CHEMISTRY COMMUNITY

Ashley Kim

The second order graph has nothing to do with the concentration, but rather the second derivative.

Ashley Kim

That probably means that one of the reactants is zero order (meaning that the rate is independent of its concentration).

Ashley Kim

The final exam will usually have a question on each topic covered, and chemical equilibrium is one of those topics. There will probably be acid-base equilibrium on the final as well.

Ashley Kim

The neutral pH can change with temperature, because pH is not constant with temperature.

Ashley Kim

I'm in 14BL right now too, and I'm taking it with 14B. I would say that everything you learned in 14A and 14B is covered. However, even if you don't remember everything fully, Professor Casey does a good job of explaining old and new concepts.

Ashley Kim

I think that there might be some electrochemistry questions too!

Ashley Kim

Oxidation has its name because in the early days of chemistry, the loss of electrons was associated with the gain of oxygen atoms. (It is a little confusing, though)

Ashley Kim

Yes, the oxidizing agent has the higher cell potential and the reducing agent has the lower cell potential.

Ashley Kim

Use the half-reaction method and add H2O and either H+/OH- to balance the reaction!

Ashley Kim

I think you should use H+.

Ashley Kim

K is a ratio, so it has no units.

Ashley Kim

The free energy equation is deltaG = deltaG(standard) + RTlnK.
K is the equilibrium constant, so the free energy depends on the equilibrium constant. Sometimes, when given partial pressures, they are used to calculate the equilibrium constant.

Ashley Kim

0.38 J/g C is the specific heat capacity of copper.

Ashley Kim

Heat capacity is extensive because it is the amount of heat required to raise a substance by one degree Celsius/Kelvin. It depends on mass because if a substance is more massive, then it is capable of maintaining more heat. Specific heat capacity and molar heat capacity are per unit of mass, so they...

Ashley Kim

Boltzmann's equation calculates positional/residual entropy using statistics.

Its form is S=kBlnW.

W is equal to the number of microstates (how many positions an element can be in in a molecule) raised to the power of the number of molecules in the system.

kB is a constnant.

Ashley Kim

That's a fair point. However, the question simply asks for you to identify the optimal heating curve based on the heat capacities given (just say that it defines how much the substance can contain before moving on to the next phase).

Ashley Kim

Another thing to note is that isothermal reactions mean that the temperature is not changing/constant. This means that delta U (change in internal energy) is zero because internal energy depends on the temperature.

Ashley Kim

The internal pressure does not matter because the only pressure that is inputted into the equation is the pressure that contributes to the work to the system - i.e. the external pressure. The initial volume was used to find the moles of gas because it is the initial state that can be accurately plug...

Ashley Kim

Ultimately, the heating curve for water shows how the phases (solid, liquid, gas) of water change over time as the water is consistently heated. It also relates with the enthalpy of fusion and the enthalpy of vaporization because the heat accumulates, resulting in these phase changes.

Ashley Kim

You have to consider whether the path is reversible and isothermal or whether it is irreversible.

Ashley Kim

Use this reaction to calculate the pH!
AlCl3 + 3H2O <=> Al(OH)3 + 3HCl

Ashley Kim

As far as I know, it depends on crystalline structure. Dr. Lavelle mentioned in class that graphite is sp2 hybridized, while diamond (which forms when graphite is subject to high pressure) is sp3 hybridized.

Ashley Kim

You will need to calculate the enthalpy of the reaction based on the information given to you by the question! e.g. if they give you bond enthalpies, you would need to draw the Lewis structures (or deconstruct/reconstruct all the bonds) to figure out the change in enthalpy.

Ashley Kim

This is for moles of gas only!

Ashley Kim

Activity is a measure of the effective concentration of a species under non-ideal (e.g., concentrated) conditions.

Ashley Kim

You can also tell from the pKa of the reaction. The smaller the pKa value, the stronger the acid.

Ashley Kim

If you increase the temperature of a reaction, you drive the equilibrium backwards (in the endothermic direction), and therefore increase the concentration of reactants and decrease the concentration of products. The two are inherently connected! This does not apply to either pressure or concentrati...

Ashley Kim

If you increase the temperature of a reaction, you drive the equilibrium backwards (in the endothermic direction), and therefore increase the concentration of reactants and decrease the concentration of products. The two are inherently connected! This does not apply to either pressure or concentrati...

Ashley Kim

Ideal gases and real gases have no physical/chemical differences! Rather, ideal gases are theoretical (meaning they do NOT exist). They fit perfectly into the equation PV=nRT, meaning that their particles obtain a negligible volume and have no attractive forces. However, this is not true for real ga...

Ashley Kim

Hello,
Would someone explain the two graphs of the Gibbs Free Energy curve at the bottom of page 435?

Sincerely,
Ashley Kim

Ashley Kim

Hello,
I was reading Chapter 5 and I was unsure of how Graham's Law of Effusion eventually was derived into an expression involving temperature. The equations are on page 170. Could someone explain the derivation/process to me?

Thank you!
Ashley Kim

Ashley Kim

Some of these oxidation states are simply the charge of the molecule, e.g. O2- will have an oxidation state of -2. An easier way to think about oxidation states is that they are if covalent bonds were split like ionic bonds - merely an intellectual model to determine which atoms are more charged tha...

