CHEMISTRY COMMUNITY

Jonas Talandis

Theoretically, yes, but not on its own. You would need other information to figure that out, namely, the temperature and the entropy to find the Gibbs Free Energy, the sign of which will tell you the spontaneity. However, it is more likely that exothermic reactions are favored, especially in cool te...

Jonas Talandis

Like you said, the ice needs two calculations because it undergoes a phase change and each phase has a separate heat capacity. Also, I think you may be referring to the change in heat energy or the heat energy transfer in which both values would be positive since heat is flowing into the ice and wat...

Jonas Talandis

Most likely at the end of the course since last quarter I didn't know it was a thing until week 4 but still got full credit because I had 30 posts overall.

Jonas Talandis

All of the Voltage values ended up being negative and asked you to order each three by strength of the OA and RA. The two that would make a cell with the largest voltage would be the two that, when added, would amount to the largest number. If I remember correctly, the correct answer happened to be ...

Jonas Talandis

Standard conditions are 1 atm and room temp. I don't think we have ever had a question on a test where the temperature isn't given.

Jonas Talandis

We include these typically when there is no solid involved on that side of the reaction. If there's no solid, there's usually no conductor to actually transfer these electrons so we use an inert one.

Jonas Talandis

I think those half reactions are only considering what is happening to the reactant ion in question. In reality, it would produce HCl, but since each half reaction only considers one ion, they don't include the other. But then again, since HCl is a strong acid, it would fully dissociate anyway.

Jonas Talandis

Even though I2 is a solid, it doesn't conduct. Therefore, we need to include platinum, which acts as an inert conductor.

Jonas Talandis

The solutions manual answer was pretty long, so I'm assuming there's not really a shortcut. However, you can determine the value of n by figuring out how many electrons are being exchanged. You can do this by just looking at the diagram and using your intuition, but to ensure that it's correct, you ...

Jonas Talandis

You can calculate all of these values in the equation in one of the replies above in order to make extrapolations about whether the reaction will be spontaneous, whether its exothermic or endothermic, etc. These qualities tell us a lot about the reaction past just the quantified values of these terms.

Jonas Talandis

It depends on which equation you use to find entropy. They will end up being the same value but positional refers to the equation with botzman's constant and degeneracy, while thermal refers to q/T.

Jonas Talandis

Once the elements are balanced, it will be clear how many electrons are involved in the appropriate half reactions.

Jonas Talandis

Like all concepts and equations in thermodynamics, etc., they always refer back to the system itself (e.g. Work the system did on the surroundings, work the surroundings did on the system). Therefore, if DeltaG is negative, we know that it represents that the system does not need to use energy to ca...

Jonas Talandis

You use a similar technique as determining the stability based on K value. Like if a K value is extremely large, we can assume that the products are more stable than the reactants because the reaction carries out so that it creates a lot more of them. Similarly, if the deltaG associated with a react...

Jonas Talandis

This is because Delta H or S fusion actually refers to the enthalpy change when a substance is melting. I know this is lowkey stupid because it would make sense for fusion to be freezing, but that's just the way it is. So when considering the S fusion for a substance, it equals deltaH fusion /T free...

Jonas Talandis

The reason the book has the enthalpy of formation of the reactants-products is because the signs of these values flip. Considering that most enthalpies of formation are given as negative values, we know that that is the energy required to break the initial bonds. For this reason, the sign of the val...

Jonas Talandis

Degeneracy and the number of micro states are the same thing. The example he used in class was that the base equaled the number of places an atom could conceivably be. He used in example of a double sided flask with a very very very small tube between them; the tube was too small for an atom to conc...

Jonas Talandis

Volume should always be in L while P is apparently in Pascals.

Jonas Talandis

I believe it's because when we find U we're only concerned with the final and initial states. Regardless of how it's calculated or what happens between the initial and final points, we are just concerned with the change in energy.

Jonas Talandis

I think it's a similar concept of not including solids or liquids in equilibrium expressions. The gas is the only phase that is able to affect volumetric change. But idk lol

Jonas Talandis

Negative Work is definitely a thing. All it means is that the system is doing work on the surroundings instead of getting work done on itself. This happens when the piston moves out for example.

Jonas Talandis

To be more clear, a shift to make more products would only occur if some change were to happen to the receptacle in which the reaction was occurring that all of a sudden increased the amount of reactants. Specifically: Addition of reactants would increase the [reactants] and the reaction would creat...

