Search found 64 matches

by Yvonne Du
Thu Mar 14, 2019 11:28 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Test 2
Replies: 6
Views: 93

Re: Test 2

For the snowflakes, delta H is negative because the snowflakes lose heat, and delta S is negative because going from a liquid to a solid is less chaotic. Negative delta H minus a negative delta S makes a negative delta G. For the sublimation, delta H is positive because heat is going in, and delta ...
by Yvonne Du
Thu Mar 14, 2019 11:22 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: pseudo rate law
Replies: 7
Views: 48

Re: pseudo rate law

I was wondering the same thing. Dr.Lavelle mentioned it during class, but I am still confused.
by Yvonne Du
Thu Mar 14, 2019 11:20 pm
Forum: First Order Reactions
Topic: integrated rate laws
Replies: 3
Views: 23

Re: integrated rate laws

This really helped! I am glad that this question was asked.
by Yvonne Du
Thu Mar 14, 2019 11:17 pm
Forum: Van't Hoff Equation
Topic: pH and van’t hoff
Replies: 6
Views: 66

Re: pH and van’t hoff

When temperature increases, the Kw increases as well, which causes the neutral [H+] to increase and neutral pH to decrease. On the flip side, when temperature decreases, the Kw and neutral [H+] decrease, so the neutral pH increases. Neutral pH of 7 is only true at 298K. Thank you this is very helpf...
by Yvonne Du
Thu Mar 14, 2019 11:14 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: catalyst vs intermediate
Replies: 2
Views: 20

Re: catalyst vs intermediate

A catalyst is at the very beginning of the reaction and gets used; while intermediates only join in the later time and get used.
by Yvonne Du
Thu Mar 14, 2019 11:12 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Catalysts in Rate Law
Replies: 5
Views: 32

Re: Catalysts in Rate Law

I asked my TA today, he said catalysts can be included in elementary step rate laws, but not the overall?
by Yvonne Du
Wed Mar 13, 2019 10:23 pm
Forum: First Order Reactions
Topic: Integrated Rate Law
Replies: 2
Views: 19

Re: Integrated Rate Law

What is the exponential first-rate law?
by Yvonne Du
Wed Mar 13, 2019 10:21 pm
Forum: First Order Reactions
Topic: Time Conversions
Replies: 6
Views: 42

Re: Time Conversions

Yes, just make sure that your units are consistent.
by Yvonne Du
Wed Mar 13, 2019 10:18 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Catalyst vs. Intermediate
Replies: 8
Views: 73

Re: Catalyst vs. Intermediate

A catalyst is involved in the starting of the reaction, while an intermediate joins in later. Both of them are not included in the rate law. Today, my TA said that a catalyst can be included in the rate law. Can someone clarify? Sorry! I made a mistake. Yes it is possible for a catalyst to appear i...
by Yvonne Du
Wed Mar 13, 2019 10:11 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Determining Catalysts
Replies: 2
Views: 21

Re: Determining Catalysts

Yes, if it is not one of the reactants of the first step, it would be an intermediate instead.
by Yvonne Du
Wed Mar 13, 2019 1:23 pm
Forum: Administrative Questions and Class Announcements
Topic: Sig Figs
Replies: 9
Views: 81

Re: Sig Figs

I think they are worth one point per question based on the midterm, so I think it is graded.
by Yvonne Du
Wed Mar 13, 2019 1:21 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Catalyst vs. Intermediate
Replies: 8
Views: 73

Re: Catalyst vs. Intermediate

A catalyst is involved in the starting of the reaction, while an intermediate joins in later. Both of them are not included in the rate law.
by Yvonne Du
Sun Mar 10, 2019 10:08 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Elementary Steps
Replies: 1
Views: 22

Re: Elementary Steps

Basically the elementary steps help you determine the rate for the whole reaction. The step that has the slowest rate would be the rate for the whole reaction.
by Yvonne Du
Sun Mar 10, 2019 10:05 pm
Forum: Administrative Questions and Class Announcements
Topic: Final
Replies: 18
Views: 203

Re: Final

The new materials would weight more percentage I think.
by Yvonne Du
Sun Mar 10, 2019 10:03 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Log version vs ln Version
Replies: 7
Views: 63

