CHEMISTRY COMMUNITY

Jessica Katz

if the equation is NH4HS(s) goes to NH3(g) + H2S(g) and the Kc = 1.6*10^-4, why does adding argon gas to the equation result in no change. If a gas is not present in the reaction to begin with and then added, does it have no impact on the reaction? I thought that was only for solids and liquids.

Jessica Katz

yeah I would think on the midterm we would have to be given the ka/kb values cause we were not asked to memorize any values. The only time we wouldn't be given it is if the question is asking us to find it but then we would be given all the necessary information in the question to create an ice tabl...

Jessica Katz

I think work is only involved in the idea that the system will have to do work on the surrounding atmosphere for something when pressure is held constant and the volume of a gas must increase in a piston. Other than that, we haven't touched on it much and should not be seen on the midterm.

Jessica Katz

I assume you will still have your disucssion section cause that would be unfair for other classes during the week to hold review/discussion sections and for yours not to hold it. Also, since it is still before the time of the actual midterm it should be fine.

Jessica Katz

the temperature increase will affect the reaction and K value depending on whether the reaction is exothermic or endothermic. If it is exothermic, heat is a product, meaning it is released, and so if you add heat to the reaction, the reactants will be favored, decreasing the value of k. But, if the ...

Jessica Katz

When given enthalpy values, that is kJ/mol so if it isn't given but talking about something like standard enthalpy of formation, assume it is kJ/mol

Jessica Katz

I was wondering if someone could explain why a lower pka means that an acid is stronger and why a lower pkb means that a base is stronger? Also, do higher Ka and Kb values correspond to stronger acids and bases or weaker acids and bases? The lower pKa means a stronger acid because the Ka is higher ...

Jessica Katz

Whether they are lewis acids and bases or bronsted they act in the same way, its all dependent on how you look at whether a species is donating an electron or receiving a proton, but I think that it would work to just look at all of them as bronsted acids and bases especially since we are looking at...

Jessica Katz

there is no temperature change until the phase change occurs because until the actual phase change is taking place, the heat needed in the system is breaking the bonds in order to have that phase change from something like solid to liquid. Then, once the change happens, the temperature will increase.

Jessica Katz

we were going up the chart for most of the discussion which represented vaporization. The enthalpy for vaporization is very high which means that heat will be released and because in the case of your hand being near water, your hand will be the surroundings, so the released heat will make contact wi...

Jessica Katz

l just is a lowercase L so it stands for a species in the liquid state. so this is normally seen with water or something like mercury which is liquid at room temperautre.

Jessica Katz

This might be because K will not change from a pressure increase, only an increase or decrease in volume. These typically go hand in hand but maybe the question wanted you to only think about the impact of pressure on the system.

Jessica Katz

Q is the relative concentrations at a given time, and k is only used when at equilibrium. so they are used in comparison to determine if more products or more reactants are going to be made in order for the Q to equal K.

Jessica Katz

That method should work and is a good way to simplify the problem before starting to solve, you just have to make sure that you are taking the square root of the other side of the equation as well. Also, for the other problem where that strategy didn't work, did the hint they gave you on sapling cle...

Jessica Katz

Pressure is the overall pressure on a chemical reaction of gases, like in a vessel, and this is typically given to you in a problem, or converted from concentration. Partial pressure is the pressure of one particular species like oxygen or nitrogen within a reaction. All of these partial pressures a...

Jessica Katz

The super acids and bases come into play when they basically break the traditional pH scale, so if the pH is lower than 0 or higher than 14.

Jessica Katz

I believe that we would have to be given the delta H for a certain equation in order to properly determine whether the reaction will be exothermic or endothermic and then in relation to that, how the temperature will affect the reaction.

Jessica Katz

I don't think so but if you just put it under any category for chemical equilibrium that should be fine cause we are using acids and bases to find k values so it would make sense to place it under that section. Also someone can correct me if I'm wrong but if you placed your question under the acid a...

Jessica Katz

I believe that if you have all the necessary information given either one can be used in the equation if all are converted from molar concentrations to pressure or vice versa. But, I do think that if all of the species in the equation are aqueous, you should be using Kc rather than Kp and when its a...

Jessica Katz

It will change the overall equation because it will change the balancing and possibly the stoichiometric coefficients but if only the concentration is changed, and the solid was already in the equation, this will not change the K value. It can change the value of the product, but the ratio will rema...

Jessica Katz

I believe that you will end up with two different values for the kp and the kc its just a matter of what numbers you are plugging into the k expression. When it is kp, all of the values will be converted to the partial pressure and for kc, the values need to be in terms of concentration. It will res...

