Search found 34 matches
- Tue Mar 14, 2017 8:04 pm
- Forum: *Alkenes
- Topic: Naming every alkene as cis or trans
- Replies: 1
- Views: 1371
Re: Naming every alkene as cis or trans
If one of the carbons has 2 of the same atom on one side, for instance if a carbon was connected to 2 H molecules, then it doesn't matter which one is on the top or bottom because both will produce the same molecule. In this case, it is not possible to say whether it is cis (Z) or trans (E). However...
- Mon Mar 06, 2017 7:39 pm
- Forum: *Organic Reaction Mechanisms in General
- Topic: Standard Gibbs Free Energy of Activation
- Replies: 4
- Views: 1263
Standard Gibbs Free Energy of Activation
In the textbook, it says that the standard gibbs free energy of activation for a second transition state is often drawn from the reactants until the second transition state rather than from the intermediates to the second transition state because it is more convenient to measure everything in terms ...
Re: 1.5 (c)
Any of the organic molecules that have a carbon-carbon triple bond are alkynes (just as how all single bonds is an alkane, and a double bond makes it an alkene). In all of the line diagrams, none of the carbons or hydrogens are drawn, just the bonds between carbons. Therefore, we know that the point...
- Mon Feb 27, 2017 5:57 pm
- Forum: *Free Energy of Activation vs Activation Energy
- Topic: 4.40
- Replies: 1
- Views: 503
Re: 4.40
You can determine if something is thermodynamically or kinetically stable based on the sign and magnitude of the free energy of the reaction and of formation. A reaction is thermodynamically stable if delta G of the reaction is negative, and thermodynamically unstable if delta G of the reaction is p...
- Wed Feb 22, 2017 11:58 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: 15.65
- Replies: 1
- Views: 437
Re: 15.65
You can tell that the reaction is endothermic because the activation energy for the reverse reaction is lower than that of the forward reaction. Because of this, it requires more energy for the forward reaction to progress than the reverse reaction, so the reverse reaction occurs more readily. There...
- Wed Feb 15, 2017 1:22 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Midterm 2014 Question 8
- Replies: 4
- Views: 786
Re: Midterm 2014 Question 8
I'm still confused on why Ka=(K)^(1/2). I understand that when we solve for the balanced equation to solve for E, it ends up as 2HF-->2H+ + 2F- with a standard cell potential of -0.16V. However, if we were to divide this equation by 2 to get HF-->H+ + F-, wouldn't we then have the correct equation a...
- Mon Feb 13, 2017 12:04 pm
- Forum: Balancing Redox Reactions
- Topic: 2016 midterm #6a
- Replies: 1
- Views: 477
Re: 2016 midterm #6a
To determine the oxidation number of an atom within a molecule, you can add up the oxidation numbers of the elements also in that molecule that generally have a constant oxidation number, and the sum of all of the oxidation numbers of the atoms within a molecule should add up to the total charge wit...
- Thu Feb 09, 2017 10:39 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Cell Diagrams
- Replies: 3
- Views: 728
Re: Cell Diagrams
To write a cell diagram, the anode of the reaction actually goes on the left and the cathode half on the right! And then the order of the molecules does not particularly matter, but they are split up by vertical lines by into groups of the same phase. i.e. The solids together, liquids together, gase...
- Mon Feb 06, 2017 3:20 pm
- Forum: Student Social/Study Group
- Topic: Quiz 1 Review
- Replies: 4
- Views: 951
Re: Quiz 1 Review
I am very interested in studying together an forming a study group! :) my email is jenna.hakel@gmail.com
- Tue Jan 31, 2017 10:45 pm
- Forum: Calculating Work of Expansion
- Topic: When to Use Different Formulas for Work
- Replies: 2
- Views: 579
Re: When to Use Different Formulas for Work
We use w=-PdeltaV when the pressure against which the gas is expanding is constant. However, we use the second equation when the pressure is variable, such as when the expansion is reversible.
- Mon Jan 30, 2017 6:07 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: HW Prob. 11.17
- Replies: 1
- Views: 469
Re: HW Prob. 11.17
I also got -2.7 kJ! All the numbers I inputted were the same as in the solutions manual also, so it may just be a typo :)
- Wed Jan 25, 2017 6:37 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Why is the oxygen (1/2)02instead of 02?
- Replies: 2
- Views: 4819
Re: Why is the oxygen (1/2)02instead of 02?
Because the questions ask about the formation of one mole of the product, if you had O2 instead of 1/2 O2, there would be too many molecules of O2. If you think of it more as just molar ratios, for every one mole of product formed you need half a mole of O2. Just try to balance the equations and mak...
