Search found 58 matches

by Sohini Halder 1G
Thu Mar 08, 2018 7:48 pm
Forum: General Rate Laws
Topic: Integrated Rate Laws
Replies: 6
Views: 207

Re: Integrated Rate Laws

I think it would never hurt to know the steps to derive them, but I feel like any test questions will focus on application, not derivation.
by Sohini Halder 1G
Thu Mar 08, 2018 7:47 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Intermediate [ENDORSED]
Replies: 7
Views: 195

Re: Intermediate [ENDORSED]

Intermediates are FORMED and then CONSUMED within the steps of elementary reactions.
Catalysts are present from the beginning and are not consumed in the reaction; this is why only a little bit of catalyst is needed to increase the rate of a specific reaction.
by Sohini Halder 1G
Thu Mar 08, 2018 7:45 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: activation energy [ENDORSED]
Replies: 3
Views: 268

Re: activation energy [ENDORSED]

At lower temperatures, there is usually not enough energy to overcome an activation energy barrier, so the pathway that has the smaller activation energy will be the faster reaction and the one that is observed. This is kinetically determined. This is also different than reactions that are spontaneo...
by Sohini Halder 1G
Thu Mar 08, 2018 7:43 pm
Forum: General Rate Laws
Topic: Problem 15.3
Replies: 4
Views: 188

Re: Problem 15.3

You dont need to. You know how much is changing in how many seconds; this gives you the rate.
by Sohini Halder 1G
Fri Mar 02, 2018 9:13 pm
Forum: First Order Reactions
Topic: Pseudo First Order Reaction
Replies: 5
Views: 427

Re: Pseudo First Order Reaction

Dr. Lavelle gave an example in class that really helped me understand this. He said that if a person has a million dogs, and gives a few away, that person will still have about a million dogs. The number doesn't realllllyyy change. Similarly, for a pseudo-first order reaction, one of the other react...
by Sohini Halder 1G
Fri Mar 02, 2018 9:10 pm
Forum: General Rate Laws
Topic: Half Life [ENDORSED]
Replies: 1
Views: 81

Re: Half Life [ENDORSED]

If I remember what Dr. Lavelle said in lecture correctly, he mentioned that they would give us experimental data or there would be a situation where only one concentration would be feasibly changing over time because the other reactants would be at a much higher concentration.
by Sohini Halder 1G
Fri Mar 02, 2018 9:09 pm
Forum: First Order Reactions
Topic: Integrated Rate Laws [ENDORSED]
Replies: 1
Views: 78

Re: Integrated Rate Laws [ENDORSED]

Say A is your reactant. As the reaction progresses, A decreases (if first order, it decreases exponentially). Therefore, the rate is the negative change of the concentration of A over time, given by -d[A]/dt. This is equivalent to saying that the rate of the reaction is proportional (with a proporti...
by Sohini Halder 1G
Wed Feb 28, 2018 12:11 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.19
Replies: 2
Views: 131

15.19

I am confused about 15.19. When I find k, I get 2.85 x 10-^12 mol/Ls. The answer key gives the same value but as mmol/Ls. This is wrong right? We have to convert the mmol to mol to get a power of 10^-12, but why is the units for the answer key still mmol/Ls?
by Sohini Halder 1G
Sat Feb 24, 2018 11:32 pm
Forum: Zero Order Reactions
Topic: Concept of Zero Order
Replies: 5
Views: 350

Re: Concept of Zero Order

mathematically it makes sense because as you do anything to the concentration, nothing changes the rate of the rxn, or 0 change.
by Sohini Halder 1G
Sat Feb 24, 2018 11:27 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7348
Views: 885807

Re: Post All Chemistry Jokes Here

Are you sharing your electrons with me because I feel a real deep bond with you.
by Sohini Halder 1G
Sat Feb 24, 2018 11:25 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Kinetics vs. Thermodynamics
Replies: 2
Views: 150

Re: Kinetics vs. Thermodynamics

As of right now, we only know about energy barriers causing this disparity between thermodynamically and kinetically favorable reactions. I'm assuming that once we know more about the actual mechanisms that go into the reactions, we can find out this.
by Sohini Halder 1G
Mon Feb 19, 2018 9:59 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.91
Replies: 1
Views: 91

14.91

"A voltaic cell functions only when the electrical circuit is complete. In the external circuit the current is carried by the fl ow of electrons through a metal wire. Explain how the current is carried through the cell itself." Can someone please explain this to me? The solution manual say...
by Sohini Halder 1G
Sun Feb 18, 2018 2:08 pm
Forum: Balancing Redox Reactions
Topic: Acidic vs. Basic Solutions
Replies: 3
Views: 154

