## Search found 20 matches

Fri Jan 26, 2018 4:42 pm
Forum: Calculating Work of Expansion
Topic: Irreversible Pathway Picture
Replies: 3
Views: 271

### Re: Irreversible Pathway Picture

There's physical movement, yes. But this doesn't mean there is "work" in the traditional sense. The change in the piston's position is a result of entropy. This only works because the piston is in a vacuum. delta U =0, q=0, and w=0. The point being made in this diagram was that there is no...
Fri Jan 26, 2018 1:08 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.57 question
Replies: 1
Views: 217

### Re: 8.57 question

Great observation! You're thought process is good, but you have to be aware of what you are given. We are given deltaH(C), which is the enthalpy of combustion. This means you have to be aware of which side your reactants and products are on. For combustion, the hydrocarbons will always be on the lef...
Fri Jan 26, 2018 12:54 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Homework Exercise 8.53
Replies: 1
Views: 213

### Re: Homework Exercise 8.53

The reason that this problem is calculated differently is because we are given the molar heat capacity of the "entire assembly", not just the CO. If we had the heat capacity of CO, then we would calculate using the typical equation of q=mCdeltaT. However, this problem is also using the pro...
Thu Dec 07, 2017 3:47 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Identifying if a molecule is monodentate, bidentate, etc.
Replies: 1
Views: 165

### Re: Identifying if a molecule is monodentate, bidentate, etc.

The surest way to determine this is to look at the lewis structure. The atoms with lone pairs on them and still able to bond (ie, they can turn the lone pairs into a covalent bond to fulfill their octect or, expand the octet in the case of d-orbital containing elements) are the elements most likely ...
Thu Dec 07, 2017 3:36 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE table
Replies: 7
Views: 624

### Re: ICE table

If x is zero, it means that there is no change in the concentrations of the products or reactants. In this case, x will be zero for both sides. This also implies that the forward and backward reactions have already achieved dynamic equilibrium. The whole point of the ice table is to determine the eq...
Thu Nov 16, 2017 11:15 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.19 b
Replies: 3
Views: 244

### Re: 4.19 b

As always, drawing the Lewis structure is the first step. When we draw the Lewis structure, Be is the central atom of the overall molecule, but the outer Cs are the respective central atoms for the right and left sides. We know that because Be does not ever attain a full octet, we should simply fill...
Thu Nov 16, 2017 7:57 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.27
Replies: 3
Views: 375

### Re: 4.27

Knowing whether or not a molecule is polar depends on your knowledge of the structure first. Since there are 5 Cs in the molecule, it's a good indication that C5H5N will be form a ring-like structure such as benzene. However, instead of a 6th C, there is an N that completes the ring. Also, we know b...
Thu Nov 16, 2017 7:35 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Chapter 4 Question 17 Part D
Replies: 1
Views: 185

### Re: Chapter 4 Question 17 Part D

A hydronium ion, H3O+, is not linear. Because it has four atoms, it must be a more complex shape. There is a lone pair on the central atom, O, which means there are three bonds on the central atom, plus this lone pair. In total, that makes four electron densities for the entire molecule. Molecules w...
Tue Nov 07, 2017 4:58 pm
Forum: Lewis Structures
Topic: Resonance Structures
Replies: 1
Views: 246

### Re: Resonance Structures

That's a good question. I think the underlying question here is about resonance: does it only exist on chemically symmetric molecules? The quick answer is no. It certainly exists on the types of atoms that ONF is. I'm not sure about the reaonance of ONF, but another example to answer this question i...
Tue Nov 07, 2017 4:39 pm
Forum: Electronegativity
Topic: electronegativity chart
Replies: 11
Views: 952

### Re: electronegativity chart

In general, I wouldn't memorize these kinds of values. The best way of thinking about electronegativity is that it is closely related with ionization energy and electron affinity (in fact, it's derived from these two values). Just consider how the trends work. Electron affinity and Ionization energy...
Tue Nov 07, 2017 4:31 pm
Forum: Octet Exceptions
Topic: Resonance Structures and Isomers
Replies: 2
Views: 340

