CHEMISTRY COMMUNITY

Olivia Monroy 1A

We have only briefly covered endo/exothermic (requiring + or releasing - heat) reactions but what Lavelle has stressed so far is that the equilibrium constant doesn't change unless temperature changes, so we'll learning how to deal with changes in temperature in a later outline.

Olivia Monroy 1A

Q=[P]/[R], K=[P]/[R] so if Q<K this has to mean there was an increase in reactant from equilibrium concentration, the reactant concentration has to be greater than the product concentration, meaning the forward reaction is favored as Lavelle said. K=1 when [P]=[R] so if [P] is greater than [R] it is...

Olivia Monroy 1A

Always better to memorize! That way when you come across something that is neither a strong acid or base you can figure it to be weak. Strong acids include HCl, HBr, HI... and strong bases are group 1/2 elements with oxide/hydroxide attached including LiOH, NaOH, KOH...

Olivia Monroy 1A

Agree with what's said above when adding reactant there's initially more reactant (which is literally explained by the adding of reactant) but with time it's observed to form more product, with both the reactant and product concentration higher after adding more reactant. *Equilibrium concentration ...

Olivia Monroy 1A

Bar and atm are what Lavelle has been using in this class but you could use other units like pascal or torr as long as all elements are in the same unit. Bar and atm are also very close at almost a 1 to 1 ratio when converting to one or the other.

Olivia Monroy 1A

Yes I believe it would mean a reverse reaction is taken place if you are given an initial value for the product of some reaction. When solving this problem and setting the reactants to 0 initially that would also signal a reverse reaction is taking place as there are initially just P going to go to R.

Olivia Monroy 1A

The process of finding Q and K is the same, if you calc the concentration ratio and find it doesn't equal K then you know it is the reaction quotient and is not yet at equilibrium (either a forward or reverse reaction will exist). You use Q when you are not at equilibrium and you are then able to de...

Olivia Monroy 1A

For forward or reverse reactions I believe you are just always subtracting from the reactants (subtracting x) and adding to the products (adding x). We're subtracting from whatever is being converted to product (reactant) and adding to whatever is the product.

Olivia Monroy 1A

The reaction quotient, Q, is a test for which direction a reaction is going, whether it is greater or less than K tells us if its a forward of reverse reaction at that point in time, if it were equal to K then Q would equal the equilibrium constant K. So Q does not tell us about stability but rather...

Olivia Monroy 1A

We're considering 1 bar to be equal to 1 atm from what Lavelle says and when calculating an equilibrium constant etc if all units are in bars there is no need to even make a conversion to atm because K has no unit.

Olivia Monroy 1A

When Q>K the system shifts left (the amount of products is greater (P/R) so to reach equilibrium it moves towards reactant) When Q<K the system shifts right (amount of reactant is greater than product so to reach eq moves toward products) When Q=K the neither are favored, Q is considered K (the equi...

Olivia Monroy 1A

De Broglie calculates the wavelength for molecules with a mass (e-, neutrons, protons) while E= hv is the energy per photon. When you find the wavelength of the particle you will see the speed has to be less than the speed of light.

Olivia Monroy 1A

I think you are right for the naming, the molecular formula is the same so the name is the same aside from cis- or trans- depending on if the Cl are next to or across from each other. The cis and trans will tell you where to put the Cl when drawing the lewis structure. And when looking up structures...

Olivia Monroy 1A

By default I think we assume is it J/photon as that is what the energy equation is telling us, energy of incoming photon, but it could be J/atom I guess in another case, it would be made clear.

Olivia Monroy 1A

The central atom As in the lewis structure for AsF3 has only four regions of e- density so the hybridization should be sp3, it must've been an error..I also think you are correct.

Olivia Monroy 1A

H2O is monodentate because in a molecule one atom can only bond to the TM once, so only one lone pair on the O atom can bond to a central atom. If you have two separate O atoms spaced out in the same molecule both can bond to an atom, which again is only one lone pair per atom.

Olivia Monroy 1A

Electron geometry describes the shape including the lone pairs, which we've learned to call the arrangement, while the molecular geometry looks at only the atoms whether or not there are lone pairs involved. The molecular geometry is what we use to state the shape but the electron geometry may influ...

Olivia Monroy 1A

A hydrogen bond is like a dipole dipole but more specific

Olivia Monroy 1A

Interactions between molecules: Ion-ion intermolecular interactions are an interaction between opposite charged ions. Ion-dipole is an ion with a nonionic molecule but nonionic molecules still have ionic behavior (dipole moment) so they can be an interaction dipole-dipole is the attraction of two di...

Olivia Monroy 1A

^HCl is completely ionized making it a strong acid whereas the CH3COOH does not loose all protons so it is not completely ionized, therefore a weak acid. Weak acids have a small % of molecules that actually give off protons because it's already in the more stable structure which is why you cannot as...

Olivia Monroy 1A

Outside of the coordination sphere (or the brackets if looking at the name) doesn't use the prefixes as the coord sphere does. To determine the charge you can look at the coordination compound as said above. Make sure to change the ending of the anion to -ide (coord compounds almost always have + ch...

