CHEMISTRY COMMUNITY

Bella Bursulaya 3G

The reason we have to do an extra process for if the second step is slow is because often times we have an intermediate, so we need to get rid of it. This makes sense because we never add intermediates to the reaction, they just form in the middle of the reaction. Therefore, they shouldn't be includ...

Bella Bursulaya 3G

He got it from the coefficient in front of NO2 (i.e. 2) and 1/a where a = 2 is how he got it.

Bella Bursulaya 3G

Kinetics was fun! It was most fun because you can see how topics can relate to your field of study.

Bella Bursulaya 3G

K = k/k' which means the rate of the forward reaction over the rate of the reverse reaction, due to how the concentrations cancel out!

Bella Bursulaya 3G

Focuses on everything from class, although I don't know if some things will be focused on more than others.

Bella Bursulaya 3G

Definitely going to take some time to just relax and exercise. Haven't been able to do that as much lately.

Bella Bursulaya 3G

I found E˚ based on the way the reaction was written (Ti is being reduced so it is the cathode as an example) and then used lnK = nFE˚/RT to solve.

Bella Bursulaya 3G

Pt is often used when there is no conductor solid. For example, if there was Fe+3 (aq) in solution, you'd still need to add Pt (s) because you need a solid conductor of metal to transfer electrons.

Bella Bursulaya 3G

I think if they write out the actual equation, you can see which one is being reduced and label it as the cathode. If asked which one would create a spontaneous reaction, you'd compare E˚ values and see which one is more positive and label it as the cathode.

Bella Bursulaya 3G

K is just the rate, so it will always be positive. You can think of it as negative when something is decomposing, but the actual sign needs to be positive.

Bella Bursulaya 3G

Strange. I am also getting the same answer as you. Make sure it is asking for the reaction in basic solutions? That is the only error I could think of. Maybe Sapling is just being glitchy.

Bella Bursulaya 3G

To add on the other answer, I believe that the more positive E˚reduction is, the more likely the substance will be to be reduced and the less positive it is, the easier it is to oxidize.

Bella Bursulaya 3G

Remember that E doesn't get affected because if we increase the amount of "stuff" in a redox reaction, we will increase both the potential energy and the charge and therefore the ratio will remain the same.

Bella Bursulaya 3G

I remember when I did this problem, I forgot to add OH- to both sides, not just one. That may be what is happening here, but I was left with 2 H+ on the right side of the equation, so I added 2 OH- to the right and left sides of the equations. Hope that helps a bit!

Bella Bursulaya 3G

I think as long as your reactants and products are on the right side, it doesn't matter what order the individual reactants/products are in. I am referring to balancing equations, so I am not sure if you are referring to something else.

Bella Bursulaya 3G

If there was no salt bridge, the charges from the reductions and oxidations build up (positive on the side of the anode and negative on the side of the cathode) and therefore the reduction potential is much smaller. The larger the difference in charges, the easier it is to transfer electrons. Theref...

Bella Bursulaya 3G

If you can do X(final) - X(initial), it is usually a state function! That's how I usually think about it.

Bella Bursulaya 3G

When there are constant pressure conditions. ∆H = q under these conditions because if the pressure is constant, the volume is changing, and therefore the heat put into the system is used for expansion work. Therefore, the total q energy supplied will equal the ∆H of the system (assuming no other typ...

Bella Bursulaya 3G

∆U is always 0 for an isolated system, because if you think about it, an isolated system cannot exchange matter or energy with its surroundings. Therefore, its internal energy doesn't change. It's interesting to think, however, if this is only theoretical. Most "isolated" systems still los...

Bella Bursulaya 3G

The Van't Hoff equation is used when you have two different temperature values, and you want to find the K at the new temperature. -RTlnK is used when you want to find the K value at a specific, constant temperature. If your temperature is not changing, then you can use it.

Bella Bursulaya 3G

If Q < K, then you know the reaction will proceed in the forward direction (towards products) because if Q is less than K, the denominator of Q is larger. Since we know the denominator is the reactants, this means that there are more reactants than there should be at equilibrium. Using the same logi...

Bella Bursulaya 3G

Open systems allow for both matter and energy to be exchanged with the surroundings. An example of this is a coffee. The cup allows for the exchange of heat with surroundings, and you can add in milk or sugar. A closed system allows only for energy to be exchanged. Think about that coffee cup and th...

Bella Bursulaya 3G

You can see in this case that 1-pentene has a less rigid structure because it is not confined to a certain shape and is more flexible, and therefore has more possible positions and should have a higher entropy.

