CHEMISTRY COMMUNITY

mbaker4E

To be on the safe side, you should always use Pt(s) when you are unsure, unless Hg is present in the first place.

mbaker4E

If you need to find frequency factor of collisions (A) and you are given activation energy (Ea) you would use the Arrhenius equation.

mbaker4E

The anode is the one being oxidized, and the cathode is the one being reduced (an ox, red cat).

mbaker4E

Since platinum is inert, it will not interfere with the overall redox reaction. Therefore it can be used in the place of a solid metal, transferring electrons from an aqueous solution to the cathode.

mbaker4E

Thank you Lyndon!!

mbaker4E

K and Kc can be the same thing, but Kc refers specifically to concentration while Kp refers to partial pressures.

mbaker4E

You should probably get your posts in before the final.

mbaker4E

I think Lavelle always has at least one question per larger section on his syllabus.

mbaker4E

Yes, because water is present in all aqueous solutions is it implied that it is already present.

mbaker4E

Yes, you should definitely know how to use all the half-life equations because they are different for every order and can sometimes be useful in finding k.

mbaker4E

You would add Pt(s) if there are no solids present on either the anode or cathode side.

mbaker4E

I definitely recommend attending step-up sessions if you are completely lost and don't know where to start and need some momentum. Workshops are really good if you already have a basic handle on everything.

mbaker4E

The x axis is time, usually in seconds but it can also be in minutes, days, etc.

mbaker4E

Correct, because if there are aqueous solutions already present it implies that water is present as well.

mbaker4E

Yes, because more energy is necessary in order for the reaction to move forward.

mbaker4E

If you are referring to Pt(s) or C(graphite), those elements are added to the cell diagram if there is no solid present in the original equation. This is because if you refer to the visual representation of the cell diagram, the anode and cathode require a solid metal to transfer electrons from one ...

mbaker4E

Yes, I am pretty sure he will provide a redox table if necessaary.

mbaker4E

I believe E˚refers to standard conditions and E refers to nonstandard conditions.

mbaker4E

I believe the test covers Gibbs Free Energy and Electrochemistry up until and not including the Nernst equation.

mbaker4E

When work is done on a system, or by the environment, energy is added to the system and is thus positive. when work is being done by the system, energy is being used by the system and is thus negative.

mbaker4E

the question should always tell you if the system is at constant volume or constant pressure, in which you would use Cv and Cp, respectively.

mbaker4E

If a reaction is endothermic, increasing temperature will favor the products while decreasing will favor the reactants. Conversely, if a reaction is exothermic, an increase in temperature will favor the reactants and a decrease in temperature will favor the products.

mbaker4E

Specific heat capacity is the heat requires to raise 1 gram of a substance by 1 degree Celsius/Kelvin, whereas molar heat capacity is the heat required to raise 1 mole of substance by 1 degree Celsius/Kelvin. Look and see if the problem gives you grams or moles, and go from there.

mbaker4E

A bomb calorimeter measures heat flow at a constant volume, as you can imagine a bomb as a rigid chamber that cannot increase in volume. A polystyrene cup calorimeter on the other hand measured changes in temperature at a constant pressure.

mbaker4E

When the work of the system on the atmosphere is positive, that means work is done by the system, and so the equation would look like delta U = Q - W. When the work of the atmosphere or environment on the system is positive, it means work is being done on the system, which would correlate with the e...

mbaker4E

Heat refers to the transfer of energy between molecules which is why heat is measured in Joules, whereas temperature merely refers to the random motion of molecules.

mbaker4E

The surroundings consists of everything outside of the system.

mbaker4E

When dealing with closed systems, you are able to assume that the number of moles remains constant. This will in most cases allow for certain equations to be utilized (such as PV= nRT and certain calorimetry problrems) in order to solve for other components of the equations. Additionally, it is much...

mbaker4E

You would only need to use an ICE table if you are specifically asked to get from initial concentrations to equilibrium concentrations or vise versa. Usually you can go through a problem and if you think you need ICE table then you can try it out but if you don't have enough information for it or it...

mbaker4E

Yes, they both use change in concentration over initial concentration times 100%

mbaker4E

These are some general strong acids/bases I memorized:
Strong Acids - HCl, HBr, HI, HNO3, HClO3, HClO4, H2SO4
Strong Bases - LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Ba(OH)2, Sr(OH)2

mbaker4E

I think as long as you turn in work from either section you will be fine, such we are still going over both in lecture.

mbaker4E

No, water cannot be aqueous since an aqueous solution is dissolved in water. That is why it is referred to as liquid.

mbaker4E

If you look at the equation pV = nRT changing either temperature or inert gas (if volume remains constant) will change pressure.

mbaker4E

If the problem has to do with concentration (Mol/L) Qc will be used. If the problem has to do with pressure or gas-state molecules, Qp will be used.

mbaker4E

You only use subscript for P when you are representing partial pressure, which will only be used in chemical equilibrium problems with gas state molecules.

