CHEMISTRY COMMUNITY

Priyanka Bhakta 1L

Also, be sure to use the appropriate half life equation based on the order!

Priyanka Bhakta 1L

In order to solve a problem with this situation, make sure to follow the procedure Dr. Lavelle lined out in lecture.

Priyanka Bhakta 1L

I believe that the axis for the reaction profile references the total energy of the substances graphed. When the book explains it that way they are just clarifying what components of the total energy for the R and P change as the reaction goes on.

Priyanka Bhakta 1L

I believe it would be sloping downwards I a curve, but it would be a less dramatic decrease with a more gradual decrease than an exponential decay curve.

Priyanka Bhakta 1L

From my understanding, you are correct.

Priyanka Bhakta 1L

The order indicates the mechanism more than just the speed of reaction, as the rate constant indicates the speed of the reaction. It is my understanding that the order itself does not indicate anything explicitly about the speed of a reaction, it merely demonstrates how many particles/molecules of t...

Priyanka Bhakta 1L

You do need to find the order for reactant C. Use Experiments 3 and 4 to find the order of reactant C.

Priyanka Bhakta 1L

I believe that both those equations are equivalent. I'm not sure where you got the equation with ln( [A]o / [A]t ) and a positive +kt, but they seem to be the same thing. Use them to find the k reaction constant value or t time it takes to get to a certain concentration from a given initial concentr...

Priyanka Bhakta 1L

In terms of entropy, the phase is always more deterministic of entropy than molecule size. Since CH4 is a gas, its phase already makes it have higher entropy than any sized liquid molecule.

Priyanka Bhakta 1L

Look for atoms within the molecule that have a consistent oxidation state. For example, if you have MnO4-, you know that oxygen atoms tend to have a 2- charge, thus Mn must be of 7+ charge to have an overall charge of 1-. You can also try and attain the oxidation state of an atom based on the charge...

Priyanka Bhakta 1L

Use platinum (Pt) if the half reaction for one (or both) sides of the cell do not have a conducting metal in them. If there is no conducting metal, use Pt on the outermost section of the cell diagram to show that you are using a platinum electrode because there are no conducting metals present natur...

Priyanka Bhakta 1L

Ion-selective electrodes are just electrodes that measure specific ion concentrations in a solution. Examples include pH meters, K+ meters, Na+ meters, etc.

Priyanka Bhakta 1L

When a process/reaction is at equilibrium or it is a reversible reaction, delta S total = 0. Thus, at these conditions, delta S sure = - delta S sys. The concept behind this is that in a reversible reaction or a reaction at equilibrium, any changes in entropy of the system or surroundings will be op...

Priyanka Bhakta 1L

No, electrochemistry will not be on the midterm. On Lavelle's site it says will only be tested on Thermodynamics and Thermochemistry (the first two outlines provided on his site / chapters 8,9, part of 11).

Priyanka Bhakta 1L

Either the question will tell you how many possible states there are, or it will be a simple enough molecule for us to draw out the Lewis structure and determine for ourselves how many possible states there are.

Priyanka Bhakta 1L

First try to look at the overall mass of the molecule; the molecule with more atoms will likely have more entropy. Then, if they have the same number, look at the variety of atoms; different types of atoms allow or different positions to be made (positional disorder increases --> entropy increases)....

Priyanka Bhakta 1L

In addition, the salt bridge is used to connect two separate electrode compartments and complete the circuit between them; the ion flow back into the compartment with the anode through the salt bridge completes the electrical circuit.

Priyanka Bhakta 1L

I believe that internal energy is usually represented in units of kJ.

Priyanka Bhakta 1L

In lecture we've been looking at entropy in a less general, "disorderly" way and more as a number we can find to represent entropy. Thus, we've kind of been looking at statistical entropy (entropy calculated from the Boltzmann formula). Positional/residual entropy is based more in calculat...