Olivia Monroy 1A

ethylenediamine H2NCH2CH2NH2

Olivia Monroy 1A

Lavelle has said since we're just dealing with the first row of the transition metals we'll see at most 6, with the expanded octet and as we go further down the periodic table that will increase, but I'm also not sure how to find the exact bond number. I just know we're only focused on the first row...

Olivia Monroy 1A

The coordination number is the number of bonds on TM, we're dealing with at most 6 in 14a, and most commonly 4, tetrahedral or square planar shape or 6, octahedral geometry. Make sure to only look at bonds to the central atoms from the ligand, if a ligand bonds at more than one site it becomes biden...

Olivia Monroy 1A

Yes, they both describe bases just slightly different definitions. Bronsted base is describing a proton acceptor and Lewis base is a species that donates an e- pair, both describe the same specie. It's just looking at the base in terms of electron or proton behavior.

Olivia Monroy 1A

For sapling #10 the first would be between the F atoms because the electronegativity vector to the F is longer than to O so the net vector is between the F and second is between O and F with the net vector between them, the H vector is also pointing towards the carbon because C is more electronegati...

Olivia Monroy 1A

Whichever atom has a higher electronegativity has a higher negative pole. Use the periodic trends to figure out which atom has a negative pole in a molecule.

Olivia Monroy 1A

When drawing the lewis structure it might look like the dipole moments could cancel each other out if you drew it with the Cl on opposite sides, but the shape of the molecule is tetrahedral meaning the bond angles are not 90 degrees but are about 109.5, so CH2Cl2 is polar because the C-Cl bond has i...

Olivia Monroy 1A

A single bond has one sigma, double one sigma and one pi, triple one sigma two pi always. I also remember there can only be one sigma bond so the others are pi.

Olivia Monroy 1A

The hybridization of the orbitals is like an average, or a mix of the higher and lower orbital so it is in between the lower and higher meaning the energy gap between the hybridization orbital and the orbital above/below is smaller than that of the s and p in this case. I assume this is always the c...

Olivia Monroy 1A

Hi! When the d orbital becomes involved an expanded octet can be seen. If you think of the valence shell of an energy level with just an s and p orbital only 8 electrons can be in it but when the d orbital becomes involved more electrons can be held in these higher energy levels. Larger atoms contai...

Olivia Monroy 1A

Hi! You should use the VSEPR model to find the correct notation of the molecule. Certain notations make the shape clear. For example CH4 and CCl4 both have VSEPR formulas of AX4 so you know they have the same shape which is tetrahedral! Also simply looking at your lewis structure and the lone vs bon...

Olivia Monroy 1A

Yes, lowest energy means most stable which is always preferred. Either achieve a formal charge of 0, or closest to 0 as those are most stable, and make sure the charges combined equal the total charge.

Olivia Monroy 1A

A dipole moment can be instantaneous or permanent. In a molecule the difference in electronegativity results in a dipole moment, however in a non polar molecule the dipole moments cancel each other out, but London interactions occur among non polar (and all other) molecules meaning an instantaneous ...

Olivia Monroy 1A

Ya! also to add to the previous responses different atoms with the same electron configuration are isoelectric or atoms with the same number of electrons are isoelectric. So once you determine the anion had a number of electrons same as Ar you know the configuration is the same.

Olivia Monroy 1A

It's a bond between a Lewis acid and base. The base is the donor of an electron pair and the acid is lacking a pair, so the sharing comes from both electrons in the lone pair of the base. BF3 and NH3 is an example as the pair from the N bonds to the central B which is lacking a lone pair to make an ...

Olivia Monroy 1A

Bonds differ on the atoms yeah. Lavelle says we're not expected to get the exact measure and are unable to with the VSEPR model because it predicts distortions qualitatively not qaunt. Different electronegativities are present with different atoms so the angles vary.

Olivia Monroy 1A

Hi, yeah there could be resonance in that all three oxygen could have a single shared bond with the central Sulfur or for another structure a double bond could be drawn between the oxygen that doesn't have a hydrogen attached to it and the central sulfur, the other two oxygen have an octet due to th...

Olivia Monroy 1A

If there is uncertainty because there are resonance structures I usually check formal charge after drawing the Lewis structure, but yeah as said also drawing a symmetric structure is a good approach. If you have any uncertainty just use the FC equation to double check. The resonance structure with t...

Olivia Monroy 1A

The most significant resonance contributor has the negative formal charges on the most electronegative atoms, and the positive formal charges on the least electronegative atoms. The most stable resonance lewis structure contributes the most and more unstable the least.

Olivia Monroy 1A

I think it's good to use brackets to indicate the overall charge because otherwise it might be assumed the formal charges balance to be zero/there's no charge. I'm not entirely sure, but I'd include it when necessary to be clear. It's also indicating that you're drawing a lewis structure for an ion.

Olivia Monroy 1A

Expanded octets only apply to atoms in the n=3 or higher level as the d orbital can be taken into account. Nitrogen is in the second period so at most it can only have an octet. In this case there can only be one double bond with one oxygen.

