CHEMISTRY COMMUNITY

inlovewithchemistry

when can you justify that it is okay to ignore the second ionization? what will be the indication that we dont have to do the second ionization?

inlovewithchemistry

what is the cut off for something to be considered "very large" for pseudo first order? how will we know to do this? i dont have a full understanding fo the process.

inlovewithchemistry

in the book, they give us this formula
NO2 + NO2 --> O2 + N2O2
and tell us the rate law for NO2 is
rate law of formation of NO2 = 2k[N2O2][O2]
ive never seen a coefficient in a rate law and was wondering why this is important.

inlovewithchemistry

when given couples like (U3+/U and La3+/La), is the only way to tell which is the reduction and which is the oxidation to compare the Ecell values? and see which is more positive?

inlovewithchemistry

if you were given enthalpy values for each of your elementary steps and had three steps, would the highest enthalpy value have the lesser "dip" (or amount of space between products and reactants) and lowest enthalpy value would have the greater "dip"? I just want to be clear on h...

inlovewithchemistry

if not specified, do we assume that k is a constant?
i was doing the fast equilibrium method and my answer was rate=k2K[NOCl]^2/[NO], but the correct answer was rate=k[NOCl]^2/[NO].
from this, i can assume k was a constant in the mechanism, correct?

inlovewithchemistry

"the lower the temperature, the higher the rate enhancement will be when a catalyst is added"

is this a correct statement? this question relates to question 7E.3 in the 7th edition- the whole process of it is very confusing to me but id like to understand the conceptual part first.

inlovewithchemistry

in the sol'n manual, why is 0.59 subtracted from the end of the Arrhenius calculation? I cant seem to find a good reason for it.
thank you!

inlovewithchemistry

do we need to know how to identify all of the organic chemistry concepts in question 7.29? none of the topics are listed on the outline

inlovewithchemistry

how do you identify radicals in a reaction mechanism?

inlovewithchemistry

I have tried to understand thins concept and how it is different from steady state equilibrium, but it is very difficult for me to conceptualize. Can someone try to describe the difference and importance of each?

inlovewithchemistry

are two intermediates always required to form when there are three steps in a mechanism? and is one intermediate always required to form when there are two steps?

inlovewithchemistry

concerning the attached picture of a reaction profile which is related to question 7.11 in 7th ed textbook, are the second two bumps higher because a catalyst was introduced after the first step?

inlovewithchemistry

the rate law of the reaction 2NO + 2H2 --> N2 + 2H2O is rate= k[NO]^2[H2] these are the written steps: step 1: NO + NO--> N2O2 step 2: N2O2 + H2 --> N2O + H2O step 3: N2O + H2 --> N2 + H2O why is the NO in the rate law squared but not the H2 when there are 2 of both molecules in the chemical equatio...

inlovewithchemistry

in deciding which of three steps is the rate determining step given the rate law, do you just match the given rate law to the reactants of one of the steps? for example step 1: NO + NO--> N2O2 step 2: N2O2 + H2 --> N2O + H2O step 3: N2O + H2 --> N2 + H2O rate= k[NO]^2[H2] is step two the slow step j...

inlovewithchemistry

can someone explain the highlighted part of the attached picture concerning zeroth order reactions?

inlovewithchemistry

Elementary rate laws can be determined from the chemical formula, but reaction rate laws must be experimentally determined and cannot be determined from the rate law.

is this statement correct? if not, why?

inlovewithchemistry

the book states: "the half life increases as the reaction proceeds and reactant concentration decreases. Because of this variation, the half-life is not very useful for describing reactions with second-order kinetics" can someone explain this in a different way? why is the second order hal...

inlovewithchemistry

in 7A15 in the 7th edition, how can we determine the order of each reactant when all of the values for reactant C are the same? I thought we were supposed to compare the reactants when they were at the same value in two different experiments, but this is not possible for reactant C. 2A+2B+C--> produ...

inlovewithchemistry

what would the overall rate for the reaction H2 + I2 --> 2HI look like if it was first order?

i know that the second order formula is rate = k[H2][I2], but dont know what to give if it asked for first order.

inlovewithchemistry

are units for initial concentration mol/L*s vs units for overall rate constant L/mol*s?
how do we know when to use one or the other?

inlovewithchemistry

are the common units for k values (mol/L*s) and the units for overall reactions (L/mol*s)? why are these different in textbook problems?

inlovewithchemistry

I was confused about whether or not we would get a reduction potential index on the test. Thanks!

