Search found 67 matches

by Helen Mejia 1I
Sun Mar 17, 2019 10:15 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Work done vs work on system
Replies: 18
Views: 772

Re: Work done vs work on system

work being done on the system is positive while work being done by the system is negative.
by Helen Mejia 1I
Sun Mar 17, 2019 10:14 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: U=0
Replies: 6
Views: 241

Re: U=0

yes it is equal to zero.
by Helen Mejia 1I
Wed Mar 13, 2019 11:18 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 7th Edition Problem 7D.5
Replies: 1
Views: 42

7th Edition Problem 7D.5

Can someone help me on how to solve problem 7D.5? It says "The rate constant of the reaction between CO 2 and OH- in aqueous solution to give HCO 3 - ion is 1.5 x 10^10 Lmol-1s-1 at 25 Celsius. Determine the rate constant at human body temperature (37 Celsius) given that the activation energy f...
by Helen Mejia 1I
Sun Mar 10, 2019 9:49 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Calculating E naught
Replies: 5
Views: 74

Re: Calculating E naught

Always remember that the goal is to have a positive E naught because a positive value indicates that it is spontaneous.
by Helen Mejia 1I
Sun Mar 10, 2019 9:47 am
Forum: Balancing Redox Reactions
Topic: Reducing power?
Replies: 3
Views: 81

Reducing power?

How can you rank elements by increasing reducing power?
by Helen Mejia 1I
Sun Mar 10, 2019 9:45 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 7th edition 6N.7
Replies: 1
Views: 45

7th edition 6N.7

Can someone explain how to do number 7 part b?
It says Calculate the cell potential for each of the following concentration cells.
B) Pt(s)|H2 (g, 1 bar)|H+ (aq, pH=4)|H+ (aq, pH=3)|H2 (g, 1 bar)| Pt(s)
Also explain why n=1
by Helen Mejia 1I
Mon Mar 04, 2019 12:15 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Pt
Replies: 14
Views: 242

Pt

When do you add Pt to the voltaic cell? Are there some conditions to memorize? Are there some special conditions that we need to remember?
by Helen Mejia 1I
Mon Mar 04, 2019 12:13 am
Forum: Balancing Redox Reactions
Topic: Acidic Solutions
Replies: 7
Views: 178

Re: Acidic Solutions

For acidic solutions, you add H20 to balance the oxygens and then you add H+ to balance the hydrogens. Then you should balance the charges.
by Helen Mejia 1I
Mon Mar 04, 2019 12:10 am
Forum: Balancing Redox Reactions
Topic: oxidizing agent and reducing agent
Replies: 15
Views: 220

Re: oxidizing agent and reducing agent

The oxidizing agent helps a substance get oxidized. It accepts an electron.
The reducing agent helps a substance get reduced. It gives an electron
by Helen Mejia 1I
Thu Feb 21, 2019 10:31 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta G = 0
Replies: 4
Views: 76

Delta G = 0

What does it mean when delta G is equal to zero? Does it have to do something with the amount of work the reaction can do?
by Helen Mejia 1I
Thu Feb 21, 2019 10:27 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy
Replies: 2
Views: 79

Gibbs Free Energy

Why is that standard delta G is not measured directly unlike heat in a calorimeter to measure standard delta H?
by Helen Mejia 1I
Thu Feb 21, 2019 10:21 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy in cal
Replies: 2
Views: 60

Gibbs Free Energy in cal

When you calculate Gibbs free energy using enthalpy and entropy in cal will our final units for Gibbs free energy be cal per mole or just cal?
by Helen Mejia 1I
Mon Feb 18, 2019 10:53 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Negative Delta G
Replies: 7
Views: 153

Negative Delta G

What are some conditions that allow delta G to be negative?
by Helen Mejia 1I
Mon Feb 18, 2019 10:50 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Van't Hoff Equation
Replies: 3
Views: 66

Van't Hoff Equation

Can someone explain why temperature is dependent on K in the Van't Hoff Equation?
by Helen Mejia 1I
Sun Feb 10, 2019 3:25 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Change of Enthalpy =Change of Internal Energy
Replies: 1
Views: 44

