Search found 50 matches

by Deborah Cheng 1F
Thu Mar 15, 2018 11:09 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Half-cell concentrations
Replies: 1
Views: 95

Re: Half-cell concentrations

I had the same question, especially for concentration cells with differing concentrations of the same ions?
by Deborah Cheng 1F
Wed Mar 14, 2018 5:13 pm
Forum: *Enzyme Kinetics
Topic: Enzymes in rate law
Replies: 4
Views: 281

Re: Enzymes in rate law

I see, so if the catalysts are not necessarily always going to be in the rate determining step and therefore will not always show up in the rate law?
by Deborah Cheng 1F
Wed Mar 14, 2018 4:29 pm
Forum: *Enzyme Kinetics
Topic: Enzymes in rate law
Replies: 4
Views: 281

Enzymes in rate law

I believe Dr. Lavelle mentioned this in class but I just wanted to clarify, catalysts can be in the rate law?
by Deborah Cheng 1F
Sat Mar 10, 2018 1:58 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Energy barrier
Replies: 3
Views: 91

Re: Energy barrier

Or is it the other way around, higher energy barriers take more time to overcome and therefore it is the slower step?
by Deborah Cheng 1F
Sat Mar 10, 2018 1:31 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Energy barrier
Replies: 3
Views: 91

Energy barrier

We were told that slower steps have higher energy barriers, but why is that? Is there direct correlation with bond length?
by Deborah Cheng 1F
Sat Mar 10, 2018 1:24 pm
Forum: General Rate Laws
Topic: Fractional Rate Law [ENDORSED]
Replies: 4
Views: 211

Re: Fractional Rate Law [ENDORSED]

Yes I believe you are both correct, you would just calculate the order according to normal exponent addition/subtraction rules.
by Deborah Cheng 1F
Sun Mar 04, 2018 7:50 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.55 a
Replies: 3
Views: 122

Re: 15.55 a

K>1 means that products are favored, K<1 means the reactants are favored. Rate constant and equilibrium constant are proportional so when the equilibrium constant is large, rate constant of forward reaction is also large.
by Deborah Cheng 1F
Sun Mar 04, 2018 7:43 am
Forum: First Order Reactions
Topic: 15.23
Replies: 4
Views: 162

Re: 15.23

I believe it's because the equation of the reaction given is 2A B + C so we need to account for the ratio of 2 mol A used to 1 mol B produced.
by Deborah Cheng 1F
Thu Mar 01, 2018 2:45 pm
Forum: First Order Reactions
Topic: Fractional Order Reactions [ENDORSED]
Replies: 3
Views: 484

Fractional Order Reactions [ENDORSED]

So we've learned in class that there are 0, First, and Second Order reactions, but is it possible to have fractional order reactions, such has half or 1.5 order?
by Deborah Cheng 1F
Wed Feb 21, 2018 12:11 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Standard Reduction Potential
Replies: 3
Views: 107

Re: Standard Reduction Potential

I saw that too, and that's the answer I had originally put but I was confused because the answer from the solutions manual did not seem to follow that upper left/upper right trend. I tried doing it the method the solutions manual gave but the Cr and Zn didn't follow that rule either.
by Deborah Cheng 1F
Tue Feb 20, 2018 11:35 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Standard Reduction Potential
Replies: 3
Views: 107

Re: Standard Reduction Potential

I was also confused by this question, I looked at Appendix 2B to try to see if there was a trend in the reduction potentials from more positive to more negative, but for part A, the Zn and Cr seemed not to follow that pattern, unless I am reading the table incorrectly?
by Deborah Cheng 1F
Tue Feb 20, 2018 11:50 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Pt in Cell diagrams
Replies: 4
Views: 204

Pt in Cell diagrams

How do you know when it is necessary to put an electrode such as Pt on each end of the cell diagram?
by Deborah Cheng 1F
Tue Feb 13, 2018 8:13 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: ΔG° vs ΔG
Replies: 5
Views: 218

Re: ΔG° vs ΔG

What types of problems would you use ΔG? Do you have any examples, especially from homework problems?
by Deborah Cheng 1F
Tue Feb 13, 2018 6:25 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: ΔG° vs ΔG
Replies: 5
Views: 218

