CHEMISTRY COMMUNITY

Leyna Dang 2H

Thank you so much! This helped a lot!

Leyna Dang 2H

maybe focus on your breathing and trying to relax? listening to music could also help you calm down a bit

Leyna Dang 2H

He said he'll update us on Saturday!

Leyna Dang 2H

I'm assuming your textbook and any lecture notes you took

Leyna Dang 2H

Does anyone know how the final is going to be given? Will it be a pdf that we have to print out and then take pictures of our answers or is it like through that respondus webcam thingie? So far all he has said is that it's going to be taken online, but we don't need to use any other apps/software l...

Leyna Dang 2H

TimVintsDis4L wrote:
Mariah wrote:Any word on how long it will be ?

He mentioned that it was going to be pretty short and simple so I would assume no more than 1.5 hours, so half of what the actual final would have been like.

His email said he was debating between 3 or 4 hours.

Leyna Dang 2H

He said it was going to be taken the same time he has scheduled, but he's still deciding on whether or not the exam is going to be 3 or 4 hours.

Leyna Dang 2H

K is dependent on temperature and activation energy I believe

Leyna Dang 2H

We usually get them back the following week so pretty sure you'll get them back week 10

Leyna Dang 2H

Cindy Adiwidjaja 1B wrote:Do you guys know if the TAs made Test 2, because I felt like it was formatted much differently than the other tests.

I think the TAs made the test and Lavelle makes the midterm and final

Leyna Dang 2H

Probably this weeks discussion

Leyna Dang 2H

review the notes and try to do all of the homework/textbook problems

Leyna Dang 2H

Osvaldo SanchezF -1H wrote:We might be asked to do this but in the form of s|g|aq||aq|g|s and not an actual picture.

I agree, I think you should memorize how to write it in this form.

Leyna Dang 2H

To maintain the charge balance between the anode and cathode

Leyna Dang 2H

When E is positive, delta G will be negative. This would mean that the reaction will be spontaneous. However, when E is negative, delta G will be positive. This would mean that the reaction will be non-spontaneous.

Leyna Dang 2H

E is typically given for reduction reactions. When you're expected to find the E of an oxidation reaction, you're supposed to flip the sign for the oxidation half-reaction

Leyna Dang 2H

kinetically controlled reactions are usually short while thermo controlled reactions are long.

Leyna Dang 2H

G(not) is at standard Gibbs free energy, thus it is under standard conditions, unlike G.

Leyna Dang 2H

Delta U represents the change in internal energy while delta H represents the change in enthalpy.

Leyna Dang 2H

It should be on the rest of thermodynamics (second page) and electrochemistry.

Leyna Dang 2H

Sydney Pell 2E wrote:If the two were in different phases, would there then need to be a 'I' separating them?

I think you'd need to separate them if they were in different phases.

Leyna Dang 2H

We use the equation to find the cell reduction potential when the product and reactant concentrations are known.

Leyna Dang 2H

When a system is doing the work, w is negative (ex. expansion), but when work is being done on a system, w is positive (ex. compression).

Leyna Dang 2H

Oxidation occurs when a molecule loses an electron. Reduction occurs when it gains an electron.

Leyna Dang 2H

∆G= the change of Gibbs free energy for a system while ∆G°= the change of Gibbs free energy for a system under standard conditions

Leyna Dang 2H

Memorizing the common ones should be fine

Leyna Dang 2H

Jacob Puchalski 1G wrote:I think the point was to relate K to the temperature? I might be wrong

I think it's the change in K and the change in temperature??

Leyna Dang 2H

Will constant pressure be told to us or do we have to assume it for things outside?

Leyna Dang 2H

How is heat capacity a state function? What does that mean for heat capacities.

Leyna Dang 2H

If the pressure change is caused by a change in volume then yes otherwise I don’t think so

Leyna Dang 2H

Cv is for constant volume and Cp is constant pressure. I don’t think they’re the same value.

Leyna Dang 2H

DesireBrown1J wrote:What was the little saying to remember the state functions other than entropy and enthalpy? The HUGS and TV one?

