CHEMISTRY COMMUNITY

Viviana Velasquez

you use OH when you are dealing with basic solutions. You still add H2O to balance the oxygens but the you had OH to make the reaction less acidic and more basic

Viviana Velasquez

I was also wondering this. His email made it seem like you would input the answer with no work but maybe there will be other ways to receive points (true or false, multiple choice)

Viviana Velasquez

yes, typically we would assume the cathode is on the right and the anode is on the left

Viviana Velasquez

yes it is timed. 3 and a half hours to complete the test

Viviana Velasquez

I think it’ll be pretty much the same. 250 points minimum to pass

Viviana Velasquez

I’m not sure but I’m sure Professor Lavelle will email us when he has all the information gathered

Viviana Velasquez

If you are solving for something besides A, it will be given to you since the constant differs with each equation.

Viviana Velasquez

Elementary reactions are the steps taken in order to get an overall reaction.

Viviana Velasquez

I think it has to do with the catalyst reacting (being a reactant) in the first step and being a product for the next step. An intermediate would begin as a product in the Step 1 or your first reaction. They both don't show up in the final equation.

Viviana Velasquez

Units of k depend on the order of the reaction
0th order= M/s
1st order=1/s
2nd order=1/(M)(s)

Viviana Velasquez

How do you determine order of a reaction?

Viviana Velasquez

Appendix 2B or you can look it up online

Viviana Velasquez

When trying to find Delta G using Delta G=-nFE, how do you determine n, number of moles of e- if you are given the reaction?

Viviana Velasquez

For test 2, are we going to be given a table for the cell potentials of the half reactions? Some homework problems do not include it, so I am guessing we have to look it up on our own to complete the problem

Viviana Velasquez

The activation energy is the amount of energy needed for the reaction to occur (reactants form products)

Viviana Velasquez

Coefficients do not change standard cell potentials.

Viviana Velasquez

Can someone explain what the salt bridge does and how it achieves it's purpose?

Viviana Velasquez

The cathode will typically be placed on the right, but you should double check anyways because I have seen diagrams where they are flipped. However, Lavelle made it seem like it will always be on the right for this class.

Viviana Velasquez

The half reactions separates the oxidation and reduction that is happening in the reaction. Also it makes it a lot easier to balance if you split them up.

Viviana Velasquez

Yes, you have to cancel out the electrons on both sides. Most times you'll have to multiply at least one of the half reactions in order to get the same amount of electrons on each side to be able to cancel them out.

Viviana Velasquez

Oxidation is losing electrons and reduction is gaining electrons (OIL RIG). If the positive charge decreases, it is being reduced. If the positive charge increases, it is being oxidized.

Viviana Velasquez

For a reaction to be spontaneous, delta G has to be negative. When delta G is negative, it means the forward reaction is favored and products are formed. When delta G is positive, the opposite happens and reactants are formed.

Viviana Velasquez

Since K=1 at equilibrium and the equation is RTln(K), ln(1)=0 making Delta G=0

Viviana Velasquez

He does not curve but they are super generous with points and your grade depends on points, not percentage.

Viviana Velasquez

I think its importance is linked back to the way temperature affects it

Viviana Velasquez

Delta g naught is under standard condition unlike delta G that can be any condition

Viviana Velasquez

There are cases where entropy increases due to an increase in volume, but I am not sure if that is the case for all reactions or if the assumption can be made

Viviana Velasquez

You can us delta H instead of q because at constant pressure, q(p)= delta H

Viviana Velasquez

You use it depending on whether you are solving for heat at constant pressure or constant volume. Often times the problem will tell you directly whether it is constant pressure or volume and other times you will have to read the problem carefully and deduce which one it is at.

Viviana Velasquez

I think either Joules or kilo joules is fine as long as you stay consistent throughout the entire problem to make sure no calculation mistakes are made. I would just make sure to read if the question asks for any units in specific

Viviana Velasquez

I think the standard free energy conditions is the one measured in the lab and the regular free energy change occurs in real life systems

Viviana Velasquez

Yes at 25 degrees it is in liquid form. If they were to not give you a temperature I would say its safe to assume its in liquid form.