ΔG° vs ΔG

What is the difference between ΔG° and ΔG?
by Deborah Cheng 1F
Tue Feb 13, 2018 12:04 am
Forum: Calculating Work of Expansion
Topic: Reversible vs irreversible
Replies: 4
Views: 170

Re: Reversible vs irreversible

How can you see whether it it goes both ways from the equation though? Could you please clarify?
by Deborah Cheng 1F
Fri Feb 09, 2018 12:17 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: conceptual entropy questions
Replies: 5
Views: 194

Re: conceptual entropy questions

Smaller atoms have fewer particles like electrons, whereas larger atoms are composed of more particles. The more components there are, the higher the number of possible states and higher entropy.
by Deborah Cheng 1F
Fri Feb 09, 2018 12:12 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic Cell
Replies: 3
Views: 118

Galvanic Cell

What exactly is a galvanic cell? I know the definition Dr. Lavelle gave in class, about it changing chemical energy to electrical energy (such as a battery) but is the main takeaway that it makes use of redox reactions?
by Deborah Cheng 1F
Fri Feb 09, 2018 12:00 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Anode and cathode
Replies: 9
Views: 266

Anode and cathode

Is there a clear, visual way to identify the anode and cathode in a cell diagram without the labels?
by Deborah Cheng 1F
Thu Feb 01, 2018 3:23 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Standard State
Replies: 2
Views: 127

Re: Standard State

I would think the standard state would be given if it's a substance that is not as well known/not common to know. If it is not given it will probably be obvious, common substances we are used to seeing and working with.
by Deborah Cheng 1F
Thu Feb 01, 2018 3:05 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Reversible vs Irreversible
Replies: 1
Views: 91

Re: Reversible vs Irreversible

Entropy is a state function, so finding the change in entropy of an irreversible reaction can be done by calculating the path of a reversible reaction since we're just looking at the initial and final states. Entropy is independent of the path taken between the initial and final states which allows ...
by Deborah Cheng 1F
Thu Feb 01, 2018 2:29 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Midterm
Replies: 6
Views: 231

Re: Midterm

I agree with both of the above; I think there are more conceptual problems now compared to past years (based off of the past midterms and finals) so I'm definitely going to make sure to have those concepts down as well as practice the actual calculations. Test 1 might be a good example of how the re...
by Deborah Cheng 1F
Thu Jan 25, 2018 6:10 pm
Forum: Phase Changes & Related Calculations
Topic: enthaply
Replies: 3
Views: 146

Re: enthaply

Delta refers to the difference or change in a quantity. In this case, deltaH is the difference in the enthalpies of vapor and liquid. It seems that so far in this chapter we're given deltaH of vaporization/fusion and we're asked to do calculations from there using those values. For the homework prob...
by Deborah Cheng 1F
Thu Jan 25, 2018 5:57 pm
Forum: Calculating Work of Expansion
Topic: Homework 8.11
Replies: 6
Views: 253

Re: Homework 8.11

Dr. Lavelle lectured on this in class on Wednesday. He derived this equation from w=-Pex V. If you missed it in lecture, it's on pages 265-266 of the textbook. Hope this helps!
by Deborah Cheng 1F
Mon Jan 22, 2018 7:42 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 8.53
Replies: 1
Views: 96

8.53

In the solutions manual for question 8.53, it says to use q = C ∆T and later to divide by the number of moles n. However, the equation sheet from Dr. Lavelle's website gives q = n C ∆T. I'm confused as to why this is, can someone explain why the equations differ?
by Deborah Cheng 1F
Fri Jan 19, 2018 12:32 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.45 question
Replies: 4
Views: 134

Re: 8.45 question

The problem asks later on, "How much heat is absorbed in the reaction of 1.25 mol S8 at constant pressure?" showing that the reaction needs energy in the form of heat. Not all chemical reactions are exothermic; some such as this one are endothermic and require energy to take place.
by Deborah Cheng 1F
Fri Jan 19, 2018 12:25 pm
Forum: Phase Changes & Related Calculations
Topic: Calculating the Enthalpy of Vaporization
Replies: 2
Views: 137

