## Search found 62 matches

Sun Mar 13, 2016 10:57 am
Forum: General Rate Laws
Topic: Coefficients in pre-equilibirum approach
Replies: 2
Views: 465

### Re: Coefficients in pre-equilibirum approach

Thank you!

What if you solve for the overall rate law instead of a rate of formation? Would the coefficients still appear then?
Sat Mar 12, 2016 8:29 pm
Forum: General Rate Laws
Topic: Coefficients in pre-equilibirum approach
Replies: 2
Views: 465

### Coefficients in pre-equilibirum approach

How do the coefficients of the overall reaction come into play when deriving the rate law using the pre-equilibrium approach? For example, I don't understand where the 2 comes from in the pre-equilibrium example in the course reader.

Thanks!
Fri Mar 11, 2016 7:53 pm
Forum: *Cycloalkenes
Topic: Winter 2013 Final Q6A, naming
Replies: 1
Views: 403

### Re: Winter 2013 Final Q6A, naming

No. You wanted the smallest number at the first point of difference.
Fri Mar 11, 2016 7:52 pm
Forum: Student Social/Study Group
Topic: Winter 2015 Question 5
Replies: 1
Views: 587

### Re: Winter 2015 Question 5

You have to check in the redox table which has a higher reduction potential. The one with the higher reduction potential will be reduced.
Fri Mar 11, 2016 7:51 pm
Forum: General Rate Laws
Topic: Pseudo rate constant
Replies: 3
Views: 2340

### Pseudo rate constant

To find the rate constant for a first-order pseudo reaction, how do we find k'? It says in the course reader "slope" but I'm not sure which slope it's referring to.
Fri Mar 11, 2016 7:51 pm
Forum: *Constitutional and Geometric Isomers (cis, Z and trans, E)
Topic: Double E/Z
Replies: 3
Views: 454

### Re: Double E/Z

So then how do we determine cis/trans? What if one pair is E and the other is Z?
Thu Mar 10, 2016 12:38 pm
Forum: General Rate Laws
Topic: Pseudo rate constant
Replies: 2
Views: 511

### Re: Pseudo rate constant

So k' is -k?
Tue Mar 08, 2016 10:57 pm
Forum: *Ethers
Topic: Ether Naming Order
Replies: 1
Views: 456

### Re: Ether Naming Order

The ethyl will come first, but you'll still give numbering priority to the functional group.
Tue Mar 08, 2016 10:42 pm
Forum: General Rate Laws
Topic: Pseudo rate constant
Replies: 2
Views: 511

### Pseudo rate constant

To find the rate constant for a first-order pseudo reaction, how do we find k'? It says in the course reader "slope" but I'm not sure which slope it's referring to.
Mon Mar 07, 2016 9:24 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell potential
Replies: 1
Views: 251

### Re: Cell potential

Well the pH tells you what your concentration of H+ is (10^-pH=[H+]). I haven't looked at the exact problem you're referring to, but if you say you're given the other concentrations, set up an equation for Q (the reaction quotient in the Nernst equation) and plug in the relevant concentrations, keep...
Sat Mar 05, 2016 6:02 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Total number of moles vs. moles of gas
Replies: 2
Views: 467

### Total number of moles vs. moles of gas

Hi,

Which trumps which when estimating whether or not a reaction will experience an increase or decrease in entropy? For example, if a reaction produces fewer moles of gas than it uses up, but it will produce more moles overall, can we say the total entropy decreased or increased?

Thanks!
Sat Mar 05, 2016 5:57 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Greater residual entropy
Replies: 2
Views: 377

### Re: Greater residual entropy

Yeah, technically NO can also be ON. BF3 has all identical "peripheral atoms" (F), so it can only adopt one orientation.
Sat Mar 05, 2016 5:18 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Problem 9.13
Replies: 1
Views: 378

### Problem 9.13

In the solutions manual answer for the homework question, they use R instead of C when calculating the change in entropy with respect to temperature. In other words, they replace C with R in the equation for change in entropy. Why is that?
Thu Mar 03, 2016 5:34 pm
Forum: *Cycloalkenes
Topic: Introduction to Organic Chemistry booklet
Replies: 1
Views: 417

### Re: Introduction to Organic Chemistry booklet

No, you only have to know the information in the sections in the "lecture outline" on the Chem 14B website.
Sun Feb 28, 2016 11:45 am
Forum: *Alkenes
Topic: Allyl and Vinyl
Replies: 1
Views: 367

