CHEMISTRY COMMUNITY

Isabella Sanzi 2E

Yes, the equation sheet gives the density of water is 1g/mol.

Isabella Sanzi 2E

I think that the two more or less accomplish the same task: to prevent charge buildup from the ions. A salt bridge is used when you have the anode and cathode separated, like using two different beakers, and a porous disk is used when the anode and cathode are not entirely separated, like when you u...

Isabella Sanzi 2E

I think the only way to determine spontaneity of a reaction is to calculate the Gibb's Free Energy. Even if you have a large, positive delta S that does not necessarily mean that you will have a negative delta H, and since the equation is deltaG = deltaH - T(deltaS), if the delta H is positive enoug...

Isabella Sanzi 2E

Catalysts are used and then regenerated, so they appear on both sides of the equation. This means that when you do the overall balanced equation, they would appear on both sides, thus cancelling out.

Isabella Sanzi 2E

No matter the temperature, a reaction will always have the same activation energy UNLESS the pathway of the reaction is altered using a catalyst. However, k (the rate constant) varies with temperature.

Isabella Sanzi 2E

I think when identifying an aldehyde you want to look for a carbon bonded to one or two hydrogens and an oxygen. Carbon being bonded to a hydroxyl group (OH) would indicate that the molecule is an alcohol.

Isabella Sanzi 2E

If you are referring to the Boltzmann formula, the calculation for the number of microstates is equal to W.
W = (number of orientations)^(number of molecules)
So if you had 10 molecules that could be in 2 different orientations, you would have W = 2^10, or W = 1024. Hope this helps!

Isabella Sanzi 2E

Unless I am misinterpreting your question, they gave you the full reaction being AgBr --> Ag+ + Br-, and they ask you to write the half reactions for the cell, meaning that you would have to determine what is being oxidized and what is being reduced so that when the two are combined you get the give...

Isabella Sanzi 2E

Based on the structure we have been following in class, this does not match up with what we have been doing. In class, Dr. Lavelle has been focusing on the method of initial rates, meaning that we use the initial concentrations of the reactants and examine the rate of reaction based on those initial...

Isabella Sanzi 2E

Because it's an elementary reaction (so basically a step of a reaction), we use the coefficients to determine the order of the specific reactant for the rate law. To illustrate, question 49 lists two different elementary reactions. Step one is HBr + NO2 --> HOBr + NO. The rate law for this elementar...

Isabella Sanzi 2E

Question 63 in the book says, "The rate constant of the reaction between CO2 and OH- in aqueous solution to give the HCO3- ion is 1.5 x 10^10 L/(mol)(s) at 25 degrees C. Determine the rate constant at blood temperature (37 degrees C) given that the activation energy for the reaction is 38 kJ/mo...

Isabella Sanzi 2E

If I am correct in assuming that this is what you are referring to, the book uses a subscript 1, 2... to indicate the step of the reaction's respective value of k (so for step one, the k would have a subscript 1 and for step two, the k would have a subscript of 2 and so fourth). I have not seen a k0...

Isabella Sanzi 2E

In the example you used, I just wanted to point out that for this problem that you may have made a small error because I got an integer for this one. I used reactions 1 and 3 because [B] changes while [A] and [C] remain the same. Since 3.02/1.25 = 2.416 and 50.8/8.7 = 5.84 (not 457, that would be fr...

Isabella Sanzi 2E

Because each reaction is broken down based on step, or elementary reactions which show how each step of the reaction occurs, we can write each step's rate law from just its balanced chemical equation and coefficients: In step one we can assume that since HBr and NO2 have a coefficient of one, they a...

Isabella Sanzi 2E

So for this half reaction, you start with P4 --> PH3, and here are the steps to go through to balance it. 1. Balance the P's: P4 --> 4PH3 2. Balance the H's using H2O and OH- since we are working in a basic solution: P4 + 12H2O --> 4PH3 + 12OH- (This step is definitely the most confusing, but just b...

Isabella Sanzi 2E

Question 33 says: (a) The standard Gibbs free energy of formation of T3+ is +215 kJ/mol at 25 degrees C. Calculate the standard potential of the Tl3+/Tl couple. (b) Will Tl+ disproportionate in aqueous solution? I understand part a, but can someone explain what disproportionate means in part b and h...

Isabella Sanzi 2E

So I understand that the anode reaction should be on the right side of the diagram and the cathode should be on the left, however, within the anode and cathode individually, what are the conventions for creating these diagrams? When do I use a comma vs. a | or when do I add Pt or another conducting ...

Isabella Sanzi 2E

So unless you have a more specific question, I can just go through the methodology of this problem. For part a, you have to calculate the delta H and delta S for the vaporization of H2O (reaction: H2O(l) --> H2O(g)). To find delta H, use the enthalpy of formation values at 25 degrees C. Then do the ...

