CHEMISTRY COMMUNITY

Charles Ang 1E

It shouldn't matter. As long as you make sure to make the T' and k' line up correctly in the formula. -Ln(k'/k)=Ln(k/k')

Charles Ang 1E

Assuming the other posts about this are correct, the solutions manual has an error. It should be LnK=.59, so the .59 is not actually subtracted.

Charles Ang 1E

if you think about it, If A=1, then Ln(A) should be 0. I'm not sure if this is correct, but its the way I think of it.

Charles Ang 1E

Yes, the way I think of it is: a rate is something changing. The opposite of change is not a negative change.

Charles Ang 1E

When working with rate laws, it is not necessary to convert to Si units immediately but is done to simplify/ make the answer more relevant. If you choose not to, just make sure to properly perform dimensional analysis to give your answer the proper units.

Charles Ang 1E

As temperature increases, the movement of molecules generally increases along with it. This allows the molecules to collide more frequently by increasing the coefficient of the collision frequently. With more collisions, molecules become more likely to collide at the correct angle with enough energy...

Charles Ang 1E

43 is a good number to stop at. In lecture, Lavelle mentioned that mechanics onward would not be on the exam.

Charles Ang 1E

The post above me explains it well. The pseudo rate law assumes two of the variables are in excess allowing us to reduce the number of variables in our equation, simplifying the calculation.

Charles Ang 1E

Yes, the answers above describe it well. The way I think if it, zero order reactions aren't affected by the reaction and as a result don't change. Therefore, graphing it would be a straight line with a slope of 0.

Charles Ang 1E

It depends on what you are going to do with the half reactions. If you are doing it simply to determine the number of electrons being exchanged or identifying the anode and cathode while finding the standard potential, then the direction of your reactions shouldn't matter.

Charles Ang 1E

Its usually in acidic conditions, as many modern batteries are in acidic solutions. If it were in basic conditions it would state so.

Charles Ang 1E

Yes we can. Gibbs free energy is a state function because it is defined by other state functions. Therefore it can be added together to find the free energy of the reaction.

Charles Ang 1E

From my understanding, it stops because as it reaches equilibrium the chemical/electrical gradient becomes smaller until it disappears and begins to grow when it passes equilibrium.

Charles Ang 1E

Yes, because the electrons need to be on both sides so they can be canceled out. If one side does not have electrons, I would double check or consider if the half reaction I identified was incorrect.

Charles Ang 1E

I don't know if this is of any help, but I start by identifying the two half-reactions and identifying the difference in electrons, then I balance it as if I were using hess's law.

Charles Ang 1E

For the homework problems, it is safe to assume that you always have to convert to Kelvin. However, if you are finding the change in temperature, you can choose to stay in C rather than K because 273 will be added to both addends.

Charles Ang 1E

The solutions manual uses the entropy generation formula which has a negative answer because the system will be releasing entropy. But the question asks for the rate of entropy your body generates. So we are answering the question, at what rate is the entropy in our surrounding changing, which would...

Charles Ang 1E

Delta H fus is negative because the phase change is going from a liquid to a solid. Since a solid has less possible positions for its atoms, there is less entropy. So the system is losing entropy when it freezes.

Charles Ang 1E

A lunch box would be an attempt at an isolated system, though in practice it is not. If it were on a test, I believe they will make it clear that they mean a very insulated lunch box or not.

Charles Ang 1E

I also have trouble with the sign of q. I found that it helps me to try to think whether the q applies to the system or surrounding and determine what is losing and what is gaining.

Charles Ang 1E

I agree that this question was poorly worded. However, aside from its flaw of failing to mention the number of moles, it is a relatively straight-forward, good question. It forces us to recall the properties of an ideal gas and standard conditions.

Charles Ang 1E

w=integralPdV and w=-PdV mean the same thing. This is because the integral is simply the sum of all pressures as the limit between them approaches zero. So when pressure is constant, we no longer need the integral and can use the formula w=-PdV.

Charles Ang 1E

Work is negative because when we work with systems that have zero internal energy, the q and w cancel out. Because in the formula U=q+w they are both on the same side, we can manipulate q=-w when U=0.

Charles Ang 1E

The reaction takes place at room temperature, and water at room temperature is liquid.

Charles Ang 1E

H_vap = kJ/moles is what the book gives as the value of enthalpy of vaporization. For the question, we are given a value in kJ and in moles. Just put those value into the formula to get the answer.

Charles Ang 1E

To solve this problem I find that it is easiest to use the definition of the enthalpy of vaporization which is as follows: H_vap=kJ/moles. Since we are given kJ and the moles, it becomes a plug and chug question.

Charles Ang 1E

In this question the q(of the cylinder) = -w(of the fuel). Which is why when calculating the work of the fuel, the value of q is negative.

Charles Ang 1E

The method explained in class is the most common and easiest way to determine if a reaction is exo- or endo- thermic because it uses the definition. If the reaction produces/releases heat to the surroundings it is exothermic, and if it absorbs heat it is endothermic.

