## Search found 47 matches

Wed Mar 13, 2019 7:22 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Homework #115 Ch.8 Ed.6
Replies: 1
Views: 288

### Homework #115 Ch.8 Ed.6

Textbook Question:"An experimental automobile burns hydrogen for fuel. At the beginning of a test drive, the rigid 30.0-L tank was filled with hydrogen at 16.0 atm and 298 K. At the end of the drive, the temperature of the tank was still 298 K, but its pressure was 4.0 atm. (a) How many moles o...
Wed Mar 13, 2019 11:32 am
Forum: Phase Changes & Related Calculations
Topic: Homework number 41 Ch.8 (6th ed.)
Replies: 1
Views: 266

### Homework number 41 Ch.8 (6th ed.)

Why is it that the heat of the ice cube requires two calculations being as opposed to water's one? I understand the the ice is undergoing a phase change; however, I am unsure as to why we add the second calculation of ice? Additionally, is the negative sign on the side of ice, -qice=qwater, because ...
Sun Mar 10, 2019 9:57 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Final Exam
Replies: 23
Views: 672

### Re: Final Exam

Yes! It is cumulative!
Sat Mar 09, 2019 9:05 pm
Forum: First Order Reactions
Topic: Homework #37 6th edition part b
Replies: 1
Views: 70

### Homework #37 6th edition part b

If the question were to say, "determine the time needed for the concentration of SO2Cl2 to decrease to 20%", would we use ln20 rather than ln10? Is the number following ln that of the percent?
Fri Mar 08, 2019 8:21 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: HW Number 17 (6th ed.)
Replies: 2
Views: 155

### HW Number 17 (6th ed.)

For number 17, when determining the order for reactant B, why did they use experiments 2 & 3 rather than 1 & 3? Does it matter?
Sun Mar 03, 2019 1:02 pm
Forum: Administrative Questions and Class Announcements
Topic: Final Topics
Replies: 6
Views: 254

### Re: Final Topics

The final is cumulative, but like last quarter in 14A it focuses on the new content a little more.
Sun Mar 03, 2019 1:00 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: TEST 2
Replies: 3
Views: 182

### TEST 2

For the question regarding pH, which equation and steps were necessary to determine the answer?
Sun Feb 24, 2019 11:32 pm
Forum: Student Social/Study Group
Topic: Test
Replies: 17
Views: 740

### Re: Test

It is posted on Dr. Lavelle's 14B website. Gibbs Free Energy and Cell potentials!
Sun Feb 24, 2019 11:30 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Replies: 2
Views: 95

Yes, cell potentials do not take into consideration the balance of the equation as it is an intensive/fixed property. The only thing that changes the value is whether or not you need to change the sign to negative to represent an oxidation reaction.
Sun Feb 24, 2019 11:28 pm
Forum: Balancing Redox Reactions
Topic: Balancing Redox Rxn Procedures
Replies: 2
Views: 99

### Re: Balancing Redox Rxn Procedures

You essentially need to make sure the overall charge including all positives and negatives from hydrogen ions an hydroxide ions are included. For acidic redox reactions specifically, -OH does not contribute to your balancing count as it is usually not in an acidic redox reaction equation. So, you're...
Wed Feb 13, 2019 12:10 am
Forum: Phase Changes & Related Calculations
Topic: Chapter 8 number 21
Replies: 4
Views: 195

### Chapter 8 number 21

Why is it that heat lost by the metal(a positive value)=-heat gained by water??? shouldn't it be reversed since heat is LOST (-) by metal??
Tue Feb 12, 2019 9:43 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: HOTDOG #12 part B
Replies: 6
Views: 301

### Re: HOTDOG #12 part B

I keep plugging in (1)(219.2)(163)+(6)(29.4)(163) but not getting the correct answer?
Tue Feb 12, 2019 9:00 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: HOTDOG#7
Replies: 2
Views: 115

### HOTDOG#7

Im a little confused as to what values of final and initial moles to use in calculating the work through -(delta)RT?
Tue Feb 12, 2019 8:53 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: HOTDOG #12 part B
Replies: 6
Views: 301

### HOTDOG #12 part B

I don't understand the values for the temperature change used for the first enthalpy changes where glucose and oxygenate added together? Where did 11.3 for glucose and 16.3 for oxygen come from?
Tue Feb 12, 2019 5:42 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: HOTDOG #5
Replies: 1
Views: 140

### HOTDOG #5

I don't understand how to calculate the entropy change for temperature change to obtain 3.48J/K. Can someone explain how to derive that answer?
Tue Feb 12, 2019 5:08 pm
Forum: Phase Changes & Related Calculations
Topic: HOTDOG #3B
Replies: 1
Views: 115

