CHEMISTRY COMMUNITY

Christineg1G

For question 4 part b, how do you get the two equations for k1 and k2?

Christineg1G

Can someone please explain the math steps involved to get the correct answer for this problem? I understand the set up, just not the steps you need to take to get the right answer of 0.42M. Thank you! Well first you’d multiply both sides by -2/0.0257 ( the reciprocal of the constant on the left sid...

Christineg1G

I think the mistake you did was using a wrong value in the equation, instead of using 0.257/2, you should've used 0.0592/n, where n is the number of mole of electrons. That change in value shouldn't matter because you should still receive the same answer. I'm just having trouble with the calculus p...

Christineg1G

Can someone please explain the math steps involved to get the correct answer for this problem? I understand the set up, just not the steps you need to take to get the right answer of 0.42M. Thank you!

Christineg1G

How do you identify catalysts and intermediates in a reaction?

Christineg1G

Molecularity would be the number of molecules or species in an elementary step, and also determine the rate. Rate law for each elementary steps comes directly from molecularity.

Christineg1G

Activation energy, Ea, is the energy that's needed to get over an energy barrier during a transition step. The free energy of activation refers to Gibbs free energy, and it is what is used when we are looking at the energy barriers of chemical reactions/ allows us to determine how likely a reaction ...

Christineg1G

k' is the rate of the reverse reaction. kr is the rate constant of a reaction that depicts the rate of a chemical reaction.

Christineg1G

As far as I know, review sessions don't get Bruin casted. But, like the previous post said, the worksheet and only the answers (no explanations or work) do get posted on Chemistry Community.

Christineg1G

I don't think that we will be asked to know how to derive the different equations given in this unit, but it is important and helpful to see the steps that it takes to get to a specific equation.

Christineg1G

Gibbs' free energy corresponds to the amount of work that can be performed in a given system. A positive delta G means that the system is not spontaneous, and a negative delta G means that the system is spontaneous.

Christineg1G

For 6L.7 C where do KOH(aq) and Ni(s) come from ? The half-reactions look like this:
Cd(OH)2(s)+2e- →Cd(s)+2OH^-(aq)
E°(anode)=-0.81V
Ni(OH)3(s)+e-→ Ni(OH)2(s)+OH^-(aq)
E°(cathode)=+0.49V

Cell Diagram: Cd(s)|Cd(OH)2(s)|KOH(aq)||Ni(OH)3(s)|NI(OH)2(s)|Ni(s)

Christineg1G

it might help to see a visual of deriving the Nernst Equation!

Christineg1G

Typically, K doesn't have units since it is a ratio of similar quantities rather than specific concentrations.

Christineg1G

You should determine n from the number of moles of electrons that are present in your half-reactions. It should be the same number for both half-reactions.

Christineg1G

Yes, Test 2 would be starting Tuesday, March 3 in discussion sections.

Christineg1G

From my experience in the 14 series, Dr. Lavelle doesn't offer extra credit opportunities in his courses.

Christineg1G

For homework 8, I would suggest doing any of the problems from outline 5 (electrochemistry and its applications) since those topics are what we have been covering this past week in lecture.

Christineg1G

The Nernst equation can be used to quantitatively determine the direction of electron transfer under non-standard conditions. Also, it has an important relation in determining a reaction's equilibrium constants and concentration potentials.

Christineg1G

Official study guides haven't been made for this class, but I would recommend making your own with the notes from class as well as going to multiple peer learning sessions since they give worksheets/additional notes.

Christineg1G

Van't Hoff Equation is derived from ∆G°=∆H°-T∆S°and ∆G°=-RTlnK.

Christineg1G

GFolk_1D wrote:Hi! Will there still be UA review sessions today despite the holiday?

Dr. Lavelle sent an email out yesterday saying that all peer learning sessions are cancelled Sunday and Monday, and everything will resume back to usual on Tuesday.

Christineg1G

My TA said that any homework problems from outline 4 should be okay to turn in since we are barely starting outline 5 this week.

Christineg1G

I found this comment in a previous Chemistry Community post and thought it might be helpful to answer your question: "The standard enthalpy of formation is at 25C, if the temperature of the reaction is different, then you can't use the listed delta G values to calculate G. Then you would use th...

