CHEMISTRY COMMUNITY

Bilal Pandit 1J

In reference to what?

Bilal Pandit 1J

Yea I think that is an assumption that we make, but they will usually specify regardless.

Bilal Pandit 1J

You essentially assume that all the other reactions happen significantly faster than all of the other reactions, so there is a buildup of product of the reaction before and reactant after, as that single slow step is what limits the entire overall reaction.

Bilal Pandit 1J

The rate law can be used to show the rate of a reaction, which is the rate of formation of the product.

Bilal Pandit 1J

It depends on the order of the reaction, but you can look at the formula sheet and plug in the values you know.

Bilal Pandit 1J

Essentially, you follow the equations on the formula sheet, plugging in the values that you know and use a system of equations to calculate the final missing value.

Bilal Pandit 1J

The integrated rate law is the result of integrating the general rate law, to give you the exact concentration of a reactant at a certain time.

Bilal Pandit 1J

The equations are on the formula sheet, but delta G = RTlnK, and u can extrapolate that out to non-standard values of delta G, which shows how Q is related as well.

Bilal Pandit 1J

It can be determined by the overall cell reaction, with the concentrations plugged in for Q (products over reactants)

Bilal Pandit 1J

What range (in volts) does a voltmeter need to have to measure pH in the range of 1 to 14 at 25 8C if the voltage is zero when pH = 7?

If I use the lower concentration value at 10^-7, I keep getting half the value of the answer in the answer booklet.

Bilal Pandit 1J

Do we have to know how a rechargeable battery works? Because I think Lavelle said that we did not need to know how it works in class.

Bilal Pandit 1J

You always need something solid that can act as the actual electrode, so you would use a metal like Pt as that electrode.

Bilal Pandit 1J

For the pH meter example he did, is the pH meter the cathode or the anode?

Bilal Pandit 1J

Can a salt bridge consist of any salt or does it have to have to include some of the material in either the cathode or anode solution?

Bilal Pandit 1J

Can you use a salt bridge for a concentration cell or do you need a permeable membrane?

Bilal Pandit 1J

Why does pressure matter for an electrolytic cell? Since they are all concentrations or solids, why would it matter what the pressure is?

Bilal Pandit 1J

How can you control which way the voltage flows in an electrolytic cell? like why would it just not go in reverse?

Bilal Pandit 1J

If you figure out the reduction equation and the oxidation reaction, and when you cancel them out you will see the exact number of electrons being transferred, which will be your n.

Bilal Pandit 1J

The more positive reduction potential makes it easier to oxidize hydrogen, which means that it will be harder to reduce hydrogen.

Bilal Pandit 1J

Everything is posted on the website basically.

Bilal Pandit 1J

All of these equations are basically derived from the ones given on the formula sheet, it just depends on which values are constant and which ones you can manipulate.

Bilal Pandit 1J

Also, Delta G cannot be calculated by itself, its a derived value basically.

Bilal Pandit 1J

We are essentially trying to find the maximum potential of the cell, which is when there is no current flowing between the two electrodes. When the electrons start to flow, that is the voltage, which decreases over time.

Bilal Pandit 1J

the R is 8.314, as that is the R that uses Joules, which is the unit we need to get into Volts

Bilal Pandit 1J

Test 2 is the last page of thermodynamics and the entirety of electrochem. The only material left that we have to be tested on is kinetics.

Bilal Pandit 1J

Essentially it works like a galvanic cell in which there are both a cathode and an anode, but unlike a galvanic cell, the base reaction has a negative E, and voltage is supplied to keep the reaction progressing.

Bilal Pandit 1J

Breaking a bond requires energy, so it would be endothermic while forming bonds releases energy (exothermic)

Bilal Pandit 1J

You only need to reverse the sign for the delta H if you are measuring the change in enthalpy in the surroundings, so the actual system will be the opposite of that.

Bilal Pandit 1J

w is given in joules.

Bilal Pandit 1J

I don't think he has released his review sheet yet, hopefully he will post it later as we get closer to the midterm.

Bilal Pandit 1J

Most of the examples of work we will be covering will be a change in volume, like the piston example discussed in class, where the gas inside pushes the piston out(work done by the system) or when the gas is compressed by the piston (work done to the system).

Bilal Pandit 1J

If there was insulation, then it would be an isolated system, as there would be no change in matter or heat.

Bilal Pandit 1J

No, in a closed system, heat and work are two different aspects of energy change.

Bilal Pandit 1J

Partial Pressure more specifically is talking about the pressure one gas exerts, while pressure talks about the overall pressure exerted by all the gases in the container, So the partial pressure of all the gases in a container can be added to find the overall pressure.

Bilal Pandit 1J

Last quarter there were a bunch of prep material that TAs and UAs gave out, along with past year exams, but Lavelle doesnt give anything himself.

Bilal Pandit 1J

No the H2O would still not affect anything, as it is the solvent, so there is so much of it that the concentration of it wont really change when the reaction occurs, because it is in so much excess.

