CHEMISTRY COMMUNITY

sarahsalama2E

This is how i approached this problem. Because the pka is less than the pH (4.75 is smaller than 6), we know that this will dissociate. This acid dissociates into its anion which does have a negative one charge.

sarahsalama2E

perhaps, if you are finding the rate of a reaction and there are many different molecules interacting, you may need to rely on pseudo ordered rates to solve this, because pseudo ordered rates are a way in which we can find the rate of reaction when one or two reactants are in excess while the other ...

sarahsalama2E

Typically, when these values are not given to you they are 0 (usually for naturally occurring compounds, such as the enthalpy of formation for O2 0). Or if no values are given to you, you may use delta G= delta H-TdeltaS

sarahsalama2E

Remember that the most positive reduction potential will be at the cathode, getting reduced, and the more negative one will be at the anode. In this case, hydrogen is SHE and is 0.00 V. because the hydrogen electrode lies on the left, in a cell diagram, for example, that means it is at the anode, an...

sarahsalama2E

Remember that the most positive reduction potential will be at the cathode, getting reduced, and the more negative one will be at the anode. In this case, hydrogen is SHE and is 0.00 V. because the hydrogen electrode lies on the left, in a cell diagram, for example, that means it is at the anode, an...

sarahsalama2E

Hi, I attached some helpful information that I wrote regarding pseudo ordered reactions. Essentially, pseudo ordered reactions are used when you have more than one reactant and one (or two) of the reactants is in excess. Because they are in excess, we can assume their rates are essentially constant,...

sarahsalama2E

Steady-state approximation is part of the method of identifying rate limiting step--> use rate law of rate-limiting step as overall rate. The steady state approximation assumes that the rate of change of intermediate concentrations in reactions that consist of multiple steps don't change.

sarahsalama2E

In kinetics, K is dependent on temperature and activation energy. You can find this relationship by using the arrhenius equation, which is k=Ae^-Ea/RT.

sarahsalama2E

The Arrhenius Equation is k=Ae^Ea/RT. We would use the arrhenius equation when you want to show the effect of changing the temperature on the rate constant. The arrhenius equation shows the relationship between the rate constant, k, temperature T, activation energy, and A, which is the proportionali...

sarahsalama2E

A first order reaction is when the rate of the reaction depends in a linear manner on one reactant's concentration. We can see this linear relationship by plotting the equation which we utilize for first order reactions. The equation we use for first order reactions is ln[A]= -kt+ln[A0]; this is cal...

sarahsalama2E

A reaction mechanism can be thought of as the summation of elementary steps through which the chemical reaction takes place.
An elementary step is a single step in a series of "simple" steps that are indicative of how the reaction progresses.

sarahsalama2E

A third order reaction is when the rate of the reaction depends on the concentration of 3 molecules that are acting as reactants. A third order reaction is difficult to attain because in order for the reaction to proceed ALL 3 of the molecules must collide with each other at the proper speed, with e...

sarahsalama2E

It is important to note the formulaic relationship between ∆G and ∆G°.
∆G = ∆G°+ RTlnQ. Make sure you are keeping this relationship in mind when seeing what direction the reaction would shift if the concentration of products or reactants changed or etc.

sarahsalama2E

Free energy by definition is the energy available to do work, so if there is a change in free energy (i.e. an exothermic reaction or a spontaneous reaction), then that amount of energy difference is ready to do work and is therefore the maximum amount of work possible.

sarahsalama2E

Additionally, just wanted to add that you can think of the E cell as the reduction happening at the cathode - the reduction happening at the anode, as well as E cathode - E anode.

sarahsalama2E

Just to clarify, do you only have to use platinum as an electrode if there are no solids present in the cell diagram? What happens if there is solid present only on one of the sides of the cell diagram?

sarahsalama2E

You can kind of think of it as the "resonance structures" that a molecule or molecules can have, because essentially the boltzmann equation refers to the amount of different ways or microstates molecules can have.