Jessica Katz

for the ice boxes, when looking at the forward reaction, the changes in the reactants will be minus x and the change in products will be plus x. This is easier to determine as well when comparing q vs k and if k is greater than q, then the forward reaction will be favored, again meaning that the rea...

Jessica Katz

Can someone briefly explain the relationship between Q and K. Like what it means when one is bigger than the other and also what the difference between them is. Thanks.

Jessica Katz

What does it mean by a pure substance? I know when dealing with equilibrium it is referring to the solids and liquids but what does it mean if a substance is pure?

Jessica Katz

if the pKa is higher than the pH, that means that the pH is lower and therefore more acidic and will allow the acid to remain neutral because the acid will remain protonated as HA (it will not give off the proton and leave the acid with an A-) . If the pH is larger than the pKa the solution will be ...

Jessica Katz

I believe that Na2SO4 is neutral because it is a salt that comes from a strong base and a strong acid. This will create a ph of 7 when dissolved in a solution and the solution will remain neutral.

Jessica Katz

The CO2 and the H20 react to form H2CO3. H2CO3 is what will remain in the solution which is an acid, making the overall solution acidic. This is how things like soda are carbonated and how acid rain is created with the carbon dioxide and water in the atmosphere.

Jessica Katz

The two s and the 2 p are essentially combined to create a 2sp state so that there can be lone pair electrons in each of the four states, rather than having an entirely filled s orbital and three lone pairs in the p orbital. The four lone pairs allows for the sharing of electrons by the central atom...

Jessica Katz

The pH describes the the acidity of the solution based on the concentration of H3O+ ions in the solution. The pkA value is the amount of the acid that can dissociate when it is not a strong acid. It allows you to determine the strength of an acid and determine how much the acid dissolves, so the low...

Jessica Katz

the concentration of the hydronium ion and the hydroxide ion are equivalent when the pH is 7. The range that you have listed is showing the entire range of pH that a solution could possibly have, that is not when it is equal. The equal point is only when ph is 7 because then both concentrations are ...

Jessica Katz

pH is definitely a good way to determine the strength of an acid. The lower the pH, the stronger the acid, because the concentration of H+ ions are higher, because they dissociate more in water. These things are all connected and all help with determining the strength when comparing two or more acids.

Jessica Katz

Neutral ligands are ions or compounds that have no charge. And sometimes even the coordination compound can be neutral and that information is useful when trying to determine the charge of the transition metal within the compound.

Jessica Katz

Those are the same exact things, just different names. Dr. Lavelle said he prefers using the term "induced dipole induced dipole" but they are all the same thing and present in all intermolecular forces.

Jessica Katz

I believe that we need to know all of the shapes in VSEPR and be able to determine the shape based on the number of bonds and lone pairs. I don't think we will be getting a chart like we do for the homework on sapling sometimes.

Jessica Katz

I don't think we need to know specifically the shape that each TM wants, I just think we need to identify the oxidation number from the charges of the other species in the coordination compound, and calculate the coordination number from the number of bonds formed. When you find the coordination num...

Jessica Katz

Yup! that's the only way we can determine the bond angle. And in some cases, we are only required to estimate by saying that the bond angle is going to be less than 109.5 degrees, when otherwise we would have to use the internet to find the exact degree.

Jessica Katz

The electron rich species will be the species with lone pairs or the species that have the ability to donate both of the electrons to the bond that is being formed.

Jessica Katz

For molecules like the ones you mentioned, the question could never be overall shape. So, if asked on an exam, it would be referring to one or both of the central atoms and then you would just determine the shape of one atom, like a central carbon fo example.

Jessica Katz

A bent shape molecule has two atoms attached to the central atom and then the central atom has one or two lone pairs. For example, H2O would be bent because oxygen is the central atom and has two lone pairs and two hydrogens attached.

Jessica Katz

molarity is a way to determine concentration of a solution so it cannot be used for solids and gas. It would normally be liquids in aqueous states because in molarity we are determining the concentration through volume rather than mass.

Jessica Katz

Yes to your first question, there is a pi bond in ethene as well as three sigma bonds so we can't fill the 2sp2 orbital with four electrons and that final electron has to go to the 2p orbital that is unhybridized. The hybridization doesn't actually change, the hybridization should always be sp2 for ...

Jessica Katz

it can be found on other, it depends on which position you pick as the lone pair. This will affect the number of 90 degree angles that the shape will have overall, with the axial having 3 90 degree angles and the equatorial having 2 90 degree angles. But, in terms of deciding the shape, the seesaw m...