Change of Enthalpy =Change of Internal Energy

Can someone explain the conditions when the change internal energy is equal to the change of enthalpy?
by Helen Mejia 1I
Sun Feb 10, 2019 3:22 pm
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: HW Prolem (4G.4) 7th Edition
Replies: 2
Views: 42

HW Prolem (4G.4) 7th Edition

Can someone explain how to identify which of BF3 or COF2 will have a higher molar entropy?
by Helen Mejia 1I
Thu Feb 07, 2019 8:50 pm
Forum: Administrative Questions and Class Announcements
Topic: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)
Replies: 179
Views: 7782

Re: DOWNLOAD SESSION WORKSHEETS HERE - Sun 7-9PM (Karen)

I need help on worksheet #4 (First Law of Thermo). On the answer key, it said -631 kJ, but I got -631J. What is the correct unit? The given information is in J.
by Helen Mejia 1I
Sat Feb 02, 2019 3:14 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Week 5 Homework
Replies: 4
Views: 75

Re: Week 5 Homework

I think we do continue on Thermochemistry because he just started to lecture on thermodynamics.
by Helen Mejia 1I
Sat Feb 02, 2019 3:13 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Absorbing and Releasing Heat
Replies: 2
Views: 58

Absorbing and Releasing Heat

Can someone explain how after a while the temperature of metal and water can have the same temperature after a while? If one is absorbing while the other is losing heat?
by Helen Mejia 1I
Sat Feb 02, 2019 3:07 pm
Forum: Phase Changes & Related Calculations
Topic: Heat Curve
Replies: 6
Views: 109

Heat Curve

Are we supposed to memorize the Heat curve or will we be given the heat curve?
by Helen Mejia 1I
Sun Jan 27, 2019 6:41 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Preferable Method?
Replies: 3
Views: 54

Preferable Method?

Since there are 3 methods can we use any in all the problems? Or is there a method that is more accurate than the other two depending on the question being asked?
by Helen Mejia 1I
Sun Jan 27, 2019 6:38 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard Temperature
Replies: 7
Views: 126

Re: Standard Temperature

For an element, it is the most stable at 1 atm and the temp of interest is usually 25 celsius
by Helen Mejia 1I
Sun Jan 27, 2019 6:32 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthaplies
Replies: 1
Views: 37

Bond Enthaplies

Can someone please explain why is the bond enthalpies the least accurate method?
by Helen Mejia 1I
Sun Jan 20, 2019 7:34 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kw
Replies: 4
Views: 79

Re: Kw

Thank you!
by Helen Mejia 1I
Sun Jan 20, 2019 7:32 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Ka and Kb as Inverses?
Replies: 7
Views: 144

Re: Ka and Kb as Inverses?

Using the formula we were given Ka x Kb= Kw will be the best thing to do.
by Helen Mejia 1I
Wed Jan 16, 2019 9:33 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Help on Question 6B.9 (7th edition)
Replies: 2
Views: 42

Help on Question 6B.9 (7th edition)

6B.9 is asking to complete a table where the concentration of H 3 O + is equal to 1.50. In the table, it is asking for the pH. I have gotten a negative answer. I get -.176 but in the solution manual it says that the pH is positive .176 Can someone please explain what happens to the negative. I have ...
by Helen Mejia 1I
Tue Jan 15, 2019 8:36 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kw
Replies: 4
Views: 79

Kw

Can someone please explain why the concentration of H3O+ equals the concentration of OH-?
I am referring to question 6A.21. This question is asking what is the concentration of H3O+ ions at 37 C. Kw= 2.1 x 10^-14
by Helen Mejia 1I
Sat Jan 12, 2019 6:20 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Intermediate Values of K
Replies: 1
Views: 41

Intermediate Values of K

Can someone explain why intermediate values of K result to neither the products or reactants are not strongly favored at equilibrium?
by Helen Mejia 1I
Sat Jan 12, 2019 6:08 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Solving for K
Replies: 7
Views: 105

Solving for K

When is it okay to use parathesis or brackets when solving for K? What is the difference between them?
by Helen Mejia 1I
Wed Jan 09, 2019 9:14 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 7th edition 5G.5
Replies: 3
Views: 58