### Allyl and Vinyl

Hi, I'm a little confused about how to use allyl and vinyl. Both have double bonds in the structure, so my gut instinct when seeing a compound containing either would be to include the double bond in the parent chain rather than making it a substituent. When should I know not to do that? Or is it up...
Sat Feb 27, 2016 10:37 pm
Forum: *Cycloalkenes
Topic: Naming problem
Replies: 1
Views: 341

### Naming problem

Hi,

Why is the compound 1,6-dimethylcyclohexa-1,4-diene not 2,3 dimethyl etc.?
Thu Feb 25, 2016 10:50 pm
Forum: *Identifying Primary, Secondary, Tertiary, Quaternary Carbons, Hydrogens, Nitrogens
Topic: Trans and Cis
Replies: 2
Views: 422

### Re: Trans and Cis

I think you can determine it from the line structure. It just depends on the location of the highest-priority substituents attached to the sp2 carbon. If they're opposite each other, then the molecule is trans. If they're on the same side, the molecule is cis.
Tue Feb 23, 2016 4:56 pm
Forum: *Electrophiles
Topic: Steps in an organic reaction
Replies: 1
Views: 369

### Re: Steps in an organic reaction

I think sometimes you can tell if there will be multiple steps, depending on how stable the product is. If, for example, substitution occurs and you end up with a positively-charged carbon, it's likely there will be another step, because the carbon does not want to be positively charged.
Thu Feb 18, 2016 4:02 pm
Forum: *Free Energy of Activation vs Activation Energy
Topic: Activation energy vs. Gibbs Free Energy
Replies: 1
Views: 495

### Activation energy vs. Gibbs Free Energy

In Self Test 4.4A (c) in Introduction to Organic Chemistry, they asked which step would have a greater activation energy if the y-axis were written in terms of potential energy instead of Gibbs Free energy. I don't quite understand why the first step, with the smaller hump, would have greater activa...
Tue Feb 16, 2016 12:20 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Settin Up An Overall Rate Law
Replies: 1
Views: 402

### Re: Settin Up An Overall Rate Law

No, you just describe the concentration of the intermediate in terms of the equilibrium constant K for that reaction, then you plug it into the slow step rate law. Essentially, you just want to rewrite the intermediate concentration in different terms, because it won't be present in the overall rate...
Sun Feb 14, 2016 3:51 pm
Forum: General Science Questions
Topic: Sig figs with fractions
Replies: 1
Views: 3479

### Sig figs with fractions

In the prep quiz questions, some numbers are written in fraction format (i.e. 1/16). How do I deal with sig figs with fractions? Should I convert it to a decimal and assume it has the same number of sig figs as another value in the problem?

Thank you!
Sun Feb 14, 2016 11:59 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Activation energy?
Replies: 1
Views: 310

### Activation energy?

Should we be concerned about the activation energy problems assigned from the textbook, since they're past the part of the textbook we're supposed to have read?

Thanks!
Wed Feb 10, 2016 7:13 pm
Forum: Administrative Questions and Class Announcements
Topic: Research/Events in Chemistry Department
Replies: 1
Views: 429

### Research/Events in Chemistry Department

Hi, My name is Deanna Necula and I'm a Academic News reporter for the Daily Bruin. We're looking for information about events/research occurring in the Chemistry (or related) department that would be of interest to a larger audience. If there is any research or events occurring in an academic depart...
Sun Feb 07, 2016 10:52 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Arranging molecules in ordr of increasing/decreasing entropy
Replies: 1
Views: 461

### Re: Arranging molecules in ordr of increasing/decreasing ent

Mass. Greater mass means more fundamental units (and therefore more ways for the units to be scrambled about and generate disorder/greater entropy).
Sun Feb 07, 2016 10:43 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: 14.55 How to determine the anode
Replies: 1
Views: 500

### Re: 14.55 How to determine the anode

It's an aqueous species, so it means it's dissolved in water. The water is the anode because it's lower down in the electrochemical table, so it's more likely to be oxidized than the sulfate.
Sun Feb 07, 2016 8:14 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Mid term 2011 #6
Replies: 2
Views: 345

### Re: Mid term 2011 #6

I haven't looked at the exact problem you're referring to, but generally the farther apart on the electrochemistry table they are, the larger the difference between their standard reduction potentials (therefore the larger their Ecell)
Sun Feb 07, 2016 7:48 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta G equals 0
Replies: 1
Views: 3495

