CHEMISTRY COMMUNITY

Fanny Lee 2K

Why is that sometimes we can add E° values together to get the overall E_cell° even though it not a state function?

Fanny Lee 2K

We do not need to derive it on the final. However you should know what it represents and why we derive it (to find the instantaneous rate).

Fanny Lee 2K

NO can pack as NO or ON which are clearly identifiable whereas the three F positions in BF3 cannot be distinguished.

Fanny Lee 2K

You would have to make one reactant concentration small and the others large which makes the reaction rate dependent on only the small concentration reactant. Since they are such in large excess, they remain constant.

Fanny Lee 2K

Lavelle did not specifically explain what the differences were between the order reactions other than the graphs of the outcome relative to the concentration of reactions. However the differences of order reactions gives insight to the reaction mechanism. The rate of the reactions depend on the reac...

Fanny Lee 2K

Before, we studied thermodynamics which tell us which way a reaction would occur in and its spontaneity. Thermodynamics is the study of energy--does not tell us how fast or slow a reaction is occurring. However with kinetics, it is the study of the rate of reaction.

Fanny Lee 2K

Usually in atm or Torr. Just make sure the units are the same when combining equations together. The constant and formula sheet provided will give you the conversion factors.

Fanny Lee 2K

The order of reaction of a reactant indicates how much the rate of reaction changes if the concentration of the reactant is changed. It predicts how the reaction speed change over time.

Fanny Lee 2K

At 0 degrees Celsius, the compound would not have vibrational or rotational entropy but will still have positional/residual entropy. That is why S is the only instance in which the elements at it's most stable form is not 0.

Fanny Lee 2K

The question should tell you whether or not it is an acidic or basic solution

Fanny Lee 2K

We add water in acidic solutions. The amount of the moles depend on how much oxygens in the reactant side. Balance the reactants with the corresponding number of hydrogens from water.

Fanny Lee 2K

When the entropy is at 0, it forms a perfect crystal. However, it still has some positional entropy. Higher entropy levels would result in higher rotational and vibrational entropy.

Fanny Lee 2K

You must take an account that microstates must occur within the same energy in order to calculate entropy.

Fanny Lee 2K

Simply, the system is the object you are observing and the surrounding is everything else.

Fanny Lee 2K

I don't think it's a major focus of the midterm but possibly!!!

Fanny Lee 2K

105085381 wrote:Will the bond dissociation energies definitely be given?

The bond dissociation energies will definitely be given but they are given in positive values assuming bonds are broken. Be sure to be careful with the signs when applying it in the midterm and final.

Fanny Lee 2K

Yes the constants and equation sheet is updated since 14A and includes conversions from atm.L to joules. However the sheet also gives the ideal gas constants in which you can convert using those constants to find the correct units.

Fanny Lee 2K

An isothermal process is a change of a system, in which the temperature remains constant: ΔT = 0. A non isothermal process is when the temperature is not constant.

Fanny Lee 2K

Adiabatic system is when delta q = 0
isochoric system is when delta v =0
isobaric system is when delta p = 0

Fanny Lee 2K

In an isothermal reversible reaction, the delta U is equal to 0. Given the equation delta U = q + w, q would equal -w.

Fanny Lee 2K

For example volume, if you have 10 L of water then add 7 L and removed 3 L, you will end up with 14 L left while the overall change in of water would be 3L even thought there were changes in the intermediate steps. With this example, it shows that state functions does not depend on the steps in-betw...

Fanny Lee 2K

When steam gets into contact with the air, doesn't it cool down immediately?

Fanny Lee 2K

Q is used to compare to K when at equilibrium. It tells us which way the non-equilbrium solution will shift in order to reach equilibrium. When this state is reached, Q = K.

Fanny Lee 2K

Unlike molarity which only limits us to use the ICE table using concentrations, partial pressures can allow for bar or atm as long as you are consistent with the units throughout.

Fanny Lee 2K

Autoprotolysis is happening automatically in aqueous solutions. Lavelle talked about how in weak acids and bases, this concept can play a role of their concentration on the pH as a whole. If values are smaller than 10^-7, their effect is not great enough to change the pH from its neutral state.

Fanny Lee 2K

If I remember correctly Dr. Lavelle noted that the group II elements would affect the pH slightly but not significant enough so that the pH is affected. Keep in mind that sometimes the textbook would write equations using the double arrows for the 2+ cation.

Fanny Lee 2K

Solids do not have a concentration, it can only be measured by mass and density. Pure liquids take part in very little of the reaction so the outcome of the liquid is quite insignificant. Dr. Lavelle used an analogy in class that explained this concept well: if you have a million dollars and you giv...

