Search found 50 matches
- Fri Mar 16, 2018 2:04 am
- Forum: Calculating Work of Expansion
- Topic: Midterm #4A
- Replies: 1
- Views: 342
Midterm #4A
For #4a, how do you know that you would use w=-PdV instead of w=-nRTln(V2/V1)?
- Fri Mar 16, 2018 2:01 am
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Midterm #6A
- Replies: 2
- Views: 648
Midterm #6A
Were A and B both correct for this question? I seem to remember being told that either would have been given credit, but I'm not sure.
- Fri Mar 16, 2018 1:56 am
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Activation energy and temp
- Replies: 3
- Views: 562
Re: Activation energy and temp
No. Activation energy is the minimum energy required to start a chemical reaction, and since the higher the temperature the more energy present, the more likely the reaction is to reach the activation energy. But the temperature does not change the activation energy.
- Fri Mar 16, 2018 1:51 am
- Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
- Topic: Monatomic vs. Diatomic
- Replies: 2
- Views: 1530
Re: Monatomic vs. Diatomic
I do not have a copy of the winter 2011 midterm, but on a previous post on chemistry community, Chem_Mod has responded to a question about #2b saying "The diatomic molecules in containers B and C, which are two atoms from container A bound together, will have to have a greater molar mass than t...
- Fri Mar 16, 2018 1:46 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: 8.77
- Replies: 1
- Views: 345
Re: 8.77
When you look at table 8.7, you can see that there are mean bond enthalphies for C-C and C=C, but also another category for the bonds between carbon atoms in benzene. If you find the sum of the mean bond enthalpies for the 3 single bonds and 3 double bonds in benzene, not considering the resonance, ...
- Fri Mar 16, 2018 1:35 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Reducing Power
- Replies: 5
- Views: 593
Re: Reducing Power
Do you mean electronegative? I don't think I understand how to tell by looking at a periodic table which elements have more reducing power. Thanks!
- Fri Mar 16, 2018 1:33 am
- Forum: Calculating Work of Expansion
- Topic: 8.117
- Replies: 2
- Views: 437
Re: 8.117
Chem_Mod has previously stated on chemistry community that the equation is already balanced. However, you are correct in that the oxygens have not been balanced yet, so hopefully Lavelle can clarify whether the solutions manual is incorrect or if we should ignore the oxygens.
- Fri Mar 16, 2018 1:19 am
- Forum: Administrative Questions and Class Announcements
- Topic: Organic Chemistry
- Replies: 1
- Views: 405
Re: Organic Chemistry
Maybe not, but I would still try to learn everything that is on the practice final since it was made to prepare us for the final.
- Fri Mar 16, 2018 1:17 am
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: 15.63
- Replies: 1
- Views: 339
Re: 15.63
That's a typo in the solution manual. It is supposed to say =0.59.
- Fri Mar 16, 2018 1:15 am
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Temperature in Entropy Change for Monoatomic Ideal Gas Midterm Question 6B
- Replies: 2
- Views: 593
Re: Temperature in Entropy Change for Monoatomic Ideal Gas Midterm Question 6B
The temperature and volume is given at a pressure of 1 atm, so you have all of the elements that you need to plug into PV=nRT and find n. When the temperature changes, you don't know if the pressure is constant. So you cannot use the final temperature because you don't know what the final pressure i...
- Fri Mar 16, 2018 1:07 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Reducing Power
- Replies: 5
- Views: 593
Reducing Power
How do you know which elements are increasing in reducing power? (referring to test 2, question 5, which asks to rank the following elements in order of increasing their reducing power)
- Fri Mar 16, 2018 12:51 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Test #2 question 4
- Replies: 4
- Views: 518
Re: Test #2 question 4
Can you explain why you don't flip the signs of the cell potential?
- Fri Mar 16, 2018 12:36 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Test #2 question 6
- Replies: 2
- Views: 381
Test #2 question 6
The following redox couple forms a galvanic cell which generates a current under standard conditions: Cr+3/Cr+2 and I3-/I- Identify the oxidizing and reducing agent, and complete the following cell diagram. When they present the ions in the galvanic cell, can we not supposed to assume that Cr+3 is g...
