CHEMISTRY COMMUNITY

DominicMalilay 1F

Good question. I have been using study breaks every 30 minutes or so for 5 minutes, and then going back to work!

DominicMalilay 1F

1st law I think to be most fundamental, energy can neither be created nor destroyed. Second is the trickiest one saying that entropy never decreases in isolated systems, and third you can think of that the molecules stop moving as T approaches 0K, so the entropy will theoretically be zero.

DominicMalilay 1F

Like some of the other replies here, the first and zero order reactions have negative slopes, but the second order reaction has a positive slope! Hope this helps

DominicMalilay 1F

Hey there, the first equation is zero order and the second one is first order because of the additional natural logarithm which makes the second one take on a negative slope.

DominicMalilay 1F

It would be the same calculations as we did in equilibrium, so you are right ! :)

DominicMalilay 1F

Is there a sheet of all the iterations for the formula to find the delta U value using the base deltaU=q+w?

DominicMalilay 1F

Intermediates cancel each other out, so you COULD include them but it would be unnecessary and overly complicated.

DominicMalilay 1F

Im having trouble for the balancing of the OH- molecules and the half reactions in general for this question:

For a particular redox reaction, NO−2 is oxidized to NO−3 and Fe3+ is reduced to Fe2+ . Complete and balance the equation for this reaction in basic solution. The phases are optional.

DominicMalilay 1F

Im having trouble for the balancing of the OH- molecules and the half reactions in general for this question:

For a particular redox reaction, NO−2 is oxidized to NO−3 and Fe3+ is reduced to Fe2+ . Complete and balance the equation for this reaction in basic solution. The phases are optional.

DominicMalilay 1F

Im having trouble with the half-reactions in this question: A galvanic (voltaic) cell consists of an electrode composed of zinc in a 1.0 M zinc ion solution and another electrode composed of gold in a 1.0 M gold(III) ion solution, connected by a salt bridge. Calculate the standard potential for this...

DominicMalilay 1F

Kind of overstating what Rich said here, but using math to prove chemistry concepts is great for the long run. If we take Ln(1), we get 0 so if they are the same concentration the value of the cell would essentially be zero.

DominicMalilay 1F

Hi, I was having trouble understanding this too, but I realized we can just think of a coulomb as a unit of charge because we do not need to go into exactly the meaning behind choosing the particular value of the unit (this is for physics haha!). Hope this helps!

DominicMalilay 1F

I always remember it by thinking that when you lose electrons, it is oxidizing because a loss of electrons means that the molecule or ion will become more net positive. On the other hand, gaining electrons increases the negativity of the molecule so it would be reduction.

DominicMalilay 1F

Hi, I would like to know what we should look for when calculating the lowest to strongest oxidizing agent in certain ions. Would this require knowledge of 14a material?

DominicMalilay 1F

Im having trouble with solving the half reactions for the lone ions in a reaction and was wondering what the correct method to solve them was?

DominicMalilay 1F

Since U=q+w, an isothermal rxn would mean no heat transfer and constant temp, making both values 0.

DominicMalilay 1F

You would need the salt bridge to maintain the ph of the battery. Otherwise, the ions cannot move freely between the anode and cathode.

DominicMalilay 1F

It would not be a state function because it does not have a delta and depends on the path taken.

DominicMalilay 1F

Enthalpy is also known as heat, while entropy is the chaos or the disorder of molecules.

DominicMalilay 1F

I always thought that you can never omit n, and usually, it would be because the n value is one so people assume it is being omitted.

DominicMalilay 1F

Yup, completely tanked that midterm :(

DominicMalilay 1F

How do atoms stay in shape? Using a calori-meter!

DominicMalilay 1F

External pressure would be the surroundings putting work on the system, hence the external force being applied to the system and is why it is called external pressure.

DominicMalilay 1F

Since the heat is being released in an exothermic rxn, heat is going out of the system and is negative. But for an endothermic rxn, heat is going in the system and so it is positive.

DominicMalilay 1F

Its like a compilation of all the heat and work put on the system which is why the formula is q + w

DominicMalilay 1F

Its because the environment is also doing work on the system, so its an externality that can not be placed on the system.

DominicMalilay 1F

Is the universe an open, closed, or isolated system?

DominicMalilay 1F

Exothermic reactions can be measured by the system and if heat is going in or out of said system. For example, ice melting would be endothermic because heat enters the system and causes the water to melt from being a solid to a liquid.

DominicMalilay 1F

The standard enthalpy of formation is the same as the enthalpy of formation with certain restrictions like the 25 C and 1 atm having to meet the requirements.

DominicMalilay 1F

The midterm exam is only for the week 1 through week 3 material as Dr Lavelle said in lecture.

DominicMalilay 1F

Every method is very accurate except calculating the bonds breaking because of the inaccuracy of rounding the breaking bonds.

