CHEMISTRY COMMUNITY

Sophia Spungin 2E

Hello! In question 7.23 of the textbook, the overall equation is ClO- + I- --> Cl- + IO-. The solution manual goes through the step of removing an intermediate from the rate law found in the slow step, however OH- is present in the overall rate law that is found using this method with the final rate...

Sophia Spungin 2E

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), a solubility equilibrium (b) H+(aq)+OH-(aq)<--> H2O(l), the Brønsted neutralization reaction (c) Cd(s) + 2 Ni(OH)3(s) S <--> Cd(OH)2(s) + 2 Ni...

Sophia Spungin 2E

While I am not sure of this, I think it would be safe to assume that we would not need to graph anything (as none of the textbook questions assigned require us to do this) and that questions relating to graphs would have to do with determining the rate of the reaction based on the axis of the graph ...

Sophia Spungin 2E

The slow step is the rate determining step, or the step from which the rate can be determined. The other steps can be considered fast. It is sometimes asked that you identify which step is the slow step, and in order to do this you would have to compare the experimentally determined rate law for the...

Sophia Spungin 2E

And intermediate is something that is produced in one step of the reaction, and used in a subsequent step. It does not appear in the overall reaction as it is created and used in the process of the overall reaction. A Catalyst is something that is necessary for the reaction to occur. It shows up on ...

Sophia Spungin 2E

Hi, I might be wrong but I believe that all ions will be aqueous in all of these reactions, for any element. Also all non-charged metal species, like Cobalt we can assume are solid. The only metal that isn't solid at standard conditions is mercury, so I'd expect that it wouldn't be found in a galva...

Sophia Spungin 2E

For the galvanic cell Co 2+ /Co and Ti 3+ /Ti 2+ , I understand how to figure out which is the cathode and anode, but how you determine what is solid, liquid, or aqueous when drawing the shorthand for the galvanic cell? Ti 3+ and Ti 2+ are both supposed to be aqueous, Co 2+ is aqueous, and Co is sol...

Sophia Spungin 2E

My TA had this helpful overview • Salt bridge: Two vertical lines (||) • Different phase: One vertical line (I) • Same phase: One coma (,) Diagram order: Inert Metal – Anode – salt bridge - Cathode – Inert Metal Thank you so much this is super helpful! Any advice on determining what goes on the far...

Sophia Spungin 2E

Could someone explain how to write cell diagram shorthand from an equation? Are there any rules for how things are ordered? is the left always oxidation and right always reduction? There aren't any clear rules set out in the textbook and I am getting a bit confused as every example seems to be order...

Sophia Spungin 2E

the half reaction where an electron is seen on the left (with the reactants) is reduction
- I remember if the electron is written with the *R*eactants, it is *R*eduction

The half reaction where an electron is seen on the right (as a product) is oxidation

Sophia Spungin 2E

To find n, write the two half reactions with equal charges. The number of electrons transferred in the overall balanced reaction is the value of n.

Sophia Spungin 2E

K is the equilibrium constant, whereas Q is the ratio of products to reactants at any point in the reaction.

Sophia Spungin 2E

When I learned how to balance Redox reactions, I learned to start by balancing both reactions in the same way: (1) balance non H or O elements (2) add H2O to balance O (3) add H+ to the opposite side to balance H (4) Balancing overall charge For an acidic reaction, you can leave it in this state, an...

Sophia Spungin 2E

For me, the most useful thing is doing all of the assigned textbook problems. I usually go through once to make sure I know how to do all of the problems, then go through again and instead of solving the problems I just think through the steps that it would take to solve the problem and comparing my...

Sophia Spungin 2E

The reaction in a standard hydrogen electrode (S.H.E.) is 2H+(aq) + 2e- <---> H2(g). Because a S.H.E. is at standard conditions, the standard cell potential, E naught, is 0. You can plug zero into the Nernst equation for the E naught slot :) As for Q, my TA explained that you can use (4.3 atm)/((0....

Sophia Spungin 2E

Question 17 states: What would the potential of a standard hydrogen electrode (S.H.E.) be under the given conditions? [H+]=0.82 PH2=4.3 atm. T=298 K the answer is calculated with a Q value that uses the concentration of the products in partial pressure but the concentration of reactants in molar con...

Sophia Spungin 2E

This formula is looking at the work of expansion done by a system do to an increase in moles of gas. You can ignore the amounts of liquid and solids as they do not contribute much to this expansion work.