Christineg1G

W, or degeneracy, in the Boltzmann formula would be defined as the number of ways that are possible to achieve a given energy state.
W would equal (# states)^(#species).

Christineg1G

I think the derivation of the formula was done to show how a specific formula that we would need to know resulted from it. So, I don’t think we’ll need to know how to derive equations.

Christineg1G

Yes, conversions that we would to do on the midterm are given on the formula sheet.
I would recommend looking at the constants and equations sheet on Dr.Lavelle’s website to familiarize yourself with what you will be given.

Christineg1G

For an isothermal reaction, the temperature is constant so the internal energy would also be constant (delta U=0).

Christineg1G

Enthalpy would be defined as the study of heat absorbed or released during chemical reactions and physical changes.

Christineg1G

AGaeta_2C wrote:Will the review session on that day be covering past exam problems?

On Dr. Lavelle’s website it says that there will be a small group Q&A on the day of the exam.
Dr. Lavelle will be going over past exam questions today during lecture.

Christineg1G

I would suggest going to the midterm review sessions that Dr. Lavelle has organized. These are helpful, taught by TAs and UAs, and each section has a specific topic that they cover which is extremely convenient.

Christineg1G

To add onto previous posts, in reversible expansion, the equilibrium isn't affected at any stage and the process is slower. While in a irreversible expansion, equilibrium may exist only after completing the process and the process is much quicker.

Christineg1G

W=0 when the volume of the work done on a gas is constant. Q=0 when there is no heat exchanged (happens if the container is thermally insulated).

Christineg1G

You should've got your test back in discussion during week 4, but if you didn't I would suggest emailing your TA or asking them in discussion about your test.

Christineg1G

Dr. Lavelle doesn't post answer keys for tests, but he does for the midterm. However, many TA's are willing to help you get clarification on the problems and understand how to do them.

Christineg1G

This week we are going over outline 3 which is thermochemistry. I would suggest doing homework problems that come from focus 4 in the textbook.

Christineg1G

A bomb calorimeter would be a isolated system that works at a constant volume where heat (energy) is exchanged and volume is constant (isochoric).

Christineg1G

For the standard enthalpy of reaction, the units would be kJ/mol.

Christineg1G

A bomb calorimeter is a constant volume calorimeter that is used to measure the heat of specific reactions.

Christineg1G

Although Lavelle said we can pick up the finals during week 3 from Young Hall 3034, I would recommend to go check to see if it’s available to pick up. I went around 8:40am and the office was open.

Christineg1G

How would you know when to use Ka x Kb= Kw when solving for pH? For example in 6D.17 (a) you would need to find the Kb value using Kb= Kw/Ka.
I know you would use it for finding the pH of salt solutions, but what are some indicators to help let us know that we need to use that constant?

Christineg1G

If we are given a problem and asked to calculate the pH, how would we know if we should follow the steps for calculating the pH of salt solutions (like finding the Ka value if we are given the Kb value) or just continue with the calculations and not solve for either Ka or Kb and just use the value w...

Christineg1G

If k<10^-3 you can attempt an approximation. To ensure the validity of your approximation, you should check by dividing the x value you received over the initial concentration. If this value is less than 5%, your approximation is valid.

Christineg1G

Exothermic reactions give off heat while forming product, and reactant formation will be favored. For exothermic reactions, you can picture heat as being a product and apply Le Chatelier's principle of what happens when you add product to a system. Therefore, increasing the temperature will shift th...

Christineg1G

An inert gas is another term for noble gas. Also, the addition of an inert gas, for example argon or krypton, to a reaction will have no effect on the system.

Christineg1G

Yes, when Q=K the solution has reached its equilibrium composition and doesn't change in either direction.

Christineg1G

pKa is the negative base-10 logarithm of the acid dissociation constant (Ka) of a solution and pKb is the negative base-10 logarithm of the base dissociation constant (Kb). pKa and pKb added together equals 14.

Christineg1G

For HW 5I.11 how would the concentration of SO2, O2, and SO3 be converted from nmol to mol. For example how is the concentration of SO2=1.20nmol converted to 1.20x10^-3 mol?