inlovewithchemistry

It is true that we want the cathode to have a greater positive reduction potential so that the galvanic cell will be able to do useful work (positive cell potential). However, the question never specified that the cell had to have a positive cell potential. It merely asks you to calculate the stand...

inlovewithchemistry

This makes so much more sense now, thank you!

inlovewithchemistry

in this equation MnO4- + 8H+ + 5Ce^3+ --> 5Ce^4+ + Mn^2+ + 4H2O how would you identify the cathode and anode? i read in the book that the half rxn with the more positive reduction potential is where reduction occurs. however, permanganate potential is more positive, but it is the anode in the equati...

inlovewithchemistry

How do you determine which is the cathode and which is the anode in this question? Im confused because it looks to me that both half reactions are losing electrons.
thank u!

inlovewithchemistry

is chapter 6O (the products of electrolysis) expected for the test this week? it comes after talk about the Nernst equation, but is in a separate chapter, so i am unsure. thanks!

inlovewithchemistry

How are we supposed to be able to come up for the half rxns for these without an appendix?
Especially for 6L7, if anyone could explain how to get the half reactions for this, that would be great. thank u!

inlovewithchemistry

204929947 wrote:how do you tell the difference between a cathode and an anode?????

A cathode is what is being reduced, or gaining electrons. An anode is what is being oxidized, or losing electrons.

inlovewithchemistry

I just dont understand why the solution manual writes the anode half rxn as O2 +4H+ + 4e- --> 2H2O when the two things listed in the left of the cell diagram are O2(g) and H+(aq). I tried to find the half rxn beginning with

O2 --> H+

but that apparently isnt right.

inlovewithchemistry

can someone help me understand how to write the half reactions for part (d) of 6L.5? the equation is as follows:

Au+(aq)-->Au(s) + Au3+(aq)

The sol'n manual says that the half reactions are :
Au+ + e- --> Au(s)
Au3+ + 3e- -->Au(s)

but i dont understand how to get there. thank u!

inlovewithchemistry

Write the half reactions and the balanced equation for the cell reaction for the following galvanic cells: (d) Pt(s)|O2(g)|H+(aq)||OH-(aq)|O2(g)|Pt(s) I don't understand how to get the answer that is in the solutions manual or how to set up a half reaction with the cathode. Can someone explain what ...

inlovewithchemistry

Write the half reactions and the balanced equation for the cell reaction for the following galvanic cells: (d) Pt(s)|O2(g)|H+(aq)||OH-(aq)|O2(g)|Pt(s) I don't understand how to get the answer that is in the solutions manual or how to set up a half reaction with the cathode. Can someone explain what ...

inlovewithchemistry

when comparing 4J5 and 4J7, why can you use the enthalpy of formation value for 4J5, but are required to calculate the enthalpy of the reaction for 4J7?
is it because there are 2H2O2 in 4J7? how can both be plugged into the formula for delta G?

inlovewithchemistry

when writing the reaction for CO(g), how are we supposed to know that it the carbon is in graphite form and not in gas form? is it because carbon is most commonly found in graphite form? I wrote the eq for 4.J.5 at first as C(g)+.5O(g)--> CO(g) but go the wrong answer for G bc the S value for C was ...

inlovewithchemistry

Will we need to be able to apply Gibbs Free Energy to equilibrium concepts on the test? there are questions surrounding that on the outlines

inlovewithchemistry

I now understand that the book wrote it like this to help us understand that the energy released from the surroundings is absorbed by the system. It was hard for me to grasp this concept, but I thinking about it in relation to the first law of thermodynamics was helpful.

inlovewithchemistry

Its important to understand it when solving problems that involve phase changes, as it allows you to visualize the steps.

inlovewithchemistry

What are some other systems that will always be isolated?

inlovewithchemistry

Why can you not use mc(delta)T=-mc(delta)T to solve this?? I keep getting 298 (if i use kelvin) and 25 (if i use celsius) as my answer.

inlovewithchemistry

can someone describe the characteristics of free expansion? Is it just that w=0, and therefore q and deltaU are zero? Thank you!

inlovewithchemistry

When calculating the total entropy change for the expansion of an ideal gas, why can we assume that deltaU=0 and therefore q=-w? I don't understand the logic behind this and may be missing something.

inlovewithchemistry

Is there a difference between specifying that there is no work versus 0 work? I was confused why the solutions manual put those as two separate answers when regarding situations in question 4.13.9 (a) and (b).

inlovewithchemistry

I know we use deltaH/T to calculate the delta S of both system and surroundings. I also know that Ssys=-Ssurr. Does it matter whether the system or surroundings side is negative? It seems to me like it shouldn't make a difference if the system is reversible, but the book always make Ssurr negative o...

