CHEMISTRY COMMUNITY

Becca Nelson 3F

Cv refers to the constant when volume is constant, for an ideal gas it is 3/2*8.314. Cp refers to when the pressure is constant and this value is higher at 5/2*8.314. Hope this helps!

Becca Nelson 3F

While I am not entirely sure if we will be tested on these, I definitely think it is a good skill to be able to identify which system is which. The first thing I do is determine if the system can exchange matter with the environment (if stuff can leave). For example, in 4A.1 they gave the example of...

Becca Nelson 3F

my chem teacher would always say LEO the lion says GER! It is a great way to remember a basic concept of redox!

Becca Nelson 3F

I believe this is because you are looking at delta T, not T. A change from 25 celsius to 900 celsius is 875 Celsius and a change from 298 Kelvin to 1173 Kelvin is 875 Kelvin. An increase in temp of one degree celsius is equal to an increase in temp of one degree Kelvin. You always can convert to Kel...

Becca Nelson 3F

Think about when you put a kettle on the stove, once you let it heat up you need something like an oven mitt to take it off because the kettle itself got heated up as well. In this case, you have a copper kettle weighing 400 grams that will also take in heat to warm it to the same 100 degrees. Becau...

Becca Nelson 3F

Do we need to know the material in this section for the midterm, if so do you guys have any good mnemonics or memory tools for this section? thanks!

Becca Nelson 3F

What did the weak acid say to the strong acid??

you are overreacting!

Becca Nelson 3F

They are not the same thing, but there are subtle differences between the two. delta H is defined as q at constant pressure. q is more generally heat. So when you see a problem with constant pressure, you can sub in the value for delta H.

Becca Nelson 3F

As Dr. Lavelle explained, theoretically the molecules in the desk of the lecture hall are expanding or contracting, but it is so so small that it is not necessary to calculate and can be ignored. If you think about the pressure you put on objects like a wooden chair, when you sit on them you can't s...

Becca Nelson 3F

by definition, delta h is the value of q at constant pressure. delta u = q +w. we are aware that w is the integral of pressure x change in volume, but if volume is constant, that whole term will just end up being 0, so all thats left is q. If you are still confused about when to use each equation, I...

Becca Nelson 3F

Like everyone else is saying, 1 mL = 1 cm^3 so 1 liter (1000 mL) is 1000 cm^3. While it may be on the conversion sheet, you can use the prefixes learned in chem 14A to determine this. milli is 10^-3 so there would 1000 more milliliters in a liter, so if you have any one conversion from cm^3 to liter...

Becca Nelson 3F

My chemistry experiment exploded...

It's ok oxidants happen!

Becca Nelson 3F

It is very helpful in these situations to write out all the equations (and phases) on paper! I like to put times 1 or -2 depending on if the reaction is flipped or not. Then just go through and cross out what is on both the reactants and products side. You should be left with only what was in the or...

Becca Nelson 3F

While I am not entirely sure when to use the absolute value of the heat of combustion value, heroes how I go about solving problems. Combustion is exothermic in nature so it should have a negative q. Look at what your system is, what way the reaction is and what equation you are using to solve. I ju...

Becca Nelson 3F

When water is boiled, the water molecules need to go from lower energy liquid phase molecules to higher energy gaseous molecules. Water is capable of hydrogen bonding so it has strong intermolecular forces. It takes energy to break these hydrogen bonds as the molecules become more spread out.

Becca Nelson 3F

One helpful tool to determining what equation to use is seeing what is given. If you write out all of your given values, you will be able to determine which equations you can use. You can even convert between the different q values using molar mass.

Becca Nelson 3F

Basically, when water reaches 100 degrees celsius, its boiling point it still needs energy to become a gas. Once it hits this temperature, we see a horizontal line with energy still entering the system but no increase in temperature. In this case this energy is used to help the phase change, higher ...

Becca Nelson 3F

One way you can look at this is the energy released from making bonds versus the energy needed for breaking bonds. We see because there is a negative enthalpy value that more energy is released from the formation of CO2 than energy required to break the bonds on the reactant side.

Becca Nelson 3F

Sublimation is endothermic because you are changing from a solid to a gas. Gaseous molecules are higher energy than solid molecules and therefore energy has to be put into the system for these reactions to occur.

