CHEMISTRY COMMUNITY

Rachel-Weisz3C

I don't think it was taught to use in lecture, but it might be tomorrow! My ta went over it in discussion, so I'm guessing it will still be good to know and understand it!

Rachel-Weisz3C

I think it is important to understand the graphs. I doubt we would need to draw them, but knowing the what the slopes are for different orders is probably useful. I think some practice problems even incorporate the graphs, and it might be hard to solve them if you do not know what the axes/slope wou...

Rachel-Weisz3C

I think frequency factor accounts for the frequency in which two compounds (reactants) will collide with each other at the correct orientation. As mentioned, in class when the frequency factor increases, k will also increase.

Rachel-Weisz3C

Yes. Each rate law has its own equation for 1/2 life. For example, the half-life for the 1st order is $t\frac{1}{2}=\frac{0.693}{k}$ and the half-life for 2nd order is $t\frac{1}{2} = \frac{1}{k[A]}$ .

Rachel-Weisz3C

Ice melting is a spontaneous reaction and when you have a spontaneous reaction, $\Delta$ G is automatically negative. If it was a non-spontaneous reaction $\Delta$ G would be positive.

Rachel-Weisz3C

1/2 life for first order is the only order that is not dependent on initial concentration but just the reaction constant (k), with units 1/s.

Rachel-Weisz3C

It represents time and it is usually measured in seconds, therefore rate = M/s, but it can also be measured in minutes, hours... depending on the reaction.

Rachel-Weisz3C

There are some rules that are helpful to identify an elements oxidations number, based on there location in the periodic table. For example, if the element is in group 1, its oxidation number is always +1. Likewise, if it is in group 2, the oxidation number is always +2.

Rachel-Weisz3C

Electrolysis uses an electric current, from an outside source, in order to produce a non-spontaneous reaction (where $\Delta$ G > 0)

Rachel-Weisz3C

I think we should be getting them back this week in discussions sections.

Rachel-Weisz3C

They are not the same things, but they are similar as a rechargeable battery can act as an electrolytic cell when they are being recharged.

Rachel-Weisz3C

 I don’t think you would specifically need to use the Van Hoff’s relationship, as long as you know the relationship conceptually.

Rachel-Weisz3C

It should be measured in cal/mol or J/mol. This conversion is 1 J= 0.239 cal but you probably won't need to convert, just use which ever is given.

Rachel-Weisz3C

I believe that if $\Delta$ G is equal to zero the reaction is at equilibrium.

Rachel-Weisz3C

Ethan Breaux 2F wrote:are there ever curves?

I don't think there are ever curves on the tests/midterm.

Rachel-Weisz3C

I would be prepared to understand/explain them conceptually as well as through calculations.

Rachel-Weisz3C

I think it will be stated in the questions, but if it doesn't specifically say isothermal, it would say that temperature remains constant.

Rachel-Weisz3C

I know that when there is constant temperature $\Delta$ U = 0, but if there is constant pressure in a system, what things can we say about it?

Rachel-Weisz3C

The Equipartition Theorem is not included on the third outline: Thermochemistry and The First Law of Thermodynamics, so I do not think we will need to know it.

Rachel-Weisz3C

I do not believe there is like a specific ideal gas, it is just a theoretical way to describe the gas. It means that it obeys the gas laws and therefore easier to analyze.

Rachel-Weisz3C

I think because the heat capacity is constant the value does not need to be included when solving a problem, therefore you can use the equation they give you for $\Delta$ S in order to find entropy, and use the values that should be provided for moles, and the two temperatures.

Rachel-Weisz3C

Work is more complex than a state property. Work is dependent on the path used to get to its current state, which is the opposite of the definition of a state property which only depends on the state of the system.

Rachel-Weisz3C

I think problems will normally specify what ids preferred or if they give you a value with J or kJ included, use the one that is given. Otherwise you should be able to do either and just make sure the units are present.

Rachel-Weisz3C

I think for pressure we use atm and for volume it should be Liters/milliliters, depending on the problem provides.