- Tue Jan 24, 2017 5:24 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Chapter 8 problem 21 [ENDORSED]
- Replies: 3
- Views: 911
Re: Chapter 8 problem 21 [ENDORSED]
Because the heat lost by the system is all gained by the surroundings, the numerical value on each side will be the same, they will just have opposite signs because one is losing energy and the other is gaining it. Because of this, it does not matter which side we place the extra negative sign on, i...
- Tue Jan 24, 2017 1:05 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Ch 8 Exercise 77
- Replies: 3
- Views: 887
Re: Ch 8 Exercise 77
So, following up on that, in terms of question 77, when you use the bond enthalpies that show that 3 of the C-C bonds are double bonds and 3 are single bonds, you get a total energy of 2880 kJ; however, when you use the given values for bond energies given that all 6 of the bonds share the delocaliz...
- Mon Jan 23, 2017 12:25 pm
- Forum: Phase Changes & Related Calculations
- Topic: 8.41
- Replies: 1
- Views: 526
Re: 8.41
The way I solved this problem was by still using the concept that all the heat lost by the water is gained by the ice cube. So qH2O=-qICE. However, the ice requires energy to both change phase to water and then to also change temperature. Therefore, the heat gained by ice (qICE) is q=(moles ice*enth...
- Mon Jan 23, 2017 12:18 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Enthalpy equation used in solutions manual
- Replies: 2
- Views: 596
Re: Enthalpy equation used in solutions manual
For the enthalpies associated with changes in phase, they are all just given in terms of kJ/mole, so in 8.37, they are simply dividing the number of kJ required to vaporize the .579 moles of CH4 to achieve this value. The equation q=moles x molar heat capacity x change in temperature wouldn't apply ...
- Mon Jan 23, 2017 12:11 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Bond Enthalpy and Energy of Formation
- Replies: 1
- Views: 405
Re: Bond Enthalpy and Energy of Formation
I think it all depends on what information is given to you. In the course reader, for example, it begins each new section by saying something along the lines of "When bond enthalpies are not available, use the standard enthalpies of formation." So although all three methods may produce the...
- Mon Jan 23, 2017 12:05 pm
- Forum: Student Social/Study Group
- Topic: Quiz 1 Prep
- Replies: 8
- Views: 1510
Re: Quiz 1 Prep
I'm also interested in comparing answers! :)
- Thu Jan 19, 2017 6:30 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Chapter 8 problem 21 [ENDORSED]
- Replies: 3
- Views: 911
Re: Chapter 8 problem 21 [ENDORSED]
So we know that the water and the copper will both have the same final temperature, because heat will continue to be exchanged between the two until the temperatures are equal. We also know that, during this process, all of the heat that is lost by the copper will go to the water, because we assume ...
- Thu Jan 19, 2017 6:22 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Heat capacity [ENDORSED]
- Replies: 5
- Views: 1088
Re: Heat capacity [ENDORSED]
Yes, because at constant pressure it also requires the heat to do work on the surroundings.
- Wed Jan 18, 2017 10:37 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Heat capacity [ENDORSED]
- Replies: 5
- Views: 1088
Re: Heat capacity [ENDORSED]
The way Dr. Lavelle described in class was to imagine a piston. To maintain constant pressure (based on PV=nRT), the volume must be able to adjust. For instance, when the gas is heated at a constant pressure, it expands, pushing the piston upward. However, for the piston to move upward, the air mole...
- Fri Jan 13, 2017 11:16 am
- Forum: Phase Changes & Related Calculations
- Topic: Phase change
- Replies: 3
- Views: 655
Re: Phase change
I would think that there would be certain vocabulary used to indicate if the problem were a phase change problem, such as vaporization, fusion, or sublimation. In the case of water, we also know the temperatures at which the phase changes occur (0C/32F, 100C/212F), so if the temperature were to pass...
- Fri Dec 02, 2016 3:34 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Names of Acids and Bases on the Final Exam
- Replies: 1
- Views: 466
Names of Acids and Bases on the Final Exam
To what extent do we have to know the names of the acids and bases on the final? For example, when we are given an acid/base problem, will we be given its formula or will it say "sulfuric acid" and we must know the formula and the difference between sulfuric and hydrosulfuric acid? I know ...
- Tue Nov 29, 2016 6:19 pm
- Forum: Calculating the pH of Salt Solutions
- Topic: Ch 13 Q 21 a
- Replies: 2
- Views: 596
Re: Ch 13 Q 21 a
In the equation pH=pKa+log([CO3(2-)/HCO3-]), the value of the logarithm is positive. So to find the value of the ratio of the concentrations, you wouldn't do 10^-.75, you would just do 10^.75, with a positive value for .75 because both sides of the equation are positive. When you do this, you find t...
