## Search found 50 matches

Fri Mar 16, 2018 2:04 am
Forum: Calculating Work of Expansion
Topic: Midterm #4A
Replies: 1
Views: 202

### 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: 349

### 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: 199

### 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: 636

### 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: 173

### 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: 242

### 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: 207

### 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: 227

### 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: 156

### 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: 244

### 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: 242

### 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: 215

### 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: 166

### 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: 215

### 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: 207

### 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: 352

### 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: 530

### 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: 172

### 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
Replies: 5
Views: 455

### 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: 311

### 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: 131

### 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: 128

### 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: 134

### 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: 144

### 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: 135

### 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: 129

### 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: 129

### 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: 346

### 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: 206

### 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: 2222

### 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: 1725

### 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: 351

### 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: 213

### 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: 358

### 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: 437

### 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: 135

### 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: 182

### 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: 545

### 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: 143

### 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: 1103

### 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: 1725

### 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: 4
Views: 2004

### 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
Sun Nov 05, 2017 11:00 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: electron density
Replies: 3
Views: 212

### 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: 189

### 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: 322

### 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: 444

### 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: 544

### 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: 231

### 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: 438

### 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: 441

### 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.