Re: 7th edition 5G.5

I second this!! Also, how did you figure out part a and b? How do we determine equilibrium by looking at the molecules? For part a, you will see that the diatomic molecules are decreasing. It goes from 11 to 8 to 5. It has reached equilibrium in flask #3 because in flask #4 it has the same amount o...
by Helen Mejia 1I
Fri Dec 07, 2018 3:14 pm
Forum: Lewis Acids & Bases
Topic: Brontsted and Lewis
Replies: 1
Views: 59

Brontsted and Lewis

Can someone explain the difference between Bronsted and Lewis acids and bases? Is there any easy way to identify what it is in an equation?
by Helen Mejia 1I
Fri Dec 07, 2018 3:05 pm
Forum: Conjugate Acids & Bases
Topic: Conjugate Acids and Bases
Replies: 1
Views: 55

Conjugate Acids and Bases

Hi I am so confused about conjugate acids and bases? Can someone explain it and provide an example?
by Helen Mejia 1I
Fri Dec 07, 2018 2:39 pm
Forum: Biological Examples
Topic: Hemoglobin Question
Replies: 2
Views: 186

Hemoglobin Question

I don't understand the biological importance of hemoglobin and how it is formed?
Can someone please explain it.
by Helen Mejia 1I
Sun Dec 02, 2018 2:51 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Weak Acid or Weak Base
Replies: 1
Views: 54

Weak Acid or Weak Base

For the problem, J.17, it says " in each of the following salts, either the cation or anion is a weak acid or a weak base in water. Write the chemical equation for the proton transfer reaction of this cation or anion with water: (a) NaC 6 H 5 O How do you start this problem? I saw the solution ...
by Helen Mejia 1I
Sat Dec 01, 2018 2:13 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Polydentate Ligand
Replies: 3
Views: 58

Polydentate Ligand

How can we determine if a ligand is polydentate? Can we tell by drawing the Lewis structure?
by Helen Mejia 1I
Sat Dec 01, 2018 2:09 pm
Forum: Naming
Topic: Ligand
Replies: 4
Views: 95

Re: Ligand

haleyervin7 wrote:Will we be expected to memorize the names of several ligands according to the naming convention?

Yes, we are expected to know the names of the ligands. The professor has a chart that will help us to memorize the name of a ligand. The chart is in the class website.
by Helen Mejia 1I
Sat Dec 01, 2018 2:06 pm
Forum: Naming
Topic: Ligand names on Final
Replies: 2
Views: 56

Re: Ligand names on Final

Memorizing the chart that he provides on the website is very helpful. I do not think we are given a chart to help us out. Most of the exercises on the textbook expect us to know the names already.
by Helen Mejia 1I
Wed Nov 21, 2018 1:12 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: VSPER Formula
Replies: 7
Views: 153

Re: VSPER Formula

The A in the VSEPR formula stands for the central atom.
by Helen Mejia 1I
Wed Nov 21, 2018 1:10 pm
Forum: Hybridization
Topic: Hybridization
Replies: 6
Views: 114

Re: Hybridization

Also can someone please explain by giving an example?
by Helen Mejia 1I
Wed Nov 21, 2018 1:10 pm
Forum: Hybridization
Topic: Hybridization
Replies: 6
Views: 114

Hybridization

How does hybridization arise from atomic orbitals?
by Helen Mejia 1I
Sat Nov 17, 2018 12:36 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Seesaw Shape
Replies: 4
Views: 90

Re: Seesaw Shape

For the Test do we have to put the exact bond angle when it is slightly less?
For example for AX3E it is slightly less than 109.5, it is 107. For the Test do have to put that the bond angle is 107 or is it okay to say it is slightly less than 109.5.
by Helen Mejia 1I
Sat Nov 17, 2018 12:17 pm
Forum: Lewis Structures
Topic: Lewis Structure and Molecule Shape (TEST #3) [ENDORSED]
Replies: 1
Views: 86

Lewis Structure and Molecule Shape (TEST #3) [ENDORSED]

