CHEMISTRY COMMUNITY

Madeline Ogden 3B

In last week's lecture, Dr.Lavelle described reaction mechanisms as being the "number of steps it takes to form products". He also notes that the rate of the reaction depends on the reaction mechanism.

Madeline Ogden 3B

Are there any trends with respect to reduction potential and the periodic table? (i.e. Are certain areas of the periodic table known for having elements that have higher reduction potentials? Or is it more random?)

Madeline Ogden 3B

On sapling #7 for homework weeks 9 & 10, I noticed that we were asked to determine the reaction order for each of the concentrations. My data is as follows and these are the (correct) answers I got: Experiment [A]0 [B]0 [C]0 1 18.0 175.0 400.0 2 36.0 175.0 300.0 3 36.0 350.0 100.0 4 18.0 175.0 2...

Madeline Ogden 3B

I think it would be wise to know both how to derive each equation as well as to be aware of which is which (i.e. which one is for first order, second order, zero order) because of the fact that many of the variables in each equation are the same/similar. From what I can tell, they are all on our con...

Madeline Ogden 3B

In regards to rate laws, k can also be the rate constant. The rate constant relates molar concentration of reactants to the rate of the reaction.

Madeline Ogden 3B

Where does the 0.693 come from in the equation t 1/2 = 0.693/k ? And what do we refer to this constant as? Thanks in advance!

Madeline Ogden 3B

Thermodynamics deals with how favorable a reaction is, whereas kinetics deals with the speed/rate at which the reaction will take place. In reference to the diamond and graphite example that a student mentioned earlier, the reason that people are willing to spend so much on diamond jewelry is that a...

Madeline Ogden 3B

Hi all, I am confused on sapling #13 and was wondering if anyone may be able to help. My first problem reads: Which of the reagents would oxidize Cr to Cr3+, but not Ag to Ag+? (And the correct answer is: Co2+.) My second problem reads: Which of the reagents would oxidize I− to I2, but not Au to Au3...

Madeline Ogden 3B

Hi all, I was wondering if anyone had any tips on remembering the rules for calculating the charges on atoms. I know I can just look them up but I worry that when the final comes around I will not know them by heart. If anyone has any tips on how they memorized them I would really appreciate it. Tha...

Madeline Ogden 3B

What my fellow classmates have said above is true. Because you are adding water to one side to presumably balance the number of oxygens, adding water to the other side would keep the equation unbalanced. The only way to balance the oxygens properly in this situation would be to add H+ ions to one si...

Madeline Ogden 3B

To add onto what previous comments have said, the reason that entropy increases as degeneracy increases is due to positional disorder. The more energy states there are, the more possible positions there are for molecules to be in, hence more potential disorder is possible.

Madeline Ogden 3B

I agree with the other comments! Typically, the first unit I try to look for is liters and atm, as this is a way of telling you that you have to use 0.08206 instead of 8.314 since these two units typically cancel out. Hope this helps!

Madeline Ogden 3B

You should be using kelvin for T1 and T2. If you ever forget which one to use, I advise writing all of your units out for each variable in the equation and making sure they all cross out in the end leaving you only with the desired unit(s) for the problem.

Madeline Ogden 3B

This is generally the right case due to positional disorder. Because the molecule is bigger, there is a greater amount of micro states available and therefore a greater amount of disorder can be achieved.

Madeline Ogden 3B

I would assume that both H and S are at standard conditions (25 degrees Celsius) because you would need to be given several other factors if this wasn't the case (i.e. temperature and/or volume and/or pressure etc.).

Madeline Ogden 3B

Hi everyone! I was wondering if anyone else noticed a typo in this problem. In the book, both of the temperatures are listed in degrees Celsius but in the answer key, they are both written as Kelvin despite no conversion being done. Thanks in advance for your help!

Madeline Ogden 3B

Hi everyone, I know that in this class 50% (200 out of 400 points) will get you a C-. How many points do we need then to achieve a plain C ? B- ? B ? etc. In other words, what is the grading scale for students who get above 200 points ? Thank you in advance for your guys' help !

