CHEMISTRY COMMUNITY

Adriana Rangel 1A

^@Nicole No, phase changes such as vaporization and melting are endothermic ( you need to add heat to an ice cube in order for it to change phase to liquid) while freezing and condensation are exothermic (I remember it as think of a glass of water. If you somehow took out all the heat in the water i...

Adriana Rangel 1A

When using the Nernst equation when do you use LnQ vs Log Q? I know the equation has Ln Q but some work I have seen has LogQ

Adriana Rangel 1A

I found the equilibrium constant to be K=6.14 x 10^-6. But it asks you to find Ka? I don't understand what Ka is supposed to represent and the solutions says its 2.5x10^3 What is Ka?

Adriana Rangel 1A

14.55 A 1.0 m NiSO4(aq) solution was electrolyzed by using inert electrodes. Write (a) the cathode reaction; (b) the anode reaction. (c) With no overpotential or passivity at the electrodes, what is the minimum potential that must be supplied to the cell for the onset of electrolysis? I don't rememb...

Adriana Rangel 1A

How do you know which Au is going to be the anode and which one is going to be the cathode? I thought in lecture today Lavelle said that the half-reaction with "more positive/less negative" value would be reversed to become the anode? So why does the solutions manual make: Au3+ (aq) +3e- -...

Adriana Rangel 1A

Write balanced half-reactions for the redox reaction of an acidified solution of potassium permanganate and iron(II) chloride.

Why doesn't the solutions manual include potassium or chloride ? I am confused

Adriana Rangel 1A

So on the equation sheet and in the textbook, it says the cell formula for calculating cell potential is Eo= Eo (right electrode, cathode)- Eo (left electrode,anode)?? But then on other websites it says to find the standard cell potential you ADD them not subtract them ? Look at these websites: http...

Adriana Rangel 1A

Ok and then what???

Adriana Rangel 1A

I don't understand how to find the half reactions when given: AgBr(s) --> Ag+(aq) + Br-(aq), a solubility equilibrium. I understand that at a cathode (reduction)occurs and anode (oxidation) occurs. I just don't understand the books explanation? Does Ag and Br in AgBr(s) each have a charge of 0? Or d...

Adriana Rangel 1A

8.57 Determine the reaction enthalpy for the hydrogenation of ethyne to ethane, C2H2(g) +2 H2(g)--> C2H6(g), from the following data: DeltaHc(C2H2, g) = -1300. kJ·mol1 DELTA Hc(C2H6, g) = -1560. kJ·mol1 DELTA Hc(H2, g)= - 286 kJ·mol1 So I used the formula: DELTA H rxn= Sum of H produc...

Adriana Rangel 1A

A) Iodine vapor or bromine vapor?
How can you determine which substance has a higher entropy since they are both in the same state?
C) What is meant by "polymerization of ethylene"? How does knowing this information help you determine which has the higher entropy value?
Thanks!

Adriana Rangel 1A

Could someone explain to me very simply what they are asking, and what the solution is telling me to do. I do not understand at all

Adriana Rangel 1A

For 15.51, I don't understand why the overall reaction ( 2NO+Br2 --> 2NOBr) is considered to be bimolecular according to the solutions manual? Wouldn't it be trimolecular, which makes the rate law= k[NO]^2[Br2] ? I thought you include the coefficients when writing a rate law for a reaction and also ...

Adriana Rangel 1A

Hi Cameron,
K can be altered by change in energy or activation energy.

Your friend,
Adriana

Adriana Rangel 1A

Hello, I am confused as to what this mechanism/ equation is used for? Could someone explain this to me simply? Thank you

Adriana Rangel 1A

What are the most important concepts we need to know about these two theories? Thank you!

Adriana Rangel 1A

This was a self-test question in the book:
How does a homogeneous catalyst affect (a) the rate law; (b) the equilibrium constant?
Could someone please explain in simple terms? Thank you!

Adriana Rangel 1A

So I know that catalysts by definition lower the activation energy of a reaction and are not consumed by the reaction itself. However, in a homogeneous reaction (say its liquid catalyst in liquid reactant) the book says that the catalyst is absorbed by the liquid. How come then the catalyst isn't co...

Adriana Rangel 1A

How do you know if you have to solve for k or any variable really to use "[A]= -kt + [A0]" vs "ln[A]=-kt+ln[A0]" ??

