CHEMISTRY COMMUNITY

Sally Qiu 2E

WE LOVE YOU 3000 TOO LYNDON

Sally Qiu 2E

i think Lavelle said we aren't going to learn how to calculate an actual value for A; just understand what it represents and why it's significant

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Delaney Smith 1C wrote:Wait, how do you solve for k if you don't have [A]t?

you're given the A naught and the half life so you can use the formula for the half life of a second order rxn in order to find k

Sally Qiu 2E

the K constant does not change with a change in pressure-- only temperature. however, the reaction will adjust to compensate any disruptions made to the equilibrium. when you decrease the volume the reaction will shift to the side with less moles of gas. if you increase the volume the reaction will ...

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when you decrease the volume of a reaction, you also increase the pressure. thus the reaction will shift towards the side that has fewer moles of gas.

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i don't believe there's any direct conversion to get from pKa to pH. instead you'll have to convert pKa to Ka and make an ICE table to find the concentration of H+. then you can solve the equation and convert H+ to pH.

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thermal disorder refers to the entropy of motion of molecules. if you add heat to a substance, the molecules move faster and thus thermal disorder increases. positional disorder refers to entropy of a molecule's orientation.

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intermediates do not show up in the rate law or overall reaction because they will cancel out on the reactants and products side.

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i believe if you tried to write the differential rate law as a function of time, you would have to manipulate it into the integrated rate law. the differential rate law equation as is relates rate to concentration

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no; adding a catalyst lowers activation energy, which increases the rate constant k because the reaction could proceed faster. however, i believe the rates of the forward and reverse reaction would increase proportionally, so mathematically you can see the equilibrium constant K is unaffected

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i think it is safest to use seconds, even if the problem doesn't specify

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a concentration cell is comprised of two half cells in which the anode and cathode are the same element but have different concentrations. also E standard=0

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when delta G is negative it means the reaction is spontaneous

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i encountered a practice problem that had this situation, i think the half reactions add together to make a bigger half reaction. therefore it doesn't make the reaction a redox.

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reducing agents cause other species to be reduced and in the process, they themselves become oxidized because they have given an electron in order to reduce the other species.

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because the unique rate sets the rate of change in concentration for species in a reaction over time equal, the unique rate will be the same for each reactant/product

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the porous disc has the same effect as a salt bridge as it keeps the charges balances

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it's okay to leave the temperature in celsius if you're just finding the change-- it shouldnt make a difference mathematically

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the charge of electrons must be maintained; same reasoning as to why we balance equations in general

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delta G is the gibbs free energy under standard conditions

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van't hoff equation is used to find the K value for different temperatures

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we are assuming the difference between the final H and initial H to remain constant, and that the temperature change isn't significant enough to affect that

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if there was a change in the number of moles, the system had done expansion work (if the volume can change)

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gibbs free energy is basically the energy that is available to do work, hence "free" energy.

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expansion means there was an increase in volume

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the temperature doesn't change during a phase change. you can keep adding heat but the temperature doesn't change. you would need to calculate the energy needed to raise the temperature to the melting point, then find the amount of energy needed to actually melt the substance

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i think isothermal always means reversible but not necessarily the other way around

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can someone explain the lex luthor problem to me? it's number 5. i think for part a, i need to use the 2 entropy equations as well as the equipartition thing. and i'm not sure about b...

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are there any specific values we need to memorize for this midterm? like heat capacities and whatnot?

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is it not a state function? if i recall correctly, entropy is in fact a state function because it does not depend on the path followed by the system--just the final and initial state. however, the entropy does depend on the size or amount of moles. entropy=q/T, and q itself is extensive

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as the temperature approaches 0 K, the change in entropy would approach 0. with the example of the perfect crystal, there is no inherent disorder and it must be at 0 K or else there will be some motion within the crystal

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the heat given off by the rxn would be absorbed by the surroundings. i'm not sure if you need to know specifically which side the negative is on, as long as one is negative?

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if you solve the integral you would get ln( V2/V1).

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in a closed system, you can change the energy by doing work/having work done on the system or by changing the temperature

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internal energy includes heat and work. sometimes change in internal energy is equal to change in enthalpy, and this happens when you are at constant pressure and volume.