Fanny Lee 2K

Adding water to the reactants will cause the yield of the products (in this case C6H12O6 and O2) to increase as well. If the partial pressure of CO2 is decreased, it will cause the products to decrease to make up for the loss of the partial pressure from the reactants.

Fanny Lee 2K

This is the link to his test dates:
https://lavelle.chem.ucla.edu/wp-conten ... hedule.pdf
The topics tested on each of the quizzes is not cumulative--meaning that it quizzes only material after each quiz. However, midterms and finals are indeed cumulative.

Fanny Lee 2K

Going off from the response above, if the value of Kc is not less than 10^-4, then you must solve for the x value using the quadratic equation (cannot use shortcut). Dr. Lavelle included the rule about quadratic and cubic to help us when dealing with math equations with these properties.

Fanny Lee 2K

yes, solids can be measured by mass and density. There is no such thing as a concentration of a solid.

Fanny Lee 2K

Pure liquids (such as the solvent water) are not considered in the k expression since there is such a large excess and the amount used in the reaction is a very small amount, we can say that the concentrations do not change significantly. If the concentrations were used to find the equilibrium const...

Fanny Lee 2K

If given both aqueous and gases, convert the pressure of the gas into a concentration unit using the ideal gas law.

Fanny Lee 2K

When you're given both units of concentration and units of pressure in an equilibrium equation, you must convert the units of pressure into units of concentration using the ideal gas law.

Fanny Lee 2K

With a transition metal, it appears first in the coordination compound formula. However when you name it with the ligands, it appears last, after the ligands alphabetically.

Fanny Lee 2K

Since the equation to calculate the pH is -log, the negative sign ensures that the value of pH is positive.

Fanny Lee 2K

It's good to know that Lewis acid and bases are the "bigger" categories that encompasses the Bronsted acid and bases. Generally speaking, a Bronsted acid and base and be a lewis acid a base, but the lewis acid and base does not necessarily have to be Bronsted

Fanny Lee 2K

Lone pairs are also considered regions of electron density!

Fanny Lee 2K

I would first draw out the lewis dot structure and use the steric numbers to determine the VSEPR shape of the molecule. If it is linear, trigonal planar, square planar, T shaped, and bent, then it is on the same plane. If the VSEPR shape is drawn using wedges, then it does not lie on the same plane.

Fanny Lee 2K

Yes, HCN is linear. The bent shape only applies to lone pairs on the central atom. The lone pairs on the central atom have a stronger repulsion and thus push the two other bonds slightly closer together.

Fanny Lee 2K

Bond angles will deviate from their ideal values according to the rule that lone pairs repel other electrons more strongly than bonding pairs. Being closer to the central atom causes lone-pairs take up more of the available 'bonding space'. Remember that lone-lone pair > lone-bonding pair > bonding-...

Fanny Lee 2K

The more electronegative atom is the delta negative and the less electronegative atom is delta positive. The dipole moment is from the positive to the negative.

Fanny Lee 2K

The individual intermolecular bonds can be polar within a molecule but in some cases if you look at the entire molecule as a whole, these dipole moments can cancel each other out, making the overall molecule non-polar while consisting of individual polar bonds. How the compounds are rearranged can d...

Fanny Lee 2K

In the VSEPR formulas, "A" stands for a central atom, "X" for an attached atom, and "E" for a lone pair.

Fanny Lee 2K

Depending on where an element is on the periodic table, you can estimate how strong the electronegativity is. The larger the difference, the more polar since elements on the upper right is more electronegative than the upper left elements. Another ways is to see if the structure of the molecule is s...

Fanny Lee 2K

Without the interactions of other atoms/molecules, the arrangement of electrons within the electron cloud would be symmetrical. Since the force is introduced, the electron cloud can be distorted, meaning it is shifted to one side. Depending on which atom has the stronger polarizing power or polariza...

Fanny Lee 2K

polarizability applies to anions and polarization power applies to cations. The bigger the atom, the bigger the distortion.

Fanny Lee 2K

yes campus is closed so no sessions for 11/12

Fanny Lee 2K

Elements in period 3 or lower on the periodic table can have an expanded octet. Elements H, He, Li, Be, and group 13 can have incomplete octets. Elements in the 2p orbital can only have an octet.

Fanny Lee 2K

Always try to have the charges in the outer elements of the Lewis Structure and have the anions on the element that is most electronegative.

Fanny Lee 2K

If an element has a high electronegativity, does that mean it has higher electron affinity?

Fanny Lee 2K

Since Br fills up the 4p orbital, it can have more than an octet.

Fanny Lee 2K

I'm pretty sure all of Group 6 and Group 11 elements are also part of the exception. I'm curious about your second question too, if anyone would please explain?

