CHEMISTRY COMMUNITY

Milena Aragon 2B

Melissa Villanueva1K wrote:Will there be a clear indication of 'k' and 'K' on the final? Such as bolding one over the other. Thanks.

I think in order to avoid confusion, it may be written out for us along with the variable e.g. "the rate constant, k,..."

Milena Aragon 2B

Will there ever be a case where using K to remove an intermediate in the rate law will introduce another intermediate and if there is, do we just have to use another elementary reaction to try and get rid of that additional intermediate?

Milena Aragon 2B

A higher activation energy means that the reaction requires a higher temperature to move in the forward direction and since this is the case you can conclude that the reaction is endothermic (since it is using the heat from the temp. to move the reaction forward). From this you know that the reverse...

Milena Aragon 2B

We briefly covered the difference between Homogeneous and Heterogenous Catalysts in lecture so I was wondering how much we would need to know about these concepts and if we should expect problems that relate to this on the final (& if so what kind)? Thank you.

Milena Aragon 2B

bonnie_schmitz_1F wrote:
004932366 wrote:At constant pressure with no nonexpansion work, delta H is equal to q.

So at constant pressure and constant volume?

At constant pressure but not necessarily constant volume.

Milena Aragon 2B

Ashley P 4I wrote:Because it is a state function, it means that you can add/subtract two different delta H’s correct?

Yes, if you're asked to find the total enthalpy change you can add/subtract enthalpy values from multiple reactions

Milena Aragon 2B

If this is the case it means that the reactant participates in the reverse reaction and thus why the rate for the forward reaction decreases when you add more of your reactant.

Milena Aragon 2B

A good way to determine the order is by using: A^n=B where A is the change that the reactant went through (e.g. doubled), n is the order, and B is how the rate changed (e.g. if it went from 4mol/Ls to 2mol/Ls, B is 2 since 4/2=2).

Milena Aragon 2B

Since the rate of a reaction is affected by the concentrations of reactants, the rate law basically just uses the reactant concentrations to determine the rate of the reaction.

Milena Aragon 2B

The unique rate actually makes it so that you can refer to the rate without having to indicate the species it's referring to since it is the same throughout the reaction (this is because the coefficient was divided from it and all you're left with is the rate for 1 mol of that reaction).

Milena Aragon 2B

When both enthalpy and entropy are negative, the temperature has to be relatively low for Gibbs to be spontaneous (i.e. negative). When both enthalpy and entropy are positive, the temperature has to be relatively high for Gibbs to be spontaneous. If you look at the equation and plug in positive or n...

Milena Aragon 2B

The only circumstance in which delta G cannot be negative(for the forward rxn) regardless of temp. is if delta H is positive and delta S is negative.

Milena Aragon 2B

I have a hard time determining what the system is in a reaction. Is there a way of easily identifying what it is or do we have to memorize that for certain examples one is the system and thus the other is the surroundings?

Milena Aragon 2B

Will be be tested on any thermo before Gibbs free energy or only Gibbs and electro?

Milena Aragon 2B

I know what the third law is but i'm not sure what types of problems will we encounter where we need to apply the third law in order to solve the problem. Can anyone explain please?

Milena Aragon 2B

Will we be told if a system is adiabatic or do we have to assume based on the information given?

Milena Aragon 2B

I would say just do 273K since that’s what’s done in the textbook and in class.

Milena Aragon 2B

Can someone please explain the concept behind the third law and what kind of problems we may encounter where we would need to use it? Thank you.

Milena Aragon 2B

It is the energy required to perform an action.

Milena Aragon 2B

Will the reverse reaction always be doing more work than the forward reaction? I think that what they are discussing is a reversible reaction (where the system isn't at equilibrium and the change will be definite) as opposed to an irreversible reaction (where the system is at equilibrium and change...

Milena Aragon 2B

q is the amount of heat energy released or absorbed by a system and it relates to enthalpy because when q happens at constant pressure, it is the same as enthalpy.

Milena Aragon 2B

Change in U can be negative. It indicates that the internal energy of the system has decreased (either because of the work it did or the fact that it released energy (exothermic) or both).

