CHEMISTRY COMMUNITY

Brandon Gruender 3F

I feel like the easiest way to not be nervous is to not think about it. The test is done and over with, and whatever happens now wont affect your score. There is nothing you can do now so being patient and relaxed is key.

Brandon Gruender 3F

Salt bridges allow the transfer of electrons across the cell, which in turn stops one side from building up too much of a charge.

Brandon Gruender 3F

No Lavelle does not teach 14C, only 14A and B :(

Brandon Gruender 3F

Organic Chemistry Tutor or Professor Dave are very good resources on youtube, I think they both explain this material very well

Brandon Gruender 3F

enzymes are catalysts because they lower the activation energy for a reaction, but aren't used up in the reaction

Brandon Gruender 3F

How are we able to tell which letters in question 18 on sapling are intermediates and which ones are catalysts.

Brandon Gruender 3F

A certain reaction has an activation energy of 33.82 kJ/mol. At what Kelvin temperature will the reaction proceed 4.50 times faster than it did at 343 K?

Im confused on how to solve this.

Brandon Gruender 3F

You find this by seeing how many times you need to divide the first concentration by 2 in order to get to the second concentration.

Brandon Gruender 3F

The question will likely tell you, so then you will know how to balance the redox reaction.

Brandon Gruender 3F

The textbook problems help a lot. By doing those and reviewing past notes I think you will do just fine!

Brandon Gruender 3F

STP is 0 degrees Celsius, which is 273 K. Normally we see 298 K because that is 25 degrees Celsius, or around room temp.

Brandon Gruender 3F

In an aqueous solution you need P(t) to be an electron conductor

Brandon Gruender 3F

You can tell that a reaction is reversible if he delta S total equals 0. It can also be found if you are given moles, temp, and the change in volume.

Brandon Gruender 3F

Calculate the cell potential for the reaction as written at 25.00 °C , given that [Zn2+]=0.819 M and [Ni2+]=0.0160 M . Use the standard reduction potentials in this table. Zn(s)+Ni2+(aq)↽−−⇀ Zn2+(aq)+Ni(s) This is my question for #14, but how do we tell which one is the anode and which is the cathod...

Brandon Gruender 3F

What would the potential of a standard hydrogen electrode (S.H.E.) be under the given conditions?

[H+]=0.40 M. PH2=1.8 atm T=298 K

Does anyone know how to do this?

Brandon Gruender 3F

A galvanic (voltaic) cell consists of an electrode composed of aluminum in a 1.0 M aluminum ion solution and another electrode composed of copper in a 1.0 M copper(I) ion solution, connected by a salt bridge. Calculate the standard potential for this cell at 25 °C. Im trying to get a head start on t...

Brandon Gruender 3F

In Isothermal reactions the temperature is constant, so there is no heat transfer. In these reactions q=-w, so they cancel out and leave delta U equal to 0.

Brandon Gruender 3F

We should have 35 points for this quarter, and 85 in total if you took 14A with Lavelle.

Brandon Gruender 3F

E is not a state function, it relies on the path that was taken in order to get to the current state.

Brandon Gruender 3F

Yes you can review your test with a TA in their office hours. It doesn't have to be your TA either, it can be any.

Brandon Gruender 3F

Entropy is also a state function that shows the number of microstates possible. There are many topics that cover this, and a few equations, so i think it will be important for this next midterm.

Brandon Gruender 3F

You need to get 200 or more points to pass with a C-.

Brandon Gruender 3F

For a gaseous reaction, standard conditions are 298 K and a partial pressure of 1 bar for all species. For the reaction C2H6(g)+H2(g)↽−−⇀2CH4(g) the standard change in Gibbs free energy is ΔG∘=−32.8 kJ/mol. What is ΔG for this reaction at 298 K when the partial pressures are PC2H6=0.200 bar, PH2=0.1...

Brandon Gruender 3F

The ΔHvap of a certain compound is 14.23 kJ·mol−1 and its ΔSvap is 75.76 J·mol−1·K−1.

What is the boiling point of this compound?

How do I do this?

Brandon Gruender 3F

Happy Valentines day to you too!

Brandon Gruender 3F

This only applies when delta U=0. The first law of thermodynamics supports this equation.

Brandon Gruender 3F

A 0.253 mol sample of CO2(g) initially at 298 K and 1.00 atm is held at constant volume while enough heat is applied to raise the temperature of the gas by 17.5 K. Assuming ideal gas behavior, calculate the amount of heat (q) in joules required to affect this temperature change and the total change ...