Jonas Talandis

As stated above, liquids are not included in Q or K equations. But as for whether to use terms of pressures or concentrations, it depends on the question. It will ask you to find either Kc (conc.) or Kp (pressure). Otherwise, if it gives you values of conc, use them and just find Kc.

Jonas Talandis

It's nothing new. Just treat each step as it's own reaction and add the concentrations from each step in question to find the overall Ka or pH or whatever. If needed, it will give you each step's Ka or whatever you need to solve the problem. You can just add the concentrations from each step to find...

Jonas Talandis

Consider what would likely happen in a reaction with water. Does the H atom have anywhere to be accepted? Or will it dissociate. Many times molecules are amphoteric and can do both but a lot of it will be memorization and understanding of where a proton can go. One big indicator for bases that Dr. L...

Jonas Talandis

Last quarter I didn't even know Chem Community was a thing until week 4 and freaked out thinking I had lost 12 points, so I freaked out and made up the posts I missed so that I had 30 at the end of the quarter and I still got 30 points. It might depend on your TA but I think the 3 posts a week thing...

Jonas Talandis

A conjugate base is any molecule that is conjugate to the original acid from the equation. In a reaction with an acid, the conjugate base is whatever molecule is made after the acid donates its proton or loses an H.

Jonas Talandis

Values of partial pressure for products and reactants affect K in the same way that concentrations do. That's why K has two forms Kc and Kp. Kc is when using concentrations and Kp is when using Partial Pressures. It's just the ratio of Partial Pressures of the Products/Partial Pressures of the React...

Jonas Talandis

The solutions manual includes answers with bars and atm so I believe either is fine. Not sure which, if either, are considered SI units

Jonas Talandis

Bars are units of partial pressure. Treat them the same way you would concentration in the product/reactant expression for Kc, only this time, it's Kp.

Jonas Talandis

What is the chemical formula for a Banana?

BaNa₂

Jonas Talandis

Substitute known values into equations. If the Frequency of the photon is known, it can be multiplied by Plank's Constant (h) to find the energy of the photon in J. Then, we know the Kinetic Energy of the resulting emitted electron to be equal to 1/2*m*v^2. The mass of the electron is known but the ...

Jonas Talandis

Biological Compounds are always assumed to be aqueous. Otherwise it should be given in a formula or reaction equation. You should be able to tell by the information given to you by the equation. You can't tell the state of a compound based on the compound alone, it only becomes known to be aqueous i...

Jonas Talandis

Every bond angle in an octahedron is 90 degrees. When there is one LP (Square Pyramidal) it is slightly less that 90 degrees. When it has 2 LPs (Square Planar) the repulsions cancel out and the bond angles are all 90 degrees. When there are three LPs it becomes T-Shaped with slightly less than 90 de...

Jonas Talandis

A dipole-dipole force is between two polar molecules that already have two oppositely charged poles as a result of their orientation/electronegativity of their bonds. This force exists because the opposite charges of the poles of two polar molecules are attracted to each other. Dipole-induced dipole...

Jonas Talandis

In lecture, while referencing a molecule with 5 regions of electron density in a trigonal bipyramidal electron region orientation, Dr. Lavelle said that a Lone Pair on the central atom would go in the trigonal plane of the orientation rather than the top or bottom "peaks" of the pyramids b...

Jonas Talandis

Think about it as if you saw the shape of the molecule blown up in size, like when Lavelle took off an atom from the Trig. Bipyramidal shape to demonstrate the see saw shape. You can't "see" Lone pairs, so they shouldn't contribute to the shape of the molecule since there is no atom being ...

Jonas Talandis

I believe Lavelle said that we would turn in two weeks worth of homework in week 9, so I'm assuming there will be no discussion, at least on wednesday.

Jonas Talandis

Because sigma bonds overlap head on and pi bonds overlap side by side. It has to do with orbital configuration. In today's lecture, the C2H4 molecule had a pi bond where the double bond was because the left over unhybridized orbital at the 2p level was oriented at 90 degrees outward, resulting in a ...

Jonas Talandis

I don't believe so, because Polarity is determined by difference in electronegativity, which isn't changed by the presence of a double bond. However, in a larger molecule I'm not sure whether or not the presence of a double bond on one side and a single on the other would create a dipole moment. I d...

