CHEMISTRY COMMUNITY

Jared Smith 1E

I'm having some trouble understanding why we can't just add the two standard potentials together from the reactions to get the total. Why exactly do we convert everything to deltaG and back again?

Jared Smith 1E

I'm having a little bit of trouble understanding this question. How exactly would we determine the half reactions given only the reactant? We would just look at the table in the back to see which reactions involve that reactant, or is there something I'm missing?

Jared Smith 1E

Can someone please walk me through how to put together a cell diagram step-by-step? I know that the reduction half goes on the right and the oxidation half goes on the left, but beyond that, I'm completely lost.
Any help would be really appreciated!

Jared Smith 1E

I did the same thing and recalculated it with 0.02357 rounded to 0.024 like it does in the answer key, and it gives 744. I think it's just a rounding error on our part.

Jared Smith 1E

Because the half-life for zero order reactions is also dependent on initial concentration, would it be calculated similarly to 15.35 (second order) but using the half-life equation for a zero-order reaction? In other words, do we need to perform the same types of manipulations because initial concen...

Jared Smith 1E

Can someone please explain why you multiply by three rather than 1/3 for this problem. I thought that it would be 1/3 of the unique rate because it is 1/a rate[A]. Why do you multiply by 3 instead?

Jared Smith 1E

From what I remember from lecture, K is the rate constant for a normal reaction. K' is the rate constant for the pseudo-reaction where the other reactants are in very high concentrations. In other words, K' is the rate constant for the experimental reaction with just the one reactant. In addition, k...

Jared Smith 1E

I noticed that depending on the reaction order, the slope of the graph can be equal to positive or negative k. For first and zero-order reactions, the slope of the graph is equal to -k, but for second order reactions, the slope is equal to +k. Can someone please explain to me why one is different fr...

Jared Smith 1E

For second and zero-order reactions, I have both half lives depending on the concentration of [A]0 (initial concentration).

For second order: t(1/2)= 1/k*[A]0

For zero-order: t(1/2)= [A]0/2*k

Jared Smith 1E

For problems involving the calculation of an unknown concentration in a concentration cell, is the basic strategy to plug everything into the Nernst equation and solve for the concentration? Are there any unit conflicts that we need to worry about?

Jared Smith 1E

Thank you both so much!

Jared Smith 1E

Can someone please explain to me how the commas work in cell diagrams? I don't know what they signify and when to use them? Are they similar to the | in the diagram or do they mean something completely different?

Jared Smith 1E

For this question, I think you have to figure out the oxidation and reduction half-reactions and those will give you the moles of electrons for the equation.

Jared Smith 1E

Can someone give me a situation where you would use the ln(k2/k1) version of this equation? Thanks!

Jared Smith 1E

Can someone please explain what the difference between delta S, delta S (surroundings), and delta S (tot) is? Also, how do these relate to each other when calculating them?

Jared Smith 1E

I am still confused about when to use Cv or Cp when determining the change in entropy for gas that has a change in temperature. Is Cp only used when there is constant pressure? I've heard conflicting things about when to use which, can someone please clarify?

Jared Smith 1E

When would we use the equation of the second law delta S=q (rev)/T? I can't seem to find a lot of example problems that use it directly. Is it meant to be used frequently for calculations, or mainly as a means of deriving the other equations we learned in lecture?

Jared Smith 1E

I think that the reason that it is negative is due to the fact that the first reservoir lost heat, and transferred that heat to the second reservoir, meaning that it gained heat. Losing heat is negative, gaining is positive.

Jared Smith 1E

So I know that when delta G is negative, the forward reaction is spontaneous. Is it then correct to assume that whenever delta G is positive, the reverse reaction is spontaneous?

Jared Smith 1E

In my lecture notes, I have written down that it is assumed that entropy and enthalpy are constant when writing the final equation. I would imagine that they would tell us if for some reason we could not make that assumption.

Jared Smith 1E

Does that mean that every element has a higher entropy than the proceeding element on the periodic table? Or does there need to be a large difference in size for the entropy to differ?

Jared Smith 1E

I think that the difference between the two is that exothermic means that deltaH is negative, and that spontaneous means that deltaG is negative. So that means that exothermic relates to enthalpy and that spontaneity relates to Gibbs Free Energy. I think that there are some situations that an exothe...

Jared Smith 1E

The enthalpy of the reaction is 0 because the bonds being broken and formed have the exact same energy as one another. For example 4 C-H bonds are broken and 4 Cl-C bonds are broken. Then between the two reactant molecules 4 C-H bonds are formed and 4 Cl-C bonds are formed. The amount of bonds broke...

Jared Smith 1E

I have a couple of questions about this homework problem. What exactly is hydrogenation? Also why to the intermediate steps in Hess's Law contain oxygen, or is it part of the hydrogenation process? Any help would be greatly appreciated.

Jared Smith 1E

I think the reason that the enthalpy of vaporization is subtracted is due to the fact that changing from a gas to a liquid is an exothermic process, meaning that it would be the negative version of the enthalpy of vaporization. The fact that it is an exothermic process determines that it is subtract...

Jared Smith 1E

If I'm understanding your question correctly, asking if calculations involving transitions between states like solid to liquid, then yes. The enthalpies of fusion and vaporization are given on the constants sheet for the class. I would assume that means they are fair game for the test. Some of the h...