### HOTDOG #3B

I am having trouble understanding how to calculate the answer. Can someone explain?
Thu Feb 07, 2019 3:48 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Study Guides
Replies: 15
Views: 571

### Study Guides

Are there any study guide/review sheets the TAs have made available for the midterm?
Thu Feb 07, 2019 11:17 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Number 31 Ch.8
Replies: 1
Views: 95

### Number 31 Ch.8

Can someone please explain the logical approach to this question?
Mon Feb 04, 2019 12:54 am
Forum: Calculating Work of Expansion
Topic: Related to Question 5 of Ch.8
Replies: 1
Views: 93

### Related to Question 5 of Ch.8

I suppose I am confused on how to know when to use the equation w=-PexdeltaV vs w=-nRTln(final/initial)?
Sun Feb 03, 2019 2:00 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Midterm Exam Content
Replies: 4
Views: 179

### Midterm Exam Content

For the midterm, does the content we are being tested on include thermochemistry, equilibrium and acid/base only? And as far as acid base, should we know Henderson-Hasselbalch?
Sun Feb 03, 2019 1:57 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Gibbs
Replies: 5
Views: 249

### Re: Gibbs

Gibbs free energy is essentially a measure of how much work/energy is available to be done by a system. When you have a (-) Gibbs free energy, the reaction is exothermic and essentially spontaneous. When the value is (+), the reaction is endothermic and non-spontaneous. By spontaneity, it means that...
Sun Feb 03, 2019 1:54 pm
Forum: Phase Changes & Related Calculations
Topic: Steam resulting in burns?
Replies: 6
Views: 291

### Steam resulting in burns?

Dr. Lavelle thoroughly explained why steam burns more than ___? I was absent that day and was wondering if someone could thoroughly explain the conceptual basis of that discussion?
Wed Jan 23, 2019 1:04 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Number 93 Ch.11
Replies: 1
Views: 110

### Number 93 Ch.11

How do we know when to use K vs the Kc value from the table?
Wed Jan 23, 2019 10:58 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Ch.11 #25
Replies: 1
Views: 77

### Ch.11 #25

Why did we assume it was a synthesis reaction? What it be the same Kc if we solved it as a decomposition reaction where HI is broken down?
Wed Jan 23, 2019 10:45 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Number 7 chapter 11
Replies: 1
Views: 66

### Number 7 chapter 11

How does flask 3 represent equilibrium?
Sun Jan 20, 2019 4:20 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Number 71 Chapter 12 Homework
Replies: 2
Views: 308

### Number 71 Chapter 12 Homework

Why does the Na+ get omitted from the CH3Co2??? Is this the case for every compound we are given. I guess I am just confused on how to accurately utilize the Ka values list when the compounds listed are a bit different from those given to us in the questions.
Sun Jan 20, 2019 4:11 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Number 69 Ch.12
Replies: 1
Views: 60

### Number 69 Ch.12

I don't understand why the Ka value used for part b is different in terms of the exponent compared to the one provided by the textbook?
Sun Jan 20, 2019 1:57 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Water in the Equilibrium Constant.
Replies: 4
Views: 178

### Water in the Equilibrium Constant.

Why is water not included in the constant?
Wed Jan 16, 2019 12:51 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Number 115 Chapter 11 HW
Replies: 2
Views: 115

### Number 115 Chapter 11 HW

for the equation 6CO2(g)+6H2O(l)-->C6H12O6(aq) + 6O2(g), would the system being compressed mean that the volume decrease and pressure increases? As a result, since technically liquid isn't included in the equilibrium constant, shouldn't equilibrium favor the reactants??
Wed Jan 16, 2019 12:41 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Homework #89 Ch.11
Replies: 1
Views: 79

### Homework #89 Ch.11

I don't understand how to know if the equation we derived from A-->B+C has coefficients as the true answer?
Sun Jan 13, 2019 10:05 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: HW PROBELM 1 PART D
Replies: 4
Views: 200

### HW PROBELM 1 PART D

How is the following true?
-If one starts with higher concentrations of reactants, the equilibrium concentrations of the products will be larger.
Wed Jan 09, 2019 11:20 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Post-Module Question
Replies: 1
Views: 77

### Post-Module Question

Determine whether the following statements are true or false:
a. When chemical equilibrium is reached, the composition of the reaction mixture remains constant.
b. If we make a reaction go faster, we can increase the amount of product at equilibrium.