Re: Acidic vs. Basic Solutions

^^, and if you would like to have H3O+ in your final balanced reaction, do the process using only H+ first, then change them to H3O+ and account for a change in O accordingly.
by Sohini Halder 1G
Sun Feb 18, 2018 2:06 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic Cells 14.3
Replies: 2
Views: 101

Re: Galvanic Cells 14.3

Maybe it's because the voltage created by concentration cells can light a bulb, hence the electrical work?
by Sohini Halder 1G
Sun Feb 18, 2018 12:57 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.11 (e)
Replies: 1
Views: 96

Re: 14.11 (e)

No, Sn2+ is reduced to Sn4+. You need to flip whatever reduction reaction you get for the anode side to make it an oxidation reaction. You may have gotten confused because Sn4+ is listed before Sn2+ in the cell diagram, but order does not matter there, as long as it is on the left side of the double...
by Sohini Halder 1G
Sun Feb 18, 2018 12:54 pm
Forum: Balancing Redox Reactions
Topic: HW 14.13d
Replies: 3
Views: 402

Re: HW 14.13d

I still don't understand this setup. Do we have to assume that Au(s) is present in both the reduction and oxidation reactions because it is the conductive metal electrode in the solution? And then knowing this, is this why Au(s) goes to both Au 1+ and Au 3+?
by Sohini Halder 1G
Sat Feb 10, 2018 9:18 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Stability
Replies: 2
Views: 114

Re: Stability

If Delta G for formation of a product A is negative, we know that the forward process is spontaneous and will "end up" as product A, meaning that product A is stable. In the same vein, lets assume the Delta G for formation of product B is positive. The forward process that forms product B ...
by Sohini Halder 1G
Sat Feb 10, 2018 9:14 pm
Forum: Van't Hoff Equation
Topic: Constants and formulas
Replies: 7
Views: 292

Re: Constants and formulas

I'm not totally certain, but I think that if it isn't explicitly given, we may just have to derive it from DeltaG = -RTlnK
by Sohini Halder 1G
Sat Feb 10, 2018 9:03 pm
Forum: Administrative Questions and Class Announcements
Topic: Practice Midterm Winter 2018
Replies: 10
Views: 2039

Re: Practice Midterm Winter 2018

When will the link be posted? Also, will the solutions that we work through during the session or an answer key be posted? Thank you!
by Sohini Halder 1G
Mon Feb 05, 2018 9:57 am
Forum: Calculating Work of Expansion
Topic: Naming Question [ENDORSED]
Replies: 5
Views: 196

Re: Naming Question [ENDORSED]

The system starts at equilibrium (think Dr. Lavelle's example where both pressures are 1 atm) but an infinitesimally small change happens which starts the reversible process.
by Sohini Halder 1G
Mon Feb 05, 2018 9:52 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: determining number of microstates
Replies: 3
Views: 139

Re: determining number of microstates

I am also very confused about this. Will we be told on the exam or do we have to draw and figure it out?
by Sohini Halder 1G
Mon Feb 05, 2018 9:51 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: DS= q/T for surroundings or system?
Replies: 2
Views: 101

Re: DS= q/T for surroundings or system?

yep! So for instance, if heat is being released from System into Surroundings, System q will be negative and Surroundings q will be positive because the surroundings are absorbing heat. Further, System T should be higher than Surroundings T. These differing values will give you a different change in...
by Sohini Halder 1G
Mon Feb 05, 2018 9:49 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Types of Disorders [ENDORSED]
Replies: 5
Views: 186

Re: Types of Disorders [ENDORSED]

As you increase volume or mix one substance with another, the molecules of substance X are spread out more, increasing their positional disorder.
As you increase temperature, the thermal motion of the molecules increases.
by Sohini Halder 1G
Wed Jan 31, 2018 11:07 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy [ENDORSED]
Replies: 6
Views: 452

Re: Gibbs Free Energy [ENDORSED]

Gibbs free energy also shows how much energy is "Free" to do nonexpansion work, whereas entropy relates to the possible number of states a system could be in.
by Sohini Halder 1G
Wed Jan 31, 2018 11:05 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Definition of Entropy
Replies: 10
Views: 265

Re: Definition of Entropy

I think we should think about entropy as corresponding to the possible number of states that could exist, which comes from the equation S = k ln W. As volume increases, the number of possible states a gas could be in increases, so does entropy of the system.
by Sohini Halder 1G
Wed Jan 31, 2018 11:02 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Question 9.5
Replies: 3
Views: 127

