CHEMISTRY COMMUNITY

Betania Hernandez 2E

The cathode is the cell reduction potential that is most positive. So if they are both negative, then it would be the smallest negative number at the cathode.

Betania Hernandez 2E

The textbook used the Arrhenius equation for two temperatures, denoted T1 and T2, when the rate constants have the value K1 and K2. At temperature T1: lnk_{1}=lnA-\frac{E_{a}}{RT_{1}} At temperature T2: lnk_{2}=lnA-\frac{E_{a}}{RT_{2}} lnA is eliminated by subtracting the first equation from the sec...

Betania Hernandez 2E

They have already posted the worksheet. https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=160&t=62044&p=236759&hilit=review+sessions&sid=50579992ed64f02ebd971ab11a38e3b0&sid=a8cd0b5608d8cc5fa29e9b0c55df7945#p236759

Betania Hernandez 2E

Yes, that is correct.

Betania Hernandez 2E

The value of R is 8.314 J/mol x K so it should be 0.008314 if you are converting to KJ/mol x K. The solutions manual seems to have missed one decimal place.

Betania Hernandez 2E

The overall order is just the sum of all the powers of the reactants in the rate law. Such as Rate=k[A]^2[B]^1 has an overall order of 3

Betania Hernandez 2E

[A]_{t} represents the concentration of reactant A that remains at time t. The problem states that the concentration of product B rises to 0.034 M. This means that the concentration of reactant A decreased by 0.068 M. You would need to subtract this number from the initial concentration given to fi...

Betania Hernandez 2E

The review sessions are up on the Chem 14B page and Lyndon usually announces that the review packets are up in lecture. So, it will probably announced some time during the week.

Betania Hernandez 2E

molecularity is the number of reactant molecules, atoms, or ions taking part in a specified elementary reaction.

Betania Hernandez 2E

C is zero order reaction which can be seen from experiments 1 and 4 where A and B are constant while C changes but the rate stays the same. Knowing this, C doesn't need to be taken into account since its concentration has no effect on the rate

Betania Hernandez 2E

The table gives the initial concentration in (mmol/L) as well as the initial rate (mmol/LxS). The textbook solution converts the mmol to mol in their calculations which results in the final answer being 2.85x10^12 L^4/mol^4xS

Betania Hernandez 2E

F is also Coulombs/mol and Volts is Joules/Coulomb. When multiplied together, the units cancel out leaving Joules for deltaG
$-nFE^{\circ}cell=-n(\frac{C}{mol})(\frac{J}{C})$

Betania Hernandez 2E

This link has an explanation:
https://lavelle.chem.ucla.edu/forum/viewtopic.php?t=5161

Betania Hernandez 2E

We know that the cell diagram is reversed when the cell potential is negative. The cell potential was given as -0.689 which means that the cathode is the left of the cell diagram and the anode is the right side of the cell diagram. This makes the unknown metal the cathode and the copper the anode.

Betania Hernandez 2E

A positive cell potential means that the cathode is the electrode on the right of the cell diagram. A negative cell potential means that the cathode is the electrode on the left side of the cell diagram. Since the problem states that the cell potential was found to be negative, then this means that ...

Betania Hernandez 2E

A chemically inert metallic conductor is needed to carry the electrons into or out of the electrode compartment. Therefore, Platinum solid is included when there are no metallic conductors on either the anode or the cathode. Both sides have to have a metallic conductor. In some cases, there may be a...

Betania Hernandez 2E

The Ecell values can be found in the back of the textbook in Appendix 2B.

Betania Hernandez 2E

n is the number of electrons in moles. This can be found by writing the two half-reactions and seeing how many electrons are transferred.

Betania Hernandez 2E

But some problems in the textbook have Pt(s) on the anode side or both sides (6L.3 (d) and (e)). Why do some have it only on the cathode or anode side and others on both? Each side of the cell diagram needs to have a conducting solid. In the problems that have Platinum on only one side, there alrea...

Betania Hernandez 2E

In the step where it balances the H, it results in this equation: 2H_{2}O(l)+O_{3}(g)\rightarrow O_{2}(g)+H_{2}O(l)+2OH^{-}(aq) Since there are two H20 in the reactants side and one H2O on the products side, the H2O on the products side cancels out with one of...

Betania Hernandez 2E

Oxidation occurs in the anode and Reduction occurs in the cathode. In this problem, Au is both the oxidizing and reducing agent. Au+ is being oxidized when it goes to Au3+ since it goes from having an oxidation state of +1 to +3. It is being reduced when Au+ goes to Au(s) since it goes from having a...

Betania Hernandez 2E

The oxidation state of O2 will be -2 even if it stands alone. For O3, the oxidation state will be 0. Oxygen is sometimes -1 such as peroxides, H2O2, since hydrogen has an oxidation state of +1

Betania Hernandez 2E

q=-w can help you figure out that the reaction is isothermal reversible which means that it has a constant temperature and that the internal energy equals zero.

Betania Hernandez 2E

The heat lost by the system is the heat gained by the surroundings. In this case, since the heat is lost by the water it is negative and the heat of the ice is positive since it gained the heat.