sarahsalama2E

Work is negative when the system does it, and work is positive when work is done on the system. You can think of it like the system doing the work, the work leaves the system and is getting "Released."

sarahsalama2E

A negative cell voltage -- reaction will occur spontaneously but in the opposite direction as compared to the forward.
A positive cell voltage--reaction will occur spontaneously.

sarahsalama2E

A salt bridge basically allows the reaction to keep happening for longer and prevents the reaction from reaching equilibrium so fast. Essentially, when a batter dies, that means that the reaction has reached equilibrium.

sarahsalama2E

Things with the largest, most positive cell potential are the best oxidizing agents, and things with the smallest, most negative cell potentials are the best reducing agents. Things with the most positive want to be reduced so much because they're positive, so it makes sense that they would be the b...

sarahsalama2E

Typically, delta H values are given per mol of the reaction which can be x mol of reactant and etc, while the question might be asking for the q value per a Y mol of reactant. To find delta q, you would need to multiply the delta H which you have by the ratio (mols of reactant the question is asking...

sarahsalama2E

I think it's important to understand the reason why a reversible graph employs the integral because the pressure is not constant so the area under the curve that needs to be found/solved as pressure changes infinitesimally while volume is simultaneously changing. The integrated area under the curve ...

sarahsalama2E

is residual entropy the same thing as positional entropy? Also how does residual entropy employ statistics? Is it because of the degeneracy term that is included in the S= kblnW equation?

sarahsalama2E

when we set delta G equal to 0, we find the boiling point at which the liquid turns into a gas state. Any temperature greater than what we find once we set delta G=0 using the formula delta G= delta H -TdeltaS, causes the delta G value to be less than one (aka negative), therefore spontaneous. Remem...

sarahsalama2E

also, for an isothermal reaction, is delta u equal to 0?

sarahsalama2E

This is a follow up question, but are isothermal processes always reversible and vice versa?

sarahsalama2E

I agree with the previous response but also remember the equation qsystem +qsurroundings=0. If something is doing work, then q is negative, and vice versa if work is being done to the system.

sarahsalama2E

I think you would use the formula q=mCdeltaT, making sure to convert g to mol. Doing so would use all the information given to you in the question. Once you solve for q which is the heat for .773 mol. You divide the q by that amount of mol to get the enthalpy of reaction which is in units of KJ/MOL.

sarahsalama2E

I think because the gas is monatomic, proportionally there are more particles in the container compared to if the container were to have a diatomic gas inside it. I think this is because a diatomic molecule is larger and occupies more space so the other diatomic molecules have less space to spread o...

sarahsalama2E

I'm not sure if this is exactly what you are referring to but molecules in their most stable state, aka H2, 02 do not have bond enthalpies because they are in their most stable state, because it takes no energy to form a naturally-occuring compound that wants to be formed.

sarahsalama2E

This is just my thought process but I believe that HBr has higher entropy than HF because since F is the most electronegative atom it pulls all the electron towards it, so in that regard they are kind of concentrated/ordered in that area. Br, on the other hand, is not as electronegative as F and the...

sarahsalama2E

Some additional important things to note are the following:
when you flip a reaction, you must flip the delta H.
when you multiply reactions by coefficients, you must also multiply the delta H by such value.

sarahsalama2E

Additionally, there are differences in the types of calorimeters that are used. There are constant pressure calorimeters and constant volume calorimeters (also known as a bomb calorimeter). Constant pressure calorimetry does not have fixed volume while a bomb calorimeter does.

sarahsalama2E

Examples of state functions are the following: Pressure, Density, Temperature, Volume, Enthalpy, internal energy, gibbs free energy, and entropy.

sarahsalama2E

Just wanted to add, when doing these types of problems that you make sure you are using the proper units and canceling them out to get your final answer. Check as you go.