- Fri Mar 16, 2018 12:28 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Test #2 question 4
- Replies: 4
- Views: 518
Test #2 question 4
On Test 2, it asks to calculate the standard potential for the galvanic cell, U (s)| U+3 (aq) || V+2 (aq) | V (s) Since U+3 + 3e- --> U E= -1.79 V+2 + 2e- --> V E = -1.18 but U is the anode, so I made the equation U --> U+3 + 3e- E= +1.79 Then I wrote Ecell = Ecathode - Eanode = -1.18 - (1.79) = -2....
- Fri Mar 16, 2018 12:13 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Standard Enthalpy of combustion
- Replies: 1
- Views: 401
Re: Standard Enthalpy of combustion
Yes, water would be liquid in the product side.
- Fri Mar 16, 2018 12:06 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: State Functions
- Replies: 4
- Views: 741
Re: State Functions
It'll probably be easier to understand the concept of state functions rather than memorize a list. Since a state function is something that doesn't depend on the path taken to get from the initial to final state, you can see why temperature and volume etc can be considered state functions.
- Fri Mar 16, 2018 12:03 am
- Forum: Phase Changes & Related Calculations
- Topic: Environmental impact?
- Replies: 6
- Views: 995
Re: Environmental impact?
I do not think you will be required to know the environmental impact of burning fossil fuels for the final since Lavelle hasn't covered it. I think that he included it because it's an important and relevant concept to understand especially in today's society, but we will not be tested on it.
- Thu Mar 15, 2018 11:56 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: 8.65
- Replies: 1
- Views: 344
Re: 8.65
Because pure substances, like diatomic molecules, do not have an enthalpy of formation.
- Thu Mar 15, 2018 11:38 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Class Study Google Doc
- Replies: 5
- Views: 954
Re: Class Study Google Doc
Thank you so much for this!
- Thu Mar 15, 2018 11:32 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: Test 3 question 5
- Replies: 3
- Views: 567
Re: Test 3 question 5
Could you post the question you're referring to? I don't know if my test 3 question 5 is the same as yours.
- Thu Mar 15, 2018 11:20 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Hw 15.55 b
- Replies: 1
- Views: 310
Re: Hw 15.55 b
k and k' would only equal each other if K=1, which we know isn't always the case. so the rate constants of the forward and reverse reactions are not always equal.
- Thu Mar 15, 2018 11:16 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: HW 15.63
- Replies: 2
- Views: 316
Re: HW 15.63
This is a typo in the solutions manual. It should say =0.59
- Wed Mar 14, 2018 3:26 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: hw #15.63
- Replies: 1
- Views: 369
hw #15.63
The rate constant of the reaction between CO2 and OH- in aqueous solution to give the HCO3- ion is 1.5 x 10^10 L*mol-1*s-1 at 25 C. Determine the rate constant at blood temperature (37 C), given that the activation energy for the reaction is 38 kJ*mol-1. I looked at the solution manual for help with...
- Wed Mar 07, 2018 11:25 am
- Forum: General Rate Laws
- Topic: Rate laws for products vs reactants
- Replies: 2
- Views: 414
Rate laws for products vs reactants
Do zero order, first order, or second order rate laws change depending on if you are considering the products or the reactants?
- Tue Mar 06, 2018 11:54 pm
- Forum: General Rate Laws
- Topic: Negative Orders
- Replies: 1
- Views: 338
Negative Orders
On page 621 in the textbook, it discusses negative orders and gives examples of rate laws with the concentration of the products in the denominators. How do you know when you write the rate law with both the reactants and products?
- Wed Feb 21, 2018 10:13 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Identifying anode and cathode
- Replies: 2
- Views: 340
Re: Identifying anode and cathode
But on the same page it says "A negative cell potential indicates that the right-hand electrode in the cell diagram is the anode (the site of oxidation, where electrons leave the cell)", but isn't the right-hand electrode being reduced in the example?