Re: Calculating the Enthalpy of Vaporization

To solve this problem, I divided heat required, 4.76 kJ by the moles, 0.579 mol, resulting in 8.22 kJ/mol as my answer. Table 8.3 offers standard enthalpies of physical change for specific substances but I think we would use those values for different kinds of problems such as 8.41 when we're lookin...
by Deborah Cheng 1F
Fri Jan 19, 2018 10:27 am
Forum: Phase Changes & Related Calculations
Topic: q water=-q ice equation
Replies: 1
Views: 80

q water=-q ice equation

In discussion, we were given the equation q water=-q ice for a problem like 8.41. Can someone please explain how this equation works, especially the reason for the negative sign?
by Deborah Cheng 1F
Wed Jan 10, 2018 5:19 pm
Forum: Administrative Questions and Class Announcements
Topic: Reading for Chapter 8
Replies: 1
Views: 130

Re: Reading for Chapter 8

Box 8.2 is referring to the content on pages 304-305 of the textbook titled "Alternative Fuels."
by Deborah Cheng 1F
Wed Jan 10, 2018 5:11 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 5
Views: 154

Re: Bond Enthalpies

The change in enthalpy is just adding the energy released when a bond is broken (a positive value) and energy needed to form the bond (a negative value). Or if it helps you to remember, you can think of it as the difference between energy released when the bond is broken and the energy required to f...
by Deborah Cheng 1F
Wed Jan 10, 2018 4:37 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.55 typo?
Replies: 2
Views: 89

Re: 8.55 typo?

I think you are correct in balancing the equation, the solutions manual seems to address this by adding the 3/2 O2 like you mentioned, making it balanced.
by Deborah Cheng 1F
Sat Dec 09, 2017 12:13 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone pairs
Replies: 5
Views: 281

Re: Lone pairs

Yes, lone pairs can affect polarization. They result in regions of electron density which repel other regions of electron density. If they contribute to asymmetry in the molecule, the molecule will be polar.
by Deborah Cheng 1F
Sat Dec 09, 2017 12:08 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: pH Significant Figures
Replies: 1
Views: 109

pH Significant Figures

How should we go about using significant figures when reporting pH? Do the same rules apply, using the the number of places given in the problem?
by Deborah Cheng 1F
Sat Dec 02, 2017 5:06 pm
Forum: Amphoteric Compounds
Topic: Amphoteric and amphiprotic compounds
Replies: 4
Views: 259

Amphoteric and amphiprotic compounds

What is the difference between amphoteric and amphiprotic compounds?
by Deborah Cheng 1F
Sat Dec 02, 2017 5:04 pm
Forum: Calculating the pH of Salt Solutions
Topic: Calculating pH
Replies: 3
Views: 262

Re: Calculating pH

There is a negative sign so that we will arrive at positive values on the pH scale.
by Deborah Cheng 1F
Tue Nov 21, 2017 11:57 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Gas concentration
Replies: 2
Views: 123

Gas concentration

How do you find the concentration of a gas given the partial pressure?
by Deborah Cheng 1F
Tue Nov 21, 2017 11:50 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium constant
Replies: 4
Views: 155

Equilibrium constant

How do you find KP of a chemical reaction if the product is a solid?
by Deborah Cheng 1F
Fri Nov 17, 2017 3:23 pm
Forum: Sigma & Pi Bonds
Topic: Pi bonds
Replies: 6
Views: 499

Pi bonds

Why can't atoms bound by pi bonds rotate like atoms bound by sigma bonds?
by Deborah Cheng 1F
Fri Nov 17, 2017 3:12 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Ligands
Replies: 2
Views: 123

Ligands

Why are some ligands written backwards in the examples and diagrams shown in class?
by Deborah Cheng 1F
Mon Nov 13, 2017 8:33 pm
Forum: Hybridization
Topic: Hybrid orbitals
Replies: 2
Views: 97

Hybrid orbitals

How can you determine the number of hybrid orbitals?
by Deborah Cheng 1F
Mon Nov 13, 2017 8:29 pm
Forum: Octet Exceptions
Topic: Radicals
Replies: 2
Views: 192

