Search found 47 matches

by Christine Van 2E
Fri Mar 11, 2016 7:52 pm
Forum: *Cyclohexanes (Chair, Boat, Geometric Isomers)
Topic: cis v trans
Replies: 1
Views: 310

Re: cis v trans

Hi! To determine if a cyclohexane has cis or trans, there must be 2 and only 2 substituents in it. After that, if the two substituents both have the same direction (both up or oth down), then it is cis. If the two substituents have opposite directions (one up, one down or one down, one up), then it ...
by Christine Van 2E
Tue Mar 08, 2016 10:29 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Winter 2011 final question 1
Replies: 2
Views: 323

Re: Winter 2011 final question 1

Hi!

Since you are solving for grams, it wouldn't make sense to use a negative ΔH because you would get negative grams, so you use positive ΔH instead.

Hope that helps!
by Christine Van 2E
Fri Mar 04, 2016 11:15 am
Forum: *Nucleophilic Substitution
Topic: Nucleophillic Strength
Replies: 1
Views: 518

Re: Nucleophillic Strength

Hi!

Nucleophilic strength increases as you go down a column because the atoms get bigger. Bigger atoms mean the electron cloud is more polarizable, thus making it easier to donate electrons.

Hope that helps!
by Christine Van 2E
Fri Mar 04, 2016 11:06 am
Forum: *Alkanes
Topic: Cycloalkanes
Replies: 1
Views: 257

Re: Cycloalkanes

Hi!

Yes, if you draw one as cis or trans, they count as separate structures.

Hope that helps!
by Christine Van 2E
Sat Feb 27, 2016 3:50 pm
Forum: *Cycloalkanes
Topic: Alphabetising Substituents
Replies: 1
Views: 246

Alphabetising Substituents

Hi! I am a bit confused with the alphabetising of IUPAC names for organic molecules. I know that di, tri, etc don't count when alphabetising substituents. I think Professor Casey said that Iso and Neo do count in the alphabetical order, but not Tert and Sec (correct me if I'm wrong). What if we had ...
by Christine Van 2E
Thu Feb 25, 2016 8:23 pm
Forum: *Cycloalkanes
Topic: Number placement
Replies: 1
Views: 228

Re: Number placement

Hi! If you are referring to the example in the course reader on page 99, and had numbered it the other way, it would be 1-ethyl-3-methyl-4-propylcyclohexane, not 1-ethyl-2-methyl-4-propylcyclohexane. The three in 1-ethyl-3-methyl-4-propylcyclohexane is bigger than two, so we go with the overall smal...
by Christine Van 2E
Thu Feb 25, 2016 8:20 pm
Forum: *Electrophilic Addition
Topic: Course Reader Example pg 85
Replies: 1
Views: 215

Re: Course Reader Example pg 85

Hi!

The double bond acts as the nucleophile because the double bond has both a sigma and pi bond within it, making it very electron rich.

Hope that helps!
by Christine Van 2E
Tue Feb 23, 2016 11:24 pm
Forum: *Organic Reaction Mechanisms in General
Topic: How to determine slow step?
Replies: 1
Views: 2023

Re: How to determine slow step?

Hi! In the electrophilic addition reaction, the slow step is the first step because you have to break 2 bonds (H-Br and C=C), which requires energy and form only 1 bond (C-H), which releases energy. Step 2 only forms 1 bond (C-Br), which also releases energy. Since you break more bonds than forming ...
by Christine Van 2E
Sat Feb 20, 2016 10:20 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 2016 Midterm Q5C
Replies: 1
Views: 275

Re: 2016 Midterm Q5C

Hi! This question gives us this reaction: ATP+H_{2}O\rightleftharpoons ADP+HPO_{4}^{2-} Since we know that K=\frac{[Products]}{[Reactants]} and Q=\frac{[Products]}{[Reactants]} , for this problem, the expression for both K and Q =\frac{[ADP][HPO_{4}^{2-}]}{[ATP][H2O]} . It says that the [ATP] is qua...
by Christine Van 2E
Fri Feb 19, 2016 6:56 pm
Forum: First Order Reactions
Topic: Integration of rate
Replies: 1
Views: 273

