CHEMISTRY COMMUNITY

Minh Ngo 4G

It is provided on your equation sheet but it is useful to know how to derive the half life ones since let's say you are asked to find the how much time it takes for the concentration to be 1/15 initial, you would first need to derive an equation for that (exactly the way you do for half life) then s...

Minh Ngo 4G

n is the number of electron that are being transferred

Minh Ngo 4G

To differentiate with the actual rate constant

Minh Ngo 4G

That's the ICE table problem!

Minh Ngo 4G

Initial rate is the rate that you use when trying to figure out what is the rate constant,k. It is when the reaction first starts so no products has formed. Reaction rate is your rate law: rate = k[P]. This is the rate of your rxn as a whole when it reaches equilibrium

Minh Ngo 4G

For this question: The half-life for the second-order reaction of a substance A is 50.5 s when [A]0 0.84M . Calculate the time needed for the concentration of A to decrease to (a) one sixteenth; (b) one-fourth; (c) one-fi fth of its original value. So for this question, I calculate k (0.0236) and th...

Minh Ngo 4G

Unit of k is depend on your order

Minh Ngo 4G

Linear

Minh Ngo 4G

You use Plt (s) when you don’t have an inert conducting metal solid

Minh Ngo 4G

You would determine it from your half reaction (making sure that both of them have the same number of electrons; if not, multiply one with another)

Minh Ngo 4G

As of the resulting balanced REDOX, no it does not matter where the H+ or OH- ends up on. Just remember if acidic, your rxn should have H+ and basic, OH-

Minh Ngo 4G

It applies like how you would in equilibrium

Minh Ngo 4G

It's vice versa with the ones being oxidized/ reduced. The oxidized one is the reducing agent (think about it, if let's say H is being oxidized, it can go around oxidizing anyone else, thus, someone has to oxidize it, thus it is a reducing agent)

Minh Ngo 4G

It doesn't affect but a positive cell potential means a negative Gibbs free energy which mean spontaneous

Minh Ngo 4G

It will always be given for reduction

Minh Ngo 4G

For cell diagram, anode always on the left, then salt bridge (||) then cathode

Minh Ngo 4G

JonathanS 1H wrote:The answer to both questions is that Hg (l) is the anode in this case. With a liquid anode, we include the liquid but since water is our solvent and not involved in either the anode or cathode, we do not include it in the cell diagram.

So if the anode is in liquid state, we don’t need any metal?

Minh Ngo 4G

Suppose that each of the following pairs of redox couples is joined to form a galvanic cell that generates a current under standard conditions. Identify the oxidizing agent and the reducing agent, write a cell diagram, and calculate the standard cell potential. a) Co 2+/Co and Ti 3+/Ti 2+ So for thi...

Minh Ngo 4G

So I have several questions regarding writing cell diagram (I'm also refering to 6M.5: For each reaction that is spontaneous under standard conditions (that is, K > 1), write a cell diagram, determine the standard cell potential, and calculate ΔG° for the reaction: (a) 2 NO3 − (aq) + 8 H + (aq) + 6 ...

Minh Ngo 4G

You have the numbers correct. but should double-check the arrangement of the final equation you are using to solve. Should be like this... Ecell = E cathode - E anode (solving for E cathode...) E cathode = E cell + E anode E cathode = -.698V + .34V = -.349V Wait im confused, why are we solving for ...

Minh Ngo 4G

A student was given a standard Cu(s)|Cu2+ (aq) half-cell containing an unknown metal M in 1.00 m M(NO3)2(aq) and formed the cell M(s)|M+ (aq) || Cu 2+ (aq)|Cu(s). The cell potential was found to be -0.689 V. What is the value of E°(M 2+|M)? So for this problem, I identify the anode (M(s)-> M+ + e)...

Minh Ngo 4G

I think we might be provided with half reactions but also it would be good to practice coming up with them on our own? If we are not given, then do you know any strategy to do so? Because for this rxn specifically, there is no way I could have come up with Ag(s) -> Ag+ + e and AgBr + e -> Ag + Br

Minh Ngo 4G

6L.7: Write the half-reactions and devise a galvanic cell (write a cell diagram) to study each of the following reactions:
a) AgBr(s)-->Ag+(aq)+Br-(aq)
For this type of question, are we refering to all the half rxn in Appendix 2A or a we expected to come up with them on our own??

