CHEMISTRY COMMUNITY

Ryan Sydney Beyer 2B

I think Dr. Lavelle is talking about a cell that runs on the concentration difference between two chambers of the cell. He went over examples of these during lecture - different from a galvanic cell b/c doesn't depend on the oxidizing power / reducing power but instead on the conc. difference betwee...

Ryan Sydney Beyer 2B

In an adiabatic process it means that there is no net heat flow in or out of the system. You can change the pressure and this will result in a change in volume. This is why the adiabatic process line on a PV diagram is the shape it takes because the temperature does not change since there is no net ...

Ryan Sydney Beyer 2B

If a King farts is it a Noble gas?

Ryan Sydney Beyer 2B

yes, the rate of the reaction is always positive. This can be confusing as the rate of disappearance can be negative (the rate at which the reactant is leaving). However, if you think about it, the rate of the reaction should never be negative because this is describing how fast the concentration ch...

Ryan Sydney Beyer 2B

The units for k depend on what order the reaction is on. This is because the concentrations - which will be to the zero, first, or second order for this. So mol / L will be raised to some exponent. We know that the rate of the reaction is going to have units of mol / L * s, so we just have to make s...

Ryan Sydney Beyer 2B

Also for medications. It could be useful to know how long a medicine is going to be active in a patient's body and how much is going to be present.

Ryan Sydney Beyer 2B

I'm sure Lavelle's exams don't have any sort of derivations on them. He could switch it up this year though

Ryan Sydney Beyer 2B

You can look at your balanced half reactions and it will show you how many moles of electrons are going to be exchanged during the reaction.

Ryan Sydney Beyer 2B

Yes, you can use water to balance chemical reactions. Also a note .. make sure that the charges are balanced as well.

Ryan Sydney Beyer 2B

For kinetics, the order of the reaction with respect to some sort of substance (ex. reactant, product) is going to be the exponent to which it's concentration form is raised. We use this in the rate equation and we can see that the concentration of this substance is raised to some sort of power.

Ryan Sydney Beyer 2B

I believe that if the activation energy is high then the rate of the reaction is going to be slower but if the reaction energy is low then the reaction rate is going to be faster.

Ryan Sydney Beyer 2B

I would think to do H+ since it was in the book and Dr. Lavelle said to do it as well. H3O makes it more complicated as well.

Ryan Sydney Beyer 2B

I think it could be that they are in different phases. We are supposed to separate the objects that are in different phases when drawing the cell diagram and I'm assuming that the Cl - ions were in solution and the Cl2 was in a gaseous phase.

Ryan Sydney Beyer 2B

The cathode equations should have a more positive value of standard potential then the anode half reactions. This makes sense because when you go to determine the standard cell potential then you will arrive at the most energetically favorable number.

Ryan Sydney Beyer 2B

You would never include H2O (s) because it is impossible to have the water electrode and just no reason to have it in the cell diagram. Also H2O (g) might sometimes be placed in the cell diagram if the pressure is large enough?

Ryan Sydney Beyer 2B

When writing cell diagrams, we are supposed to have the anodic compartment on the left and the cathodic compartment on the right. To go more into detail about the anodic compartment, the far left side is supposed to have the metal or solid electrode, right side of the anodic compartment is supposed ...

Ryan Sydney Beyer 2B

Arrange the following in order of increasing standard molar entropy: CHF3, CF4, CH3F, CH2F2 (all are in the gaseous phase) The correct answer has CH3F < CH2F2 < CHF3 < CF4 but shouldn't have a higher standard molar entropy then since there are more ways to orientate the molecules?

Ryan Sydney Beyer 2B

The change in entropy of the surroundings is going to equal zero during an irreversible process. During an irreversible process, the change in entropy of the system is equal to the change in entropy total and the change in entropy of the surroundings is equal to zero. However, during a reversible pr...

Ryan Sydney Beyer 2B

I remember learning in physics this equation relates internal energy to temperature. I don't think we will have to use this equation on any test to calculate anything but we might have to understand what the equation. I generally think of this equation when an isothermal process comes into play ... ...