Becca Nelson 3F

What kind of dogs do chemists have? Laboratory retrievers!

Becca Nelson 3F

Lets say your equation is O2 +2H2 -> 2H2O and you start with only 1 mol hydrogen gas and oxygen. For every two water molecule made you will loose 2 hydrogens and 1 oxygen, so your ICE table would have -x for change for oxygen, -2x for hydrogen and +2x for water. In your equilibrium it would be 1-x a...

Becca Nelson 3F

I like thinking about them by their latin roots "exo" means outer and "therm" means heat. Exothermic reaction heat the outside (release heat). "endo" is inside and therefore endothermic reactions heat the inside (absorb heat) and cool the the outside. Hope this helps!

Becca Nelson 3F

The best thing to do is the textbook problems. I also really like using the audio visual post test as a way to study and see what I got right and wrong as those questions are separated by topic and designed by Lavelle!

Becca Nelson 3F

Oxygen and Magnesium were going out together.

I said "OMg that is a party!"

Becca Nelson 3F

Hi! I think when you look at the energy released it makes the most sense. So to get to from 100 degree water to 25 degree water that will be the same for both the water and the steam once the steam becomes water. For the phase change to happen, steam absorbs quite a bit of heat and therefore when it...

Becca Nelson 3F

The R values are only different due to the the different units of pressure and their conversions. In order to know which R value to use, just see what units fit correctly! I am pretty sure Lavelle's constant sheet has units and that can be a great way to figure out the right R value, especially on t...

Becca Nelson 3F

Q should reach K if the reaction is left alone. Once Q equals K the reaction is at equilibrium and the forward and reverse rates of the reaction are the same. If Q > K more reactants will be formed and if Q<K more products will be formed until these values are the same.

Becca Nelson 3F

H2O is a liquid, therefore it is not included in K. Moreover, there would also be a large amount of H2O in the numerator as solvents tend to be in large excess. Instead of writing water in both the numerator and denominator, we just ignore it all together. I really liked Dr. Lavelle's millionaire an...

Becca Nelson 3F

What do you call a mixture of carbon and aluminum?

The second best public university in the nation!

Becca Nelson 3F

We are always trying to see how Q compares to K when trying to see what will happen with non-equilibrium conditions, and solids and liquids are not included in the equation for K, so they should be disregarded. Also, pressure really only relates to gases anyways.

Becca Nelson 3F

The only change to a system that will change the value of K is temperature. Pressure is really changing the number of mols by changing the volume. Therefore, depending on how the mols change, the equilibrium will shift to get back to that constant K. Temperature does not change the number of mols of...

Becca Nelson 3F

I know that with concentrations both aqueous and gaseous substances are included in the equation, but what happens when you are trying to calculate Kp and there are aqueous substances in the equation? Can there be a partial pressure for an aqueous substance? Should you convert the gaseous pressures ...

Becca Nelson 3F

Why do chemists learn about ammonia first?

Because its pretty BASIC stuff

Becca Nelson 3F

From my understanding, the partial pressure is the pressure of the specific gas if it occupied the volume by itself. We can find the partial pressure if we have the number of moles, volume, temperature, and R value using PV=nRT. The sum of all of the partial pressure is the pressure. I hope this hel...

Becca Nelson 3F

I am not totally sure if this is going to answer what you were asking but I will give it my best shot. Equilibrium reactions generally have both a forward and reverse reaction component to them. If Q>K (too much product), the reverse reaction will take place and the product will react and become rea...

Becca Nelson 3F

In cases of adding more reactants or products, K does not change, but Q will change as you are no longer in equilibrium. If you add more products Q will now be greater than K and if you add more reactants Q will now be less than K

Becca Nelson 3F

I went to a TA office hour as I had the same issue and we discovered it is in fact a typo. Using the method with the correct initial value, in your case the 0.494 + x, you will get the correct answer. The feedback/hint section is incorrect but the solution guide is correct. Just use the correct numb...

Becca Nelson 3F

Hi! I always just look at the values to see which one makes more sense in context. Also, if you already know K and are evaluating using non-equilibrium conditions, you can check your work by plugging in the answer. Generally, the smallest positive answer works, but I would always check to see which ...