Madeline Ogden 3B

Hi everyone, I have seen an equation for calculating internal energy for an ideal gas that looks like this: Utot = (3/2)nRΔT . However, I have also seen a similar equation that instead has the fraction 5/2 . I was wondering what the difference between these two equations was, when we would use each ...

Madeline Ogden 3B

I'm not completely sure on this so please don't quote me, but this is what I've gathered from my notes: Delta S (the change in entropy) can be negative but the total entropy of the universe is positive/increasing due to the fact that natural processes in the universe trend towards disorder. Hope thi...

Madeline Ogden 3B

qrev is the amount of heat generated in a reversible process. So does deltaS = q/T only apply to reversible expansions and compressions? I believe that if the problem reads deltaS = q/T, it can be used for both reversible and irreversible reactions, but if it reads deltaS = qrev/T then q is only su...

Madeline Ogden 3B

This is what I have in my notes: If ∆G° = 0 (not common) then K = 1 and all [P] & [R] are in their standard state. If ∆G° is positive then K < 1 and the reverse reaction is favored (reactants favored). The reaction is not spontaneous (spontaneous in reverse). If ∆G° is negative then K > 1 and th...

Madeline Ogden 3B

Adding onto what has already been said, the Van't Hoff equation can also look like this depending on certain conditions:
ln (k2/k1) = (-ΔH°/(RT2)) + (ΔH°/RT1) assuming that ΔS° is constant
ln (k2/k1) = (-ΔH°R) [ (1/T2) - (1/T1)] assuming that ΔH° is constant

Madeline Ogden 3B

qrev is the amount of heat generated in a reversible process.

Madeline Ogden 3B

Hi everyone! One of the points on outline 4 reads: Show how the Gibbs free energy change accompanying a process is related to the direction of spontaneous reaction. So far I have this: If ∆G° = 0 (not common) then K = 1 and all [P] & [R] are in their standard state If ∆G° is positive then K < 1 ...

Madeline Ogden 3B

He did mention adiabatic system (but not adiabatic wall) in lecture today but other than that I have yet to see these terms discussed in lecture or in homework problems.

Madeline Ogden 3B

You can also tell if a process is irreversible or reversible by looking if there's a change in temperature. Because irreversible processes occur much faster than reversible ones, there is little to no time for the system to slowly let in heat from the surroundings. Because of this, irreversible proc...

Madeline Ogden 3B

Irreversible reactions occur very quickly in comparison to reversible ones. Because of this, when the irreversible reactions' pressure changes, there isn't enough time for heat to enter the system, therefore causing a change in temperature.

Madeline Ogden 3B

Work is normally given in relation to the system. If a system is having work done to it by the surroundings, work's value will be positive. If the system is losing energy to its surroundings, then the value of work will be negative.

Madeline Ogden 3B

Hi everyone! I was wondering if anyone would be able to help me on this sapling problem. It reads: The molar heat capacity for carbon monoxide at constant volume is CV, m=20.17 J/(K·mol). A 6.00-L fixed-volume flask contains CO(g) at a pressure of 8.00kPa and a temperature of 25.0 °C. Assuming that ...

Madeline Ogden 3B

Megan Sparrow 1A wrote:Thank you for the help because I had this same question. On another note, if the question said that the volume was held constant, would deltaU=q ?

Yes! If the change in volume is constant that means that there is no change in delta V (delta V = 0). When this occurs, delta U = qv.

Madeline Ogden 3B

I think he meant that more heat will be used in the reaction. Since the reaction he was using as an example was endothermic, this means that more products will be formed.

Madeline Ogden 3B

According to Le Chatelier's principle, all systems want to minimize any effect happening to them as much as possible. With that said, if you increase the heat in an endothermic reaction, the reaction will then begin to favor the products, and in turn, K will increase.