Ryan Sydney Beyer 2B

I think you're talking about the equation where the free energy of the reaction is equal to the standard free energy plus RTlnQ. I think there was some derivation that was not covered that got the RTlnQ part but all we have to know is that we take the standard free energy and alter it in some way wh...

Ryan Sydney Beyer 2B

The 3/2 is a number specific to monoatomic ideal gases. R, the ideal gas constant, is avogadro's number * Boltzmann's constant. This equation can be expressed in a different way as E = (3NK_{b}T)/2 , where N in the number of molecules. This shows that there is a direct relation between the n...

Ryan Sydney Beyer 2B

I'm not too certain that we will have to calculate the number of microstates for a specific molecule, but rather if the molecule can be in place A or place B. I think it'll more like probability in place A vs. place B and that is the number of microstates.

Ryan Sydney Beyer 2B

We can also say that an endergonic process has a positive delta g and is non spontaneous, an exergonic process has a negative delta g and is spontaneous so it makes sense that a process at equilibrium has a delta g of zero.

Ryan Sydney Beyer 2B

I think what the book is trying to say here is that the change in entropy (delta S) is going to be the same for an irreversible path or a reversible path. This is because they said entropy is a state function so all that matter is the final state minus the initial state and nothing in between.

Ryan Sydney Beyer 2B

A reversible reaction means that the system and the surroundings can be restored to the initial state from the final state without changing any thermodynamic properties. There are two main conditions for the reversible process to occur. 1) the process should occur in infinitesimally small increments...

Ryan Sydney Beyer 2B

I think a partial answer could stem from what Dr. Lavelle mentioned in class about the element with more electrons having greater entropy because there are more possible positions of the electrons. I think the same can be applied to your question ... if there is a heavy and light version of a simila...

Ryan Sydney Beyer 2B

When a reaction feels cold then it is endothermic since it is taking in heat for the reaction. When a reaction is exothermic then it feels hot because heat is being released from the reaction.

Ryan Sydney Beyer 2B

I believe that bond enthalpies are the most unreliable method for calculating reaction enthalpies because the bond enthalpies are not specific to the specific molecules in the reaction. Instead, the bond enthalpies are averaged over many different molecules. For example, a C-H bond in one molecule m...

Ryan Sydney Beyer 2B

It might also be helpful to know the relationship between the two::

Precisely enthalpy is obtained from internal energy when the variable entropy S is substituted by the variable temperature T.

Ryan Sydney Beyer 2B

It could also be helpful to know the relationship between the two::

Enthalpy is obtained from internal energy when the variable entropy S is substituted by the variable temperature T.

Ryan Sydney Beyer 2B

I've heard that some TAs are saying CH 9 but we have hardly touched that so it might be better to focus on CH 8 since we have an upcoming test on that material as well.

Ryan Sydney Beyer 2B

In addition to these two types of enthalpies you might want to be familiar with enthalpies of fusion, enthalpies of vaporization and when to use them. I'm sure you won't have to memorize any values but just be aware of when to use them as we might get a problem of melting ice or something along thos...

Ryan Sydney Beyer 2B

Both heat and work are not state functions. Work can't be a state function because it depends on the distance an object is moved, which depends on the pathway. If work is not a state function then heat can't be either based on the first law of thermodynamics. Heat is energy transferred between the s...

Ryan Sydney Beyer 2B

Another way of thinking about this type of problem is from the perspective of work. If there is no expansion / contraction on the system then work must be zero since there is no work being done on the system and the system is not doing work. Looking back to the equation, Delta U = q + w, then if wor...

Ryan Sydney Beyer 2B

I think a good way of seeing whether or not to use the ideal gas law is based on the information that the problem gives you. If the problem gives you temp info, volume info and info about moles. Then we can work this equation and solve for pressure. Also, there may be problems where we have to know ...

Ryan Sydney Beyer 2B

So the example at the end of class was using bond enthalpies to calculate the rxn enthalpy. The answer came out to -58kj which is exothermic. I was thinking about this ... in order for this reaction to occur, you would have to take out 58kj from the system. So would you ever naturally find the react...