Ashley Kim

You can tell by finding the hydrogen that will be donated to form a hydronium ion, and then determining which bond between that hydrogen and the rest of the molecule is stronger.

Ashley Kim

If anyone is interested, here are a couple of fairly recent abstracts on cisplatin (the chemical we talked about in lecture today). One of these is about general cisplatin chemotherapy and the second is about targeted chemotherapy, which avoids healthy cells. Both are fascinating! Hope you enjoy! ht...

Ashley Kim

Yes, the hybridization is still sp3 and the regional geometry is tetrahedral. However, the molecular shape is only based on the existence of atoms and not lone pairs.

Ashley Kim

Tetrahedral has the VSEPR formula AX4 (no lone pairs, four bonds).
Square planar has the VSEPR formula AX4E2 (two lone pairs, four bonds).

Ashley Kim

You would do separate sigma and pi bond descriptions for each resonance structure. Since they are two different structures, you would not count them together.

Ashley Kim

Sigma bonds are larger and stronger covalent bonds formed by the direct overlap of atomic orbitals.

Pi bonds are due to less overlap and are generally weaker. They consist of double and triple bonds.

Ashley Kim

As far as I know, hybridization can go into orbitals like the f and g ones. It's basically how all atoms, especially ones in the later periods, bond. However, the scope of CHEM 14A only covers up to the d orbitals.

Ashley Kim

The order doesn't matter as long as you know that the hybridized orbitals combine to make bonding occur.

Ashley Kim

Some shapes must have lone pairs because the angle is determined by the lone pair and bonding pair repulsion. Others, like the linear shape, may or may not have lone pairs depending on the structure.

Ashley Kim

O2 is not an exception, necessarily. All diatomic molecules are nonpolar.

Ashley Kim

Degeneracy means that the first two quantum numbers are the same and that the orbitals are equivalent.

e.g. 2px, 2py, 2pz

Ashley Kim

Looking at it through the hybridization lens, any atom past the 2p orbital can be an exception to the octet rule because the orbitals become degenerate.

Ashley Kim

The textbook readings are up to 3.11!

Ashley Kim

Nonmetals also tend to gain electrons more frequently due to their high electronegativity.

Ashley Kim

I honestly prefer the one where you use the lines to represent the bonds. In a Lewis structure, it's important to distinguish between the bonded electrons and the lone pairs. However, it's more difficult to do so if you represent the bonds with dots instead of lines.

Ashley Kim

It's important to note that some transition metals are capable of having multiple charges, hence the need for the Roman numerals in the first place. Transition metal ions involve a rearrangement of both the d and s orbitals. This is because according to the Aufbau principle, the electrons fill the 4...

Ashley Kim

This is because the p orbital has three degenerate orbitals: px, py, and pz. There are 3 orbitals (electron probability clouds) that have the same energy. The electrons in these clouds have the chance of moving in different places with the SAME energy.

Ashley Kim

It depends on both the type of ionic or covalent bonds. It's also important to remember that no bonds are truly ionic or covalent. All charges are shared to a degree. In ionic bonds, the charges are more unequally distributed than those on covalent bonds.

Ashley Kim

You can also figure out that nonmetals have higher electronegativity by considering the following: The electrons in the valence shell of a nonmetal have a higher attraction because they are closer to having a full valence shell. Therefore, it makes sense that nonmetals would have a higher electroneg...

Ashley Kim

I thought this question was interesting, so I decided to search it up. It turns out that you cannot change the frequency of a specific sample of light (as far as I know, you would have to get a different sample), but you can change the wavelength by passing light through a filter. There is also a ph...

Ashley Kim

Solving all the problems (both in the modules and in the textbook) is a good way to prepare for the test. Mark the ones you got wrong, and then resolve the wrong ones to understand the concepts.

Ashley Kim

Hello, I'm reviving an old post. However, I don't understand why you can figure out that n2=7 using the Balmer series. Can someone please explain?

Ashley Kim

This might be repetitive, but I used the M1V1=M2V2 equation. I converted the grams of KCl to moles and then found the molarity - then multiplied that value by the original volume (in liters). Then, I put in 0.125 L on the other side and solved for the second molarity. It's definitely quite repetitiv...

Ashley Kim

I thought of a comprehensive solution! First, find the moles of P4O6 formed for each reactant. The substance that makes the lowest amount is the LM. With that value, you now know how many moles of P4O6 you have for the next reaction. You still need to figure out how much O2 is left for the next reac...

Ashley Kim

Hello Ashley!
Thank you so much for your tips to study chemistry. I will definitely take advantage of them as I go through college at UCLA!

Ashley Kim

Is it one pea per second per PERSON, or just one pea per second OVERALL?

Ashley Kim

Thank you! I appreciate it.

Ashley Kim

Other than beginning with the least abundant element and using inspection, you can also try the proportions method. This is similar to the matrix method, where you put variables to represent each coefficient in the equation. Then, you solve it like a mathematical equation with multiple variables. Ho...

Ashley Kim

I found that there were two ways to solve stoichiometric calculations regarding limiting reactants. The first way is to find the number of moles of each reactant and calculate the mole ratio of the reactants. Personally, I don't use this one because I find it impossible to use with more than two rea...

Ashley Kim

However, the case where there are two limiting reactants is pretty rare - most chemistry problems will result in only one limiting reactant. (It also doesn't happen often in real life, because experiments usually put one reactant in excess.)

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