Madeline Ogden 3B

If I remember correctly, the reason for this is because bond enthalpies are an average of many different bonds, hence why this is the least accurate method of the three that we learned in class. For the textbook problems, I would just use the table provided to you as this will help you get the answe...

Madeline Ogden 3B

Exothermic reactions give off a net release of heat, therefore making their change in temperature (delta H) negative. Likewise, endothermic reactions require heat. Because of this, heat is being added to the reaction and we can therefore say that delta H is positive. If Q > K then [R] > [P], whereas...

Madeline Ogden 3B

Hi everyone, I know Dr.Lavelle isn't teaching chem 14c for spring quarter but I was unsure of where else I should ask my question. For spring quarter I'm planning on taking chem 14BL, chem 14C, and stats 13, all of which I've heard run out of space very quickly. I was wondering if chem 14BL and/or C...

Madeline Ogden 3B

Hi everyone, I am having trouble with number 14 on sapling and would really appreciate it if someone could help me out. I have attempted the problem several times and read through the feedback to no avail. For reference, this is the problem: A sample of an ideal gas in a cylinder of volume 4.15 L at...

Madeline Ogden 3B

Once you've determined the value of the equilibrium constant, you can use it to predict solubility. A large K (K>10^3) signifies that the products are more favored than the reactants, meaning that the reactants are more soluble. A small K (K<10^-3) signifies that the reactants are more favored, so t...

Madeline Ogden 3B

Cv is molar heat capacity at constant volume, whereas Cp is molar heat capacity at constant pressure. The reason for the differentiation is because for gases, these values can differ.

Madeline Ogden 3B

Akemi Karamitsos 1E wrote:Do different calorimeters each have their own specific heat capacities?

I'm pretty sure the answer to your question is yes. I remember him stating this in today's lecture but I'm not entirely sure of the reasoning/science behind it. I'm sure he'll talk more about it in the future.

Madeline Ogden 3B

Heat is required to break bonds. Because of this, reactions involving breaking bonds are endothermic.

Madeline Ogden 3B

When doing problems that involve a calorimeter, you're solving for q of the system. Because of this, the sign of both qsys and qsurr would depend on whether or not the system was losing or gaining heat. This can tell you whether the sign of qsys will be positive or negative. Whatever sign qsys is, q...

Madeline Ogden 3B

are you guys attempting the number problems too (i.e 4.1, 4.5, 4.7, etc.) or only the ones from sections 4D and 4E ?

Madeline Ogden 3B

Hi everyone, I saw the email Dr.Lavelle recently sent that we only have to focus on 4D.3, 4D.4, 4D.5, and 4E.3 in the textbook for the upcoming midterm. However, I was confused on what problems for in outline 3 we should be doing to help us study. All of section 4E (#s 5,7, and 9) seem to be things ...

Madeline Ogden 3B

We omit solids and liquids from equilibrium expressions due to the fact that their concentrations do not change. Therefore there's no use in putting them in the equation.

Madeline Ogden 3B

I typically put concentrations in my ICE boxes. This allows me to do the conversion from moles to concentration at the beginning of the problem rather than the end so I don't forget to do it.

Madeline Ogden 3B

I agree with the above statements! To summarize, -x is usually on the side of whatever initial value you've been given (this can be either the reactant or product) and +x is on the side of whatever value you're trying to find. Hope this helps!

Madeline Ogden 3B

We would need to know delta H in order to determine whether or not the reaction is endothermic or exothermic. If delta H is positive, the reaction is positive, the reaction is endothermic, whereas if delta H is negative, the reaction is exothermic.

Madeline Ogden 3B

The conjugate of a weak acid is a strong base. Similarly, the conjugate of a weak base is a strong acid.

Madeline Ogden 3B

As the person above has stated, I'm sure you getting an imaginary number was simply a calculation error. I'm not sure what numbers Sapling gave you but when plugged in correctly there should have been a positive answer beneath the square root. Kudos to you for still getting the right answer though!

Madeline Ogden 3B

After balancing your equation, you would raise each substance's concentration to the power of its coefficient.