Minh Ngo 4G

Yes, always

Minh Ngo 4G

To keep the electrons flowing back so that the "negative" doesn't build up on the cathode side

Minh Ngo 4G

No they refer to anything. Hydrogen is just the standard use to measure E knot

Minh Ngo 4G

Depends on the equation you are using but I think if in doubt, just convert it to K (unless they are problems that involve a specific heat capacity ones)

Minh Ngo 4G

Basically to produce electricity (eg. battery)

Minh Ngo 4G

For this equation: deltaG = deltaG knot + RTlnQ. If we are given the pressure to find Q, what would be the unit for the pressure? I am refering to 5G.13

Minh Ngo 4G

Use the ideal gas law. Usually when you are not given anything,there is a high chance you are able to get it by the ideal gas law

Minh Ngo 4G

Because P and V has an inverse relationship. If you increases one, one wil decreases (PV=nRT)

Minh Ngo 4G

d is delta. In Calculus, it is the derivative. In this case, it is the change in volume.

Minh Ngo 4G

Because all the heat lost by water ( - sign) has to be gained by ice ( + sign). Even though it doesn't matter, it is conventional to put the negative sign on the side that lost heat, and since heat flows from hot to cold, in this case, you would put the negative sign on q water

Minh Ngo 4G

We are not having any cubic equation on the test. If there is, you would use an approximation.

Minh Ngo 4G

Write a balanced chemical equation for the formation reaction of (a) NH3 (g ); (b) H2O (g ); (c) CO; (d) NO2 (g) . For each reaction, determine Δ G ° from data in Appendix 2A. For this problem, my understanding is that we just need to find the Δ G ° from the table right? However, all the answers are...

Minh Ngo 4G

Calculate the change in molar Gibbs free energy for the process NH3(l) S NH3(g) at 1 atm (b) -180 deg C. In each case, indicate whether vaporization would be spontaneous. So for this one, I did exactly what I did for part a which is dG = dH - TdS. dH is 23400 J/mol dS is 97.6 J/K.mol T is -180 + 273...

Minh Ngo 4G

Janet Nguy 2C wrote:For diatomic molecules, Cv = 5/2R and Cp = 7/2R. I'm not sure about the other kind, though. But I don't think we would be asked something that's not monatomic or diatomic.

So, we just have to remember for diatomic then?

Minh Ngo 4G

Use data in Table 4H.1 or Appendix 2A to calculate the standard reaction entropy for each of the following reactions at 25°C. For each reaction, interpret the sign and magnitude of the reaction entropy. (d) The decomposition of potassium chlorate: 4KClO4 -> 3KClO4 + KCl So for this problem, why don'...

Minh Ngo 4G

I know the equations for Cv and Cp for monoatomic gases are given on the equation sheet but what about for diatomic and nonlinear? Are we expected to know them for the midterm?

Minh Ngo 4G

Can someone explain this concept to me please? Like why and when are we using it? I know it has something to do with the probabilities of how the atoms can arrange but other than that, I don't get all the calculation and its meaning

Minh Ngo 4G

Elizabeth Harty 1A wrote:In the thermodynamics outline what does the bullet point "calculate enthalpy changes from calorimetric data" mean?

I think he is referring to deltaH rxn so like the 3 ways and the q=mcdeltaT

Minh Ngo 4G

Both of them would have to be given to you if they are needed in a problem. R is the gas constant and there are different constants depending on their unit. c is the (specific or molar) heat capacity, which is different for each substances or element etc.

Minh Ngo 4G

Enthalpy is the heat transferred. So change in enthalpy, delta H, is the change in heat during a rxn. A negative value means the rxn gives off heat, hence exothermic. Simillarly, a positive value means the rxn requires heat, hence endothermic.

Minh Ngo 4G

Extensive property is anything that can change, mainly based on your mass. Such as weight, the more you have of something, the "more" weight you have. Other examples would be volume or length

Minh Ngo 4G

a) Calculate the work that must be done against the atmosphere for the expansion of the gaseous products in the combustion of 1.00 mol C6H6 (l) at 25C and 1.00 bar. So for this question, I first use PV=nRT (R= 8.314 x 10^-2) to get V. I got V = 24.8L. Then convert P into atm (1 bar = 0.987 atm) and ...

Minh Ngo 4G

A piston confines 0.200mol Ne(g) in 1.20L at 25C. part (a)The gas is allowed to expand through an additional 1.20L against a constant pressure of 1.00 atm. b) The gas is allowed to expand reversibly and isothermally to the same final volume. So I want to calculate the work done for part b but I don'...

