CHEMISTRY COMMUNITY

pmokh14B

I think the homework problems are the best way to prepare.

pmokh14B

kelvin because the gas constant is always in terms of kelvin.

pmokh14B

The first order graph is of ln[A] vs time, and the second-order is 1/[A], whichever is linear is the order of the reaction.

pmokh14B

I think that would make sense but usually, the effect of the catalyst is represented in the Arrhenius equation as a lower Ea value.

pmokh14B

A catalyst is different from an intermediate. An intermediate is produced and then consumed in a reaction mechanism, while a catalyst is present, to begin with, consumed and then regenerated.

pmokh14B

The graph should be a decreasing linear function.

pmokh14B

Usually, this will be the case when there is one reactant forming two products. Because the oxidation of one of the components of the reactants will increase with respect to one product and decrease with respect to the other.

pmokh14B

rate law describes the rate of the reaction in terms of concentrations of its reactants and the order to which they influence the reaction.

pmokh14B

Usually, you should use platinum, but other nonreactive metals (i.e graphite) are also possible.

pmokh14B

you should usually simplify if the question asks for the overall reaction.

pmokh14B

Because you need a material that can act as an electrode but not be involved in the reaction.

pmokh14B

It can be salt as well.

pmokh14B

The half-reactions must be balanced with each other as well as themselves.

pmokh14B

I think you could use a salt bridge because the anion would still be able to move through it.

pmokh14B

The voltage we are calculating represents the maximum potential difference.

pmokh14B

we use Cv when the volume is constant(isochoric) and Cp when pressure is constant (isobaric)

pmokh14B

Yes, you can use this for any ideal gas.

pmokh14B

Any equations, depending on whether or not the work/effect on the system is adiabetic/isothermal/isochoric, etc...

pmokh14B

I think most people take C and BL together and I've heard a lot of people just hold off on CL until C-sesh or senior year.

pmokh14B

The units for each are on the equation sheet. Depending on that you decide which to use.

pmokh14B

I think thats what most people do.

pmokh14B

Either works, unless it's specified in the problem.

pmokh14B

it depends on the units of the other variables in the equation/calculation you are doing.

pmokh14B

Yes, this can be used for an ideal gas.

pmokh14B

Gibbs free energy, which is determined by enthalpy and entropy.

pmokh14B

Do we need to know how to find final equilibrium concentrations for multistep reactions? If so, where can I find examples and solutions?

pmokh14B

What Biological examples are important to know for the midterm?

pmokh14B

H and G can either be in kJ/mol or J/mol.
U is either kJ or J based on the units for q and w (which need to be the same).
S can be J/K or J/K/mol.

pmokh14B

a system goes from disordered to less disordered when you decrease the temperature of the system, for example.

pmokh14B

You raise the constant to the stoichiometric coefficient by which you multiply the reaction.

pmokh14B

I don't think so. You are raising the temperature for heat capacity, which would require a positive input of energy/heat.

pmokh14B

Are we allowed to do problems from the end of Acids and Bases Equilibria for this weeks homework?

pmokh14B

Enthalpy is positive for endothermic reactions or indicates energy needs to be put in (i.e breaking bonds). negative enthalpy indicates exothermic reactions, or breaking bonds.

pmokh14B

Yes, they would just be the opposite sign of the phase changes that require energy (i.e (delta)Hfreezing, is -(delta)H melting)

pmokh14B

I think you use kelvin.

pmokh14B

In biology a small amount of energy is needed, but once that phosphate binds to another molecule, enzyme, etc. it releases a lot more energy than what was required to break it.

pmokh14B

The diatomic molecules form very naturally and don't require much energy to form from their respective atoms.

pmokh14B

My TA said we'll usually get things in bar.

pmokh14B

Because those conjugates are more stable than their respective acids/bases, so they stay in solution rather than reacting to form hydronium or hydroxide.

pmokh14B

I would review my notes and do the homework sections for Equilibrium and acids and bases equilibria.

pmokh14B

Test 1 is during the discussion section of week three.

pmokh14B

Yes they are, but I dont think the tests are.

pmokh14B

K does not have units it is a constant.

pmokh14B

As long as we cover the information during the week.

pmokh14B

I think you can use aqueous solutions and gasses, but not solids or liquids.

pmokh14B

When Q equals K the system is at equilibrium. In all other situations, it is not.

pmokh14B

You can use it to convert between partial pressure and concentration.

pmokh14B

K can be used to abbreviate for either Kc or Kp.

pmokh14B

the reaction quotient is basically the equilibrium constant at a moment where the reaction is not at equilibrium. It can provide insight into which direction the reaction will proceed.

pmokh14B

Larger K value indicates that there are more products at equilibrium, and smaller K value indicates that there are more reactants at equilibrium.

pmokh14B

Yes, because when Q is equal to K the ratio of products to the reactants at the moment in question is the concentrations for the equilibrium of that reaction.

pmokh14B

I think for gasses you can use either concentration or pressure, because they can be converted.

pmokh14B

pH is usually used to refer to a solution. Depending on the ion in solution, the pH varies.

pmokh14B

Polyprotic acids can essentially lose a proton (H+) more than once, or they can lose more than one H+.

pmokh14B

Everything should be in the syllabus. I assume anything else he includes would be mentioned during class.

pmokh14B

I feel like most things will be in terms of pH, but I've seen problems where information is given in pOH which we'd need to use for calculations to maybe determine pH. For that you could use pH + pOH = 14

pmokh14B

I think you should have a general idea of them. At least the ones he mentioned in class.

pmokh14B

180/500 so 36%

pmokh14B

The angle would be less than 90 for axial, and less than 120 equatorial.

