CHEMISTRY COMMUNITY

Nancy Dinh 2J

15.61 states: "The rate constant of the rst-order reaction 2 N2O(g) + S --> 2 N2(g) + O2(g) is 0.76 s 1 at 1000. K and 0.87 s 1 at 1030. K. Recall that the rate constant changes with different temperatures. We are still doing the same reaction, but simply at different temperatures with differen...

Nancy Dinh 2J

The equations are basically a mathematical definition of A (collision frequency) and a more complex version of ln(k)=\frac{E_{a}}{RT} + ln(A) . I am 99% that you only be using the this equation and not the one that they give you in section 15.12. As for what you should know from the ...

Nancy Dinh 2J

First you're finding the balanced equation. After that, look at the number of different reactants of the balanced equation. This will determine the molecularity. 1 reactant is unimolecular, 2 is bimolecular, 3 termolecular. Finally, you draw the activated complex, which will form at the top of the a...

Nancy Dinh 2J

Of course, it is very possible for the forward and reverse reactions to follow different pathways, especially since the reverse reaction will face a higher energy barrier and possibly be an endergonic reaction (assuming that the forward is favorable). In this case, the intermediate could react anyth...

Nancy Dinh 2J

I also find it helpful to redraw the steps using numbers or letters corresponding to each different molecule. It makes it a bit simpler to see than that complicated mess.

Nancy Dinh 2J

If you picture the reaction profile, the transition state is that hump between the products and reactants. Because the transition state is higher on the graph, it indicates that it is higher in energy.

Nancy Dinh 2J

Are there other inert conductors, other than platinum that we should familiarize ourselves with for this class? Not really. Platinum is usually the go-to one, at least for this course. That being said, remember that other solid metals can serve as conductors too, along with the special case of liqu...

Nancy Dinh 2J

In cell diagrams, how do we order the compounds or molecules on one of the sides of the salt bridge. For example, for the anode, are we supposed to order the electrodes in a specific order? Like by alphabetical order of states or by reactants then products? I'm not sure this question made any sense...

Nancy Dinh 2J

The H+ and Cl- are implied in the HCl(aq). They just chose to combine them instead of writing them both out separately.

Nancy Dinh 2J

i think this is referring to the external wire circuit. From what i know, salt bridges don't exist in Electrolytic cells. It mentioned the external wire circuit in the problem so I don't think it's that. The problem wants to know how the "current is carried through the cell itself." What ...

Nancy Dinh 2J

In problem 13, part d, how do we know which side is the cathode and which side is the anode? When you write out your half reactions, write them both with e- added. Then when you look at your given skeleton equation, figure out which half reaction you need to flip in order to get the equation. That ...

Nancy Dinh 2J

How come for both of the half reactions derived from the cell diagram, you add the electron in both cases? Shouldn't the left side of the cell diagram be an oxidation reaction, in which the species loses an electron instead of gaining an electron? Yes, but they're usually written with the electron ...

Nancy Dinh 2J

14.33 (b): Will Tl+ disproportionate in aqueous solution? The solution manual uses the half equations Tl^{+} + e^{-} \rightarrow Tl and Tl^{+} \rightarrow Tl^{3+} + 2e^{-} . Why can't you use Tl \rightarrow Tl^{3+} + 3e^{-} instead of Tl^{+} \rightarrow Tl^{3+} + 2e^{-} ? Both would get you the equa...

Nancy Dinh 2J

Helen Shi 1J wrote:So the complexity of the molecule overrules positional disorder?

I think so. As far as my memory goes, I've only seen positional disorder come to play when T=0K.

Nancy Dinh 2J

Does standard Gibbs free energy stay the same for the molecule at whatever condition? I thought it changed based on temperature due to the equation delta G standard = delta H standard - T*delta S standard. So when you plug in any temperature, you get a delta G standard based on the temperature. How...

Nancy Dinh 2J

4.184 J/(C*g) is the heat capacity for water when it is in the liquid state. The specific heat capacity of ice functions exactly like the Cp for liquid water only it is for when the water is a solid.

Nancy Dinh 2J

How do you know if you need to break a bond or not? For example in 8.73 you didnt need to break the c-h This is much easier to see if you draw out both the reactants and products. I compare the two structures and see which ones I have to break and form. As for why you didn't need to break the C-H b...

Nancy Dinh 2J

9.25 If SO2F2 adopts a positionally disordered arrangement in its crystal form, what might its residual molar entropy be? I am not sure how to approach this problem. Can someone please explain to me the difference between "positionally disordered arrangement" and "residual entropy&qu...

Nancy Dinh 2J

For this problem, why isn't the free energy of the reaction converting ADP to ATP added in along with reactions 2 and 3? The ATP reaction requires energy, which means that to produce ATP, the reaction needs to be coupled with another reaction that gives off energy. Reactions 2 and 3 both give off f...