- Wed Feb 21, 2018 10:07 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Identifying anode and cathode
- Replies: 2
- Views: 340
Identifying anode and cathode
At the top of page 575 in the textbook, for the reaction Cu(s)|Cu2+(aq)||Zn2+(aq)|Zn(s), it says that Cu(s) is the cathode and Zn (s) is the anode. But shouldn't it be the other way around since Cu is being oxidized and Zn is being reduced?
- Wed Feb 21, 2018 9:12 am
- Forum: Balancing Redox Reactions
- Topic: 14.5 part d
- Replies: 7
- Views: 827
Re: 14.5 part d
You wouldn't add H+ since it is in basic solution. You would have to balance with OH- and H20.
- Wed Feb 21, 2018 8:29 am
- Forum: Balancing Redox Reactions
- Topic: HW #14.3 d
- Replies: 3
- Views: 474
HW #14.3 d
For problem #14.3d, since Cl2 is both the oxidizing and reducing agent, would there still be two half reactions? Or only one?
- Wed Jan 24, 2018 12:53 am
- Forum: Administrative Questions and Class Announcements
- Topic: Week 3 Test Topic is endorsed
- Replies: 37
- Views: 4619
Re: Week 3 Test Topic is endorsed
Yes, he wrote on his website that the test will only have material covered in weeks 1 and 2.
- Fri Dec 08, 2017 6:38 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: dipole moment of O3
- Replies: 2
- Views: 4559
Re: dipole moment of O3
Does formal charge affect dipole moments and polarity?
- Fri Dec 08, 2017 6:36 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Do net dipole charges affect bases and acids?
- Replies: 2
- Views: 561
Re: Do net dipole charges affect bases and acids?
Because a large net dipole means a stronger bond, that would also mean a weaker acid.
- Fri Dec 08, 2017 6:31 pm
- Forum: Bronsted Acids & Bases
- Topic: Bronsted acids in products
- Replies: 2
- Views: 424
Bronsted acids in products
Are Bronsted acids and bases only found in the reactant side of an equation or is it possible to have one on the product end as well?
- Fri Dec 08, 2017 6:29 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: HF Acid Vs HBr Acid
- Replies: 2
- Views: 1176
Re: HF Acid Vs HBr Acid
In diatomic acids, the stronger acids are the larger compounds. Because Br is larger, there is a longer bond which is easier to break.
- Fri Dec 08, 2017 6:22 pm
- Forum: Dipole Moments
- Topic: Specific Dipole moment for PO4^3-
- Replies: 1
- Views: 774
Re: Specific Dipole moment for PO4^3-
There is no dipole moment because PO4^3- has a tetrahedral shape and therefore the electrons are distributed evenly around the phosphorous.
- Fri Dec 08, 2017 6:11 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Example 12.7
- Replies: 1
- Views: 316
Re: Example 12.7
The "-x" is eliminated because the Ka is so small that the change in initial concentration is insignificant.
- Fri Dec 08, 2017 6:07 pm
- Forum: Resonance Structures
- Topic: square pyramidal resonance
- Replies: 1
- Views: 287
Re: square pyramidal resonance
A compound with a square pyramidal shape like IF5 doesn't have resonance because all of the bonds are single bonds.
- Fri Dec 08, 2017 6:06 pm
- Forum: *Titrations & Titration Calculations
- Topic: ICE Box: How to find the equation to plug into the Quadratic Formula
- Replies: 2
- Views: 1081
Re: ICE Box: How to find the equation to plug into the Quadratic Formula
You get the equation by cross multiplying (x^2)/(0.0237-x)=6.28*10^-5. You solve the equation by multiplying either side with (0.0237-x) to get x^2= -6.28*10^-5 x + 1.48836*10^-6. Then you move everything onto one side to get 0=x^2+6.28*10^-5 x - 1.48836*10^-6.
- Fri Dec 08, 2017 6:02 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: pH at the same concentration
- Replies: 1
- Views: 262
Re: pH at the same concentration
At the same concentration, strong acids have a higher concentration of hydrogen ions than weak acids. Even though the acids are at the same concentration, the concentration of hydrogen ions differs.