pmokh14B

You should usually give the answer in terms of the number of the value given to you in the problem with the least number of sig figs.

pmokh14B

You would either use
M=moles/Liters
or M1V1=M2V2 for dilutions.
Usually, just see which variables you have and manipulate the equations to determine the value you are looking for.

pmokh14B

Oxidation states are basically the charge of different ions. They usually align with the group number of the atom, but for transition metals, they vary.

pmokh14B

From the positive to the negative charge. Within a bond, not the entire molecule.

pmokh14B

Double and Triple bonds are accounted for in the same way that single bonds are: as a single bonding group/domain.

pmokh14B

2E. 1
for this question I thought the structure in part a (bent) must have a lone pair, but on the manual it says that it may have lone pairs. I don't understand how.

pmokh14B

The first molecule has a hydrogen attached to an Oxygen (one of the three atoms that make hydrogen bonding possible). diethyl ether doesn't have a hydrogen bonded to either N, O or F so it cannot exhibit hydrogen bonding

pmokh14B

I think they might give us one during the peer review session.

pmokh14B

H bonds can only form with these three atoms.

pmokh14B

no most metals are cations and will have polarizing power, not be polarizable.

pmokh14B

Yes, the larger the difference in electronegativity the stronger the dipole moments of the molecule are.

pmokh14B

The larger the size of the atoms, the more likely their bond length will be greater.

pmokh14B

The other atoms will be repelled by the lone electrons. The bonds between the central atom and peripheral ones contain negatively charged electrons which will tend to move as far as possible from the concentrated negative charge of the unpaired e-.

pmokh14B

The first electron being removed from oxygen comes out of a full orbital. The electron-electron repulsion of the two e- decreases the magnitude of the force of the nucleus these electrons experience, decreasing the energy necessary to remove them from the atom.

pmokh14B

The greater difference in the electronegativity between two atoms, the more polar the bond between them will be because the more electronegative atom will have a greater pull on the electrons, and that side of the bond will be more negative.

pmokh14B

Yes, single bonds are the weakest and longest, triple bonds are the shortest and strongest. Also, atomic radius comes into play. Smaller atoms tend to be closer and more strongly held together.

pmokh14B

10 electrons. The d subshell has 5 orbitals, each able to hold one pair, or two electrons, adding up to a max of 10 e-.

pmokh14B

I think we should have the grades by Wednesday.

pmokh14B

Calculating bond length is just adding the radii of the two atoms bonded.

pmokh14B

The 4s shell is filled first, any energy level that is higher is always filled first. But you write it second because it has higher energy and if any electron is removed from the atom it's removed from a higher energy shell first>

pmokh14B

I think you can provide the answer anyway, but sometimes it makes it easier to count sig figs when changing the units.

pmokh14B

Using formal charges can help with this. A double bonded O with two lone pairs would have a formal charge of zero, whereas if it had a single bond with three unpaired e- the formal charge would be -1, which is unfavorable. The same thing goes for F.

pmokh14B

Yes but there can also be multiple structures with different formal charges. It's mostly dependent on the fact that double or triple bonds can be distributed to other bonds between the same to atoms in a molecule.

pmokh14B

molecules with resonance, or those having atoms with expanded octets would be exceptions to bonding rules and the octet rule.

pmokh14B

I think we get all the information we had ont he 1st test.

pmokh14B

3d fills up after 4s but 4s would still have higher energy because it is in the fourth energy level. Electrons are removed from the outermost/highest energy levels/shells.

pmokh14B

A molecule/compound has resonance when there can be a double/triple bond placed at multiple bond sites without changing the orientation or atoms bonded.

pmokh14B

does anyone know how to check our grade in the class?

pmokh14B

Kinetic energy is zero when the work function iis equal to the energy of the photon hitting the metal. If a problem asks how much energy is required to eject an electron from a surface of the metal you would also make KE equal to zero.

pmokh14B

Isoelectronic atoms have the same number of electrons but one is an ion of some sorts and the two behave chemically differently. For example, F- and Ne both have 10 electrons, but behave differently when it comes to bonding, chemical reactions, etc....

pmokh14B

For this, you would probably have to see which has a stronger type of intermolecular bonds, the stronger the bond between molecules, the more energy would be required to sever them, which would lead that molecule/compound to have a higher boiling point.

pmokh14B

The fact that increasing the frequency is what determined electrons being ejected or not showed the particle aspects of light. The intensity of light would just be shining more of the same frequency light on the metal, but increasing frequency increased energy and herefore emitted electrons from the...

pmokh14B

Yes you assume that KE is zero because that will make the energy of the photon equal to the work function.

pmokh14B

I usually meditate, and work out. and get a lot of sleep.

pmokh14B

You use rydberg's equation if you need to calculate the energy level of a hydrogen atom. at any level equal to n.

pmokh14B

I usually just review my notes until I understand the concepts. Then go through the suggested problems in the syllabus and make sure I can do all of them.

pmokh14B

The electron would move to the surface of the metal, but because in the experiment the detector that records the KE of electrons has a positive charge the electron would be pulled away by charge of the detector.

pmokh14B

In a ground state, the electrons of an atom occupy their lowest energy levels possible.

pmokh14B

You use this equation during dilution questions. like when you're asked how much of one solution you would need to achieve certain molarity of another volume solution. Anytime you'd be given three of the variables of the equation and asked to find the other.

pmokh14B

Im pretty sure the information provided to us the first test is what we're given every time.

pmokh14B

You can leave it in either moles or grams. Unless the question itself asks for either grams or moles.

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