If you’re under Pressure and feeling Dense, all you want is to watch TV and get HUGS.

Leyna Dang 2H

DesireBrown1J wrote:Why is delta H always q but q is not always delta H? What exactly does he mean by that?

DeltaH by definition is q at constant pressure. But if q is not at constant pressure then it is not deltaH.

Leyna Dang 2H

905373636 wrote:Will it focus more on the new content than what we’ve already learned for Test 1 or just even distribution?

I'm not sure about distribution, but I'm pretty sure some of the material we were tested on for Test 1 will be on the midterm.

Leyna Dang 2H

Yes, they need to be on opposite sides to cancel out. When the equal number of moles of the reactant and product you're looking at are on opposite sides, they balance out and therefore cancel.

Leyna Dang 2H

Closed systems are able to exchange energy, and therefore heat, with their surroundings. Isolated systems can't exchange energy with their surroundings.

Leyna Dang 2H

yes, because the molecules will have less space to move around

Leyna Dang 2H

The unit for ∆H is usually kJ/mol, but I think it would be kJ when you're given moles and expected to find the change in enthalpy.

Leyna Dang 2H

I'm not sure but I think it has to do with the fact that the bond enthalpies of all molecules other than diatoms are averages. Since the averages are given and not the actual values, they aren't as accurate.

Leyna Dang 2H

He ended the lecture on method 3 today so we'll probably go over it in the next lecture.

Leyna Dang 2H

When Q<K, the forward reaction is favored because the concentrations/partial pressures of the products are too low compared to reactants for equilibrium. Therefore, the excess reactants would form more products in order to reach equilibrium.

Leyna Dang 2H

Make sure you balance all of your equations. Not doing so could cause you to end up with the wrong K value since your coefficients might be wrong.

Leyna Dang 2H

No, strong acids would have a lower pka

Leyna Dang 2H

Neither of them affect the equilibrium or equilibrium constant because they're pure substances. Solids don't have a concentration, and liquids act as solvents and their concentrations don't change.

Leyna Dang 2H

you usually use ice tables when the initial concentration is given

Leyna Dang 2H

Yes, at 25 degrees celcius, Kw will always be equal to 1.0 x 10^-14

Leyna Dang 2H

You use the ICE table for weak acids and bases (doesn't fully dissociate)

Leyna Dang 2H

You should work on the practice homework problems and review your lecture notes. You could even work on problems together with your friends and go over what you guys need more help/clarification on.

Leyna Dang 2H

I understand the fact that you omit solids and liquids when calculating the equilibrium constant, but why? What's the logic behind it? Solids and liquids aren't included because they do not have a significant effect on the concentration. Lavelle also mentioned during lecture that solids do not have...

Leyna Dang 2H

neither the reactants nor the products are strongly favored

Leyna Dang 2H

No, the reverse reaction is favored because the concentration/partial pressure of the reactants is less than that of the products. Therefore, more reactants need to be produced so that the reaction can reach equilibrium. (Hope this is right and helpful!)

Leyna Dang 2H

When a reaction isn't at equilibrium, you would try to find the reaction quotient, Q, in order to determine which direction the reaction will favor. When Q<K, the FORWARD (goes toward products) reaction is favored because the concentrations/partial pressures of the products are too low compared to r...

Leyna Dang 2H

Solids are not included in the equilibrium constant because they do not have a concentration. Liquids are also not included because they are in excess and their concentrations do not change (it stays constant throughout the reaction).

Leyna Dang 2H

Pi bonds are unhbyrdizied p orbitals and can also be d orbitals i think

Leyna Dang 2H

If you are referring to the final, I think it asked about more polarizing, not polarizability. The above answer looks right.

Leyna Dang 2H

Guess we didnt really have to memorize it since there was no naming on the final...

Leyna Dang 2H

You'd use the AXE formula where you'd look at the central atom of the compound and determine how many atoms are bonded to it and how many lone pairs it has.

Leyna Dang 2H

You could find pH using pH=-log[H+]. Or, if you have the pOH, you could subtract it from 14 to find the pH.