### Re: Delta G equals 0

Equilibrium (no likelihood of proceeding either direction)
Sun Feb 07, 2016 7:47 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Calculating Standard Cell Potentials
Replies: 2
Views: 351

### Re: Calculating Standard Cell Potentials

The reaction with the more positive (less negative) reduction potential will be the one undergoing reduction (it has a higher potential for reduction). The other one therefore must be the anode, and must be reversed.
Mon Feb 01, 2016 9:40 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Order of same-phase species in cell diagram/14.5
Replies: 1
Views: 324

### Order of same-phase species in cell diagram/14.5

Hi, Does it matter in which order I put same-phase species in my cell diagram, if they are separated by commas? Also, how do I know where to put "miscellaneous" ions such as "H+" in my cell diagram? Also, in hw 14.15 c), they separated two species at the cathode that were of the ...
Sat Jan 30, 2016 7:05 pm
Forum: Balancing Redox Reactions
Topic: Redox reactions in Basic or Acidic conditions
Replies: 3
Views: 1794

### Re: Redox reactions in Basic or Acidic conditions

Will we be told if a reaction is basic or acidic?
Sat Jan 30, 2016 3:47 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Quiz 1 Preparation Winter 2015 #3
Replies: 4
Views: 714

### Re: Quiz 1 Preparation Winter 2015 #3

I think that when a reaction is isothermal, that just means that the internal energy change is 0. The temperature as a whole does not change from the start to the end of the reaction, but it doesn't mean that no work or no heat transfer has occurred; it just means that any factors that can affect th...
Mon Jan 25, 2016 10:19 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Finding Range of Temperatures and Delta G
Replies: 2
Views: 1171

### Re: Finding Range of Temperatures and Delta G

You're solving for ∆G=0 because at that point the reaction shifts from spontaneous to non-spontaneous and vice versa. Therefore, if you calculate the temperature of reaction that would allow you to have ∆G=0, below (or above, depending on the problem) that temperature you will have negative ∆G, mean...
Mon Jan 25, 2016 10:15 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 2015 workbook problem
Replies: 4
Views: 598

### Re: 2015 workbook problem

The external pressure of 3 atm. The "P" in that equation always represents the external pressure.
Sun Jan 24, 2016 9:08 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 2015 workbook problem
Replies: 4
Views: 598

### Re: 2015 workbook problem

I think for this instance, because the volume is changing, you can assume it already takes into account the change in pressure (because by changing volume you change pressure). So, you just have to use the volume change for your work equation.
Sun Jan 24, 2016 5:56 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Change in Internal Energy in Workbook Problem
Replies: 1
Views: 302

### Change in Internal Energy in Workbook Problem

Hi,

For Winter 2014 workbook problem #11, in Step 2 ("getting back to the original internal energy"), ∆U suddenly becomes positive 158 J when just previously we had calculated -158 J for the change in internal energy. Why does it become a positive value?

Thank you!
Sun Jan 24, 2016 5:51 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Quiz 1 Preparation Winter 2015 #3
Replies: 4
Views: 714

### Re: Quiz 1 Preparation Winter 2015 #3

Because it's an isothermal reaction, you know that ∆U=0. Therefore, q must be -w, which you've already calculated. And I think it asked for change in internal energy, not enthalpy.
Thu Jan 21, 2016 9:01 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Cv for Textbook Example 9.5
Replies: 1
Views: 250

### Cv for Textbook Example 9.5

The textbook example 9.5 states: "In one experiment, 1.00 mol O2(g) was compressed suddenly (and irreversibly) from 5.00 L to 1.00 L by driving in a piston, and in the process its temperature was increased from 20.0 C to 25.2 C. What is the change in entropy of the gas?" I know that to cal...
Thu Jan 21, 2016 8:59 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Highest Entropy at Lower Temp.
Replies: 1
Views: 327

### Re: Highest Entropy at Lower Temp.

I think you're right that entropy as a singular, absolute value is highest at high temperature, but the change in entropy is maximized the lower the initial temperature. You can see this effect from the equation ∆S=qrev/T; the lower the temperature of reaction, the higher the change in entropy. Conc...
Thu Jan 21, 2016 12:05 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Sig Figs for equations with ln
Replies: 1
Views: 3776