Nancy Dinh 2J

For problem 9.13, why is R used instead of heat capacity for the entropy equation regarding temperature change? Heat capacity by definition is the amount of energy required to raise the temperature of a certain amount of substance by 1 kelvin. In the problem however, you're not raising or lowering ...

Nancy Dinh 2J

Adding on to that, for this specific problem the number of states will be the number of orientations. In a, all of the molecules face the same way and therefore have only one possible orientation. In b, you will have four orientations so w = ln(4^# of molecules).

Nancy Dinh 2J

In part a in question 9.1, the solution manual puts a negative sign in front of the rate of heat generation then drops it in the final answer. Is this an error in the manual? I think it might be because the question is asking for only the rate or the magnitude at which the body generates entropy in...

Nancy Dinh 2J

How do you know when to use q=mc(delta)T vs when to use q=nc(delta)T? This all depends on whether you have the specific heat capacity (Csp) or the molar heat capacity (Cm). If you have the specific heat capacity, use q=m*Csp*deltaT. If you have the molar heat capacity, use q=n*Cm*delta T. Note that...

Nancy Dinh 2J

William Lan 2l wrote:If delta P = 0 (constant pressure), why is delta U = q + w? I thought that w = -PdeltaV. If P is 0, there would be no work then right?

In w = -P * delta V, you would plug in the constant pressure for P, not the change in P which would be delta P.

Nancy Dinh 2J

Because ZnCl2 is aqueous, just treat them as Zn2+ and 2Cl-.

Nancy Dinh 2J

One of the equations we are given for work is w=-PexΔV, where external pressure is constant. Will the pressure always be constant or are there instances where the pressure will be different? For that equation to be used, the pressure has to be constant. However, if the pressure is not constant, the...

Nancy Dinh 2J

Why is 982 delta U? Wouldn’t it be 982J- 492J? Aren’t work and delta U the same thing as according to 8.3 c? The internal energy of a system is delta U, so delta U is given at 982 J. The equation is delta U = w + q, where heat is given at +492 J, so 982J - 492J will give you how much work is done. ...

Nancy Dinh 2J

It looks that way. I would memorize the values for the heat capacity at constant volume and add R to that value to get at constant pressure.

Nancy Dinh 2J

Given in this example: A piston confines 0.100 mol Ar(g) in 1.00L at 25 degrees Celsius. a) The gas is allowed to expand through an additional 1.00L against a constant pressure of 1.00 atm. The book says to use Equation 3 (w= -P ex \Delta V ) to part a because it is an "irreversible path"...

Nancy Dinh 2J

Open system - matter in a system are free to interact with the surrounding environment. Ex: Breathing in and out air Closed system - matter in a system is separated from matter in the environment but heat/energy can still be exchanged. Ex: Closed water bottle. Isolated system - neither matter nor en...

Nancy Dinh 2J

When calculating net enthalpy using Method 2 (not Hess's Law), are the bonds of the reactants always broken and the bonds of the products always formed? Or can the bonds of the products be broken and the bonds of the reactants be formed? If you're breaking bonds in the products and forming bonds in...

Nancy Dinh 2J

You could also think about it in terms of the intermolecular bonds. In the gas phase, the molecules are too far apart to have any effect on each other but in the liquid phase, the molecules form intermolecular bonds that more or less hold the molecules together, thereby "fusing" them in a ...

Nancy Dinh 2J

I think the crux of the problem here is that you are assuming that the added electron doesn't pair with the lone electron on B. The reason why most atoms tend to want 4 bonds is so it can fulfill its octet, but remember, boron is one of those weird ones that do not need their octets filled. Instead,...

Nancy Dinh 2J

Also, all Bronsted acids are Lewis acids and all Bronsted bases are Lewis acids. The Bronste acids and bases are just a special case of Lewis acids and bases.

Nancy Dinh 2J

You will still keep them in alphabetical order for the formula.

Nancy Dinh 2J

Why do you raise each species in the equilibrium constant to its coefficient because when doing an ICE table you already add/subtract the change by the coefficient times x? For example, for 3H2 + N2 --> 2NH3, why do you raise the coefficent to each species after you already subtract or add by -3x o...

Nancy Dinh 2J

No because they're the same molecule, water. The only difference is that OH2 emphasizes that it is O that does the bonding.

Nancy Dinh 2J

When Q > K, that means that you start with the product first, and then the reaction will start to occur to create more reactants. However, the reaction will never create more reactants than is required for the equilibrium. That's what Dr. Lavelle meant by "not overshooting the equilibrium"...

Nancy Dinh 2J

Why do we say bonds are less than 109 degrees or less than 120 degrees? I don't understand why it is "less than" Lone pairs exert more repelling force against bonded pairs than do bonded against bonded. So if we know that a molecule is usually 120 degrees with all three electron densities...