Rachel-Weisz3C

Dr. Lavelle said that a state property is a value determined by its current state, independent of the path taken to obtain that state. Enthalpy does fall under this category, along with temperatures, volume, pressure, energy, density and heat capacity.

Rachel-Weisz3C

I don't think you need to have any particular compounds memorized as strong acids or bases, but it would probably be good to know a couple (like some that show up frequently in lectures/homework problems). More importantly, just know how to identify compounds as acids/bases.

Rachel-Weisz3C

I think that is totally correct, and Dr. Lavelle mentioned the metaphor that if a person has a million dollars giving away a couple thousand doesn't make much of a difference to them, because they are still very close to a million. So basically even though we don't know x, we know it is going to be ...

Rachel-Weisz3C

I think that if you increase the temperature the rate of the reaction increases, but I do not believe it affects concentration or pressure in any way.

Rachel-Weisz3C

How can you tell if something is a conjugate base? Any info about conjugate bases would be helpful!

Rachel-Weisz3C

That sounds right! Also, as Ka increases, Kb decreases and vice versa, since Ka x Kb = Kw.

Rachel-Weisz3C

I think that as long as you know that the brackets represent concentration you should be good. Once you begin to solve the problem, I don't think it is necessary to differentiate between parentheses or brackets.

Rachel-Weisz3C

Aqueous solutions are also left out when finding K and these also apply when finding Q.

Rachel-Weisz3C

I think the ICE table is just a way to organize the work and to go from Initial molarity(I) to Change in molarity(C) to the Equilibrium Molarity(E). I found this video helpful with explaining and showing an example: https://www.youtube.com/watch?v=iDr5DMiJ1j8

Rachel-Weisz3C

I think k' refers to the inverse of k, meaning if we know k of a forward reaction, the reverse reaction equals k' or 1/k.

Rachel-Weisz3C

Ethyl alcohol is a larger compound, as you can see in its formula, this means that the LDF/VDW forces that are acting on it are stronger than those forces present in the Methyl alcohol, therefore making it more difficult to dissociate, which is why the boiling point is higher.

Rachel-Weisz3C

I think that thinking of this aside from the size of atoms, you can think about the electronegativity differences to determine bond strength.

Rachel-Weisz3C

I don't think we will be tested on this information. I think Prof. Lavelle was just informing us that the textbook has more information on blood pH, as he didn't go into much depth on it.

Rachel-Weisz3C

If HF could easily ionize into a solution it would not be as weak, however it does not fully ionize because its bonds are too strongly bound.

Rachel-Weisz3C

Sulfur wants 6 valence electrons, so whether there are two or three oxygens attached, there will be double bonds attached to all the oxygens, and therefore the bond lengths will be the same in both molecules.

Rachel-Weisz3C

When a compound has a high electronegativity it can be considered more ionic and bonds that have more ionic characteristics they can be considered polar. Oppositely, compounds are non-polar if they have have a low electronegativity, because the electrons share more equally.

Rachel-Weisz3C

I think as long as you can recognize them, and understand the concept of hybrid d-orbitals you should be good!

Rachel-Weisz3C

I think if you are given a structure name or you can determine the structure based on a chemical formula, you can also determine bond angles, you do not need to draw the molecular shape, but it can be helpful to visualize it.

Rachel-Weisz3C

Molecular shape can help to determine the molecules properties. For example, water is a good solvent because of its bent structure and bond angle of 104.5.

Rachel-Weisz3C

If something is highly electronegative, electrons from another ion will be pulled away, distorting the shape. A good example of this is XeF4, where the F molecules are highly electronegative and so the electrons will be pulled to the F.

Rachel-Weisz3C

One example that Dr. Lavelle gave in class was that H2O has a lower bond angle than methane (CH4) because we know that methane has a bond angle of 109.5 degrees, and H20 is smaller than that, but we do not need to know that it is exactly 104.5 degrees.