- Tue Nov 22, 2016 4:23 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Course Reader pg. 156-157
- Replies: 1
- Views: 430
Re: Course Reader pg. 156-157
If there is a weak acid in which equilibrium strongly favors the reactants, not a lot of H+ will be produced in the reaction. Because of this, the concentration of H+ in the solution may be very, very low, such as 1.0x10^-10. According to the method to calculate pH, the pH should then be equal to -l...
- Mon Nov 14, 2016 11:51 am
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Questions about coordination compound (mainly quiz 3 preparation)
- Replies: 2
- Views: 589
Re: Questions about coordination compound (mainly quiz 3 preparation)
1. In class, he said that square planar is the more common structure for a coordination complex with 4 ligands. He said that to determine if a structure is square planar or tetrahedral requires information that is not covered in class (such as the ligand field theory), but usually structures will be...
- Mon Nov 07, 2016 11:15 am
- Forum: Administrative Questions and Class Announcements
- Topic: Chem 14B and 14BL [ENDORSED]
- Replies: 12
- Views: 5490
Re: Chem 14B and 14BL [ENDORSED]
I was thinking of taking 14B winter quarter, but does that mean I should take 14BL and 14C winter quarter or just 14BL? I had the same question. If anyone knows, if we put off taking 14BL (which I have also been advised to do) until after we take 14B, the following quarter should we take 14BL and 1...
- Mon Oct 31, 2016 6:51 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: H2CBr2 Polarity
- Replies: 2
- Views: 940
Re: H2CBr2 Polarity
Following on the above comment, if you look at the shape of a tetrahedral molecule, none of the atoms connected to the central atom are completely opposite each other. The bond angle is 109.5 for every bond, never 180. Because of this, even if the atoms appear to be directly across from each other i...
- Mon Oct 24, 2016 6:26 pm
- Forum: Bond Lengths & Energies
- Topic: Bond Order
- Replies: 2
- Views: 605
Re: Bond Order
Oh wait sorry I missed this! It also discusses it on page 77 of the textbook in the second to last paragraph, which then would be in Chapter 3, Section 6: Lewis Structures of Polyatomic Species.
- Mon Oct 24, 2016 4:51 pm
- Forum: Bond Lengths & Energies
- Topic: Bond Order
- Replies: 2
- Views: 605
Re: Bond Order
The explanation of bond orders in the book is in Chapter 4, Section 10 (Electron Configurations of Diatomic Molecules). So we haven't reached this point in the textbook in class yet! But if you're looking for it, it's on page 134 and 135 in the textbook :)
- Tue Oct 18, 2016 4:39 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Textbook Question #2.47 [ENDORSED]
- Replies: 1
- Views: 1108
Re: Textbook Question #2.47 [ENDORSED]
Pretty much yes! To make an ion with a charge of +1, you only have to remove one electron. So once you know the configuration of the electrons of an atom, this question is basically just asking where the last electron (the one that will need to be removed) is located. For example, if the configurati...
- Tue Oct 11, 2016 7:30 pm
- Forum: Empirical & Molecular Formulas
- Topic: Fall 2015 Quiz Prep question #5 [ENDORSED]
- Replies: 3
- Views: 975
Re: Fall 2015 Quiz Prep question #5 [ENDORSED]
So to find the empirical formula, you first find the number of moles of Carbon and Hydrogen given the masses produced of carbon dioxide and water. The tricky part in this question is that it is burned in air, so O2 can also contribute to the oxygen in the products; it is not only from the reactant t...
- Wed Oct 05, 2016 10:39 am
- Forum: Properties of Light
- Topic: Balmer and Lyman Series [ENDORSED]
- Replies: 4
- Views: 1300
Re: Balmer and Lyman Series [ENDORSED]
We talked about this in my discussion yesterday and my TA told us that for each series grouped together, the energy levels where the electrons start is always the same. For example, for the Lyman series, the electrons always either start at or return to (depending on if the light is absorbed or emit...
- Thu Sep 29, 2016 5:25 pm
- Forum: Photoelectric Effect
- Topic: Photoelectric Effect Post-Assessment #22 & 23
- Replies: 1
- Views: 496
Re: Photoelectric Effect Post-Assessment #22 & 23
For 23, I used the equation E=(hc)/wavelength to find the energy of the light with the wavelength of 194 nm. I then subtracted the number that I calculated in #22 (since that is where we calculated the threshold energy for the metal) according to the equation E(light)=threshold energy + KE(electron)...