CHEMISTRY COMMUNITY

Emma Miltenberger 2I

The oxidized reaction is on the left side, where the anode is, and the reduced reaction is on the right side, where the cathode is.

Emma Miltenberger 2I

In this case, the volume cancels out. However, it is good practice to use the volume to solve for molarity and use molarity in the equation to ensure you do not make an arithmetic mistake on a test.

Emma Miltenberger 2I

Yes, this equation yields the same answer. The book uses logarithm rules to rearrange the equation to make kt positive. ln(Af/Ao)=-kt is the same as ln(Ao/Af)=kt.

Emma Miltenberger 2I

Yes, the rules of logarithms make this possible. ln(At/Ao)=-kt is the same as ln(Ao/At)=kt.

Emma Miltenberger 2I

The graph of a 0 order reaction plots time and concentration. The graph is linear and has a slope of -k and a y intercept of the initial concentration.

Emma Miltenberger 2I

The rate constant is a "constant" for that particular reaction, and therefore does not change between experiments. While it isn't necessary, doing this calculation twice can ensure your arithmetic is correct and therefore might be helpful on a test.

Emma Miltenberger 2I

I believe this only covers problems up through #39.

Emma Miltenberger 2I

I don't think we will be asked to directly derive the equations. However, understanding the derivations may help with the conceptual questions on Test 3.

Emma Miltenberger 2I

The electrons on the left side of the equation must cancel with the electrons on the right side of the equation. It is simplest to do this using the least common multiple. However, as long as the electrons cancel, you can use a higher multiple and then simplify the equation after.

Emma Miltenberger 2I

N is the number of electrons transferred in the reaction. To find this value, write out the half reactions and balance them so the number of electrons gained equals the number of electrons lost. This is the value of n you should use in the equation.

Emma Miltenberger 2I

The sign changes because pH is equal to -log[H+]. Therefore, when converting, you must account for this negative sign in front of the log.

Emma Miltenberger 2I

N is the number of electrons transferred in the reaction. To find this value, first balance the reaction so the electrons gained match the electrons lost. This is the value you should use for n.

Emma Miltenberger 2I

You should use the appendix to find the half reaction.

Emma Miltenberger 2I

This is an error. It should be n=1.

Emma Miltenberger 2I

Yes, you would reverse it when you use the equation E(cell)=E(anode)+E(cathode).

Emma Miltenberger 2I

Why does T=1015.5 K in the last step?

Emma Miltenberger 2I

As long as you are consistent, I do not believe it matters whether you use kj or j.

Emma Miltenberger 2I

It does not necessarily mean that delta H an delta S are zero. When delta G =0, the system is at equilibrium. Therefore, either delta H or delta S is zero or delta S is equal to delta H.

Emma Miltenberger 2I

He does not post the lecture slides online.

Emma Miltenberger 2I

Condensation is exothermic because bonds are being formed.

Emma Miltenberger 2I

Lavelle clarified this in lecture. As a general rule of thumb:
+deltaH and +deltaS= spontaneous at high temperatures
+deltaH and -deltaS=not spontaneous
-deltaH and +deltaS= spontaneous at all temperatures
-deltaH and -deltaS= spontaneous at low temperature

Emma Miltenberger 2I

In this case, both the pressure and volume contribute to the overall deltaS. Therefore, you would calculate each individually using Cp and Cv and add those respective values together.

Emma Miltenberger 2I

This is the equation for isothermal reversible expansion. It is derived from PV=nRT and w=-P*deltaV. However, Professor Lavelle specified that we do not need to know this for the test.

Emma Miltenberger 2I

It produces water in the liquid state. However, if you are referring to enthalpy of combustion, the H2O should normally cancel out in a Hess's Law problem and therefore the state does not matter.

Emma Miltenberger 2I

In this problem, the ice melts and turns into water. Therefore, you use the specific heat capacity of water.

Emma Miltenberger 2I

A bomb calorimeter is a more advanced form of a calorimeter. A bomb calorimeter consists of a sealed metal container which is sealed and thus provides constant pressure and volume. It is an isolated system. A normal calorimeter is more simplified and cannot withstand high pressures and volumes. Howe...

Emma Miltenberger 2I

Yes, delta U is the change in internal energy of the system. It can be found in the first law of thermodynamics which states deltaU=(q+w), where q is the net heat transfer of the system and w is the net work done on the system.

Emma Miltenberger 2I

Is there a specific question you are referring to? I believe it is referring to calibrating the thermometer of the system, meaning the thermometer was adjusted to accurately measure the change in temperature of the reaction.

Emma Miltenberger 2I

I would ask your TA! Last quarter, my TA accepted homework in pencil but it would be a good idea to check, just in case. However, make sure to use pen for tests.