Christineg1G

What did Dr. Lavelle mean in lecture 1 today when he said that 10^-12 is actually and would be correct if it were written as 10^-7 for the concentration of H3O+?

Christineg1G

In addition to the post made before this, we also reviewed the meanings of neutralization (reaction between acid and base, product is salt and water), amphiprotic (proton donor and acceptor, like water), and autoprotolysis (proton transfer between same type of molecule).

Christineg1G

According to Le Chatelier's principle, removing NO will lead to the formation of more products. So to maintain equilibrium, the amount of NH3 will decrease. Hope this helps!

Christineg1G

You would use Le Chatelier's principle and know that if a reactant is increased, in this example being CO, the system will shift the equilibrium to the right towards the products, thus increasing the concentration of H2.

Christineg1G

For part (a) you should double check their I.C.E table as well as the expression for Kc which should be (N2O4)/(NO2)^2. After inputting the values from your I.C.E table into the Kc expression, you should be solving for the equation: 6.4x10^2 x^2 - 14x + 0.064=0. After you plug this equation into the...

Christineg1G

Equilibrium constants don't have units because we used the active masses of the substances, hence why they are unit less/eliminated from the equilibrium constant expression.

Christineg1G

Gases and aqueous solutions would only be used and considered in equilibrium expressions since the concentration of pure solids and liquids does not change.

Christineg1G

You would use the values of K in the table to determine the value of K for the reaction. So you would use K=377 for the expression 2BrCl<->Br2+Cl2 and K=4.0x10^31 for the expression H2+Cl2<->2HCl. You would then multiply the values of K1 and K2 to get your answer.

Christineg1G

Yes, you would include gases in equilibrium expressions, but you wouldn't include solids or liquids.

Christineg1G

K would be known as the equilibrium constant, Kc. K can also be used to calculate the partial pressure of a species at equilibrium, Kp. Q is the reaction quotient and it is used to determine which direction a reaction will proceed. Q or Qc or Qp are calculated the same way as K, but for Q, the react...

Christineg1G

When solving for pH, how would you know to use 2OH- or OH- in your calculations? Does it have to do with the present of an oxide?

Christineg1G

why is HClO2 stronger than HBrO2 ?

Christineg1G

From the pKa and Ka example done in lecture today, what factors would show that the Ka=6.0x10^-5 is a weak acid and that the equilibrium constant is small?

Christineg1G

Remember that the trends for electronegativity are that it increases as you go up a group and increases as you go across a period. To answer your question it will be: indium<tin<antimony<selenium

Christineg1G

Remember that bond length increases with atomic radius. So, the longer the bond is between two elements, the stronger the acid is. For example, H-I has the longest bond, so it will be the strongest acid. And vice versa, the shorter the bond is, the weaker the acid is. So, H-F would be the weakest ac...

Christineg1G

After your calculation, how would you determine which value is your pH and your pOH?
For example in 6B. 5D how would you determine that 3.15 is your pOH and 10.85 is your pH?

Christineg1G

The pH scale is most common between 0-14, but it is possible to go above or below 0 or 14. In the case of very acidic acids known as super acids, the pH scale goes below 0.

Christineg1G

How would you write the complete ionic equation for reactions?
For example, J.9C which asks to write the ionic equation and identify the salt produced from calcium hydroxide and bromous acid.

Christineg1G

The acid which would be HNO3 would be determined because acids usually have a H atom attached to it and you can see that the conjugate base to the HNO3 would be NO3-. As for the base, it will be HPO4^2- because you can see that its conjugate acid, which is H2PO4-, has a one extra H atom attached to ...

Christineg1G

How would you know that As2O3 and Bi2O3 are amphoteric, while BaO is basic?

Christineg1G

How do you find the charge of a ligand and also the oxidation state?

Christineg1G

Whatever is inside the brackets is directly bound to the transition metal and is in the coordination sphere. Hope this helps!

Christineg1G

Why would HI have a higher boiling point than HBr if HBr has a stronger dipole-dipole force? Would we go based off of the fact that HI is larger than HBr?

Christineg1G

What is the role of polarizability when determining higher and lower melting/boiling points of compounds?

Christineg1G

The wedge and dash would be used for VSEPR 3D structures of molecules. The wedge would be used to show that the element is sticking forward/coming towards us and the dash would be used to show that the element is pointing away from us/sticking back.
Hope this helps!

