Search found 92 matches
- Sun Mar 17, 2019 1:15 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Heat Capacity Intensive or Extensive?
- Replies: 4
- Views: 677
Heat Capacity Intensive or Extensive?
I've seen some chem mods say it is intensive and others say it is extensive. I believe it is extensive because it is not standardized to grams or moles and as such depends on how much "stuff" there is. Is this wrong?
- Sat Mar 16, 2019 12:39 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: What is a porous disk?
- Replies: 3
- Views: 983
What is a porous disk?
Does anyone know what a porous disk is? What is the use?
- Sat Mar 16, 2019 12:39 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: what is an electrolyte?
- Replies: 1
- Views: 284
what is an electrolyte?
What is an electrolyte in the context of a cell diagram? Can you give an example?
- Thu Mar 14, 2019 1:43 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Concentration changes on Cell Potential
- Replies: 1
- Views: 257
Concentration changes on Cell Potential
Can someone explain how cell potential changes with changes of concentrations of reactants and products? What is the justification behind these changes?
- Thu Mar 14, 2019 12:42 am
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: How to Find Reverse Activation Energy for Endothermic Processes?
- Replies: 1
- Views: 290
How to Find Reverse Activation Energy for Endothermic Processes?
How do you find the reverse activation energy for endothermic processes?
- Wed Mar 13, 2019 12:22 am
- Forum: Second Order Reactions
- Topic: 2nd order rates
- Replies: 6
- Views: 832
Re: 2nd order rates
Yes, that is true. The total rate order involves summing the exponents of each reactant.
- Tue Mar 12, 2019 11:57 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Log vs Ln
- Replies: 2
- Views: 326
Re: Log vs Ln
Oh apologies, I realized the simplification is different so the values probably somehow cancel out. Follow up question, how was this derivation solved?
- Tue Mar 12, 2019 11:52 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Log vs Ln
- Replies: 2
- Views: 326
Log vs Ln
In the constants and equations sheet, there is an equation that simplifies the scalar quantity of ln(Q). However, it changes the ln to log. Can you do this? This seems fundamentally different?
- Sun Mar 10, 2019 11:23 pm
- Forum: General Rate Laws
- Topic: Graphs
- Replies: 2
- Views: 372
Re: Graphs
I don't think we have to memorize the graphs per se, but it is important that we learn how to derive the relationships for the graphs. We do this by rearranging our dA and dt terms so we can integrate. Then, we change the graph to some form similar to y=mx + b. The graphs allow us to make evaluation...
- Sun Mar 10, 2019 11:17 pm
- Forum: First Order Reactions
- Topic: reaction orders
- Replies: 3
- Views: 372
Re: reaction orders
If for example, a reaction is forming something, the reactant would have to be a negative reaction order. We can also see this as the reverse reaction of something that is decomposing--this is why the equilibrium constant has concentration of products in the denominator.
- Sun Mar 10, 2019 11:10 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: Units of k
- Replies: 7
- Views: 1060
Re: Units of k
The units are different because the reaction order affects the exponent--a first reaction order means an exponent of 1, a second reaction order means an exponent of 2, etc. Because we are raising the concentration (moles/Liter) to a different power, the units change accordingly. For example, by rais...
- Sun Mar 10, 2019 11:05 pm
- Forum: First Order Reactions
- Topic: Pseudo rate laws
- Replies: 2
- Views: 296
Re: Pseudo rate laws
Essentially, because the concentration of one reactant is so high, we can neglect the excess reactant to make the rate law easier to work with. So for a second order reaction involving two concentrations, if one of the concentrations is high, we can ignore it, and say the reaction is a pseudo first ...
- Thu Mar 07, 2019 9:57 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Inert Electrode
- Replies: 2
- Views: 343
Re: Inert Electrode
There are inert electrodes like mercury, but for the purposes of this class, I am sure platinum is the main one we should be concerned with.
- Thu Mar 07, 2019 9:48 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: What does unique rate of reaction mean?
- Replies: 6
- Views: 618
Re: What does unique rate of reaction mean?
I am so glad that you have recognized this. I make an active goal to engage in pragmatism, especially in the realm of kinematics. Are you saying you divide the rate of A by the stoichiometric coefficient of A?
- Thu Mar 07, 2019 9:37 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: What does unique rate of reaction mean?