Madeline Ogden 3B

The molar concentration of pure substances does not change in a reaction. Because solids and liquids are considered pure substances, they are not included in the equilibrium constant expression.

Madeline Ogden 3B

Although we do not include solids and liquids in equilibrium constant equations, they do factor into whether or not a substance is heterogenous or homogenous. This is because while they do not affect the equilibrium constant, they still are apart of what makes up the substance.

Madeline Ogden 3B

ICE tables are helpful to use when a student is being asked to find an equilibrium constant and is given the initial value(s) of a substance(s) concentration. They are used as a visual aid and help in organizing a student's thoughts when they wish to set up an equation in order to find an equilibriu...

Madeline Ogden 3B

H2O should only be included in an ICE table if it's in gaseous form. We also disregard liquids and solids when making ICE tables due to the fact that there concentrations do not change.

Madeline Ogden 3B

Since a higher pH signifies a more basic solution, weaker acids tend to have a higher pH than stronger ones. This is because pH refers to the content of hydronium (H30+) ions present in a solution. Weaker acids tend to not completely disassociate in water meaning that they'll have a higher content o...

Madeline Ogden 3B

A pure substance is generally a homogenous liquid or solid that's only made up of one type of molecule.

Madeline Ogden 3B

K is used as a broad term for equilibrium constants whereas Kc is used more specifically for equilibrium constants dealing with concentration. I think Kp is used for equilibrium constants dealing with partial pressure but am not entirely sure to be honest.

Madeline Ogden 3B

I agree with the post above! K is a broad term for all equilibrium constants whereas Kc is a more specific term for equilibrium constants dealing with concentration.

Madeline Ogden 3B

Hi everyone! On outline 6, one of the topics is to be able to "Explain why salts of weak bases produce acidic solutions and salts of weak acids produce basic solutions." This is what I have written so far and I was wondering if someone may be able to correct me or confirm what I'm saying i...

Madeline Ogden 3B

Both mean pretty much the same thing. I think H+ is used as shorthand for H3O+ in the same way that we say "pH of 7" rather than "-log(1.0 x 10^-7)". One is just a more descriptive form of the other.

Madeline Ogden 3B

Yes this is correct! The nucleus of the hydrogen ion is a proton.

Madeline Ogden 3B

From what I've gathered from my notes, the heme complex + protein = myoglobin, whereas hemoglobin contains 4 myoglobin-like molecules and assists with oxygen transportation in the blood. (For those wondering, these are my notes for Week 9, Lecture 1). Hope this helps!

Madeline Ogden 3B

I was wondering why Pi bonds are specifically sideways overlapping? I think it has something to do with the fact that when they overlap this way, the axes of each molecule remain parallel to each other. Because of this, pi-bonds are always weaker than sigma-bonds since there's less material overlap...

Madeline Ogden 3B

Yes! Acidic solutions have more H3O+ ions than OH- ions. As well as this, the equation for pH is -log[H3O+]. Therefore a solution with a higher amount of H3O+ ions will have a lower pH. The closer the pH is to 1, the stronger the acid. Hope this helps!

Madeline Ogden 3B

Iodine is a larger atom with more electrons than fluorine. Because of this, it has stronger bonds. This not only explains why CHI3 has a higher melting point than CHF3 but also why F2 is a gas at room temperature while I2 is a solid.

Madeline Ogden 3B

Kind of as a follow-up question, how would you determine which element in a molecule would create a bigger difference in electronegativity? Like when trying to compare two molecules' iconic character? In order to determine the exact difference in electronegativity you would need to be given the val...

Madeline Ogden 3B

H2S has no hydrogen bonds while H2O does. Because of this, we're able to explain why water has both a higher boiling and melting point than hydrogen sulphide. (Water's boiling point is 100 degrees Celsius vs hydrogen sulphide's boiling point of only -60 degrees Celsius. Water also has a higher melti...

Madeline Ogden 3B

You cannot assume this because of the fact that if the molecule is symmetrical the charges might cancel out despite the atoms having lone pairs.