Ryan Sydney Beyer 2B

The definition of a state function i some property whose value doesn't depend on the path taken to get there. Enthalpy is a state function because it only depends on the initial and final conditions, and not the path to establish these conditions. We can also see this from the equation :: ΔH=Hfinal−...

Ryan Sydney Beyer 2B

It might also be important to note that in a bomb calorimeter there can be change in pressure while in a coffee cup calorimeter there is no change in pressure. We would use coffee cup calorimeters to directly find enthalpies since pressure is not changing and we would use bomb calorimeters to direct...

Ryan Sydney Beyer 2B

Thank you!!

Ryan Sydney Beyer 2B

Does anybody know if discussion starts this week?

Ryan Sydney Beyer 2B

In a soln. of water, the hydroxide conc multiplied by the hydronium conc is going to equal 1 X 10^-14. If you take the negative log of both sides of this eqn it shows you that the pH added to the pOH is going to equal 14. [H+] [OH-] = Kw = 1 X 10-14 Take the -log of both sides of the equation - log ...

Ryan Sydney Beyer 2B

The pH of pure water decreases with increasing temp. If the pH falls and the temp is increased, this does not mean that water becomes more acidic at higher temps. For pure water, there is always the same concentration of hydrogen ions and hydroxide ions so water is still neutral (pH = pOH) even if i...

Ryan Sydney Beyer 2B

According to the classical definition, a super acid is an acid with an acidity greater than that of 100% pure sulfuric acid. A super base is an extremely basic compound that has a high affinity for protons. Don't know too much besides their definition but hopefully this cleared up some things!

Ryan Sydney Beyer 2B

I don't know the entire reason but this may be part of the reason why: In a biological system like the stomach, there is a double mucus layer. The inner mucus layer acts as a diffusion barrier for HCL while the outer cells secrete bicarbonate which dumb the pH down to a neutral pH at the cells surfa...

Ryan Sydney Beyer 2B

I remember Dr. Lavelle saying that we won't be tested on our drawing skills so I don't think that we are going to be tested on how well our 3d drawings look. I think that we are going to be expected to visualize different types of molecular structures in our head and then manipulate them as we add l...

Ryan Sydney Beyer 2B

If the reaction is going to the right then the products will gain some partial pressure so it will be a positive x value for the product and a negative x value for the reactants. The same is true for the opposite in which a reaction going to the left should have a negative x value for the products a...

Ryan Sydney Beyer 2B

Sometimes we use the "ate" suffix to differentiate between whether it is a cation or an anion. In this specific situation, the coordination sphere has an overall negative charge and therefore we should be indicating that this is an anion.

Ryan Sydney Beyer 2B

We know that at equilibrium the forwards reaction rate and the backwards reaction rate are equal to each other. When the reaction is favoring the reactants and going backwards, then we know that Q > K. Q is going to become less and less until it equals K and then the two will be at equilibrium. An e...

Ryan Sydney Beyer 2B

I assume you're just talking about the different phase states of molecules. The reactants and products could be in a gaseous phase when they are in the gaseous state. They could be in aqueous phase when dissolved and present as ions. They could be in solid phase when in a solid state but we don't in...

Ryan Sydney Beyer 2B

I am fairly sure that any type of molecule that is held together by pi bonds is unable to rotate and will create a rigid planar structure for that molecule. When there are two pi bonds in place, rotation will become irrelevant since the molecule is linear. What I'm getting at is that if you flip the...

Ryan Sydney Beyer 2B

We should know the bond angles of the ones that Dr. Lavelle went over in lecture. I think that most of them are fairly easy to figure out in that it is just basic geometry. Like if two atoms are in a line then you know that they are 180 degrees apart from one another just like 3 atoms would be 120 d...

Ryan Sydney Beyer 2B

A coordination sphere is the central metal ion plus the attached ligands of a coordination compound. There is a difference between the first and second coordination spheres which I don't think we are going to go into depth about ... but the first sphere refers to the molecules that are attached dire...