- Replies: 6
- Views: 618
What does unique rate of reaction mean?
What does the textbook mean when it asks us to find the unique rate of reaction? What is the process of solving for it?
- Thu Mar 07, 2019 4:02 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Why does F/RT equal this value?
- Replies: 1
- Views: 3198
Why does F/RT equal this value?
I'm trying to figure out why F/RT equals 1/.02569 V. On number 14.35 of the book, it says this is so. I am confused because I am getting a different value. I plugged in 96485 for F, 8.314 for R, and 298.15 for T. For reference, this is number 14.35 and the solutions manual simplifies F/RT to this va...
- Tue Feb 19, 2019 11:24 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs free energy
- Replies: 7
- Views: 788
Re: Gibbs free energy
In terms of the equations, gibbs' free energy sees a relationship with enthalpy and entropy where delta G = Delta H - T * Delta. Heat is a measurement of how much energy is transferred, but in terms of energy that is not able to do work, whereas Gibbs free energy is a measurement of how much work so...
- Tue Feb 19, 2019 11:17 am
- 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: Third Law concept and problem types
- Replies: 4
- Views: 663
Re: Third Law concept and problem types
We use the third law to identify changes in entropy in systems, surroundings, etc. Applications would be calculating delta s in terms of isothermal, isobaric, and isochoric conditions, calculating S in terms of Boltzmann's equation, and finding relationships in terms of delta s of the system, surrou...
- Tue Feb 19, 2019 11:14 am
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: System vs Surroundings
- Replies: 14
- Views: 2138
Re: System vs Surroundings
Usually, the system is the actual thing we are dealing with in the question. For example, if we are looking at the piston and identifying characteristics like work, heat, etc., the piston is the system, while the surroundings is what is supplying heat or what the system is losing heat to or the surr...
- Mon Feb 11, 2019 3:51 pm
- Forum: Calculating Work of Expansion
- Topic: Why are Work and Heat Considered Path Dependent?
- Replies: 1
- Views: 191
Why are Work and Heat Considered Path Dependent?
I know what the difference between state functions and path dependent functions are. However, how would we rationalize the fact that work and heat are path dependent using our formulas or just conceptually?
- Sat Feb 09, 2019 7:42 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: 8.57 6th Edition
- Replies: 1
- Views: 246
8.57 6th Edition
On 8.57 of the 6th edition, we are given Standard Delta H with a subscript of c. I assumed we could use this value as the standard enthalpy of formation, but the answer manual is using Hess' law. How do you do this? And what does the subscript c mean?
- Sat Feb 09, 2019 7:00 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: 4D.9 7th Ed.
- Replies: 1
- Views: 239
Re: 4D.9 7th Ed.
Hi, so you know standard enthalpy formation is based off the moles of each reactant and product. Refer to table 8.4 to find the enthalpy of the whole reaction. Remember that diatomic molecules will have an enthalpy of zero, that product enthalpy will be negative and that reactant enthalpy will be po...
- Sat Feb 09, 2019 6:44 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Is there a significance with 298 degrees Kelvin?
- Replies: 5
- Views: 7604
Is there a significance with 298 degrees Kelvin?
In 8.49 of the 6th edition, we're asked to find the change in internal energy, knowing the reactions' change in enthalpy, and given the change in moles. We're not given a temperature, but we need a temperature to solve for work, or -p times delta V. We can solve for this using the ideal gas law. The...
- Sat Feb 09, 2019 6:26 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Closed, Open, and Isolated Systems
- Replies: 5
- Views: 559
Re: Closed, Open, and Isolated Systems
The application of what people said before comes from the equation, delta U = q + w. If for example, something is isolated, that means that there can be no change in energy or matter, so delta U is zero.
- Sat Feb 09, 2019 6:21 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Positive or Negative Entropy Change
- Replies: 2
- Views: 364
Re: Positive or Negative Entropy Change
I feel like there are a lot of ways to evaluate the change of signs for entropy--heat conventions is one of them, but because there are so many derivations of heat, you could also look at entropy change through different variables (this is good because then if you're not given heat or do not know ho...
- Sat Feb 09, 2019 6:11 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Midterm [ENDORSED]
- Replies: 49
- Views: 4936
Re: Midterm [ENDORSED]
I would say review notes, read textbook for unfamiliar concepts, do lots of homework problems, and go to review sessions! Lavelle has so many resources!