Jessica Katz

Some dipole moments are almost irrelevant because of the minimum difference in electronegativity between the atoms like two nonmetals, N and O. And, for two of the same elements like when N2 and N2 interact, there is only going to be a dipole moment for a brief period which is why we call it induced...

Jessica Katz

They are directly related because if a molecule has a high boiling point that means that the intermolecular forces are stronger keeping the molecules tightly held and harder to separate to then change into a gaseous state. That same molecule is going to take more energy to melt it as well, resulting...

Jessica Katz

i think it is shown this way because k3p is an ionic bond rather than a covalent. And the normal lewis structures we are used to drawing are for covalent molecules where the electrons are shared between elements. in k3p they are transferred so no bonds are formed and no lewis structure is drawn.

Jessica Katz

It has a higher melting point because iodine has a much higher amount of electrons than fluorine, so it will occupy a larger volume and create a larger surface area. The larger surface area creates a stronger force between two CHI3 molecules versus two CHF3 molecules. The increase in atomic size and...

Jessica Katz

a subshell for example is 3d or 2p while the orbitals are the individual parts that make up the subshell where electrons can occupy. for example the 2p subshell has 3 orbitals and can hold six electrons in total. I try to remember that orbitals are held within subshells.

Jessica Katz

the ion interactions are the strongest but i believe you are correct when you assume that it isn't included in that chart as the highest because it is not an intermolecular force whereas hydrogen bonding is. Ion to ion is between to elements rather than two molecules like H-bonds. But, overall when ...

Jessica Katz

They are the elements that occupy enough orbitals to accommodate a larger amount of electrons around the central atom like Xe or P.

Jessica Katz

I think since the cation has a positive charge, it is able to distort the electrons and shape of the anion, so it is not highly polarizable, but has polarizing power. The anion however, depending on how easily distorted the atom is, like with the increase in the amount of electrons and increase in s...

Jessica Katz

I think it would be very helpful to know the resonance structures of the molecules and how to draw them, because even though we won't be asked to draw them on the midterm, we most likely will need to know how to identify them, and understand which drawing is right and which is wrong for multiple cho...

Jessica Katz

Just like h2O, Co2 has two dipole moments, but because of the linear shape of co2, those dipole moments will cancel each other out. The question might want you to identify if there is ever a dipole moment in the molecule, so then even though it does cancel, co2 would have dipole moments. But, if the...

Jessica Katz

will the topic of molecular shapes like trigonal planar and tetrahedral be on the midterm 2?

Jessica Katz

I believe this relates to the formal charge. When the formal charges are a majority of zero, this is the most stable and appropriate structure for that molecule. In this case, N has to have four bonds to bond with the four hydrogens.

Jessica Katz

This is just for radicals. The other octet exceptions like with phosphorus with an expanded octect, or Boron with only 6 valence electrons are stable and are not reactive like radicals are. These octet exceptions are appropriate for those molecules and don't cause the "damage" that radical...

Jessica Katz

The radicals come from highly reactive and unstable molecules like CH3 where carbon has 7 valence electrons or OH where oxygen has an uneven number of valence electrons as well. The radicals can damage DNA when they react with it and food supplements that we ingest can also react with radicals but t...

Jessica Katz

I think sulfur can have 10 valence electrons which means it can bind to 5 bonds to other elements. It shouldn't have an uneven amount, because that would make the molecule reactive and unstable.

Jessica Katz

a broad overview would be that there are certain radical molecules that have an uneven amount of valence electrons like 7 in CH3. Then you have elements like phosphorus and sulfur that can have 10 electrons, called an expanded octet. And then in group 13, you have elements like Boron that can have 6...

Jessica Katz

in really simple terms, the ground state is the most stable and has the lowest energy. It is the electron configuration we are used to writing, where configuration of the electrons match up with the configuration of the periodic table.

Jessica Katz

do you know where to go in order to access the grades once they are released?

Jessica Katz

When an electron is not in the ground state, the electron configuration will change. This can be seen in the position of the final electron. So if the element for example is nitrogen and the last part written for the electron configuration is not the normal, ground state, 2p^3, then you know that el...

Jessica Katz

it is always n final minus n initial, but the final isn't always necessarily the lower energy state. you will typically see in the problem that it tells you where it started, so that would be your n initial, or what state the electron ended up, n final. If the problem says an electron went from the ...

Jessica Katz

He has not actually gone through the steps for calculating effective nuclear charge in his lectures. But to solve for the ENC you take the number of electrons in the element and subtract it by the number of shielding electrons. The number should get bigger as you move from left to right on the perio...

