CHEMISTRY COMMUNITY

Alyssa Wilson 2A

How can I tell the difference between a catalyst and an intermediate? Adding on to this, if a molecule is cancelled out in step 1 on the reactants side of the equation when you are taking one of the approaches to solve the mechanism it is known as the catalyst, since it has been there from the begi...

Alyssa Wilson 2A

Julia Lee wrote:Do you guys know what he said he's gonna call his review sheet?

He might come into lecture on Friday and make an announcement before the class.

Alyssa Wilson 2A

I'm not positive, but I know that we will be given A (frequency factor or pre-exponential factor) in the problem, when asked to solve for the rate constant.

Alyssa Wilson 2A

Maybe try to separate your calculations into solving for -Ea/RT first, then plug that answer into e^(answer). After that try multiplying your value by A, and you should end up with the right rate constant. k (rate constant) is highly dependent on Ea, the activation energy.

Alyssa Wilson 2A

Adding on to this, if a molecule is cancelled out in step 1 on the reactants side of the equation when you are taking one of the approaches to solve the mechanism it is known as the catalyst, since it has been there from the beginning and is not consumed. You will be able to tell an intermediate, if...

Alyssa Wilson 2A

Thank you so much! :)

Alyssa Wilson 2A

I believe one of the TA's will be holding a review session next week where they will be going through the entire test.

Alyssa Wilson 2A

I believe we just need to know the definition, which is that the average rate is the change in [R] or [P] per unit of time. (Average rate= change in concentration/change in time). We only need to solve for the average rate when we are looking for the gradient (slope). The average rate of reactants w...

Alyssa Wilson 2A

Hi, I missed lecture on Wednesday due to travelling to NCAA Championships with Athletics. I was wondering if anyone could please post a picture of their notes? Thank you.

Alyssa Wilson 2A

A differential rate law expresses the reaction rate in terms of changes in the concentration of one or more reactants (Δ[R]) over a specific time interval (Δt). They change based on the reactants and each order of reactant (n), which then gives us further insight into the reaction mechanism. I belie...

Alyssa Wilson 2A

How do you know when to solve for a unique rate, rather than just a normal instantaneous rate? Is it when there is only one [R] and one [P] on either side of the reaction?

Alyssa Wilson 2A

MadelineHlobik wrote:What sort of energy/cell potential does Nernst equation tell us?

I believe the Nernst equation tells us the equilibrium potentials of the cell. For each ion, the equilibrium potential is the membrane potential where the net flow is zero through any open channel.

Alyssa Wilson 2A

Gibbs free energy= -nFE
Where n stands for the number of molecules of that compound.
F is Faradays constant.
E is the cell potential for the entire cell.

Alyssa Wilson 2A

Yes, it starts with everything from Gibbs free energy and goes until and not including the Nernst equation. (Weeks 6-7 material)

Alyssa Wilson 2A

What is the difference between a galvanic and a voltaic cell?

Alyssa Wilson 2A

When K=1, Gibbs free energy will =0.
When K<1, Gibbs free energy will be + and will result in a non spontaneous reaction.
When K>1, Gibbs free energy will be - and will be a spontaneous reaction.

Alyssa Wilson 2A

What happens when K<1, and Gibbs free energy is a positive value, assuming P and R are in their standard states?

Alyssa Wilson 2A

I'm a little confused on why the Van't Hoff equation shows the temperature dependence of K. I understand that it relates the difference in standard Gibbs free energy to K, because it's easy to measure, but why does it show that the temperature depends on K?

Alyssa Wilson 2A

Yes, I believe the midterm covers outlines 1-4 all the way until the end of entropy.

Alyssa Wilson 2A

I believe we should be focusing on the topics that are on the outlines all the way through the end of entropy. It's easier if you read based off of the outlines Dr. Lavelle gives us.

Alyssa Wilson 2A

Residual entropy is the difference in entropy between a state that is not in equilibrium and the state of a substance close to absolute zero. An example is carbon monoxide, which has a dipole moment.

Alyssa Wilson 2A

Other than the definitions of the different types of energy: internal, transitional, rotational, and vibrational, will we ever be asked to describe the type of energy that is being absorbed or released from the system in a question?

Alyssa Wilson 2A

The higher the temperature, the higher the gas pressure will be, so the expansion takes place against a stronger opposing force and therefore must do more work. So therefore, the reversible reaction will be doing more work compared to the others.