Re: Log version vs ln Version

The ln version might be more convenient, but both log and ln give the same ratio/result.
by Yvonne Du
Sun Mar 10, 2019 10:01 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Test 2
Replies: 12
Views: 142

Re: Test 2

Since a combustion releases heat, you can therefore say that the reaction is exothermic and Gibbs free energy is negative
by Yvonne Du
Sun Mar 10, 2019 9:59 pm
Forum: First Order Reactions
Topic: Molar coefficients
Replies: 4
Views: 40

Re: Molar coefficients

No, the coefficients do no effect order
by Yvonne Du
Wed Mar 06, 2019 5:17 pm
Forum: Zero Order Reactions
Topic: General Meaning of "Zero Order" Reactions
Replies: 7
Views: 62

Re: General Meaning of "Zero Order" Reactions

Danielle_Gallandt3I wrote:This typically occurs when the reactant concentration is already very high, so adding more reactant doesn't change the rate

Thank you for clarifying!
by Yvonne Du
Wed Mar 06, 2019 5:16 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Units for rate laws
Replies: 2
Views: 37

Re: Units for rate laws

It is not necessary, but make sure to keep the units constant.
by Yvonne Du
Sat Feb 16, 2019 11:45 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 4
Views: 58

Re: Bond Enthalpies

If you know the lewis structures, it would be very helpful since you would know what bonds are breaking/forming.
by Yvonne Du
Sat Feb 16, 2019 11:40 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Pressure Equation
Replies: 7
Views: 86

Re: Pressure Equation

When the temperature is constant, you can either use V2/V1 or P1/P2 depends on what you are given because in the formula PV=nRT, P and V has a proportional relationship.
by Yvonne Du
Sat Feb 16, 2019 11:35 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Converting to q rev
Replies: 4
Views: 61

Re: Converting to q rev

Yes, qrev/Delta T would be the formula for irreversible reaction.
by Yvonne Du
Sun Jan 27, 2019 6:15 pm
Forum: Administrative Questions and Class Announcements
Topic: Lecture Slides
Replies: 5
Views: 77

Re: Lecture Slides

Nope but the book covers pretty much everything that he mentions.
by Yvonne Du
Sun Jan 27, 2019 6:12 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard Temperature
Replies: 7
Views: 60

Re: Standard Temperature

I think it might be 25 Celcius degree.
by Yvonne Du
Sun Jan 27, 2019 6:09 pm
Forum: Ideal Gases
Topic: SI Units
Replies: 5
Views: 66

Re: SI Units

atm, but other units can also be used. Ps, different units of pressure are correspond to a different value of R.
by Yvonne Du
Sun Jan 27, 2019 6:07 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Catalysts in Kc
Replies: 6
Views: 64

Re: Catalysts in Kc

They speed up the process but do not change the concentrations.
by Yvonne Du
Sun Jan 27, 2019 6:07 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Inert Gas
Replies: 6
Views: 79

Re: Inert Gas

Since the volume is not changed after gas is being inserted, the partial pressure for each molecule is not changed therefore the equilibrium stays.
by Yvonne Du
Sun Jan 27, 2019 6:04 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Exothermic vs. Endothermic
Replies: 10
Views: 96

Re: Exothermic vs. Endothermic

An exothermic reaction has a negative delta H while an endothermic reaction has a positive delta H. Delta H=Change in enthalpy.
by Yvonne Du
Sun Jan 27, 2019 6:02 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: ICE
Replies: 19
Views: 200

Re: ICE

The concentration of reactants and products(excluded solids and liquids) in the equilibrium state.
by Yvonne Du
Sun Jan 27, 2019 5:54 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5%
Replies: 10
Views: 105

Re: 5%

If the concentration of H+ or OH- is less than 5% of the concentration of HA or HB, you can ignore the x when it is being subtracted or added(i.e. 2-x=2).
by Yvonne Du
Sun Jan 13, 2019 10:12 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: HW PROBELM 1 PART D
Replies: 4
Views: 61