Milena Aragon 2B

I don't think he'll add modules for other topics as he did not do that for Chem 14A. I would recommend taking the post-module practice exams first and see how you do (since it tells you what you got wrong or right) and go from there (i.e. watch the module if necessary).

Milena Aragon 2B

Yes, the reverse reaction would be exothermic. Remember this so that If you're ever given the enthalpy for the reaction from liquid to vapor for example, you would know to change the sign from + to - and that would be the enthalpy for the reverse reaction.

Milena Aragon 2B

I'm not sure what you mean by move faster than other ions but H3O+ and OH- are related to autoprotolysis because they are the result of the autoprotolysis of water. It basically means that two identical molecules (in this case, water molecules) are able to transfer protons between one another. One a...

Milena Aragon 2B

Endothermic reactions require energy so an increase in temperature will cause the reaction to shift towards the products (The inverse is true for exothermic reactions). Since the reaction is producing more products and consequently less reactants, K will increase as a result of the temperature incre...

Milena Aragon 2B

Hi I'm still a little unclear as to why an inert gas will not effect the equilibrium constant despite increasing the pressure (when the volume is constant), and was wondering if someone could please explain the concept behind that. Thank you.

Milena Aragon 2B

I think it would be zero if the question starts off by mentioning that the amount of reactant that will be used in a chemical reaction to produce some product. Since the reaction is just being carried out, all you're starting with is the initial concentration of the reactant(s), so in the beginning,...

Milena Aragon 2B

I think it might be none of the above because the value of K gives you a sense of where the equilibrium lies for a chemical reaction. If the value is large, it means equilibrium favors the products (since P is in the numerator). If the value is small, it favors the reactants (because the value of R ...

Milena Aragon 2B

There are some problems in the book that mention that the net ionic equation must sometimes be used when determining K and I was wondering when this would be the case.

Milena Aragon 2B

I'm not sure how to approach this problem and was wondering if someone could explain how to solve it, thank you. A sample of ozone,O3, amounting to 0.10mol is placed in a sealed container of volume 1.0L and the reaction 2O3(g)->3O2(g) is allowed to reach equilibrium. Then 0.50mol O3 is placed in a s...

Milena Aragon 2B

Yes, they are the same thing. The difference is just what characteristic of the molecule you are using to define it as an acid or base. A Lewis acid is a molecule that accepts electrons, a Bronsted acid is a molecule that donates a proton. An acid will have both of these characteristics. H2SO4 is a...

Milena Aragon 2B

I was also wondering this as well. Is it actually just the H+ being donated?

Milena Aragon 2B

It's mainly because Butanol has the ability to form hydrogen bonds whereas diethyl ether cannot. This additional bond that butanol can form means it has a higher melting point. Just think of it as more/stronger bonds=harder to break apart and thus higher melting/boiling point.

Milena Aragon 2B

This info can be found in
(7th edition):
Focus 3F.4 and 3F.5
Problems 3F: 1, 3, 5, 11, 13, 15, 19
(6th Edition):
Ch 6.4-6.5
Problems 1, 3, 5, 9, 11, 19, 99

Milena Aragon 2B

Can someone explain what it is that we have to know in order to be able to:
Explain why lone pairs are more likely to found in certain locations around a central atom and
how and why they affect the bond angles in a molecule, cation, or anion.

Milena Aragon 2B

Riley Dean 1D wrote:Does it matter if we put the 2 in front of it on tests? or are both ways counted correct?

I would recommend including the coefficient in the front just to be safe since it tells the grader that you know what period the element is found in.

Milena Aragon 2B

Does it matter where the unpaired electron is placed in a molecule? There was a question (focus 2.61 -7th edition) that asked whether HOCO was a radical and why so I placed the unpaired electron on the oxygen and gave carbon its octet but the solutions manual said that it was a radical because carbo...

Milena Aragon 2B

Since single, double, and triple bonds are all just considered one region of electron density (for the VSEPR model), they do not differ in bond angles; as long as the shape remains the same, so should the angle.