Madeline Ogden 3B

For elements not in the d-block the amount of valence electrons can be found by looking at the periodic table. Group 1 (hydrogen, lithium, etc.) has one, group 2 (beryllium, magnesium, etc.) has two and so on up until the 8th group where the noble gases are. To find valence electrons in the d- or f-...

Madeline Ogden 3B

Electronegativity, atomic radius, and bond multiplicity all effect covalent bond length. -The higher the electronegativity, the stronger the electrons will be pulled toward the atom. This leads to stronger, shorter bond length (higher pull = stronger bond). -If the atom has a small atomic radius, th...

Madeline Ogden 3B

This is due to the fact that the rod shaped molecules will have a higher level of surface area touching than the two spherical molecules. The way I like to remember it is this: if someone asked you to hold a beach ball in your hand it would be much harder than trying to hold a baseball bat due to th...

Madeline Ogden 3B

To restate what others have said, you can tell if a bond is more ionic than another by comparing the difference in electronegativity. If you aren't given the value of each molecule/atom's electronegativity then a good rule of thumb is whichever one has atoms that are further away from each other on ...

Madeline Ogden 3B

This is correct! Ionic bonds typically have a higher boiling point than covalent bonds due to the fact that they are stronger. This is because the stronger the bond, the more energy (in this case, heat) is required to break the bond.

Madeline Ogden 3B

Normally a higher boiling point means that there is a stronger bond. This is because in order to break that bond it will require a lot of energy and in this case, energy comes in the form of heat.

Madeline Ogden 3B

Thank you both so much!! Looking back at it I see now that my Si only had 2 bonds so this makes a lot of sense and so do the points about FC. Thanks again! Going to leave this up incase anyone else had the same question. :)

Madeline Ogden 3B

Are we expected to know the equation for electric dipole moments for midterm #2? If so, will we be expected to do any equations using it or are we just expected to understand it conceptually?

Madeline Ogden 3B

For problem #3 in section 2B in the textbook, part c asks for the Lewis structure of SiO2. I drew each oxygen with 3 lone pairs and connected each of them to the Si using a single bond. However, the answer in the book shows each oxygen with 2 lone pairs, both connected to Si with a double bond. Can ...

Madeline Ogden 3B

For one of the problems in the book for outline 3 (problem #3, part b in section 2A), it asks us to write the ground state electron configuration for As^3+ . For my answer I put [Ar]3d^10 4s^2, but the book has the solution as [Ar]4s^2 3d^10. Does the order I put my answer in matter? Or do both of t...

Madeline Ogden 3B

On Outline 2, it says that we need to be able to “Describe the interpretation of atomic orbitals in terms of probability.” I know this relates to Schrodinger’s equation. In regards to midterm #2, I was wondering if anyone knows whether or not we’re expected to know how to perform calculations with t...

Madeline Ogden 3B

Along with what everyone else has already said, a rough guideline for finding out if a bond is ionic or covalent is to find the difference in electronegativity between the two molecules. If the difference is greater than 2 then the bond is ionic, whereas if the difference is less than 1.5, the bond...

Madeline Ogden 3B

Hi everyone,
On outline 3, it says that we're expected to know how dissociation energy for covalent bonds relates to unpaired electrons. If anyone could tell me what the correlation is between the two of them I would really appreciate it. Thank you in advance!

Madeline Ogden 3B

Along with what everyone else has already said, a rough guideline for finding out if a bond is ionic or covalent is to find the difference in electronegativity between the two molecules. If the difference is greater than 2 then the bond is ionic, whereas if the difference is less than 1.5, the bond ...

Madeline Ogden 3B

Van der Waal, London Dispersion, and Induced Dipole-Induced Dipole are all names for the same thing. This type of interaction is always present, exists between all molecules (whether they are polar or non-polar), and is always attractive. It's a weak type of bond that exists due to differences in ch...

Madeline Ogden 3B

From my understanding, induced dipole-induced dipole attraction exists between all molecules. How is this possible between two non-polar molecules?