inlovewithchemistry

Why is entropy change smaller at higher temperatures? Does this only occur in special circumstances?

inlovewithchemistry

On the midterm, will we be expected to know how to write out the equations that we will use to utilize Hess's law? Like in book problem 4D15? If so, can someone explain going about that?

inlovewithchemistry

When can you assume that no work is done on a system so that deltaU=heat?

inlovewithchemistry

is there a difference between standard reaction enthalpy and reaction enthalpy? I don't understand why you have to use Hess's Law for 4D15 but not for 4D17, and they use the different wording. thank you!

inlovewithchemistry

In some problems, it will also specify whether or not these values are constant.

inlovewithchemistry

The LA in a review session I went to today also said that Gibbs free energy, or delta G, is a concept that helps us determine spontaneity. We haven't learned about it yet in lecture, but I think this would be a good reference point for your question.

inlovewithchemistry

A negative q value stands for negative heat. This corresponds to vaporization and melting.

inlovewithchemistry

Thank you for this reply! After looking back and comparing your answer to some high school notes, this would have been a lifesaver.

inlovewithchemistry

The E is the final step in an ice chart. It adds up the I and C steps and it is what you will put into an equation to get your x value when given K.

inlovewithchemistry

Q is calculated with values that are at any point in the reaction. We can use our answer from Q and compare to to the constant K value to determine whether the reaction will proceed forward or reverse.

inlovewithchemistry

Can someone define what a buffer is and the significance of it in calculations?

inlovewithchemistry

How can we use equilibrium constants to predict solubility?

inlovewithchemistry

I don't understand why in this question the solutions manual uses 0.80 as the x value without using the quadratic formula or anything. Can someone explain why it is like this?

inlovewithchemistry

Can both molar values and concentrations go into the ice chart? I have seen it used both ways in the homework and it was confusing me.

inlovewithchemistry

The concept presented in this question is confusing me. Why is part b considered the square root of the original equation? In part c, how it is the square of the original equation if 3^2 is 9?

inlovewithchemistry

How do you determine which product or which reactant is more favorable based on the K value? This question is referring to 7th edition 5H13 part C. Thank you!

inlovewithchemistry

I have a couple questions about this question that are confusing me. Why do we need to be doing this set up at all if H2So4 is a strong acid? I thought we did the ICE chart for weak acids? Does this relate to why there is a "second ionization in the solutions manual? What is that? Lastly, Where...

inlovewithchemistry

I remember discussion a Ksp constant in high school and was wondering if anyone else was familiar with it and if it is something we have already discussed in class. Can anyone explain or define it? Thanks!

inlovewithchemistry

Can someone explain the significance of pressure when discussing equilibrium constants? For example, how would adding an inert gas to a system at equilibrium change anything?

inlovewithchemistry

I was wondering in class today- is water always a liquid in equations? Can it ever be aqueous? If not, why not?

inlovewithchemistry

Both gaseous and aqueous reactants and products can be used when calculating K or Q. We cannot use solids or liquids as they do not effect the amount of products or reactants at all, so we keep them at value=1.

inlovewithchemistry

The equilibrium constant is K and Q is the reaction quotient. While they are calculated the same way ([products]/[reactants]), they are different. Q is the quantity of products and reactants that actually changes as the system approaches equilibrium. K is the numerical value of Q at the end of the r...

inlovewithchemistry

I noticed in the solutions manual that when writing the equation for the K value, the concentrations were always written as the reactant or product as a subscript of P. Do we have to write it like that? I don't want to lose credit on my homework for that. Thank you!

inlovewithchemistry

Referring to #21 on churro questions ("The overall molecule as shown is neutral. What is the oxidation state of the iron?") Can someone explain to me why the answer is +2? When I added up all of the formal charges for the surrounding N atoms, I got +6, and I don't understand how a +2 charg...

inlovewithchemistry

A question from the midterm identified the statement "the lowest value that the magnetic quantum number ml can take is -9" as incorrect. Can someone explain WHY it is incorrect?
.'

inlovewithchemistry

how would we go about ranking strong bases? what is the first thing we should look for when doing so?

inlovewithchemistry

How would you go about ranking which strong acid is stronger or which strong base is stronger? For example, how would you compare HI and HClO4 or Ca(OH)2 and KOH?

inlovewithchemistry

I think concerning bond angles, you are better off memorizing them specific to their shape.

inlovewithchemistry

When you have a radical, how do you know where to place the one extra electron? Is it just in the place that would ensure the most stability about the central atom?

