CHEMISTRY COMMUNITY

Sophia Kalanski 1A

you just want to plug in the factors of how they are changing in the rate law equation. Since it is rate=k[A][B]^2, you can see that if A was halved it would be A/2 and that if B was tripled it would be [3B]^2 which would be 9B and therefore 9/2 would be by how much the rate increases

Sophia Kalanski 1A

yes! you would omit solids and liquids because their concentration basically stays the same

Sophia Kalanski 1A

an intermediate is a molecule produced in the middle of the reaction but is later consumed before the final products are created

Sophia Kalanski 1A

another thing to note that since deltaH is positive, it is endothermic and you know that the activation energy of the forward reaction will be greater than the activation energy of the reverse. You can then evaluate your units from there

Sophia Kalanski 1A

Here you would set up the equation Kcat/Kuncat=Ae^-Ea/RT of the catalyzed a=/Ae^-Ea/RT of the uncatalyzed and then plug in the values to get the answer

Sophia Kalanski 1A

kinetic stability refers to the energy barrier. There is more stability if the energy barrier is really large because then even if the reaction is favorable, it will be extremely small and therefore will not occur for a very long time. This can be seen with diamonds turning into graphite

Sophia Kalanski 1A

[A]o/2K =t(1/2) is the equation and this shows that the half life of a zero order reaction is dependent on the initial concentration of A

Sophia Kalanski 1A

order refers to the number of reactants that can form the product. first order is one reactant and so on

Sophia Kalanski 1A

it is possible but because of that energy barrier it will take a very long time for that process to happen. You would need a catalyst to speed of the process but it is spontaneous

Sophia Kalanski 1A

yes! It can only change when the temperature changes

Sophia Kalanski 1A

The one with the highest reduction potential is likely to be more easily reduced and that makes it the best oxidizing agent

Sophia Kalanski 1A

How would i balance this equation given that its a basic solution?

N2H4(g)+ClO−3(aq)⟶NO(g)+Cl−(aq)

Sophia Kalanski 1A

also make sure to convert to kj because F is given in terms of joules but the answer wants it in Kj

Sophia Kalanski 1A

I'm so confused on why I keep getting this wrong. I found that E for the anode is 2(1.498) and the cathode is 3(0.76) and it would end up with Ecell=.716 . Is this correct?

Sophia Kalanski 1A

For a particular redox reaction, BrO− is oxidized to BrO−3 and Cu2+ is reduced to Cu+ . Complete and balance the equation for this reaction in basic solution. The phases are optional. So I am really confused on how to balance the acidity and add in H20 and OH- in the equations... can someone please ...

Sophia Kalanski 1A

An electrode is like a more general term that includes both the anode and cathode. The cathode is the positive charged side and anode is the negative charged side.

Sophia Kalanski 1A

it is not a state function because it depends on the path taken. Usually a state function will have delta in its equation

Sophia Kalanski 1A

because the reduction potential depends on the amount of electrons lost or gained rather than the moles of the reaction, it wouldn't change.

Sophia Kalanski 1A

a reaction is spontaneous when it can occur by itself. It can be either exo or endothermic and all depends on if deltaG is negative

Sophia Kalanski 1A

raise it to the power of e!

Sophia Kalanski 1A

try converting it into kelvin or maybe what happened is you didn't convert between j and kj

Sophia Kalanski 1A

you would have to break apart each change in entropy into sections. From there you can add them together and get the answer.

Sophia Kalanski 1A

you would use the hess method. reverse the sign so that it goes from c to d and make sure your units are aligned but yes it is very similar to the enthaply questions we learned for the last midterm

Sophia Kalanski 1A

Just be sure you take into account the moles that are given in the problem! At first I assumed n was 1 and that Cvm was the same and kept getting an incorrect number and then it was correct when I account for n

Sophia Kalanski 1A

Hi! So in this case you would use delta s=q/t when the temp and volume are constant, delta s = Cvln(t2/t1) when the temperature is changing and the volume is constant (or just not measured) and delta s=nRln(v2/v1) when there is a change in volume but the temperature is constant

Sophia Kalanski 1A

extensive properties depend on the amount of substance/matter present or being measured while intensive properties do not

Sophia Kalanski 1A

isn't the equation already balanced though? What kind of stoichiometry do you mean? Sorry I am just kind of confused how I can convert it from solid to gas in this equation

Sophia Kalanski 1A

you can only assume w=0 when both the volume and pressure are constant. In this case you would need to use the ideal gas law to find the change in volume and then calculate w=-pdeltav

Sophia Kalanski 1A

Yes so this just talks about the way the molecules are arranged. If it is linear, then the degree bond angles are 180 degrees and there is no polarity. It's like a review from chem14A

Sophia Kalanski 1A

Hi! I'm having trouble on this question. Honestly I have no clue where to start. I know how to find q but the second experiment is throwing me off a bit

Sophia Kalanski 1A

Hi! I've tried to solve this question and still continue to get the wrong answer... someone pls help :)!! Ok so I need to Calculate the value of work, w, for the system if 39.2 g NaN3 reacts completely at 1.00 atm and 22 ∘ C. and I am given the equation 2NaN3(s)⟶2Na(s)+3N2(g) So from here I know tha...