Nancy Dinh 2J

They are just like when you are figuring out the shape of the molecules, only you don't exactly call them "tetrahedrons" or "trigonal planners" and such. Instead, you say that the orbitals are oriented towards the corners of [insert shape] (with the exception of the linear shape,...

Nancy Dinh 2J

Also, sigma bonds are formed by hybridized orbitals overlapping. Unhybridized orbitals formal pi bonds.

Nancy Dinh 2J

A - Means atom. You will always have this. X - Number of bonded pairs to the central atom. You will have at least on X in order for there to be a molecule. E - Number of lone pairs on the central atom. It is possible to not have any lone pairs, so you will simply omit E if needed. The number of bond...

Nancy Dinh 2J

Starting with the base model where both bonds and lone pairs are included, you place the lone pairs where it will affect the least number of bonded pairs at the lowest angle. For example, let's say you first have a trigonal bipyramidal model and are trying where to place the lone pairs. You would pl...

Nancy Dinh 2J

In addition to Be and B like you mentioned, I wanted to note that H and He also never follow the octet rule because they are more than happy only filling the 1s orbitals, which is the only type of orbitals the n=1 energy level.

Nancy Dinh 2J

I think it might have something to do with there being only 1 electron in the p orbital. The elements in Group 13 are more likely to give up electrons to empty the 1 electron in the p orbitals and then 2 in the s orbitals than to gain 5 electrons to fill p.

Nancy Dinh 2J

I think it was because O is more electronegative than C, and therefore H is more attracted to O than to C. Also, if H were to bond with one of the C, then that C atom cannot form any double bonds with O. When you try to calculate the formal charges, you'll see that this molecule will yield a net cha...

Nancy Dinh 2J

can anybody explain why according to the solutions manual, in question 3.5 the ground-state electron configuration from Ga^3+ is [Ar]3d^10 instead of [Ar]3d^8 4s^2, and also why the ground-state configuration for Tl^3+ is [Xe]4f^14 5d^10 instead of [Xe]4f^14 5d^8 6s^2? The ground state for the neut...

Nancy Dinh 2J

The hydrogen atom has a radius of approximately 0.05 nm. Assume that we know the position of an electron to an accuracy of 1 % of the hydrogen radius, calculate the uncertainty in the speed of the electron using the Heisenberg uncertainty principle. Comment on your value obtained. How would we dete...

Nancy Dinh 2J

The d-block actually belongs to the shell above, but because the energy difference between each principal level gets smaller and smaller as n increases, the electrons start to fill in the ns orbitals before they start filling in the (n-1)d orbitals. (I like to think of it as the electrons getting co...

Nancy Dinh 2J

Yup! :)

Nancy Dinh 2J

NH4+ and SO4- are held together by ionic bonds. The Lewis dot diagrams represent covalent bonding so you can't use it to represent the entire ionic compound.

Nancy Dinh 2J

You don't have to, but I usually do it anyway so I can keep track of how many unpaired valence electrons I have and how many I need.

Nancy Dinh 2J

To add on to that, by definition core electrons do not include any valence electrons. The noble gases have all of their orbits filled in their highest principle quantum level and therefore contain only core electrons. These electrons are almost guaranteed to be stable and nonreactive, so you don't h...

Nancy Dinh 2J

Can you clarify the difference between shells and subshells? Shells correspond to the principle quantum number (n). Within these shells are the different types of subshells (s, p, d, f), which are the angular momentum quantum number (l). So for example, the orbitals 2s and 2p are within the same sh...

Nancy Dinh 2J

Yes, the greater the intensity, the more photons you'll have. Since theoretically, each photon ejects one electron given that it has enough energy, the number of electrons ejected will increase too. This is based on the assumption that the photon already has enough energy to eject an electron. If th...

Nancy Dinh 2J

21. According to the wave model, a greater intensity would result in more energy, but this still did not eject the electrons. This was surprising because it meant stripping the wave model and viewing the rays as photons, which requires you to increase the frequency/decrease the wavelength to increas...

Nancy Dinh 2J

You won't get a negative value because the value for n_{1} (initial) is always going to be lower than n_{2} (final). When you put those values under a fraction, the previously larger value will become the smaller one, and vice versa. Let's use your example of 1 and 5: v=R(\frac{1}{n_{1}^{2}}-\fr...

Nancy Dinh 2J

I can't see a correct answer either. Maybe the book is trying to pull one over us, and there is none???

Nancy Dinh 2J

I understand the inverse relationship between the wavelength and frequency, $c=\lambda v$ , and I know that amplitude apparently does not affect this relationship. But why? Wouldn't the amplitude also affect the frequency because of the extra distance traveling up and down the wave with a fixed speed?

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