Bella Bursulaya 3G

You need to use the equation ∆G = ∆G˚ + RT*lnQ, You are given ∆G˚ and the values to find Q, so plug those in and you should get ∆G!

Bella Bursulaya 3G

Basically you need to convert from W to J and then your enthalpy is your J divided by your mol (take the grams and convert them to moles). Then you have ∆H(vap). In order to find ∆S(vap), you need to use the equation ∆S = ∆H/T and make sure that your T is in Kelvin and not ˚C

Bella Bursulaya 3G

First we need to think about this equation: ∆G˚ = ∆H˚ – T∆S˚ Spontaneous at all temperature: ∆H = – and ∆S = +. If you have a negative ∆H, and a positive ∆S, you will be subtracting a negative value from a negative value, leading to a negative value overall and therefore ∆G˚ is negative. This means ...

Bella Bursulaya 3G

So basically one of these processes is reversible and the other isn't. Therefore, you need different equations for work. For reversible, you would use w = -nRT*ln(Vf/Vi) and for irreversible expansion w = -Pex*∆V. You can use the initial conditions given to find n!

Bella Bursulaya 3G

Yep you can change R into kJ instead of J! It works.

Bella Bursulaya 3G

Depending on the units given, you'll use different R values OR you could convert other things in your equation to get them to the same units as your desired R. Just be careful when using 0.0821 L*atm/mol*K because you need to use 101.325 J = 1 L*atm to get J, while 8.314 J/mol*K will give you J righ...

Bella Bursulaya 3G

I don't think an irreversible expansion can ever do more work, because a reversible expansion by definition is the infinitesimal decrease of external pressure, so the gas does MAX amount of work. There can never be a case where irreversible does more work.

Bella Bursulaya 3G

Vapor and gas are the same thing.

Bella Bursulaya 3G

Yes the temperature must be held constant and therefore be isothermal.

Bella Bursulaya 3G

I think we kind of do, because it says 0.5 L, and the L of reactants add up to create 0.5 L. Since it's a calorimeter, we know that q(cal) = -q(rxn) so therefore we don't really need any of the other things. We just need to make sure that there are 0.5 L because that is what the calorimeter is calib...

Bella Bursulaya 3G

Your temperature is wrong. The change is 20.1 K, therefore that is the ∆T. You do not need to subtract anything for the T. Hope that helps!

Bella Bursulaya 3G

Usually about a week!

Bella Bursulaya 3G

Strong acids are: HCl, HI, HBr, H2SO4, HNO3, HClO4, and HClO3. Everything else in this class is a weak acid. Strong bases include the first and second groups of metal oxides, such as NaOH, and Ca(OH)2. Everything else is a weak base. These should be memorized, especially in the context of acid base ...

Bella Bursulaya 3G

I believe you can ignore the Ka2 if it is << Ka1, and this is true for most acids EXCEPT H2SO4, so just use Ka1 and Ka2 for that acid. This is because H2SO4 is strong, so it's first Ka essentially goes to completion, while the other acids are weak, so H+ does not equal HA. And the Ka2 is smaller bec...

Bella Bursulaya 3G

The way that I understood it is that at the time the water reaches 100 ˚C, the energy supplied doesn't go into raising the temperature of the gas, but rather the bonds between water molecules so that they may be converted to gas molecules. Then, when all the liquid water molecules have been converte...

Bella Bursulaya 3G

Enthalpy is the heat or energy contained, such as in bonds (where if ∆H is negative, the reaction is exothermic and so the bonds have lower enthalpy than the reactants meaning they are more stable). Entropy is the measure of disorder. According to the laws of thermodynamics and Muse, the entropy of ...

Bella Bursulaya 3G

Vacuums can be isolated systems, but not all isolated systems are vacuums.

Bella Bursulaya 3G

When Q = K

Bella Bursulaya 3G

I think that spectator ions are just there in solution, but they are present on both sides of the equation. So if you had Na2SO4, you would break it up into 2 Na+ and SO4-2 and those are ions, which if they appear on both sides of the equation they can cancel out. It's often called a net ionic equat...

Bella Bursulaya 3G

Work done on a system is positive, and when it does work it is negative because it is losing energy. Are we supposed to know q and w for the first midterm exam?

Bella Bursulaya 3G

Nope! The addition of an inert gas might slow down the reaction of equilibrium (i.e equilibrium will take longer to achieve because of competing collision) but it will not change equilibrium because the concentrations of the gases that are reacting do not change. Inert gases hardly ever react, so th...