Sophia Kalanski 1A

i think you just memorize them. They have to be pure elements.

Sophia Kalanski 1A

this is because it is releasing heat not only as it is slowly becoming cooler but also in its phase change. It releases a lot of heat as it goes from gas to liquid

Sophia Kalanski 1A

well we assume that the equation that was given is with 1 moles of s8 and when you are given more than that, like 1.21 moles, you would multiply the enthalpy by the amount of moles that are given

Sophia Kalanski 1A

well here you can tell combustion is involved because the products are CO2 and H2O and the reactant has O2

Sophia Kalanski 1A

a phase change is just when a substance, like water, changes its state of matter and we try to find how much heat must be put in or taken out to allow that chnage to occur.

Sophia Kalanski 1A

i don't think there is a specific cut off but we need to know and assume that the second reaction will be way weaker and the K value will be extremely small

Sophia Kalanski 1A

generally, we are given the initial concentration of one of the reactants which means that initially the products start with 0. From there, you know that in order for both products and reactants to exist, the reaction must happen and therefore some of the concentration of the reactants will have to ...

Sophia Kalanski 1A

in this case, I would not approximate the x value because you'll end up with a weird solution. keep x^2/M-x. M is what the initial concentration is and that is what we are trying to find. We can find x by using the pH and from there you can plug in X to find M.

Sophia Kalanski 1A

depends on what you are given. They should generally be in that but for example, if it given in bar, then use that.

Sophia Kalanski 1A

here you are comparing the concentration of HA and A-. A- is the charged form and HA is the neutral form. In this case, you want to make a ratio of how much of these products exist... and knowing that the solution will try to go to of a pH of 7 to stabilize and in that case they will try to take out...

Sophia Kalanski 1A

since the K value is not less than 10^-4, the approximation is not accurate enough so you would have to use the K formula and go the long way of using the quadratic formula to find a more accurate answer. It should be less than 9%

Sophia Kalanski 1A

hello! I think this is why we have the 5% rule in place so that if it is over the 5% mark, it is better to use the quadratic equation because the approximation isn't as accurate

Sophia Kalanski 1A

Hi! So K will change because the change in temperature has an affect on the equilibrium constant. If the delta H is positive (endothermic reaction) and heat is added, it will cause K to increase because it will favor products being made since an increase in heat will favor the forward reaction. If d...

Sophia Kalanski 1A

we don't count Na+ as something that changes the pH because it comes from a strong base and since it fully dissociates, it will not affect the pH. Anything that dissociates from a weak base/acid will always affect the pH so we only put that into the ICE table

Sophia Kalanski 1A

when Q>K, there are more products than there should be and therefore the reaction will shift towards the reactants so that the Q can balance out to equal K. When Q<K, there are more reactants than there should be which is why the quotient is not equal to K so the reaction will shift towards and favo...

Sophia Kalanski 1A

yes! Then make sure you set up the equation in a quadratic equation where you can then use the quadratic formula

Sophia Kalanski 1A

Hi! So Q is the reaction quotient and it can be used at any time of the reaction, while K is used when the reaction is at equilibrium. If Q is not equal to K, then we can predict what way the reaction will go until K and Q are the same.

Sophia Kalanski 1A

ok but how do you figure out x from here?

Sophia Kalanski 1A

in the problem that Lavelle showed us in the lecture, the effect of the decrease in volume caused the Q to not be equal to the K and from there, you will see a shift in products and reactant concentrations so that K can be equal to Q

Sophia Kalanski 1A

the pressure can really only increase if there is a change in the volume because unless you take the moles of solute out, they shouldn't change. Therefore, you can infer that volume has to change in order for pressure to change and that will cause the concentration to change as well.

Sophia Kalanski 1A

it depends on the units given! Each R value uses different kinds of units so be extra sure to use the right R value and to pay close attention to the units given in the problem

Sophia Kalanski 1A

Hi! the question isP: 2SO(3)=>2SO(2)+O(2) and you are given that At a certain temperature, 0.980 mol SO3 is placed in a 4.00 L container and that at equilibrium, 0.120 mol O2 is present. Calculate Kc. I did the ICE chart and found that at equilibrium the concentrations should be: (0.245-2X). (2x). a...