DominicMalilay 1F

When the equation satisfies PV=nRT in all except one value like pressure, volume, etc, you can use the ideal gas law.

DominicMalilay 1F

The two basic formulas you have to remember are -log(h/oh)=ph or poh and that if you are given the ph or poh values, put 10^(-ph/-poh) to get the concentrations.

DominicMalilay 1F

Depending on the reverse or forward reactions, the -x is usually when you already know one of the concentrations while the x is usually for if you don't know the concentrations and are solving for them at first.

DominicMalilay 1F

I use ice box when I need to find concentrations of the molecules because you set up a quadratic or algebraic problem to solve for your concentration. You need to know the K value!

DominicMalilay 1F

I don't believe there is another method, and there shouldn't have to if you are given all the right information on the midterm/homeworks!

DominicMalilay 1F

I like to think of it as the state function being something that doesn't concern how you got to where you got to, just where you ended up. In other words, the journey doesn't matter! Only the start and end places.

DominicMalilay 1F

Usually when you need to find the concentration of a compound, use the ice chart. When finding the Kc value you'll need the concentrations in order to plug your values.

DominicMalilay 1F

The most common mistake on this one is forgetting to inverse the function if it is in the wrong order! You need to find the reciprocal to do this.

DominicMalilay 1F

Make sure that the p/r, the values are the power of the coefficient in the chem rxn! This is essential to solve the problem.

DominicMalilay 1F

Being more general, Q is the more specific term compared to K which specifies a specific instance in the rxn!

DominicMalilay 1F

When doing the problem, make sure you know Q= products/reactants. The coefficients turn into powers and just plug in the values they give for the compounds!

DominicMalilay 1F

In terms of pure stability, q and k have no effect on one another because they are separate variables that assess different values of the reaction.

DominicMalilay 1F

Since the factor affecting the concentration is not the volume, and volume changes concentration, then it will have no effect!

DominicMalilay 1F

The exact effect would require calculations and since we are just doing general trends it will not be tested!

DominicMalilay 1F

Non-ideal gases are not tested for this course because it isn't on the syllabus or lecture!

DominicMalilay 1F

Pressure and volume always have an inverse relationship.

DominicMalilay 1F

The large k value is usually for 10^3 while small k value is 10^-3!

DominicMalilay 1F

Only include it for gases because solids and liquids are not a part of the ice table!

DominicMalilay 1F

I personally never keep my units in celsius for the t variable as its just easier to remember!

DominicMalilay 1F

I think it's just the opposite of the ionic character!

DominicMalilay 1F

Count lone pairs and regions of electron density. A double bond is still 1 region of electron density as is a single or triple bond.

DominicMalilay 1F

I make sure to count the electrons and remember that the charge of the overall molecule matters for adding/subtracting electrons!

DominicMalilay 1F

Its the same table as the one we used for the 2 midterms!

DominicMalilay 1F

It exists because of naturally existing chemicals in the atmosphere (CO2,SO2) forming acids in the presence of water, making the rain slightly acidic.

DominicMalilay 1F

How do you determine the shape of this molecule? Also, how do you know that the compound's formula is SOCl2 from the name of the compound? This was a sapling problem

DominicMalilay 1F

What VSEPR shapes do we have to memorize for the exam?

DominicMalilay 1F

I always thought they are interchangeable. Wikipedia says "The oxidation state, sometimes referred to as oxidation number," so I think they are the same!

DominicMalilay 1F

The excess energy is thought of as kinetic energy because excess energy is transferred into the electron to give it the energy to move from the metal. Hence, it is kinetic.

DominicMalilay 1F

The photoelectric effect was focused on electrons emitting from metals, but there could be a correlation with the structure of the metals (with different alloys and so on) which can have an effect on the amount of electron emission. It's a stretch, though.

DominicMalilay 1F

In a double or triple bond, where would the sigma bond be in relation to the pi bond, and vice versa?

DominicMalilay 1F

Yes, along with others the main point is that it would be bound to a transition metal for it to be called a ligand.

DominicMalilay 1F

How would coordination numbers work for more complex and lengthy ions? For example Ba[FeBr4]2?

DominicMalilay 1F

Also,w remember that the types of bonds in a real molecule are not actually there; the atoms are just arranged to maximize efficiency. A molecule with a single and double bond in its lewis structure has the same bond lengths in real life!

DominicMalilay 1F

Types of bonds do not change the shape of the molecule! It would only be for lone pairs or the number of separate bonds.

DominicMalilay 1F

Because of the lone pairs forming electron repulsion, it takes on a bent shape.

DominicMalilay 1F

Even though it is an ion, the charges cancel so it is nonpolar.

DominicMalilay 1F

Yes, you are correct but also note that for double and triple bonds they would also have pi bonds.