Bella Bursulaya 3G

I believe so for both, but on our midterms and final, Lavelle doesn't ask you to round everything to the exact sig figs (for example, there won't be answer choices like A). 2.00 or B) 1.99. It'll be obvious if your answer is there or not, but overall I believe they do impact sig figs.

Bella Bursulaya 3G

Gases because they are the only ones that have partial pressures. Aqueous, liquids, and solids do not have partial pressures so increasing the system's pressure won't do anything to them or their concentrations.

Bella Bursulaya 3G

Happened to me as well. Make sure at the beginning of any problem to check if the equation is balanced or not. Even if there are already numbers in front of the molecules, this may be a trick so always double check!

Bella Bursulaya 3G

We know that in water, the concentration of H3O+ is 1.0 x 10^-7 M and the concentration of OH- is also 1.0 x 10^-7. These two concentrations multiplied together give Kw. In water, if an H3O+ molecule is formed, then an OH- one must be formed as well. Therefore, their concentrations must be equal.

Bella Bursulaya 3G

Yep, only for gases because remember that solids and liquids cannot have partial pressures. Therefore, partial pressures only apply to gases.

Bella Bursulaya 3G

K can be changed with temperature! It doesn't change with pressure or a change in concentration but temperature is a different story. Heat is like a reactant in an endothermic process, so adding heat would shift the process to the right (the forward reaction) and favor products, leading to a larger ...

Bella Bursulaya 3G

Yep! Just memorize them! Although anything organic will be a weak acid, and for bases the only strong ones are with cations from groups 1 and 2. Everything else is weak. I think there are some strong acids that we do not memorize in this class that exist in nature, but we don't really focus on them ...

Bella Bursulaya 3G

I believe you now have the equilibrium concentrations, but then need to add 1 to NO2, so now your equilibrium concentrations become your initial, and that NO2 + 1 mole is also your initial. Then set up an ICE box and solve. However, also remember that you are adding more product, so the reaction wil...

Bella Bursulaya 3G

well if the concentration of a reactant or product increases or decreases, the system will shift to create equilibrium again. Remember that k is just a constant of product ratio over reactant ratio, so there may be more or less reactants or products, but their overall ratio will remain the same. The...

Bella Bursulaya 3G

As others have said, the concentration of x is both the concentration of CH3COO- and H3O+ due to their coefficients. If it was 3 CH3COO-, it would be initial - 3x.

Bella Bursulaya 3G

I agree with the above poster. After doing some problems, I realized that even if the Kc constant is really small, Q can still be smaller, so overall the products are not as stable as the reactants but there still needs to be equilibrium, so products are formed even if they are not favored. When equ...

Bella Bursulaya 3G

That's a way of doing it I think! I personally stumbled upon this question as well, and what I did was I took the equilibrium concentrations of all products and reactants and made that the initial concentrations, and then just changed the initial concentration of what you are asking, in this case, I...

Bella Bursulaya 3G

Inert gases are the nobles gases, named inert because they do not react easily. It's not a gas that isn't in the reaction, because if you add another gas, it may somehow react with the other gases in the equation and form different products. However, inert gases are very unlikely to react with the o...

Bella Bursulaya 3G

Yes it will be covered later on in thermodynamics. For right now, I believe it is used to figure out if a reaction is exothermic (and Gibbs free energy is negative) or endothermic (where Gibbs free energy is positive).

Bella Bursulaya 3G

Yep! you need to manipulate the equations. Then you need to cancel out like terms until you get the original equation. Whenever you manipulate something, you must change the K value. When multiplying, say by 2, you need to raise K to the power of the number you multiplied, so K^2. If you flipped the...

Bella Bursulaya 3G

P is pressure, and the SI unit is Pascals but often we use bar or atm (be careful to look out for this because it will change which gas constant R you use) V is volume in liters or m^3 n is the moles R is the gas constant (varies with pressure and volume) T is the temperature (in Kelvin) conversion ...

Bella Bursulaya 3G

If the moles were equal, the equilibrium wouldn't shift anywhere. Also, if the problems says that the pressure is increased by adding an inert gas, the equilibrium wouldn't shift either, regardless of whether there are less moles on one side of the equation. I believe that the pressure must change d...

Bella Bursulaya 3G

Their concentrations could be equal, but that is not the rule for equilibrium. The concentration of reactants could be 0.1 M and the concentration for products could be 0.6 M. The key is that the forward reaction and reverse reactions are occurring at the same rate. I'm not sure about a direct examp...