Jonas Talandis

Since each C atom only has 3 regions of electron density, and we know that the number of these regions needs to be equal to the number of hybridized orbitals, the resulting hybrid orbitals will be 3 orbitals at the sp2 level. However, since there is one p orbital unaccounted for (there are 3 p orbit...

Jonas Talandis

It's a matter of different isomers. I think that the important thing to consider is knowing that if dipole moments cancel, it will result in a non polar molecule overall and vice versa. It probably doesn't matter as much as to how different isomers exist for our purposes.

Jonas Talandis

The word dipole refers to any molecule that experiences Polar sides with the negative charge on one side and a positive charge on the other side. The word induced refers to a molecule that is not necessarily polar all the time but experiences a positive charge on one side and a negative charge on th...

Jonas Talandis

An induced dipole occurs either randomly as a result of increased concentration of e- on one side of an atom/molecule or by the repulsion of said e- from another dipole. These molecules experience van der waals forces bc opposites attract.

Jonas Talandis

Hybridization comes from the random dispersion of electrons in an atom or molecule. The e- are in constant motion, so if they randomly all happen to be mostly to one side, that creates a dipole dispersion, allowing for another dipole molecule to bond via Van der Waals forces to the opposite charge o...

Jonas Talandis

We haven't learned that yet. No need to worry about it for the midterm.

Jonas Talandis

This is listed as one of the solution manual errors, the full list of which you can find here: https://lavelle.chem.ucla.edu/wp-conten ... rs_7Ed.pdf . You are correct

Jonas Talandis

39.1 g is approximately the mass of a mole of K ions. You need to divide by avogadro's number to find the actual mass of a single ion. Hope that helps.

Jonas Talandis

You use the equation Coulomb Energy = (Charge 1*Charge 2)/Distance between e-

I not sure if we will use it on the test, though because I don't know if it is on the equation sheet. But it could be.

Jonas Talandis

I'm assuming its just for clarity/ease. The value +1/2 or -1/2 doesn't actually affect the energy levels of the electron in any equation, its just a symbolic notation of which specific electron is being referred to.

Jonas Talandis

I think it has something to do with electron affinity and inter-molecular forces, which we haven't learned about yet. But for know, I think we just need to understand that 4s comes is filled before 3d except for when the d orbital steals an e- from the 4s for Cr and Cu.

Jonas Talandis

The Solutions Manual for 1.45 is incorrect. This is listed on Prof. Lavelle's list of Solution Manual errors. You can find the link into a post of mine from tonight. The value for delta v would be 0.2.

Jonas Talandis

I believe its the other way around. I wrote in my notes that s<p<d<f in the same shell/energy level. Hope this helps.

Jonas Talandis

When considering the wave-particle duality of matter, the wave part comes from the experiment showing that electrons are capable of diffraction because diffraction occurs when there is constructive and/or destructive interference of waves. If an electron is capable of diffraction, then that implies ...

Jonas Talandis

A bowling ball of mass 8.00 kg is rolled with velocity 5.00 +/- 5.0 m/s. What's the uncertainty of position? For the question pasted above, I got a different answer than the solution manual because I inserted a value of 10 for the velocity uncertainty because it is +/- 5, but the manual only put a v...

Jonas Talandis

Hi,

Using the De Broglie equation (Wavelength = h/m*v), we can insert the given wavelength, the Planck constant, and the known mass of an electron, which is given on the test btw, to solve for v. Hope that helps.

Jonas Talandis

Hi,

Since electrons have wave-particle duality, you can use the De Broglie equation for this, inserting the velocity into the calculation for p. Hope that helps!

Jonas Talandis

Hi all,

How much of the H-Atom Atomic Spectroscopy Information are we expected to memorize? For example, do we have to know the wavelengths and the series names for lines in the series? Will the energy (n) levels for these lines be given or will we have to derive them. Please advise. Thank you!

Jonas Talandis

Hi Madison, You would have to use the equation E K = 0.5(m)(v 2 ). We know the mass of the electron and 0.5 is a constant so by inserting the uncertainty of the velocity, it would return the uncertainty of Kinetic Energy for one electron. Then use stoichiometry to find the value for a mole of electr...

Jonas Talandis

Hello,

I was wondering if anyone could please help explain how the Bohr equation specifically (V=(Change in E)/h) relates to the origin of the lines on a spectroscopic analysis and how we derive them from this equation. Thanks!

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