Emma Miltenberger 2I

You get to choose what problems you would like to do as long as it is a recent topic we have gone over. So you can choose to submit chapter 8 or chapter 9 problems next week. However, make sure to remember that you have to turn in 14 problems next week as opposed to the usual 7!

Emma Miltenberger 2I

In this case, you are only concerned with the change in temperature, not the actual temperatures themselves. Since the conversion between Celsius and Kelvin is additive, the change in temperature is the same, regardless of units. Therefore, it does not matter if you use Celsius or Kelvin. However, i...

Emma Miltenberger 2I

It requires energy, in this case, heat, to break apart a molecule. Therefore, the forward reaction is endothermic and will be favored.

Emma Miltenberger 2I

Reducing the volume will result in the reaction shifting in the direction that minimizes the number of moles of gas produced.

Emma Miltenberger 2I

The reaction will favor the direction that makes the reaction endothermic. In this case, the formation of reactants is favored because it makes the reaction endothermic as opposed to exothermic.

Emma Miltenberger 2I

Dr. Lavelle said in class today that we do not need to know polyprotic acids so you can omit problems 12.79 and 12.81 in the textbook.

Emma Miltenberger 2I

I believe they are the same thing. Molecular geometry and molecular shape are synonymous. However, there is a difference between electron geometry and molecular shape/geometry as molecular geometry/shape only considers bond arrangement and does not consider lone pairs.

Emma Miltenberger 2I

The ratio of products to reactants would be exactly 1:1. For every mole of reactants, there is one mole of reactants.

Emma Miltenberger 2I

I don't think you need to know any other specific angles as long as you know the general trend. For example, I think it would be acceptable to know that a trigonal pyramidal molecule has a bond angle slightly less than 109.5 degrees if you are able to explain why.

Emma Miltenberger 2I

I think it is different every year depending on the class average. I think the curve is meant to help our grades and not hurt them, so I wouldn't worry about it.

Emma Miltenberger 2I

If n=5, it is the row of the periodic table and the actual shell for the s and p orbitals. However, it is not for d and f.

Emma Miltenberger 2I

A good example of this was on the midterm. The question asked if N2 and SO2 were polar or non polar. N2 is non polar because the N atoms do not have a difference in electronegativity. SO2 is polar because the S and O atoms have differences in electronegativity less than 2.

Emma Miltenberger 2I

The second ionization energy is always higher than the first because it is harder to remove an electron from a cation than a neutral atom.

Emma Miltenberger 2I

If you are referring to part C, it asks for the valence-shell configuration of the group 5 transition metals. I was confused on this as well. I think the solution manual made an error and is referring to the group 7 transition metals (Mg, Tc, Re, etc.).

Emma Miltenberger 2I

I agree that the solution manual's answer was somewhat vague. I think it is trying to say that because the energy spacing between orbitals is smaller, the energy pattern is not very rigid as it requires less energy to rearrange it. Therefore, there are exceptions to the regular order of orbital conf...

Emma Miltenberger 2I

As long as you are consistent with your units, it does not matter unless the homework or test problem specifies that the answer should be in meters or picometers. However, it is very simple to convert between meters and picometers if the question does specify. A picometer is equal to 1*10^-12 meters...

Emma Miltenberger 2I

There are no exceptions to this as far as I am aware. The Balmer series represent all of the spectral lines within the visible spectrum and the Lyman series represents all of the spectral lines within the UV region of the spectrum. Therefore, for each transition to n=2 and n=1 respectively, is part ...

Emma Miltenberger 2I

I asked Lavelle about this on the first day of class and he said that they are no longer allowed to sell course readers. However, because of Lavelle's extensive website, I don't think course readers make that much of a difference.

Emma Miltenberger 2I

The photoelectric effect is highly important because it demonstrates that light has both wave and particle characteristics. Before the photoelectric experiment, light was largely regarded as being a wave and was modeled as a wave in the scientific world. However, the photoelectric effect demonstrate...

Emma Miltenberger 2I

Yes, c is a constant. C is the speed of light and does not change. Therefore, in all C=λv problems, you should set c equal to 3.00*10^8 m/s. The wavelength and frequency are what will change in this equation.

Emma Miltenberger 2I

A good way to ensure you have the correct number of sig figs is to convert each value to scientific notation. Therefore, if you were given the number 0.0020, you should write it as 2.0*10^-3. It is thus clearer that this number has 2 significant figures.

Emma Miltenberger 2I

Dr. Lavelle mentioned in class today that we will be given a periodic table, list of equations, and list of constants for every test. Avogadro's number should be listed on this list of constants so you do not need to worry about memorizing it. However, you should be familiar with how to use it since...

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