Minh Ngo 4G

Standard enthalpies of formation is when all the R are in their most stable state, forming P

Minh Ngo 4G

If you are asking for when to use what, it is obviously going to depend on the information you are given. However, as of like theoretical accuracy, bond enthalpies method is the least accurate because the value that are given to you are the average bond enthalpies, not exact. So it would be off comp...

Minh Ngo 4G

System is the one that you are focusing on. In most cases, it is the chemical rxn

Minh Ngo 4G

Because the energy it takes for liquid to become steam require more energy. So when the steam touch your skin, the steam has to condensate, meaning turns back into liquid phase and when it does that, it releases all the energy

Minh Ngo 4G

Because all the energy are being used to either break a bond or form a bond, thus no energy is used for heating up the material

Minh Ngo 4G

You need the mass to use q=mc(delta)T

Minh Ngo 4G

I think right now it is 4C and 4E

Minh Ngo 4G

I highly doubt that we'll be required to memorize enthalpies of formation, so I assume they'll be given on a test. This would be a good question for Dr. Lavelle himself. Remember which ones can be cancelled because they're in their base state, though. You might have to memorize those, but I believe...

Minh Ngo 4G

Hi, for questions such as 4D.9, are we supposed to Google the delta H for each compound?? I can't seem to find any table or something like that in the book? Is that the case for all the other problems that want us to find deltaH too?

Minh Ngo 4G

Weak acids and bases are just those not considered strong. I think you just need to memorize them. The strong acids include most halogens and some oxoacids like HCl, HI, HBr, HClO4, HNO3, and H2SO4. The strong bases include Group 1 and heavy group 2 hydroxides, like LiOH and B(OH)2. Thank you for y...

Minh Ngo 4G

Rank the following solutions in order of increasing pH: A) .00005 M HCl B) .2 M CH3NH3Cl C) .2 M CH3COOH D) .2 M C6H5NH2 justify your ranking. So for this one, I believe we are using the ICE box for the weak ones but (might be a silly question) but how would I know if those solutions are weak bases ...

Minh Ngo 4G

Basically the digit before the “.” doesn’t count as sig fig. For example, pH =3.98 only has 2 sig fig. You count after the decimal place. However, the concentration of OH or H3O follow the usual rule.

Minh Ngo 4G

Because your Ka is less than 10^-3. Since Ka then is so small, you can ignore it for the denominator

Minh Ngo 4G

When something is disturbing your chemical equilibrium and you want to see what happen next

Minh Ngo 4G

Reaction Quotient, Q, tells us the direction the rxn will shift in order to achieve equilibrium

Minh Ngo 4G

If all the reactants are gas then use Kp. You can calculate Kc for gas too but they would have to explicitly tell you so

Minh Ngo 4G

So the question ask for the pH of 0.15M H2SO4. Since it is a strong acid, I just take the negative log of it and gets 0.82 as the answer. However, the back of the book's answer is 0.80. Did I do something wrong?

Minh Ngo 4G

I didnt get the same ans as the back of the textbook either! For i i got -0.176 for pH instead of 0.176. There's probably a typo somewhere (??!), I hope

Minh Ngo 4G

It basically says that the rxn likes to be in its equilibrium state and it will always try to be(adjust) in its equilibrium state. Therefore, when you change the rxn in someway such as adding a reactant or increasing the volume, etc. the rxn would shift to the corresponding side to adjust back to it...

Minh Ngo 4G

If we add N2, then NH3 would increase since the rxn wants to maintain its equilibrium state. In order to make NH3, you need both N2 and H2 so your H2 concentration would decrease as the result.

Minh Ngo 4G

Strong acids or strong bases disassociate completely in rxn. Therefore if you want theirs concentration, you only need the concentration of the acid/base since they are also the concentration of your H+ and OH-. However, weak acids/base do not disassociate completely. That’s when your ICE table come...

Minh Ngo 4G

Only use aqueous and gas for K. You probably misunderstood aqueous for liquid.

Minh Ngo 4G

It would make the rxn shifts to one way or another but K is remains unchanged

Minh Ngo 4G

K is the value of molarity of P/R at equilibrium while Q is not at equilibrium (usually at initial condition). They are, however, calculated the same. Molarity or partial pressure ratio of P/R

Minh Ngo 4G

R is a gas constant so it is given. There are multiple R correspond to the different units so choose the one that fits your data the most! And all of the ones we need are on the equation sheet

Minh Ngo 4G

Taking them out doesn’t mean there’s nothing there. Since K is Product over Reactant, you have to indicate that there is Product, so you put 1 there. If you just put [A][B], it would mean that those are the concentration of your products

Minh Ngo 4G

Since K is just Product/ Reaction. A large K means a large amount of Product, so the rxn would mainly producing product or shifting to the right

Minh Ngo 4G

If everything is gas then you use P but otherwise, use concentration […]

Minh Ngo 4G

Yes you would look at the same characteristics to determine the strength of a base. Essentially a stronger base, wants to accept a proton easier, and will give off more hydroxide ion. So how would that work though? Cause like for acid, you look at the strength between H and A (the bigger the A, the...

