Search found 58 matches
- Thu Mar 08, 2018 7:48 pm
- Forum: General Rate Laws
- Topic: Integrated Rate Laws
- Replies: 6
- Views: 825
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.
- Thu Mar 08, 2018 7:47 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Intermediate [ENDORSED]
- Replies: 7
- Views: 924
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.
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.
- Thu Mar 08, 2018 7:45 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: activation energy [ENDORSED]
- Replies: 3
- Views: 762
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...
- Thu Mar 08, 2018 7:43 pm
- Forum: General Rate Laws
- Topic: Problem 15.3
- Replies: 4
- Views: 786
Re: Problem 15.3
You dont need to. You know how much is changing in how many seconds; this gives you the rate.
- Fri Mar 02, 2018 9:13 pm
- Forum: First Order Reactions
- Topic: Pseudo First Order Reaction
- Replies: 5
- Views: 1926
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...
- Fri Mar 02, 2018 9:10 pm
- Forum: General Rate Laws
- Topic: Half Life [ENDORSED]
- Replies: 1
- Views: 282
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.
- Fri Mar 02, 2018 9:09 pm
- Forum: First Order Reactions
- Topic: Integrated Rate Laws [ENDORSED]
- Replies: 1
- Views: 324
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...
- Wed Feb 28, 2018 12:11 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: 15.19
- Replies: 2
- Views: 498
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?
- Sat Feb 24, 2018 11:32 pm
- Forum: Zero Order Reactions
- Topic: Concept of Zero Order
- Replies: 5
- Views: 2543
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.
- Sat Feb 24, 2018 11:27 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3891815
Re: Post All Chemistry Jokes Here
Are you sharing your electrons with me because I feel a real deep bond with you.
- Sat Feb 24, 2018 11:25 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Kinetics vs. Thermodynamics
- Replies: 2
- Views: 467
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.
- Mon Feb 19, 2018 9:59 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: 14.91
- Replies: 1
- Views: 300
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...
- Sun Feb 18, 2018 2:08 pm
- Forum: Balancing Redox Reactions
- Topic: Acidic vs. Basic Solutions
- Replies: 3
- Views: 524
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.
- 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: 374
Re: Galvanic Cells 14.3
Maybe it's because the voltage created by concentration cells can light a bulb, hence the electrical work?
- Sun Feb 18, 2018 12:57 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: 14.11 (e)
- Replies: 1
- Views: 299
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...
- Sun Feb 18, 2018 12:54 pm
- Forum: Balancing Redox Reactions
- Topic: HW 14.13d
- Replies: 3
- Views: 747
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+?
- Sat Feb 10, 2018 9:18 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Stability
- Replies: 2
- Views: 383
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 ...
- Sat Feb 10, 2018 9:14 pm
- Forum: Van't Hoff Equation
- Topic: Constants and formulas
- Replies: 7
- Views: 1069
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
- Sat Feb 10, 2018 9:03 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Practice Midterm Winter 2018
- Replies: 10
- Views: 3151
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!
- Mon Feb 05, 2018 9:57 am
- Forum: Calculating Work of Expansion
- Topic: Naming Question [ENDORSED]
- Replies: 5
- Views: 816
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.
- 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: 454
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?
- 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: 361
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...
- Mon Feb 05, 2018 9:49 am
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Types of Disorders [ENDORSED]
- Replies: 5
- Views: 775
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.
As you increase temperature, the thermal motion of the molecules increases.
- Wed Jan 31, 2018 11:07 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs Free Energy [ENDORSED]
- Replies: 6
- Views: 1357
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.
- Wed Jan 31, 2018 11:05 am
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Definition of Entropy
- Replies: 10
- Views: 1425
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.
- Wed Jan 31, 2018 11:02 am
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Question 9.5
- Replies: 3
- Views: 460
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...
- 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: 241
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
- 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: 379
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.
- Mon Jan 22, 2018 11:25 am
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: First Law Concept
- Replies: 4
- Views: 441
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.
- 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: 311
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...
- Tue Jan 16, 2018 12:20 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: living plant
- Replies: 4
- Views: 409
Re: living plant
It is exchanging both matter (ex. CO2, O2) AND energy (ex. heat), so it is an open system.
- Tue Jan 16, 2018 12:18 pm
- Forum: Calculating Work of Expansion
- Topic: Ch 8.1 Solving work
- Replies: 2
- Views: 322
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...