Priyanka Bhakta 1L

A reversible pathway tends to take longer because the differences in temperature or pressure between the system and its surroundings are so small that the change only occurs in small, slow increments (which is why we derived the equations used for reversible functions from an integral). Since the ch...

Priyanka Bhakta 1L

Yes, exactly! Since we assume/approximate that the systems we see in thermodynamics are reversible, we can use the q(rev)=-w and deltaS=q(rev)/T equations in our problems.

Priyanka Bhakta 1L

If the bond enthalpies are given and/or the question asks for us to calculate the reaction enthalpy by using the given table/values, I would use them and solve the problem that way. I think Dr. Lavelle told us that bond enthalpies are the least accurate way just as a note and maybe for conceptual qu...

Priyanka Bhakta 1L

Internal energy is a state function because it merely measure the energy difference that the system holds from one time to another; since internal energy is not affected by how it gets from one state to another, it is a state function.

Priyanka Bhakta 1L

U is the internal energy, which is the amount of energy a system holds in both kinetic and potential energy. H is the enthalpy, which is the amount of heat released or absorbed by a system at constant pressure. Thus, U is the total energy held by a system while H is specifically the energy that is t...

Priyanka Bhakta 1L

For Hess's Law the enthalpy of the reactants is subtracted from the products due to the general form of the change in enthalpy for the reaction being, simply, the final enthalpy of the reaction minus the initial enthalpy of the reaction. For bond energies it's the opposite because of how energy flow...

Priyanka Bhakta 1L

Heat is energy transferred as a result of a temperature difference while enthalpy is the amount of heat released by a system at a constant pressure.

Priyanka Bhakta 1L

Hi! So you don't need to know the mass because you just need to use the definition of heat capacity.

Since C=q/deltaT you can plug in the given q value and temperatures to find the heat capacity. Hope that helps!

Priyanka Bhakta 1L

Hi! So the jist of it is that a reversible process is one so sensitive (and most likely heavily controlled in the lab) that even an incredibly small change to a variable (such as pressure) would reverse the reaction. On the other hand, an irreversible process, an infinitely small change in the varia...

Priyanka Bhakta 1L

Hi! So based on the topics covered in this unit's outline on Dr. Lavelle's website, we do not need to know how to draw out the path of change of state nor do we have to know how to describe the change of state. This is merely an educated guess, I would try asking a TA or Lavelle himself as we learn ...

Priyanka Bhakta 1L

Based on what he discussed in lecture on Monday, I can only assume he meant to begin where the textbook discusses enthalpy. That is section 8.8 on page 278; although (disclaimer) I am not entirely sure if that's what he meant.

Priyanka Bhakta 1L

The key thing to remember for this problem is that for acids is that if they have more electronegative atoms attached, they will be stronger acids. And if there are more oxygens attached, they will be stronger.

Priyanka Bhakta 1L

I believe you use the equilibrium arrows if it is not a strong acid or base because strong acids and bases are 100% ionized in solution, while weak acids and bases are not; hence the equilibrium arrows because the reaction will continue to go back and forth without the reaction fully being completed...

Priyanka Bhakta 1L

The rules are all outlined on page 741 in the textbook, in Toolbox 17.1. Here is the outline, hope this helps!

Priyanka Bhakta 1L

The rules for naming coordination compounds are on page 741 Toolbox 17.1.

For ligands, the prefixes are based on how many molecules/atoms of that ligand are present in the compound.

Priyanka Bhakta 1L

You have to look at the molecule and see if it has any atoms that can serve as part of a Lewis base. To know if it's polydentate you need to kind of have the Lewis structure of the molecule in mind to see if there is more than 1 lone pair that can be bonded to the same central metal ion. I try to dr...

Priyanka Bhakta 1L

Hi! I believe in lecture Dr. Lavelle said that they are synonymous so I don't think you need to know of any differences between bent and angular.

Hope that helps!

