Search found 49 matches

by Rachel Wang
Sat Mar 17, 2018 5:32 pm
Forum: Calculating Work of Expansion
Topic: What w equation to use
Replies: 5
Views: 356

Re: What w equation to use

Kristin Ishaya 1A wrote:Was question 4A from the midterm a reversible expansion problem? I didn't know which formula to use so I did it both ways.


I was confused too, actually, but because pressure was constant I think it's w=-PdeltaV
by Rachel Wang
Fri Mar 16, 2018 7:13 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Fast or Slow
Replies: 8
Views: 286

Re: Fast or Slow

So far the instances I've seen are: 1. If given a free energy vs time graph, the step with higher activation energy (higher camelback) is the rate-limiting step. 2. If one of the steps involves breaking bonds and the other doesn't, breaking bonds requires more energy. 3. If given the rate law and as...
by Rachel Wang
Fri Mar 16, 2018 7:09 pm
Forum: Zero Order Reactions
Topic: Units of k
Replies: 12
Views: 589

Re: Units of k

0 order: M/s or mol/L.s

1st order: 1/s

2nd order: 1/M.s or L/mol.s

3rd order: 1/M^2.s or L^2/mol^2.s

etc.
by Rachel Wang
Fri Mar 16, 2018 7:07 pm
Forum: Second Order Reactions
Topic: 3rd order?
Replies: 7
Views: 560

Re: 3rd order?

It's very rare for 3rd order rxns to occur unless it's the overall rxn's order. The units are 1/M^2.s
by Rachel Wang
Fri Mar 16, 2018 7:05 pm
Forum: *Enzyme Kinetics
Topic: Catalysts and Intermediates
Replies: 5
Views: 561

Re: Catalysts and Intermediates

Intermediates are not present at the beginning of the rxn and are instead produced during the rxn. They are always consumed by the end of the rxn. Catalysts are present at the beginning AND the end as they are not consumed by the rxn. They speed up the rxn but are not present in the overall rxn equa...
by Rachel Wang
Fri Mar 16, 2018 7:02 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Negative activation energy?
Replies: 2
Views: 110

Negative activation energy?

Is it possible to get a negative activation energy cuz I got one for Lyndon Bui's Practice Final 2018 Q.8D?
by Rachel Wang
Fri Mar 16, 2018 6:54 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Q vs. K
Replies: 8
Views: 394

Re: Q vs. K

K is the equilibrium constant. Q is the constant when the rxn isn't at equilibrium and when compared to K can predict which way the rxn will proceed at that particular state. They are calculated the same way.
by Rachel Wang
Fri Mar 16, 2018 6:53 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Cell Concentration
Replies: 3
Views: 241

Re: Cell Concentration

A concentration cell has the same electrode/element for both half cells BUT with different concentrations. All concentration cells have E(nought) = 0. Use the Nernst equation E = Eo - 0.05916 V/n x log Q or E = 0 - 0.05916 V/n x log Q. You get Q from the overall redox rxn, which usually has the smal...
by Rachel Wang
Fri Mar 16, 2018 6:48 pm
Forum: Balancing Redox Reactions
Topic: Test 2 #1
Replies: 6
Views: 303

Re: Test 2 #1

Given the reaction: C (s) + O 2 (g) --> CO 2 (g) Why is the oxidation state of C in CO 2 4+ and why is O 2 the species that is reduced, when their oxidation states as reactants and products are essentially the same? C has an oxidation state of 0 and is oxidized to an oxidation state of 4+ because O...
by Rachel Wang
Fri Mar 16, 2018 6:45 pm
Forum: Balancing Redox Reactions
Topic: Winter 2013 final Q4
Replies: 9
Views: 417

Re: Winter 2013 final Q4

Kinda stumped too but I thinkkkkk it's because Fe has an oxidation state of Fe0 -> Fe+2 + 2e-. And because there are 2 of Fe and 2 Fe(OH)2, 2x2e- = 4e- = n?
by Rachel Wang
Fri Mar 16, 2018 6:37 pm
Forum: Balancing Redox Reactions
Topic: Balancing in a basic solution
Replies: 4
Views: 2487

Re: Balancing in a basic solution

Balancing in basic is same as acidic, just add OH- to both sides to get rid of the H+, then cancel out the resulting H2O's.
by Rachel Wang
Fri Mar 16, 2018 6:34 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: A?
Replies: 6
Views: 426

A?