Jared Smith 1E

I know that both sections 8.7 and 8.10 are included in the reading, and problems appear in the assigned homework. Are we responsible for these topics on the exam? If so, can someone please explain the topics and their related calculations in a way that is a little easier to understand?

Thanks!

Jared Smith 1E

I have a couple of questions relating to calculation's using Hess's Law. First, why is it ok to use fractions in the chemical equations? I read the explanation in the textbook, but it didn't really help. Second, when should I use fractions as stoichiometric coefficients in Hess's Law calculations? T...

Jared Smith 1E

Hess's law and using bond enthalpies are different ways of accomplishing the same task. Both will give the change in enthalpy. I think that we are supposed to select either one method or the other based on the information provided in the problem. In the examples we did in class, we were given the ch...

Jared Smith 1E

For this problem, you would calculate the q values for raising the copper to 100 degrees and the water to 100 degrees separately, and then add the q values together to get the final answer.

Jared Smith 1E

I learned in discussion that the formula for this kind of problem is q= m*C*deltaT or q=n*C*deltaT.
m= mass
n=moles
C= heat capacity
deltaT= change in temperature (final- initial)

Sometimes the heat capacity will be specific heat capacity (in grams) or molar heat capacity (moles).

Jared Smith 1E

We know from lecture that transition metal complexes typically form tetrahedral, square planar, or octahedral shapes. This means that the transition metal cation can form at most 6 bonds with other atoms or molecules. The iron metal in the diagram is shown bonded to 4 Nitrogen atoms. This leaves 2 b...

Jared Smith 1E

I was wondering if there were any common groupings of atoms that could help determine whether a molecule was mono or polydentate. I know COO was mentioned as one in a review session, are there any other common ones?

Jared Smith 1E

I think that when they say "s character" they mean the proportion of the hybridized orbital that the single s orbital makes up. For example as p and d orbitals get added (sp, sp^2, sp^3, sp^3d...etc), the s character of the hybridized orbital goes down because it makes up a smaller part of...

Jared Smith 1E

You know it has the -ate at the end of the transition metal name when the overall charge of the complex is negative, as indicated by the 2- after the brackets.

Jared Smith 1E

I never went over the ideal gas law in high school, what is exactly is it used for, and where did it come from?

Jared Smith 1E

I know that the textbook explains how to find the coordination number for the complex, but I also know that Professor Lavelle explained it in lecture in a much simpler way. Does anyone remember how he explained it in lecture, and/or an easier way than the textbook describes?

Jared Smith 1E

Can someone explain, in figure 4.7 in the textbook, why some of the shapes can be both polar and non polar, especially when there are no lone pairs in the shape depicted?

Jared Smith 1E

I understand that the formulas for linear combinations are the wave functions for the hybrid orbitals, but where do the positive and negative signs in between the s and p orbitals come from?

Jared Smith 1E

Why are some types of electron interactions stronger than others? For example why do lone pair-lone pair interactions repel more strongly than bond-bond interactions?

Jared Smith 1E

Could someone please explain to me why some atoms have multiple degree values for their bond angles and others only have one?

Jared Smith 1E

For an ionic compound like K+CL-, when potassium transfers its valence electron to chlorine, does the radius for potassium get smaller? If so, are the radii the same for Potassium and Chlorine, or will Potassium's radius become smaller due to its increased nuclear charge?

Jared Smith 1E

Does all that a diagonal relationship means that the two elements that share the relationship have similar properties, or does it imply something else as well?

Jared Smith 1E

I know that the textbook provides an explanation of how to calculate the probability of finding an electron in a specific place. Could somebody walk me through it step-by-step, in terms that are a little easier to understand?

Jared Smith 1E

Two questions in one here, first do we need to know how to use/derive the shrodinger equation for the exam?
Also, I know in class that the professor said that the solutions for the equation are the electron orbitals, is that all the equation is used for?

Jared Smith 1E

Can someone explain why the values of (1/2) are positive or negative for the magnetic spin numbers?
In other words, what determines if it is spin up or spin down?

Jared Smith 1E

Can someone please explain to me in a little more detail what each of the orbital letters means, and how that relates to their positions on the x,y,z axes?
He went over them kind of quickly in class, and I didn't learn this in high school.

Jared Smith 1E

How did DeBroglie determine that the wavelength of a "matter wave" is inversely related to the its linear momentum?

Jared Smith 1E

Could someone please the energy levels of electrons to me?
I understand that they are limited to discrete values and that they have to do with spectral lines, but other than that I'm confused.

Jared Smith 1E

Once you have determined the limiting reactant, you look at the formula and determine how many moles of product can be formed based on the moles of limiting reactant present (the molar ratio of the limiting reactant to the product). Then convert the moles to grams by multiplying by the molar mass.

Jared Smith 1E

Once you have converted the tons to grams, divide by the molar mass of NaBr which will give you the moles of NaBr that need to be produced. Then multiply the by the mole ratio of (1mol Fe(sub3)Br(sub8)/8mol NaBr). Then refer to the previous equation for the mol ratio of (3mol FeBr(sub2)/1mol Fesub3)...

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