Brandon Gruender 3F

q would be negative if the system is exothermic, or releasing heat. And q would be positive if it is endothermic, or taking in heat.

Brandon Gruender 3F

Personally, I find the homework questions from the outline to be a very good study technique. You can review the ones you struggle on over and over and once you have a good grip on these you should be pretty good for the test. Also, a lot of times Dr. Lavelle sneaks some of these questions into the ...

Brandon Gruender 3F

A constant‑volume calorimeter was calibrated by carrying out a reaction known to release 2.14 kJ of heat in 0.300 L of solution in the calorimeter (q=−2.14 kJ) , resulting in a temperature rise of 3.80 ∘C . In a subsequent experiment, 150.0 mL of 0.20 M HClO2(aq) and 150.0 mL of 0.20 M NaOH(aq) were...

Brandon Gruender 3F

Well we know that it is the heat required to raise one mole of a substance by 1 degrees Celcius, we may have to use these on textbook problems.

Brandon Gruender 3F

When do you guys plan on taking Chem 14BL? I dont know if I should take both Chem 14C and Chem 14BL together, what is everyone else doing? thank you!

Brandon Gruender 3F

A sample of an ideal gas in a cylinder of volume 2.61 L at 298 K and 2.22 atm expands to 7.61 L by two different pathways. Path A is an isothermal, reversible expansion. Path B has two steps. In the first step, the gas is cooled at constant volume to 1.15 atm . In the second step, the gas is heated ...

Brandon Gruender 3F

A hot lump of 27.8 g of copper at an initial temperature of 50.8 °C is placed in 50.0 mL H2O initially at 25.0 °C and allowed to reach thermal equilibrium. What is the final temperature of the copper and water, given that the specific heat of copper is 0.385 J/(g·°C)? Assume no heat is lost to surro...

Brandon Gruender 3F

yes because it can not exchange energy or matter with the surrounding environment

Brandon Gruender 3F

You would use the ICE table for weak acids/bases because they do not completely dissociate during a reaction, so we have to calculate how much changes using x.

Brandon Gruender 3F

Normally, anything smaller than 1x10^-4 is safe to assume, however I would always check that it is less than 5% of the initial concentration. If it is not then you need to use the quadratic equation to find x for that problem.

Brandon Gruender 3F

Actually the tables on 6C.1 and 6C.2 show you! I would just memorize those.

Brandon Gruender 3F

I think the hardest part is just knowing where to start, as you said. Although normally we have done ICE tables for the equilibriums of weak acid, this question gives us a weak base and the process is the exact same. First, write out the equation for the weak base NaClO in solution. When dissolved ...

Brandon Gruender 3F

HClO is a weak acid ( Ka=4.0×10−8 ) and so the salt NaClO acts as a weak base. What is the pH of a solution that is 0.037 M in NaClO at 25 °C?

Can you guys help me solve this problem, I don't know where to start.

Brandon Gruender 3F

If the Ka of a monoprotic weak acid is 8.6×10−6, what is the pH of a 0.33 M solution of this acid?

How would I do this problem?

Brandon Gruender 3F

Yes, partial pressure only applies to gases.

Brandon Gruender 3F

You find Q by using the equation Q=products/reactants. Make sure you remember that the numbers in front get used as exponents, and products go on top.

Brandon Gruender 3F

Total pressure is all pressures combined at equilibrium. It is found by adding up the partial pressures of all the compounds in a reaction.

Brandon Gruender 3F

Im honestly struggling to see any faults in your work. Was your final answer 0.825 M? If it was I do not know, maybe contact your TA to help.

Brandon Gruender 3F

At a certain temperature, the given reaction has an equilibrium constant of Kp=369 .

PCl3(g)+Cl2(g)↽−−⇀PCl5(g)

PCl5 is placed in a sealed container at an initial pressure of 0.0800 bar . What is the total pressure at equilibrium?

How would I go about doing this?

Brandon Gruender 3F

The only time that this is included in the table is when it is in gas (g) form. The compound is not included if it is in liquid or solid phases.

Brandon Gruender 3F

Based on the results you get, one should be the obvious answer. For example, if your two answers are 2 and -2, the answer is 2 as you use the positive number. Additionally, if that number is larger than the original concentration, then it won't be the answer. You can't have more of a change than the...

Brandon Gruender 3F

At a certain temperature, 0.820 mol SO3 is placed in a 4.50 L container.