Minh Ngo 4G

How do you determine the relative strengths of 2 bases to see which one is stronger? I know for acids, you look at bond length and the anion’s stability so does the same logic apply to bases too?

Minh Ngo 4G

You would look at bond length first. If it’s the same then you look at the resulting anion’s stability (electronegativity, resonance...)

Minh Ngo 4G

For 1E.5 part d, the problem asks to tell whether a statement is true or false. d) Zeff e for an electron in a p-orbital is lower than for an electron in an s-orbital in the same shell I approach this question by thinking that since both are on the same shell, their distance from the nucleus are the...

Minh Ngo 4G

For question such as 6C.21, are we expected to know the formula trichloroacetic acid or formic acid?
I know he says that naming things is not on the test but in class, he did go over it so is it fair game?

Minh Ngo 4G

Usually the more resonance it has the more stable it is since electrons are "floating" around.

Minh Ngo 4G

Whatever your acid is in the reactant side, it would become your conj. base in the product side. Let's say your acid is HBr, after it gives of the H+, Br- is your conjugate base
And of course, vice versa with base and conj. acid

Minh Ngo 4G

You are trying to make all the formal charges of each element equal to 0. Of course, if the compound as a whole has a negative or positive charge, at least one of them have to have a charged. When that happens, put the negative charge on the more electronegative one.

Minh Ngo 4G

It would be a smart move to do so!

Minh Ngo 4G

Since in both HBrO and HClO has the same OH bond, you have to look at the anion after the H+ has been removed. Then, the one with the element that is more electronegative is the stronger acid. Why? Because higher electronegativity means that element would pull on the electron from the partially nega...

Minh Ngo 4G

I think memorization is the best way

Minh Ngo 4G

The way I do it is to look which compound in the products side have gained or lost a H+. If it has gained then the similar reactant must have been a base and vice versa

Minh Ngo 4G

Lewis acid is a compound that accepts electrons while lewis base donates electron

Minh Ngo 4G

Single bond: 1 sigma
Double: 1 sigma and 1 pi
Triple: 1 sigma and 2 pi

Minh Ngo 4G

Bronsted acid is a compound that donates H+ in solution while Bronsted base is a compound that accepts the H+

Minh Ngo 4G

For question 9C.3, the problem tells us to use the table to write the formula for the coordination com#. My question is on the final exam, if we have one of these questions, are we gonna be given the table or do we have to memorize it?

Minh Ngo 4G

Angela Prince 3B wrote:Do coordinate covalent bonds happen only in transition metals?
And does it occur in all transition metals or are there exceptions?

I think just in transition metal

Minh Ngo 4G

Whether it dissociate completely in water or not. Strong acid theoretically would dissociate 100% in water

Minh Ngo 4G

It’s fair game since he did talk about it in class. Cis means the dipole moment cant cancel each other out while trans they do

Minh Ngo 4G

They are the same shape

Minh Ngo 4G

Yes since different atoms have different strengths or forces

Minh Ngo 4G

Minh Ngo 4G

Yes, you are correct when saying that the dipole is based on the distance so that's why structure I is greater. Since the 2 Cl- with the same (-) charge repel each other more when they are closer together, creating a stronger dipole moment. If the 2 Cl- are far from each other (II), then the repulsi...

Minh Ngo 4G

Draw the Lewis structure and predict whether each of the following molecules is polar or non-polar? a) CH2Cl2 For this one, correct me if I am wrong please but when I draw the Lewis structure out, C is the central atom. From here, I can either place the 2 Cl opposite each other on the axial position...

Minh Ngo 4G

Could someone explain the shape and bond angles of C2H4? I don't understand why it's trigonal planar. Also, I don't understand the answer for the shape and bond angles of N2H4. If someone could explain that as well that would be great! As of shape and bond angles of N2H4, the lewis structure for it...

Minh Ngo 4G

C2H4 is trigonal planar around the C atom because it bonds to 2 H and double bond to another C, therefore it has 3 e- density around it => trigonal planar.

Search found 137 matches