Sophia Spungin 2E

unless the value for temperature is a change in temperature (ie ∆T as in the equation q=mC∆T), then it matters whether you use K or Celcius. For most equations that use a value of R, temperature must be in Kelvin, so a safe bet would be to convert to Kelvin however it is always important to look at ...

Sophia Spungin 2E

Musicology 68 is an amazing GE for Foundation of Arts and Humanities -Visual and Performance Arts Analysis and Practice. I believe that is offered winter each year. Its all about the history of the Beatles, and most classes you get to sit and listen to an entire album or watch a movie, and the lectu...

Sophia Spungin 2E

I would suggest converting kPa into atmospheres or another quantity for pressure that is listed as part of an R value. To determine what form to convert the pressure to, look at the units of the other quantities given (ie moles, liters, etc)

Sophia Spungin 2E

I believe that if a molecule is stable, its standard gibbs free energy of formation will be negative, indicating that the molecule in its standard state is more stable than its elements in their most standard state. Conversely, if a molecule is unstable, its standard gibbs free energy of formation w...

Sophia Spungin 2E

for the question: (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 25 8C and 1.00 bar. (b) Using data in Appendix 2A, calculate the standard enthalpy of the reaction. (c) Calculate the change in interna...

Sophia Spungin 2E

Air in a bicycle pump is compressed by pushing in the handle. The inner diameter of the pump is 3.0 cm and the pump is depressed 20. cm with a pressure of 2.00 atm. (a) How much work is done in the compression? (b) Is the work positive or negative with respect to the air in the pump? (c) What is the...

Sophia Spungin 2E

It is useful to look at a graph of phase change. The areas where the line is horizontal represent a constant temperature. This represents the time when all of the incoming heat is used to break intermolecular bonds, as opposed to raising the temperature of the substance.

Sophia Spungin 2E

In order to find Q, use the following equation where aA+bB --> cC+dD and P indicates partial pressure: (P_C^c)(P_D^d)/(P_A^a)(P_B^b). In this case, you would use PNH3²/ PH2³ PN2

Sophia Spungin 2E

I write out all of the units in my calculations in order to determine which value of R to use. Depending on what units the equation already has and what units you need to cancel, you can then choose R accordingly. Sometimes it is easier to match your other units to R, such as converting an energy te...

Sophia Spungin 2E

Units may be the issue in this case. To solve, I converted all energy terms to Joules and all temperature terms to Kelvin so that they would cancel with R=8.314 J/Kmol. I then calculated Q using the equation (PNH3)^2/(PH2)^3 (PN2). Finally, I converted my final answer back to kJ as prompted by the a...

Sophia Spungin 2E

When I first did this problem, my issue was with the unites! Make sure that temperature is in Kelvins, and that you use the correct version of the gas constant (8.314 J/Kmol). Since the values for ∆Gº are given in kJ/mol, make sure you convert to J/mol so that the units cancel with the gas constant....

Sophia Spungin 2E

I believe that any molecule with just a singular configuration (or distribution/arrangement/micro-state) will have an positional/residual entropy of 0. This includes diatomic molecules.

Sophia Spungin 2E

I believe entropy=0 when there is only 1 structural configuration. For example, O2 gas only has 1 structural configuration and therefor has an entropy of 0.

Sophia Spungin 2E

I believe that because nothing in reality is a perfect heat engine (all heat converted to work), calculating using equations for reversible expansion provides the maximum possible work.

Sophia Spungin 2E

I believe that you consider whether work is being done on the system (+) or whether the system is doing the work (-)

Sophia Spungin 2E

I think it might depend on your TA but I know last quarter as long as you had the correct number by the end of the quarter you would get full credit, even if from week to week you were missing posts.

Sophia Spungin 2E

I believe that it is only dictated by the stoichiometric coefficient. It is during the 'E' row that molarity is taken into account.

Sophia Spungin 2E

Thank you so much! I didn't even realize both K values were given that makes so much more sense!

Sophia Spungin 2E

Hello! In the following question from the textbook, how are we supposed to determine the effects of heating? I understand that the equation was initially heated in order to reach equilibrium, which leads me to believe that it is endothermic, and that heating an endothermic reaction favors the produc...

Sophia Spungin 2E

Thanks everyone this really cleared it up!

Sophia Spungin 2E

Hello! I've seen a few posts about polyprotic acids that seem to provide differing responses. To clarify: - Can the first deprotenation of sulfuric acid be considered complete meaning you just calculate pH using calculations for a strong acid? The textbook says that the first deprotenation can be co...

