CHEMISTRY COMMUNITY

Crystal Pan 2G

Dr. Lavelle tells us to write the chemical reaction with the (l) or (aq), as an easier way to identify if something is a pure liquid. Typically problems will include the chemical reaction, specifying which of the reactants and products are liquids or solids, and which are aqueous and gases.

Crystal Pan 2G

Kc is the equilibrium constant, so we use it to describe the forward reaction. When we are describing the reverse reaction(when products are making the reactants), we will use 1/Kc to describe the equilibrium constant. Another two to remember are when we multiply the moles of the entire reaction by ...

Crystal Pan 2G

We do not use solids or liquids because they do not have concentration. We will include all gases, and aqueous solutions as well because they have concentration (we can calculate their molarity)

Crystal Pan 2G

We do not exclude any gases. We will only exclude H2O when it is in liquid form. All liquids and solids are excluded because they do not have concentration. All gases and aqueous solutions will be included in the equilibrium constant/expression.

Crystal Pan 2G

From all the examples we have done so far, when there are two positive values, one of the x values will be larger than the initial concentration we need to subtract x from. Since it's not possible to have a negative concentration, the one that is smaller than the initial concentration will be the an...

Crystal Pan 2G

Since we will probably be dealing with weak acids and bases this quarter, every acid and base that is not part of the strong acids and bases is a weak acid/base. So the strong acids are HCl, HClO4, HClO3, HNO3, HBr, HI, H2SO4. and the strong bases are the groups one and two metal oxides.

Crystal Pan 2G

The conjugate seesaw essentially says
- the stronger the acid, the weaker the conjugate base.
- the stronger the base, the weaker the conjugate acid.
- the weaker the acid, the stronger the conjugate base
- the weaker the base, the stronger the conjugate acid.

Crystal Pan 2G

The answer is C, because even during equilibrium, there are chemical reactions happening at a "molecular level." Equilibrium is achieved when the rate of the forward reaction equals the reverse reaction, therefore C is false.

Crystal Pan 2G

Depends on what the problem gives you. If it gives you units in bar/atm, it will most likely be Kp. If it gives you units in M or x moles in x L, it will probably be Kc.

Crystal Pan 2G

It's easier to use whole numbers because you will usually end up with a quadratic equation already, and it's easier to calculate when you have as many whole numbers as possible. Theoretically though, you could, as long as you don't mind the decimals.

Crystal Pan 2G

Yes, if the number is between 10^-3(or 10^-4 in some cases) and 10^3, they are not strongly favoring neither reactants or products.

Crystal Pan 2G

We should be using Kelvins

Crystal Pan 2G

K is the equilibrium constant and can be Kp or Kc. Kc is used for concentrations.

Crystal Pan 2G

F is very electronegative, so the bond between H and F are stronger than with the other H-halogen acids, which means its a weaker acid!

Crystal Pan 2G

They are basically the same thing. When we say we donate a proton, typically means donating an H+ which will form H3O+, so theyre essentially saying the same thing.

Crystal Pan 2G

ABCDE were just points in the data collection where S is the pH at 7 where the solution is at the stoichiometric point.

Crystal Pan 2G

The more oxygen atoms there are, the stronger the acid.

Crystal Pan 2G

The bond between HF is very strong because F is very electronegative. A strong acid dissociates/ionizes almost completely. It would be hard for the aqueous solution to dissociate HF, therefore it is not a strong acid.

Crystal Pan 2G

I also had this problem with today's lecture. I took a break and refreshed it 40 minutes later and it was fine again. It might be due to the amount of people on CCLE since finals are coming up.

Crystal Pan 2G

In terms of looking at salts, you can tell which salts will behave as acids or bases. For example, NH4+ Cl- + H2O -> NH3 + H3O+ Cl-, chlorine does not affect the pH which means it has no effect as an acid or base. However, H3O+ concentration increases, which lowers the pH. You will need to see whic...

Crystal Pan 2G

CO2 and H20 mix to make carbonic acid which is H2CO3. H2CO3 can give off protons and become HCO3-, another common acid (bicarbonate).

Crystal Pan 2G

25 degrees is considered the standard, much like we consider room temperature.

Crystal Pan 2G

Na2SO42- would be the neutral salt that occurs when the strong acid and strong base are combined into one solution. The result of the combination of a strong acid and strong base would be the salt and H20 at the stoichiometric point where the pH is neutral

Crystal Pan 2G

In the textbook problems that Dr. Lavelle has assigned, specifically 9C.9, it asks us to determine the coordination number of the metal ion in the following complexes. For c and d, it gives [PtCl2(en)2]^2+ and [Cr(edta)]^-. Without knowing the structure and formula of ethylenediamine and EDTA, how w...

Crystal Pan 2G

You see how many bonds are formed with the Transition metal, by counting the number of atoms/molecules inside the square brackets.