Becca Nelson 3F

Does anyone know how to approach 33B and C? Thanks!! Yes! So NaOH is a strong base, which means it dissociates 100%, so the concentration of NaOH is also our OH concentration when dissociated. To calculate the pH, I first got the pOH, by doing -log(0.55) and then to convert to pH, I did 14-pOH. For...

Becca Nelson 3F

Screenshot (23).png For 41D, which 6 atoms can form a hydrogen bond? I thought a hydrogen bond was when H is bonded to two highly electronegative atoms. Therefore, H2O could only form hydrogen bonds with 4 atoms (the two N atoms and the two H atoms bonded to N). Hi! I think there are also lone pair...

Becca Nelson 3F

A photon checks into a hotel. They ask if he needs any help with his luggage. He responds...

No, I am traveling light!

Becca Nelson 3F

With the burning of natural gases and coal, sulfur dioxide is released into the air. The equation he showed demonstrates how sulfur dioxide and water together create acid rain. Acid rain really hurts the environment, especially our oceans. Acid rain continues to be an environmental problem that is v...

Becca Nelson 3F

When the H breaks off from the Cl-O-H structure, the Oxygen is left with a negative charge. Since the bond breaking is the same on all of these structures, we look at the resulting anion. There is not resonance, so we can look at the anion to see what happens. Chlorine being highly electronegative p...

Becca Nelson 3F

does anyone now the breakdown of the final? Like what portions will be predominately featured etc. Dr. Lavelle said the final will be cumulative and sections will be on there according to the amount of time we spent on them. We spent the most time on quantum, so that will be the most, but topics li...

Becca Nelson 3F

Yes. If for example there was a strong acid with a molarity greater than 1M, it would have a pH less than 0. In the same way, if a strong base had a molarity greater than 1M it could have a pH greater than14. For chem 14A, I believe it is not important that we know this.

Becca Nelson 3F

Memorizing a couple examples can be very helpful to understanding the topic! If you know a couple, you can generally apply that knowledge to other parts of the periodic table.

Becca Nelson 3F

why are chemists so great at solving problems?

because they have so many solutions!

Becca Nelson 3F

I first look at the CO. I know this is mono dentate and there are 2 of them. The en is bidentate which means it ends in 2 spots. So we do 2x2+2 to get a final coordination number of 6. The amount of times each ligand is attached is super important to determining the coordination number!

Becca Nelson 3F

Hello! these transitions metals can help in the active site. The active site is essential to the enzyme as this is where the substrate binds.

Becca Nelson 3F

You are totally right... ironate does sound weird. These are derived from latin and there are some notable exceptions that you should know. I think these just have to be memorized, something that kind of helps me is that these already tend to have strange abbreviations. Iron is Fe not I or Ir like w...

Becca Nelson 3F

What do you do with a dead chemist...

Barium!

Becca Nelson 3F

Yes, the number before the sp2 refers to the energy level of that. So Silicon would have 3sp3 hybridization if it was bonded to 4 atoms.

Becca Nelson 3F

The shape of the water molecule or any AX2E2 molecule is bent or angular. The electron density distribution is in a tetrahedral shape however.

Becca Nelson 3F

Yes. I do believe we will have to know the bond angles for the common geometries and we should be able to know how lone pairs impact these bond angles. We will have to know the general bond angle for that shape, but not the specific, experimentally derived values for each molecule.

Becca Nelson 3F

Regions of electron density are counted by adding the number of lone pairs (not each electron in the lone pair) to the number of bonded atoms. For example, H2O has 4 regions of electron density.

Becca Nelson 3F

I like to think about periodic trends in the way that makes sense instead of memorizing how they move, there are quite a few trends and it can be easy to get them muddled if you do not think about how it may work. Ionization energy is the amount of energy required to remove an electron from a gaseou...

Becca Nelson 3F

Bond angles in specific molecules are calculated experimentally. We can tell by the structure what the approximate bond angles may be. We also know that lone pairs cause more repulsion, so bond angles away from the lone pair may be smaller. We can not determine to what extent they will be smaller, h...

Becca Nelson 3F

When do I tell bad chem jokes?