- Sun Feb 03, 2019 11:38 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Entropy
- Replies: 3
- Views: 369
Re: Entropy
This is a bit of a manipulation of our equation Delta u = q + w. If we know that there is a constant volume, we can assume there is zero work. As such, delta u = qp. We learned that qp is the same as delta H so u = delta H.
- Sun Feb 03, 2019 11:36 pm
- Forum: Calculating Work of Expansion
- Topic: Different ways to derive work
- Replies: 3
- Views: 278
Re: Different ways to derive work
I might also add that it would be helpful to know the equation Delta U = qp + w, where work can be rearranged. It's helpful to know as many derivations of the same term as possible.
- Sun Feb 03, 2019 11:32 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Hess's Law
- Replies: 3
- Views: 487
Re: Hess's Law
Hess's Law allows us to manipulate equations where one constituent appears in one equation's reactants while the same constituent appears in another equation's products. As such, you can cancel out the constituent by adding the equations together. In doing so, you must also add up the enthalpies. In...
- Tue Jan 22, 2019 12:17 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Justifying what is favored based off temperature changes and Delta H
- Replies: 2
- Views: 291
Justifying what is favored based off temperature changes and Delta H
How do you justify that an increase in temperature for endothermic reactions favors product and vice versa for exothermic reactions? Can we reason this out without just memorizing?
- Tue Jan 22, 2019 11:37 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Given Equilibruim Partial Pressures and a Volume
- Replies: 2
- Views: 210
Given Equilibruim Partial Pressures and a Volume
If you are given equilibrium partial pressures and an overall volume, can you just ignore the overall volume, assuming you're finding Kp? In other words, would the overall volume just be extraneous information?
- Tue Jan 22, 2019 11:30 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: 6th Edition 11.61
- Replies: 1
- Views: 143
6th Edition 11.61
I have a question regarding sig figs. In 11.61, all the initial concentrations are given in three sig figs, but the Kc is given in two sig figs (the value is 0.56). The question asks to find the equilibrium concentrations of all the reactants and products. Why does the answer manual have the answers...
- Tue Jan 22, 2019 11:16 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: 5G.3 7th Edition (When to use P vs molecular formula/concentrations)
- Replies: 5
- Views: 480
Re: 5G.3 7th Edition (When to use P vs molecular formula/concentrations)
Also, it could depend on what phase your reactants and products are in if you are not given actual values.
- Tue Jan 22, 2019 11:15 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: 5G.3 7th Edition (When to use P vs molecular formula/concentrations)
- Replies: 5
- Views: 480
Re: 5G.3 7th Edition (When to use P vs molecular formula/concentrations)
If the question just asks for K, you can use either, but it is probably better to use what you are given. In this case, I am sure you were given partial pressure which is why you got a Kp value. However, if the question asked for Kc, you would need to convert your partial pressures to concentration ...
- Tue Jan 22, 2019 11:13 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: What Happens to a Reaction if Inert Gas is Added?
- Replies: 7
- Views: 2296
What Happens to a Reaction if Inert Gas is Added?
Is there any change in a reaction if inert gas is added?
- Tue Jan 22, 2019 12:03 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: What does Kc have to be less than for you to estimate?
- Replies: 3
- Views: 309
What does Kc have to be less than for you to estimate?
What value does Kc have to be less than for you to estimate, meaning you can negate the -x term when employing ice method to solving for concentrations of products given initial reactant concentration? Is it less than 10^-3 or something else? Just making sure!
- Wed Jan 16, 2019 7:31 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: 6th Edition 12.23
- Replies: 1
- Views: 83
6th Edition 12.23
The question asks you to find the concentration of H3O+ given the Kw as 2.1(10)^-14. I realized that the concentration of H3O+ would be the same as the concentration of OH- so I made 2.1(10)^-14 equal to x^2. I ended up solving for x and got 1.45(10)^-7, but of course, in interest of sig figs, round...
- Tue Jan 15, 2019 5:43 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: If you calcuate Kp and Kc for the same reaction, will they be the same?
- Replies: 2
- Views: 310
If you calcuate Kp and Kc for the same reaction, will they be the same?