- Fri Dec 08, 2017 5:44 pm
- Forum: Properties of Electrons
- Topic: Velocity of Ejected electron
- Replies: 4
- Views: 14515
Re: Velocity of Ejected electron
No we were not required to use the work function for #7b
- Fri Dec 08, 2017 5:41 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: dipole moment of O3
- Replies: 2
- Views: 4559
dipole moment of O3
Why is there a dipole moment in O3 when there is only one element?
- Wed Nov 29, 2017 2:54 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Equilibrium and Disassociation of a Diatomic Molecule (11.7)
- Replies: 8
- Views: 3868
Re: Equilibrium and Disassociation of a Diatomic Molecule (11.7)
For part c, K = (partial pressure of X)^2/(partial pressure of X2)
You find the partial pressure of X by using the formula listed above, (12 molecules/17 molecules)x0.10 bar= 0.071
The partial pressure of X2 is (5 molecules/17 molecules)x0.10 bar= 0.030
K= (0.071)^2/(0.030)
= 0.017
You find the partial pressure of X by using the formula listed above, (12 molecules/17 molecules)x0.10 bar= 0.071
The partial pressure of X2 is (5 molecules/17 molecules)x0.10 bar= 0.030
K= (0.071)^2/(0.030)
= 0.017
- Sun Nov 05, 2017 11:00 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: electron density
- Replies: 3
- Views: 475
Re: electron density
Electron density is a representation of the probability of finding an electron in a specific location around an atom or molecule. In general, the electron is more likely to be found in regions with high electron density.
- Sun Nov 05, 2017 10:57 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Orbitals of subshell
- Replies: 3
- Views: 333
Re: Orbitals of subshell
ml is found by using -l...l. so if l=2, ml=-2, -1, 0, 1, and 2. electrons fill the orbitals from lowest to highest.
- Sun Oct 22, 2017 11:31 pm
- Forum: Properties of Light
- Topic: Mathematical Error with 1.55 (a) [ENDORSED]
- Replies: 2
- Views: 570
Re: Mathematical Error with 1.55 (a) [ENDORSED]
since the unit is cm^-1, you would have to multiply 3600 by 100 to get m^-1.
- Sun Oct 22, 2017 9:37 pm
- Forum: DeBroglie Equation
- Topic: units for mass
- Replies: 6
- Views: 941
Re: units for mass
You only have to use kilograms as your units when you are doing an equation that has joules in it since a joule is equivalent to kg^2m^2/s^2.
- Sun Oct 15, 2017 4:57 pm
- Forum: Properties of Electrons
- Topic: Conversions [ENDORSED]
- Replies: 4
- Views: 918
Re: Conversions [ENDORSED]
This conversion would be provided if you needed it. It's on the constants and equations sheet on the Chem 14A website.
- Sun Oct 15, 2017 4:54 pm
- Forum: Properties of Light
- Topic: Units for HW Problem 1.23 [ENDORSED]
- Replies: 2
- Views: 392
Re: Units for HW Problem 1.23 [ENDORSED]
If the question specifies which units to use, then you have to put your answer in that form. But if it doesn't specify, it shouldn't matter much whether you write your answer in nm or pm.
- Fri Oct 06, 2017 12:41 am
- Forum: Molarity, Solutions, Dilutions
- Topic: G7 - Homework Problem
- Replies: 5
- Views: 773
Re: G7 - Homework Problem
No, you just need to find the mass of each by calculating 5.45% of 510 g to find the mass of the substance (27.8 g) and then you subtract that from the 510 g to get 482.2 g H2O.
- Thu Oct 05, 2017 11:59 pm
- Forum: Significant Figures
- Topic: Sig Figs- Addition and Subtraction [ENDORSED]
- Replies: 4
- Views: 937
Re: Sig Figs- Addition and Subtraction [ENDORSED]
You pay attention to the number with the fewest decimal places when adding and subtracting. So if you were doing 10.026 + 0.4, your answer would be 10.4 since 0.4 has one decimal place.