Re: HW PROBELM 1 PART D

Since the equilibrium constant(K) does not change, that means the ratio of product/reactant has to be constant. If you add more concentration to one of them, the other has to increase in order to make the ratio constant.
by Yvonne Du
Sun Jan 13, 2019 10:10 pm
Forum: Administrative Questions and Class Announcements
Topic: Test Dates
Replies: 3
Views: 65

Re: Test Dates

It depends on when your discussion session is. Test 1 should be in week 3 and test 2 should be in week 7
by Yvonne Du
Sun Jan 13, 2019 10:07 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Pure Solids and Liquids
Replies: 4
Views: 58

Re: Pure Solids and Liquids

My TA said they dont affect equilibrium
by Yvonne Du
Sun Dec 02, 2018 12:04 am
Forum: Hybridization
Topic: lone pairs
Replies: 20
Views: 167

Re: lone pairs

Yes, one lone pair is considered as one electron density. Since hybridization is based on the number of electron density, you consider lone pairs too.
by Yvonne Du
Sun Dec 02, 2018 12:01 am
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: polarizing power and polarizability
Replies: 5
Views: 90

Re: polarizing power and polarizability

Since polarizing power describes the power of cations pulling electrons from the anions, small and highly charged cations would have a strong polarizing power to distort the electron clouds from the anions. Polarizability is the ability for anions to pull their electrons. Big and highly charged anio...
by Yvonne Du
Sat Dec 01, 2018 11:54 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone pairs
Replies: 4
Views: 67

Re: Lone pairs

Lone pairs create strong repulsions since the charges are the same(negative). Therefore, they try to get away from each other and cause the bond angle to decrease. Also, the bonded atoms would most likely end up being close together since the lone pairs are getting away from each other.
by Yvonne Du
Tue Nov 27, 2018 12:42 pm
Forum: Ionic & Covalent Bonds
Topic: Question 6.9 ranking dipole forces
Replies: 1
Views: 93

Question 6.9 ranking dipole forces

6.9 Place the following types of molecular and ion interactions in order of increasing strength: (a) ion–dipole; (b) induceddipole–induced-dipole; (c) dipole–dipole in the gas phase; (d) ion–ion; (e) dipole–dipole in the solid phase. Can someone explain why is the order dipole-induced-dipole=dipole ...
by Yvonne Du
Sun Nov 25, 2018 5:26 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal charge vs octet rule
Replies: 4
Views: 67

Re: Formal charge vs octet rule

You should try to give every atom an octet, then you can see if the formal charges are all equal to zero. If not, then check to see if the central atom is in 3p orbital, therefore, you can violate the octet rule. Most of the times the structure should satisfy both the octet rule and the formal charge.
by Yvonne Du
Sun Nov 25, 2018 5:20 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Dipole
Replies: 2
Views: 61

Re: Dipole

A dipole is when a positively charged atom bonds with a negatively charged atom. The electronegative force between the two atoms is not the same, thus a dipole moment happens which is that one of the atoms is more electronegative than the other.
by Yvonne Du
Sun Nov 25, 2018 5:14 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Sigma vs pi bonds
Replies: 7
Views: 73

Re: Sigma vs pi bonds

A sigma bond is the very first bond between two atoms, while pi bonds are the ones that come after the sigma bond. For example in a triple bond, there is one sigma bond and two pi bonds.
Hope this helps.
by Yvonne Du
Sun Nov 18, 2018 10:05 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone pairs
Replies: 5
Views: 62

Re: Lone pairs

Yes, the lone pairs also affect the bond angles, and different type of VSEPR models have different bond angles.
by Yvonne Du
Sun Nov 18, 2018 10:02 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles for H2O
Replies: 8
Views: 67

Re: Bond Angles for H2O

In my notes I have that since H2O has two lone pair electrons and two pairs of bonding electrons, the lone pairs make the bond angle decrease a bit.