If you calculate Kp and Kc of the same chemical equation with the same conditions, would the values of Kp and Kc be the same? There is the logic that because both Kp and Kc are simply rations of products/reactants, they would be the same. If they are not the same, why not?
- Tue Jan 15, 2019 5:37 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Changes to K value
- Replies: 9
- Views: 720
Re: Changes to K value
The reason why only temperature changes the K value is because the other variables e.g. pressure only really change the initial concentration of reaction or product. However, because of this, the Q value changes which will shift the chemical equation.
- Tue Jan 15, 2019 5:34 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Exothermic vs. Endothermic Reaction
- Replies: 9
- Views: 3244
Re: Exothermic vs. Endothermic Reaction
I know the triangle on top of the arrow indicates there is heat involved, so you know that equation can be endothermic or exothermic. However, to determine whether a reaction is exothermic or endothermic, I would assume we would be given delta H or some variation of it.
- Tue Jan 08, 2019 12:05 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: H20's Concentration in Gas Phase?
- Replies: 1
- Views: 173
H20's Concentration in Gas Phase?
Over lecture and in the textbook, we went over the idea that liquids and solids have concentrations we can ignore in context to finding the equilibrium constant--or in other words, concentrations of 1. Because H20 is a universal solvent, this makes sense. But what if H20 is in the gas phase? During ...
- Mon Jan 07, 2019 11:57 pm
- Forum: Ideal Gases
- Topic: R in PV=nRT
- Replies: 34
- Views: 6729
Re: R in PV=nRT
It's essentially a constant usually equal to 8.315 JK^-1mol^-1. I am sure it will be on our constant sheet.
- Mon Jan 07, 2019 11:54 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Large/Small Equilibrium Constant
- Replies: 2
- Views: 202
Re: Large/Small Equilibrium Constant
If I remember correctly, a larger equilibrium constant occurs due to a larger concentration of product than the concentration of reactant. This is because Kc = [Product]/[Reactant]. Alternatively, a smaller equilibrium constant occurs due to a larger concentration of reactant than that of product.
- Sun Dec 09, 2018 6:10 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Why HF is a weaker acid than HCl
- Replies: 17
- Views: 16355
Re: Why HF is a weaker acid than HCl
This comparison is different because in your first comparison, you are comparing bond lengths, but in your second comparison, you are comparing the electronegativity. The reason why we compare electronegativity in your latter comparison is because H is attached to O in both molecules; thus, comparin...
- Sun Dec 09, 2018 6:05 pm
- Forum: Properties & Structures of Inorganic & Organic Acids
- Topic: Boiling point
- Replies: 4
- Views: 810
Re: Boiling point
In this question, it is specified that H2Se has a higher boiling point. Normally, we cannot determine which intermolecular force dominates, but in this question, we know that since the LDF and the dipole dipole forces contradict each other, the LDF is more dominant. It's a really weird nuance!
- Sun Dec 09, 2018 6:03 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: coordination compound shape
- Replies: 3
- Views: 501
Re: coordination compound shape
The shape is determined by how many ligands are attached. Even more so, we have to consider whether something is polydentate. For example, three bidentate ligands would be octahedral in shape.
- Sun Dec 09, 2018 5:53 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3706080
Re: Post All Chemistry Jokes Here
Did you know that oxygen went for a second date with potassium?
How did it go?
It went OK2!
How did it go?
It went OK2!
- Fri Dec 07, 2018 10:49 pm
- Forum: Bronsted Acids & Bases
- Topic: Why Can't Double Bonded O's Accept Protons?
- Replies: 1
- Views: 253
Why Can't Double Bonded O's Accept Protons?
I encountered this problem I 12.127 in the 6th edition book where the question asked how many protons could interact with thymine. My question is how come double bonded O can't accept H. Someone told me that it was because this would make O have a formal charge of +1, but when you add the proton to ...
- Fri Dec 07, 2018 9:24 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Chem 6th Edition 12.25
- Replies: 2
- Views: 317
Chem 6th Edition 12.25
Hi, I need help with question 12.25 with figuring out the concentration of H3O+. I understand how to calculate everything else, but I don't understand why there would even be a concentration of H3O+ if we are just dealing with a Bronsted base. In the solution manual, it mentions Kw. How would you do...