Jessica Katz

since your solution for problem above, when it was asking about calculating the work function, is in the units joules per photon, divide the total energy (just joules) by that value. This will allow you to cancel out joules and be left with the number of photons. The number of photons is then equal ...

Jessica Katz

the problem should be solved normally but you should convert 2.45 GHz to just Hz by making it 2.45 * 10^9 1/s. What is the rest of the problem asking you to solve for? If it is wavelength then use the equation c=(wavelength)(frequency) because it has given you the frequency. And from there determine...

Jessica Katz

interpret Δx as the unit it gives you. In this case plug in the value it gives you into the equation as Δx, once you convert to meters.

Jessica Katz

Should we be able to answer this question already? If so does anyone know the steps to solve it? Any help would be great. Thanks! What is the minimum uncertainty in an electron's velocity (Δvmin) if the position is known within 15 Å. What is the minimum uncertainty in a helium atom's velocity (Δvmin...

Jessica Katz

To add on to my previous comment, this equation can apply to more things besides light. It is anything with a mass and velocity.

Jessica Katz

the De Broglie equation is actually wavelength=h/mv or wavelength=h/p(momentum). This is a different equation from the wavelength equation of c=hv. This equation is used when there is a velocity and/or mass value given in the problem and you solve for the wavelength. You use the De Broglie equation ...

Jessica Katz

Use the rynberg equation to calculate the frequency for when n (final) = 4 and n(initial) =5 and then convert this into wavelength. Then use the same equation but make the n(final) = 1 because that is the biggest jump that can be made and again convert this to wavelength. Then for the blanks put the...

Jessica Katz

The enthalpy of fusion is the change in enthalpy (or the providing of energy) the substance requires to change from the solid state to liquid state. So, that question was asking about the enthalpy of fusion for ice, the solid state, to change into water, the liquid state. For this problem, you can u...

Jessica Katz

Does anyone know how to approach this problem? I'm having difficulty figuring out how to set up the problems. The energy levels in my question are n=2 and n=1 with the wavelength 656.3 nm.

Jessica Katz

for the equation units, do we always need to convert the mass to kg?

Jessica Katz

I believe that when an electron starts at the fourth energy level, it has been excited to that level and is now going back down. Also, if the electron moves from n=4 to n=2 for example, that electron will eventually go back to the ground state.

Jessica Katz

convert the unit KeV to eV by multiplying it by 1000. Then use the conversion of 1.602 x 10^-19 joules to 1 eV to convert to joules. This will allow you to continue the problem in joules which is the more commonly used unit.

Jessica Katz

How can you determine the number of spectral lines with only being given the information that the energy level of the H atom electron is at shell n=5?

Jessica Katz

the Bohr frequency condition is the idea that you can manipulate the formula of delta E=hv into v=delta E/h. This can be used for other elements besides H so we will be using this throughout the class I assume. The thing that only applies to H is the rynberg equation that involves the jump between n...

Jessica Katz

He didn't really go into detail about the atomic spectra at all in today's lecture. I think more information on it will be given in future lectures. There are also modules on his website that go into detail that are solely on the atomic spectra if you want more info. But overall, the atomic spectra ...

Jessica Katz

I am the roommate and I know that is true. Some problems require the use of Kelvin and others use Celsius. You typically won't see Fahrenheit, but the formulas used for certain problems will determine whether you should keep your answer in celsius, if that's what's given, or convert to Kelvin when p...

Jessica Katz

I'm struggling to answer this question because it wasn't mentioned in the lecture module attached. Does anyone know how to go about solving these? Light hits a sodium metal surface and the velocity of the ejected electron is 6.61 x 105 m.s-1. The work function for sodium is 150.6 kJ.mol-1. Answer th...

Jessica Katz

I think for c, once you find your answer to letter b, you can use that to find the grams of CO2 and then multiply that by 75% because it is asking for the 75% yield, rather than 100%. Not sure how to answer D either though sorry. Does anyone else know?

Jessica Katz

bond length can be done experimentally, but it can be estimated by doing a lewis structure of the molecule and see whether it is a triple, double, or single bond because that will tell you its relative length compared to the other bonds in the molecule. Triple bond is the shortest while single bond ...

Jessica Katz

I think this is the simplest way to look at the dilution problems and will work for most of them, but I assume there will be more complex answers later in the class and he will explain how to find those. But for now, I think this works as the only formula.

Jessica Katz

The molar masses are defined constants so they do not affect the significant figures that need to be included in your answer. I think it's because every periodic table could have the molar masses rounded to a different number and because they are the same in every single problem so they don't influe...

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