Betania Hernandez 2E

When a reaction is reversible, the delta S (total) equals 0, because the delta S of the surrounding is the same as the delta S of the system with opposite sign.

Betania Hernandez 2E

Delta E is the change in energy and it can be used interchangeably for the change in internal energy.

Betania Hernandez 2E

Calculations vary for monoatomic gases since Cv is 3R/2 under constant volume and Cp is 5R/2 under constant pressure.

Betania Hernandez 2E

If the equilibrium constant and the temperature is given, then you can find delta G

Betania Hernandez 2E

You would just use the conversion of 101.325 J/ 1 L* atm.

Betania Hernandez 2E

Yes, the same constants and equation sheet will be be provided on the midterm.

Betania Hernandez 2E

A car is an open system because it exchanges both heat and matter. Matter in the form of gasoline to start the engine and heat is released when the car is running.

Betania Hernandez 2E

A bomb calorimeter is constant volume which means that since there is no change in volume then there is no work done.

Betania Hernandez 2E

The combustion of fossil fuels releases carbon dioxide into the atmosphere which contributes to global warming. Some alternatives for fossil fuels are ethanol, methane, and biodiesel. One way that this could be asked on the midterm is calculating the heat of combustion.

Betania Hernandez 2E

Bond enthalpies are the least accurate method to calculate enthalpy changes because they are an average of many bonds.

Betania Hernandez 2E

Yes, they must be on the opposite sides of the reaction equation in order to cancel out.

Betania Hernandez 2E

It would be positive since work is being done on the system.

Betania Hernandez 2E

Heat and work are not state functions because they depend on the paths they take.

Betania Hernandez 2E

They are interchangeable because the change in temperature is the same whether you use Celsius or Kelvin. The change in degrees Celsius is the same as the change in degrees Kelvin.

Betania Hernandez 2E

Khan Academy videos are very helpful: https://www.khanacademy.org/science/che ... ases-topic

Betania Hernandez 2E

A catalyst only increases the rate of reaction, it would not favor the formation of reactants or products.

Betania Hernandez 2E

It would be better practice to do the homework from outline 2 since it will also be on the test.

Betania Hernandez 2E

Yes, all aqueous and gases are included in the equilibrium expression

Betania Hernandez 2E

No, the order in which you write the reactants and products do not matter as long as the products are in the numerator and reactants in the denominator

Betania Hernandez 2E

Yes, both statements mean the same thing. When Q<K, there is more reactants than products and it is not at equilibrium. In order for it to get to equilibrium, the reaction proceeds to the right to form products.

Betania Hernandez 2E

Using the quadratic formula can be skipped if the equilibrium constant is less than 10^-3. The value of x would be so small that it would be negligible in the final answer when figuring out the equilibrium concentrations.

Betania Hernandez 2E

If you get two positive answers, you could rule out the value that is greater than your initial concentration since it would result in a negative number when plugged in to the equilibrium expression.

Betania Hernandez 2E

Kc can be used with gases if they give the concentrations of reactants and products in molarity.

Betania Hernandez 2E

The x-term can be omitted when the equilibrium constant is small (less than 10^-3) since the difference would be negligible.

Betania Hernandez 2E

Both are applicable because they are both units for measuring pressure.

Betania Hernandez 2E

A homogeneous equilibrium has to have all reactions and products in the same phase. Such as they all have to be gases, or all aqueous,... If even one of the reactants or products are in a different phase then it is a heterogeneous equilibrium.

Betania Hernandez 2E

Kc uses brackets because it is dealing with the molar concentration while it isn't used with Kp because it is dealing with gases which is in the units of bar or atm.

Betania Hernandez 2E

Kc and Kp will be two different values since Kc uses the molar concentration value while Kp is uses partial pressure.

Betania Hernandez 2E

The C stands for the change in molar concentration. C is figured out by looking at the chemical equation and its coefficient for the reactants and products.

Betania Hernandez 2E

Strong bases dissociate completely in water unlike weak bases which don't dissociate completely.

Betania Hernandez 2E

This will be covered in Chem 14B

Betania Hernandez 2E

sp2 should be fine if the question didn't specifically ask for the orbitals that they were in.

Betania Hernandez 2E

Thank you Dr. Lavelle for providing us with many resources to assist us in our learning!

Betania Hernandez 2E

You do not have to add anything to positively or neutral charged ones. It is only if it is negatively charged that you add the -ate

Betania Hernandez 2E

Yes, they do have hybrid orbitals. The lone pairs count as a region of electron density.

Betania Hernandez 2E

Yes, single bonds always have one sigma bond.

Betania Hernandez 2E

We won't be provided a chart so we have to have the common ligands memorized.

Betania Hernandez 2E

I believe that this is all that we need to know. As long as you know how this is applied in the homework problems then it should be fine.

Betania Hernandez 2E

It can be written as either!

Betania Hernandez 2E

Atoms will be in the same plane if they have a double or triple bond since they can't rotate due to having a pi bond. Furthermore, if they are either trigonal or square planar the atoms also lie in the same plane.