### Sig Figs for equations with ln

I remember there was a different way to do sig figs last unit, when calculating pH using log. For this unit, when we are using ln, must we apply the same sig figs rule? Also, is it applied right after using ln or log, and that truncated number is used in further calculations, or is it applied at the...
Tue Jan 19, 2016 12:37 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy and Pressure
Replies: 1
Views: 393

### Entropy and Pressure

I'm unsure as to why entropy would decrease when there is an increase in pressure. Is this statement only applicable if the pressure increase is done by decreasing the volume? That would make more sense to me. But if, for a given volume, the pressure increases (say by pumping in more molecules of ga...
Wed Jan 13, 2016 7:05 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: When can we assume standard state?
Replies: 1
Views: 255

### When can we assume standard state?

In problem 8.49, we needed to know temperature in order to use the equation PV=nRT. However, there was no given temperature in the problem. The solutions manual assumed 25C. When can we assume that a reaction is occurring at standard state (this particular problem gave no mention that the problem wa...
Tue Jan 12, 2016 7:32 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Final temperature in 8.21
Replies: 1
Views: 362

### Final temperature in 8.21

8.21 asks to calculate the final temperature of water after adding a piece of copper. However, the solutions manual calculations inputs the same final temperature variable for the copper and the water in the equation "heat lost by metal=-heat gained by water", and solves for it that way. H...
Fri Jan 08, 2016 5:34 pm
Forum: Phase Changes & Related Calculations
Topic: Celsius to Kelvin conversion
Replies: 2
Views: 653

### Celsius to Kelvin conversion

In example 8.3 in the textbook, where we were asked to calculate the heat necessary to increase the temperature of (a) 100 g (b) 2 mol of water from 20 to 100 degrees Celsius, the textbook used Kelvin in (b) because molar heat capacity is expressed in Kelvin rather than Celsius. However, it used 80 ...
Sun Nov 29, 2015 10:34 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Delocalizing charge of acid
Replies: 1
Views: 382

### Re: Delocalizing charge of acid

A greater electronegativity means that H will acquire a more positive partial charge. Therefore, it's more likely to dissociate and "attach" onto a base, because the base will supply it with the electrons it needs. Also, the more electronegative the halogen the more the electron density is...
Sun Nov 29, 2015 10:26 am
Forum: Ionic & Covalent Bonds
Topic: Question 3.9 Ground state electron configuration
Replies: 2
Views: 3256

### Re: Question 3.9 Ground state electron configuration

You know that the M2+ ion has lost two electrons. Therefore, for each electron configuration, just tack on two extra electrons to determine what each M is without any lost electrons. However, be careful; remember that after the d-orbitals are filled up, next come the "s" orbitals for that ...
Sun Nov 29, 2015 10:16 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Pressure aspect of Le Chatelier's Principle
Replies: 2
Views: 596

### Re: Pressure aspect of Le Chatelier's Principle

The equilibrium constant K for a certain chemical reaction is the "goal" of that particular reaction, because it describes a favorable state where reactants and products are constantly being replenished and the direction of the reaction is not skewed towards any one direction. Any changes ...
Sat Nov 28, 2015 4:34 pm
Forum: Lewis Structures
Topic: Structure of N02
Replies: 1
Views: 428

### Structure of N02

The answer to the Lewis structure of N2O on the Fall 2012 midterm has a central N connected to another N and an O via double bonds. However, my drawing has a central N connected to an N via a triple bond and a single bond linking to the other O. In my Lewis structure, the oxygen (which is more elect...
Thu Nov 26, 2015 3:49 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Electron withdrawing power of CH3
Replies: 1
Views: 370

### Electron withdrawing power of CH3

Why does CH3 have less electron withdrawing power than H? Is carbon (which is the atom attached to the rest of the structure) not more electronegative than H, and thus better able to withdraw electrons from the O-H bond to strengthen the acid?