Does A stay the same even if activation energy or k changes, as long as temperature is the same?
by Rachel Wang
Fri Mar 16, 2018 6:29 pm
Forum: Calculating Work of Expansion
Topic: What w equation to use
Replies: 5
Views: 356

What w equation to use

I'm a little confused under what conditions do we use

W = - P x ∆V
or
w = -nRT ln V2
by Rachel Wang
Fri Mar 16, 2018 6:28 pm
Forum: Calculating Work of Expansion
Topic: Midterm 4a
Replies: 4
Views: 233

Re: Midterm 4a

I assumed I use w=-PdeltaV when it's isothermal and isobaric.
by Rachel Wang
Fri Mar 16, 2018 6:27 pm
Forum: Calculating Work of Expansion
Topic: Midterm Q3B
Replies: 7
Views: 336

Re: Midterm Q3B

Copper pots would be most energy efficient b/c it has the lowest heat capacity constant and thus would heat up faster for an overall lower value of q.
by Rachel Wang
Fri Mar 16, 2018 6:21 pm
Forum: Calculating Work of Expansion
Topic: Conversion of R
Replies: 7
Views: 368

Re: Conversion of R

I've found that I generally use 8.314J/mol.K because it cancels out n (mol) and T(K).
by Rachel Wang
Fri Mar 16, 2018 6:15 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: State functions?
Replies: 9
Views: 384

State functions?

What is an example of a state function?

Is enthalpy or entropy a state function?
by Rachel Wang
Fri Mar 16, 2018 5:27 pm
Forum: Balancing Redox Reactions
Topic: Oxidation state
Replies: 7
Views: 257

Re: Oxidation state

104922499 1F wrote:why is O3's oxidation state 0?


It's a triatomic gas with the same element -> no oxidation state
by Rachel Wang
Fri Mar 16, 2018 5:25 pm
Forum: Balancing Redox Reactions
Topic: Basic conditions with OH
Replies: 3
Views: 123

Re: Basic conditions with OH

-log10H = pH.
14-pH = pOH.
-logpOH = pOH
by Rachel Wang
Fri Mar 16, 2018 5:19 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst Equation
Replies: 2
Views: 103

Re: Nernst Equation

I've seen 0.0257 as the numerator before and I think it's when they calculate RT/F at T=298K. However the eq is most likely lnQ instead of logQ.
by Rachel Wang
Fri Mar 16, 2018 5:16 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Predicting if a metal will be dissolved in a solution
Replies: 2
Views: 122

Re: Predicting if a metal will be dissolved in a solution

Proceed about problem as normal; find E(nought) and plug into Nernst. If deltaG is positive the rxn is nonspont and thus the metal won't dissolve. If deltaG is negative the rxn is spont and thus the metal will dissolve.
by Rachel Wang
Fri Mar 16, 2018 5:14 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Weird Cell Diagram
Replies: 1
Views: 103

Weird Cell Diagram

On a practice final exam the cell diagram is

2Ag(s) + Br2(g) -> 2AgBr(s)

The cell diagram is Ag(s)|AgBr(s)||Br-(aq)|Br2(g)|Pt(s)

I'm a little confused where the Br-(aq) came from?
by Rachel Wang
Fri Mar 16, 2018 5:11 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test #2 question 6
Replies: 2
Views: 118

Re: Test #2 question 6

You cannot assume in this case. You have to find the Ecell that would be positive first, flip whichever one, and then identify the element that is reduced as the oxidizing agent.
by Rachel Wang
Fri Mar 16, 2018 4:58 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Mnemonics
Replies: 1
Views: 85

Re: Mnemonics

Not sure if this helps but there's

Red Cat - Reduction occurs at Cathodes
An Ox - Oxidation occurs at Anodes
by Rachel Wang
Fri Mar 16, 2018 4:57 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Test #2 question 4
Replies: 4
Views: 137

Re: Test #2 question 4

For the equation Ecell = Ecathode - Eanode, it assumes you have not already flipped the sign of the anode. Therefore Ecell = -1.18-(-1.79).
However, you made the equation E=+1.79. In this case you have already flipped the sign and hence the eq is -1.18+1.79.
by Rachel Wang
Fri Mar 16, 2018 4:53 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.13 B
Replies: 3
Views: 127