Adriana Rangel 1A

In part C, why isn't [A]t going to be equal to .034? Why do we have to multiply it by two and then subtract that from the concentration of [A] 0 ?

Adriana Rangel 1A

Could someone explain for parts a and b how do they know which experiments is ok to solve for the rate and order? Does it matter which ones you use?

Adriana Rangel 1A

So since the formation of HI is second- order wouldn't the formula for finding the rate = k x concentration^2?
The solutions says " From the units of the rate constant, it follows that the reaction is second-order; therefore, rate= k [H2] [I]

Adriana Rangel 1A

Hello this is a stupid question but (hey it'll be easy points for someone to answer!) Ok for 15.3 part b when you are finding the rate of formation of O2, the solutions manual has O2= (6.2 x -3) (1 mol O2/ 2 mol NO2) So is the general structure for that formula a rate law ? Why do they multiply the ...

Adriana Rangel 1A

Ok thank you but how do you know Mn changes to 2+ ??

Adriana Rangel 1A

When acidifying the potassium permanganate the solutions manual doesn't include potassium ? What happened to it? And chloride in iron chloride?
Also, how do you know Mn is +2 in the product side??

Adriana Rangel 1A

For example 14.13 part b when writing the cell diagram how do you know to include Platinum since the problem didn't indicate you needed it?

Adriana Rangel 1A

I balanced the elements and have: H20 + O3 --> O2 + 2OH But the solution manual has + 2e- on the left side. If both O3 and O2 have a neutral charge how do you know which is oxidized/reduced?? Shouldn't the two electrons be on the right side because O3 has a charge of -6 and O2 has a charge of -4 (-4...

Adriana Rangel 1A

The following redox reaction is used in acidic solution in the Breathalyzer test to determine the level of alcohol in the blood.. Hi I know this is going to be a stupid question for y'all but I don't understand how by looking at the reaction you know that Cr is reduced and C is oxidized. Why isn't H...

Adriana Rangel 1A

Can someone explain simply what SHE (standard hydrogen electrodes) are and how exactly does it work? I'm reading about it in 14.6, page 578 but I am very confused. Thank you

Adriana Rangel 1A

I think the phase depends on if it is ionized or not. Ionized elements (they have a charge) are written (aq), where an element in its neutral state has its standard state. For example the oxidation of hydrogen would be H2 (g)/ H+ (aq).
Hope this helped!

Adriana Rangel 1A

Hello can someone please explain to me what I just read in simpler terms please (page 572): "There is a hidden assumption in the derivation of Eq. 1. Maximum nonexpansion work is obtained when a cell is operating reversibly. Therefore, Eq. 1 applies only when the pushing power of the cell is ba...

Adriana Rangel 1A

Could someone explain this please? It is 3H from the practice midterm

Adriana Rangel 1A

Irreversible processes have increasing delta S, so I think it depends on what your temperature and enthalpy are?

Reversible processes have DELTA S=0, so a reversible process will be spontaneous if it is exothermic.

I hope this helped!

Adriana Rangel 1A

Hi everyone, I am making a little table for thermodynamic definitions and including examples and the equations to use. I am mixing up the definitions and get a little confused on when to use which equation and also how to identify in a word problem what kind of thermodynamic equations are being done...

Adriana Rangel 1A

Some entries for Sm in Appendix 2A are negative. What is common about these entries, and why would the entropy be negative?
I read the book's explanation and I do not understand what they are talking about when they mention aqueous solutions and reference points

Adriana Rangel 1A

9.81 Which is the thermodynamically more stable iron oxide in air, Fe3O4(s) or Fe2O3(s)? Justify your selection. The solutions manual states that Fe2O3 is more stable but I don't understand the explanation. I thought that since Fe3O4 has a higher entropy (it has more particles), than Delta G is more...

Adriana Rangel 1A

9.69 Coupled reactions are used in organisms to drive important biochemical processes. Individual chemical reactions may be added together to form a net reaction, and the overall reaction Gibbs free energy is the sum of the individual Gibbs free energies of reaction. For example, ATP is the primary ...

Adriana Rangel 1A

I'm going to use 55 part a to answer your question. So you CAN find ΔH°using: ΔH°reaction= sum of ΔH°products- sum of ΔH°reactants . If you plug in the known standard enthalpy values into the equation, you'll get: ΔH°products= -46.11 kJ/mol -[0+0]. So since the known ΔH° values for H2 and O2 you don...