Re: Integration of rate

Hi! Since the course reader is deriving an integrated rate law for the reaction: A--->P, that means that the coefficient of the reactant, A, is 1. That means that a=1. So, when you plug in a=1 to -1/a, you get -\frac{1}{1} \frac{\mathrm{d[A]} }{\mathrm{d} x}=k[A] or just -\frac{\mathrm{d} [A]}{\math...
by Christine Van 2E
Sun Feb 14, 2016 12:26 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Rate Constant Units
Replies: 3
Views: 2273

Re: Rate Constant Units

Hi! Yes, the units of the rate constant, k, changes from zero, first or second order reactions. In a zero order reaction, the rate constant unit is typically M/sec (Note: the time can be in sec, min, days, years, etc). In a first order reaction, it is 1/sec (again, time can be any units). In a secon...
by Christine Van 2E
Tue Feb 09, 2016 8:28 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Winter 2014 Midterm #5c
Replies: 1
Views: 292

Re: Winter 2014 Midterm #5c

Hi!

Yes, I believe the E stands for the emf in electrochemistry, which is not a state function. Internal energy would be a U.

Hope that helps!
by Christine Van 2E
Mon Feb 08, 2016 8:11 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Midterm 2013 - Q2C
Replies: 1
Views: 245

Re: Midterm 2013 - Q2C

Hi! Specific heat capacities tell us how much heat is required to raise the temperature of 1 gram of a substance by 1°C. If the specific heat capacity is small, then that means it takes less energy to change its temperature. Thus, that will also mean that it will take less energy to cool that same o...
by Christine Van 2E
Thu Feb 04, 2016 10:41 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Abbreviated Galvanic Cell
Replies: 1
Views: 181

Re: Abbreviated Galvanic Cell

Hi!

I believe that the anode will always most likely be written on the left side and cathode on the right in a cell diagram. It's a convention. For actual drawings of galvanic cells, however, they can be switched.

Hope that helps!
by Christine Van 2E
Wed Feb 03, 2016 6:19 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram Question
Replies: 1
Views: 299

Cell Diagram Question

Hi! There's a homework question in the textbook, #14.13 that I am confused on with writing the cell diagram for part (b). The question states: Write the half-reactions, the balanced equation for the cell reaction, and the cell diagram for each of the following skeletal equations: (b) Ce4+(aq) + I-(a...
by Christine Van 2E
Tue Jan 26, 2016 6:40 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Homework 9.35 - More Particles?
Replies: 1
Views: 276

Re: Homework 9.35 - More Particles?

Hi! When a molecule is diatomic, such as O2, N2, etc, they come in pairs. As opposed to monatomic particles which consist of just one particle, diatomic molecules would occupy less positions. This is because if you have 6 monatomic particles, that would mean you have 3 diatomic particles. There woul...
by Christine Van 2E
Tue Jan 19, 2016 11:32 pm
Forum: Phase Changes & Related Calculations
Topic: Determining whether a reaction is exothermic or endothermic
Replies: 2
Views: 381

Re: Determining whether a reaction is exothermic or endother

Hi! Besides calculating the enthalpy change directly, you can tell the reaction is endothermic just by looking at its states. In the reaction: C(s) + H2O(g) ---> CO(g) + H2(g) the reactant has one solid and the products are all gases. This means the reaction will REQUIRE energy to convert the solid ...
by Christine Van 2E
Tue Jan 19, 2016 11:24 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Compression
Replies: 2
Views: 265

Re: Compression

Hi! When gas in a system is compressed, work is done ON the system. When gas expands, work is done BY the system. Work is positive when gas in a system is compressed because you put energy into the system (the system gains energy). Mathematically, with the work equation, w=-PΔV, when you compress a ...
by Christine Van 2E
Wed Jan 13, 2016 12:09 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.73 Bond Enthalpy of Benzene
Replies: 4
Views: 2968

Re: 8.73 Bond Enthalpy of Benzene

Hi! Benzene has a ring structure of 6 carbons and one hydrogen attached to each carbon. Each C-C bond in the ring structure has resonance, and its bond enthalpy can be found in the tables. The bond enthalpy for C-C with a dashed line on top (indicating resonance) is 518 kJ/mol. For this problem in p...
by Christine Van 2E
Wed Jan 13, 2016 11:58 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Work of expansion question?
Replies: 3
Views: 408

Re: Work of expansion question?