Bella Bursulaya 3G

I'm not sure if this one has been done before :D Cop: Do you have any idea how fast you were going? Heisenberg: No, but I know exactly where I am. Cop: You were doing 55 in a 30. Heisenberg: Great, now I'm lost. Cop: What's in the trunk? Schrodinger: My cat. The cop opens the trunk. Cop: Your cat is...

Bella Bursulaya 3G

It's a cation and an anion that are attracted to one another through ionic bonds! Such as NaCl, KCl, etc

Bella Bursulaya 3G

It is different in the name. ONO is nitrito while NO2 is nitro.

Bella Bursulaya 3G

Lewis acids and bases have to do with electrons, while the Bronsted definition includes H+ and OH- ions. Lewis acids accept electrons, Lewis bases donate electrons, Bronsted acids donate H+ and form H3O+ in solution and Bronsted bases accept H+ ions and form OH- ions solution.

Bella Bursulaya 3G

The larger the Ka value, the stronger the acid because this means that the products outweigh the reactants, and the lower the pKa.

Bella Bursulaya 3G

Well, the actual wavelength number will depend on the n value, so yes, the n value determines which series you use.

Bella Bursulaya 3G

You ate when the ligand has a negative charge on the outside of the brackets.

Bella Bursulaya 3G

H2O in the air reacts with SO2, CO2, and NO2 to form acids that then dissociate and lower the pH of the water. It is because of pollutants, and some things that can be done is to lower CO2 emissions and use clean coal instead of dirty coal.

Bella Bursulaya 3G

Just to also add on, I believe that small, positively charged elements, such as Al+3, create a more acidic solution and are known as Lewis acids because they pull electron density towards them, and make the OH bond easier to break.

Bella Bursulaya 3G

Your original concentration was 0.366 mol/L, meaning that if you took out 25 mL you would have 0.00915 moles. Then, 0.00915 moles/.125 L, because the total volume is 125 mL, not 125 + 25 mL, since the volume flask cannot exceed 125 mL, giving you a 0.0732 M. Hope this helps!

Bella Bursulaya 3G

Nope! I think it would be impossible to know. When given H2O, it could be in the gas, liquid, or solid phase but unless we're given the state or temperature, we won't know just from the Lewis structure (because remember the different states are based on intermolecular forces, so the overall shape of...

Bella Bursulaya 3G

Hi! Yep, Lewis acids accept electrons! Acids will have a different pH depending on what they are dissolved in. Remember that it is not HCl that is acidic, but it acts as an acid, meaning that in water there will actually be very little amounts of HCl and more H+ and Cl- ions. In another substance, t...

Bella Bursulaya 3G

I think you also have to include sodium at the beginning. It would be sodium triamminetrichlorocobaltate (II) (Co has a +2 charge because you get a -1 overall charge outside the brackets due to only a +1 charge from Na to balance it out, and the 3 Cl- atoms give a -3 charge, meaning that to get an o...

Bella Bursulaya 3G

I am pretty sure we'll need to memorize that list. As for the toolbox, we won't be given that; we need to memorize the formula to how to write the names of chemical compounds.

Bella Bursulaya 3G

I think (OH2) is more common, but since the final is multiple choice, you don't have to worry about it because you'll see how it'll be written.

Bella Bursulaya 3G

It's a compound that can act as an acidic or a basic compound, depending on what it interacts with. For example, water is amphoteric because it can behave as an acid or a base. Hope this helps!

Bella Bursulaya 3G

Polar bonds are bonds in which the electrons are not shared evenly. Such as in C-H, C will pull the electron from H more strongly than H pulls the electron from C, so C will have a partial negative charge and H will have a partial positive charge. A nonpolar molecule can have polar bonds, because if...

Bella Bursulaya 3G

So for seesaw, you have 5 regions of electron density with 1 lone pair, and you have 5 regions of electron density with 2 lone pairs for T-shape. The angles between the equatorial bonded atoms facing you and facing away from you is less than 120 degrees, and the angle between one of the axial atoms ...

Bella Bursulaya 3G

Because there are lone pairs, they repel the bonded atoms/electrons more strongly. In NH3, that lone pair will repel the H atoms more strongly and push them together, creating smaller bond angles between them. In CH4, the repulsion levels are the same between all bonded electrons, so the shape is te...