Isabella Sanzi 2E

Just for clarification, what is the difference between specific heat capacity and heat capacity and is either a state property? Thanks!

Isabella Sanzi 2E

So for number 4 on the practice midterm, the problem talks about several different transformations done to a system in three distinct steps: 1. 0.60 moles, 50.0L, and 1.0 atm --> 0.60 moles, 20.0 L, and 1.0 atm (isobaric) 2. 0.60 moles, 20.0 L, and 1.0 atm --> 0.60 moles, 20.0L, and 8.0 atm (isochor...

Isabella Sanzi 2E

I know that Professor Lavelle gives us a substantial list of equations for each test that we will get to use for the midterm exam as well, so I do not think that we need to know any derivations specifically for the test. However, understanding where each equation comes from might be useful to help y...

Isabella Sanzi 2E

So according to what I see in the solution manual, all you have to do is use the formulas deltaS = nRln(V2/V1) and deltaS = nRln(T2/T1), so you don't have to worry about a constant for C at all. Just plug in what is given to solve for the entropy for the whole system based on each step of the reacti...

Isabella Sanzi 2E

"Initially a sample of ideal gas at 323 K occupies 1.67 L at 4.95 atm. The gas is allowed to expand to 7.33 L by two pathways: a) isothermal, reversible expansion; b) isothermal, irreversible free expansion. Calculate deltaS(total), deltaS, and deltaS(surroundings) for each pathway." So I ...

Isabella Sanzi 2E

On the last test, one of the questions was discussing whether or not heat was being transferred when a balloon filled with gas was expanded to a larger volume and lower pressure while maintaining the same temperature. I thought that it was not because the temperature was not changing, however the an...

Isabella Sanzi 2E

I think that Gibbs free energy isn't necessarily a measurement, but a calculation to describe the energy of a system available to do work based on a system's entropy, enthalpy, and temperature. I believe Professor Lavelle mentioned in class you can't explicitly measure free energy-just to clarify. H...

Isabella Sanzi 2E

Question 5 asks: What is the total entropy change of a process in which 40.0 kJ of energy is transferred as heat from a large reservoir at 800. K to one at 200. K? I understand that you would carry out the deltaS = q/T two separate times, but the solution manual has 40.0 kJ as a negative value in th...

Isabella Sanzi 2E

In problem 8.67, we are supposed to find the enthalpy of formation of several compounds the liquid state. In the solution manual, they say we have to "atomize" the solid Carbon in order to get the solution for parts b, c, and d. What does this mean? And how do I know when to atomize someth...

Isabella Sanzi 2E

How do you know to use q = C(deltaT) instead of q = mC(deltaT). Referring specifically to a problem in the textbook, why for number 53 part b do we use C(deltaT)? The question asks: The reaction of 1.40 g of carbon monoxide with excess water vapor to produce carbon dioxide and hydrogen gases in a bo...

Isabella Sanzi 2E

The opposite of vaporization is condensation, the opposite of fusion (or melting) is freezing, and I don't think that we explicitly went over it, but I found on the internet that the opposite of sublimation is deposition. Hope this helps!

Isabella Sanzi 2E

Yes, Delta U is the change in internal energy of a system. It can be found by adding work and heat (q + w) or by the formula: DeltaH = DeltaU + P(DeltaV). I hope this helps!

Isabella Sanzi 2E

How do you calculate the enthalpy of vaporization of a substance? For instance, the problem 8.37(part a) asks us to calculate the the enthalpy of vaporization of 0.579 mol of methane which requires 4.76 KJ of heat. How do you solve this? I know that there are given values for some Delta H's of vapor...

Isabella Sanzi 2E

What does it mean when a problem states that a calorimeter has been calibrated and what significance does this hold in a calorimetry problem?

Isabella Sanzi 2E

So in a very basic form, a regular styrofoam calorimeter is just an insulated styrofoam cup, a stirring rod, and a thermometer. Basically what happens is that the reaction mixture inside the cup is stirred and the temperature is monitored (of the reaction mixture) to see how much it increases or dec...

Isabella Sanzi 2E

Hello everyone! So today in class we talked about properties that make acids strong. I am a bit confused on what it meant when Dr. Lavelle said that the resulting anion must be stable relative to the neutral form. What does this mean exactly, and how do I tell if an anion is stable? Also, we went th...

Isabella Sanzi 2E

So basically when the value of k is very small, the value of x is also very small in comparison to the initial concentration. Let me illustrate this with an example: The problem that we talked about today in class had an equilibrium constant Ka = 1.8 x 10^-5 for the equation CH3COOH(aq) + H2O(l) <> ...

Isabella Sanzi 2E

In reference to 11.45 specifically, parts a and b give an initial concentration of Cl2 or F2, respectively (and are meant to assume that there is no 2Cl or 2F present so their concentrations would be 0M). Both also give the equilibrium constant of the dissociation reaction. Because you only have an ...