Re: Question 9.5

To calculate the total entropy change, you need to first find the entropy change for each reservoir: one is giving off heat, and one is absorbing heat. 400kj should therefore have two signs because q=(-) when the hotter reservoir is giving off heat and q=(+) when the cooler reservoir is absorbing he...
by Sohini Halder 1G
Mon Jan 22, 2018 11:31 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.77 [ENDORSED]
Replies: 2
Views: 117

Re: 8.77 [ENDORSED]

I think that the lower DeltaH given when finding benzene with resonance shows a lowering of energy, so formation of benzene with resonance is more stable. 228kj/mol vs -1kj/mol
by Sohini Halder 1G
Mon Jan 22, 2018 11:29 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard enthalpies of formation [ENDORSED]
Replies: 2
Views: 124

Re: Standard enthalpies of formation [ENDORSED]

If you are finding the standard enthalpy reaction of 1/2 N2(g) + 1/2 02(g) ==> NO(g), that will be the same as finding the enthalpy of formation of NO(g). Only when your reactants are in gas form and and pure substances that form 1 mole of a product are they the same.
by Sohini Halder 1G
Mon Jan 22, 2018 11:25 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: First Law Concept
Replies: 4
Views: 155

Re: First Law Concept

Dr. Lavelle mentioned that the change in internal energy of a isolated system is 0, because neither mass or energy can leave the system and therefore Delta U is = 0.
by Sohini Halder 1G
Tue Jan 16, 2018 12:27 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Ch. 8 #67
Replies: 2
Views: 137

Re: Ch. 8 #67

C) Benzene without resonance means that there are 3 single bonds and 3 double bonds in the Lewis structure you will use for reference. It helps if you draw out the structure so you can visually see which bonds are being formed! 6 C(s) + 3 H2(g) --> C6H6(l) Breaking: 3 H-H bonds, using energy Forming...
by Sohini Halder 1G
Tue Jan 16, 2018 12:20 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: living plant
Replies: 4
Views: 171

Re: living plant

It is exchanging both matter (ex. CO2, O2) AND energy (ex. heat), so it is an open system.
by Sohini Halder 1G
Tue Jan 16, 2018 12:18 pm
Forum: Calculating Work of Expansion
Topic: Ch 8.1 Solving work
Replies: 2
Views: 145

Re: Ch 8.1 Solving work

I got the same answer as you. For those who need help solving the problem, here is my work: Volume of water as liquid: 100 g / (1g/cm^3) = 100 cm^3 Volume of water as solid: 100 g / (0.92g/cm^3) = 108.696 cm^3 Change in volume: 8.696 cm^3 Converted to Liters: 0.008696 L External pressure: 1070 atm w...
by Sohini Halder 1G
Mon Jan 08, 2018 9:51 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Strength of Interactions in a Solid
Replies: 3
Views: 149

Re: Strength of Interactions in a Solid

I think the extra kinetic energy allows the liquid molecules to flow past one another more easily than molecules of solids.
by Sohini Halder 1G
Mon Jan 08, 2018 9:49 pm
Forum: Phase Changes & Related Calculations
Topic: Question on 8.21
Replies: 3
Views: 127

Re: Question on 8.21

Essentially, -q(copper)=q(water), which is saying that the heat given off by the copper is the heat absorbed by water. You have to use the q=m(delta)T equation to solve given the information you have. I set the equations to each other and solve.
by Sohini Halder 1G
Mon Jan 08, 2018 9:40 pm
Forum: Phase Changes & Related Calculations
Topic: Question 8.25
Replies: 4
Views: 215

Re: Question 8.25

In this case, you can ignore the moles of reactant and product because those do not matter in the equation for finding q.
by Sohini Halder 1G
Mon Dec 04, 2017 12:17 pm
Forum: Identifying Acidic & Basic Salts
Topic: Stronger Acid [ENDORSED]
Replies: 2
Views: 433

Re: Stronger Acid [ENDORSED]

Oxygen is electrognegative so the more there are, the stronger they pull the electrons away from the O-H bond, weakening it and making the overall acid stronger.
by Sohini Halder 1G
Mon Dec 04, 2017 12:15 pm
Forum: Lewis Acids & Bases
Topic: Donating electrons versus protons [ENDORSED]
Replies: 4
Views: 225

Re: Donating electrons versus protons [ENDORSED]