2SO3(g)↽−−⇀2SO2(g)+O2(g)

At equilibrium, 0.170 mol O2 is present. Calculate Kc.

For this would you just have to find the molarity of each compound and then plug it into the equation for Kc?

Brandon Gruender 3F

Consider the reaction of NH3 and I2 to give N2 and HI. 2NH3(g)+3I2(g)↽−−⇀N2(g)+6HI(g)K Using two or more of the given equations, determine the equilibrium constant, K , for the reaction of NH3 with I2. H2(g)+I2(g)↽−−⇀2HI(g)I2(g)↽−−⇀2I(g)N2(g)+3H2(g)↽−−⇀2NH3(g)H2(g)+Cl2(g)↽−−⇀2HCl(g)Ka=160Kb=2.1×10−3...

Brandon Gruender 3F

I believe for pressure bars are what we use (they are very similar to atm).

Brandon Gruender 3F

Slightly less than 90 degrees as the electron pairs have repulsion.

Brandon Gruender 3F

The new due date is thursday, so it wont be updated until then!

Brandon Gruender 3F

Tetrahedral has 4 bonds to atoms, and no lone pairs (AX4). Square planar has 4 bonds to atoms, and 2 lone pairs(AX4E2).

Brandon Gruender 3F

There is no curve, but he did say that he is adding 10 points to the final grade. That should help!

Brandon Gruender 3F

yes! that is what that means!

Brandon Gruender 3F

After guessing a few times I got that the coordination number for [Co(SO4)(NH3)5]+ is 6.
Does anyone know why this is?

Brandon Gruender 3F

Yes it is. The energy of the photon-the threshold energy is = to the kinetic energy.

Brandon Gruender 3F

In this case, this will only be the speed of light. It may change in future classes (I'm not sure), but for now this is the speed of light. The constant is around 3 x 10^8

Brandon Gruender 3F

To find the coordination number, you need to look at how many ligands are connected to the central atom. For example, in the compound [CuCl2]-, the coordination number is 2. There are 2 Cl atoms around the Cu atom. Another example would be Ba[FeBr4]2. Since you only count whats on the inside of the ...

Brandon Gruender 3F

When naming compounds, what does en mean?

Brandon Gruender 3F

From the lectures, we learn that the left side (alkali metals) usually give rise to base oxidation. On the right side you generally see acid oxides being formed from the halogens, etc. In the middle, near the transition metals and metalloids you will see amphoteric atoms. Hope this helps!

Brandon Gruender 3F

Bent molecules are asymmetrical, generally leading to a polar molecule. For example, since water is bent and the two H atoms are electronegative towards the O atom, it does not cancel out. This is why water is polar, and most bent molecules follow that trend.

Brandon Gruender 3F

They are similar, but have some differences. A Lewis base is a base in which an electron is donated to another atom. A Bronsted base is one who accepts a proton (from an H), making that atom basic. They talk about different reactions but lead to the same concept.

Brandon Gruender 3F

Does anyone know how to answer this? My questions asks what the name of this compound is. Thank you!

[Co(NH3)4Cl2]Cl

Brandon Gruender 3F

Hi! Coordination number refers to the number of ligand atoms bonding to the central transition metal. For example, if the compound is ZnCl4 there are 4 chlorine atoms bound to the central atom, Zinc. If you have brackets (e.g K4[Fe(Cn)6]-) you would only count the atoms on the inside. So in this cas...

Brandon Gruender 3F

What is the hybridization of phosphorus in each of the molecules or ions?
The first molecule shown is PCl3
thank you!

Brandon Gruender 3F

H will never be the central atom because it is only allowed to form 1 bond to fill its octet.

Brandon Gruender 3F

Usually, atoms after the 3p subshell can have an expanded octet, but I'm not sure what the rule is for atoms in the 6p subshell.

Brandon Gruender 3F

How do you determine ionic/covalent character again?
There was a question on the midterm that I was stuck on.

Brandon Gruender 3F

How many outer atoms and lone pairs are present in a molecule with a see‑saw shape?

Do you guys know?

Brandon Gruender 3F

Because we haven't been taught nomenclature of names of compounds yet they will be provided in this midterm.

Brandon Gruender 3F · Re: Homework due date Sunday at 11:59 pm, not Sunday at 12:00 am.

Sunday at 11:59 pm, not Sunday at 12:00 am.