Bella Bursulaya 3G

Yea you got it! n is the energy level, and it can be 1, 2, 3, etc. Such as when we write 2p^2 for C, we write 3p^2 for Si. It shows the relative energy levels of the valence electrons, and it would be the same for the hybridized orbitals.

Bella Bursulaya 3G

Yes! When decimals are included, it means that you count everything before and after them. 40.0 would have 3 sig figs, and 40. would have two. 4.0 would also have 2.

Bella Bursulaya 3G

I have the TI-89 and I really like it! But I also have the TI-84, and it's not my favorite but it gets the job done just as well! I just use a periodic table in a chemistry book. I'm not sure why the numbers you're using would be that off. Hope this helps!

Bella Bursulaya 3G

The ionization energy increases going to the right because the atoms become more electronegative and want to hold onto their electrons more tightly. It decreases going down a group because the electrons in the outer shell are not held onto as tightly and can be removed more easily.

Bella Bursulaya 3G

There can be polar bonds, but if they all cancel each other out, overall the molecule will be nonpolar. It's like if you are pulling a wagon one way and your friend is pulling it the other way. You're pulling different ways but you cancel each other out and the wagon doesn't move.

Bella Bursulaya 3G

I don't think so, because that might just be a coincidence, but an interesting observation! I don't think that things fit that nicely in reality however.

Bella Bursulaya 3G

I believe it is the mole of H bonds being bonded. He said that if there were 20 kJ/mol of energy per something, and there 10 H bonds for that molecule, there would be 200 kJ/mol overall, so that implies that it's per mole of bonds. I could be completely wrong so please someone feel free to correct me!

Bella Bursulaya 3G

If both of the electrons that fulfilled the octet from the base come from the same element, it will be a coordinate covalent bond. Like in NH3 and BF3. Both electrons to fulfill the octet for B come from N, so it will be a coordinate covalent bond.

Bella Bursulaya 3G

A coordinate covalent bond is one formed between a Lewis acid and a Lewis base, but also the electrons that are from the base come from one atom, not any more.

Bella Bursulaya 3G

Hi! The valence electron shell are the electrons in the outermost shells. So in sulfur, for example, the core electrons are the electrons leading up to the nearest noble gas, in this case Neon, and the rest of the electrons are the valence. I also wanted to say that for transitional metals, you need...

Bella Bursulaya 3G

I think that the p orbital that you are talking about has to do more with quantum numbers rather than valence electrons? Correct me if I am mistaken. Yeah, I agree. I think this has to do more with the shape and the wave function, but I'm not positive Regarding the p orbitals, I mean they fill up w...

Bella Bursulaya 3G

I think that valence electrons are every electron after the noble gas, but do we include d electrons? In the textbook problems, it sometimes does and sometimes doesn't include the d electrons as the valence. For example, how many valence would Sb +3 have? It's electron configuration is 4d105s2, so w...

Bella Bursulaya 3G

HCl would have greater ionic character, since Cl is more electronegative. Because it is more electronegative, it pulls electrons in more closely to it, and the electrons are shared less equally (i.e. less covalently). Therefore, it would have an ionic character higher than that of HI. You can also t...

Bella Bursulaya 3G

Typically, London forces are nonpolar because they don't have permanent dipoles, and nonpolar molecule interactions can only do so through dispersion forces. Look at whichever molecules are nonpolar and those should be the correct answers!

Bella Bursulaya 3G

You can argue that all bonds are just electrostatic forces of attraction. In bonding, there is no solid thing linking the two atoms. They're the same bonds, just intramolecular are stronger than intermolecular.

Bella Bursulaya 3G

Yes they exist when 8 electrons are involved in bonding, but are mostly found in the d block elements. I believe there are also quintuple bonds.

Bella Bursulaya 3G

When atoms are far away from each other on the periodic table, they will most likely form an ionic bond, such as Ca and Cl. When they are closer, they will most likely form covalent. I do want to mention that no there is no true ionic or covalent bond. Each of these characters will have a little bit...

Bella Bursulaya 3G

Look to see which one would have the lowest formal charge, but also it would make sense for the higher ionization element/more electronegative element to get the partial negative charge if you couldn't form a double bond. Also you need to make sure that Cl wouldn't have a + charge, because Cl is ver...

Bella Bursulaya 3G

Yes! Energy is released when bonds are formed, and energy is required to break them. This is why ATP is important; it is not the breaking of bonds of ATP that releases the most energy, but the energy formed when ATP breaks and then recombined with other molecules to form bonds.

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