Leyna Dang 2H

You can determine the roman numeral by finding the charge of the transition metal. If the charge is not given, you can calculate the charges of each ligand and subtracting it from the overall charge.

Leyna Dang 2H

We didn't really focus on spectroscopy, so I don't think we'll see in on the final?? I'd focus more on what he went over in class.

Leyna Dang 2H

You would label the sigma and pi bonds separately for the double bond. The same would apply for a triple bond.

And yes, when there are multiple single bonds, labeling every single bond with a sigma is correct.

Leyna Dang 2H

You can determine the coordination number by counting the number of ligands that are bonded with the central atom. For Ba[FeBr4]2, you would focus on what is in the bracket. Iron, the transition metal, has 4 ligands bonded to it. Therefore, the coordination number for your example would be 4.

Leyna Dang 2H

Polydentate ligands have two or more lone pair donating sites.

Leyna Dang 2H

Dipole-dipole in a solid phase would be stronger. The bonds in a solid are tightly held and rigid unlike those of a gas. This would mean that the attraction between the molecules in the solid phase would be greater.

Leyna Dang 2H

Yes, it's definitely possible! You just have to be able to know which formula corresponds with which shape.

Leyna Dang 2H

Honestly I think it depends on your TA, but just to be safe you should use the right number of sig figs.

Leyna Dang 2H

You could draw the Lewis structure and determine the VSEPR formula. A formula of AX2E or AX2E2 would indicate that the molecule is bent. AX2 or AX2E3 would be linear.

Leyna Dang 2H

EthanPham_4D wrote:Can anyone provide an example of the naming with these prefixes? I would like to see how it's used.

An example could be the compound ChloroBISethyleneDIaminecobalt(III)Sulfate. Because the ligand has the same prefix as the polydentate (di-), the second prefix, bis- is used.

Leyna Dang 2H

I don't think it's necessary, but I think it can help you determine the VSEPR structure if there are lone pairs.

Leyna Dang 2H

A single bond would have 1 sigma bond, a double bond would have a sigma bond and a pi bond, and a triple bond would have a sigma bond and 2 bonds.

Leyna Dang 2H

There are three types of covalent bonds: polar, nonpolar, and coordinate. Polar and nonpolar covalent bonds can be distinguished by differences in electronegativities and coordinate covalent bonds involve sharing electrons in order to order fill up shells.

Leyna Dang 2H

The VSEPR formula is AXnEm, where A is the central atom, Xn represents the atoms attached to the central atom, and Em represents the lone electron pairs.

Leyna Dang 2H

I'm guessing everything we covered after the midterm?

Leyna Dang 2H

You could use Formal Charge= Valence Electrons + (Lone Pairs - Bonds/2), but an easier way to calculate the formal charge is to check the valence electron of the element and subtract the number of dots and lines it has.

Leyna Dang 2H

According to the photoelectric effect, frequency is directly proportional to the ejection of electrons. However, these electrons will only be ejected if the threshold energy is met.

Leyna Dang 2H

Elements that can go into the d-orbital can follow the same exception and have more than 8 electrons.

Leyna Dang 2H

I don't think there are

Leyna Dang 2H

Count the valence electrons, try to make each element form a complete octet, and then check your formal charges.

Leyna Dang 2H

the conversion from eV to J should be given on the test I think

Leyna Dang 2H

Going from a higher energy level to a lower, the change is negative, but photon energy is always positive, so if you set them equal to each other you would need a negative sign.

Leyna Dang 2H

Yes I am pretty sure you have to write it in order of increasing number or you will lose points. It also helps when writing configurations for cations to tell which electrons to remove.

Leyna Dang 2H

Lyndon was talking about an exception to the trend with ionization energy and electron affinity. Electronegativity does not have those same exceptions. O is more electronegative than N.

Leyna Dang 2H

It is the threshold energy, or the energy required to remove an electron from a metal surface. The threshold energy will vary based on the type of each metal. When the unit is J/mol, it is calculating the energy required to remove a mol of electrons.