For test #3, can we draw the Lewis structure symmetrically? Or do we need to draw the Lewis structure as it would look with its molecular shape? For example, in class, the professor drew the Lewis structure for SF 4 and he put the fluorines all in the right side of Sulfur and the lone pair in the le...
by Helen Mejia 1I
Sat Nov 17, 2018 12:00 pm
Forum: Sigma & Pi Bonds
Topic: Pi Bonds
Replies: 1
Views: 71

Pi Bonds

Can someone please explain pi bonds?
And also why double bonds have one sigma bond and one pi bond
by Helen Mejia 1I
Sat Nov 10, 2018 3:43 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Polarizability
Replies: 4
Views: 136

Polarizability

Can someone explain why polarizability depends on the number of electrons and the size of the atom?
by Helen Mejia 1I
Sat Nov 10, 2018 3:28 pm
Forum: Dipole Moments
Topic: Dipole-Induced Dipole
Replies: 3
Views: 58

Dipole-Induced Dipole

Hi can someone explain dipole and induced dipole?
by Helen Mejia 1I
Fri Nov 02, 2018 11:25 pm
Forum: Photoelectric Effect
Topic: Test #2 Question #2b
Replies: 4
Views: 361

Re: Test #2 Question #2b

okay, thank you!
by Helen Mejia 1I
Fri Nov 02, 2018 10:44 pm
Forum: Photoelectric Effect
Topic: Test #2 Question #2b
Replies: 4
Views: 361

Test #2 Question #2b

Hi, can someone explain how does the speed of the ejected electron in part (a) change when the intensity of the light is increased?
by Helen Mejia 1I
Wed Oct 31, 2018 5:42 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Test #2 Question #2
Replies: 3
Views: 338

Test #2 Question #2

Hi, can someone help me on question 2 on the midterm? My T.A. tried to explain it but they only said to change km to m. Question 2: The uncertainty in the momentum of a cricket ball which is traveling at 150 m/hour is 2x 10^-6 times its momentum. Its mass is .160kg. Calculate its minimum uncertainty...
by Helen Mejia 1I
Thu Oct 25, 2018 10:10 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Nodal Planes on f-orbitals
Replies: 4
Views: 222

Re: Nodal Planes on f-orbitals

Yes it does relate with the shape of orbital.
by Helen Mejia 1I
Thu Oct 25, 2018 10:07 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Nodal Planes on f-orbitals
Replies: 4
Views: 222

Re: Nodal Planes on f-orbitals

So memorize that
s= 0 nodal planes
p=1 nodal planes
d= 2 nodal planes
f= 3 nodal pleanes
by Helen Mejia 1I
Thu Oct 25, 2018 9:57 pm
Forum: Properties of Light
Topic: b15
Replies: 2
Views: 120

Re: b15

You need to find the energy of the photon in order to find the wavelength.
The formula to find the energy of a photon is the work function plus kinetic energy.
Work function is 1.66 x 10^-17 J a
Kinectic Energy: 1/2(m)(v^2)
by Helen Mejia 1I
Fri Oct 19, 2018 7:40 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Ground State Question
Replies: 1
Views: 34

Ground State Question

What does it mean for an electron configuration to be in ground state? Can someone give an example?
by Helen Mejia 1I
Fri Oct 19, 2018 7:19 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Multi-Electron Atoms
Replies: 2
Views: 56

Multi-Electron Atoms

Hi, can someone please explain multi-electron atoms and electrostatic (coulomb) potential energy?
I did not understand today's lecture at all.
by Helen Mejia 1I
Fri Oct 19, 2018 7:07 pm
Forum: Quantum Numbers and The H-Atom
Topic: 4th Quantum number m subscript s
Replies: 1
Views: 41

Re: 4th Quantum number m subscript s

So there is two values for ms which are -1/2 and 1/2. If it is negative then the electron will spin down and if it is positive it will spin up.
by Helen Mejia 1I
Fri Oct 12, 2018 3:09 pm
Forum: Properties of Light
Topic: Car Example in Class with De Brogile Equation
Replies: 8
Views: 112

