CHEMISTRY COMMUNITY

McKenna_4A

If the temperature increases, that means that T2 will be larger. You've essentially answered your own question, because if T2 is larger, the right side ispositive, meaning the left must be positive as well. For this to occur, the value inside ln must be greater than 0. Therefore k2 must be larger th...

McKenna_4A

It would be linear, confirming that it is a 2nd order rxn.

McKenna_4A

Why isn't NO3 included in the overall equation for O2 ---> ozone if it is used as a reactant?

McKenna_4A

will the presence of a catalyst effect the equilibrium constant, K?

McKenna_4A

Plot the initial concentrations as 1/c, ln(c), and just c. Whichever one gives a linear plot is the correct order.

McKenna_4A

Would adding a catalyst to a reaction change the value of K?

McKenna_4A

What is implied when we say that an integrated rate law depends on time? Could the differential not be written as a function of time?

McKenna_4A

not related, just same notation

McKenna_4A

Reaction of chlorine in water:
Cl2(g) ¡ HClO(aq) 1 Cl2(g)

How do I balance this?

McKenna_4A

All of thermo that wasn't covered on the midterm and ll of electrochemistry

McKenna_4A

When being asked what Reactant is Oxidized/Reduced, Do we consider the whole molecule or just the atom?

McKenna_4A

Could someone give be an actual definition of reaction order?

McKenna_4A

How much of thermodynamics will be on test 2?

McKenna_4A

Kinetics will not be on test 2

McKenna_4A

Not a joke but it belongs here: What's the name of the absolute banger of a song Lavelle threw on after lecture today?

McKenna_4A

If electron flow is spontaneous, what will the sign of E be?

McKenna_4A

Salt bridges are more of a conceptual thing. I doubt we'll be asked to do any calculations regarding them.

McKenna_4A

Could someone explain the difference between E and E(standard)?

McKenna_4A

Simply look up the value of R for the units being used

McKenna_4A

The Platinum electrode isn't reduced or oxidized, It is simply used as a pathway for the electrons to enter solution (and reduce FE3+, with respect to the example in class.

McKenna_4A

An atom of U can be oriented in one state, but in the USA, U can be 4 states at once.

McKenna_4A

Yes. The path required to get to a value doesn't matter with G, so it is a state property. This is why you can perform a Hess's Law-type problem with an equation given G values.

McKenna_4A

Because O2 is the most stable for of oxygen, so it forms without an input of energy.

McKenna_4A

Yes, use partial pressures in an ICE table and use them for the K expression afterwards.

McKenna_4A

I believe this has to do with molecular shape/structure. Don't worry about it for the midterm, you will be given molar heat capacities.

McKenna_4A

Use (Delta)S = nR(V2/V1)

McKenna_4A

Could someone explain wha reversible and irreversible mean?

McKenna_4A

will we be asked to calculate degeneracy on the midterm?

McKenna_4A

why is the change in entropy sometimes equal to (-deltaH/T)? in other words, what does the - imply?

McKenna_4A

why is molar heat capacity sometimes given as a specific value for a compound but sometimes (3/5)R or (3/2)R??

McKenna_4A

is a bomb calorimeter constant V or P??

McKenna_4A

Wouldn't using -P mean the system lost energy? Lavelle said this in lecture today but the solutions manual says that the system has work done on it.

McKenna_4A

Because graphite is the lowest energy arrangement of pure carbon molecules

McKenna_4A

Forming a bond is a favorable/lower energy state for atoms to be in, so that energy is released. Consider the chart we looked at in 14A-- two atoms decreased in their energies as they became closer, the lowest energy being when they formed a bond; however, when they got any closer, the energy skyroc...

McKenna_4A

I started doing homework in the thermo section and was faced with a bunch of problems referring to work, delta U, and heat capacity problems that didn't use moles or grams. We haven't gone over any of this in class, so should I read the textbook to understand this or will we be talking about it this...

McKenna_4A

Simply use q=g(Csp)T for both copper and water and add the two values together. This will give you total heat.

McKenna_4A

Because each bond enthalpy AVERAGES can be found on a table. The bond enthalpy of a specific bond depends on the molecule it is in (electrons may be shared unequally). Therefore, using average bond enthalpies will provide an inaccurate value.