inlovewithchemistry

I thought that two p orbitals could hybridize with a pi bond.

inlovewithchemistry

What is the biological importance of hybridization? When and where is it most likely to occur?

inlovewithchemistry

I have found that googling "VSEPR Chart" brings up great charts that you can help use to memorize these bond angles. Some can be inferred, but many, in my opinion, should just be memorized.

inlovewithchemistry

It is important to understand, though, that while the names are interchangeable, there are bent shapes for structures with three and four areas of electro density. Follow the pictured bond angles when recognizing the difference.

inlovewithchemistry

Here is the correct lewis structure for HClO.

inlovewithchemistry

I find it helpful to separate their definitions. I think that a cation has a plus sign, so it's fitting that polarizing power has one more word than polarizability. Polarizability is therefore associated with anions, and polarizing power with cations.

inlovewithchemistry

Can someone explain the difference between polarizing power and polarizability?

inlovewithchemistry

We learned about the wedge and dash model in discussion today. The wedge represents the idea that the atom is coming out at you, and the dashes represent the atom falling behind the structure. This model is just a way to interpret the shape in your head.

inlovewithchemistry

My TA told us to be familiar with linear, trigonal planar, angular (bent), tetrahedral, trigonal pyramidal, trigonal bi-pyramidal, seesaw, T-shaped, octahedral, square planar, and square pyramidal. You need to also know bond the different bond angles for each of these and understand the fact that st...

inlovewithchemistry

I've found that when I draw out structures, even if I have all of the valence electrons represented and correct, I will still get the structure wrong. I know this is because I need to make my structure have a formal charge close to 0. But, how can I be sure that it is the most stable it can be? How ...

inlovewithchemistry

My TA tried to explain to us today about the difference, but it was hard to understand with the given definitions. Can someone explain the difference better and give an example comparing two elements?

inlovewithchemistry

An important thing to remember about resonance structures, along with the above definitions, is that all of the bonds in the Lewis Structure have the same length. This displays that drawing resonance is just a way of showing that all of the bonds have the same length no matter where they are placed.

inlovewithchemistry

I think that this is the most efficient way and only way to be completely sure of stability.

inlovewithchemistry

How important is it to put, for example, 3d10 before 4s1? Does order matter even though you are conveying the same information? Are there any exceptions? Thanks!

inlovewithchemistry

Hund's Rule is important to remember in answering this: every orbital must be filled in order for any of them to be doubly occupied. If you ever see two electrons in one orbital, two in the second and none in the third, or a diagram where one arrow is pointing up, one down, and then one up (in case ...

inlovewithchemistry

I always have literally typed 3E8 in my calculator and have never had a problem with it. Also, if you have a TI 36 calculator, there is a constants section that has the full number in there, so I use that a lot too.

inlovewithchemistry

Can someone explain the difference between constructive and destructive waves and why they are important in determining the properties of an electron? How are they unique?
Thank you!

inlovewithchemistry

Does anyone have a helpful list of equations that pertain to this unit? I've been trying to compile one, but lose track of units and constants. If anyone could post a complete list (with labeled constants), that would be very helpful!
Thank you!

inlovewithchemistry

Today in class we discussed an "incorrect atomic model" situation worded like this: AN electron is located inside the nucleus of an atom. For H-atoms, the electron is confined to its nuclear diameter, 1.7*10^-15 m. The process to get to the answer, which was 3.4*10^10 m/s, was very confusi...

inlovewithchemistry

I've found that it depends on both the question and the units that were given in the question. Whether your answer is in liters or mL doesn't matter as long as it isn't specified in the question. I like to stick to liters, as the units for molarity are mol/L.

inlovewithchemistry

Anjali_Kumar3E wrote:In the formula E=hv what does the letter v respresent? I know E is energy and h is a given number which is the constant but what is v.

V represents velocity of the particle.

inlovewithchemistry

V represents the velocity of the object.

inlovewithchemistry

I think workforce may be a term he used in class in reference to physics as part of an example? I could be wrong.

inlovewithchemistry

How do you tell if an object has wavelike properties? Is it solely based on the answer?

inlovewithchemistry

When balancing, where does everyone start? Does everyone always balance the one that occurs the least first? I was wondering if there are any other methods that people use because I have had trouble with balancing equations for a while. Thanks!

inlovewithchemistry

In high school, we learned to remember them with a phrase pronounced "Br-inkl-hoff," which is Br(bromine), I(iodine), N (nitrogen), Cl(chlorine), H(hydrogen), O(oxygen), and F(fluorine). Helped me a lot back then and now.

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