CHEMISTRY COMMUNITY

Katie Nye 2F

One of the x's cancel so you are left with 2/x = 10. This can be flipped to be x/2 = 1/10 and after multiplying both sides by 2 you get x=0.2

Katie Nye 2F

Intermediates do not affect the rate because they are produced and then used up. They are not a significant part of the equation as a whole.

Katie Nye 2F

It is on the equation sheet so I would try it out a few times and make sure you understand how to use it.

Katie Nye 2F

Catalysts are not produced or used up so they will be added onto a reactant side and then be with the products at the end. They will not change or bond with anything at all. Intermediates are produced and then used up so they will first appear on the product side and then be used up in the following...

Katie Nye 2F

Thank you Dr. Lavelle! You are such a wonderful teacher and it was truly a joy to be in your class. I wish we could have been in person but despite this challenge, you made Chem 14A and B enjoyable, understandable, and somehow fun! Your clear love of the subject inspires me to work hard and find my ...

Katie Nye 2F

Last quarter, the majority of the questions focused on information that we hadn't been tested on yet. However, there was info from the first two midterms intermixed so I would study everything with a little emphasis on kinetics.

Katie Nye 2F

I think temperature is the only factor that changes k. A catalyst also changes the rate of the reaction but we haven't done a lot with those yet.

Katie Nye 2F

You need the concentration and rate changes to find the orders!

Katie Nye 2F

Go to the workshops and step up sessions! The TA's and UA's typically explain them in simpler terms and can give a good summary while the lectures go more in depth.

Katie Nye 2F

I prefer to hand write my notes because I find that I memorize the information better if it's written by hand. i use one colored marker that I use to highlight/underline important things and box in the equations and then one black pen so that I can return to the important information while not havin...

Katie Nye 2F

Spontaneous reactions always have a positive E!

Katie Nye 2F

Hi!
I've been struggling with memorizing which half equations are reduction and which are oxidation... Does anyone have a better way of memorizing this? Any anagrams or images or something?

Thanks!

Katie Nye 2F

I think it has something to do with the fact that ClO4 is a polyatomic ion so Cl is not considered to be monoatomic in this particular situation.

Katie Nye 2F

I also got stuck on this one for a bit! The two lines in the middle represent the salt bridge so the chemical that is in closest contact to the bridge also has to be closest to the two lines.

Katie Nye 2F

Without the salt bridge the reaction would be disturbed because it maintains the flow of ions between the solutions.

Katie Nye 2F

Yes! If the lid is closed and no energy/heat is allowed to escape then it is an isolated system.

Katie Nye 2F

That is Gibbs free energy equation! It is applicable at constant temperature and pressure. deltaG = deltaH - TdeltaS

Katie Nye 2F

The Van't Hoff is just another relationship between those three variables. However, it includes K and shows the temperature dependence of the equilibrium constant.

Katie Nye 2F

It depends on whether or not the system includes the piston. If the system is the gas inside the container, the work of compression would be positive because the piston is doing the work on the gas. If the piston is being released and pushed out (in a reversible reaction) the compression would be ne...

Katie Nye 2F

You calculate Q in a similar way to the equilibrium constant! It is the concentration of the products raised to their coefficient divided by the reactants raised to their coefficients. the only difference is for Q, the reaction is not at equilibrium.

Katie Nye 2F

Generally, I change everything to Kelvin because it is what is normally needed. However, in calculations where the change in temperature is important, it doesn't really matter which unit you use.

Katie Nye 2F

A closed system allows heat to be transferred between the system and surroundings while an isolated system is insulated. A bomb calorimeter or a high quality thermos is an isolated system. Closed systems include plastic water bottles with the cap on or a sealed beaker.

Katie Nye 2F

In the problems that I have done, G has been in kJ so I would stick to that but I don't think it quite matters as long as everything is properly converted. I just take it question by question and pay special attention to the units because I've made mistakes in the past.

Katie Nye 2F

I am also having a rough time in this class. Workshops have always been the most help for me because they focus on what will be on the midterm and explain problems step by step.

Katie Nye 2F

Kaili Valenzuela 2B wrote:I'm currently obsessed with Criminal Minds!

Same!! 100% would recommend. Also, I just finished Pysch which is really entertaining too!!

Katie Nye 2F

In a calorimeter, the system should be isolated meaning no work is being done from outside the system and no energy is being released. Therefore, the calorimeter absorbs all the energy lost by the reaction.

Katie Nye 2F

Going to review sessions, discussion, and workshops has been a huge help to me! Also the questions on the syllabus are very helpful, I use those to study!

Katie Nye 2F

I believe external pressure refers to the pressure outside of the system. So that would be the pressure that pushes on the piston.

