CHEMISTRY COMMUNITY

Maya_Peterson1C

What will we be required to know about concentration cells?

Maya_Peterson1C

Why does the equilibrium constant K equal the ratio of the forward and reverse rate constants?

Maya_Peterson1C

Yes, a bomb calorimeter maintains a constant volume (isochoric) for reactions.

Maya_Peterson1C

The y-axis is the inverse of the concentration of A. Thus, the slope shows that as time increases, the inverse of [A] increases (not [A] itself).

Maya_Peterson1C

Different order reactions have different reaction mechanisms, or the number of steps to form the product.

Maya_Peterson1C

They are not necessarily the same, but in some occasions they are. It is best not to assume they are the same and to find the order itself.

Maya_Peterson1C

I think it depends on the test version you had, but if you used the Van't Hoff equation and used the equilibrium constant equation to then convert [H+] to a pH value, you should get the right answer.

Maya_Peterson1C

If you are referring to the exponent n in the rate law, then I do believe it can be a negative value. This would be when the increase of the concentration of a reactant causes the rate of the reaction to decrease.

Maya_Peterson1C

The overall order of a reaction is the total sum of the orders of all the reactants.

Maya_Peterson1C

Does anyone know if it will also include entropy and previous thermodynamic concepts?

Maya_Peterson1C

I think it's safe to say the anode is on the left and the cathode is on the right because that's how it was presented in the lectures. The standard reaction potentials are given as reductions, so which ever one is being oxidized in the actual reaction, needs to be reversed.

Maya_Peterson1C

I think it would be best to have an understanding of how it works. Knowing that, drawing the diagram should come easier.

Maya_Peterson1C

The standard Gibbs Free Energy is fixed for a certain reaction and temperature. It is also under standard conditions and the difference between the Gibbs free energy of pure products and reactants.

Maya_Peterson1C

There are different values for the constant R depending on the units used in the problem.

Maya_Peterson1C

This is for an isothermal reaction. (We can also infer from this that q=-w)

Maya_Peterson1C

The internal energy is zero when it is a reversible reaction or if it is at a constant temperature.

Maya_Peterson1C

They do not affect the concentrations of other substances in equilibrium because they do not react.

Maya_Peterson1C

Can someone explain when and why we use 3/2 R and 5/2 R as the C_v value when finding enthalpy?

Maya_Peterson1C

If $\Delta$ U is a state function, how is it that we can use work, which is pathway-dependent, to calculate it?

Maya_Peterson1C

For Chem 14A last quarter Lavelle did have review sessions led by TAs and UAs the week leading up to the Midterm, so I would think that would be the case this quarter too?

Maya_Peterson1C

Why is "coolant in a refrigerator coil" considered an isolated system? I am not familiar with the contraptions inside a refrigerator, so I am just wondering.

Maya_Peterson1C

I believe that it depends on the type of information given in the problem. However, I recall Dr. Lavelle saying that Method 1 would give the most reliable and accurate answer.

Maya_Peterson1C

Are heat and enthalpy considered the same thing, or are there any differences between them?

Maya_Peterson1C

You would need to know the energy expenditure for each step of the reaction to get the total amount of work versus just calculating the net change when finding enthalpy.

Maya_Peterson1C

If K>1 then there are more products at equilibrium. If K<1 then there are more reactants. If K=1 then there are equal amounts of reactants and products at equilibrium.

Maya_Peterson1C

There is no difference within the ICE table itself, just the type of species that are put into it.

Maya_Peterson1C

In lecture Dr. Lavelle stated that all Group 1 and MOST Group 2 salts do not affect the pH of a solution. However, he did not state specifically which ones do not, so I do not think that is something we are required to know.

Maya_Peterson1C

Can someone clarify why there needs to be a change in volume for there to be a change in pressure of a reaction in equilibrium?

Maya_Peterson1C

I believe the general assumption is that a gas acts more "ideal" at higher temperatures and at lower pressures. I think most of the problems we will be given deal with ideal gases unless otherwise stated.

Maya_Peterson1C

We use K_p for gases, and it is calculated by using the partial pressures of those gases, so I don't believe this would apply to solids or liquids.

Maya_Peterson1C

A neutral ligand contributes no charge to the coordination compound. An example would be H20 (aqua) or NH3 (ammine).

Maya_Peterson1C

I believe this is because Co is the transition metal cation and F is considered the ligand in this case.

Maya_Peterson1C

A polydentate ligand has multiple binding sites that donate multiple electron pairs. You can look for and count the two dots denoting lone pairs as a sign.

Maya_Peterson1C

The molecules are normally written in an order where the atom with the lone pair is right next to the atom that receives it. Thus, because oxygen has the lone pairs in a H20 molecule, you would write it 0H2 if the atom that receives the electrons is to the left of the water molecule (such as when dr...

Maya_Peterson1C

Yes, generally non-metals tend to be more electronegative than metals, as the non-metals are located on the right side of the periodic table (and from the periodic trends, we know that from left to right electronegativity increases.)

Maya_Peterson1C

Fluorine is the most electronegative atom on the periodic table.

Maya_Peterson1C

A double bond consists of one sigma and one pi bond. (Sigma and pi bonds are different because of the different orientation of the orbitals of the bond.)