sarahsalama2E

enthalpy is the amount of total heat in the system. It can be associated with a particular process––such as formation, sublimation, vaporization. Also, keep in mind that enthalpy is a state function. Heat, on the other hand is a form of energy that can be transferred from one thing to another. Entha...

sarahsalama2E

I think that the sapling learning is helpful if you want to see what other kinds of problems can be asked regarding special topics. I also think that going to the workshops is super helpful.

sarahsalama2E

I would say that it's important to just know how strong acids and bases interact and how weak acids and bases interact. Be able to complete the ICE table calculations. It's also important to know that a strong acid/base dissociates or protonates completely, and for a weak acid/base it does not.

sarahsalama2E

% protonation measures how much of the initial compound was protonated (aka gained an H, whereas deprotonation is the opposite, and how much the compound dissociated). The way you figure out % deprotonation/protonation is the same and you take the final amount of H+ or Oh- created and you divide it ...

sarahsalama2E

remember that pka+pka= 14. we need the pkb values because the question asks us to arrange the BASES in order of strength based on the pkA values of their conjugate acids. the lower the pKa/pKb the stronger of an acid or a base it is. hope that helps you.

sarahsalama2E

this is related to K, but does the only way the equilibrium constant changes is with a change in temperature?

sarahsalama2E

yes pH can be negative and greater than 14, that just means it is super acidic or super basic.

sarahsalama2E

a buffer consists of a weak acid or base and its conjugate acid/base. The purpose of a buffer is that its pH doesn't change when a strong acid or base is added to it. Essentially, a buffer resists changes.

sarahsalama2E

remember that pH and H concentration are inverses, so something with a very high hydronium (h+) ion concentration, would be very acidic meaning that that its very low on the pH scale (lower is more acidic and basic is higher). So because of this logic, we know that a weak acid who has a low hydroniu...

sarahsalama2E

I believe adding an inert gas does not alter the pressure in a rxn system, because the inert gas is not really reactive and does not participate in the reaction that is happening. But, what would happen if you added a reactant that did participate in the reaction, such as a non-inert gas?

sarahsalama2E

Because as you can see in the graph the energy of the products is higher than that of the reactants in an endothermic reaction than you know that you require heat to go to this higher energy state. On the other hand, in an exothermic reaction, you are going from a higher energy state to a lower ener...

sarahsalama2E

You can tell which one to use by what's given in the question; if the values are given in brackets, then you know the values are concentrations rather than partial pressures and you should use Kc.

sarahsalama2E

The strong acids are:
HClO4
HCL
HBR
HI
HNO3
H2SO4

The strong bases are:
LiOH
NaOH
KOH
Ca(OH)2
Sr(OH)2
Ba(OH)2
---------
Everything else does not dissociate/ionize completely and is therefore a weak acid and/or a base.

sarahsalama2E

how does changing the volume affect the equilibrium constant? Say, for example the volume of the container in which the rxn is taking place is halved.

sarahsalama2E

Q is calculated the same way as k. If Q is less than K than the reaction proceeds forwards and vice versa if its the opposite.

sarahsalama2E

you omit the h20 from the expression because its liquid and also the concentration unchanged.

sarahsalama2E

As long as you do 5 per week, but make sure to do problems from different sections from the outline so that you get exposed to different types of questions and show that you have done the hw.

sarahsalama2E

concentration does have units, moles per liter, but equilibrium constant does not.

sarahsalama2E

Yes you would also leave out solids and liquids because their concentrations do not change. Also just to refresh, Q is the reaction quotient when the reaction is NOT at equilibrium and if Q <K, reaction favors the forward direction, and if Q>K, then reaction favors the backwards direction, and if Q=...

sarahsalama2E

Typically a good rule of thumb is to always assume "x" is negligible when you have a cubic equation so that you can just solve a quadratic equation as normal.

sarahsalama2E

Additionally, it's very rare that k=1 because that would mean that the two compounds which are different have the same stability.