Bilal Pandit 1J

It depends, because if the K is given as a constant, then you do not include it when counting sig figs, but if you are calculating the K, then you will have to use its sig figs

Bilal Pandit 1J

It all depends on what is present when you measure the pH, as a buffer will have concentrations of an acid and a base, rather than just the acid or just the base.

Bilal Pandit 1J

Usually, enthalpy is given in Joules, but other units can be calories, kJ, kilocalories...

Bilal Pandit 1J

Adding the inert gas will not change the pressure of the actual gases in the reaction, as that gas will be present in both the reactants and products, as it is inert. As a result, adding an inert gas does not change the pressure for the actual gases, so there is no shift in the equilibrium.

Bilal Pandit 1J

For exothermic reaction, increasing the temperature will decrease the K, while for endothermic, increasing the temperature will increase the k

Bilal Pandit 1J

There will be a different equilibrium constant values for the reactions, but all of it will be relative anyways.

Bilal Pandit 1J

Equilibrium constants just describe how the reaction will be at equilibrium (the relative concentrations of the products and reactants), so you can use it to predict the behavior of any reaction.

Bilal Pandit 1J

When you are given a random chemical equation, does it matter if you use K or Kp (concentration or pressure) if the question doesn't specifically state what it wants?

Bilal Pandit 1J

It can be less than 10^-3 or greater than 10^3

Bilal Pandit 1J

K is all about the concentrations, and the change in the liquid and solid-state is negligible so we can just ignore that.

Bilal Pandit 1J

What helps me visualize this is to treat the energy almost like a product or reactant. So if the reaction is exothermic, energy is a "product" and vice versa. If you increase the temp, you would increase the delta H, so whichever side it is on will end up decreasing.

Bilal Pandit 1J

When the pressure changes, then the Q will be different than the Kp, so you can figure out which way the experiment will shift according to that.

Bilal Pandit 1J

Its honestly all about being consistent, so if you use the same units for every single calculation, you should be fine.

Bilal Pandit 1J

K is a constant, so it will essentially always stay the same, with the single exception being temperature due to the change in the kinetic energy of the gas molecules.

Bilal Pandit 1J

There would be no shift in the equilibrium, as if you calculate the new pressure/concentration of the gases after the compression, they will balance out in the K equation, so it would not matter.

Bilal Pandit 1J

You use these when there is a prefix for the logans, so u use bis instead of having bi in the name of the coordination compound and the ligand itself - bis instead of bi bi(ligand)

Bilal Pandit 1J

Hybridization is the orbitals combining, I don’t think it’s really related to the electro negativity.

Bilal Pandit 1J

I think we have to know them by the general trends, like the alkali metals make strong bases.

Bilal Pandit 1J

Sigma bonds will not break if the atoms rotate, only pi bonds will.

Bilal Pandit 1J

The greater the difference in the electro negativity between the two atoms is generally the way to determine which is more electronegative.

Bilal Pandit 1J

The easiest way for me to memorize hybridization is to simply count the number of bonds. From there you can fill out the orbitals, with s being one bond, sp going from 2 bonds to 4 with sp3, continuing on with d.

Bilal Pandit 1J

The reason that molecule is polar is that the shape is tetrahedral, which means the two Cl atoms aren't going to be opposite of each other. Since they aren't opposites of each other, they will not cancel out and as a result, the molecule will have a net dipole

Bilal Pandit 1J

He sent out an email with all of the ligand names and stuff that you need to memorize for the final.

Bilal Pandit 1J

The bond angles are less than 120 and 90, as it would be a trigonal bipyramidal without the "top" electron, so the lone pair repulsion pushes down and makes the angles slightly less than they were originally with the trigonal bipyramidal shape.

Bilal Pandit 1J

They are used when the ligand has a prefix itself, so the ligand would have a di, tri, etc, so instead of saying didi, you would just say dis.

Bilal Pandit 1J

If you draw out I^3-, the central I atom ends up having 5 bonding regions, with 2 bonds and 3 lone pairs. If you look on the VSEPR chart, that would give u a formula of AX2E3, which gives u the linear shape with 180-degree bond angles

Bilal Pandit 1J

Linear is any situation in which there are simply two atoms bonded to each other (because it resembles a "line"). Trigonal planar is when the central atom has 5 bonding regions, with 3 bonds and 2 lone pairs. Bent is when the central atom has 4 bonding regions, with 2 bonds and 2 lone pairs.

Bilal Pandit 1J

I think the majority of the test will be material from the molecular shape and structure homework.

Bilal Pandit 1J

Personally, I try to kinda visualize all of the basic shapes (tetrahedral, trigonal pyramidal, trigonal bipyramidal), and in these shapes, all the angles are pretty easy to deduce once you have already kinda visualized the name. The remaining bond angles are usually just less than the "base&quo...

Bilal Pandit 1J

I think he said it is going to cover bonding, VSEPR, and intermolecular interactions. It is not gonna include any content from the midterm, so basically from Outline 2D and onwards to where we are now basically.

Bilal Pandit 1J

Its essentially all determined by how close the electrons are to the actual nucleus.