Christineg1G

In terms of repulsion and VSEPR, if a compound has lone pairs, should they always be placed in the equatorial plane instead of the axial plane?

Christineg1G

Naren_Ramesh_4D wrote:What room in Covel is the study session in?

The study sessions are in Covel 210

Christineg1G

Dipole moments will be drawn with the arrow pointing towards the partial negative element, rather than the partial positive.

Christineg1G

The final is cumulative, so yes I'm assuming hybridization will be covered on the final.

Christineg1G

Test 2 will start the week of November 19 in discussion.

Christineg1G

What do the series of short lines represent in bonds? For example, the hydrogen bonding in water example that was shown in class on Friday.

Christineg1G

A lewis structure is a dot diagram that shows the valence electrons as well as various bonds present in elements. While VSEPR is used to draw and name the different molecular shapes like bent, linear, tetrahedral, etc. These shapes are determined based off of the lewis structure and the VSEPR theory.

Christineg1G

A dimer would be two monomers that are linked together by intermolecular or covalent bonds and/or interactions.

Christineg1G

What are some key factors to remember when trying to distinguish between dipole-dipole, London forces, induced dipole-induced dipole, and hydrogen bonding?

Christineg1G

How do you know when to use the De Broglie equation or the equations for electromagnetic radiation like E=hV

Christineg1G

Orbitals within a shell are divided into subshells that have the same value of the angular quantum number l, which determines which orbital the element is in (s,p,d,or f). l=0, corresponds to the s orbital, l=1 corresponds to the p orbital, l=2 corresponds to the d orbital, and l=3 corresponds to th...

Christineg1G

After determining the number of valence electrons for each element, you would use the element with the lowest ionization energy. Also, know that H can never be the central atom.

Christineg1G

When writing shorthand electron configurations, you would use brackets to indicate the element that comes before the compound you are writing the configuration for. For example, for Sc you will write [Ar] 3d^1 4s^2

Christineg1G

Attending the review sessions are helpful as well if you need help on specific concepts/sections.

Christineg1G

Every student is assigned to a specific testing location based on their last name and if they're either in a 10am, 12pm, or 2pm lecture. The list is on the class website.

Christineg1G

I understand that we are supposed to use the indeterminacy equation to solve 13 (c), from the midterm practice, but when I input the values into the calculator, I am not getting the correct answer, which is supposed to be 2.8x10^-32 m. I have converted the 2.8 g to kg and am solving for delta x. Can...

Christineg1G

Would we be given a table on tests in order to determine electronegativity of elements?

Christineg1G

In homework problem 2A.13, part (b), why would a 3p orbital need to be removed from Cl in order to form a +1 ion?

Christineg1G

I had trouble figuring out why this occurred as well, but I found a post made by Dr. Lavelle a few years ago on Chemistry Community stating, "It seems that the correct answer is based off molecular orbital arguments that are outside of the scope of this course."
Hope this helps!

Christineg1G

I recommend taking it step by step or by portions because this will ensure that the correct atoms as well as the correct number of atoms will be bonded with each other. You can also take a look at the solutions manual for help with drawing the lewis structure. Hope this helps!

Christineg1G

I believe it will be the same as our first test, where we were given formulas as well as the periodic table.

Christineg1G

He has not said anything recently about posting any new modules

Christineg1G

700 nm would be 7000 angstrom
(1nm is equal to 10 angstrom)

Christineg1G

You would use 1.6022 x 10^-19 J/eV to convert between the two units

Christineg1G

Is it possible to determine the number of orbitals in a shell by only being given the principle quantum number, n, or would you need the angular momentum quantum number as well?

Christineg1G

Shell=All electrons are in the same shell when they have the same value for n (the principle quantum number) Sub-shell= Within a shell (same n), all electrons that share the same l (the angular momentum quantum number, or orbital shape) are in the same sub-shell Orbital= When electrons share the sam...

Christineg1G

l, which is the angular quantum number, represents the shape of the orbital.
m shows the number of orbitals in a sublevel. For example, m=-1,0,+1 shows that there is 3 orbitals in the p sublevel.
n is the energy level of the orbital.

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