Sophia Spungin 2E

If the reaction is proceeding from Reactants to Products, all of the reactants will have a -X value determined by stoichiometric coefficients, and all of the products will have a +X value determined by stoichiometric coefficients.

Sophia Spungin 2E

This happened for a lot of people last quarter, and many people mentioned that downloading the "bookshelf" app for viewing the textbook fixed the problem!

Sophia Spungin 2E

I think any type of calculator is allowed, but it does not necessarily need to be graphing, as long as it can express scientific notation you should be set!

Sophia Spungin 2E

Yes, I believe that the values of X correspond to the ratios between the stoichiometric coefficients, and you can decide the way in which to use these ratios.

Sophia Spungin 2E

The textbook mentions that combustion reactions are always exothermic and reactions in the form X₂(g)⇌2X(g), where X is a halogen is endothermic. Other than that, I think we most likely would have to be given more information

Sophia Spungin 2E

While I am not positive, I would assume after today's lecture that we are responsible for knowing weak vs strong acids and bases as the calculations depend on knowing whether or not an acid or base is fully dissociated. I would probably review the list of strong acids and bases and know concepts lik...

Sophia Spungin 2E

I believe that the difference between Q and K is only that Q is measured before the reaction has had adequate time to reach equilibrium whereas K is measured once the reaction has reached equilibrium. I do not think that they are necessarily measured at different temperatures. A value of K for a rea...

Sophia Spungin 2E

As mentioned, K should be less than 10 -3 and ideally less than 10 -4 . If you want to check whether this approximation is valid, at the very end you can calculate percent ionization using the concentrations you calculated using the approximation. If the value for percent ionization is less than 5%,...

Sophia Spungin 2E

Here is the derivation for how you can determine pH given pOH. You would not have to go through all of these steps in order to solve a problem, but it can be helpful to see why this calculation works! The ionization constant for water is Kw=[H 3 O + ][OH - }= 1x10 -14 knowing that log ab = log a + l...

Sophia Spungin 2E

What happens to a system at equilibrium when there is an increase in temperature? Will it favor products or reactants? Will Q be greater than, less than, or equal to K? I don't remember this from lecture. I don't think we covered it yet lol. But if you know, please let me know! Thank you :) I had a...

Sophia Spungin 2E

I found it useful to think of concentration in this case as Molarity. Molarity is calculated by taking the number of moles of a solute and dividing by the volume of the solution, or n/V. in the ideal gas law, solving for n/V is thereby solving for concentration.

Sophia Spungin 2E

The version of K used is dependent on how the value of K is calculated. If you used concentration of products and reactants to calculate K, then use Kc to denote this. If you used partial pressures to calculate K, them use Kp.

Sophia Spungin 2E

They are calculated the same way, however when calculating K the concentrations of product and reactants must be those at which the reaction is at equilibrium, whereas the concentrations of products and reactants used to calculate Q can be from any given point at which the reaction is occurring.

Sophia Spungin 2E

As people have mentioned, I would always use temperature in Kelvin as the alternative would be changing the units on the constants and pressure values. Its super simple to convert from Celsius to Kelvin if the temperature happens to be given in Celsius, all you have to do is take the temperature in ...

Sophia Spungin 2E

Hello! I am looking for some clarification on what classifies as a strong base. According to Sapling learning, only LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2 and Ba(OH)2 are strong bases. However, in the textbook as well as in lecture, group 1 and 2 oxides are listed as strong bases as well as G...

Sophia Spungin 2E

I believe that in non-metal acids, the Hydrogen is always attached to the Oxygen. This also applies to acids like Sulfuric acid, Nitric Acid, and phosphoric acid. You can confirm this increased stability using formal charge. If you want to look into this more, you can look up oxoacids which I believ...

Sophia Spungin 2E

from what I have learned in a class I am taking on water quality, hard water is more alkaline due to the presence of cations (like Fe 2+ or Mg 2+ ).In the lecture Dr. Lavelle mentioned that alkaline materials have a soapy feel so it seems like maybe hard water would have this soapy feel since it is ...

Sophia Spungin 2E

From what I have learned in other classes about water quality, hard water is more alkaline and has to do with the presence of multivalent metallic cations. Soft water is more acidic.

Sophia Spungin 2E

A polydentate ligand is chelating ligand. I believe that chelating just refers to the structure that is able to form in the presence of a polydentate ligand.

Sophia Spungin 2E

Not sure if you are referring to naming coordination compounds, but here are the rules for using ate in these compounds: I believe that you use 'ate-' on the metal when the entire coordination compound has a negative charge. For example [Co(CN) 2 (OH 2 )] 2- has an overall charge of negative 2, so i...