Maya_Peterson1C

I think we just need to know the angles for the basic geometry (electron density geometry) because those values are known and consistent I believe (like 90, 120, 180 degrees). For the electron density geometry, I think we just need to know how the lone pairs affect the bond angles.

Maya_Peterson1C

My TA told us that posts were cumulative, and thus built up and counted at the end. So, just in case we miss a week or something we could make it up. I am not completely sure if this is the case with all TAs though.

Maya_Peterson1C

Because the dipole moments are not symmetrically distributed and are different strengths, there would be a net dipole moment, thus making it polar.

Maya_Peterson1C

The electron density geometry does take into account all the bonding and lone pairs linked to the central atom. Molecular geometry only takes into account of the bonds that are actually attached to other molecules. If there are no lone pairs, these shapes are the same.

Maya_Peterson1C

There were resonance structures for the molecule that included single and double bonds, so the actual molecule would have an average of those two bonds. I took the average of the two lengths and got 130pm.

Maya_Peterson1C

There are also other names of shapes when there are lone pairs such as bent, T-shaped, see-saw, etc.

Maya_Peterson1C

Would a neutral K atom or K+ ion have a more negative value of electron affinity and why?

Maya_Peterson1C

I am not sure why that is, but during the TA review sessions, they mentioned that you should put brackets around ions when completing their Lewis structure.

Maya_Peterson1C

The concept basically follows that having a half or full filled subshell is more stable for an atom. Regarding electron affinity, N would have a lower E.A. than expected because it doesn't want to gain another electron due to the fact that it already has a half filled 2p subshell. Carbon, on the oth...

Maya_Peterson1C

If you look up the electronegativity values of H, C, and F, they are 2.1, 2.5, and 4.0 respectively. So, the electronegativity values for Carbon and Hydrogen are a lot closer than the value for Fluorine. Just because they appear closer on the periodic table doesn't necessarily mean their values are ...

Maya_Peterson1C

If you remove an electron, you are creating a cation. This net positive charge creates a stronger electrostatic attraction that holds the electrons tighter to the nucleus, thus requiring more energy to separate.

Maya_Peterson1C

This depends on the environment because in an aqueous solution covalent bonds would be stronger as ionic bonds would beak and separate due to the polar characteristics of water. However, ionic bonds out of water would be stronger due to the attraction of opposite charges.

Maya_Peterson1C

In high school I remember being allowed to draw straight lines whenever there were two valence electrons on a Lewis structure diagram, as a kind of shorthand method instead of drawing all dots. However, in lecture we learned to use straight lines only for shared electrons. Is the other way incorrect?

Maya_Peterson1C

It was not said exactly if there have been experiments done on this. However, I would think that anything at the atomic level would be affected by the light source.

Maya_Peterson1C

I believe in lecture Dr. Lavelle said it is safe to assume the visible light spectrum range is from about 400 to 700nm.

Maya_Peterson1C

If the speed of light was given at 2.998 x 10^8 and you want to round it, I would use 3.000 x 10^8 because it has the same amount of sig figs but would require less digits to input in the calculator. Using that value with 4 sig figs and given a value 2.55 nm with 3 sig figs, your answer should have ...

Maya_Peterson1C

I know the electron spin, or ms quantum number, is used because every electron had their own unique set of quantum numbers, but why is it +1/2 and -1/2? Was the value of 1/2 arbitrary?

Maya_Peterson1C

The s, p,d,and f orbitals correspond to the main types of shapes of the atomic orbitals. For example, the s orbitals are in the shape of a sphere and the p orbitals are two lobes with a nodal plane through the center. The periodic table is also split up in to s, p, d, and f blocks in which the valen...

Maya_Peterson1C

In the equations involving n, I know its value has to be a whole integer. In the book, it's followed by an ellipsis, implying that the value continues forever. Is there a certain value of n that becomes unreasonable?

Maya_Peterson1C

I did some research behind it, and some sources are claiming that recent studies show light doesn't always travel at the speed proposed by Einstein's theory. However, for the purposes of this class the speed of light is assumed to be constant.

Maya_Peterson1C

I don't see a question 1B.15 in the textbook. Is it at the end of the chapter?

Maya_Peterson1C

We learned in class that the equation E{n}= -(hR)/n^2 was only used for Hydrogen atoms because it was based on experimental data, but how different would an empirical equation like this be for other atoms?

Maya_Peterson1C

When something is neutralized, water is formed. So, taking the reactants of that second equation, Mg(OH)2 and HCl, you would have H2O as a product. This would be formed from the OH- in the Mg(OH)2 and the H+ from the HCl. Then, the remaining Mg2- and Cl- ions would form a compound, MgCl2. Once you h...

Maya_Peterson1C

43123230_162077154732160_7899198701413859328_n.jpg 43102606_2120414714877915_907926004423458816_n.jpg I did the work for the problem step by step. To solve it you need to know that the compounds given dissolve and break up into ions. The answer was 0.01 off from the textbook solution mostly likely ...

Maya_Peterson1C

A mole is 6.022 x 10^23 units of something, whether it be particles, atoms, molecules, etc. So, for example, there should be 6.022 x 10^23 separate water molecules in one mole of H20. The characteristic that differentiates moles of different particles would be their mass.

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