- Tue Dec 04, 2018 5:36 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Identifying Ligands
- Replies: 2
- Views: 330
Re: Identifying Ligands
You can determine if a molecule is a ligand by first looking for a coordination sphere. If there is a bracket, there is a coordinating covalent compound, which means there are ligands. You can probably also look for them by looking for a transitional metal. Transitional metals can bond with 6 ligand...
- Tue Dec 04, 2018 5:22 pm
- Forum: Naming
- Topic: Which nonmetal do we name first if the ligand has 2 of them?
- Replies: 1
- Views: 92
Re: Which nonmetal do we name first if the ligand has 2 of them?
I believe it's safe to assume that when we name ligands, we can just go left to right because the ligands are already in alphabetical order in the chemical equation. When we write the chemical notation for coordinating compounds, we start with the transitional metal, and then name the compounds base...
- Mon Dec 03, 2018 9:31 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: Is there a difference between concentration and molarity?
- Replies: 2
- Views: 12908
Is there a difference between concentration and molarity?
I noticed when we did pH computations, we used the concentration of specific ions or molecules. When we did this, we used M, which is the unit for molarity of moles/liters. However, I always understood concentration as g/L of Kg/L. What is the difference between molarity and concentration? Is there ...
- Sat Dec 01, 2018 6:56 pm
- Forum: Naming
- Topic: 6th Edition 17.29
- Replies: 2
- Views: 127
Re: 6th Edition 17.29
I actually bought an answer solution in the book form, so my solutions manual is a physical copy.
- Sat Dec 01, 2018 6:39 pm
- Forum: Naming
- Topic: 6th Edition 17.29
- Replies: 2
- Views: 127
6th Edition 17.29
On 17.29, in the chapter 6 edition, it says in the answer manual that the CN portion of the coordinating compound will be cyano (not including everything else). However, on page 742 of the book with the chart of common ligands, it says that CN is cyanido. How come the answer solution changed cyanido...
- Wed Nov 28, 2018 1:46 am
- Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
- Topic: 4.46
- Replies: 4
- Views: 577
Re: 4.46
As stated before, you will need to find the total sigma and pi bonds in the molecule. This will involve counting the single bonds for sigma bonds and characterizing the excess bonds as pi bonds.
- Wed Nov 28, 2018 1:16 am
- Forum: Dipole Moments
- Topic: Drawing dipole moments
- Replies: 3
- Views: 431
Re: Drawing dipole moments
I know what you're talking about when you say the textbook and lectures are different when it comes to drawing dipole. I would stick with what Lavelle said though. You are right about how we draw it--the arrow points to the more electronegative atom while the "tail" is near the less electr...
- Wed Nov 28, 2018 12:37 am
- Forum: Dipole Moments
- Topic: Polarity of Asymmetrical Molecules
- Replies: 4
- Views: 514
Re: Polarity of Asymmetrical Molecules
No, these shapes cannot be nonpolar because of the inherent asymmetry of the molecules. The lone pair in each shape pushes the other atoms so bond lengths are slightly different than that of their arrangement structure counterparts. Thus, the dipole vectors will not cancel out.
- Sun Nov 25, 2018 12:48 am
- Forum: Octet Exceptions
- Topic: Why Doesn't I Break Octet in IO3-
- Replies: 1
- Views: 463
Why Doesn't I Break Octet in IO3-
I am currently working on number 4.13, question C in the 6th Edition book. When drawing the lewis structure of IO3-, I noticed the solution manuals had three single bonds for each I-O and one lone pair which means I has a formal charge of +2 and each O has a formal charge of -1. Sure, this makes I h...
- Sat Nov 24, 2018 4:06 am
- Forum: Polarisability of Anions, The Polarizing Power of Cations
- Topic: Distortion and London Dispersion Forces
- Replies: 2
- Views: 319
Distortion and London Dispersion Forces
I was reviewing my notes, and saw that increasing electrons increases the distortion, which in turn increases london dispersion force. To me, this seems counterintuitive because I typically attribute the increase in electrons to an increase in atomic radius, which I associate with weaker bonds. Can ...