sarahsalama2E

For example, if you have a reaction and you want there to be more product to be made you can cause this to happen by removing some of the product, the reactions wants to be as stable as possible and it does so by creating more product to reach this sort of equilibrium state. As mentioned in lecture,...

sarahsalama2E

Solids and Liquids are left out when writing the equilibrium expressions because essentially their concentrations stay the same during the reaction. Also, pure substances such as pure liquids and pure solids are left out when writing equilibrium expressions because their concentrations can't change....

sarahsalama2E

Essentially equilibrium concentrations are the concentrations that you determine using the ice table.

sarahsalama2E

Yes, as mentioned above Q is not the same as K. Q is the reaction quotient and K is when the chemical reaction is at equilibrium ONLY. If q is less than K, then the reaction will proceed to the right and if q is greater than K then the reaction will proceed to the left.

sarahsalama2E

I am wondering if it is because the H that is attached to one of the O, so then the dipoles wouldn't cancel?

sarahsalama2E

I had a question regarding a question about HNO3, When I drew the lewis structure I got that it is a trigonal planar structure, and the N is sp2 hybridized. Because all the atoms attached to the N are the same (they are all O), and the structure is trigonal planar, I thought that that the molecule o...

sarahsalama2E

pi orbitals are also involved in the mixing of orbitals that occurs when the creation of hybridized orbitals happen. It is important to note that a pi bond occurs between two overlapping p-bonds, and no s-bonds, to my knowledge, are involved in pi bonds. So, for example a pi bond between two carbons...

sarahsalama2E

I think a good way to go about these problems when you are trying to see what kind of polydentate a particular ligand is, is to first draw the lewis structure. If you see that the two attachments are on roughly the same side, then it can be bidentate, etc.. If you can visualize the ligand acting as ...

sarahsalama2E

Yes you would look at the same characteristics to determine the strength of a base. Essentially a stronger base, wants to accept a proton easier, and will give off more hydroxide ion.

sarahsalama2E

what is the difference in the chemical structures of hemoglobin and myoglobin? Both consist of the same heme complex and a binded protein correct?

sarahsalama2E

Seeing if OH- or H+ ion is produced is a way to see if the salt given will act as an acid or a base in water. You must write out the reaction in order to see this.

sarahsalama2E

Are polyprotic acids stronger or weaker with the more hydrogens that they have? I thought that if something has multiple hydrogens it is more likely to give off a proton, therefore dissociates more, and is therefore stronger of an acid.

sarahsalama2E

Where can I find the acid rain problems in the textbook?

sarahsalama2E

Potential options to reduce acid rain are the following--> reducing the use of fossil fuels (i.e. burning of coal), using renewable energy sources, coal burning plants, etc. Keep in mind that acid rain can be neutralized if it reacts with something that is more alkaline (closer to the very basic sid...

sarahsalama2E

Also, remember that typically shapes that have lone pairs are usually always polar even if all the attached atoms are the same; however AX4E2, square planar, is an exception to that rule because it becomes nonpolar because the dipole moments cancel. You can see this if you draw the 3-D shape.

sarahsalama2E

I remember in lecture that the most stable configuration for a ligand was LP-SPACER-SPACER-LP. But i was wondering if it's more stable/better for a ligand to have only sigma bonds (to allow for rotation?) or is pi bonds just as stable?

sarahsalama2E

how do you determine if a ligand is polydentate? i.e. if it is monodentate, bidentate, polydentate? Do you look at how many lone pairs it has (i.e. that function as bonding sites?). Also, when a ligand bonds to an atom, if it has multiple attachments (i.e. its polydentate), can it only bind on the s...

sarahsalama2E

would someone be able to provide examples of when you would use these examples? I understand the concept but I actually haven't seen any problems in the HW or have come across any problems that deal with this...

sarahsalama2E

Yes, as mentioned above intensity is NOT the determining factor as to whether or not electrons will be ejected from a given material, but it is rather the frequency as the frequency is the determinant of whether or not the threshold energy, or the work function will be met which is needed to eject e...