Viviana Velasquez

The system's q is equal to the -q of the surroundings

Viviana Velasquez

The equation for that is w=-nRTln(V2/V1).

Viviana Velasquez

I don't think its necessary, but I think he was trying to show how the equation is derived.

Viviana Velasquez

I think he was just showing how the equation is derived.

Viviana Velasquez

I don't remember going over this either. I feel like he might have specifically gone over it in class since that is what he did last quarter in 14A.

Viviana Velasquez

Increasing the temperature will shift the reaction to the left and decreasing it will shift it to the right. This has to do with the fact that exothermic reactions have heat as a product

Viviana Velasquez

Which gas constant are we expected to use for the equation PV=nRT?

Viviana Velasquez

Only temperature can change the value of K.

Viviana Velasquez

He explained that because steam experiences a phase change when it comes into contact with skin, it releases a big amount of heat and therefore causes severe burns.

Viviana Velasquez

In 14A we had to memorize a list from the textbook, so I'm assuming you just have to refresh your memory on those for this course

Viviana Velasquez

They're inversely related:
lower pKa= stronger acid
higher pKa= weaker acid

Viviana Velasquez

Lavelle mentioned that it had something to do with their concentrations not changing so they were insignificant.

Viviana Velasquez

It's usually because it is in liquid form, but you only include H2O when it is aqueous or gas form.

Viviana Velasquez

X was ignored since K was so small (less than 10^-3) and X would make such a small change to .10

Viviana Velasquez

It's unlikely that we will have to memorize them, but I suggest asking your TA just to be sure.

Viviana Velasquez

K is the equilibrium constant and Q tells you the constant of the equation when it is not at equilibrium. Q helps you judge whether it is a forward or backwards reaction.

Viviana Velasquez

Naren_Ramesh_4F wrote:When asked the equilibrium constant of a chemical reaction involving gases, do we solve for Kc or Kp?

You would solve for Kp since the P stands for partial pressure. Remember that if they ask for the equilibrium constant of a gas always assume you use Kp unless stated otherwise.

Viviana Velasquez

The best way to study for the test is to make sure you know what's on his outlines. He goes based off of that for the most part.

Viviana Velasquez

Kc is the equilibrium constant in concentrations and Kp is the equilibrium constant for gases which is in partial pressure.

Viviana Velasquez

There are more examples, but this one was talked about heavily in class and at various review sessions.

Viviana Velasquez

I know some of the more important ones are DNA bonding and cisplatin (the chemotherapy drug talked about in class).

Viviana Velasquez

I think it would just be considered an intermolecular force.

Viviana Velasquez

It would be helpful! Here are a few
Strong Acids: HCl, H2SO4, HNO3, HI, HBr, HClO4, HClO3
Strong Bases: LiOH, NaOH, Ba(OH)2, KOH, Ca(OH)2

Viviana Velasquez

Some strong bases that you should know are :
LiOH, NaOH, Ba(OH)2, KOH, Ca(OH)2

Viviana Velasquez

Is it true that we only need 250 points to pass the class?

Viviana Velasquez

Yeah the best way to do it is just to practice a bunch. There's charts with the naming rules that might be helpful if you memorize.

Viviana Velasquez

The proton acceptor would be the base and the proton donor is the acid.

Viviana Velasquez

Yes, hydrogen bonding only occurs when H is bonded with N, O, or F.

Viviana Velasquez

I'm having trouble understanding when to use hybridization or when it's being used, can someone explain?

Viviana Velasquez

How do we determine bond lengths?

Viviana Velasquez

Yes, you should be able to determine the shape of a molecule based on the AXE formula.

Viviana Velasquez

He said everything that we learned after the midterm will be included in test 2.

Viviana Velasquez

The atom points in the direction of the more electronegative atom.