Sophia Kalanski 1A

Hi! I am having trouble on this question. It's the one where Kc=53.3 and the equation is H(2)+I(2)=2HI and at a certain temp at equilibrium, 0.7 mol of I(2) and 0.7 mol of H(2) are placed in a beaker of 1.00 L and it asks for the concentration of HI at equilibrium. I did an ICE chart and found that ...

Sophia Kalanski 1A

No this doesn't really help :/ for this question, how would you get to find X without knowing the Kc. I get how to do the rest of the problem, I am just stuck on the part where at the end of the ICE chart, we are trying to find what X is and I cant seem to figure out how

Sophia Kalanski 1A

water is amphoteric! it can act as both an acid or a base

Sophia Kalanski 1A

pH=-log[H+]
it's also helpful to note that pH+pOH=14 and that [H+][OH-]=1*10^-14

Sophia Kalanski 1A

if the anion of the salt comes from a strong base and the cation comes from a strong acid, they cancel out and have no effect on the pH and therefore they are neutral

Sophia Kalanski 1A

So when I do this, I first separate the salt into its anion and its cation. From there, I try to see whether or not one of them belong to a strong acid or base and if so, they do not affect the pH of the solution. The one that does belong to the pH can affect it.

Sophia Kalanski 1A

hi! A salt is an ionic compound, with both an anion and a cation. It can also become basic or acidic when in an aqueous solution depending on if the cation or anion belong to weak acids or bases

Sophia Kalanski 1A

well a polyprotic acid can break off an H+ ion more than once so when you see an acid consist of more than one H, it can indicated that

Sophia Kalanski 1A

Yes!! For conjugate acids, you would add an H+ but remove an H+ for a conjugate base

Sophia Kalanski 1A

an amphoteric substance can act as both an acid and a base and an amphiprotic substance can both accept protons and donate them. When a substance is amphiprotic it implies that it is also amphoteric.

Sophia Kalanski 1A

To determine whether it is a strong acid, it would dissociate more or completely under water, in order for that to happen, the bonds in a certain molecule need to be broken more easily and therefore the bonds need to be weak. This would mean that the size of the atom in an acid would mean a lot beca...

Sophia Kalanski 1A

Yes they are the same! We just decribe them differently! For bronsted bases, we describe them by the fact that they receive protons while for lewis bases, we describe them through them donating electrons.

Sophia Kalanski 1A

In this case, the way I see it is that if you have NH3 which has a lone pair and wants to complete its octet and you have a H+ which can make a bond to complete its own octet, it would bind to NH3 and therefore since it doesn't have any electrons, it would be a lewis acid because it is accepting the...

Sophia Kalanski 1A

I don't think we need to fully memorize the exact pH level of each item but it would help to have general knowledge of what items would be considered acidic or basic.

Sophia Kalanski 1A

delocalized pi bonds occur when there are resonance structures. If a pi bond can exist in a different region, then it is delocalized.

Sophia Kalanski 1A

regardless of what type of bond it is, it will count as one electron density. A double bond will only count as one so there are in fact only 4 electron density regions and therefore it will have an sp3 hybridization

Sophia Kalanski 1A

well the hybridization for NH3 would be sp3 because the nitrogen central atom has 3 bonded regions and one lone pair region (which is 4 different electron densities). When calculating the hybridization you want to first find that it is sp3 and then get more specific into finding which quantum number...

Sophia Kalanski 1A

every bond and lone pair are seen as their own electron density yes, and on top of that a double bond would count as one electron density

Sophia Kalanski 1A

I think that it's because it is written as H2CCCH2 instead of just C3H4. I believe that they were implying that the hydrogens will be connected only to the outer carbons.

Sophia Kalanski 1A

It depends on the amount of electron regions there are attached to one atom. If there are 2 then it is an sp orbital since 1s is its own region and one p is another region. Double bonds count as one region.

Sophia Kalanski 1A

Yes! These shapes exist because they are the ones that have the least amount of repulsion. For the square planar shapes, you want to make sure that the lone pairs are furthest away from each other and in that case, since only 4 of the 6 positions are occupied by bonded atoms, it will create a shape ...

Sophia Kalanski 1A

I think that its fine to list an answer that falls in the correct margin of the answer. In this case, since we knew that there were 4 bonds, and 2 of them were lone pairs, they would cause the angle between the lone pairs to be greater than 109.5 and the angles between the lone pairs and bonding pai...

