CHEMISTRY COMMUNITY

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E naught is E in standard conditions.

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Yes, you do need to use the coefficients as exponents.

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Half-reactions are most likely going to be things we will be asked to produce.

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I like to think the order in the cell notation is directly relative to the order in the actual half-cell. The electrode is furthest away from the salt bridge, the solution is closer, and the ions that can travel through the bridge are the closest.

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When we are given that a galvanic cell consists of two chambers with solution x and y respectively, how do we determine which is the anode and which is the cathode?

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They're the same thing! The #of electrons divided by avogadro's number = moles of electrons.

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Standard Gibb's free energy is the gibbs free energy at standard conditions for temperature, pressure, etc.

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A salt bridge essentially lets the the negative ions on the cathode side to travel over to the anode side, so that the electrons will continue to flow towards the cathode.

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Each question will probably provide the relevant/necessary values. Looking at how this course is laid out, there's no way we would be expected to memorize any of those values, and definitely not all of them.

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Think about which solution already has an abundance of H^+ and which has an abundance of OH^-.

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Basically like,,i a situation isn't doing any work, the internal energy is the same as the enthalpy, because enthalpy is the heat energy stored in a system.

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Same thing. If a chemical is usually in a liquid state, one might refer to the gaseous form as a vapor but the definition of both is identical.

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Bomb calorimeter = constant volume.

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Hfusion is for the phase change between solid and liquid.

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Honestly you can always use units to figure it out. Whichever constant has the desired units is the one to pick.

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Steam will do more damage because there is more energy in the steam than in liquid water of the same temperature.

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Sorry to ask, but I'm still confused as to how to calibrate a calorimeter and how to use that value.

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If T is represented just as T, not as delta T, then that means T is a constant for a specific situation and the question should give it.

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Yes K is always the equilibrium constant we learned about in 14a.

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Anything "naught" is typically at standard conditions. Most things don't occur under standard conditions, so you would have to use deltaG instead. Think of deltaGnaught as like, the unobtainable ideal.

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Basically, use the equeation deltaG=deltaH - TdeltaS. The delta G value will tell you if the rxn is spontaneous or not.

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Entropy will always have a net increase, no matter what happens. The disorder of the universe is constantly increasing.

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Is it ever possible to create a system that is truly, 100% isolated? I feel like it's impossible to fully shield a region from the outside universe without at least a microscopic amount of energy entering and exiting.

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Honestly whenever you aren't sure which constant to use, always refer to the units and find the one that will give you the proper units in the end.

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Q is heat, and it is usually just a single number, where H is enthalpy and it's usually thought of as change of H.

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CO2 is linear, because it's nonpolar.

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No they can't be. All matter has the ability to take in heat.

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What's the best way to remember how to calculate the specific heat capacity of a calorimeter?

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If the same specific heat value appears on both sides of an equation you can just divide them out.

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I believe it goes on the side that is losing heat, aka exothermic. Like, the water is negative if an ice cube is dropped into it.

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Na+ doesn't affect the pH.

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10^-7, and that is important because it means OH- is also 10^-7.

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Use the ICE box whenever you're trying to figure out how concentrations change before and after a reaction reaches equilibrium, basically.

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This one is tricky because you have a lot of moving parts. But basically, if you can lockdown the BH+ value, you just add that to B.

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The percent ionization is like, the percent of acid turned into the conjugate base when the reaction reaches equilibrium. So, basically, you take the concentration of whatever the conjugate base is, divide that by the INITIAL (before the reaction started [ in this case that is 0.1029M]) concentratio...

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A solvent like H2O is usually in such a large excess that it's affect on the system is so minimal it's a waste of time to include it.

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If the reaction is going towards products, there will be positive X's on the product side and negative on the reagent side. The opposite is also true.

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Use the positive value from the quadratic equation, not the negative one.

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Yes. The temperature can change, but that will result in a different K value. However, if the temp were to suddenly change, and all conc.s remained constant, q wouldn't change.

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Q is calculated the same way as K, just when the system is not at equilibrium.