I also think it is important to differentiate between Lewis, Bronsted, and Arrhenius definitions of acids and bases. Arrhenius definition states that a compound that dissociates in water to form hydronium ions is an acid, so a compound like HCL is an Arrhenius acid as well as a Bronsted acid and a L...
by Sohini Halder 1G
Mon Nov 27, 2017 10:24 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Chemical Equilibrium Part 2 Post-Module #19 & 27
Replies: 2
Views: 165

Re: Chemical Equilibrium Part 2 Post-Module #19 & 27

Balance the equation. The coefficients change how you raise the numbers to a power. You are likely messing up there.
by Sohini Halder 1G
Mon Nov 27, 2017 12:56 pm
Forum: Naming
Topic: Naming with an anionic complexes [ENDORSED]
Replies: 1
Views: 166

Re: Naming with an anionic complexes [ENDORSED]

I believe it is just a matter of memorization, unfortunately :( This confused me too, but I think generally, most follow the trend of the metal name followed by "-ate", such as "cobaltate". Iron (ferrate) is an exception we will just need to know.
by Sohini Halder 1G
Mon Nov 27, 2017 12:54 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Endothermic vs. Exothermic [ENDORSED]
Replies: 1
Views: 143

Re: Endothermic vs. Exothermic [ENDORSED]

The question will always tell you. However, if the enthalpy value given is negative, it is exothermic, meaning the rxn gives off heat, and if the enthalpy value given is positive, the rxn requires heat.
by Sohini Halder 1G
Mon Nov 20, 2017 9:19 pm
Forum: Biological Examples
Topic: Fe and proteins
Replies: 6
Views: 652

Re: Fe and proteins

Myoglobin has a heme complex + protein with Fe as the metal. Hemoglobin has 4 myoglobin molecules.
by Sohini Halder 1G
Mon Nov 20, 2017 9:17 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Maximum number of ligands
Replies: 3
Views: 185

Re: Maximum number of ligands

I believe that the octahedral shape is the maximum number of ligands that can be added. If there are more it may be unstable.
by Sohini Halder 1G
Mon Nov 20, 2017 9:13 pm
Forum: Naming
Topic: H2O in Coordination compounds
Replies: 2
Views: 182

Re: H2O in Coordination compounds

I believe that when there is a compound and a dot(multiplication) sign next to it, we call it a hydrate. Otherwise water is a ligand.
by Sohini Halder 1G
Mon Nov 13, 2017 12:35 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: AXE notation [ENDORSED]
Replies: 3
Views: 287

Re: AXE notation [ENDORSED]

Add up the subscripts on AXE and you will know how many regions of electron density there are. The subscript below X tells you how many atoms are attached to the central atom. When naming the molecule's shape, you need to know both in order to discern how the lone pairs, if there are any, affect the...
by Sohini Halder 1G
Mon Nov 13, 2017 12:33 pm
Forum: Hybridization
Topic: Electron Promotion of Carbon [ENDORSED]
Replies: 2
Views: 226

Re: Electron Promotion of Carbon [ENDORSED]

We write it the first way when asked for the ground state configuration of just the carbon atom itself. However, you are right, in most cases carbon forms 4 bonds and when it is in these molecules, one electron is promoted to the 2p orbital, leaving 4 unpaired electrons to form 4 bonds. Since the bo...
by Sohini Halder 1G
Tue Nov 07, 2017 1:36 pm
Forum: Dipole Moments
Topic: Finding Dipole Moments
Replies: 3
Views: 405

Re: Finding Dipole Moments

Look for the more electronegative element in the molecule. This element will have the electrons around them most of the time. For example: H2O Because oxygen is more electronegative than hydrogen, the dipole moment will go towards oxygen. That is why oxygen-side of H2O has a slightly negative charge...
by Sohini Halder 1G
Tue Nov 07, 2017 1:31 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Xenon Tetrafluoride?
Replies: 4
Views: 369

Re: Xenon Tetrafluoride?

Hi! This confused me at first too, as noble gases do not usually form compounds. However, Dr. Lavelle states that because Xenon is an element with multiple shells and valence electrons that are quite shielded from the nucleus's pulling power, they can be shared. You might notice that we have only se...
by Sohini Halder 1G
Mon Oct 30, 2017 9:43 am
Forum: Formal Charge and Oxidation Numbers
Topic: Ionization energy vs. electron affinity [ENDORSED]
Replies: 5
Views: 363

Re: Ionization energy vs. electron affinity [ENDORSED]

Ionization energy and electron affinity are definitely related! Ionization energy is the energy to remove an electron, or ionize it, from an atom. Ionization energy increases left to right across a period, which makes sense because as the valence shell fills in the atom moving left to right, the ele...
by Sohini Halder 1G
Mon Oct 30, 2017 9:38 am
Forum: Ionic & Covalent Bonds
Topic: Study Habits [ENDORSED]
Replies: 8
Views: 468