mbaker4E

There is no difference in the way we calculate Q and K, the difference is that Q is associated with initial values and K is associated with equilibrium values.

mbaker4E

What are the differences in using K, Kc and Kp? Are K and Kc interchangeable?

mbaker4E

If you have an acid, its conjugate base would be the result of losing a H+, and if you have a base, its conjugate acid would be the result of gaining an H+.

mbaker4E

I think the parenthesis are just to separate the two ligands.

mbaker4E

The coordination number would be 6 because a single edta compound forms 6 bonds to the Fe atom, as it is hexadentate, and the number of bonds that are formed to the central atom make up the coordination number. Similarly, the bidentate compound en can form two bonds with a central atom.

mbaker4E

1 has the largest dipole moment because since the chlorines are positioned close to one side of the molecule, that side of the molecule will have a polarized charge in comparison to the other side with no chlorines. 3 has the smallest dipole moment because since the molecule is symmetrical, any char...

mbaker4E

All molecules have LDFs because an LDF is just a weak, short-range electrostatic force between uncharged molecules, arising from the interaction of transient electric dipole moments. Any molecule, for example a nonpolar covalent molecule with normally no charge, can have its electrons positioned in ...

mbaker4E

Usually, if a molecule is asymmetrical or has lone pairs of electrons then it will be polar. If two polar molecules come together, they can form a dipole-dipole interaction from the partially positive side of the molecule attracting a partially negative side of another polar molecule.

mbaker4E

When first learning VSEPR shapes I would recommend googling "VSEPR Geometry" in images and going off of that table until you memorize the shapes because it it very easy to follow. Steric number refers to how many bonds (single, double, or triple) AND electron pairs surround the shape.

mbaker4E

My TA specified that only one-dimensional Lewis structure diagrams will be necessary for 14A, and shape should be known but does not need to be drawn out.

mbaker4E

I don't think any discussions are cancelled except for those on the official days off (thursday and friday)

mbaker4E

You can tell significant 0's by whether or not they contribute to the number's specificity. For example, 0.0850 is more specific than 0.085 because the latter is rounded, but 0.0085 is not a more specific version of 0.0850, it is just an entirely different number.

mbaker4E

When asked to draw resonance, you should always draw all possible structures and then a combination of all those structures as the hybridization of those structures.

mbaker4E

The molecule will most likely be polar if there are different atoms around the central atom. A molecule will most likely be nonpolar if the molecule is symmetrical and has the same atoms around the central atom.

mbaker4E

If he does curve it, it will only help your grade. I don't think this class will be curved by much though.

mbaker4E

What is more important when drawing a Lewis Diagram of the lowest energy - the octet rule or formal charge?

mbaker4E

How do you know if an element is an exception to the octet rule?

mbaker4E

An easy way to tell if a neutral molecule is a radical is to count up the number of valence electrons in each atom and add them together - if your number is odd then it is most likely a radical.

mbaker4E

P in the center and 3 Ks branching out connected by single bonds, with a lone pair of electrons also attached to P. Every element is "happy" because K only has 1 valence electron and P has 5 valence electrons.

mbaker4E

Oxygen is more electronegative than nitrogen, thus nitrogen is the LEAST electronegative of the two and should be in the center.

mbaker4E

You can definitely place the negative charge on the central atom, just make sure to change the charge of the entire molecule as a whole as well.

mbaker4E

Electronegativity is how well an atom can attract electrons towards itself while electron affinity is the amount of energy released when an electron is added to an atom.

mbaker4E

Why do certain elements tend to have certain ions like Cu ---> Cu+ and Cu2+? but not Cu3+?

mbaker4E

Atomis radius increases down and to the left, and since they are all in the same Period you would check for which is closest the the right hand side to find the smallest.

mbaker4E

Spin up is +1/2 and spin down is -1/2.

mbaker4E

Electrons are always removed from the outermost shell because those are the electrons with the highest energy and are therefore the most unstable. 5s has more energy than 4d and therefore when Ru is ionized electrons are taken from the 5s orbital first.

mbaker4E

I'm pretty sure leaving it as Joules would be considered correct units.

mbaker4E

Wavelengths in the ultraviolet band are always in the Lyman series and wavelengths in either the visible light spectrum or the solar spectrum are in the Balmer series.

mbaker4E

Since light always travels at the speed of constant c, light is never at rest and therefore has zero rest mass. This is why photons have no rest mass and De Broglie's equation cannot be used.

mbaker4E

Why is it that as the temperature of a black body increases, the wavelength at which the max intensity is found decreases?

mbaker4E

When limestone, which is principally CaCO3, is heated, carbon dioxide and quicklime, CaO, are produced by the reaction CaCO3(s) --> CaO(s) + CO2(g). If 17.5g of CO2 is produced from the thermal decomposition of 42.73g of CaCO3, what is the percentage yield of the reaction? How would you go about fin...

mbaker4E

Should you ever round molar mass from the periodic table based on sig figs or should you always use the given number without rounding?

mbaker4E

When figuring out sig figs do you include the sig figs of the molar mass of an atom?

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