Hi!

There's a negative in front of the equation because when you do work, you lose energy.

Hope that helps!
by Christine Van 2E
Tue Jan 12, 2016 7:42 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Phase changes
Replies: 1
Views: 222

Re: Phase changes

Hi!

The 44.0 kJ/mol can be found in Table 8.3 on page 284 of the chemistry textbook. It's the amount of heat released when gaseous water condenses to the liquid phase at 25 °C.

Hope that helps!
by Christine Van 2E
Tue Jan 12, 2016 7:33 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Homework Problem 8.67 - Part d
Replies: 1
Views: 231

Re: Homework Problem 8.67 - Part d

Hi! In the solutions manual, it says 6 mol C-C bonds, but they didn't print the one with a dashed line included (maybe because they didn't know how), but it does say resonance next to it. Since resonance indicates that there is a partial double bond character, all C-C bonds in benzene are the same l...
by Christine Van 2E
Sun Jan 10, 2016 8:45 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Molar heat capacity
Replies: 3
Views: 502

Re: Molar heat capacity

Hi! So for part (a) of this problem, you would use the equation: q=n*Cp*ΔT The Cp is the molar heat capacity of a gas at constant pressure. In the solutions manual, it states that this is (5/2)R. So using the above equation, you would convert the given grams to moles of Kr and multiply that by (5/2)...
by Christine Van 2E
Sun Jan 10, 2016 8:34 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies~Clarification
Replies: 2
Views: 285

Re: Bond Enthalpies~Clarification

Hi! Since breaking bonds is an endothermic process, it is a positive value. Forming new bonds is an exothermic process, so it's a negative value. When using bond enthalpies to calculate the standard enthalpy of a reaction, you would use this: Σ(bonds broken) + Σ(bonds formed) For the bonds broken, y...
by Christine Van 2E
Sat Jan 09, 2016 10:57 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard Enthalpy
Replies: 1
Views: 201

Re: Standard Enthalpy

Hi! Professor Lavelle was referring to the standard enthalpy of formations for compounds in a reaction. You can find these values in the back of the chemistry textbook in Appendix 2A. These values can be used to find the standard enthalpy of a reaction by using the formula: ΔH°rxn = Σ ΔH°f (products...
by Christine Van 2E
Sat Dec 05, 2015 12:23 am
Forum: Calculating the pH of Salt Solutions
Topic: Why do we assume complete dissociation of salts?
Replies: 1
Views: 916

Re: Why do we assume complete dissociation of salts?

Hi! We assume that the initial concentration of the acidic/basic ion as equal to its concentration if the salt completely dissociated because usually the salt contains a spectator ion that doesn't change the pH of the solution. For example, if given the [NH4Cl] to be 0.100 M, we know that NH4Cl in w...
by Christine Van 2E
Sat Dec 05, 2015 12:14 am
Forum: Lewis Acids & Bases
Topic: Ka = 10^-14 / Kb
Replies: 1
Views: 286

Re: Ka = 10^-14 / Kb

Hi! You would need to use this formula if you are given the Ka value for a chemical reaction, but the reaction isn't acidic. If the reaction forms an alkaline solution (produces OH- ions), then you would need the Kb to calculate for the [OH-] and use that to find the pOH then the pH, if told. Hope t...
by Christine Van 2E
Mon Nov 23, 2015 7:07 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Determining pH given 2 Ka Values
Replies: 2
Views: 5464

Determining pH given 2 Ka Values

Hi! There's a homework problem in Chapter 12 #77 that says: A 3.38-g sample of the sodium salt of alanine, NaCH3CH(NH2)CO2, is dissolved in water, and then the solution is diluted to 50.0 mL. For alanine, Ka1=4.57 X 10^-3. Ka2=1.30 x 10^-10. What is the pH of the resulting solutions? I looked in the...
by Christine Van 2E
Sat Nov 21, 2015 1:19 pm
Forum: Bronsted Acids & Bases
Topic: pH of Water at Body Temperature
Replies: 1
Views: 828

pH of Water at Body Temperature

Hi! I think there's a mistake in the solutions manual for a homework problem in Chapter 12 #23 Part (a) that states: The value of Kw for water at body temperature (37 °C) is 2.1 x 10^-14. (a) What is the molarity of H3O+ ions and the pH of neutral water at 37 °C? I found the molarity of the H3O+ ion...
by Christine Van 2E
Tue Nov 17, 2015 3:44 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sig Figs for Chemical Equilibrium Calculations
Replies: 2
Views: 383