Betania Hernandez 2E

Yes, lone pairs do count. Hybridization takes into account all areas of electron density.

Betania Hernandez 2E

Yes, it is.

Betania Hernandez 2E

London dispersion forces increase in strength with increasing polarizability of the molecule. The polarizability of a molecule increases with the number of electrons, therefore the larger molecule will have stronger London Dispersion force.

Betania Hernandez 2E

Dipoles have the arrow pointing towards the more electronegative atom.

Betania Hernandez 2E

Yes, you are correct.

Betania Hernandez 2E

The bent shape can have 1 lone pair when its electron geometry is trigonal planar and 2 lone pairs when its electron geometry is tetrahedral.

Betania Hernandez 2E

Dipole moments cancel out when there are same signs on different sides of the molecule.
Lavelle explained it further in this post:https://lavelle.chem.ucla.edu/forum/viewtopic.php?t=2234#p4519

Betania Hernandez 2E

Yes, dipole moments occur when there is a difference in electronegativity. If there is a greater difference in electronegativity, there is a larger dipole moment.

Betania Hernandez 2E

Anything after the midterm, so anything after 2D and up to Monday's lecture.

Betania Hernandez 2E

I believe Lavelle said that we wouldn't have to draw the dash/wedges during lecture.

Betania Hernandez 2E

I think it is best to remember all of them, just to be safe.

Betania Hernandez 2E

The exceptions are chromium and copper. Chromium is an exception because a half filled d-sub level is more stable than a partially filled d sub level. The same goes for Copper where it is more stable as a completely filled d-sub level.

Betania Hernandez 2E

It uses a wave function to describe an electron in an atom. The wave function squared shows the probability of finding a region of electron density at some point. Orbitals are solutions to Schrodinger's equation and gives the energy of the electron.

Betania Hernandez 2E

I think it would be fine to do problems from either section since we haven't really gone in depth in the new section yet.

Betania Hernandez 2E

Yes, electronegativity is an atom's tendency to attract electrons to itself. Fluorine is the most electronegative atom in the periodic table.

Betania Hernandez 2E

Any element below and including the 3rd period is able to have expanded octet. The first two periods cannot have expanded octets because they only go up to the p block.

Betania Hernandez 2E

Oxygen has a higher electronegativity when you look at the periodic trend for increasing electronegativity.

Betania Hernandez 2E

It's not going to be on the midterm since there are no homework problems on it.

Betania Hernandez 2E

Yes, the threshold energy is represented by the work function. In order for an electron to be ejected from the metal surface, the photon has to have more energy than the work function.

Betania Hernandez 2E

The uncertainty in velocity would be 10 m/s because that is the range that velocity could be between.

Betania Hernandez 2E

The central atom is usually the least electronegative one. Electronegativity increases as you go from left to right across a period and increases as you go up a group in the periodic table.

Betania Hernandez 2E

Electrons that are further away from the nucleus are easier to remove because there is less attraction between the electron and the nucleus due to the distance between them.

Betania Hernandez 2E

Yes, changing the intensity of a particular light will cause a change in the number of electrons being ejected. So if the intensity of a light is increased, the number of electrons being ejected will increase as well.

Betania Hernandez 2E

I don't think you have to know how to find the bond lengths but rather the general concepts that double bonds are shorter than single bonds

Betania Hernandez 2E

I would think it would be on Chemical Bonds since we are moving into this topic more this week

Betania Hernandez 2E

Either one would be fine but on tests you should use the one given on the equations and constant sheet in order to be precise as possible.

Betania Hernandez 2E

This week we can still do the problems from "The Quantum World" section since we will be working on this unit on Monday.

Betania Hernandez 2E

I find that going through all the suggested practice problems on the syllabus works best for me. I work through as many problems as I can and also go to some of the workshops provided.

Betania Hernandez 2E

The mass of an electron, proton, and neutron is a set mass that is provided on the constants and equations sheet.

Betania Hernandez 2E

Kg is used often because it is an SI unit which is used in DeBroglie's equation.

Betania Hernandez 2E

The speed of light is always a constant. It would be better to use the exact number provided on the equation sheet (2.99792*10^8) on the exams.

Betania Hernandez 2E

Increasing the intensity of light would only increase the number of photons. If the photons don't have sufficient energy to overcome the binding between the electron and the metal then just increasing the number of photons won't cause an electron to eject since each photon has the same energy. You w...

Betania Hernandez 2E

Yes, we would submit a different set of 5 problems within "The Quantum World" section.

Betania Hernandez 2E

Actual yield is usually given in the problem if you are trying to find percent yield. Also, theoretical yield is usually less than the actual yield due to impurities or other side reactions that occur.

Betania Hernandez 2E

For the peer learning groups/sessions, do you come ready with your own questions, do other people lead what you're going to be talking about? Or do you guys all do it together? For the peer learning sessions that Dr Lavelle provides, the workshops are led by a UA and they provide additional workshe...

Betania Hernandez 2E

I think that as of right now, you shouldn't worry about knowing them but you should know some of the more common or simple ones that are usually used.

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