McKenna_4A

I’ve often heard the terms “endergonic” and “exergonic” instead of exothermic and endothermic. Is there a difference?

McKenna_4A

Which factors can actually change K in a reaction? I'm fairly sure temperature will, however I'm getting mixed messages about pressure having an effect as well.

McKenna_4A

Usually the problem will ask for final partial pressures or concentrations, so it depends on the context. However using either one works as long as you are consistent with Kc vs. Kp

McKenna_4A

We only learned to calculate the pH of buffer solutions and didn't go into how they actually resist changes in pH. I don't think its part of the 14B curriculum and certainly wouldn't worry about it for the upcoming test.

McKenna_4A

Usually if a question asks for pressure as an answer, I will specify which units to use. However if it does not, make sure your gas constant (R) corresponds to the correct units (which are given to us during tests on the equation sheet).

McKenna_4A

I'd recommend going through all the homework problems s on the syllabus, as the test will be very similar. You don't necessarily have to work them all out, but reading through the questions and corresponding solutions will help you locate any knowledge gaps.

McKenna_4A

This is a good point, but when dealing with equilibrium concentrations, assume the other reactants/products are in excess

McKenna_4A

Q is a ratio, therefore it doesn't have units, just like K.

McKenna_4A

Yes, however it is very uncommon

McKenna_4A

One is measuring based on concentration and the other by pressure. They both represent the same thing because they are simply a ration between chemical compounds, not values with units.

McKenna_4A

Increasing the total pressure of the system will cause equilibrium to shift to the side with fewer moles

McKenna_4A

Activity is equal to 1 in order to not change any values

McKenna_4A

K is a ration, so all units cancel

McKenna_4A

Convert all the pressures from the start

McKenna_4A

Why exactly aren't solids and liquids included in equilibrium expressions?

McKenna_4A

Will we still be using the 7th edition in 14b?

McKenna_4A

aqua refers to water being within the coordination sphere and actually covalent bonded to the central atom. Hydrated refers to water molecules being attracted to the ion.

McKenna_4A

I think this problem wanted you to refer to a table of K values, because they're two very different compounds. So base your answer off that.

McKenna_4A

Understand the process. Aka, why certain solutions of equal acidic/basic properties can still have a pH not equal to 7. Also what Ka/Kb values represent, and how they decrease as protons are removed from polyphonic acids.

McKenna_4A

We'd be given Kb or Ka values. the "p" just tells us to take the -log of the Ka/Kb. As far as actually calculating them, I don't think so (unless we're given the concentrations of A, H, and AH, in which case its simple algebra).

McKenna_4A

Yes. Boron often draws an electron pair when it already has 3 bonds. Also, the 3 Fs are very electronegative and will delocalize this negative charge. Because it's accepting a lone pair, it's a Lewis Acid.

McKenna_4A

Should we memorize the specific compounds Dr. Lavelle mentioned in class and their functions?

McKenna_4A

I understand how Oxides like CO2 and SO2 react with water to for acids, so would we consider CO2/SO2 an acid in a reaction that creates the acid?
i.e. H20 + CO2 = H2CO3.... is CO2 an acid?

McKenna_4A

Still consider the electron as a region of electron density, but understand the shape will be somewhat different. A single electron will not exert as much force on surrounding atoms as a lone pair. For example, NO2+ has a bent shape with an O-N-O bond angle of greater than 120 as opposed to less than.

McKenna_4A

Polydentate refers to a ligand forming multiple bonds with the central atom. If a Ligand has multiple sites that can bond (Polar regions, lone pairs etc..) it is said to be polydentate

McKenna_4A

if it is (OH)2 then hydroxyl. (OH2) would be hydro

McKenna_4A

For the test this week, should we know the VSEPR shapes mentioned in the textbook but not class (ie. AX2E, T-shaped, Square pyramidal)

McKenna_4A

aren't ion-ion IM forces and ionic bonds essentially the same thing?

McKenna_4A

Are dipole-induced dipole forces always between separate compounds (one polar and one non-polar)?

McKenna_4A

If we are asked to identify the types of molecular forces compounds may exert on each other and the compound has Hydrogen bonds, should we also say Dipole-Dipole (Because an h-bond is a strong dipole-dipole interaction)?

McKenna_4A

Do all compounds have London Forces no matter what?