Re: Sig Figs for Chemical Equilibrium Calculations

Hi Jonathan! Thanks for your reply! So you said that the sig figs depend on the problem and I understand that, but there are some problems that don't always have the same number of sig figs as the numbers given in the problem. Like in the green workbook Fall 2014 quiz preparation 3 #10, the problem ...
by Christine Van 2E
Mon Nov 16, 2015 8:53 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Sig Figs for Chemical Equilibrium Calculations
Replies: 2
Views: 383

Sig Figs for Chemical Equilibrium Calculations

Hi! There's a homework problem in Ch.11 #93 part (a), where I am confused about the sig figs for the concentration of NO2. The problem goes: In an experiment, 0.020 mol NO2 was introduced into a 1.00-L flask and the reaction 2NO2(g) <---> N2O4(g) was allowed to come to equilibrium at 298 K. (a)Using...
by Christine Van 2E
Mon Nov 09, 2015 10:19 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Effects of Pressure on Chemical Reactions
Replies: 1
Views: 404

Effects of Pressure on Chemical Reactions

Hi! There is a homework problem in chapter 11 #73 that says: State whether reactants of products will be favored by an increase in the total pressure (resulting from compression) on each of the following equilibria. If there is no change, explain why that is so. I understood parts (a), (c), and (d),...
by Christine Van 2E
Fri Nov 06, 2015 8:37 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Calculating K Using Gibbs Free Energy
Replies: 1
Views: 230

Calculating K Using Gibbs Free Energy

Hi! So there's a homework problem in chapter 11 #29 that says: If Q=1.0 for the reaction N2(g) + O2(g) <--> 2NO(g) at 25 °C, will the reaction have a tendency to form products or reactants, or will it be at equilibrium? I know that we will need to compare the Q to K and then get an answer from that,...
by Christine Van 2E
Wed Nov 04, 2015 10:35 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Molecular Orbital Diagram for NF
Replies: 1
Views: 1583

Molecular Orbital Diagram for NF

Hi! I have a quick question about the molecular orbital diagram for NF. Lavelle said that whenever we have a heteronuclear molecule, if one or both atom(s) has Z<8, then we would use the diagram where the pi px and pi py are lower than the Sigma pz. However, I've also heard of a method where you can...
by Christine Van 2E
Wed Oct 28, 2015 10:57 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Electron Configuration
Replies: 2
Views: 373

Re: Electron Configuration

Hi!

I think Lavelle said that either way is fine.

Hope that helps!
by Christine Van 2E
Wed Oct 28, 2015 10:48 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: MO Energy Level Diagram
Replies: 1
Views: 245

Re: MO Energy Level Diagram

Hi! For homonuclear diatomic molecules with a nuclear charge greater or equal to 8 (Z>=8), you would use the molecular orbital diagram that has sigma-bonds lower in energy than pi-bonds. For homonuclear diatomic molecules with a nuclear charge less than 8 (Z<8) or heteronuclear diatomic molecules wi...
by Christine Van 2E
Tue Oct 20, 2015 7:36 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Resonance Stucture Stability
Replies: 1
Views: 190

Re: Resonance Stucture Stability

Hi! The electrons would be removed from the equatorial position because it will only affect 2 regions of electron density (at each pole). If you were to remove electrons from the poles, it would affect 3 regions of electron density (at the 3 equatorial positions), which takes more energy because the...
by Christine Van 2E
Sat Oct 17, 2015 11:45 am
Forum: Bond Lengths & Energies
Topic: Bond Strength
Replies: 1
Views: 316

Re: Bond Strength

Hi!

Shorter bonds are the strongest because the atoms are closer together, so it will take more energy in order to break bonds that are tightly held if they are closer to each other.