Re: Car Example in Class with De Brogile Equation

What is the exact reason that the car does not have any wavelength properties even though it is moving? The car does not have any wavelength properties because the wavelength was too small. The professor mentioned how it was even smaller than the gamma rays. I think he said that the smallest wavelen...
by Helen Mejia 1I
Fri Oct 12, 2018 2:48 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Wavelength Worked Example from Lecture
Replies: 3
Views: 36

Re: Wavelength Worked Example from Lecture

I recall that the professor said that the smallest wavelength is 10^-18. Anything smaller such as 10^-38 is too small to be detected
by Helen Mejia 1I
Fri Oct 12, 2018 2:07 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Explain an example in Lecture
Replies: 3
Views: 47

Explain an example in Lecture

Hi confused why a number (4.09x10^-19J) that is negative was used as positive in a further step. Why did it change from negative to positive? The professor gave an example that said, "Calculate the frequency of light emitted by a hydrogen atom when an electron makes a transition from the fourth...
by Helen Mejia 1I
Sat Oct 06, 2018 3:57 pm
Forum: Molarity, Solutions, Dilutions
Topic: Help with G5
Replies: 5
Views: 121

Help with G5

Hi can someone explain how to do G5 (edition 7) It says " A student prepared a solution of sodium carbonate by adding 2.111g of the solid to a 250.0 mL volumetric flask and adding water to the mark. Some of this solution was transferred to a buret. What volume of solution should the student tra...
by Helen Mejia 1I
Thu Oct 04, 2018 11:27 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Moles and Molar Mass
Replies: 10
Views: 137

Re: Moles and Molar Mass

Lynsea_Southwick_3F wrote:
Helen Mejia 3F wrote:Hey, so consider using Avogadros number (6.022 x 10^23) and multiplying it by twice the radius (which would be 288 pm).


6.022 x 10^23) Ag x (288 pm x 10^-12)= 1.73 x 10^14


Why do you multiply the radius twice?



Because you need to know how long the fiber will be.
by Helen Mejia 1I
Thu Oct 04, 2018 11:26 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Moles and Molar Mass
Replies: 10
Views: 137

Re: Moles and Molar Mass

So you are given 1.00 mol of Ag, but what you are supposed to find is the number of Ag atoms from this given info. because only then can you use the radius given (144pm) to figure out how long the fiber is. Step 1: you would convert the mol of Ag to number of Ag atoms 1.00 mol Ag x (6.0221x10^23)/m...
by Helen Mejia 1I
Thu Oct 04, 2018 11:00 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Moles and Molar Mass
Replies: 10
Views: 137

Re: Moles and Molar Mass

Hey, so consider using Avogadros number (6.022 x 10^23) and multiplying it by twice the radius (which would be 288 pm).


6.022 x 10^23) Ag x (288 pm x 10^-12)= 1.73 x 10^14
by Helen Mejia 1I
Tue Oct 02, 2018 12:14 pm
Forum: Molarity, Solutions, Dilutions
Topic: Molarity and Dilution of a Solution:Post-Module Assessment Question 19
Replies: 2
Views: 53

Re: Molarity and Dilution of a Solution:Post-Module Assessment Question 19

Thank you! I see the mistake I did! I think the answer you got is correct since it was one of the options! (:
by Helen Mejia 1I
Tue Oct 02, 2018 12:07 pm
Forum: Molarity, Solutions, Dilutions
Topic: Molarity and Dilution of a Solution:Post-Module Assessment Question 19
Replies: 2
Views: 53

Molarity and Dilution of a Solution:Post-Module Assessment Question 19

Hi, I am having trouble with question 19 from the molarity post-assessment. The question says, calculate the volume of a 0.06 M sodium chloride solution containing 0.03 moles of sodium chloride. What I did to solve this was using the molarity formula. Molarity (M)= moles (n)/ volume(v). since it was...
by Helen Mejia 1I
Sat Sep 29, 2018 6:14 pm
Forum: SI Units, Unit Conversions
Topic: How does grading for discussion posts work?
Replies: 80
Views: 2583

Re: Reading for Class

Hi Cecilia, for the readings for Chem, I am reading based on what the lectures are going to be about. For example, you can look at the lecture outlines he provided online. I am guessing that the lecture outline #1 is for week one and so on.

Go to advanced search