Re: 14.13 B

The electrode is a solid metal that can conduct electricity. I2 is a solid halogen and therefore unable to conduct electricity -> hence the platinum.
by Rachel Wang
Fri Mar 16, 2018 4:50 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: porous disk
Replies: 3
Views: 131

Re: porous disk

A porous disk is also known as a salt bridge. It allows ions to balance charges in the two half-cells when electrons are being exchanged and offsetting the charges.
by Rachel Wang
Thu Mar 15, 2018 4:49 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Midterm Question
Replies: 4
Views: 262

Re: Midterm Question

In this question they provided heat capacity constants in both J.K-1.mol-1 and J.C-1.g-1. You'll have to pay attention to which temperature the use based on which heat capacity constant you use. Personally I find it very helpful to write down the units as you are solving instead of only incorporatin...
by Rachel Wang
Mon Mar 05, 2018 8:21 pm
Forum: First Order Reactions
Topic: 15.23C
Replies: 6
Views: 306

15.23C

The problem states :
Determine the rate constant for each of the following
first-order reactions, in each case expressed for the rate of loss
of A:

But part C) has the rxn equation : (c) 2 A -> B + C

Isn't this a second order, not a first order, rxn in respect to A?
by Rachel Wang
Sun Jan 28, 2018 5:40 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Change in Temperature Equation?
Replies: 2
Views: 117

Change in Temperature Equation?

In Hmwk question 9.7 we used the equation
∆S = n C (ln T2/T1)
but in question 9.13 we use the equation
∆S = n R (ln T2/T1).

When do we know which one to use?
Thanks!
by Rachel Wang
Fri Dec 08, 2017 11:06 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Le chateliers principle
Replies: 3
Views: 259

Re: Le chateliers principle

le Chatelier's principle is the idea that if a restraint is applied, the equilibrium will shift so as to counteract the effect of the restraint. Adding products will shift the rxn left; adding reactants will shift the rxn right. Adding pressure (decreasing volume) will shift rxn to side with less ga...
by Rachel Wang
Fri Dec 08, 2017 10:30 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Reaction Quotient
Replies: 3
Views: 252

Re: Reaction Quotient

The reaction quotient is the same equation as K, but for any time in the reaction - not just at equilibrium. Compare Q to K to predict which direction the reaction will proceed. If Q<K, reaction proceeds foreward and makes more products. If K<Q, reaction goes backwards and makes more reactants.
by Rachel Wang
Fri Dec 08, 2017 10:25 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Endothermic v. Exothermic Reactions
Replies: 9
Views: 840

Re: Endothermic v. Exothermic Reactions

Endothermic: requires heat to carry forward the reaction and therefore deltaH is on the left. Increasing heat in this case would produce more products. Exothermic: releases heat once reaction has occurred and therefore deltaH is on the right. Increasing heat causes equilibrium to favor reactants and...
by Rachel Wang
Fri Dec 08, 2017 10:23 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Pressure Effect
Replies: 3
Views: 164

Re: Pressure Effect

Assuming A is also a gas, increasing the pressure (decreasing volume) would shift the equilibrium to the side with less gas molecules - in this case left.
Decreasing the pressure (increasing volume) would shift the equilibrium to the side with more gas molecules - in this case right.
by Rachel Wang
Fri Dec 08, 2017 10:19 pm
Forum: Naming
Topic: Names of Polydentates
Replies: 2
Views: 147

Re: Names of Polydentates

It's good to memorize these three:

ethylenediamine (en) - bidentate
diethylenetriamine (dien) - tridentate
ethylenediaminetetraacetato (edta) - hexdentate
by Rachel Wang
Fri Dec 08, 2017 10:16 pm
Forum: Lewis Structures
Topic: Expanded octet or not?
Replies: 1
Views: 129

Expanded octet or not?