Olivia Monroy 1A

There's a rough guideline to follow that he went through in the lecture. If electronegativity is greater than two then there's an ionic bond and less than 1.5 covalent. He said if it was somewhere in-between 1.5 and 2 you'd need to look further at the behavior of the molecule to see if its acting li...

Olivia Monroy 1A

inner core electrons are not focused on as much as the valence are what's being used for reactions/lewis structures. You can identify the inner core with the closest noble gas previous to the element you're looking at, and that gas is often used when writing the electron configuration out to make it...

Olivia Monroy 1A

Shielding and distance from the nucleus decide the energy of these electrons. s-electrons are closer to the nucleus, which blocks the p-electrons located further from the nucleus and so on.

Olivia Monroy 1A

Ya! A maximum of two electrons can be held in the valence level, making them exceptions to the otherwise applicable octet rule. And then going further there are the elements that can have an expanded octet/can hold more than 8 electrons.

Olivia Monroy 1A

Yes you can have the first three be the same the fourth being the spin will be different if the first three quantum numbers are the same. Two electrons that have the same first three quantum numbers are in the same orbital, but then will have different spins (up or down)

Olivia Monroy 1A

I'd say eventually memorizing would be smart just so you can quickly apply them to problems, but as people said some are given on the formula sheet. Eventually after using them so many times it should just stick!

Olivia Monroy 1A

I prefer using the equation with just h, as that's what Lavelle teaches, but the textbook uses the other just to symbolize h/2pi.. they're the same thing/interchangeable.

Olivia Monroy 1A

Aw that's a bummer he won't be making modules moving forward but there are so many hours to get extra help/practice.. he's probably noted how helpful they are and will make them for 14a in the future.

Olivia Monroy 1A

Agreed with not needing to known exact ranges, other than that for visible light as that's what Lavelle has told us, and then the order from longest to shortest wavelength. It should be clear from the answer calculated which em radiation you answer falls under.

Olivia Monroy 1A

Hi! I follows (n-1) describing the subshell the electron is in at a given energy level, n. The maximum value of l is always one under the energy level given. Once you find l you are able to find ml.

Olivia Monroy 1A

Ground state would be the lowest energy state, so filling the previous orbital to 2p3 rather than 2p2 3s1. N is the element for the excited state given.

Olivia Monroy 1A

Not sure where you went wrong but I came out with 6.17x10^14 Hz. I found the Energy at each principal quantum level then found the difference in energy which is equal to Energy per photon, and used E=hv as you suggested to find the frequency. Maybe double check that your energy difference is correct...

Olivia Monroy 1A

Up to you, but be careful when assigning values to either making sure n1 is less than n2.. also Lavelle used n1 and n2 during lecture.

Olivia Monroy 1A

As said above the blue light indicates visible light and just remember that visible light is the Balmer series so the e- will go down to n=2 as the final energy level.

Olivia Monroy 1A

Use what Lavelle's constant sheet gives us! He always uses 3x10^8 and 6.626x10^-34 for the constants you mentioned.

Olivia Monroy 1A

To put it simply divide 1 wave by 1,650,763.73 m to get 6.0578x10^-7 m per wavelength then with that you can find the energy per photon using E=hc/wavelength to get an answer of 3.281x10^-19 J, matching option D.

Olivia Monroy 1A

Light intensity is the number of photons hitting the surface, while frequency is the number of waves. Frequency determines if the energy is high enough to emit electrons in the photoelectric effect. If you have a high intensity, but the energy is not at or above the threshold then no electrons will ...

Olivia Monroy 1A

I would also imagine UV travels faster because it is a higher energy (shorter wavelength) than visible light.

Olivia Monroy 1A

If you increase the intensity of the light you are creating a greater number of photons, the energy per photon is not increasing. So increasing intensity when the energy per photon is not strong enough to eject an electron will not increase the energy per photon. Increasing the energy per photon to ...

Olivia Monroy 1A

Either should be acceptable but often converting the final answer of m to nm is best/makes the most sense. Just make sure if it asks specifically for nm you give the answer with that measure.

Olivia Monroy 1A

I have a TI-nspire cx.. it hadn't occurred to me we might not be able to use certain calculators! Have you heard anything about this calculator or just the rules if there are any for calculators during exams?

Olivia Monroy 1A

Ya you're right in not rounding during calculations to keep your work as precise as possible and then I learned in hs chem to round to three sigfigs after finding an answer.. I'm not sure if that's what you mean when you say rounding to the nearest sigfig but yes round afterward.

Olivia Monroy 1A

Yes, disregard it because it is in excess meaning the other is the limiting reactant. Since there is a limiting reactant you only use that reactant to find the theoretical yield on the product.

Olivia Monroy 1A

I would be interested! We should plan a couple a week to have an alternative if we can't make it to one.

Olivia Monroy 1A

Use the structures given in image for 2-butanone to be able to write out C4H8O and from there you can use the .25mL given and use the density given to find the amount of grams. Then use the molar mass (calculate with the C4H8O you found) and grams to find moles. Then because it is a 1 to 1 ratio wit...

Olivia Monroy 1A

d gives density! You use the density to find the grams of the reactant given .25ml (.81g/ml)= 0.2025g.

Search found 68 matches