Ryan Sydney Beyer 2B

You can also calculate the exact value of this tetrahedral angle using a cube and it's vertices. The exact value comes out to be \arccos (-1/3) = 109.4712206 I've attached the link below but I think for the purposes of this class, we should know that if there is a central molecule with 4 bon...

Ryan Sydney Beyer 2B

Hybridization was brought about to explain molecular structure when the valence bond theory failed to correctly predict. According to our knowledge of valence bonding, carbon should form two covalent bonds, resulting in a CH2, because it has two unpaired electrons in its electronic configuration. Ho...

Ryan Sydney Beyer 2B

Electrostatic potential has everything to do with dipole moments, electronegativity, and partial charge. Electrostatic potential helps us to know the relative polarity of a molecule. Negative electrostatic potential corresponds to a attraction of a proton by the concentrated electron density in the ...

Ryan Sydney Beyer 2B

It's going to be given to us on the list of constants and equations so no need to memorize it!

Ryan Sydney Beyer 2B

The definition of effective nuclear charge is the net charge that an electron experiences in an atom with multiple electrons. Basically as the number of electrons increases in an atom, the effective nuclear charge that the outermost electron feels is lowered. The effective nuclear charge can be calc...

Ryan Sydney Beyer 2B

In the 1900's a man named Edwin Hill came up with a system of writing chemical formulas that is still used widely today. His system states that carbon atoms are listed first, hydrogen atoms next and then the number of all other elements in alphabetical order. There are many exceptions to his system ...

Ryan Sydney Beyer 2B

When figuring out whether to place a double or triple bond you should always look at the number of valence electrons present as well as the number of bonds a central atom is likely to form. Another good way to know whether to use double or single bonds is to calculate the formal charge on each atom ...

Ryan Sydney Beyer 2B

Main group elements that form more bonds than what would be predicted by the normal octet rule are called hypervalent compounds. These compounds have an expanded octet meaning that there are more than eight electrons around one atom. The octet can be expanded by some elements by utilizing the empty ...

Ryan Sydney Beyer 2B

I would go with the more specific answer with the principle quantum number in front of the letter.

Ryan Sydney Beyer 2B

Solutions Manual Error! I copied this from the link on Dr. Lavelle's website titled Solution Manual Errors :: In the picture, it shows A (smaller atom) + B (larger atom) --> C (larger ion) + D (smaller ion) The solution manual says that A=Na and B=Cl, and it references Figure 2.20 which explicitly l...

Ryan Sydney Beyer 2B

I think that a trend still does hold true for the noble gases. You are right that it would require energy put into the system in order to attach another electron because the atoms already have a full octet. All of the halogens as well as the elements Beryllium and Magnesium have electron affinities ...

Ryan Sydney Beyer 2B

The electron configuration for Titanium should be [Ar] 3d^2 4s^2 because the 3d orbital has a lower energy level when the electrons enter the 3d orbital so the 3d would be written before the 4s in this situation.

Ryan Sydney Beyer 2B

The Heisenberg Uncertainty Equation can be stated as following:: \Delta p \Delta x \geq \frac{h}{4\pi } We can either know momentum to extreme precision or position to extreme precision but either way it has to be greater than or equal to Planck's Constant divided by 4pi. So in the problem, as the u...

Ryan Sydney Beyer 2B

When we begin to enter the 4s orbital with the elements potassium and calcium, the 4s orbital has a lower energy than the 3d orbital which is why the 4s orbital is filled first. Then as we enter the 3d orbitals, for reasons which I believe we have not been taught or reasons too complicated, the ener...

Ryan Sydney Beyer 2B

I think to answer this question a distinction needs to be made between blocks and groups. The reason why Helium is considered a noble gas is because it's outermost shell is fully occupied by its 2 electrons. However, when you look at the electron configuration of Helium on the Periodic Table, you ca...

Ryan Sydney Beyer 2B

Solutions Manual Error! I copied this from the link on Dr. Lavelle's website titled Solution Manual Errors :: In the picture, it shows A (smaller atom) + B (larger atom) --> C (larger ion) + D (smaller ion) The solution manual says that A=Na and B=Cl, and it references Figure 2.20 which explicitly l...