Adriana Rangel 1A

9.55 Write a balanced chemical equation for the formation reaction of (a) NH3(g); (b) H2O(g); (c) CO(g); (d) NO2(g). For each reaction, determine H, S, and G from data in Appendix 2A When I go to the appendix and I'm looking at the DELTA H standard for NH3, how do I know whether to use the NH3...

Adriana Rangel 1A

When using the Ideal Gas Law to find the number of moles, how does one know for V which volume to use (initial or final?)

Adriana Rangel 1A

Hello, number 43 I thought we were supposed to use Cp because the question asks you to find entropy change with a change in temperature and constant pressure. Using the formula Delta S= nCln (T2/T1), the solution manual uses the heat capacity of water instead of the (5/2R) for C. Why is that ???? Ho...

Adriana Rangel 1A

"Container A is filled with 1.0 mol of the atoms of an ideal monatomic gas. Container B has 1.0 mol of atoms bound together as diatomic molecules that are not vibrationally active. Container C has 1.0 mol of atoms bound together as diatomic molecules that are vibrationally active. The container...

Adriana Rangel 1A

"The enthalpies of reactants and products are both affected by a temperature rise, and the difference between their values changes only a little with temperature"
Can someone explain this to me please

Adriana Rangel 1A

I thought an exothermic process would lead to a decrease in entropy due to the fact that it is losing heat. When a substance loses heat then wouldn't it go from gas to liquid to solid and therefore entropy is decreasing?

Adriana Rangel 1A

I saw somewhere that reactions with a negative enthalpy change are exothermic and thus more favorable than reactions with a positive enthalpy change (endothermic). But according to the 2nd Law of Thermodynamics (states that reactions tend to go from low to high entropy) then why is a reaction with a...

Adriana Rangel 1A

Hello I am reading in 9.4:
"2. At the temperature of a phase transition, the transfer of heat is reversible."
Can someone explain to me what is meant by this please?

Adriana Rangel 1A

I think Delta H is going to be 0 because there is no transfer of heat taking place.

Also this link I found helpful
https://chemistry.stackexchange.com/que ... tic-system

Adriana Rangel 1A

In 9.3, page 325 it reads: "To calculate a change in entropy for a process, we find a reversible path between the initial and final states. It is immaterial whether the actual process is irreversible or reversible. Because entropy is a state function, the change for that path will be the same a...

Adriana Rangel 1A

Hello, I was not able to go to lecture today. Would someone be able to share their notes or summarize what we learned about in today's lecture (1/29/18)?
Thank you :)

Adriana Rangel 1A

Why are these equations derived?

Adriana Rangel 1A

I know about the bomb calorimeter, which measures the heat of a reaction via combustion (burning an object). Is there another kind we learned about?

Adriana Rangel 1A

Hello, for today's lecture could someone summarize what Lavelle was talking about with the integral equations, and where can we find that section in the book?
Thank you :)

Adriana Rangel 1A

What is the difference between heat capacity and specific heat ?

Adriana Rangel 1A

Where can we pick up last quarter's final

Adriana Rangel 1A

So for part a) for the molar heat capacity of a monatomic ideal gas at constant pressure is Cp,m= 5/2 R. Why? Where did this value come from? ( in the solutions I see it is 20.8J/mol x C) ?
Also same for part b) the molar heat capacity of a monatomic ideal gas at constant value is 3/2R. Why??:???????

Adriana Rangel 1A

What does it mean by not depending on "paths taken"?

Adriana Rangel 1A

Can someone please explain what exactly is a state function? I've found definitions online but I still don't get it. And why is enthalpy a state function and heat is not a state function?
Thank you

Adriana Rangel 1A

I am pretty sure that you have to memorize them. For example the noble gases are gas in standard state with the exception of Br2 (liquid) and Iodine (solid). If it was an element we don't usually talk about, I think they would give us on the test

Adriana Rangel 1A

Could someone explain to me in simple terms so I can understand what is standard enthalpy of formation? I've read about it but I don't get it??? Or any videos or links that would help explain it to me pls

Adriana Rangel 1A

So why is that that the values for boiling and freezing point are expressed in Kelvin while Delta H fus and Delta H vap are expressed in kJmol -1???