Charles Ang 1E

The method that the solutions manual uses for phase changes uses the molar heat capacity because it is the one we use with H_fus. The specific heat is also used for the second half of the question because the information we were given is in grams, making specific heat easier to use.

Charles Ang 1E

For the tests, we will be given all the constants. Just make sure you know how to use them. The textbook provides very helpful tables which provide all the constants you will need to do the hw. To my knowledge, lavelle doesn't make us memorize anything.

Charles Ang 1E

If there is a question on the final regarding Pka and Pkb values, just make sure you know how to use/find those values. All the constants and equations are always given.

Charles Ang 1E

Acids are both bronsted acids and lewis acids. The difference between the two are what defines them as acids. Using the lewis definition we look at the electron pairs, and the bronsted look at the protons. Essentially they are the same thing, just described differently.

Charles Ang 1E

Wayland Leung wrote:How do you determine just by looking at a molecule that it is a weak base?

I'm not quite sure, but I do know that there is chart towards the end of the course reader, right before the sample tests, listing common weak bases.

Charles Ang 1E

the H3- is electron-donating relative to hydrogen and it donates electrons to the carboxyl group which makes it more negative. This causes the acid to be weaker, because the proton now has to be separated from a more negative conjugate base. likewise, CH3CH2- is more electron-donating than CH3-, an...

Charles Ang 1E

Timothy Kim 1F wrote:If the atoms have a formal charge of 0, it will not want to bind with anything, correct?

I may be mistaken, but I think that the potential to bind is not caused by the formal charge, but rather the presence of lone pairs on an atom.

Charles Ang 1E

As mentioned above, both are correct. If you choose not to use the naming from the textbook, go to the class website and you can find a list of the alternate accepted names.

Charles Ang 1E

No, they are not stable. It is very likely that another atom/molecule seeking to finish its valence shell with one electron will bond with the radical.

Charles Ang 1E

Alex is correct. Even if the molecule is symmetrical, it is still possible to be polar. The bond polarities, which can be determined by electronegativity, must be checked in order to determine this. A good example is HCN where despite being linear, is polar.

Charles Ang 1E

An easy way to remember this is to think of delta v as the change in v like in math. So, we arent concerned with the value of v, but rather the difference between the two limits to its domain.

Charles Ang 1E

A quick way to know which element has a higher electron affinity is to look at the number of valence electrons it has. Chlorine has 7; whereas nitrogen has 5. Therefore, Chlorine is going to hold its outer electrons more strongly.

Charles Ang 1E

Depending on the wording of the question, it may be more appropriate to draw the most stable Lewis Structure rather than all of the resonance structures. However, if the question asks specifically for resonance structures the list as many as you can. Usually, there aren't too many.

Charles Ang 1E

When finding the lewis structure of SO 4 2- , it can be drawn where each oxygen has a single bond with sulfur. However, the most stable diagram is one where sulfur has 12 valence electrons and 2 of the oxygen atoms have double bonds with sulfur while the other 2 have single bonds. Are there elements...

Charles Ang 1E

Cu was one of the exceptions that was discussed in lecture. The electron configuration of Cu takes an electron from the s orbital and places it in the d orbital in order to fill it because of pairing energies. Because you are working with Cu+, you take away another electron from the s orbital.

Charles Ang 1E

45 gives us the electron configuration [Rn] 7s² 6d². Initially I thought that the answer was rutherfordium; however, the correct answer is Thorium. Why is this the case?

Charles Ang 1E

Would you plug in the mass of a hydrogen atom? So the atomic mass 1.01? I haven't seen the original problem, but the way the question is described by the OP makes it seem as if you are finding the uncertainty of finding an electron. In which case, you would use the mass of an electron ("9.1x10...

Charles Ang 1E

I believe that the difference in symbol between Planck's constant and h=h/2pi is denoted by a serif near the peak of the h. So if you see the letter h, it might be safe to assume it refers to Planck's constant.

Charles Ang 1E

Does this mean that even large objects like cars and balls still demonstrate wavelike behavior even though we can't visibly detect it? I believe it does. However, in one of the peer learning workshops, I recall the UA telling me that the DeBroglie equation generally only works with things that are ...

Charles Ang 1E

What causes electrons to move up in energy levels? I understand that once they have enough energy they can "hop" up or down energy levels, but what causes this change in energy?

Charles Ang 1E

In ionic equations, how do you know when to split up molecules (as Kourtney did for both reactant molecules) vs keeping molecules together? (Such as keeping Cu(OH)2 together in the products but splitting up 2NaNO3 to 2Na+ + 2NO3-? When in an aqueous solution, solubility rules apply. 2NaNO3 is solub...

Charles Ang 1E

For part B of this question, how is the name of the oxide determined? To my understanding, the roman numeral refers to the subscript of the metal. Why is SnO₂ called tin(IV) oxide?

Search found 50 matches