Rachel-Weisz3C

In discussion, we had to draw the Lewis Structure of ClCN. Which looks like: Cl-C \equiv N (with 2 lone pairs on Cl and one lone pair on N). I was wondering if there was anyway this compound could be represented with a triple bond on the Cl instead of the N, like: Cl \equiv C-N . And if this is not ...

Rachel-Weisz3C

Will we be having discussion sections next week if they are Monday-Wednesday?

Rachel-Weisz3C

Localized electrons remain close to an atom or in the same place, however delocalized electrons are shown in different places between different resonance structures.

Rachel-Weisz3C

Aside from the number of bonds (single, double, etc.), the overall length of a bond also determines how strong it is. When the bond length is larger, the bond is weaker because the atoms are further apart and therefore they can break apart easier. H2O has a bond length of about 1A and H2S has a bond...

Rachel-Weisz3C

When asked to draw resonance structures, is it necessary to draw all the possible structures or just a few?

Rachel-Weisz3C

When there is a negative charge, it means that it is more negative than it would have been without the charge, this means that another electron has been added. You represent this by drawing another electron or dot when drawing the Lewis Structure. So when you add up all the valence electrons from th...

Rachel-Weisz3C

I'm not sure if the directions will specify or not, but I would recommend writing them all out and drawing attention to the one with the lowest energy.

Rachel-Weisz3C

In one of the review sessions, it was asked what the maximum number of electrons would be present when n=2 or when n=3. I thought about how if n=2 then l=1 or l=0, which corresponds to the p-block and s-block, respectively. This would mean that the maximum electrons would be 6 (in the p-block). Is t...

Rachel-Weisz3C

Lavelle also mentioned that we would not be asked a question that resulted in a value like 1.6. He will make it more clear whether it is >2 (ionic) or <1.5 (covalent).

Rachel-Weisz3C

Can someone explain the reason to why H, He, Li, and Be are the exceptions to the octet rule?

Rachel-Weisz3C

When atoms bind together, there is a release of energy. Therefore bound atoms have less energy than single atoms. This is also the reason that bound atoms are more stable, because of the lower energy.

Rachel-Weisz3C

Did you know protons have mass? I didn't even know they were Catholic!

Rachel-Weisz3C

I believe the answer to this is C, because we can’t know both the position and the momentum precisely, and if we know one of them precisely, we cannot precisely know the other. Lavelle also stated that there is a limit on the accuracy to which the momentum & position of a particle can be known s...

Rachel-Weisz3C

I don't think they are ever interchangeable since v (nu) in E=hv for instance stands for frequency, but v represents velocity in an equation like KE=1/2mv^2. They are two different things and can't be looked at as interchangeable.

Rachel-Weisz3C

I think Lavelle wants us to know what the orbitals would look like and understand the differences but I don’t think it is required, and he said he would not make us draw any orbitals.

Rachel-Weisz3C

Although kJ/mol is a valid unit for energy/material, or something like finding $\Delta$ G. But for I’d use Joules.

Rachel-Weisz3C

I think what they mean is that electrons have a range of values instead of continuous energy levels, implying an unending range, which is why an electron can’t exist in every case but rather a specific or quantized level.

Rachel-Weisz3C

I believe in lecture, we were told that for the sake of answering questions that ask if there can be measurable wavelike properties the cutoff is at 10^-18 (even though it is extremely small), but in the lab, it would be rare that anyone measures pat 10^-12.

Rachel-Weisz3C

C states that the extent of the change in the electric field at a given point decreases. This is true when the frequency decreases because if frequency is decreasing, wavelength must increase based on the equation c= \lambda x v When wavelength increases the 'extent of change' aka the slope (of the ...

Rachel-Weisz3C

Some of the module videos also have an additional example or slightly different material than what we had for lectures, so they are not only helpful to go over examples we already saw but also a little bit of different information as well!

Rachel-Weisz3C

Can the mass of a product (or products) be greater than the total mass of reactant (or reactants)?
I would like to say that the mass of the reactants=mass of the product so no it isn't possible, but an option for an answer is: “under some conditions”… is it ever possible??

Search found 66 matches