- Wed Nov 21, 2018 4:04 pm
- Forum: Sigma & Pi Bonds
- Topic: Clarification of Pi Bonds and Rotation
- Replies: 3
- Views: 1151
Clarification of Pi Bonds and Rotation
Can someone clarify the point Lavelle made about rotating with pi bonds? I recall he used two pencils to try to rotate the atoms, but I think he said something along the lines of "if there is a pi bond, it means there can be no rotation." Could someone clarify this concept?
- Wed Nov 21, 2018 3:52 pm
- Forum: Hybridization
- Topic: Hybridization
- Replies: 6
- Views: 544
Re: Hybridization
Hybridization occurs because it rectifies the problem of unequal energy in bonds that unhybridized models imply. Let's look at the molecule CH4. If we were to look at the C-H bonds, we would do so by drawing the valence electrons in the outermost shell of Carbon in its ground state. Thus, we would s...
- Wed Nov 21, 2018 3:35 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: predicting dipole moments
- Replies: 4
- Views: 428
Re: predicting dipole moments
As Ashley said, the systematic approach is to first look if there are any dipole moments. We can look for dipole moments by looking at the symmetry of the molecule and the vectors of the dipoles. If the molecule is asymmetrical, we know there is a dipole dipole force. If it is symmetrical and the di...
- Sun Nov 18, 2018 6:54 pm
- Forum: Ionic & Covalent Bonds
- Topic: Electron Distortion
- Replies: 1
- Views: 259
Re: Electron Distortion
Electron distortion refers to an interaction between a cation or anion where a cation (because of the positive charge) alters the electron cloud of the anion. In this sense, electron distortion is very important in ionic bonds. The power a cation has to distort the electron cloud of an anion refers ...
- Sun Nov 18, 2018 12:14 am
- Forum: Polarisability of Anions, The Polarizing Power of Cations
- Topic: Polarizability vs Polarizing Power Trends
- Replies: 1
- Views: 1536
Polarizability vs Polarizing Power Trends
What is this trend on the periodic table for polarizability and polarizing power and how do you justify these trends using ideas like more shells and greater effective nuclear charge?
- Fri Nov 16, 2018 1:13 am
- Forum: Lewis Structures
- Topic: Picking Central Atom Special Cases
- Replies: 2
- Views: 322
Picking Central Atom Special Cases
When we draw the lewis structure for for ClO2, we usually pick the atom with the lowest ionization energy. However, between the two atoms, there is a conflicting trend where Cl gets more rightward and gets more downward in comparison to O. This is counterintuitive because ionization energy increased...
- Thu Nov 15, 2018 11:08 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Vsepr Formula
- Replies: 7
- Views: 446
Re: Vsepr Formula
In addition, when we are working with VSEPR theory, we might be asked to put the molecule in the form AXnEm. This helps us predict the actual 3d shape of the molecule while a lewis structure really only predicts the molecule in the 2d plane. Also, the lewis structure has things like single bonds, do...
- Thu Nov 15, 2018 10:53 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Double/Triple Bonds
- Replies: 5
- Views: 1014
Re: Double/Triple Bonds
Lavelle discussed in lecture that the number of bonds should not affect the regions of electron density. Thus, with the information we have now, it is best to assume that double and triple bonds do not affect shape. However, of course there may be nuances to this, but I think that we can stick to th...
- Thu Nov 15, 2018 10:47 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Vespr Formula
- Replies: 6
- Views: 562
Re: Vespr Formula
Also, to add a quick thing--it's actually VSEPR, not VESPR. This is because VSEPR stands for valence shell, electron pair, repulsion theory. As stated above, the basic formula AXnEm where A represents the central atom with an implicit subscript of 1, X represents a ligand (the atom attached to the c...
- Wed Nov 14, 2018 11:27 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Octet Rule
- Replies: 6
- Views: 791
Re: Octet Rule
Another common exception to the octet rule that we don't often talk about is hydrogen just because it's so intuitive to make a single bond without completing its octet. It's one we don't think about often breaking the octet, but one that does nonetheless.
- Mon Nov 12, 2018 10:22 pm
- Forum: Ionic & Covalent Bonds
- Topic: Noncovalent Interactions
- Replies: 4
- Views: 266
Re: Noncovalent Interactions
Another thing to add that I have down in my notes is that greater force in interactions leads to greater melting points. But as reiterated before, your understanding thus far seems spot on!