Katie Nye 2F

I think of enthalpy as the change in energy that is provided by heat while temperature is simply the measurement OF heat. They are very interconnected because temperature changes cause enthalpy (energy) changes.

Katie Nye 2F

How do we know if a reaction is reversible or irreversible? Is there a rule or do we have to memorize?

Katie Nye 2F

I believe its most important purpose is to switch between concentration and pressure.

Katie Nye 2F

Yes! Aqueous solutions will always be included in Kc equations. Kp only requires gases, however, so if it asks for pressures, you disregard the aqueous solutions.

Katie Nye 2F

What always helps me is actually putting the heat into the equation! If it is exothermic, I add "heat" as a product so I know if more heat is applied, it has the same effect as adding more product, so it would shift to the left. Same for endothermic, I add it as a reactant and know that ad...

Katie Nye 2F

It depends on the information that they give you. All gas equations are the only equations that can have a Kp. I'd assume that if they give you all concentrations or all pressures that the answers should be Kc or Kp, respectively. However, you can always solve for the other with PV=nRT.

Katie Nye 2F

I believe those phrases are interchangeable. Saying the equation shifts to the right simply means the products are being favored so the equation can return to equilibrium and vice versa.

Katie Nye 2F

Generally, when dealing with Ka and pH and all those other values, the concentration that you need is the concentration at equilibrium! The initial concentration is vital to solve for the change and the final but most equations need the equilibrium concentrations.

Katie Nye 2F

He generally has review sessions with UA's and TA's and make sure to utilize office hours for any questions! If you can't attend those, the textbook questions are super helpful as he bases his midterm questions on those!

Katie Nye 2F

If the bonds on the product side are stronger than the reaction will be exothermic. Less energy is required to break the reactant bonds than is released when forming the product bonds. The opposite is true for endothermic reactions. The reactant side will have stronger bonds because more energy is r...

Katie Nye 2F

In a standard state, the element will be most stable so you can use that information to find out whether or not it is standard.

Katie Nye 2F

In water we assume that the concentration of [H3O+] = [OH-] (such as when Kw = 1.0 x 10^-14, [H3O+] = 1.0 x 10^-7 and [OH-] = 1.0 x 10^-7) so Kw = 2.1 x 10^-14 = [H3O+][OH-] but since [H3O+] = [OH-] Kw = 2.1 x 10^-14 = x^2 so x = square root 2.1 x 10^-14 Then, you get the pH by taking the -log of x...

Katie Nye 2F

Dr Lavelle emphasized how difficult it is to solve cubics so I was under the impression that the only time cubics will be involved is when the x value is small enough to not affect the other numbers so that solving for x will be simplified. If we did ever have to solve for a cubic, I am sure he woul...

Katie Nye 2F

Both refer to acids and bases but pKa is specifically related to dissociation and how much the substance will dissociate in water while pH is simply the acidity of the substance.

Katie Nye 2F

I would say the same thing. Unless specified, the solvent used to dilute can be assumed to be water.

Katie Nye 2F

Pressure with a change in volume will always only be applicable to gases. In order to use Le Chatelier's principle that it will balance out pressure, the substances need to be gaseous.

Katie Nye 2F

This happened to me when I was doing the sapling homework! Most of the time, when it comes to calculating equilibrium concentration, there is an initial value that you subtract x from. The larger value is most likely the one that will not work because once you subtract the larger number from the ini...

Katie Nye 2F

For 14A, the audio-visual topics were only used before the class as an intro and a reminder of what we've learned. I assume it will be the same and the sapling and textbook questions will be the practice throughout the course.

Katie Nye 2F

K becomes inverted. The way to remember this is that when an equation is reversed, what was once the products (numerator) becomes the reactants (denominator) and vice versa so the K equation would flip.

Katie Nye 2F

I think it would depend on the equation. If the K equation is entirely gas you can use Kp but if some are aqueous solutions and some are gases then you have to use concentration and solve for Kc.

Katie Nye 2F

The tests were all multiple choice for 14A but he might change it up for this quarter! Though he does say that the two are similar so I have a feeling they'll be the same. And to proctor you have to have a second device so that you can zoom your TA and show your work station while Respondus is on yo...

Katie Nye 2F

Yes, Kc is always calculated from molarity which is the concentration but Kp is always calculated by partial pressure.

Katie Nye 2F

You can look at the number of protons, or H+, that are taken away or added and change the charge for that! When you take an H+ from an acid, the conjugate base has a charge that is one less from the acid. When you add an H+ to a base to form a conjugate acid, the resulting acid has a charge that is ...

Katie Nye 2F

For induced dipole-induced dipole bonds, or dispersion, those are present in every intermolecular interaction so it can occur both with non-polar and polar molecules. However, with non polar molecules, they are the only intermolecular force present. Dipole-dipole and hydrogen bonds require polar mol...