Only periodically

Becca Nelson 3F

Does anyone know if 14B sessions will be recorded lectures as well? There is a fiat lux I would like to do, but it is at the same time as my chem lecture and I was hoping to just watch the chemistry lecture recording and go to my fiat lux live.

Becca Nelson 3F

I do believe the final will be different. It has a longer time segment and should therefore have more questions. If I am not mistaken I believe it is also cumulative. Moreover, as we are all taking it at the same time, the proctoring may be a little different.

Becca Nelson 3F

I tell a lot of chem jokes, but I never get a reaction!

Becca Nelson 3F

While I am not exactly sure if naming polyatomic atoms will be on the exam, I expect that we should be able to take an ion name and transform that to a chemical formula. For example if they say Magnesium chloride, you should be able to know that is MgCl2.

Becca Nelson 3F

Expanded octets occur when elements have access to the d-block. So neon for example could not have an expanded octet.

Becca Nelson 3F

In this case, you want the configuration that has the lowest formal charge possible. That may mean making double bonds or rearranging electrons so that it is most favorable with the lowest number of atoms with formal charge. You may also have to look at which atoms have a formal charge, fluorine for...

Becca Nelson 3F

We can look at trends in the periodic table to determine what charge ion an element is most likely to form. a)Sulfur is group 16, so it is most likely to have a charge of -2 b)Tellurium is also group 16 so it will likely have a charge of -2 c)Rubidium is group 1 so it will most likely have a charge ...

Becca Nelson 3F

This relates I believe to the ion in NH4+. If you look at NH3 is does follow the principle that you were stating before. The cation means that an electron needs to be subtracted from the total number of electrons. I hope this helps a little bit. Many times the rules we learn can be broken in specifi...

Becca Nelson 3F

There are many steps in some of the mathematical problems we are doing. There is an answer that may be one of the steps, but is not fully there. For example, a problem could ask for the number of kJ/mol released, and you likely calculated the number of J per atom first. That could be an answer choic...

Becca Nelson 3F

L represents lone pairs. It is the number of dots surrounding an atom. Count each dot around the atom as 1 for L.

Becca Nelson 3F

Lewis structures are a great way to visually represent a molecule, but do have many limitations. Resonance is not in itself a limitation but a factor to be considered. Resonance is the idea that multiple bonds can be shared in multiple locations. For example, through bond lengths we see in the nitra...

Becca Nelson 3F

It helps to look at the groups! For groups 1 and 2 it is pretty simple, but for groups 13 through 18, 10 needs to be subtracted to determine the number of valence electrons. Remember that the periodic table is grouped by quantum numbers and is why 10 needs to be subtracted from the group.

Becca Nelson 3F

I post pretty corny chemistry jokes because all of the good ones Argon!

Becca Nelson 3F

A nodal plane is a region where the probability of finding an electron is 0. This has more to do with how bonding and atomic structure relate than just quantum numbers.

Becca Nelson 3F

If you remember Dr. Lavelle's drawings it can help you see how the d orbitals work. There is only one orbital s can be (a sphere), p has 3 different orbitals and d has 5 orbitals.

Becca Nelson 3F

What is the 2nd best public university's favorite element?

Berkelium!

Becca Nelson 3F

To convert eV/atom to kJ/mole you need to use the conversion from eV to J. From there multiple by 10^-3 to convert from J to kJ. Lastly multiply by Avogadro's number to get from kJ/atom to kJ/mole. Hope this helps!

Becca Nelson 3F

Yes! Delta v is uncertainty in velocity. If your velocity is 10+/- 2 you could have a velocity of either 8 or 12, so there is a difference of 4. This is the value you will plug into the equation.

Becca Nelson 3F

Has anyone found a good way to prop your phone up to let it see your workspace. I am using my phone, but struggling to find a clear way to have it point at my workspace.

Becca Nelson 3F

Has anyone found a good way to prop your phone up to let it see your workspace. I am using my phone, but struggling to find a clear way to have it point at my workspace.

Becca Nelson 3F

It is final - initial. In the case of energy being emitted it will be positive and absorbed will be negative. While your equation is correct, I find it easier to use v=R(n1^-2 - n2^-2). Hope this helps!