Priyanka Bhakta 1L

Hi! So to answer your question about lone, unpaired electrons on radicals: I believe that Lavelle might have said this quickly or in passing, but it is my understanding that unpaired electrons on radicals are considered a region of electron density. Although, because there is only 1 electron and not...

Priyanka Bhakta 1L

Hi! So this is kind of confusing, given how we haven't really gone over these more difficult situations. I have attached a graphic I found on the internet for this example. I think it ends up being linear because the 3 lone pairs on the Iodine repel each other and push against each other from both d...

Priyanka Bhakta 1L

The maximum oxidation numbers can be found by figuring out how many electrons the element would need to lose or gain to end up with a filled valence shell. So, for Chlorine, the maximum positive oxidation number would be +7 because it would have to lose 7 electrons to have the complete valence shell...

Priyanka Bhakta 1L

Hi! So my understanding is that most p-block elements from Period 3 and on are capable of having expanded octets and thus have more than 8 electrons in their valence shell for Lewis structures and this is because they have unfilled d-orbitals that can hold electrons above the octet. The book mention...

Priyanka Bhakta 1L

Yes, as David said, the Na+ ion (and all cations) becomes smaller because it loses an electron, which means there is less electron repulsion, and the electrons left are more attracted to the nucleus which results in a smaller atom. On the other hand, the Cl- ion (and all anions) becomes larger than ...

Priyanka Bhakta 1L

In the ground state, the electrons follow the Hunds Rule and Pauli Exclusion Principle. So, the electrons must have one electron in each orbital to start off, then begin pairing electrons. When there are only one electron in each/most of the orbitals of the valence shell, they should all have parall...

Priyanka Bhakta 1L

Hi! So the wave function is a mathematical expression and it represents a solution to the Schrodinger wave equation. When that solution (the wave function) is accurate, it describes the atomic orbitals of a certain atom. Thus, each wave function is the mathematical expression of an orbital. The 3 qu...

Priyanka Bhakta 1L

Hi! So electron affinity is the energy released when an electron is added to an atom in the gas phase. A positive election affinity means that energy is released when an electron attaches to an atom, and this occurs if the atom has many electrons in its valence shell and thus prefers to gain electro...

Priyanka Bhakta 1L

I believe that as long as you understand the concepts behind the experiments and the discoveries they led to, you should be okay. Here are a couple of key points: - Photoelectric experiment = shine light on a metal surface to measure how much energy (and thus, the wavelength and frequency) of light ...

Priyanka Bhakta 1L

Yes, as stated above, the groupings for the atomic spectra series are based on the lowest energy level involved in an electron's jump to a higher energy level or fall down to a lower energy level. Something key to remember is that when a question asks which series the wavelength of light that caused...

Priyanka Bhakta 1L

To answer your question Alissa, the energy would increase if the frequency increased because in the equation E=hv, h is a constant. Thus, the only thing that has an effect on the energy is the frequency. So, if the frequency increases and is multiplied by a constant, the energy will increase. If the...

Priyanka Bhakta 1L

I believe that 4 is n2 and 2 is n1 because the formula is looking at the energy levels n1 and n2 in reference to the actual formation of the electron levels. So, n1 is always the lower energy level and n2 is greater. Think about the sketch that Dr. Lavelle drew on the board in lecture, as well as in...

Priyanka Bhakta 1L

Never mind. I figured it out, im just not sure if my reasoning is correct. Is it 0.0134 mol of cu2+ because there is one mole of cu in the compound? (1:2 ratio in CuBr2) Yes, you've pretty much got it. Since the question is only asking for the amount of Cu^2+ ions in 0.0134 moles of CuBr2, there is...

Priyanka Bhakta 1L

Hi! So you're using the 454 grams of fat in part (b) because the question asks "What mass of oxygen is needed to oxidize this amount of tristearin?" and the fat mentioned in the solutions manual is the fat introduced in the intro of the question as tristearin. So the question is actually a...

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