### Re: Resonance Structures and Isomers

Good question! The main thing to keep in mind is that isomers have different chemical properties, while different resonance structures have the same essential properties (in other words, they are different versions of the same molecule). The temptation to confuse resonance with isomers may arise fro...
Tue Nov 07, 2017 4:21 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.3
Replies: 1
Views: 165

### Re: 4.3

Yes, it will still be a linear shape. Even though the molecule "feels" skewed since on one side there are three covalent bonds, and on the opposite side there is only one covalent bond, this isn't the case. Remember that covalent bonds, whether single, double, or triple, have the same effe...
Tue Oct 31, 2017 6:53 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 4s and 3d
Replies: 2
Views: 248

### Re: 4s and 3d

I found this concept to be quite confusing at first as well. If we are taught that 4s fills up before 3d, then why, in the case of transition metals, do the cations formed always lose the 4s electrons before they lose the 3d electrons? I've considered this concept at length and have found this very ...
Sat Oct 21, 2017 1:57 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Uncertainty of Velocity [ENDORSED]
Replies: 2
Views: 311

### Re: Uncertainty of Velocity[ENDORSED]

Upon seeing Dr. Lavelle's Module on the Heisenberg Uncertainty Principle, I would add to this explanation by reiterating the fact that the momentum doesn't really tell us much about the electron, since it's a value combined with the mass of the electron. You can see Dr. Lavelle explain this in more ...
Fri Oct 20, 2017 11:30 pm
Forum: Photoelectric Effect
Topic: Self test 1.5B part b
Replies: 1
Views: 260

### Re: Self test 1.5B part b

I have to agree with your reasoning, Peyton. We find the kinetic energy, EK in part (a). And we know that Ephoton - \phi = EK So, in order to find the wavelength of the photon, the logical thing to do is to add the energy of the work function, \phi , to algebraically isolate the energy of the photon...
Fri Oct 20, 2017 10:22 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Uncertainty of Velocity [ENDORSED]
Replies: 2
Views: 311

### Re: Uncertainty of Velocity[ENDORSED]

The Heisenberg uncertainty principle hinges on the fact that it is impossible to measure the speed of the electron without altering its path (and therefore its velocity).Velocity is essentially a measure of speed, and is given in units of m/s. Momentum, on the other hand, is mass x velocity, given i...
Fri Oct 13, 2017 1:26 pm
Forum: Properties of Electrons
Topic: Energy Levels
Replies: 6
Views: 516

### Re: Energy Levels

This reminds me of the concept we were discussing in a workshop. The movement of the electron between energy levels is known as either an emission or an absorption. My question is, which kind of movement of the electron is which? Due to the conservation of energy, there will always be some kind of e...
Fri Oct 13, 2017 1:19 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: How to find initial number from spectral light
Replies: 1
Views: 230

### Re: How to find initial number from spectral light

When you say “initial numbers in a series”, this indicates a particular spectral line. Perhaps the most sure-fire way to approach this question would be to memorize an arsenal of these spectral lines, as I'll mention later. Beyond just this, however, you can reason that for each series, there are sp...
Thu Oct 05, 2017 11:11 pm
Forum: Limiting Reactant Calculations
Topic: Explanation of Review Problem M.28 [ENDORSED]
Replies: 1
Views: 557

### Explanation of Review Problem M.28[ENDORSED]

This problem incorporates concepts of atom:mol ratios to solve for the empirical formula. Without a key understanding of the combustion reaction or the nature of a chemical analyzer, this problem may be more challenging. Tu-jin-pi is a root bark used traditional medicines for the treatment of "...
Thu Oct 05, 2017 9:21 pm
Forum: Balancing Chemical Reactions
Topic: Combustion Reaction Water Phase
Replies: 2
Views: 389

### Re: Combustion Reaction Water Phase

Fascinating question, joshusaxian. This discussion has interesting implications in regards to biological systems. I think we would all be fascinated to explore this in the lens of physiological combustion, or metabolism. As biology students, we are taught that there is a "net" release of H...