Madeline Ogden 3B

Maddie Turk Disc 2C wrote:So this is why H can never be in the center of a molecule right? Since it can only hold 2 electrons?

Yes this is correct. A hydrogen atom can never be a central atom because it's only capable of forming 1 bond.

Madeline Ogden 3B

Color coding!!!!! The best way to study for me personally is compiling a list of all of the topics on a test and color coding them to see what topics I need the most review on and what topics I only need a refresh on. For this class, I've copy and pasted all of the topics from Outline 1 and all but...

Madeline Ogden 3B

To add onto what others are saying, c=freq*wavelength can only be used for electromagnetic radiation/light because both of those things are traveling at the speed of light, or "c", whereas an object that you may wish to plug into the De Broglie equation, such as an electron, cannot travel ...

Madeline Ogden 3B

Adding onto what others have said, technically all objects have wavelike properties but because of mass being a factor in whether or not we can detect them, only objects with an extremely small mass (electrons, protons, etc.) have detectable wavelike properties.

Madeline Ogden 3B

I'm pretty sure you can use whichever one you like and that it just depends on the information that you're given in the problem. Hope this helps!

Madeline Ogden 3B

When doing calculations, wavelength should always be converted to meters in order to ensure that the correct SI unit is being used. However, when giving an answer dealing with wavelength, it's best to give the answer in nm as this is normally the length that they are given in. From what I know, radi...

Madeline Ogden 3B

I agree with the statement above. When someone says that a molecule has a lewis structure that exhibits resonance it simply means that the lewis structure can be drawn in a variety of different ways. What we think of as being the "true structure" of a molecule is the resonance hybrid, or c...

Madeline Ogden 3B

Color coding!!!!! The best way to study for me personally is compiling a list of all of the topics on a test and color coding them to see what topics I need the most review on and what topics I only need a refresh on. For this class, I've copy and pasted all of the topics from Outline 1 and all but ...

Madeline Ogden 3B

Just to double check… I was told that if an electron falls from a higher energy level to n=1 then it’s in the Lyman series and if it falls to n=2 it’s in the Balmer series. I’ve also heard that this information depends on whether or not it’s on the emission or absorption spectrum. Is this correct?

Madeline Ogden 3B

At the end of Outline 2, Dr.Lavelle says that we should be able to “understand the difference between electronic transitions in atomic orbitals (atomic spectroscopy) and electronic transitions in molecular orbitals (molecular spectroscopy)” with respect to transitions that give rise to a UV or visib...

Madeline Ogden 3B

One of the last things we went over in lecture that will be on Midterm 1 is the Heisenberg Indeterminacy Equation. I’m still a little confused on how one would find the change in p and change in x of this equation. If anyone knows how to and can help I would really appreciate it. Thank you!

Madeline Ogden 3B

On the list of things we should know for Outline 2, Dr.Lavelle says that we need to know how to derive the DeBroglie equation. Does he just mean that we need to know how/why it works the way it does? Or do we have to know how to derive it mathematically?

Madeline Ogden 3B

Dr.Lavelle uses the analogy of runners to describe the fact that if the wavelength of light isn't high enough that no matter how high the frequency, electrons will not be emitted from a surface. Does anyone know what the range is that a wavelength has to be in order for electrons to be emitted from ...

Madeline Ogden 3B

To back up what others are saying, I asked this question in my discussion section last week and my TA said that Dr.Lavelle would provide most of the chemical formulas for compounds on our tests, with the exception of well known ones like water, oxygen, etc.

Madeline Ogden 3B

I was also wondering this earlier and thinking about how its possible for light to have no mass if its made up of photons which I assumed to have a very small mass. What other people are saying would make sense though as light has no mass.

Madeline Ogden 3B

I know that an object with a large mass (say, a baseball) doesn't have detectable wavelike properties due to the fact that its mass is so large. My question is would wavelike properties be detectable in a baseball (or some other "large" object) if it was going incredibly slow? (Like really...

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