Sophia Spungin 2E

Does anyone know if theres a list of what must be memorized in naming?

Sophia Spungin 2E

I believe you would attempt to minimize the formal charge, and this often does take trial and error of drawing lewis structures. You can also consider how many bonds and lone pairs an atom would need to have a formal charge of zero and then try to form the lewis structure this way.

Sophia Spungin 2E

I believe it depends on whether you are drawing a lewis structure or trying to represent the shape. In a lewis structure, I think all that matters is the correct bonds, atoms, and lone pairs so placement of lone pairs wouldn't matter.

Sophia Spungin 2E

Professor Lavelle mentioned that when you see 'p' in chemistry it means take the negative log. So 'pH' means to take the negative log of the species with H+, or H3O+

Sophia Spungin 2E

As previously mentioned, they are listed alphabetically excluding the prefix. For example 'pentaamine' comes before 'chloro' because you reference the a in amine and not the p in penta

Sophia Spungin 2E

I have found the textbook reading and questions to be extremely helpful. I watch all of the lectures first, and take notes on them, and then in the few days before the test I do every assigned problem and read through the textbook. The textbook is great for reinforcing what we learned in lecture, bu...

Sophia Spungin 2E

A single bond is a sigma bond. A double bond has one sigma bond and one pi bond. A triple has one sigma bond and two pi bonds.

Sophia Spungin 2E

A molecule with 4 regions of electron density, 2 lone pairs, and 2 bonding pairs, is bent. However, I believe that this could be characterized as having tetrahedral arrangement of electron density.

Sophia Spungin 2E

I may be wrong, but I believe that the 60º angle comes from the structure in which the three carbons form a triangle-shape. Since the angles of a triangle add up to 180º, each angle between carbons in this structure should be around 60º.

Sophia Spungin 2E

A single bond is a sigma bond. Each subsequent bond (2nd, third, etc) is a pi bond. If you have a double bond, for example, one of the bonds is a sigma bond in the other is a pi bond. If you have a triple bond, one of the bonds is a sigma bond and the other two are pi bonds. I don't believe that you...

Sophia Spungin 2E

They can be expanded further! For example, when Xe bonds with 4 fluorine atoms, it can make 4 single bonds and have 2 lone pairs and still have a formal charge of zero, giving it 12 valence electrons! (4 bonds+2 lone pairs= 8, 8-8=0). A lot of the time I like to think about expanded octets in terms ...

Sophia Spungin 2E

If you have a single bond, it is a sigma bond. If you have a double bond, one is a sigma bond and one is a pi bond. If you have a triple bond, one of the bonds is a sigma bond and the other two are pi bonds.

Sophia Spungin 2E

To answer the question about triple bonds, if the bond includes a pi bond then it is locked (ie it cannot rotate). A molecule with a triple bond has one sigma bond and two pi bonds, and therefore it cannot rotate.

Sophia Spungin 2E

This is from Professor Lavelle's website under enrollment questions; 'I play no administrative role. In other words I play no role in determining the size, venue or number of times a first-year chemistry course is offered and I cannot help with class or discussion section enrollment questions. I als...

Sophia Spungin 2E

It depends on if the arrangement of atoms surrounding the central atom (are they all the same?). Then, depending on how these atoms are arranged and whether the dipole moments of these atoms cancel, you can determine whether it is polar or non polar.

Sophia Spungin 2E

I believe that we are expected to know how to figure out the shape based on the lewis structure and the rules for VESPR. This would involve memorizing the names of the shapes, their bond angles, and the basic rules for figuring out how a molecule will be shaped.

Sophia Spungin 2E

Yes, I believe that the formal charges of individual atoms should add up to the overall charge of the molecule, which is seen both in the chemical formula (ie CO₃^2- which would have an overall 2- charge, and in the lewis structure as you mentioned.

Sophia Spungin 2E

I have this problem too with many questions not loading. I would suggest possibly downloading the bookshelf app as professor mentioned in his latest email and trying to view it that way as it requires downloading the entire book.

Sophia Spungin 2E

I believe that we don't have to memorize it and if we needed to do a calculation the values would be provided. You should just know the general trend on the periodic table and why this is!

Sophia Spungin 2E

Since it is multiple choice, I would expect that we would have to choose the diagram with formal charge minimized.