Alyssa Wilson 2A

I believe we just need to know that a calorimeter is a device in which energy is transferred as heat is monitored by recording the change in temperature produced by a process taking place within it. Also it is important to know the equation: q=-Ccal (delta) T. Here, if delta T is positive, then q wi...

Alyssa Wilson 2A

Yes, the steps are exactly the same as calculating without a salt (though the calculations might be a bit more difficult). In these types of problems, the thing to note is that the initial concentration for the salt (or product of the salt) will not be zero. Therefore, the equilibrium concentration...

Alyssa Wilson 2A

Can someone please explain the difference between endothermic and exothermic?

Alyssa Wilson 2A

Yes, I agree. The 5% rule states that your amount has to be within this range of the initial concentration, if it is not you will have to solve for the variable using the quadratic formula and you would pick the positive x value that’s within the range.

Alyssa Wilson 2A

Delta H is the change in enthalpy and if delta H is greater than zero, this means that a system absorbed heat and is known as an endothermic reaction. When delta H is less than zero, this means that a system released heat and the change in enthalpy had a much larger initial enthalpy value than the f...

Alyssa Wilson 2A

When a forward reaction is exothermic and is at equilibrium, increasing the temperature decreases the value of the equilibrium constant (k). If the forward reaction is endothermic, increasing the temperature increases the value of the equilibrium constant (k). When pressure increases, the equilibriu...

Alyssa Wilson 2A

This is a double replacement reaction, and we assume the aluminum ion is attached to a H2O molecule, because it is formed with a ligand complex that forms when AlCl3 reaches equilibrium. Al(H2O)5 OH2 is Pentaaqua-hydroxyaluminum(iii) ion.

Alyssa Wilson 2A

Would it be best if we memorized the rules of when k is large, small, Q>k, Q<k, and Q=k rather than just going through the process of what occurred in the reaction?

Alyssa Wilson 2A

Can someone please clarify when we use brackets vs. parentheses to denote materials in the gas law?

Alyssa Wilson 2A

I agree with the above statements, and Q is known as the reaction coefficient, which is similar to k, but it can be used in any stage of the reaction, where k is used and solids and liquids do not contribute into k. K is the equilibrium constant and the rate of the forward reaction will equal the ra...

Alyssa Wilson 2A

Dr. Lavelle never clarified that, I would assume everything will be fair game, so make sure you understand everything on the outlines.

Alyssa Wilson 2A

A transition metal is often found bound to a cage-like molecule, for example the porphyrin ligand. (4 nitrogens in a plane, creating a tetra-dentate square planar) Iron is bound to this porphyrin ligand, and therefore creates a HEME complex. A heme complex and a protein create myoglobin, which is th...

Alyssa Wilson 2A

I believe you are referring to amphoteric, which is when a compound has both basic and acidic character. Between metal oxides (bases) and nonmetal oxides (acids) there is a diagonal band, of these amphoteric oxides closely matching the diagonal band of metalloids.

Alyssa Wilson 2A

I believe potassium's oxidation state is 3, because the name of the element ends with the number 3, in roman numerals.

Alyssa Wilson 2A

I think he wanted us to just look over them, and have an understanding of it. Dr. Lavelle might talk about it on Monday in lecture, and we will find out if it will be on the final.

Alyssa Wilson 2A

I believe the structure of the molecule tells you whether that specific atom is a Lewis base or a Lewis acid. For example, if it can attach itself to a molecule or ion that makes it a Lewis acid. The Lewis base has the lone pair of electrons on it in fact, so if it has a lone pair of electrons, it c...

Alyssa Wilson 2A

Can someone please give an overview of when you would end up with a seesaw structure?

Alyssa Wilson 2A

Van Der Waals forces also consist of the potential energies of the dipole-dipole interactions of rotating polar molecules in the gas phase of the London interactions and the dipole-induced-dipole interactions.

Alyssa Wilson 2A

Hi, I was told we should know everything on the outlines for "Chemical Bonds" and "Molecular Shape and Structure," I believe it will be a mixture of both conceptual questions as well as drawing the lewis structure, calculating the bond angles, and the molecular shape.

Alyssa Wilson 2A

I believe we will only be expected to know the shapes that Dr. Lavelle will cover in the following lectures, I think there are seven or eight shapes we will have to know.

Alyssa Wilson 2A

Polarizability is the measure of how easily an electron cloud is distorted by an electric field. Typically the electron cloud will belong to an atom, molecule, or an ion. Anions have a high polarizability, while cations are positive having less electrons, which makes them have lower polarizability.