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All of that is correct. A lot of those phrases are simply different ways to personify reactions, which makes it easier to comprehend. When K is larger than 1000, there is simply more product than reagent. One could describe this in a plethora of ways, by saying the reaction is product heavy, it sits...

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Temperature does change K. The only two variables that can change K are temperature, and the exact reaction that is occurring. Change the reaction or change the temperature, you change K.

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Catalysts don't change K, because they simply change the speed at which a reaction takes place, and they lower things like activation energy. The concentrations of species with or without a catalyst will remain constant.

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Partial pressure is the pressure a specific gaseous species is responsible for contributing to the total pressure of a system.

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R is the universal gas constant. It will be given on exams as a part of the constants and equations sheet. Lavelle doesn't expect us to memorize it.

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Mauricio Maravilla 3C wrote:If it can accept more than one proton

If it's a base^^. If an acid is polyprotic, it can give up 2+ protons.

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A base or acid is polyprotic when it can surrender (acid) or accept (base) more than one proton. For example, H2SO4 can become HSO4^- which can become SO4^2-.

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HF isn't a strong acid because F bonds so tightly to H, that it is hard to get the two to separate. It's still a super dangerous compound though.

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Strong acids want to give up their proton more willingly. So, I suppose its possible to say that weak acids have a more stable structure because they are less willing to surrender a proton.

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Amphoteric compounds rely on their environment. So, if there is a more common environment for a chemical to exist in then yes it can be considered to most likely act basic or acidic.

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I'm pretty sure dentate literally means "teeth" in French. In this context, it means how many sites a molecule has that can bind to the metal ion in a coordination compound.

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A coordination number is basically the amount of bonds the metal ion has with ligands.

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Ligands are the molecules found in the brackets, or a coordination sphere, of a coordination compound. They are basically just the things that are directly connected to the metal ion. If a ligand is present, I suppose that just implies that you are working with a coordination compound.

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Most coordiantion compounds are either created by humans, or produced by organisms. So as the other commentor stated, heme is probably the most abundant considering how many organisms rely on it and how much each organism produces.

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They can have numerous biological applications! Complex ions are used by your body naturally, can be used as medication, etc. etc.

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H2O is bent, because of the 2 lone pairs on the oxygen.

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Unfortunately, shape alone wouldn't give you enough information. You would also need to know the lewis structure.

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A delocalized pi bond is when there are multiple resonance structures for a molecule, and they include double bonds that are in different positions. You could recognize this in a structure like benzene with rings.

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Yes. Count all the bonds, and thats the number of sigma bonds. Then count the additional bonds in double or triple bonds and that's the number of pi bonds.

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I'm pretty sure the only place it can bond to in a dna strand is two guanines, and that's why Lavelle named it something-to-do-with-guanine inhibitor.

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Yes, london dispersion forces always exist when molecules are interacting.

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The ONLY angle found would be 180.

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Lone pairs have a larger region of electron density associated with them, because they are only being pulled towards one atom, rather than "stretched" between two. This gives them the ability to "diffuse" through space more than bonding electrons.

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I also had this same question. I believe that axial atoms are ones that form about a 90º angle; equatorial atoms are ones that form an angle smaller than 90º. However, what I'm confused on is whether the angle is to the central atom or to another molecule. I believe the angle is to other atoms surr...

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I'm pretty sure they're both very interchangeable terms.

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No. H-H, is not a hydrogen bond. It's just a normal bond between two hydrogens.

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He meant that in its lowest energy state, nitrogen has 8 electrons, a complete octet. When not part of a compound, nitrogen has only 5 electrons in the valence shell.

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Zeff refers to the effective nuclear charge. If you are trying to calculate the charge the nucleus has on the valence electrons, you need to consider A how many protons there are and B how many other electrons there are between the valence electrons and the nucleus. These electrons are "shieldi...

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They aren't a bond, but they are an intermolecular force. They're the weakest because they only exist thanks to induced dipole-induced dipole interactions, which are inherently weak, if you compare them to any other interactions.

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If you're drawing a lewis structure and notice there's a single lonely unpaired electron.

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Elements in the 3rd row and beyond that use d-orbitals can do some funky stuff and have expanded octets.