Fanny Lee 2K

Allotted time is two hours!

Fanny Lee 2K

Knowing the formal charge on a particular atom in a structure is an important part of keeping track of the electrons and is important for establishing and predicting the reactivity. The formal charge on an atom in a molecule reflects the electron count associated with the atom compared to the isolat...

Fanny Lee 2K

The correct answer should be b because it releases more energy from n=5 to n=1 than n=4 to n=1. Since more energy is released, the wavelength of should be shorter for n=5 to n=1 than from n=4 to n=1.

Fanny Lee 2K

The electron absorbs energy and moves to a higher energy level. It then produces a line emission spectrum when it moves back down to a lower energy level (goes from an excited state to the ground state) and releases energy. The energy released is negative and should equal to the amount of energy put...

Fanny Lee 2K

You would use the Rydberg Equation 1/λ = RZ2(1/n12 - 1/n22) and figure out the wavelength. N2 and n1 is related to the principal quantum number or energy quantum number. This formula works very well for transitions between energy levels of a hydrogen atom with only one electron. Use the initial ener...

Fanny Lee 2K

Lectures should be the same! Lavelle has lectures at 10am-10:50, 12pm-12:50, and 2pm-2:50pm

Fanny Lee 2K

Yes you touched upon the important aspects of what the photoelectric effect shows in which electromagnetic radiation has the properties of particles. Albert Einstein suggested that light consisted of particles (or packets) of energy called photons. The energy of the photon has energy when you multip...

Fanny Lee 2K

To find the n values of the orbitals, you need to use the Rydberg equation: v=R((1/n(Initial)^2)-(1/n(Final)^2). First you need to find the frequency which you calculated as 2.922 x 10^15 s^-1. Plug in the frequency and n(initial) as 1. solve for n(final)^2 which should equal to 9. If we want to fin...

Fanny Lee 2K

Hey Tyra, 5Cl and Cl5 are both the same thing but if you're comparing in terms of molar ratios, the form of 5Cl would be best. Technically speaking, both contain 5 moles of Chlorine. Also on the quiz, you don't need to know how to name to molecule/compounds, but definitely on future tests! Hope this...

Fanny Lee 2K

Hello!
You would use the formula Molarity = number of moles / volume (L). The reason we use this formula as opposed to the other one is that this question is asking for volume, not relating to dilution.

Fanny Lee 2K

The wavelength is the distance between the peaks or trouphs of a wave. The frequency is how many waves occur within a given time. The wavelength and frequency of light are closely related. The higher the frequency, the shorter the wavelength. Because all light waves move through a vacuum at the same...

Fanny Lee 2K

Your result will be 15.00

-Hope this helps :)

Fanny Lee 2K

The professor said that anything on the test relating to naming compounds are given to you. However once we learn about the composition of the molecules and the names associated with it, then we are expected to know the formula.

Fanny Lee 2K

Hello,
If you purchased the periodic table sheet with the formulas in the back, the Rydberg constant is listed on it. I'm not sure if Lavelle would allow us to use it considering the tests are closed book and notes! It doesn't hurt to memorize it :)

Fanny Lee 2K

I'm pretty sure it is due for the end of this week but to be 100% sure, email your TA and ask them for clarification!

Fanny Lee 2K

Hello! I believe we should be moving onto new topics for week two's homework. I'm aware that those who have discussion sessions earlier in the week have an disadvantage but I would suggest reviewing some of the content in the textbook and browsing Dr. Lavelle's website for helpful modules for help o...

Fanny Lee 2K

First you would balance the equation: C6H9Cl3 + 3AgNO3 --> 3AgCl + C6H9(NO3)3. Next, use the given masses of the reactants, convert 0.750 grams of C6H9Cl3 and 1000 grams of AgNO3 to moles by dividing by its molar mass. You should get 0.004 moles of C6H9Cl3 and 5.887 moles of AgNO3. Then determine th...

Fanny Lee 2K

You need to double it to find the diameter!

Fanny Lee 2K

With the equation balanced, convert the two given grams to moles by dividing it by its molar mass. For NH3 you should get 1.26 moles and for O2 you should get 1.33 moles. Looking back at the balanced equation, there are 4 moles of NH3 and 5 moles of O2. Divide 1.26 moles by 4 and 1.33 moles by 5. Yo...

Fanny Lee 2K

First start of by balancing the equation and you should get C6H9Cl3 + 3AgNO3 --> 3AgCl + C6H9(NO3)3. Make sure the given masses of the reactants are converted into grams. In this case, 1.000 kg is equal to 1000 grams. Convert the grams to moles by dividing it by the molar mass. Determine the limitin...

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