Alyssa Wilson 2A

To add to the previous replies, the most stable structure would be the one with all of the atoms having a formal charge of zero. Usually we want the central atom to have a formal charge of zero, and if the whole molecule has a charge on it, then the outer atoms could have a formal charge that doesn'...

Alyssa Wilson 2A

What do you do with a sick chemist?
If you can't helium, and you can't curium, then you might as well barium.

Alyssa Wilson 2A

Dipole interactions are weaker since they occur when the partially positively charged part of a molecule interacts with the partially negatively charged part of the neighboring molecule.These intermolecular ion-dipole forces are much weaker than covalent or ionic bonds that are involved in hydrogen ...

Alyssa Wilson 2A

The ability of a cation to distort an anion is known as its polarizing power. The tendency of the anion to become polarized by the cation is known as its polarizability. I believe they are always associated with one another and they go hand in hand.

Alyssa Wilson 2A

Hi, I believe we are allowed to answer any of the problems in the Chemical bond section, although it is best to do questions on the new material we just covered in class.

Alyssa Wilson 2A

I believe Dr. Lavelle wrote -1 since we know from the question that NO3^- has a negative charge, because it is an anion. Therefore we have to add one valence electron into the equation of our lewis structure. Hope this helps!

Alyssa Wilson 2A

For example a covalent bond would be (H-H) they can either be polar/non-polar. Since ionization energies are too high, it will therefore form between nonmetals.

Alyssa Wilson 2A

Beryllium does not follow the octet rule because it doesn't require eight electrons surrounding it to be stable. Since beryllium is in the second group, it only has two valence electrons, which means it can only form two bonds. I believe it has 10 valence electrons in this specific problem, because ...

Alyssa Wilson 2A

I was told to just know the concept behind Shrodinger's equation and how it was derived, instead of being able to calculate it since it becomes complicated with derivatives. Hope this helps!

Alyssa Wilson 2A

No, I believe we do not since we didn't cover any practice problems using Coulomb's equation of F=((qa)(qb)/(r)).

Alyssa Wilson 2A

The momentum might not be given, for instance the question could give you the wavelength and ask you to solve for the momentum using the DeBroglie Equation where momentum is p=h/lambda. So you know lambda (the wavelength) and h is a constant given to you, so therefore you can solve for the momentum ...

Alyssa Wilson 2A

kellyzhang1210 wrote:Do we have to memorize all the formulas we'll have to use?

I believe most of the formulas will be given to us on the coversheet of the test.

Alyssa Wilson 2A

Hi, will the work function always be given to us in the problem when solving for the kinetic energy?

Alyssa Wilson 2A

When looking at problems that call for the Heisenberg uncertainty Equation, do we always solve for delta p (indeterminacy in momentum) first, because we are given the delta x (position), or does it just depend on what the question is asking for?

Alyssa Wilson 2A

A node is a point where the electron probability is zero, it is the point at which the nodal plane intersects. As with all orbitals the number of radial nodes increases as the principle quantum number goes up.

Alyssa Wilson 2A

When an atom absorbs a specific wavelength or light, they're gaining energy so if there's enough energy, an electron will jump to a higher energy state. I agree, whereas light sources with shorter wavelengths(higher frequencies), can eject electrons even with low intensity light. One photon interac...

Alyssa Wilson 2A

Amplitude is distance divided by the frequency. The wavelength can be found by dividing the speed of light by the frequency. The amplitude is how tall a wave can get, where the frequency means how quick a wave can be, as well as how many peaks are in the cycle. I believe that frequency and amplitud...

Alyssa Wilson 2A

I believe it states that the wavelength and frequency are inversely proportional; as one increases, the other decreases. So both sides of the expression have to be equal energies to cancel one another out, so that you are left with Rydberg's formula in the end.

Alyssa Wilson 2A

AlexandraZuniga1L wrote:I also have a question regarding chemistry community, does anyone know by when we are supposed to post responses on here or new topics?

I believe we have to post our three questions or topics on this site before Friday's lecture to receive full credit.

Alyssa Wilson 2A

tiffanyteguh1C wrote:Hi! Are there any good chem video resources that anyone recommends ??? (aside from Dr. Lavelle's videos)

Khan Academy offers some great resources that are available along with some crash course videos online.

Alyssa Wilson 2A

Solving a stoichiometry problem involves solving for the limiting reagent. For step number 5 in solving a stoichiometry problem, you compare the calculated moles from the step before, with the required moles to determine if there is a limiting reagent. And with that being said, solving a limiting re...

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