sarahsalama2E

I am a bit unclear on how to determine the hybridization of lone pairs in a given structure. For instance, in formic acid, I understand the hybridization of all the bonds, such as the C-H bond is sigma and is (H1S, C2SP2), but why is the lone pair on the oxygen that is in between the C and the H hav...

sarahsalama2E

if all the atoms attached to the central are not the same, then the molecule is polar. As you can see in the tetrahedral diagram, the differing attaching atoms creates dipole moments, resulting in the atom being polar as a whole.

sarahsalama2E

en = Ethylenediamine (abbreviated as en when a ligand) is C2H4(NH2)2. (first photo shown)

edta= Ethylenediaminetetraacetic acid; C10H16N2O8

sarahsalama2E

the weaker the bond between the atoms in the acid, the stronger of an acid it is because that means it dissociates easier. If you have a stronger bond between the atoms, you would then have a weaker acid because that acidic compound is less likely to dissociate completely. When looking at the relati...

sarahsalama2E

make sure you are putting adequate parenthesis.

sarahsalama2E

is the only way to determine if compounds are acids, bases, or amphoteric is if you draw the lewis structure for them and see if they give off or accept a lone pair? or is there another way to do so?

sarahsalama2E

When it is a transition metal, because the oxidation number can change. So, denoting the oxidation number through roman numerals and parentheses is necessary to denote exactly what compound you are talking about.

sarahsalama2E

Cisplatin has the Cl atoms on the same side while trans-diamine dichloro-platinum (ii) has them located on opposite, or diagonal sides from one another. Cisplatin is a well-known chemotherapy drug that works by forming a coordinate compound with DNA. Cisplatin binds to the exposed N in guananine and...

sarahsalama2E

TM complex --> transition metal --bond with ions or molecules linked
organometallic complex--> compounds with carbon-metal bond

sarahsalama2E

I think so yes,
Cr--> assists insulin in control of blood sugar
Fe--> myoglobin, hemoglobin, electron transfer in the oxidation of carbohydrates, proteins, fats (respiratory chain)
Co--> vitamin B12
Mn, Ni, Cu, Zn--> critical for enzyme function

sarahsalama2E

when determining what can form a chelating complex, should the lone pairs be as close to one another as possible so that way it can attach to the atom on the same side? do the attachments have to happen on the same side of the atom always?

sarahsalama2E

how do you determine the number of dentate sites on a ligand?

sarahsalama2E

Is CH2I2 polar or nonpolar?

sarahsalama2E

Is CH2I2 polar or nonpolar? the lewis structure has the I atoms opposite from each other and the H atoms opposite from each other.

sarahsalama2E

Would CH2I2 be polar or nonpolar? if the picture in the problem has the I opposite from one another.

sarahsalama2E

this is a question about polarity: but just wondering would CH2I2 be a polar or nonpolar molecule?

sarahsalama2E

I thought T-shaped had more than one bond angle does it not?

sarahsalama2E

you can think of molecular geometry as the actual (bonded vs lone pairs) and the electron geometry as the "parent" structure, so if its AX4E2, it would be octahedral, and the molecular geometry would be square planar.

sarahsalama2E

what is an acceptable justification to the question--why does X compound have a higher boiling point?

sarahsalama2E

does the bigger the atom mean the stronger the ldf and dipole-dipole forces?

sarahsalama2E

doesn't the strength of london disperson forces take priority over dipole-dipole forces when determining which compound has a higher boiling point?

sarahsalama2E

if something had hydrogen bonding, it would have a high boiling point correct?

sarahsalama2E

CHI3 has a higher boiling point because it has stronger/more london dispersion forces. Although F is more electronegative than I, the strength of london disperson forces takes precedence when comparing boiling, melting, freezing points, and etc. Because I is a bigger atom than F, it has more surface...

sarahsalama2E

What are the bond angles for T-shaped?

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