Adriana Rangel 1A

In the book chapter 8.11, there is a part: The difference in molar enthalpy between the vapor and the liquid states is called the enthalpy of vaporization... The enthalpy of vaporization of most substances changes little with temperature. *** For water at its boiling point, 100 C, Hvap 40.7 kJm...

Adriana Rangel 1A

So the equation for Cv= Delta U/ Delta T and the equation for Cp= Delta H/ Delta T My question is: how come in the equation for Cv it has Delta U (change in internal energy) while the equation for Cp it has Delta H (change in enthalpy)? How do those differences help determine Cv vs Cp? I think if so...

Adriana Rangel 1A

Hello, I do not understand what Lavelle was doing with the Lewis structures and bond enthalpy in class today (1/10) . Could someone please explain ?

Adriana Rangel 1A

how do you know ba(oh)2 is a small base

Adriana Rangel 1A

Calculate the initial molarity of Ba(OH)2 and the molarities of Ba2+, OH- and H3O+ in an aqueous solution that contains .43g of Ba(OH)2 in .100L
I do not understand how to begin this problem. Please help

Adriana Rangel 1A

Ok so I understand that: -An acidic oxide is an oxide that reacts with water to form a solution of a Bronstead acid. (Co2+ H2CO3) -A basic oxide is an oxide that reacts with water to form a solution of hydroxide ions -Amphoteric are substances that react with both bases and acids How can I determine...

Adriana Rangel 1A

Table 12.2 and 12.3 lists basicity and acidity constants for acids and bases. Do we need to know these constants for the final or would they be given if we need them?

Adriana Rangel 1A

Hi I'm reading through the book right now and I saw this on page 472. It doesn't provide an answer but I was wondering if this is important? Thank you

Adriana Rangel 1A

Or is water JUST amphiprotic? Also can someone distinguish/explain the difference between the two more clearly? Thank you!

Adriana Rangel 1A

Between figures 1 and 2 I understand they are polar because the Cl creates dipole moments. Between the two figures, how do you determine which one has the larger dipole moments?

Adriana Rangel 1A

13. State whether the equilibrium shifts towards products, reactants, or neither when the given change occurs. 2 HI(g) + Cl2(g) ⇌ 2 HCl(g) + I2(s) delta H° = -238.0 kJ.mol-1 i. The volume of the system is compressed. ii. The temperature of the system is decreased. A. i = Products, ii = Products B. ...

Adriana Rangel 1A

Hello, Ok So you first calculated everything to molarity values which is good. You should have gotten the concentration of H20 to be .05 M. So you are given an initial concentration value of H20 and equilibrium concentration value of H2. Kc= [H2][CO]/[H20] (Omit C in your setup as it is a pure solid...

Adriana Rangel 1A

That was helpful thank you!

Adriana Rangel 1A

yes ^

Adriana Rangel 1A

27. A mixture of 2.5 moles H2O and 100 g of C are placed in a 50 L container and allowed to come to equilibrium subject to the following reaction: C(s) + H2O (g) ⇌ CO (g) + H2 (g) The equilibrium concentration of hydrogen is found to be [H2] = 0.040 M. What is the equilibrium concentration of water,...

Adriana Rangel 1A

^ No, in the problems we've been doing in the book, partial pressure from Kp is in atm not Pascals

Adriana Rangel 1A

27. For a reaction with K > 1 what do we know? I put B. The initial concentration of product(s) is higher than the initial concentration of reactant(s). I understand that K>1 means that the reaction lies to the right because then the initial concentration of products must be greater than initial con...

Adriana Rangel 1A

A ligand (polydentate) can bond 2 to 9 max. To determine the number of binding sites a ligand has, count the number of atoms that have lone pairs and can act as donor atoms. For example, if there are two donor atoms then it has two binding sites and thus is a bidentate ligand (like ethylenediamine)

Adriana Rangel 1A

I understand that a complex with coordination number 4 can either be a tetrahedral or square-planar complex. How can you know which one it will be exactly? I read the book definitions: -Tetrahedral complex-"the four ligands are found at the vertices of the tetrahedron, as in the [CoCl4]^2-"...

Adriana Rangel 1A

I understand that a polydentate ligands are able to occupy more than 1 binding site simultaneously. How can you determine if a complex is a polydentate and if so, the type (bidentate, tridentate) and if it will form a chelate? I already memorized the ones mentioned in our book such as EDTA and theyl...