McKenna_4A

Yes- think of Hydrogen bonds as especially strong dipole-dipole interactions

McKenna_4A

Yes indeed. The shape of a molecule can determine the strength of intermolecular forces between compounds.

McKenna_4A

Yes- most likely Friday

McKenna_4A

When all 4 atoms coming off the center atom aren't the same. Ex.) CH4 vs CH3Cl.

McKenna_4A

A different definition from Lavelle's I used in High school- A Van Der Wall Interaction (London Forces) results from instantaneous (shot lasting) dipoles created by the random movement of electrons in atoms or molecules. The larger an atom or molecule, the more electrons, so the more likely for inst...

McKenna_4A

I can't log into Dr. Lavelle's website. I enter my password and it just loads for a second and nothing happens. I don't get any "wrong password" notification or anything. Anybody else having this problem/have a solution?

McKenna_4A

or 2D) 3 and 5, should we be using the periodic trend to determine electronegativity difference or the given chart? I understand the trend, but there it doesn't always work when comparing atoms close together on the table (the trend isn't perfect).

McKenna_4A

Is it important to understand all the experiments we discussed in the quantum unit?

McKenna_4A

Ionic bonds involve an anion "giving away" an electron to an anion. So each has an octet and an equal/opposite charge.

McKenna_4A

It couldn't hurt to memorize a few common radicals (i.e. the ones we talked about in lecture).

McKenna_4A

When drawing Lewis Structures, should we try and make the central atom have a formal charge of zero almost always (Ions, covalent bonds, etc...)?

McKenna_4A

The presence of unpaired electrons on atoms within a compound result in them repelling from other because of the negative charges working on each other. Consider F2, where each F atom has 6 unpaired electrons. They exert repulsive forces on one another because of the unpaired electrons in their vale...

McKenna_4A

Will we be given an equation sheet for the midterm?

McKenna_4A

Will there be another review session for the fundamentals unit?

McKenna_4A

This is more quantum, but when do we include the d-orbital elements in the valence shell when a question asks how many valence e- a certain element had? I was under the impression you just counted atoms in the largest shell (so only s and p).

McKenna_4A

is it more important for an atom to have a low formal charge or an octet?

McKenna_4A

Atoms will arrange in the structure that corresponds to low energy, so atoms will try and space out to avoid repulsive positive forces

McKenna_4A

Can't access the syllabus foe some reason. When is our midterm for 14A?

McKenna_4A

Also remember that this bond isn't actually "rotating" around the atom. Lots of chem textbooks make it out to be like this. Just remember that the bond lengths will be an average.

McKenna_4A

You won't ever be asked to calculate the actual value of atomic radii. Just know the trends.

McKenna_4A

Yes, lager elements have larger ionic radii, meaning less interference from the positivity charged nucleus. Even noble gasses, like Xenon, can form up to 6 bonds.

McKenna_4A

Generally yes. Just remember that ionic bonds result in "giving away" or "reviewing" electrons and covalent bonds result in sharing electrons

McKenna_4A

If it is of the same atom, an anion will have more electrons that a cation, therefore its ionic radius will be larger. So yes

McKenna_4A

If we are given a cation ion in the d-block, should we remove electrons from the d orbital first or the outermost s-orbital?

McKenna_4A

Either you will be told the work function for a specific metal, or you'll be able to calculate it based on the energy values provided. No need to memorize any.

McKenna_4A

Shrodinger's equation is a model for the wave function of an electron. We simply look at it conceptually to understand what orbitals are. Don't worry about any calculations with this equation.

McKenna_4A

use m^-1

McKenna_4A

Δx = change in position

McKenna_4A

Psi is the height of a wave at any position on a 3D plane (x,y,z). Psi^2 represents the probability of finding an electron at any point (x,y,z). It's a pretty confusing concept that isn't really analyzed further until more advanced chem classes. Don't stress on it to much.

McKenna_4A

Should we memorize the EM Spectrum (wavelengths and their corresponding types of radiation) or will it be provided on exams?

McKenna_4A

You'll just have to pay attention to the font, because frequency is the greek letter "nu."

McKenna_4A

Wavelengths of light exhibit specific energy levels that match up with the energy of an electron. Electrons have energy due to their motion. Electrons don't fall into the nucleus because they are moving (this is more physics). The same reason why the earth doesn't fall into the sun.

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