- Mon Nov 12, 2018 10:16 pm
- Forum: Electronegativity
- Topic: Electronegativity Graph
- Replies: 4
- Views: 474
Re: Electronegativity Graph
I noticed what Christopher noticed as well. Could it have something to do with the fact that this decrease tends to cluster more to the right of the transitional metals? I am looking at a periodic table with the actual electronegativities for each element and it seems like this is somewhat of a trend.
- Mon Nov 12, 2018 10:06 pm
- Forum: Ionic & Covalent Bonds
- Topic: London Van Der Waals Force?
- Replies: 5
- Views: 540
London Van Der Waals Force?
I recall my TA saying that all molecules undergo London Van Der Waals Forces in some way, and that for example, diploe-dipole forces are just stronger forces of this nature. What exactly are these London Van Der Waals Forces and are they synonymous to dispersion and induced diploe-induced dipole for...
- Mon Nov 12, 2018 10:01 pm
- Forum: Ionic & Covalent Bonds
- Topic: What is Distortion?
- Replies: 3
- Views: 1322
What is Distortion?
During Lavelle's lecture, we learned that higher distortion results in greater interaction potential energy which ultimately leads to higher boiling points. What exactly is distortion though?
- Fri Nov 02, 2018 11:00 am
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: How to Find Number of Nodal Planes?
- Replies: 1
- Views: 1108
How to Find Number of Nodal Planes?
How does one find the number of nodal planes given principle quantum number and the subshells? So how does the number of nodal planes relate to s-,p-,d-,and,f- and other things like that?
- Thu Nov 01, 2018 11:55 pm
- Forum: Trends in The Periodic Table
- Topic: Electronegativity Trend: Contrasting Trends
- Replies: 1
- Views: 184
Electronegativity Trend: Contrasting Trends
For trends like electronegativity, what do we do if the atom we are comparing gets more rightward but more downward in position? Does one of the values (period versus group) affect the electronegativity more significantly?
- Thu Nov 01, 2018 11:40 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: How to Find Unpaired Electrons?
- Replies: 2
- Views: 9947
Re: How to Find Unpaired Electrons?
Furthermore, will we be expected to know how to do so on the test?
- Thu Nov 01, 2018 11:40 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: How to Find Unpaired Electrons?
- Replies: 2
- Views: 9947
How to Find Unpaired Electrons?
How do you find the number of unpaired electrons?
- Thu Nov 01, 2018 11:33 pm
- Forum: Resonance Structures
- Topic: Definition of resonance
- Replies: 7
- Views: 907
Re: Definition of resonance
Moreover, to add on to all of these answers, the "true" model for the bonds would be a blend of all the resonance structures, meaning that every bond between nitrogen and oxygen has characteristics of both a single bond and a double bond. Drawing multiple lewis structures of the same molec...
- Thu Nov 01, 2018 11:28 pm
- Forum: Resonance Structures
- Topic: 6th Edition 3.21
- Replies: 2
- Views: 300
Re: 6th Edition 3.21
Just writing the ground state as [Ar] would be an acceptable answer, as the charge of plus 2 means the Calcium atom lost two electrons, equal in valence electrons to that of the noble gas Argon.
- Sat Oct 27, 2018 12:34 am
- Forum: Trends in The Periodic Table
- Topic: Atomic Radius
- Replies: 8
- Views: 786
Re: Atomic Radius
Knowing the trend like you mentioned is probably something we need to know, but knowing the actual values will be given, as we are not expected to memorize the values of atomic radii.
- Mon Oct 22, 2018 1:15 pm
- Forum: Properties of Light
- Topic: Chem Homework 1.55 Mistake?
- Replies: 2
- Views: 253
Re: Chem Homework 1.55 Mistake?
That makes sense, thank you!
- Mon Oct 22, 2018 1:37 am
- Forum: Properties of Light
- Topic: Chem Homework 1.55 Mistake?
- Replies: 2
- Views: 253
Chem Homework 1.55 Mistake?
(This question requires the solution manual in hand) In the solution manual for 1.55, the way the question is solved is v/c = wavelength. However, this means frequency = speed of light times wavelength which makes no sense. Am I misinterpreting this problem, misinterpreting the solution manual, or i...
- Mon Oct 22, 2018 1:34 am
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Chem Homework 1.45 Question Mistake?
- Replies: 3
- Views: 364
Chem Homework 1.45 Question Mistake?