Adriana Rangel 1A

So I drew the Lewis Structure for a) CH2Cl2 and drew it out with C as the central atom and two Cl attached to it (single bond) and two H atoms attached to it (single bond). How can I predict polarity? I know that a molecule is nonpolar when the dipoles cancel each other out and polar when the dipole...

Adriana Rangel 1A

I understand what sigma and pi bonds are, but there is an example in the text asking how many sigma and pi bonds there are in a) CO2 and b) CO?
I do not understand how I can determine the number of sigma and pi bonds there are in these molecules.

Adriana Rangel 1A

So I have a general understanding of what a sigma and pi bonds are. Correct me if I am wrong but what I understand so far is: A sigma bond forms when the electron orbitals from different atoms overlap along the internuclear axis. They are cylindrically symmetrical with no nodal planes containing the...

Adriana Rangel 1A

Nonmetal atoms in period 3 or later can expanded their valence shells because they have empty d-orbitals where they can store electrons.
For example, Sulfur e-configuration is: [Ne] 3s2 3p4. However, it has a 3d orbital available for bonding

Adriana Rangel 1A

So 3.9 asks "Which M2+ ions (where M is a metal) are predicted to have the following ground-state electron configurations: a) [Ar] 3d7 b) [Ar]3d6 and so on. So for a) I got Co2+ and b) Fe2+ because those are the neutral electron configurations for those metals. And then I check the answer in th...

Adriana Rangel 1A

Hello, I am confused for question: 3.5 Give the ground state electron configuration expected for each of the following ions: a) Cu+ b) Bi3+ c) Ga3+ d) Tl3+ So originally I thought the question was asking me what is the regular configuration for them since it said ground state (so I wrote the neutral...

Adriana Rangel 1A

Hello, I am reviewing for tomorrow's test and I looked on the Chapter 2 Outline for what we should know. One of the points we should know states "Describe interpretation of atomic orbitals in terms of probability". Is a fair statement to describe atomic orbitals in terms of probability: &q...

Adriana Rangel 1A

So this statement found in the book (2.7 page 49) "Hydrogen occupies a unique position in the periodic table. It has one s-electron, and so it belongs in Group 1; but it is also one electron short of a noble-gas configuration, and so it can act like a member of Group 17". I am confused as ...

Adriana Rangel 1A

Hi, I think you only need to understand the theory part of the equation and NOT how to calculate using it. So the most important thing to understand about Schrodinger's is that it calculates the wavefunction for a given particle (electron) and corresponding energy. What this means is that the wavefu...

Adriana Rangel 1A

For sure, H is Planck's Constant which is 6.626 x 10^-34 Jxs^-1. It relates the energy in one quantum (photon) of electromagnetic radiation to the frequency.

Adriana Rangel 1A

"In order to find the speed, you must use the values given to you and plug it into the Heisenberg equation. The only value you should be missing is speed since for the momentum part of the equation is equal to (mass)(velocity). The rest of the equation is either constants or given to you in the...

Adriana Rangel 1A

You are caught in a radar trap and hope to show that the speed measured by the radar gun is in error due to the Heisenberg uncertainty principle. If you assume that the uncertainty in your position was +/- 5 m when your speed was measured, and that the car has a mass of 2150 kg, what is your calcula...

Adriana Rangel 1A

Hi, I am a bit confused on what is Rydberg's Constant, is it 3.29x10^15? Because I watched a video on Khan Academy and R is 1.097x10^7? And when you google "Rydberg's Constant" that is what comes up

Adriana Rangel 1A

The tests are going to begin starting next week in discussions 10/17. So if your discussion is next Wednesday, it'll be then. If your discussion is on Tuesday, it'll be then

Adriana Rangel 1A

Hello I am having trouble with this question and would like some guidance please. 29. B. How much energy is required to remove an electron from one sodium atom? (Work function for sodium is 150.6 kJ.mol-1. ) Hello, so I understood how to do the previous question and found the kinetic energy of the e...

Adriana Rangel 1A

I took high school chemistry my sophomore year of high school and have not taken AP Chemistry. Since I am a bit "rusty", something that helped me review what I learned about chemistry was outlining the chapters, completing the modules, doing the homework problems, and going to the night st...

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