Hope that helps!
by Christine Van 2E
Sat Oct 17, 2015 11:39 am
Forum: Lewis Structures
Topic: HW 3.39 part (b) and (c)
Replies: 2
Views: 395

Re: HW 3.39 part (b) and (c)

Hi! The potassium ions aren't bonded to the phosphorus atom because these are ionic compounds, not molecules(where electrons are shared). Ionic compounds don't usually have paired electrons because the anion usually takes electrons from the cation. In this case, the phosphorus(anion) takes electrons...
by Christine Van 2E
Sun Oct 11, 2015 12:25 pm
Forum: Administrative Questions and Class Announcements
Topic: Green Workbook Quizzes
Replies: 2
Views: 479

Green Workbook Quizzes

Hi!

I was wondering, only the Quiz 1 that has no answers given in the back is the one that will be graded and must be done in pen right? Not the other two from Fall 2013 and Fall 2014 with the answers?

Thank you!
by Christine Van 2E
Sat Oct 10, 2015 5:44 pm
Forum: Administrative Questions and Class Announcements
Topic: Green Workbook (Pen or Pencil)
Replies: 2
Views: 358

Re: Green Workbook (Pen or Pencil)

Hi!

So only the quiz that says "Hand in your workbook to your TA before taking Quiz 1 in discussion section" is graded, correct? Not the other two from Fall 2013 and Fall 2014?

Thank you!
by Christine Van 2E
Fri Oct 09, 2015 4:48 pm
Forum: Photoelectric Effect
Topic: Photoelectric Effect Question
Replies: 1
Views: 318

Re: Photoelectric Effect Question

A. No, because the experimental light is not acting like a wave. In the photoelectric effect experiment, scientists tried to eject electrons out of a metal surface by using a long wavelength light, but it didn't work. So then, they tried to do it using a higher intensity, long wavelength light becau...
by Christine Van 2E
Fri Oct 09, 2015 4:32 pm
Forum: Administrative Questions and Class Announcements
Topic: Green Workbook (Pen or Pencil)
Replies: 2
Views: 358

Green Workbook (Pen or Pencil)

Does anyone know if the green workbook needs to be done in pen or can it be done in pencil? I think the quizzes and exams have to be done in pen, so I was wondering if that was the same for the workbook as well.

Thanks!
by Christine Van 2E
Fri Oct 09, 2015 4:20 pm
Forum: Limiting Reactant Calculations
Topic: Limiting Reactant Question
Replies: 7
Views: 741

Re: Limiting Reactant Question

Hi Meredith! The mole ratio comes from the stoichiometric coefficients of the balanced chemical equation, which in this case is C6H9Cl3 + 3AgNO3 ---> 3AgCl + C6H9(NO3)3. To find the limiting reagent, you have to convert the two given masses of reactants to moles, then choose one of the reactants to ...
by Christine Van 2E
Tue Oct 06, 2015 11:31 pm
Forum: Quantum Numbers and The H-Atom
Topic: HW 2.27 - Number of orbitals
Replies: 1
Views: 250

Re: HW 2.27 - Number of orbitals

Hi! So for this problem, it is kind of similar to 2.17, where it asks for how many orbitals are in subshell with l equal to... The orbitals refer to s-orbitals, p-orbitals, d-orbitals, f-orbitals, etc. The s-orbital has a max of 1 orientation (or one type of orbital which is just spherical on any ax...
by Christine Van 2E
Fri Oct 02, 2015 5:53 pm
Forum: Properties of Electrons
Topic: Relevance/Difference btwn the series of hydrogen constants?
Replies: 1
Views: 2015

Re: Relevance/Difference btwn the series of hydrogen constan

Hi! We know that when an electron is excited to a higher energy level by a light source, it will return back to its original state of energy. The Lyman, Balmer, Paschen, and Brackett series are basically different transition states for the Hydrogen atom when an electron is excited. So if an electron...
by Christine Van 2E
Fri Oct 02, 2015 5:26 pm
Forum: Limiting Reactant Calculations
Topic: Limiting Reactant Question
Replies: 7
Views: 741

Re: Limiting Reactant Question

Hi! This question was already answered in a previous post, but I'll explain it. So you first want to balance the chemical equation for this problem: C6H9Cl3 + 3AgNO3 ---> 3AgCl + C6H9(NO3)3 Then, convert the 0.750 g of C6H9Cl3 to moles and the 1.000 kg of AgNO3 to moles too. Use the molar ratio from...

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