Bilal Pandit 1J

An instantanous dipole is basically when a nearby atom has a dipole moment which causes another atom to have its charges shift as a result of the other atom.

Bilal Pandit 1J

The shape basically shows the electron density, so there will only be those interactions where there is/isnt an electron.

Bilal Pandit 1J

For the final/upcoming test, will we have to calculate how polarizing an atom is using electronegativity?

Bilal Pandit 1J

Elements that have a d-orbital are able to have more than an octet, as the electrons will go into the d-orbital. These are basically all the elements in the 3rd row and down.

Bilal Pandit 1J

You can use the c = lambda nu, and then use E = kv to get the energy.

Bilal Pandit 1J

Covalent character means that the bond is expressing covalent characteristics, which means that the atoms are sharing electrons. The covalent character means that the atoms are sharing the atoms, so they cannot be separated in water and other properties like that. A compound that has a high covalent...

Bilal Pandit 1J

We just need to know that all the bonds in resonance structures are the same length. I think he said that the rest of the information would not be covered but I am not sure.

Bilal Pandit 1J

Usually, for the larger molecules, there are differences in the way the formula is presented that gives hints, as atoms that are bonded to each other are usually next to each other in the molecular formula.

Bilal Pandit 1J

Essentially energy is conserved throughout the entire experiment, as the energy of the photon equals the work equation and the energy of the electron ejected. That means that the energy is conserved throughout the reaction. In reference to the conceptual change, photons were no longer only looked as...

Bilal Pandit 1J

That kind of detail isnt really necessary, so only draw it out if the question specifically asks for it.

Bilal Pandit 1J

The charge of an electron is a constant, and the distance between the charges is the same as the radius of the atom.

Bilal Pandit 1J

We have to use the formula for finding the energy of an energy transition (E = Rh/n^2) and E = hv to get the frecuency

Bilal Pandit 1J

I am sure that all the review sessions will go over all the proper and necessary material - I doubt you will get punished for having other commitments.

Bilal Pandit 1J

I believe he is referring to the number of bonds that there are (the number of lines drawn on the Lewis structure for that specific atom.

Bilal Pandit 1J

All the equations we will need to know will be on the first sheet of any test we take, so we wont have to memorize or keep track of all of them and their constants. You will need to know which variable means what, which will allow you to use the right equation for any set of given information

Bilal Pandit 1J

Yea, multi-electron atom refers to all atoms outside of Hydrogen

Bilal Pandit 1J

They change with ionic bonding, where the electrons are transferred but not with covalent bonding.

Bilal Pandit 1J

This basically shows that if an electron was centralized in the nucleus, the level of uncertainty would be so large that it would be basically useless. As a result, the size of an atom must be greater so that the Heisenberg equation was actually applicable.

Bilal Pandit 1J

The Heisenberg principle highlights that the exact position of an electron cannot be found and that there will always be a level of uncertainty. When they used the size of the nucleus of a hydrogen atom to find the level of uncertainty, they got a value that was so large (greater than the speed of l...

Bilal Pandit 1J

The way to derive the exact equation is really complicated and involves really high-level math, so I do not think you need to know how to derive it, rather just what it's used for and how to use it.

Bilal Pandit 1J

I don't think we need to know the specific n values for specific types of waves. I think we just need to know that as n increases, the overall energy decreases.

Bilal Pandit 1J

Essentially everything has both normal particle properties and wave properties. It's just that the larger particles have such small wavelengths that they are basically not identifiable, which is seen through the de Broglie equation. That's why even a baseball has wave properties, but they are so sma...

Bilal Pandit 1J

I am pretty sure everything in the universe has its own energy. An electron can absorb energy from photons, which causes it to jump up electron levels. When the electron loses that energy, it drops down energy levels, releasing the energy it absorbed originally from the photon. It has its own wavele...

Bilal Pandit 1J

How can we practically manipulate intensity? (like we can change wavelength and frequency by changing the color of the light)

Bilal Pandit 1J

We talked in class about how changing the intensity (amplitude) of the light did not change the energy of the photon. However, how does increasing the amplitude result in more total photons?

Bilal Pandit 1J

What exactly characterizes all the lines in the series? I understand it has to do with lower and higher energy states but how exactly are the series grouped together?
This is HW #1A 11.

Bilal Pandit 1J

Would we ever have to calculate the amount of remaining reactant in a calculation (how much of the reactant that isnt limiting is left)

Bilal Pandit 1J

For the test it says there are only 7 questions, does that mean all the questions are going to be free-response with no multiple choice?

Bilal Pandit 1J

Usually you want a whole number, but most of the time it doesn't get to an exact number, so I think plus or minus 0.1 should be fine.

Bilal Pandit 1J

One of the homework problems requires you to know what a heptahydrate is, is that necessary to know for the test?

Bilal Pandit 1J

For the test, do we have to memorize any formulas for certain compounds? Certain questions on the homework expected you to know certain formulas, so want to clarify before the test if there is anything we need to memorize.

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