Re: Study Habits [ENDORSED]

Hi! I've been doing relatively well in the class so far and here are the study tips I use: 1) read the chapter AND take notes before you attend the lecture on the same material -this allows me to have at least a shallow understanding of the material that Lavelle will cover in class -taking notes fro...
by Sohini Halder 1G
Mon Oct 23, 2017 12:03 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electronic Configuration for d-block elements [ENDORSED]
Replies: 9
Views: 529

Re: Electronic Configuration for d-block elements [ENDORSED]

It is because of the shielding effect. The electrons with the highest energy, and therefore least bound to the nucleus, will be removed first. That's why we write the d block elements first, to represent that the last electrons are the ones that will be removed.
by Sohini Halder 1G
Mon Oct 23, 2017 11:58 am
Forum: Trends in The Periodic Table
Topic: Electron Affinity vs Ionization Energy [ENDORSED]
Replies: 2
Views: 316

Re: Electron Affinity vs Ionization Energy [ENDORSED]

Fluorine is the most electronegative element, therefore its electron affinity is high because it "desperately needs" one more electron to fill its valence shell. Similarly, because it "desperately needs" an electron, it will be very difficult to remove an electron from it, causin...
by Sohini Halder 1G
Mon Oct 16, 2017 10:29 am
Forum: Photoelectric Effect
Topic: Excess Energy [ENDORSED]
Replies: 2
Views: 278

Re: Excess Energy [ENDORSED]

It needs a discrete amount. That's why only specific wavelengths are absorbed/emitted, because those exact frequencies give energies that move the electron from one level to the next. Each atom has a unique absorption and emission spectrum.
by Sohini Halder 1G
Mon Oct 16, 2017 10:26 am
Forum: Properties of Light
Topic: Chapter 1: Question 1.9 [ENDORSED]
Replies: 3
Views: 254

Re: Chapter 1: Question 1.9 [ENDORSED]

It helps to think about what kind of wavelength each activity has. popcorn - microwave Reading - visible light Suntan - UV dental - x ray You can see the energy increase as you move down the list, the frequency increase, and the wavelength decrease. Using this, you can reason if your calculated answ...
by Sohini Halder 1G
Wed Oct 11, 2017 4:03 pm
Forum: Photoelectric Effect
Topic: Energy in kj or j when solving a problem?
Replies: 10
Views: 541

Re: Energy in kj or j when solving a problem?

Set up the problem using J because that is the standard unit for energy, but you can either leave your answer in J or convert to kJ if youu want.
by Sohini Halder 1G
Wed Oct 11, 2017 3:42 pm
Forum: Photoelectric Effect
Topic: How to calculate the kinetic energy, energy and frequency? [ENDORSED]
Replies: 14
Views: 2765

Re: How to calculate the kinetic energy, energy and frequency? [ENDORSED]

As Dr. Lavelle said in lecture, it always helps to write out the equation in words first. For example: Energy of incoming photon = Workfunction of metal (or energy needed to remove electron) + Kinetic energy of the electron emitted After this, you can rearrange whatever way you need to for the probl...
by Sohini Halder 1G
Fri Oct 06, 2017 9:44 am
Forum: Limiting Reactant Calculations
Topic: M19
Replies: 3
Views: 245

Re: M19

Can someone explain why all of the oxygen in the products seems to come from the original compound and not the surrounding excess oxygen?
by Sohini Halder 1G
Fri Oct 06, 2017 9:43 am
Forum: Significant Figures
Topic: All students read this sig fig post [ENDORSED]
Replies: 91
Views: 8949

Re: All students read this sig fig post [ENDORSED]

Remember that when looking at sig figs for numbers that have decimals, the placement of the ZEROES is important! For example: 0.05 has 1 sig fig. 0.0500 has 3 sig figs. In decimals, zeroes placed after a digit in the decimal places are significant, while those placed before are not. An alternate way...
by Sohini Halder 1G
Fri Oct 06, 2017 9:42 am
Forum: Significant Figures
Topic: All students read this sig fig post [ENDORSED]
Replies: 91
Views: 8949

Re: All students read this sig fig post [ENDORSED]

Remember that when looking at sig figs for numbers that have decimals, the placement of the ZEROES is important! For example: 0.05 has 1 sig fig. 0.0500 has 3 sig figs. In decimals, zeroes placed after a digit in the decimal places are significant, while those placed before are not. An alternate way...

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