Ryan Sydney Beyer 2B

The most important factor which influences the energy of an orbital is the size which is related to the principal quantum number. For an atom that contains just 1 electron there is no difference between the energies in the different subshells. As soon as an atom contains more than 1 electron, the di...

Ryan Sydney Beyer 2B

Well for this problem right off the bat I believe the correct answer is C. We can obtain the first value by manipulating the de broglie equation and solving for speed like so :: v = \frac{h}{\lambda m} Now to figure out what makes this a reasonable speed ... Dr. Lavelle told us in lecture today that...

Ryan Sydney Beyer 2B

15. C - Only specific wavelengths of light are absorbed or emitted. Spectrum consists of lines. This is because only certain wavelengths (and therefore frequencies) match the energy difference from one energy level to the next. So only certain wavelengths of light could possibly be absorbed / emitt...

Ryan Sydney Beyer 2B

The correct answer is D for this question. The results of the photoelectric experiments came as a surprise to scientists because light was not acting like a typical wave in that when intensity was increased, energy was increased. Instead the photoelectric experiments showed that when the frequency o...

Ryan Sydney Beyer 2B

I believe that since we have only covered up to de broglie in lecture we should only be expected to cover homework up to that point. Dr. Lavelle has told us that the test on Wednesday will only cover assigned homework problems 3 to 41 from Chapter 1 so these are the types of problems we are currentl...

Ryan Sydney Beyer 2B

Yes all matter exhibits wave particle duality. This means that matter is best described not only as a wave or not only as a particle but as both. These large object have wavelike properties according to de broglie even though these wavelengths are too small to detect. Let us just say that we can onl...

Ryan Sydney Beyer 2B

For part C, the question is asking for the wavelength of the electromagnetic radiation that hit the metallic surface. We also know that the energy of a singular incoming photon, E, is equal to the work function added to the kinetic energy of the electron. This is because the energy that was put into...

Ryan Sydney Beyer 2B

You can also think of the equation to be \nu = -R((1/n(final)^2)- 1/n(initial)^2)) . This might make things a little bit clearer because the change in energy levels is going from 4, which is the initial state, and ending at 2, which is the finial state, because th...

Ryan Sydney Beyer 2B

By looking at all of the lines in the spectrum of hydrogen atoms, an empirical model was derived that explains emission patterns of hydrogen atoms. The frequencies (or wavelength or energy) could be predicted based upon the Rydberg constant and two integers. One integer is meant to represent the ini...

Ryan Sydney Beyer 2B

The question states that the emission given off is in the ultraviolet so we know that it is in the Lyman Series. From this we know that n1 = 1. I think any problem has to give us some clue as to which energy level it is referring to or else we would have to resort to guess and check methods. From th...

Ryan Sydney Beyer 2B

The question states that the emission given off is in the ultraviolet so we know that it is in the Lyman Series. From this we know that n2 = 1. I think any problem has to give us some clue as to which energy level it is referring to or else we would have to resort to guess and check methods. From th...

Ryan Sydney Beyer 2B

So the net ionic equation from my understanding is basically getting rid of anything that didn't participate in the reaction. A net ionic equation gets rid of all spectator ions. So our equation is :: Cu(NO3)2 (aq) + 2 NaOH (aq) --> Cu(OH)2 (s) + 2NaNO3 (aq) We then write out the total ionic equatio...

Ryan Sydney Beyer 2B

For question G9 you don't actually use the M[i]V[i] = M[f]V[f]. Instead we'll be using the M = n/V. In this problem they are asking for the mass of silver nitrate which needs to be added into the 500.0 ml flask for the molarity to equal 0.179 M. The way we'll find mass from the information given is ...

Ryan Sydney Beyer 2B

To find the limiting reagent you need to convert both grams of C6H9Cl3 and AgNO3 to moles. So you take the 0.750g C6H9Cl3 and divide it by its molar mass of 187.50 g/mol and you'll have 0.004 mol C6H9Cl3. Do the same for AgNO3 which will be 1000. g AgNO3 divided by its molar mass of 169.88 g/mol and...

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