Viviana Velasquez

How do you determine the bond angle? Do we have to know the exact angle measurement or just as long as we phrase it as "less than ___"?

Viviana Velasquez

I think it will probably be on what we learn after the midterm and maybe include chemical bonding.

Viviana Velasquez

Copper and Chromium are two exceptions.

Viviana Velasquez

Shape will probably matter when we go over that lecture, but right now it does not matter.

Viviana Velasquez

I believe it is Wednesday, but if not then by Friday.

Viviana Velasquez

What are magnetic quantum numbers and how do you find them?

Viviana Velasquez

Are expected to memorize the masses of electrons, protons, and neutrons? Only asking because the homework has problems where these values are not given in the problem.

Viviana Velasquez

Can somebody explain why you would put 3d^6 4s^2 instead of the other way around?

Viviana Velasquez

When the energy of the photon is equal to the work function, the electron will be ejected. However, there will no excess energy (kinetic energy).

Viviana Velasquez

Yes, as long as the frequency is equal to or greater than the threshold energy needed to eject an electron, increasing the light intensity will increase the # of electrons ejected. It won't affect the kinetic energy.

Viviana Velasquez

What exactly do we need to know about black body radiation for the midterm?

Viviana Velasquez

Do we need to do homework for chemical bonding this week or can we still do quantum to review?

Viviana Velasquez

The ionization energy of the second electron is always higher because when you remove an electron, the pull between protons and electrons become stronger (requiring more energy to remove)

Viviana Velasquez

Usually, you want the central atom to be the one with the formal charge of 0 if it is not possible for all atoms to have a formal charge of zero.

Viviana Velasquez

Hydrogen is an exception. It will never be the central atom.

Viviana Velasquez

Can somebody break down how to figure out electron configuration?

Viviana Velasquez

Are we expected to know a specific formula for ionization energy or only the general trends of ionization energy?

Viviana Velasquez

Do we always assume that it's spin up and spin down for this class?

Viviana Velasquez

If the class isn't curved, how many points are needed to pass the class? I remember reading something about using the class average at the end and needing at least 50% on the syllabus.

Viviana Velasquez

Hz would be s^-1 which implies 1 cycle per second

Viviana Velasquez

When frequency decreases, the wavelength would increase because you'd be dividing the speed of light by a smaller frequency. wavelength= (speed of light)/(frequency)

Viviana Velasquez

We should be getting an equation sheet with constants as well, if I'm not mistaken.

Viviana Velasquez

So only the change in energy of a photon can be negative?

Viviana Velasquez

Can somebody explain why the energy of a photon is always positive?

Viviana Velasquez

This equation can be used when you are given any of the three values needed for the completion of the equation. For example if you are asked to find the V1, you will need to have M1, M2, and V2 in order to be able to use this equation.

Viviana Velasquez

You should convert the grams to a percentage when you are given the amount of grams of each element and the total mass of the compound to find the mass percentage composition. Then assuming you have 100 g, you would convert the percentage to grams and then moles. Sometimes the mass percentage compos...

Viviana Velasquez

You would have 3 significant figures because the zeros after the decimal are counted as significant figures.

Viviana Velasquez

The theoretical yield is what you're supposed to get if there are no errors or other factors that affect the experiment. However sometimes factors such as the experiment sticking to the side of the test tube will reduce the amount of yield (actual yield).

Viviana Velasquez

Hi, I could use some help doing homework problem H.19:
Write balanced equation for the combustion of the solid C11H18N2O5 to carbon dioxide gas, liquid water, and nitrogen gas.

Viviana Velasquez

I've heard the 6th edition and the 7th edition are pretty much the same, but you might want to ask your TA to be sure that you can use any other edition besides the 7th.

Viviana Velasquez

That .0 makes the difference between only using one sig fig and using 3 sig figs.

Viviana Velasquez

You're supposed to go based off the value with lowest significant figures given in the problem. For example, if you were given the values 6.38 and 43.58 in a homework problem, your final answer should include 3 significant figures.

Search found 97 matches