- 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: 259
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.
- Mon Jan 08, 2018 9:49 pm
- Forum: Phase Changes & Related Calculations
- Topic: Question on 8.21
- Replies: 3
- Views: 414
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.
- Mon Jan 08, 2018 9:40 pm
- Forum: Phase Changes & Related Calculations
- Topic: Question 8.25
- Replies: 4
- Views: 684
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.
- Mon Dec 04, 2017 12:17 pm
- Forum: Identifying Acidic & Basic Salts
- Topic: Stronger Acid [ENDORSED]
- Replies: 2
- Views: 927
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.
- Mon Dec 04, 2017 12:15 pm
- Forum: Lewis Acids & Bases
- Topic: Donating electrons versus protons [ENDORSED]
- Replies: 4
- Views: 1543
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...
- 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: 330
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.
- Mon Nov 27, 2017 12:56 pm
- Forum: Naming
- Topic: Naming with an anionic complexes [ENDORSED]
- Replies: 1
- Views: 389
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.
- Mon Nov 27, 2017 12:54 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Endothermic vs. Exothermic [ENDORSED]
- Replies: 1
- Views: 270
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.
- Mon Nov 20, 2017 9:19 pm
- Forum: Biological Examples
- Topic: Fe and proteins
- Replies: 6
- Views: 1125
Re: Fe and proteins
Myoglobin has a heme complex + protein with Fe as the metal. Hemoglobin has 4 myoglobin molecules.
- Mon Nov 20, 2017 9:17 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Maximum number of ligands
- Replies: 3
- Views: 937
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.
- Mon Nov 20, 2017 9:13 pm
- Forum: Naming
- Topic: H2O in Coordination compounds
- Replies: 2
- Views: 517
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.
- Mon Nov 13, 2017 12:35 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: AXE notation [ENDORSED]
- Replies: 3
- Views: 1808
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...
- Mon Nov 13, 2017 12:33 pm
- Forum: Hybridization
- Topic: Electron Promotion of Carbon [ENDORSED]
- Replies: 2
- Views: 1003
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...
- Tue Nov 07, 2017 1:36 pm
- Forum: Dipole Moments
- Topic: Finding Dipole Moments
- Replies: 3
- Views: 759
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...
- Tue Nov 07, 2017 1:31 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Xenon Tetrafluoride?
- Replies: 4
- Views: 1378
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...
- Mon Oct 30, 2017 9:43 am
- Forum: Formal Charge and Oxidation Numbers
- Topic: Ionization energy vs. electron affinity [ENDORSED]
- Replies: 5
- Views: 1140
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...
- Mon Oct 30, 2017 9:38 am
- Forum: Ionic & Covalent Bonds
- Topic: Study Habits [ENDORSED]
- Replies: 8
- Views: 1233
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...
- 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: 1399
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.
- Mon Oct 23, 2017 11:58 am
- Forum: Trends in The Periodic Table
- Topic: Electron Affinity vs Ionization Energy [ENDORSED]
- Replies: 2
- Views: 680
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...
- Mon Oct 16, 2017 10:29 am
- Forum: Photoelectric Effect
- Topic: Excess Energy [ENDORSED]
- Replies: 2
- Views: 605
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.
- Mon Oct 16, 2017 10:26 am
- Forum: Properties of Light
- Topic: Chapter 1: Question 1.9 [ENDORSED]
- Replies: 7
- Views: 1705
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...
- Wed Oct 11, 2017 4:03 pm
- Forum: Photoelectric Effect
- Topic: Energy in kj or j when solving a problem?
- Replies: 10
- Views: 2078
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.
- Wed Oct 11, 2017 3:42 pm
- Forum: Photoelectric Effect
- Topic: How to calculate the kinetic energy, energy and frequency? [ENDORSED]
- Replies: 25
- Views: 7608
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...
- Fri Oct 06, 2017 9:44 am
- Forum: Limiting Reactant Calculations
- Topic: M19
- Replies: 3
- Views: 516
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?
- Fri Oct 06, 2017 9:43 am
- Forum: Significant Figures
- Topic: All students read this sig fig post [ENDORSED]
- Replies: 170
- Views: 36410
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...
- Fri Oct 06, 2017 9:42 am
- Forum: Significant Figures
- Topic: All students read this sig fig post [ENDORSED]
- Replies: 170
- Views: 36410
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...