Katie Nye 2F

Is there a way for me to access my past midterms to see what mistakes I have made and fix them? I tried CCLE but I can't access the test even though it has been graded and I wanted to make sure that I don't make the same mistakes on the final.

Katie Nye 2F

When calculating pH, I have seen calculations that use the concentration of H+ and calculations that use the concentration of H3O+. Is there a different calculation between the two? Or are they different because the question provided different information?

Katie Nye 2F

The simplest way to do this would be to subtract the pOH from 14 to get the pH. Then, use pH=-log[H+] to solve for [H+], which would be 10^(-pH).

Katie Nye 2F

Counting the regions of electron density is the simplest way to find the hybridization. 2 regions = sp, 3 regions = sp^2, and so on.

Katie Nye 2F

I think the most common usage of this idea would be boiling/freezing/melting points! The stronger the intermolecular force, the higher the boiling/melting points because they require more energy to break the stronger bond.

Katie Nye 2F

For me, a table was actually the most helpful for me! I used the table for every problem I completed until I was naturally doing it without checking the table because it became a force of habit! Maybe try to memorize them in order so you don't have to match them up individually, but you know the lis...

Katie Nye 2F

If the compound ends in -ate, then it is a negative compound but I believe the charge would be specified if it was positive rather than neutral. I just assume the compound is neutral and because of that assumption, you must have 3 potassiums to balance out the charge.

Katie Nye 2F

If the atoms are outside of the bracket they are not within the coordination sphere so they are not a part of the coordination compound. Because of that, you name them as you would normally, not with the ligand endings.

Katie Nye 2F

He introduced the force and listed all the potential names but those are the same thing! He did say he prefers the term induced dipole induced dipole, I think because it gives a good summary of what is occurring when these forces are at play.

Katie Nye 2F

I also believe that one of those shared regions is considered a sigma bond, if I remember correctly. One overlap represents a sigma bond but any additional overlap are pi bonds.

Katie Nye 2F

The atoms bonded to the central atom should be as far away from each other as possible because of repulsion. I think that is the greatest determining factor as to what shape the molecule is and then you can see which atoms are equatorial and which are axial.

Katie Nye 2F

The type of bond is based on how many bonds exist in one region of density. Shape can only help you determine how many sigma bonds there are because one exists in each bond but you have to create the Lewis structure to determine if any bonds are double or triple because that is where pi bonds come in.

Katie Nye 2F

He used -o in his lecture so to be safe, I'd say use -o because that's what he presented to us.

Katie Nye 2F

Dipole moments are based on electron density and with COF2, the two F's are balanced but there are far more electrons in an F atom than an H atom so the electron density is less balanced than if there are two of the same atoms on either side.

Katie Nye 2F

I always look to see if there's a way that i can fold the molecule to find symmetry. So if you were to cut the molecule in half and fold it, you would have two pieces that are identical which means the dipole moments cancel out.

Katie Nye 2F

CO2 is nonpolar because it is symmetrical and has no lone pairs. The lone pair on the S atom in SO2 distorts it and repels the atoms down into a bent molecular shape.

Katie Nye 2F

I also got confused on this question because I assumed that you needed an even number of lone pairs in order to distort it back to linear but I think it has to have more than 2 lone pairs in order to distort it back to linear.

Katie Nye 2F

Equatorial atoms are the atoms that are bonded above or below the central atom and axial atoms are located around the atom on the same plane. When you change your perspective on the atom, I think the same atoms would be axial or equatorial. It depends on how many are bonded. For example, in the trig...

Katie Nye 2F

Intramolecular forces will always be stronger than intermolecular forces because "intra" suggests that the bond in present WITHIN the molecule, which hold tighter that the forces BETWEEN molecules. Hydrogen bonding is an INTERmolecular force and the ion-ion forces are INTRAmolecular. So io...

Katie Nye 2F

Polyatomic ions that end in "-ite" will always have one less Oxygen than its "-ate" counterpart.

Katie Nye 2F

You're not looking for the charge of the compound because the compound should be neutral once it is complete. The charges of the atoms have to be balanced so if the cation and the anion have, respectively, a positive and negative charge that are opposite to each other than you only need one of each....

Katie Nye 2F

The dashed lines are present when the structure allows for resonance. It is representative of the fact that the average bond length for this structure is 1.5 because the double bond and the single bond have the potential to be in either place.

Katie Nye 2F

Lewis acid accept electrons while Lewis bases give the electrons.

Katie Nye 2F

Negative ions are larger than the positive or neutral counterparts.

Katie Nye 2F

The charge outside of the bracket represents the charge of the whole molecule. This can be seen in the charge placed on the molecular formula (such as NH4+) or by combining the formal charges of individual atoms.