Isabella Sanzi 2E

Which of the following ligands can be polydentate? If the ligand can be polydentate, give the maximum number of places on the ligand that can bind simultaneously to a single metal center: a. HN(CH2CH2NH2)2 b. CO3^2- c. H2O d. Oxalate So I understand that polydentates are where the molecule has two o...

Isabella Sanzi 2E

Hi guys, I know this question is kind of throwing it back to the beginning of the year, but I am confused on part A of question 75 in chapter 4: An organic compound distilled from wood was found to have a mole mass of 32.04 grams/mol and the following composition by mass: 37.5% C, 12.6% H, and 49.9%...

Isabella Sanzi 2E

I believe that we have to know pretty much all the shapes discussed in class basically going from 2 areas of electron density up to 6 areas of electron density (including variations with lone pairs). And yes, pretty much you have to be able to do the bond angles and shapes from memory, however it is...

Isabella Sanzi 2E

So it depends on the number of lone pairs and the number of atoms on each central atom. Here are some examples that illustrate how bond angles are affected: If a central atom has 4 atoms attached to it, the shape is tetrahedral and the bond angles are 109.5 degrees. If a central atom has 3 atoms att...

Isabella Sanzi 2E

Do you think it's fine for us to just put bond angles with greater than or less than signs? like the bond angle is <109.5 I believe the answer to that is yes because many bond angles with lone pairs as a region of electron density are determined experimentally as they are different for many molecul...

Isabella Sanzi 2E

I am just seeking some clarification on how many ligands can attach to a transition metal. Does it just depend on the number of orbitals the metal could potentially hybridize, or is it dependent on another factor?

Isabella Sanzi 2E

To answer your first question, I do not think we will need to know nomenclature like this on the midterm as we have not gone over it in class at all, nor has it been in the readings. Second, yes, you would include the hydrate in your calculations as it is part of the compound for which you are tryin...

Isabella Sanzi 2E

I would just also like to add that amplitude affects the intensity of light, so increasing the amplitude would only affect the intensity at which the light is shining on the metal. Only increasing the frequency or decreasing the wavelength (which would both result in increasing energy of the light w...

Isabella Sanzi 2E

So for this problem, you have to look at the order of removal based on an electron's configuration. In the case of part a, the book asks for the metal (M) that would have the configuration for M3+: [Ar]3d^6. We know that when electrons are removed from an atom, they are removed from the highest ener...

Isabella Sanzi 2E

I would usually say that to find a calculated value of electronegativity, you would need the given values from the periodic table. However, you can sometimes infer from the positions of atoms on the periodic table and trends of electronegativity whether a bond is ionic or covalent. For example, an a...

Isabella Sanzi 2E

Yes! We do know when it is best to stop changing the structure of a molecule. You are correct that the formal charge of an element is most stable when it is 0, and that adding the double bond between the sulfur atom and the oxygen atom made the formal charge for oxygen 0 (implying that it should the...

Isabella Sanzi 2E

I am confused as to what it means when an element has a high electron affinity. Does a high electron affinity imply that an element easily adds an electron, or that it takes a high energy level to add the electron to the element. Additionally, what is the difference (if there is one) between electro...

Isabella Sanzi 2E

I am just wondering under what circumstances that we can use the De Broglie equation. I understand that it solves for wavelength, but why use the de Broglie equation instead of another way to solve for wavelength? Does it simply depend on what information you are given? Also, why doesn't the equatio...

Isabella Sanzi 2E

I do not think that there is a limit on the energy level that an excited electron can reach. If enough energy is used, an electron will respond accordingly. I suppose that there is a practical limit to how much energy we (as experimenters) can input into a system, which would act as the only limitat...

Isabella Sanzi 2E

When I did this problem, I used process of elimination. Option A is "The speed of the radiation decreases," which we know is incorrect because we use a constant to measure the speed of electromagnetic radiation (3.00 x 10^8 meters per second or the speed of light). For option B, "the ...

Isabella Sanzi 2E

Hey guys, The question for chapter 1 number 15 is: In the ultraviolet spectrum of atomic hydrogen, a line is observed at 102.6 nm. Determine the values of n for the initial and final energy levels of the electron during the emission of energy that leads to this spectral line. I already found the fre...

Isabella Sanzi 2E

To help further illustrate this, one of the examples that Dr. Lavelle used in class compared a reaction to baking brownies. If you have a lot of flour, sugar, and chocolate but only a few eggs, the amount of eggs will limit the amount of brownies you can make. This is the same for a chemical reactio...

Isabella Sanzi 2E

I believe that the answer is that it depends on the element that is being added in addition to C, H, or O. For example, with an element like Nitrogen in a combustion analysis, the product would be N2(g). For other elements, however, it may be different.

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