Re: Radicals

I don't think they are stable because of the unpaired electron. They are highly reactive and only exist for a short amount of time.
by Deborah Cheng 1F
Sat Nov 04, 2017 3:39 pm
Forum: Ionic & Covalent Bonds
Topic: Ionic and Covalent Bonds
Replies: 9
Views: 373

Re: Ionic and Covalent Bonds

Ionic bonds join two ions, covalent bonds join two nonmetal atoms. If the electronegativity difference is >2 then it is considered an ionic bond, if electronegativity difference is <1.5 then it is considered a covalent bond.
by Deborah Cheng 1F
Sat Nov 04, 2017 3:32 pm
Forum: Resonance Structures
Topic: Resonance and energy
Replies: 2
Views: 146

Resonance and energy

Why does resonance lower the energy of a molecule?
by Deborah Cheng 1F
Sun Oct 29, 2017 3:52 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Ground state and electron configuration
Replies: 2
Views: 148

Ground state and electron configuration

How can you tell if an atom is in the ground state by looking at the electron configuration?
by Deborah Cheng 1F
Sun Oct 29, 2017 3:50 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Configuration of Gallium
Replies: 3
Views: 860

Re: Electron Configuration of Gallium

My TA explained that even though it is listed that way in the periodic table, 3d has lower energy when 4s is filled. Dr. Lavelle wants us to list them in order of energy level, so the correct electron configuration for Gallium would be [Ar]3d^10 4s^2 4p^1
by Deborah Cheng 1F
Sat Oct 21, 2017 9:31 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Solving
Replies: 2
Views: 145

Re: Solving

No, ≥ cannot "change" into = since they are different signs. However, in uncertainty problems, if it helps you to think of ≥ as = while solving, you can since you will never be dividing by a negative number (but you should still write/read ≥).
by Deborah Cheng 1F
Sat Oct 21, 2017 9:18 pm
Forum: Quantum Numbers and The H-Atom
Topic: The 4 Quantum Numbers [ENDORSED]
Replies: 5
Views: 511

Re: The 4 Quantum Numbers [ENDORSED]

n is the principal quantum number that indicates shell and energy level. The higher the value n, the larger the orbital is. l is the angular quantum number that indicates sub-shell and shape of the orbital (s, p, d, or f) m sub l is the magnetic quantum number that specifies the orientation of the o...
by Deborah Cheng 1F
Sat Oct 14, 2017 1:47 pm
Forum: Properties of Light
Topic: Electromagnetic Spectrum [ENDORSED]
Replies: 2
Views: 184

Re: Electromagnetic Spectrum [ENDORSED]

I don't think we have to know the specific wavelengths, but it would probably be a good to have a general idea of where each group should be, especially the order of shortest to longest wavelengths.
by Deborah Cheng 1F
Fri Oct 13, 2017 12:32 am
Forum: Properties of Light
Topic: Difference Between Photon and Electron
Replies: 5
Views: 361

Re: Difference Between Photon and Electron

I believe electrons are the negatively charged particles in the atom, and photons are packets of energy. Light is made up of photons, which can remove electrons from the surface of a metal if they have sufficient energy to overcome the threshold energy of the electron (as discussed in the photoelect...
by Deborah Cheng 1F
Thu Oct 05, 2017 11:58 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: G17
Replies: 2
Views: 206

Re: G17

I believe that is just due to significant figures from the given 250 mL and 0.20 M. Otherwise, I'm getting a similar answer to yours before rounding.
by Deborah Cheng 1F
Thu Oct 05, 2017 11:50 pm
Forum: Limiting Reactant Calculations
Topic: Limiting Reactant info [ENDORSED]
Replies: 6
Views: 374

Re: Limiting Reactant info [ENDORSED]

Not necessarily, sometimes you have to see how many moles are needed in the balanced reaction. For example, if 4 moles of substance A is needed while only 2 moles of substance B is needed for a reaction, but you have 7 moles of A and 5 moles of B, substance A is your limiting reagent even though the...

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