Crystal Pan 2G

The longer the bond length, the weaker the bond, which means it is more easily dissociated/ionized. In lecture, Dr. Lavelle said that strong acids are almost completely ionized/dissociate in solution, therefore the longer the bond, the stronger the acid. (In most cases)

Crystal Pan 2G

The coordination number is the number of ligands attached to the central TM atom, which is essentially the stuff inside the square brackets.

Crystal Pan 2G

A strong acid(or even base) is almost completely ionized/dissociated in solution. The longer the bond, the more easily the acid dissociates, which is why HBr would be a stronger acid than HCl

Crystal Pan 2G

coordination number is the number of ligands attached to the transition metal, essentially the atoms inside the square brackets.

Crystal Pan 2G

Hemoglobin is in blood, and myoglobin is in tissue ie. muscles etc. essentially myoglobin gets oxygen from hemoglobin, and hemoglobin gets oxygen when it passes through our lungs when we breathe in the oxygen, the local partial pressure of oxygen is the highest in the lungs which is why hemoglobin b...

Crystal Pan 2G

Yes, bent and angular are both terms used for that shape.

Crystal Pan 2G

The hw is due on Sunday at 23.59!

Crystal Pan 2G

Tetrahedral should be correct, maybe check your spelling!

Crystal Pan 2G

It is sp^2 because there are three regions of electron density. The double bond with the other N, the lone pair, and the single bond with C. The double bond still counts as 1 region of electron density, so there are 3 regions which means it is sp^2.

Crystal Pan 2G

The dipole moments do not cancel out in NO2 similarly to SO2, but unlike CO2 because CO2 has a linear shape. NO2 and SO2 both have lone pairs, which due to electron repulsion cause the shape to be bent/angular, therefore the dipole vectors do not completely cancel out and you will have a polar molec...

Crystal Pan 2G

We should know the approximate angle, ie. greater than, less than 109.5, etc.

Crystal Pan 2G

The most stable lewis structure is the structure with the lowest formal charge. The more electronegative atoms would be more likely to hold the negative formal charge in the molecule.

Crystal Pan 2G

You would look at the electronegativity of the atoms. The most electronegative would be the more negative pole of the dipole moment.

Crystal Pan 2G

This kind of shape can be called angular or bent.

Crystal Pan 2G

Bond angles will depend on what molecule you are examining.

Crystal Pan 2G

You would draw the dipole moments on the lewis structure(by determining en) and then using vector addition, you could see which of the dipole moments cancel.

Crystal Pan 2G

Hydrocarbons are typically nonpolar, and molecules that have cancelling dipole moments are also nonpolar. It would be much more efficient to know how to draw the lewis structures and the dipole moments to know which cancel out.

Crystal Pan 2G

Lone pairs count as e- density regions as well.

Crystal Pan 2G

calculate the number of electrons, then find the atom with lowest ionization energy to put in the center, then find the number of lone pairs on the central atom and how many bonds the central atom forms, and then you draw the structure out with as much symmetry as possible. Then you can calculate th...

Crystal Pan 2G

The electronegativity of H is 2.2, F is 4.0(the most electronegative element), and C is 2.6. The EN difference between C and H is only 0.4 while the EN difference between C and F is 1.4. So CH4 could even be classified as a nonpolar covalent bond, while CF4 would display more ionic character.

Crystal Pan 2G

These are both intermolecular forces, but LDF and dipole-dipole are different. LDF could be used interchangably with induced dipole-induced dipole/van der waals forces/dispersion.

Crystal Pan 2G

Radicals have an unpaired electron, you can usually tell when the total number of valence electrons you calculate out before you draw the lewis structure are odd.

Crystal Pan 2G

It is of course best for the whole structure to have a formal charge of 0, but if that doesn't happen, i think the second most stable form is when the central atom has a formal charge of 0.

Crystal Pan 2G

The equation is the most straightforward way to find the formal charge and find the most stable lewis structure.

Crystal Pan 2G

n gives the energy level, and every orbital can hold up to two electrons. l=0 would correspond to s sublevel, l=1 would be p, l=2 would be d, and l=3 would be f, etc. for instance, n=5 l=2 would be 5d based on the definition we gave for n and l.

Crystal Pan 2G

We will need to know the trends, but it is not expected of us to memorize the specific electronegativity of each element.

Crystal Pan 2G

Yes, the first three quantum numbers can be the same, but the fourth must be different as each electron on that orbital would have a different spin.

Crystal Pan 2G

In the example Dr. Lavelle gave during lecture, the lone pair donor(lewis base) was NH3 and it was on the N atom, and the lone pair acceptor(lewis acid) is B from BF3.

Crystal Pan 2G

Lucy's analogy of people standing around the fire pit is a good example! Since s-orbitals are closer to the nucleus, they are more effective at shielding.