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it's equal if you are at constant pressure and volume.

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in an open system, you can add or remove products/reactants. in a closed system, you can change the pressure by compression/expansion (work) or changing the temperature. you cannot change the energy of an isolated system.

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i think there are few, if any, isolated systems in the world. maybe there's such minuscule amount of change that it's negligible?

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it depends on whether or not the value of bonds formed is greater than that of bonds broken.

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hess's law is basically stating that because enthalpy is a state function, enthalpy is additive. you can simply add the enthalpies of reactions; regardless of how many steps a reaction has, the total enthalpy change is just the sum of all changes

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you would have to draw out the lewis structures and see which bonds were broken and formed in the products.

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the examples done in lectures are the most accurate representations of what show up in exams. Make sure you thoroughly understand the concepts behind each example so that you are able to recognize what steps to take when you encounter a similar problem on an exam.

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i got 8.62

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leave out pure liquids and solids

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wait so for this problem we had to make sure which direction it went in?

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homework problems are good practice, i wouldn't bank on them being on the test though. and yes, the test covers outline 1 and 2.

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you usually get partial credit yeah

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if the K value is less than 10^-3, then you can assume x is very small relative to the initial concentration. this makes sense when you think about the formula for K (the concentration of reactants is much greater than that of products). if this is the case, you can disregard the x (that is subtract...

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it's ignored if it's in a liquid state. as a solvent, it's in large excess, the concentration isn't really gonna change so it's not included in the K equation

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usually Kc is used, but i believe the problem would specify which one to use. you can also tell by the information given by a problem

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i don't think you would get 2 positive answers often, but just in case i'd plug the values back into the ICE table to see which value is more reasonable

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change in concentration, pressure (from volume), and temperature. temperature is the only one that affects the K value

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if the reaction is not at equilibrium, or if you aren't sure, then you are calculating the reaction quotient. It is the same equation as K. it can be used, when compared to K, to determine which way the reaction is proceeding

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The change would be x if you aren't given the equilibrium concentrations. Unless there are coefficients, then it would be corresponding coefficient times x.

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you would use Kp if you are given the partial pressures.

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definitely study outline 1, but i'm not sure if some of outline 2 will be covered

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basically the reaction will "adjust" to keep K constant. if you add more products and throw off the equilibrium, the reaction will proceed to the left to form more reactants. Regarding the change in pressure, the reaction will proceed towards the side with less moles of gas; however, it is...

Sally Qiu 2E

the equation to calculate K and Q is the concentration of products over concentration of reactants. If Q is less than K, that means that there must be more reactants compared to the concentrations at equilibrium. Therefore, the reaction will shift to the right to produce more products. the same logi...

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R is a gas constant and the numerical value depends on the units being used to measure the gas

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yes, strong acids dissociate completely in water. whether or not an acid (or a base) ionizes completely in water depends on the polarity. when there is a significant electronegativity difference, there is less electron density associated with hydrogen and it is easier to ionize

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ka is the acid dissociation constant, and pka is the -log of Ka

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bases are proton acceptors, so they gain a H+. acids are proton donors, so they lose a H+

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i think Lavelle said to memorize the diagonal line of elements on the periodic table.

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you'll know based on the kb value. i believe there are strong acids and bases you can memorize, and anything else not on that list is a weak acid/base

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the best way to be sure would be to draw the structure and see how many bonds the ligand can form. if there can be multiple bonds formed, then the ligand is polydentate

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for monoatomic ions, the oxidation state is the same as the charge, so just look at the periodic table.

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in a coordinate covalent bond, the electrons involved in bonding comes from one of the atoms, while in normal covalent bonds both atoms will contribute electrons

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a bronsted acid describes acids as proton donors, as in they lose an H+. the lewis definition of an acid is that they are electron acceptors, so they gain electrons.

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draw the lewis structure. a single bond is one sigma bond, a double bond is one sigma bond and one pi bond, and a triple bond is one sigma bond and two pi bonds.