Which is true/false?
Wed Jan 09, 2019 11:03 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Stability
Replies: 3
Views: 132

### Stability

During the first lecture, Dr. Lavelle noted that the products were more stable than the reactants? Is this ALWAYS the case? Or was it simply because the diagram he drew was exothermic?
Wed Jan 09, 2019 11:01 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Ratios of Concentration
Replies: 1
Views: 32

### Ratios of Concentration

So, essentially, the ratios of concentration between the products and reactants of a reaction at equilibrium do not change in spite of changes in the coefficient that may change in the equation?
Fri Dec 07, 2018 10:51 pm
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: number 38 of the churro practice exam
Replies: 1
Views: 269

### number 38 of the churro practice exam

Why did the LDF forces overrule the dipole-dipole interactions to make H2Se to have a greater boiling point?
Wed Dec 05, 2018 8:20 pm
Forum: Einstein Equation
Topic: Midterm Question 6 part A
Replies: 1
Views: 349

### Midterm Question 6 part A

"Microwave ovens heat food by exciting water to a higher vibration mode....... What is the energy and wavelength of this radiation?" For this question, I used the Einstein equation to solve for the energy and got it correct; however, looking back to review, I recall being told that that eq...
Tue Nov 27, 2018 3:44 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Determining Central Atom
Replies: 2
Views: 246

### Determining Central Atom

Why is carbon the central atom in ClCN and not in HCN?
Tue Nov 27, 2018 3:37 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Number 19 Chapter 4 part b.
Replies: 1
Views: 28

### Number 19 Chapter 4 part b.

How exactly would the lewis structure for (CH3)2Be look like?
Tue Nov 27, 2018 2:49 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Determining Bond Angle
Replies: 3
Views: 78

### Determining Bond Angle

When determining the bond angle of a moleucule, for example, SOCl2, do we consider the atom arrangement (tetrahedral with 109.5 degree bonds) or the actual shape's (trigonal pyramidal) bond angle? I know the answer is slightly less than 109.5 but im not completely sure why?
Sun Nov 25, 2018 9:03 pm
Forum: Lewis Acids & Bases
Topic: Conjugate Acid and Base
Replies: 1
Views: 52

### Conjugate Acid and Base

Does the concept of conjugate acids and bases only apply to Lewis acid and bases or is it inclusive to bronsted acid and bases?
Sun Nov 11, 2018 11:47 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Chapter 4 Homework Number 1
Replies: 6
Views: 184

### Chapter 4 Homework Number 1

Just to confirm, the reason why bond angles vary is based on the electron-electron repulsion due the presence of lone pairs on each distinct structure, correct?
Sun Nov 04, 2018 5:29 pm
Forum: Lewis Structures
Topic: HOCO Lewis structure
Replies: 1
Views: 44

### HOCO Lewis structure

Why is it that the Hydrogen is bonded to the oxygen rather than the carbon in HOCO?
Sun Nov 04, 2018 11:11 am
Forum: Administrative Questions and Class Announcements
Topic: Midterm Exam Time Conflict
Replies: 2
Views: 189

### Midterm Exam Time Conflict

Hi, I recently asked my professor for my 5-6:15 English class if I would be able to leave class a bit early to make it to my chemistry midterm at 6pm. She responded saying I needed to work it out with my chemistry professor/proctor of the exam. I am unsure of what to do at this point? Are there exam...
Tue Oct 23, 2018 3:29 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Number 15 for chapter 1
Replies: 1
Views: 94

### Number 15 for chapter 1

I was wondering why the Rydberg equation is being set up to be equal to nu (v)? What is the correlation? Also, would a question like this ever be on an exam?
Thu Oct 18, 2018 11:34 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: 1.15 Homework Problem
Replies: 2
Views: 162

### 1.15 Homework Problem

I did my research on the forum on how to do this problem; however, the approach taken in the solutions manual uses the shortcut equation that Dr. Lavelle frowned upon. How can I solve this problem using the approach he uses with the equation En=-hR/n^2 as opposed to nu=R(1/n^2-1/n^2)?
Mon Oct 08, 2018 11:44 pm
Forum: Limiting Reactant Calculations
Topic: Confused on how the solutions manual arrived to this answer?
Replies: 1
Views: 147

### Confused on how the solutions manual arrived to this answer?

On M.5, the question asks to determine how many moles of each product will be produced. What I did is perform a mole to mole ratio by multiplying 5mol of BrF3 by the 6 moles of ClO2F and dividing that by 2 mol BrF3 to obtain the moles of ClO2F left. I got 15 moles for ClO2F but the solutions manual ...
Fri Oct 05, 2018 4:04 pm
Forum: Limiting Reactant Calculations
Topic: Mole Ratios Within the Conversion
Replies: 3
Views: 154

### Mole Ratios Within the Conversion

When given a chemical equation like 6 CO2 + 6 H2O → C6H12O6 + 6 O2, the ratio between CO2 and H20 is 1:1. However I have seen in a few post-module questions that it asks about the mass of, perhaps, of O2 when given 3 moles of CO2 and 6 moles of H20. When it says three moles of CO2, do I disregard th...