C2H6, 0.40 mol C3H8, and 0.20...
by Emilie Hoffman 1E
Tue Jan 16, 2018 11:54 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.51
Replies: 2
Views: 111

8.51

Can anyone clarify why in this problem the reaction enthalpies of N2 and O2 aren't included in the initial caluclation of the formation enthalpy? 8.51 The enthalpy of formation of trinitrotoluene (TNT) is -67 kJ·mol-1, and the density of TNT is 1.65 g·cm-3. In principle, it could be used as a rocket...
by Emilie Hoffman 1E
Sat Dec 09, 2017 3:33 pm
Forum: DeBroglie Equation
Topic: Wavelike properties
Replies: 3
Views: 183

Re: Wavelike properties

If the wavelength is 10^(-15) or larger, we can measure it, meaning we can discern wave-like properties.
by Emilie Hoffman 1E
Sat Dec 09, 2017 3:30 pm
Forum: Hybridization
Topic: Ionization energy
Replies: 1
Views: 125

Re: Ionization energy

You can usually determine this through the idea that an atom that is most likely to want to collect electrons (such as fluorine) does not want to give them away, meaning that it's ionization energy would be comparatively higher than an atom that usually becomes a cation (such as sodium), as these at...
by Emilie Hoffman 1E
Sat Dec 09, 2017 3:16 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Hexadentate / Octahedral?
Replies: 1
Views: 180

Re: Hexadentate / Octahedral?

The shape of the compound relative to the central transition would be octahedral because it is bonding to six different sites, which all happen to be part of the same compound. You might want to check how many of the actual sites are being bound to the central atom though as the way to determine it'...
by Emilie Hoffman 1E
Sat Dec 09, 2017 3:10 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Using electronegativity to determine acidity
Replies: 2
Views: 284

Using electronegativity to determine acidity

Is there a certain range of electronagativity differences that would guarantee that a compound is acidic or basic? Or for that matter what camn classify as amphoteric? In the book (12.17 specifically) asks us to determine whether or not a given oxide is acidic, basic, or amphoteric and I was unsure ...
by Emilie Hoffman 1E
Sun Dec 03, 2017 7:27 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Different chemical equations in J.5
Replies: 1
Views: 119

Different chemical equations in J.5

For J.5 in the fundamentals chapter focuses on multiple different equations that have not explicitly been outlined in class with Lavelle. Does anyone know whether this difference is an important thing to know for the class?
by Emilie Hoffman 1E
Sun Nov 19, 2017 6:31 pm
Forum: Hybridization
Topic: Hybridization in General
Replies: 3
Views: 334

Re: Hybridization in General

Hybridization is the idea that when an atom is exposed to an amount of energy, the energy levels surrounding it get jumbled enough to migrate from one orbital to another. I think Lavelle said in class that we cannot externally determine the hybridization state of an atom without knowing what it's bo...
by Emilie Hoffman 1E
Sun Nov 19, 2017 6:29 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.13
Replies: 2
Views: 157

Re: 4.13

My best guess would be that the octet for the central atom is satisfied fro both of the book variations.
by Emilie Hoffman 1E
Sun Nov 19, 2017 6:27 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Polar ve non polar [ENDORSED]
Replies: 7
Views: 356

Re: Polar ve non polar [ENDORSED]

I would say that a molecule whose charges cancel to make an overall charge of zero or one that has no charge to begin with it what we classify as non-polar. A polar molecule is a molecule whose charge is overall in one direction or another.
by Emilie Hoffman 1E
Sun Nov 12, 2017 10:06 pm
Forum: Lewis Structures
Topic: Atomic Structure of HOCO
Replies: 2
Views: 165

Re: Atomic Structure of HOCO

HOCO was considered a radical because it had an uneven number of electrons, but the actual sturcture of it changes from when you look in the book at it being a radical to when you look on the internet as being an ion (the book being a line, the internet having all of the other atoms connected to the...
by Emilie Hoffman 1E
Sun Nov 12, 2017 10:02 pm
Forum: Ionic & Covalent Bonds
Topic: Covalent Bonding: Polar and Non-polar
Replies: 6
Views: 371

Re: Covalent Bonding: Polar and Non-polar

The way my TA phrased it was that when the electronegativity between two atoms is zero, the bond is perfectly covalent. Then anything with an electronegativity difference greater than two was considered ionic. In between, he classified everything as polar covalent, or a bond that has both covalent a...
by Emilie Hoffman 1E
Wed Nov 08, 2017 8:44 pm
Forum: Bond Lengths & Energies
Topic: Homework Problem 3.87
Replies: 5
Views: 325