Sophia Spungin 2E

This doesn't conceptionally explain it, but a friend suggested that for formal charge you should just count the number of items drawn around each element. For example, for an element which is connected to a double charge and 2 lone pairs (which is 4 dots), the formal charge would be 6 (2 lines+4 dot...

Sophia Spungin 2E

The charges are not the same, isoelectronic just refers to atoms with the same number of electrons! For example, when elements like B, C, O, or F gain electrons in order to get an octet, they all have the same number of electrons as Neon, therefore B,C,O,F and Ne would be isoelectronic.

Sophia Spungin 2E

The number on the outside is the overall charge of the molecule. This has to do with the total number of electrons present versus the expected number present from the elements. The numbers next to the individual atoms is the formal charge, and the sum of all of these formal charges is equal to the n...

Sophia Spungin 2E

I believe you usually try to minimize the formal charge (get it closest to 0) for the most electronegative element.

Sophia Spungin 2E

It's dependent on whether the number of electrons in the diagram is more or less than the number of expected electrons from the elements present. For example, if the number of electrons expected from the elements present is 26, but only 25 are present in the lewis structure, the diagram would have a...

Sophia Spungin 2E

I believe according to his email, the first sum of posts will be calculated this Thursday, so you should have 20 posts by this Thursday.

Sophia Spungin 2E

I believe that you can always use the smaller n (ie n=1) value as n1 and the larger value as n2 (ie n=6), and then figure out the sign at the end depending on if light was emitted or absorbed.

Sophia Spungin 2E

I did the same thing originally, and when a question uses +/- for uncertainty, I find it easier to apply this to a number. For example, if you apply +/-5 to 10, you get 15 and 5. Here, it is easier to see that the range in position is 10 units, and not 5.

Sophia Spungin 2E

The mass of an electron is provided on the equation sheet

Sophia Spungin 2E

everything should match the units of h (kgm^2/s)
if a value isn't in kg, m, or seconds, you should convert it!

Sophia Spungin 2E

Im pretty sure thats just R/c, which allowed you to set the equation equal to 1/wavelength

Sophia Spungin 2E

5 posts are due every Sunday night before midnight :)

Sophia Spungin 2E

I believe that he was demonstrating that the upper bound of l is n-1. It can take on any possible values from 0 to n-1, with n-1 being the upper bound value. I don't think that if n=2 l could equal 1, but it could equal 0 or 1. This is a chart that I used to better understand it. When n=3, l can hav...

Sophia Spungin 2E

Basically, this question wants you to solve for the molar mass of 'M' and identify it by finding the correct element on the periodic table with this molar mass. You do this by subtracting the molar mass of the known elements from the total molar mass. Looking at the periodic table, M is revealed to ...

Sophia Spungin 2E

I believe that the first and second waves in the right column would work! Basically, if you repeated this same wave segment where the previous wave segment ended, it should create a continuous wave. Because the first and the second waves create a pattern in which the last iteration of the wave could...

Sophia Spungin 2E

In discussion, my TA said any type of calculator should be fine!

Sophia Spungin 2E

This isn't exactly the same concept but its how I visualize it: Imagine you are holding a rope and moving it in a wave pattern. If someone stands on the other side of the rope and creates their own wave, there are essentially 2 possible outcomes: 1. when their wave reaches your wave, the two waves c...

Sophia Spungin 2E

There are rules for SIG FIGS depending on what kinds of calculations you are doing. For addition and subtraction, usually precision matches the lowest number of decimal places of any number given. For multiplication and division, typically you match the number of sigfigs of the least precice number....

Sophia Spungin 2E

He mentioned that anything at the quantum level elicits some wave-like properties. Like with light, electrons have some properties that are best described using a particle model. In the experiments discussed last week, the particle model was best suited to describing the properties of electrons. How...

Sophia Spungin 2E

The photoelectric effect is important because it demonstrates that light cannot be modeled only as a wave. In a wave-only model of light, increasing the amplitude of the wave should increase the energy. With this assumption, adequately increasing the 'intensity' of the light should allow an electron...

Sophia Spungin 2E

The ratios of elements are the same, however, the multiples are different. Empirical equations are the simplest, whole number ratios of atoms, whereas Molecular formulas take into account the compound's molar mass and appear as a multiple of the empirical formula. These formulas can be the same if t...

Sophia Spungin 2E

It's often easiest to begin with an element that does not become split up in the products!

For example, in
C5H12 + O2 --> CO2 + H2O it is easiest to NOT begin with oxygen, as this element appears in both products! In this case, I would probably start with C, followed by H, and then assessing O.

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