Becca Nelson 3F

I think it would be good to know about Paschen (n=3), but I do not think it is necessary to know Brackett. I think you should be able to explain that as energy levels get higher they get closer together and patterns like this but not necessarily the name.

Becca Nelson 3F

This statement is False. The way I determined this is through the E=hv equation. An increase in intensity does not increase the energy of the photon as it does not change the constant h or increase the the value of v.

Becca Nelson 3F

Wavelength can be measured in many different quantities, but in formulas you should use meters. Through the sapling hw, I have seen nm, m and angstrom. When you see these different notations, just adjust the scientific notation accordingly.

Becca Nelson 3F

I found the greatest importance in DeBroglie in that all matter in motion displays wavelength, but things with lots of mass (like things we see in everyday life) have such small wavelength that we can not see it. I think the baseball in motion example gave me much greater understanding. In this situ...

Becca Nelson 3F

why did the white bear dissolve in water?

because he was POLAR!

Becca Nelson 3F

Hello! One way that I study is by sitting specific times for specific studying. I like to review all of my notes, review practice problems and formulas, and then do some of the assigned textbook questions. These all really help me succeed on tests. BTW, I am feeling the same way... it is scary being...

Becca Nelson 3F

These variables are h for Planck's constant (6.6.26 x 10^-34) and v for frequency. The v for frequency can also be seen in c=(wavelength)(v). With the only terms in E=hv being a constant and v, we see how it does not matter the intensity of the light but only the frequency. This goes back to Dr. Lav...

Becca Nelson 3F

Protons and neutrons both have a mass of around 1 amu and electrons have a negligible mass. Knowing these values can be incredibly helpful when determining what isotope an atom is when given the total weight of the atom.

Becca Nelson 3F

The Lyman series has to do with the transition of electrons of higher levels to the first orbit. These transitions emit ultraviolet photons (makes sense because they are higher energy photons and more energy will be released when the electron transitions from higher levels). The Balmer series has to...

Becca Nelson 3F

What was Avogadro's favorite sport?

Golf... He always got a MOLE in one.

Becca Nelson 3F

A very helpful step in knowing what steps you have to take is to list your knowns and unknowns. Some problems will give you a balanced equation, some problems will ask for the answer in moles of product produced, some questions will just ask what is the limiting reactions. Based on what is asked and...

Becca Nelson 3F

Your issue is likely that you need to convert to the proper units. GHz is gigahertz. Giga is a prefix meaning 10^9. In this equation, you need to convert to hertz to get the proper value. So to convert Gigahertz to hertz you will multiply the value by 10^9 and then continue to use that value through...

Becca Nelson 3F

No, they have different rules. For multiplication and division your answer should have as many significant figures as the smallest number of sig figs in your data. For example: (98.0/5.071)*5.322 = 102.851 In this case our smallest number of sig figs comes from 98 (3) so our answer with sig figs is ...

Becca Nelson 3F

When using a calculator I always take the value that I already computed and hit enter so it will have the most amount of decimal points. It can also be helpful if you set up exactly what you need to plug in before hand and do it all in one go. Just make sure to check that your answer seems reasonable.

Becca Nelson 3F

As a general rule of them look at the unit in the equations you are using. While kilograms is the SI unit, there are many lab instances where using grams is preferred. Just make sure to always check the equation and what it requires (g or kg) and to see what units the final answer asks for and do yo...

Becca Nelson 3F

Sometimes, you will not get a whole number of moles. For example, in the example Dr. Lavelle did in the Audio Visual Topics, there was a ratio of 1 C to 1.33 H to 1 O. Here we multiple to get integers for all 3 numbers, in this case we multiply by 3 to get an EF of C3H4O3. In some cases, you will ju...

Becca Nelson 3F

I tend to use one decimal point for Molar Mass values on the problems we have been doing. If the Molar Mass is need for a lab, I will use more decimal points to have the most precise data as I can for that value. I do not think there should be much variation in the values especially after sig figs a...

Becca Nelson 3F

What do you do if nobody laughs at your chemistry jokes?

You wait for them to have a reaction!

Becca Nelson 3F

There are major implications of accuracy and precision in the lab. Precision is one of the main reasons we have significant figures. Our resulting value needs to reflect the instrument with the most error that we used. We want other scientists to see how precise our data is which is a reflection of ...

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