Assuming formal charge is the same, do central atoms n=3 and up (ie nitrogen) prefer to have an extended octet or not? Does the extended octet expend less energy in ground state?
by Rachel Wang
Fri Dec 08, 2017 10:11 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Different Shapes
Replies: 4
Views: 315

Re: Different Shapes

Image
by Rachel Wang
Fri Dec 08, 2017 10:08 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Dipole Moment
Replies: 2
Views: 174

Re: Dipole Moment

Usually if it's symmetrical we can assume they cancel out. :^)
by Rachel Wang
Fri Dec 08, 2017 10:06 pm
Forum: Octet Exceptions
Topic: Midterm Question 8B
Replies: 2
Views: 208

Re: Midterm Question 8B

The lone electron is on Carbon because oxygen is more electroegative and therefore is more likely to attract enough e- to fill its octet.
by Rachel Wang
Fri Dec 08, 2017 10:03 pm
Forum: Hybridization
Topic: Chemical reasoning for hybridization
Replies: 2
Views: 155

Chemical reasoning for hybridization

I can tell what kind of hybridization an atom has, but I don't understand the chemical reasoning behind hybridization.
by Rachel Wang
Fri Dec 08, 2017 9:57 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Determining whether ligand is mono-, bi-, or polydentate
Replies: 3
Views: 247

Re: Determining whether ligand is mono-, bi-, or polydentate

Look for the number of nitrogens and oxygens with a negative charge. Usually they have lone pairs for additional bonding.
by Rachel Wang
Fri Dec 08, 2017 9:56 pm
Forum: Biological Examples
Topic: Biological Importance
Replies: 2
Views: 254

Re: Biological Importance

chromium - assists insulin in control of blood sugar
iron - myoglobin, hemoglobin, e- transfer in the oxidation of carbohydrates, proteins, fats (respiratory chain)
cobalt - vitamin B12
Mn, Ni, Cu, Zn - critical for enzyme functions
by Rachel Wang
Fri Dec 08, 2017 9:52 pm
Forum: Naming
Topic: What is delocalized bonding? [ENDORSED]
Replies: 5
Views: 362

Re: What is delocalized bonding? [ENDORSED]

Delocalized e- bonding occur everytime there's resonance involved, esp. evident with the 6 carbon ring.
by Rachel Wang
Mon Oct 16, 2017 10:44 pm
Forum: Photoelectric Effect
Topic: Post- Module Assessment #24
Replies: 3
Views: 171

Re: Post- Module Assessment #24

I think UV light is typically used because it has sufficient energy (higher frequency than visible light) to eject e-.
by Rachel Wang
Mon Oct 16, 2017 10:42 pm
Forum: Photoelectric Effect
Topic: 1.33 Part A
Replies: 4
Views: 231

1.33 Part A

Here's the question: The velocity of an electron that is emitted from a metallic surface by a photon is 3.6 * 10^3 km/s. (a) What is the wavelength of the ejected electron? I tried doing this question two ways: once using the de Broglie equation, which gave me the right answer (2.0*10^-10m), and onc...
by Rachel Wang
Fri Oct 13, 2017 1:44 pm
Forum: Photoelectric Effect
Topic: hw problem 1.33 c
Replies: 2
Views: 344

Re: hw problem 1.33 c

You find in part a) the kinetic energy of the ejected e-: 5.909x10^-18 J. You find in part b) the work function, aka threshold energy because it's the minimum required energy to eject the electron, not the incident light. To find the energy of the incident light, E - 1.658x10^-17 = 5.909x10^=18 E = ...
by Rachel Wang
Fri Oct 13, 2017 12:13 pm
Forum: Properties of Light
Topic: Balmer Vs. Lyman
Replies: 12
Views: 770

Re: Balmer Vs. Lyman

Balmer series is the visible region of the light spectrum and Lyman is the UV region. When the electron jumps from quantum level n=2 to n=1, this releases much more energy than when it jumps from n=3 to n=2. Lyman's principle quantum level is n=1 because UV light has higher energy. Balmer's principl...
by Rachel Wang
Thu Oct 05, 2017 5:51 pm
Forum: Limiting Reactant Calculations
Topic: M11
Replies: 5
Views: 636

Re: M11

I did it a little differently from the book but got similar answers (around .05 off - not sure if that's a huge problem), so hope this helps c: You have to find the limiting reactant of P4O6 first. I converted 5.77g P4 to moles: The molar mass of P4 is 123.88g 5.77g/123.88g = 0.0466 mol P4. The rati...
by Rachel Wang
Thu Oct 05, 2017 5:09 pm
Forum: Balancing Chemical Reactions
Topic: Fundamentals H.21
Replies: 2
Views: 495

Fundamentals H.21

Here is the question: H.21 The psychoactive drug methamphetamine (“speed”), which is sold as the prescription medication Desoxyn, C10H15N, undergoes a series of reactions in the body; the net result of these reactions is the oxidation of solid methamphetamine by oxygen gas to produce carbon dioxide ...

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