Katie Nye 2F

I also agree with the above posts. The molecule is symmetrical, making the molecule itself non-polar. Though each bond is polar, they are evenly spaced out and counteracting each other. Since the molecule is non-polar, the only forces present would be LDF.

Katie Nye 2F

You can either calculate the number of valence electrons based on the number of electrons and then subtracting the inner ones or looking at the periodic table. Personally, I prefer the periodic table because it is faster and easier. You just look at what group the element is in and that is the numbe...

Katie Nye 2F

As you go across a period, there are more protons in the nucleus. Because of this, the attraction to the electrons is stronger so they are pulled in tighter, making the atom smaller. My high school teacher always described it as "Coulombic attraction" and it increases as protons are added ...

Katie Nye 2F

Intermolecular bonds are between molecules (LDF, Dipole-Dipole, Hydrogen). Intramolecular bonds are within molecules (Covalent, Ionic, Metallic).

Katie Nye 2F

I imagined how they would look when wrapped around in a circle. If they end in places that don't match up when wrapped and are not continuous, then the waves are not regular.

Katie Nye 2F

A hydrogen bond is only possible between hydrogen and either fluorine, oxygen, or nitrogen. I always remember this by "a hydrogen bond can only be formed by a Freak Of Nature (FON)"

Katie Nye 2F

Ionization Energy is the energy required to remove an electron from an atom. Electron affinity is the energy that is released when an electron is added to the shell of an atom. And effective nuclear charge, if I remember correctly, is the positive charge experienced by an electron that has more than...

Katie Nye 2F

Avogadro's number is 6.02 x 10^23. It identifies how many particles are in a mole and is often used in unit conversions between moles and particles.

Katie Nye 2F

It becomes just unit conversion! eV to joules is given on the equation sheet (1 eV=1.602e-19) which then needs to be converted into kilojoules (1 kJ = 1000 J). Since it is eV per proton, you also have to multiply it by 6.02e23 so as to make it per mole.

Katie Nye 2F

The indeterminacy equation gives the general idea of where the electron may be. It is impossible to tell with certainty where an electron is located, because of its wave and particle properties, so this equation is used to estimate position, velocity, and momentum.

Katie Nye 2F

I think both because diffraction talks about how the waves interact with each other once they've gone through a barrier with holes :)

Katie Nye 2F

Amplitude is unrelated to frequency and wavelength because it is solely the height of the waves and not the distance between them.

Katie Nye 2F

When it comes to certain questions, we need the mass of electrons or certain atoms in order to solve it. Does that always need to be in kilograms? And will we be given the value or do we need to memorize the basic ones?

Katie Nye 2F

I'm not sure about color but it does change the type of light. The amount of energy emitted changes from energy level to energy level and that changes type of the light. If the electron falls to level 1, the light is Ultraviolet, level 2 is visible and level 3 is infrared.

Katie Nye 2F

I think it's in reference to light and how it acts both as groups of photons and waves. So electrons themselves aren't waves and require certain quanta of energy to eject but there are certain aspects of behavior that are similar to that of waves.

Katie Nye 2F

The connection was between the runners and the photoelectric effect and why increasing light intensity doesn't have an effect on ejected electrons. Increasing light intensity is adding to the number of photons, or in the analogy, the number of runners. But if the runners can't jump the barrier (or t...

Katie Nye 2F

Frequency and wavelength are inversely related, so as wavelength increases, frequency decreases and vice versa.

Katie Nye 2F

To my understanding, if the electrons are interacting with the molecules in the air we wouldn't get an accurate representation of how the electrons react with the light. We can't get an accurate velocity of the escaping electrons because they're colliding with what's already in the air. It keeps the...

Katie Nye 2F

There's no correct order but I have found it easiest to balance polyatomic ions first, then elements that only exist in one molecule on each side, which normally leaves me with H's and O's. When it comes down to those, it normally isn't easier one way or another but for combustion, I tend to end wit...

Katie Nye 2F

When a liquid is measured in a volumetric flask, the final volume will always match that of the flask. The initial 15 mL are poured in there in order to be diluted by an additional 85mL of water, meaning the final volume is 100mL.

Katie Nye 2F

As a whole, once that number is plugged into different equations, it won't matter too much whether you used 15.999 or 16.000 because of the minute difference but I would use exactly the number seen on the periodic table that he provided. I think if the answer asks for a lot of significant figures, a...

Katie Nye 2F

Personally, I use four sig figs from the masses on periodic table and then adjust the final answer after every calculation is complete to get the most accurate and precise answer possible.

Katie Nye 2F

When it comes to stoichiometric coefficients being fractions, it can be helpful during the actual balancing process because it suggests that the final molecule was balanced. However, once the reaction is balanced, the whole reaction must be multiplied by the denominator of the fraction in order to r...

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