Milena Aragon 2B

If we are asked to determine if there is a dipole moment, will we be given the atoms' electronegativities or will the atoms be typical enough (e.g. F-H) that we can identify the dipole moment without the exact electronegativity value?

Milena Aragon 2B

It would be safe to just draw out the Lewis structure and determine it that way. Just remember that a single bond= 1 sigma, double bond= 1 sigma & 1 pi, triple bond= 1 sigma, 2 pi

Milena Aragon 2B

13d) draw Lewis structure,Molecular shape,... for N2O I was wondering why a structure where N has a double bond with N and O (where the structure has a partial - & + charge on both the Ns) is preferable over a structure where N has a single bond with N, a double with O, & a lone pair (but no...

Milena Aragon 2B

Why is it that hydrogen bonds are the strongest intermolecular bonds?

Milena Aragon 2B

Will we ever be asked to find the bond angles of a molecular structure? And if so, how would we go about doing that?

Milena Aragon 2B

When the atom's electron cloud can be easily distorted (due to the relatively weak pull of the nucleus), it is considered to be highly polarizable. When the atom can cause a large distortion, it is considered to have high polarizing power.

Milena Aragon 2B

Riley Dean 1D wrote:how would one know that O>Cl?

Can someone please explain how oxygen has a higher electronegativity that chlorine when chlorine is a halogen and should want electrons more than oxygen?

Milena Aragon 2B

Molecules in the 3rd period and above can access the d-orbitals (which can accommodate 10 more electrons since there are 5 d-orbitals) since their angular momentums are l=2 or more.

Milena Aragon 2B

"Draw the Lewis structure, including typical contributions to the resonance structure for a)periodate ion (IO4-) the solutions manual said that this molecule had 4 resonance structures because it alternated the positions of the three double bonds. However, I found three other structures (one wi...

Milena Aragon 2B

And to add on to that, the duplet rule just means that the element is looking to fill the 1s orbital since it is the most stable that way. This rule only applies to the first five elements of the periodic table.

Milena Aragon 2B

2A1.a asks for the number of valence electrons in Sb including the d electrons so why is it that the answer is 5 instead of 15 (since the d electrons should be included in the total, according the the way the question is worded)?

Milena Aragon 2B

I'm kind of confused as to how to determine the electron affinity of an atom since it's not a perfect trend like ionization energy, atomic radii, etc. For example= 1F.11c) Which element of the following pair has the higher electron affinity: oxygen or sulfur? I was wondering why the answer is sulfur...

Milena Aragon 2B

We don't actually have to solve any problems with the Schrodinger's equation which is why Lavelle didn't assign any homework problems from the wavefunctions section.

Milena Aragon 2B

If we get asked any questions regarding Schrodinger's equation on the test, I believe they will be purely conceptual since Lavelle didn't cover any examples and said not to worry about its actual application. As long as you understand what the equation represents, you should be fine.

Milena Aragon 2B

You can use De Broglie's equation (wavelength=h/(m)(v)) since it relates wavelength to the momentum of the electron.

Milena Aragon 2B

You also have to make sure that the energy of the photon exceeds that of the threshold energy in order to release an electron.

Milena Aragon 2B

The numeric value of a proton will depend on the frequency of the wavelength since the formula to find the energy of an electron is: E=hv. Since h is a constant (Planck's constant) the value will differ depending on the frequency.

Milena Aragon 2B

Yes, if the photon contains the minimum amount of energy needed (threshold energy) for an electron to be released from the metal, then it will do so.

Milena Aragon 2B

I would use the value that is given on the periodic table that you are referring to. For our tests, we'll be given a periodic table and the answers will be based off of the sig figs on that periodic table. So we just stick to the number of sig figs provided by the periodic table and not the questio...

Milena Aragon 2B

An O atom cannot simply be added because then that would indicate that it was created through the chemical reaction which is not possible since atoms cannot be created or destroyed in a reaction.

Milena Aragon 2B

Should we maintain the amount of sig figs as determined by the periodic table that we're using or should it be determined by the problem (i.e. use the number with the least amount of sig figs)?

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