DominicMalilay 1F

Hybridization is usually for a specific atom, so you have to look at phosphorous first!

DominicMalilay 1F

It would be angular!

DominicMalilay 1F

In other words, it is pretty much like resonance!

DominicMalilay 1F

Yes, and the larger the atom the more polarizable because its electrons are further from the nucleus

DominicMalilay 1F

The expanded octet rule cannot be applied to period 2 elements as well!

DominicMalilay 1F

Yes because the dipoles cancel

DominicMalilay 1F

It can be any 2 electrons that repel each other!

DominicMalilay 1F

Quizlet is a life saver!

DominicMalilay 1F

That is the charge for the individual atoms if they were to lose or gain electrons. For the BH4- ion, if you draw the lewis structure and calculate formal charges, the total charge is -1.

DominicMalilay 1F

I think the general tip is that the more symmetrical the lewis structure is, it will probably be the lowest formal charge. Of course, you can check each structures' formal charges and the one with the most formal charges of 0 would be the lowest.

DominicMalilay 1F

BaBr2 is more ionic because the difference in electronegativity is the greatest. Be is more electronegative than Ba so when bonded with Br it's less ionic. FOr example, F2 is covalent even though F is the most electronegative. It's about the difference in electronegativity, not the atoms that add up...

DominicMalilay 1F

The lewis structure should just be the same as the lewis structures for phosphate and clo3- with a hydrogen attached to the oxygen. This cancels the -1 formal charge for the oxygen so instead of po4(3-) it would be hpo4(2-) and hclo3 instead of clo3-.

DominicMalilay 1F

From end of mt1 to chemical bonding

DominicMalilay 1F

What exactly is a quantum state?

DominicMalilay 1F

that's a good visualizer, thanks!

DominicMalilay 1F

x-ray diffraction is used to determine the bond length.

DominicMalilay 1F

They are omitted because they are inert and don't need any more e-

DominicMalilay 1F

Sunday 11:59 pst

DominicMalilay 1F

No, you don't need to draw the bonds shorter or longer!

DominicMalilay 1F

I would assume a the more covalent the character, the smaller the ionization energy because it would be easier to remove an electron since the electron is further away from the nucleus.

DominicMalilay 1F

How do the water molecules interact with NaCl to dissociate them?

DominicMalilay 1F

Why do electrons have spin? Are we just supposed to take this as a truth because of experimental data, or is there deeper reasoning behind electrons having spin properties?

DominicMalilay 1F

I don't have a mnemonic device to memorize the EM spectrum, but I just remember counting even powers down from 10^-10 being x rays, 10^-8 UV, 10^-6 and 10^-4 infrared, and then 10^-2 microwaves. This is in meters.

DominicMalilay 1F

For the electron affinity of thulium given 1064 nm and an energy of .137 ev, I'm confused how to find the electron affinity in ev/atom. I know it has something to do with debroglies equation, but I cant find the right units to solve it. Thanks in advance!

DominicMalilay 1F

Id say its true because with the equation E(photon)-work function=Kinetic energy, the higher the frequency, the larger the energy of photon, so the larger the kinetic energy.

DominicMalilay 1F

The hydrogen atom has a radius of approximately 0.05 nm. Assume that we know the position of an electron to an accuracy of 1 % of the hydrogen radius, calculate the uncertainty in the speed of the electron using the Heisenberg uncertainty principle. Comment on your value obtained. I solved using the...

DominicMalilay 1F

It's still a bit unclear about the amount of material we are able to use for the midterm; I thought I heard he was going to provide a printout sheet for the formulas, but I have not gotten an email about this.

DominicMalilay 1F

I was confused initially, but remember to also square the values of the energy levels if you use the Rydberg equation.

DominicMalilay 1F

Solve this exercise without using a calculator. The reaction 6 ClO 2 (g) + 2 BrF 3 (l) → 6 ClO 2 F (s) + Br 2 (l) is carried out with 12 mol ClO 2 and 5 mol BrF 3 . (a) Identify the excess reactant. (b) Estimate how many moles of each product will be produced and how many moles of the excess reactan...

DominicMalilay 1F

When given problems like how to calculate the volume of solution to obtain mol of Na in Na2CO3, the molar bridge conversion is 1 mol Na2CO3/2 mol Na+, so you would divide by 2. However, in other problems like the number of moles of nitrogen atoms a plant can receive, the bridge conversion is 2 mol N...

DominicMalilay 1F

As a good baseline, whenever I run into problems involving the velocity/speed of something, I think of the De Broglie equation!

DominicMalilay 1F

Professor Lavelle said that the midterm material will cover all lectures until Wednesday week 3, and he also said that these include all sapling problems until Q19. However, all the problems from Sapling stated above are material we have not covered. Will we still be expected to know these?

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