Brandon Gruender 3F

Using number 9 in the sapling hw as an example, how do you find the oxidation number? And how do you know which structure is applies to? Thank you!

Brandon Gruender 3F

The last 8 on outline 2 and all of outline 3!

Brandon Gruender 3F

Hi! There are no exceptions, only happens when F, O, N, H are present.

Brandon Gruender 3F

Nope, any ones that aren't given on the constants and equations sheet will be given in the problem!

Brandon Gruender 3F

I hate online school, I wish we were on campus!

Brandon Gruender 3F

Select which intermolecular forces of attraction are present between CH3CHO molecules.

does anyone know what they are?

Brandon Gruender 3F

Urea is an organic compound widely used as a fertilizer. Its solubility in water allows it to be made into aqueous fertilizer solutions and applied to crops in a spray. What is the maximum theoretical number of water molecules that one urea molecule can hydrogen bond with? Ignore shape for the purpo...

Brandon Gruender 3F

My other classes are having us change to another day, so i'm guessing it is either cancelled or postponed.

Brandon Gruender 3F

No it is not relevant, just plug in the uncertainty in velocity to find the uncertainty in position.

Brandon Gruender 3F

On the Sapling HW, it asks

What is the minimum uncertainty in an electron's velocity (Δvmin) if the position is known within 13 Å.

How do I solve this?

Brandon Gruender 3F

Question #25 asks

The E Coli bacterium is about 2.4 μm long. Suppose you want to study it using photons of that wavelength or electrons having that de Broglie wavelength.

What is the energy E photon of the photon?

How do I solve this?

Brandon Gruender 3F

The l # represents the subshell. In this case, when l=1 it represents the p subshell. As we know, there can be a total of 6 electrons. To take it even further, they could ask using the ml value as well. For the p subshell, there are three possible orbitals: -1, 0, and 1. We know that each orbital ca...

Brandon Gruender 3F

Here is my question on number 23. The electron affinity of thulium has been measured by a technique known as laser photodetachment electron spectroscopy. In this technique, a gaseous beam of the anions of an element is bombarded with photons from a laser. Electrons from the anion are then ejected an...

Brandon Gruender 3F

Im studying for the midterm and going over questions from the book. There is one asking you to find the wavelength of a baseball traveling 92 mph, and I know how to solve it. However, I know that you need a number to convert miles to kilometers, will we need to memorize this and other conversions fo...

Brandon Gruender 3F

Yes this is used for photons as there is no mass, but when there is mass (an electron has a constant mass listed on the constants sheet) then you use DeBroglie's equation to solve for wavelength. Hope this helped!

Brandon Gruender 3F

My TA said that it would be around 10 questions, with no more than 4 long multiple step problems. To study I recommend doing the book questions and going over lectures.

Brandon Gruender 3F

I would use how ever many are shown on the sheet of equations and constants that we print out, but the more that you use the closer your answer will be to the correct answer.

Brandon Gruender 3F

That number is the universal mass of an electron. I'm guessing we don't have to memorize it, if it's on the midterm i'm sure it will be provided.

Brandon Gruender 3F

In my practice quiz, the question had the unit keV. What is that?

Brandon Gruender 3F

If the question asks, then I assume that you would need to convert to nm. However, if it doesn't mention anything Lavelle said that meters will work in the solution.

Brandon Gruender 3F

I think going over the textbook problems is the best overall way to study as these will be like the questions on the midterm. When it comes closer to the exam I would go over notes, and even though you don't need to memorize equations I would make sure you know when and how to use each one.

Brandon Gruender 3F

These terms mean the same thing and are used interchangeably in a question. You calculate them both the same way!

Brandon Gruender 3F

Yes, they are the same thing. They both are the amount of energy required from a wave of light to remove an electron from a metal.

Brandon Gruender 3F

The state of matter doesn't affect how you should balance the equation (law of conservation of mass), but it should be written out when writing the equation down.

Brandon Gruender 3F

Im guessing that it would just be a capital A, but if not then you could probably write it out (10^-10 m).

Brandon Gruender 3F

In order to get these points (maximum 5 points per week), you must post on the chemistry community page, this could be either asking questions or answering other people's questions.

Brandon Gruender 3F

HI! So first I would change the radius to diameter, so multiply the 144 by 2. Next you need to find how many atoms come in one mole of Ag, and to do that you would multiply 1 mole by 6.02x10^23 (avagadro's constant). When you find out how many atoms, multiply that by 288 pm (the length each atom tak...

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