Leyna Dang 2H

You can look at the group numbers on the periodic table, but this doesn’t apply to d-block elements. For groups 13-18, the valence electrons correspond to the number that is in the ones place. So oxygen, for instance, is in group 16 so it would have 6 valence electrons.

Leyna Dang 2H

I had problems with this at first too, but I think it has to do with the element being ionized. You're supposed to fill the d block first so that it's more stable(?), and you do this by taking the 2 electrons from the 4s orbital and moving them to the 3d orbital. This now makes the configuration for...

Leyna Dang 2H

I think you meant [He] haha but anyways, I think one thing you could do is count up the number of electrons in the given configuration and compare the total to the element on the periodic table that has the total as its atomic number. If the elements match, then the configuration is in the grounded ...

Leyna Dang 2H

The number of valence electrons an element has corresponds with the group/ column it is under on the periodic table. For example, oxygen is in group 6 of the periodic table, therefore it has 6 valence electrons.

Hope this helps!

Leyna Dang 2H

Going down the table, elements in the same column, or group, have the same number valence electrons and share similar characteristics.

Leyna Dang 2H

An ionic bond is a bond that is shared between a metal and a non-metal. These metals can also be referred to as ions (atom/molecule that loses or gains an electron). Ions that gain an electron (have a negative charge) are known as anions and those that lose electrons (positively charged) are cations...

Leyna Dang 2H

So far, I've been reviewing the modules on Lavelle's website and worked on all of the homework problems listed on the class syllabus.

Leyna Dang 2H

I believe they were copper (Cu) and chromium (Cr). The configuration for copper would be [Ar]3d10 4s1 and chromium would be [Ar]3d5 4s1.

Leyna Dang 2H

On the periodic table, 3d starts from Scandium (Sc) and ends at Zinc (Zn). You can think of it as each element having a humber that corresponds with their position or order in that row. So Sc would be 1, Ti would be 2,..etc. Because Sc is first in the 3d row its configuration would be [Ar]3d1 4s2 an...

Leyna Dang 2H

You can try to solve for the frequency and once you get that, use the formula E= (Plank's constant)*(frequency), or E=hv, in order to get the energy of the photon. If you are given the wavelength and not the frequency, you could use wavelength to find the frequency by using formula v (frequency) = s...

Leyna Dang 2H

"In the ultraviolet spectrum of atomic hydrogen, a line is observed at 102.6 nm. Determine the values of n for the initial and final energy levels of the electron during the emission of energy that leads to this spectral line."

I'm not sure how to approach this problem. Can someone help?

Leyna Dang 2H

keV is the notation for kiloelectron volt. If you want to convert this to joules you could convert keV into units of eV by multiplying the amount given in keV by 1000 eV/1keV to cancel out the keV's. Now that your units are in eV you could convert eV into joules by using the conversion factor 1 eV =...

Leyna Dang 2H

The textbook uses "in phase" to describe the relationship between two waves. When both waves have the same frequencies and coincide with each in terms of their peaks and troughs, they're said to be in phase. "Out of phase", on the other hand, would mean that the troughs of one of...

Leyna Dang 2H

The relationship between a particle's wavelength and its energy is what establishes the quantization of energy levels. Imagine a particle that's in a box. Unlike classical mechanics which states that the energy of an object could be at any value, the particle could bounce off on any direction of the...

Leyna Dang 2H

I'm not sure if we are expected to derive the formulas on our own, but hopefully this helps: For part a, it helps to know that acids contain hydrogen and usually begin with an H. So, that gives you the first element of nitric acid. For the rest of the formula, I had to work backward. When you are us...

Leyna Dang 2H

Because it's not specified, I think using 3 or 4 sig figs would be fine. Having 4 sig figs would make your answer a bit more accurate, but I think using 3 would also be completely fine.

Leyna Dang 2H

You have the right idea! Positive powers indicate that you move the decimal point to the right, while negative powers indicate that you move the decimal point to the left. So keeping that in mind, giga- would be in factors of 1,000,000,000 while nano- would be .000000001.

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