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The number of valence electrons does have to do with which group, generally. This is true for elements that aren't in the middle chunk of the periodic table.

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Delocalized meaning the electrons aren't involved in just one bond between two atoms, but that the electron density clouds are involved in multiple places throughout the molecule.

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No they have the shortest wavelength.

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ħ, or h bar is simply h/2pi. h as you know is plancks constant. h bar exists just to save space. So (1/2)ħ is the same as h/4pi.

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We know we have to use the Heisenberg equation when we are asked for uncertainty in momentum or position. When given states of an electron we would probably be asked to use the Rydberg equation, like you described.

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Anions have a larger atomic radius than cations, because the added electron decreases the net charge of the nucleus, i believe.

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I noticed that when an anion is formed in a lewis dot structure, they get a bracket around the chemical symbol with 8 electrons shown as their new octet. Are we supposed to only use brackets in lewis structures for anions or do other species get them too?

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This is, more than anything, a convention. We could set some random letter to equal h/4pi, but regardless you'd have to plug h/4pi into your calculator each time, because pi is an irrational number. You COULD simply memorize a simplified version of h/4pi, but then your answers would lose accuracy.

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Orbitals are regions of space where it is likely for an electron to be found. This concept is somewhat confusing, because electrons have both wave and particle like properties. So, you can think of orbitals as regions where an electron exists. Also, yes there are more hypothetical orbitals above f, ...

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For this class, I would use 2.99792 x 10^8 m.s^-1 because that is the value given on the constants and equations worksheet Lavelle sent in an email. However, whatever value you use just depends on how accurate you want to be.

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I believe that when the information of state is given, it is best practice to include it in your balanced equation. Otherwise, I don't think we need to include the state (unless we are for some reason given sufficient information such as temperature and pressure to determine state).

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Yes!
The equation E=hv shows that as frequency (v) increases, so does E (energy). The h is Planck's constant.

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The vacuum is only necessary to remove as many variables from an experiment as possible. If electrons interacted with molecules in the air, they would lose energy, bounce in different directions, etc. That is to say - a vacuum is used to collect the most accurate scientific data possible, the photoe...

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This is why particle/wave duality is so funky! Light has properties of both waves AND particles (as do all things), which is why we observe that an increase in intensity is not the same as an increase in energy (decrease in wavelength). If light solely had the properties of a wave, then yes an incre...

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Hi!
In this context of the lecture, intensity means the amount of photons being fired at a surface, and the energy referred to how much energy each individual photon possesses.

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Hello! The ejection of an electron is when it gains so much energy it leaves an atom altogether. You could also think of this as the electron being excited to the infinite energy level. Exciting an electron is when you give an electron some energy, and it jumps up energy level(s) within the orbit of...

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Hello! While it is possible to ionize an atom by ejecting an electron, it isn't possible to ionize an electron itself. Ionization specifically refers to changing the charge of an atom or molecule in a specific way. An electron's negative charge is static. I believe you may have misheard or misunders...

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A mole is just an amount. If you wanted to, you could have a "mole of moles", however that many moles would form a planet larger than earth. Here's a youtube video https://www.youtube.com/watch?v=SvtMl-V4Uv4&ab_channel=DanielChevy . Moles are just a unit we use to quantify large number...

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Technically yes it would still be mathematically correct from the surface level. However, if you think about the situation logically, you will realize it's impossible to have half an atom (in that regard), or to just split a molecule down the middle. So, while the math is basically correct, non-whol...

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Yes! M = molarity, n = moles, and v = volume (in liters). If you're given some other unit of volume, it would be best to convert it into liters, but you can still use the same formula regardless.

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The state of a molecule isn't a requirement to be included when balancing equations, because it doesn't alter the ratio of atoms in any way. However, if we are given the information then it would be a good idea to include as much detail as possible, for practice, but that's up to you.

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Personally, when using set values like molecular weight, I don't round at all until the very end, and then I round to the sigfigs of the experimentally recorded data (like grams of reagent). On exams we will all be given identical periodic tables, and I think it would be best to use the complete val...

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