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i don't believe there's a difference? the textbook may say angular but lavelle referred to it as "bent"

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dissociation energy is the energy required to break a bond, and since breaking bonds requires energy, the dissociation energy will be positive

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the stronger the intermolecular force, the higher the boiling point. for example, the boiling point of water is 100 C, while the boiling point of methane (CH4) is like -260 C. water molecules are polar, which means there will be dipole-dipole forces as well as LDF (LDF are present in all molecules i...

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yes, because of the partial charges

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i prefer to draw the lewis structure; then you can see if the structure is symmetrical or not.

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dipole moments are the result of differences in electronegativity, and the atoms share electrons unequally. this creates a partial charge of +/-.

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i don't think you need to memorize the actual numbers, but you can at least have a general, relative estimate of the values maybe

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h bonding is an intermolecular force, so attraction between molecules. it is the stronger than dipole-dipole, which is also an intermolecular force. h bonding is weaker than covalent or ionic bonds though.

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the charge isn't necessarily for the central atom. the most electronegative atom should have the negative charge

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yes; shape can determine how close molecules are able to get to each other.

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ions with high polarizing power cause large distortions in another atom's electron cloud. to determine polarizing power, you'll have to take into consideration the atomic radius and charge; small cations that are highly charged have the most polarizing power. due to the small size, the nucleus of th...

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kind of yeah? i see it more as resonance describing the delocalization of electrons. but yes the bond length is the average

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radicals are compounds that have a lone electron. this makes them very reactive, and they're significant because they can damage DNA and cause mutations.

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a dipole moment occurs when atoms in a molecule share electrons unequally. this means there's a difference in electronegativity, and this creates partially negative and positive regions which gives the molecule ionic character

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a hydrogen bond is a type of dipole-dipole interaction, but it's specifically between hydrogen and N, O, or F. it's the stronger than dipole-dipole because of the partially positive hydrogen atom and partially negative N O or F

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i would assume we have to draw the lone pairs since we haven't been told otherwise. just draw them to be safe

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ml is actually the quantum number that is from -l to +l. it means that ml can take on integer values from -l to +l; for example, if l was 2, then ml can be -2, -1, 0, 1, or 2. and ms is either -1/2 or +1/2

Sally Qiu 2E

electronegativity is how well an atom can attract electrons, or basically an atom's ability to attract electrons. electron affinity is the amount of energy released when an electron is added to a neutral and gaseous atom

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atomic radius is the distance from the nucleus to the outmost shell. i don't think we need to calculate it; i would assume the atomic radius would be either given to us in a problem, or we can solve for it with basic math (correct me if i'm wrong though).

Sally Qiu 2E

the electrons in resonance structures are delocalized, and this spreads multiple-bond character over the whole molecule. the resonance structures don't depict how the molecule actually looks like, so the bond lengths are the average between the single and double bonds

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the l value is determined by the n value, and ml is determined by l. ml can be any whole number from -l to +l; for example, if l=1, then ml can be -1, 0, and +1

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the inner electrons "shield" the outer electrons from the electrostatic pull of the nucleus. this reduced electrostatic attraction is the "effective nuclear charge". this becomes important later when it comes to ionization and bonding

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a shell is the energy level, which is n. orbitals are denoted by ml, and are the shapes that can hold up to 2 electrons. i'll attempt to give an example: n=2, l=1, so we have 2p. there can be 3 values for ml, so we have px, py, and pz. if you remember high school chemistry and electron configuration...

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schrodinger's equation solves for a wave function (treating electrons as matter waves) and it can be used to find the relative location of an electron and the probability of finding an electrons in a location.

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nodal planes are where the probability of finding electrons is zero. they're derived from schrodinger's equation

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in order to use the uncertainty equation, you need to have some value for mass. because photons have no mass, you cannot use the momentum equation p=mv and thus, you cannot calculate the uncertainty

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when an electron is excited, it means that it has absorbed energy and has jumped to a higher energy level.

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the speed of light changes depending on the medium it is traveling through; however, the constant 3.00x10^8 m/s is used when assuming the light is traveling through a vacuum. therefore, in our case, the speed of light is constant.

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i try to balance the coefficient one by one by making a list, but when i get an odd number, I double the coefficients and that usually works out in the end

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we use the constant c when we are assuming the situation is in a vacuum. however, it is true that light travels different under different mediums.

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To convert from nanometers to angstroms, you multiply by 10.

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