In question 1.45, the bowling ball is rolling down an alley at 5 plus or minus 5 meters per second. In Lavelle's lecture, I recall the uncertainty in position would be 10 because the maximum value is 10 meters per second while the minimum value is 0 meters per second. However, in the solution manual...
- Sat Oct 20, 2018 6:59 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Post Module Question
- Replies: 1
- Views: 172
Post Module Question
I need help with the following question: 18. The hydrogen atom has a radius of approximately 0.05 nm. Assume that we know the position of an electron to an accuracy of 1 % of the hydrogen radius, calculate the uncertainty in the speed of the electron using the Heisenberg uncertainty principle. Comme...
- Thu Oct 18, 2018 2:16 am
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Atomic Absorption Spectroscopy versus Atomic Emission Spectroscopy
- Replies: 3
- Views: 390
Atomic Absorption Spectroscopy versus Atomic Emission Spectroscopy
Hi, I need help with the following question on the module: 13. In the above experiment if only the absorbed wavelengths of light are detected what is the experiment called? What is the spectrum called? I know this is a question about the definition but why is it not: A. Atomic absorption spectroscop...
- Sun Oct 14, 2018 6:14 pm
- Forum: Properties of Light
- Topic: Wave vs. Particle Behavior
- Replies: 5
- Views: 515
Re: Wave vs. Particle Behavior
The fact that they act as particles manifests in the one to one interaction in the photoelectric experiment. However, diffraction is one of the main characteristics that show that they act as waves.
- Mon Oct 08, 2018 9:57 pm
- Forum: Properties of Light
- Topic: Chem Homework Question Number 1.9
- Replies: 1
- Views: 122
Chem Homework Question Number 1.9
On number 1.9, in the 6th edition book, the wavelength of the third type of radiation solves to be 1 meter. Looking at an electromagnetic chart, 1 meter is the approximate wavelength of radio waves (or relatively close to that value). However, on the answer key, the radiation event is supposedly &qu...
- Mon Oct 08, 2018 5:18 pm
- Forum: Properties of Light
- Topic: Quanta & Photons
- Replies: 5
- Views: 434
Re: Quanta & Photons
Doctor Lavelle used a very pertinent example of a water faucet in his discussion of the difference between discrete and quanta variables. Essentially, the holistic view of water exiting a water faucet is comparable to a discrete value because water is seen as continuously flowing. An example of this...
- Mon Oct 08, 2018 5:06 pm
- Forum: Administrative Questions and Class Announcements
- Topic: DOWNLOAD SESSION WORKSHEETS HERE - Sundays 4-6pm (Karen) [ENDORSED]
- Replies: 135
- Views: 39414
Re: DOWNLOAD SESSION WORKSHEETS HERE - Sundays 4-6pm (Karen) [ENDORSED]
This is very helpful! Thank you for this! I'll make sure to study it, and I look forward to seeing you on Sunday!
- Mon Oct 01, 2018 9:41 am
- Forum: SI Units, Unit Conversions
- Topic: Grams/mole
- Replies: 12
- Views: 1203
Re: Grams/mole
Yes, they are the same notation. Negative powers just indicate that the exponent will appear in the denominator. For example, x^(-1) is simply 1/(x)^1. Another way to think of it is looking at the term as the reciprocal of the absolute value of the exponent. Because the grams are multiplied by (mole...
- Sun Sep 30, 2018 10:11 pm
- Forum: Balancing Chemical Reactions
- Topic: Short cuts/methods for balancing equations
- Replies: 15
- Views: 1804
Re: Short cuts/methods for balancing equations
The way I balance equations is I always scan for an element that appears on the reactant side of the equation and product side of the equation once. In doing so, I make sure that there are no other elements affecting the balancing of the element. After this, I look to see if the element I balanced w...
- Sat Sep 29, 2018 6:40 pm
- Forum: Limiting Reactant Calculations
- Topic: Is there a specific way to solve limiting reactant problems?
- Replies: 4
- Views: 440
Re: Is there a specific way to solve limiting reactant problems?
The way I solve limiting reactant problems is the way you highlighted in your first description. Converting the grams of reactants to moles allows one to compare the moles of the actual reaction to those in the molecular equation. I understand what you mean about comparing the two values as being co...