Hope this helps.
by Yvonne Du
Sun Nov 18, 2018 10:00 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Molecular Shape Patterns
Replies: 5
Views: 86

Re: Molecular Shape Patterns

I think in the lecture we went over some notations about the VSEPR model: A=central atom X=bonded atom E=lone pair For example, AX3 is trigonal planar, AX2E2 is bend, AX4 is tetrahedral, AX4E is trigonal bipyramidal, and AX4E2 is Square planer. I think remembering these can save you some time. Hope ...
by Yvonne Du
Tue Nov 13, 2018 3:12 pm
Forum: Administrative Questions and Class Announcements
Topic: Test 3
Replies: 8
Views: 132

Re: Test 3

For 6th edition, do we also study chapter 6.4 and 6.5?
by Yvonne Du
Tue Nov 13, 2018 1:08 pm
Forum: Administrative Questions and Class Announcements
Topic: MIDTERM PRACTICE - Garlic Bread Review Session [ENDORSED]
Replies: 121
Views: 4568

Re: MIDTERM PRACTICE - Garlic Bread Review Session [ENDORSED]

Elle_Mendelson_4I wrote:Will someone explain 10A?


As more electrons and photons are added to the atom from left to right, the force of increasing protons creates a stronger pull that attracts the electrons to get closer to the nucleus. Therefore the atom shrinks for silicon and has a smaller radius than aluminum.
by Yvonne Du
Tue Nov 13, 2018 12:58 pm
Forum: Administrative Questions and Class Announcements
Topic: MIDTERM PRACTICE - Garlic Bread Review Session [ENDORSED]
Replies: 121
Views: 4568

Re: MIDTERM PRACTICE - Garlic Bread Review Session [ENDORSED]

For number 5, I keep getting .127 M after setting the problem up like (.211 M)(.150 L) = M2(.250 L). But in my notes, I believe Lyndon got 1.69 x 10^-2. I was wondering if anyone knows what I am doing wrong. Thanks! Hi! Since the problem stated that only 20ml was removed to the 2nd flask, you put 0...
by Yvonne Du
Tue Nov 13, 2018 12:55 pm
Forum: Bond Lengths & Energies
Topic: Drawing resonance structures?
Replies: 6
Views: 75

Re: Drawing resonance structures?

The resonance structures should be equally stable. However, the Lewis structure for this specific compound does not represent its real appearance because a compound that has resonance structures actually have the resonance bond constantly changing from atom to atom, so that is why we said we can hav...
by Yvonne Du
Sun Nov 04, 2018 4:14 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: HW 1.15, 6th edition
Replies: 1
Views: 53

Re: HW 1.15, 6th edition

1)Convert 102.6nm to 1.03*10^-7m.
2)Use c=v*lamda to find the frequency.
3)Use Rydberg formula, v=R(1/(n^2)-1/(n^2)) to find n2. Note that the first n is n1 and the second n is n2.
4)Since it's Lyman's series, you know n1=1.
by Yvonne Du
Sun Nov 04, 2018 3:43 pm
Forum: Administrative Questions and Class Announcements
Topic: MIDTERM PRACTICE - Garlic Bread Review Session [ENDORSED]
Replies: 121
Views: 4568

Re: MIDTERM PRACTICE - Garlic Bread Review Session [ENDORSED]

For number 5, I keep getting .127 M after setting the problem up like (.211 M)(.150 L) = M2(.250 L). But in my notes, I believe Lyndon got 1.69 x 10^-2. I was wondering if anyone knows what I am doing wrong. Thanks! Hi! Since the problem stated that only 20ml was removed to the 2nd flask, you put 0...
by Yvonne Du
Sun Nov 04, 2018 11:31 am
Forum: Administrative Questions and Class Announcements
Topic: MIDTERM PRACTICE - Garlic Bread Review Session [ENDORSED]
Replies: 121
Views: 4568

Re: MIDTERM PRACTICE - Garlic Bread Review Session [ENDORSED]

Hi can anyone explain 8a? I don't know how to correctly word my answers...
by Yvonne Du
Sun Oct 28, 2018 11:10 pm
Forum: Lewis Structures
Topic: Electron Configurations
Replies: 3
Views: 48

Re: Electron Configurations

You remove electrons starting with the highest level. Since there is only one electron in the 4s shell, you need to subtract another electron from the 3d shell.