Re: Homework Problem 3.87

Could someone explain in another way because the solution book specifically points that the electronegativity of CF4 would predict a weakest bond for CF4.
by Emilie Hoffman 1E
Sun Nov 05, 2017 9:20 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Regions of Electron Density
Replies: 2
Views: 144

Re: Regions of Electron Density

I think that Lavelle said something in class about counting lone pairs as places in which a bond cannot go when we are creating Lewis structures or VESPR models, but they should be places of high electron density based on the fact that there are two electrons somewhere in that area around the atom.
by Emilie Hoffman 1E
Sun Nov 05, 2017 9:17 pm
Forum: Empirical & Molecular Formulas
Topic: textbook problem M.22
Replies: 1
Views: 148

Re: textbook problem M.22

In this problem we are assuming that we do not know a lot about the original reaction that took place and that oxygen could conceivably be a factor in this reaction if the mass percentage composition you calculate and the one supplied don't match up. So maybe they're asking if oxygen could have init...
by Emilie Hoffman 1E
Sun Nov 05, 2017 9:12 pm
Forum: Lewis Structures
Topic: 3.25 part d
Replies: 2
Views: 130

3.25 part d

In this problem, the hydrogen is used as the cation and the tellurium as the anion to make a balanced exchange of electrons between the two. So, is hydrogen allowed to basically act like a cation and not have any electrons, or is it assumed that when hydrogen is doing this the bond is more covalent ...
by Emilie Hoffman 1E
Tue Oct 17, 2017 10:08 pm
Forum: DeBroglie Equation
Topic: When to use De Broglie Equation [ENDORSED]
Replies: 11
Views: 1173

Re: When to use De Broglie Equation [ENDORSED]

The De Broglie equation equation outlines the idea that things that have rest mass (i.e. something that has weight) can behave like waves through having an oscillating way of moving (like basically they move back and forth over the line of their projected path) and thus wavelength. We can't use this...
by Emilie Hoffman 1E
Tue Oct 17, 2017 10:02 pm
Forum: Properties of Light
Topic: test 2 topic
Replies: 9
Views: 573

Re: test 2 topic

I don't believe that this kind of information fits what Lavelle expects us to know because it doesn't revolve around problem solving or any basic concepts for the equations we use in this chapter. Also, since he didn't specifically cover any other experiment other than the photo-electric effect, I w...
by Emilie Hoffman 1E
Tue Oct 17, 2017 9:59 pm
Forum: DeBroglie Equation
Topic: Particle-Specific/Light-Specific Equations
Replies: 1
Views: 139

Re: Particle-Specific/Light-Specific Equations

Th kinetic energy equation (KE = .5mv^2) is the only equation that we've specifically touched on in class that requires an object to have a rest mass. Other than that I don't think we've covered anything else that is mass-dependent yet.
by Emilie Hoffman 1E
Sun Oct 15, 2017 4:23 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Question 1.17
Replies: 1
Views: 123

Question 1.17

I know this isn't on the assigned list of problems, but does anyone know how to go about solving it?

1.17: The energy levels or hydrogenlike one-electron ions of atomic number Z differ from those of hydrogen by a factor of Z^2. Predict the wavelength of the transition from n=2 to n=1.
by Emilie Hoffman 1E
Sun Oct 15, 2017 3:39 pm
Forum: Properties of Light
Topic: Lyman and Balmer Series Significance
Replies: 4
Views: 428

Re: Lyman and Balmer Series Significance

The most basic reason why they are important is because of what these values/groupings mean in the evaluation of other elements or molecules. So it's more of a "these people happened to be connected to the experiments that found that hydrogen reacted to these set of wavelengths" in terms o...
by Emilie Hoffman 1E
Mon Oct 02, 2017 4:52 pm
Forum: Empirical & Molecular Formulas
Topic: How to tell if Empirical and Molecular Formula are the same? [ENDORSED]
Replies: 2
Views: 257

Re: How to tell if Empirical and Molecular Formula are the same? [ENDORSED]

You have to check whether the molar mass that you derive from whatever empirical formula you calculate is equivalent to the molecular formula molar mass that the problem supplies. The empirical molar mass is either equal to or proportional to the molecular molar mass.
by Emilie Hoffman 1E
Mon Oct 02, 2017 4:47 pm
Forum: Empirical & Molecular Formulas
Topic: Problem F21
Replies: 2
Views: 202

Re: Problem F21

Dr. Lavelle explained today that most empirical/molecular formulas should have whole number stochiometric coefficients but that there can be exceptions when a certain amount of an element or compound was analyzed, though they would not appear in Chem 14A.

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