Crystal Pan 2G

Sunday at 11.59 pm or 23.59.

Crystal Pan 2G

We don't have to draw them to be longer vs shorter, but we should know double bonds are shorter and single bonds are longer.

Crystal Pan 2G

Honestly, going to UA sessions and office hours is super helpful. Going through each of Dr. Lavelle's lectures and processing the information, and then APPLYING the actual stuff we learned is also important. Doing all the homework problems in the outlines. Going to as many UA sessions as possible re...

Crystal Pan 2G

Yes, during lecture 12(10/30), Dr. Lavelle used the example of Potassium Chloride to show the lewis structure of an ionic compound.

Crystal Pan 2G

It's probably better to draw the lone pairs as pairs of dots, and to leave the lines to denote bonds.

Crystal Pan 2G

Dr. Lavelle has said that he would prefer for us to use the longer notation because it will tell us more about the configuration ie. which orbital the electron is occupying rather than writing 2p3.

Crystal Pan 2G

A polar covalent bond occurs when electrons are shared unequally, so if the difference in electronegativity is greater than or equal to 0.5, the bond is polar. A nonpolar covalent bond occurs when the atoms bonded together are of relatively similar electronegativies.

Crystal Pan 2G

Dr. Lavelle multiplied the number of oxygen valence electrons by 4 because there are 4 oxygen atoms in sulfate. In ammonium, there are 4 hydrogen atoms bonded to a nitrogen atom, therefore Dr. Lavelle multiplied the hydrogen valence electrons by 4.

Crystal Pan 2G

Dr. Lavelle wants us to use $En=\frac{-hR}{n^{2}}$ precisely because it is easy to mix up the n1 and n2. In the equation he gives us, it is E=nfinal- ninitial.

Crystal Pan 2G

Yes, we should know the relative regions and order for the test, because that will not be given to us.

Crystal Pan 2G

Dr. Lavelle has said during lecture that we will mostly be dealing with UV, visible, and infrared regions, so that would be Lyman, Balmer, and Paschen series. It might also be good to know that n=4 is the Brackett series

Crystal Pan 2G

For 1B.15 part b, you use the E=h\nu which is E=(6.626x10^{-34}J.s)(2.50x10^{16}s^{-1}) = 1.66x10^{-17}J , and since no electrons are emitted until frequency reaches 2.50x10^{16}s^{-1} , we can assume that is the work function. For part c, you use E(photon)= work function + E...

Crystal Pan 2G

remember $\Delta E$ is Efinal - Einitial, so n2 is initial energy level and n1 is final energy level.

Crystal Pan 2G

E= hv

h= planck's constant $6.626*10^{-34}J.s$

v(nu)= frequency (Hz or $s^{-1}$ )

Crystal Pan 2G

Dr. Lavelle just sent an email out regarding the necessary equipment.

Crystal Pan 2G

\frac{5.00 mg Na}{1}\cdot \frac{1 g}{1000 mg}\cdot \frac{1 mol Na}{22.99g Na}\cdot \frac{6.022*10^{23}atoms}{1 mol Na}\cdot \frac{3.37*10^{-19}J}{1}= 44.1 J 1. you take 5.00 mg and get grams of Na 2. divide by the molar mass of Na (22.99) 3. multiply by avogadro's number to get amount of Na atoms i...

Crystal Pan 2G

the Paschen series is in the infrared region.

Crystal Pan 2G

1 Hz= s^-1, so (m/s)/s^-1, so m/s x s, which cancels out s to get m for wavelength.

Crystal Pan 2G

Energy(photon) must be greater or equal to work function in order for an electron to be emitted. if light only had wave properties, then increasing intensity should eject electrons(in wave model, intensity would be amplitude), but we need to consider light as photons(packets) of energy. So frequency...

Crystal Pan 2G

there are four sigfigs. the leading zeroes don't count as significant figures.

Crystal Pan 2G

In excess basically means that there is more than enough of this element to react, and that the other reactant is the limiting reactant.

Crystal Pan 2G

The moles at the bottom are describing the stoichiometric coefficients. As you can see in the reactants, there are 4 mol of H as 2mol of H20 = 2mol H2 which is 4 mol of H. And then at the right hand side, there are 2 mol of NaOH and H2, which means that there are 2 mol of H in the NaOH and 2 mol H i...

Crystal Pan 2G

I started by balancing the equations which I see you already did. Then you take 2.50 t and multiply by 1000 kg/1t and 1000 g/1kg to get the mass in grams. Next you multiply by 1 mol NaBr/102.9 g NaBr (so divide by the molar mass of NaBr to get the moles of NaBr) and then you multiply 1 mol Fe3Br8/8 ...

Crystal Pan 2G

Nitrogen gas is a diatomic element, along with 6 other elements that are classified as Halogens.

Search found 78 matches