Thank you!
Tue Nov 24, 2015 10:04 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Ligands and Chelating Complexes
Replies: 3
Views: 533

### Re: Ligands and Chelating Complexes

I have uploaded the video in a different (.mov) format.
Tue Nov 17, 2015 9:03 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Diethylenetriamine
Replies: 2
Views: 432

### Re: Diethylenetriamine

It's actually tridentate.
Mon Nov 16, 2015 9:11 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Endothermic and Exothermic Reactions
Replies: 3
Views: 670

### Re: Endothermic and Exothermic Reactions

Typically dissociation reactions are endothermic, because it requires energy to break bonds. Similarly, reactions involving a compound being "built" are typically exothermic, because energy is released when you form bonds.
Mon Nov 16, 2015 10:56 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Calculating Partial Pressure
Replies: 1
Views: 460

### Re: Calculating Partial Pressure

They give you the equilibrium concentrations for all the products and reactants so just set up the K expression and calculate K by plugging in the equilibrium concentrations. Then redo your ice box, starting with half the initial quantity of BrCl. Set your new equilibrium concentrations equal to the...
Sun Nov 15, 2015 11:16 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Homework Question 11.1 (d)
Replies: 2
Views: 394

### Re: Homework Question 11.1 (d)

The thing is, if you add more of a certain reactant, the final concentrations can't be the exact same as before, because now you have more matter. The only thing that is always the same at equilibrium is your K constant. This doesn't necessarily imply that your concentrations are the same; instead, ...
Sun Nov 15, 2015 11:13 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Determining Chelating complex based on shape
Replies: 1
Views: 315

### Re: Determining Chelating complex based on shape

I'm not sure cis molecules will always chelate...if there's an obstructing atom in the structure between the two atoms that could potentially chelate, then it won't likely chelate because that atom will prevent them from being close enough to do so. For example, look at (b) and (c) 17.36 in the text...
Tue Nov 10, 2015 12:11 pm
Forum: Naming
Topic: Adding -ate at the end of names
Replies: 2
Views: 359

### Re: Adding -ate at the end of names

Yes, even when there's a cation outside the complex you must add -ate at the end of the transition metal name along with the oxidation state in roman numerals. The cation outside the complex implies that the complex itself is anionic, and whenever the entire coordination complex is anionic you add -...
Tue Nov 10, 2015 12:02 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Conditions favoring production - pressure
Replies: 6
Views: 792

### Re: Conditions favoring production - pressure

Yes, there are in total 2 moles on the left side of the equation and three on the right. Therefore, there will be a greater perceived pressure on the right side than on the left, because when you decrease the volume (which is how we're assuming we increase pressure because otherwise the change in pr...
Sun Nov 08, 2015 11:03 pm
Forum: Ideal Gases
Topic: Net ionic equations?
Replies: 1
Views: 343

### Net ionic equations?

There is an example in the textbook of a chemical equation involving the dissociation of ionic compounds, where an aqueous product is not included in the equilibrium expression. The textbook says that the reason it's not included is because the concentrations of the spectator ions cancel and only th...
Mon Nov 02, 2015 3:25 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Fall 2010 Midterm Q.7 b Polar or Non Polar
Replies: 2
Views: 536

### Re: Fall 2010 Midterm Q.7 b Polar or Non Polar

The bromine atoms have a different electronegativity than the hydrogen atoms, so the dipole moments won't be of equal size. Therefore, they won't fully cancel each other out. Tetrahedral structures are only non-polar when all the peripheral atoms are identical.
Thu Oct 29, 2015 2:30 pm
Forum: Significant Figures
Topic: How many significant figures does this question require?
Replies: 1
Views: 436

### How many significant figures does this question require?

The question is: calculate the moles of nickel chloride in 20 mL of a 0.01 M solution. In this problem I convert the volume to liters, where the number of liters would be 0.02L. Therefore, does my answer require the number of significant figures that I get during the conversion or as many as there a...
Sat Oct 24, 2015 12:38 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Determining bond angles
Replies: 3
Views: 407

### Determining bond angles

When determining bond angles, should they be calculated around each central atom? For example, if you have two carbons linked together surrounded by hydrogen atoms, should the C-H bond angle be calculated around each carbon? So you would have two bond angles around a central atom, not just one. Than...
Mon Oct 19, 2015 12:13 pm
Forum: Lewis Structures
Topic: How many unpaired electrons does the molecule O2 have?
Replies: 2
Views: 12793

### How many unpaired electrons does the molecule O2 have?

In the textbook, it says that the molecule O2 has 2 unpaired electrons. However, when I draw the Lewis structure (and count the number of valence electrons, which happen to be even), no electrons are unpaired.
Wed Oct 14, 2015 9:59 pm
Forum: Electronegativity
Topic: Does a greater difference in EN correlate to a stronger bond
Replies: 2
Views: 680

### Does a greater difference in EN correlate to a stronger bond

If there is a greater difference in electronegativities between atoms present in an ionic bond, is that bond considered "stronger"? Does the same concept apply to covalent bonds?