Hope this helps.
by Yvonne Du
Sun Oct 28, 2018 11:04 pm
Forum: Ionic & Covalent Bonds
Topic: Cations/Anions
Replies: 4
Views: 38

Re: Cations/Anions

For your first example, the whole 5p1 represents one electron only. In the future, you can know the number of electrons in each shell by looking at their superscript. For example, 5p5 means there are 5 electrons in the 5p shell. For your second example, p shells contain 6 electrons in total. In orde...
by Yvonne Du
Tue Oct 23, 2018 10:21 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg Equation
Replies: 7
Views: 223

Re: Rydberg Equation

I think in the book they stated that it should be n(initial)-n(final). I ran into the same problem. For one of the homework questions, I got a negative answer when I put n(initial)-n(final), but the answer key says it is positive. They flipped the other to get a positive number. I think I'll go with...
by Yvonne Du
Sun Oct 21, 2018 11:04 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Heisenberg equation
Replies: 2
Views: 55

Re: Heisenberg equation

I have the same question too.
by Yvonne Du
Sun Oct 21, 2018 11:00 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Coulomb's Law and Effective Nuclear Charge on test
Replies: 2
Views: 24

Re: Coulomb's Law and Effective Nuclear Charge on test

I think you should at least be familiar with it. Even though we didn't do too much on those topics, but it doesn't hurt to learn a little more.
by Yvonne Du
Sun Oct 21, 2018 10:55 pm
Forum: Properties of Light
Topic: Test 2 Equations
Replies: 14
Views: 208

Re: Test 2 Equations

I think you should be familiar with them, but don't try too hard to memorize them. I would recommend knowing the E of photon formula, De Broglie Equation, the Uncertainty Principle, and the Photoelectric effect.
by Yvonne Du
Thu Oct 11, 2018 11:34 pm
Forum: Properties of Electrons
Topic: Quantum World
Replies: 6
Views: 70

Re: Quantum World

Yes, short wavelength lights have high frequency and long wavelength lights have low frequency. This can be proved by using the electromagnetic equation c=vλ where c is the speed of light, v is the frequency, and λ is the wavelength. They have a universal relationship.
by Yvonne Du
Thu Oct 11, 2018 11:23 pm
Forum: Balancing Chemical Reactions
Topic: Balancing Chemical Equations [ENDORSED]
Replies: 4
Views: 139

Re: Balancing Chemical Equations [ENDORSED]

In order to balance a chemical equation, you need to figure out the reactants and products first. In this case, you only have one compound which means this is not a chemical equation. After you have had all the reactants and products, you can then try to come up with accurate coefficients in front o...
by Yvonne Du
Thu Oct 11, 2018 11:19 pm
Forum: SI Units, Unit Conversions
Topic: formula units [ENDORSED]
Replies: 68
Views: 21108

Re: Solution Concentration [ENDORSED]

How do you know which is the initial molarity, initial volume, final molarity, and/or final volume from a given problem? How do you figure it out? I think most of the questions will state them if not, you can look for hints in the question. For example, if the question is adding water to dilute the...
by Yvonne Du
Thu Oct 04, 2018 4:19 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Conversion of grams to moles
Replies: 4
Views: 72

Re: Conversion of grams to moles

Yes. For example, if the question asks you to convert 2.0g of CO2 to moles. What you do is first add up the molar mass for CO2 which is 12.011(C)+15.999*2(O)=44.009grams. Then you use 2/44.009 to get the moles. You always consider the subscripts.
by Yvonne Du
Thu Oct 04, 2018 4:16 pm
Forum: Molarity, Solutions, Dilutions
Topic: Concentration- Calculating Volume
Replies: 4
Views: 61

Re: Concentration- Calculating Volume

When asked to look for Molarity/volume/moles, one of the common equation that we use is M=moles/volume. You are given the moles and molarity, which means you can use this formula to find the volume.
by Yvonne Du
Thu Oct 04, 2018 4:02 pm
Forum: Empirical & Molecular Formulas
Topic: Problem F.1b
Replies: 3
Views: 74

Re: Problem F.1b

I think as long as your answer is close enough to the book answer, TAs won't make you wrong. In this case, your answer is very close.

Go to advanced search