Sophia Kalanski 1A

yes they count as their own separate region and have a stronger repulsion power than the rest of the regions. the powers go from lone pair to lone pair>lone pair to bonding pair>bonding pair to bonding pair. This will in turn also cause the angles between the other regions to be greater.

Sophia Kalanski 1A

I agree with the above statements, these sigma and pi bonds occur with any type of covalently bonded molecule since these molecules may consist of both double and triple bonds.

Sophia Kalanski 1A

Well I think its best to start with drawing out the lewis structure to figure out how many bonds are present and from there when you know that there are lone pairs or not, you can figure out approximately how far the angles would be from each pair of electrons that require the least repulsion effort...

Sophia Kalanski 1A

I don't believe that a double bond are called pi bonds since it contains both a sigma bond and a pi bond. I think that the thing you need to know though about double bonds is that since it has a pi bond, it is unable to rotate.

Sophia Kalanski 1A

I agree with the above comment, when saying "ample" it is way more closer to the middle of the two bond lengths and therefore wont have significantly more than one or the other.

Sophia Kalanski 1A

I would keep in mind that since there is delocalization of electrons, there could be many variations as to where you can include a double bond. The whole point is to find a resonance structure that has the least amount of individual formal charges among the atoms but still keeps the same overall for...

Sophia Kalanski 1A

I doubt you would need to memorize it since we haven't learned how to formulate lewis structures or formulas based off names

Sophia Kalanski 1A

No, the hydrogen needs to be attached to either F,N,O but the other atom just has to be electronegative.

Sophia Kalanski 1A

In order to find the formal charge, you look at each atom within the molecule and find its formal charge. The resonance structure with the lowest amount of charges and changes will be the best one

Sophia Kalanski 1A

It's just something you would need to know conceptually. Like for carbon, it would be a +4 because all the electrons move away from it to the more electronegative atom

Sophia Kalanski 1A

The negative sign will be on the outside of the molecule and it is used to dictate the charge of the molecule based on how many electrons it will need to complete an octet and to be stable

Sophia Kalanski 1A

L represents the number of lone pairs and they can be counted in the lewis dot diagram

Sophia Kalanski 1A

The way to draw this: you first start by making a single pair of each oxygen to the carbon. You notice that carbon still has a free electron that could bond with one of the oxygens to fill its octet, so it forms a double bond with one of the oxygen atoms which fills up the octet for that atom as wel...

Sophia Kalanski 1A

to have several resonance structures allows for the electron density to be more evenly distributed and therefore the overall charge of the components in the molecule will be more neutral and therefore more stable.

Sophia Kalanski 1A

Hi! So I don't think we will have to know the exact value of the electronegativity of each element but we will need to know the general trends of electronegativity that occur in the periodic table and where electronegative atoms are found more.

Sophia Kalanski 1A

I agree with everyone above, it must fill its octet and have 6 valence electrons. The book probably forgot to input the 2 electrons

Sophia Kalanski 1A

yes! They usually are easier to lose or cause the atom to want to gain an electron to finish the orbital

Sophia Kalanski 1A

ionic bonds are usually stronger because they are causing a transfer in electrons rather than a quick sharing of them. Covalent bonds are created by electronegativity and tend to be weaker

Sophia Kalanski 1A

typically electronegative atoms make covalent bonds and are non metal. It is more electronegative when it wants more electrons. For example, in H2O, Oxygen is very electronegative and that is why it bonds with 2 hydrogen atoms.

Sophia Kalanski 1A

Use the atom with the lowest ionization energy (this is the least electromagnetic atom)

Sophia Kalanski 1A

Hey! So im pretty sure both terms can be used interchangeably since noble gases are in the outermost level of the periodic table and don't partake in chemical reactions and inert gases are defined as not partaking in chemical reactions.

Sophia Kalanski 1A

H, He, Li, Be are not part of the octet rule because H and He only need to fill up an S orbital to satisfy the orbital and since Li and Be are closest to Helium, they will lost electrons to reach the amount of valence electrons/the state of helium and therefore they don't and won't have to fill an 8...

Sophia Kalanski 1A

Hi! So I think that the electron is affected by the photon due to its size and mass. It was said during the lecture that a baseball wouldn't be affected because it is so big and therefore wouldn't feel the affects of the photon

Sophia Kalanski 1A

Hi! So since it is excited to the n=6 level, it can return to any level below it (n=5,4,3,2,1) so it will have 5 different spectral lines.
To find the wavelength, we can use the rydberg formula to find the frequency and then, in turn you can use c=(wavelength)(frequency) to get the wavelength.

Sophia Kalanski 1A

Hi! So I think what he meant in his lecture was that the energy of the photon has to be atleast equal to/match the energy needed to move the electron up an energy level. It just can't be less than the needed energy to eject it.

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