CHEMISTRY COMMUNITY

Kylie Lim 4G

To solve this, use the equation E = Eo - (RT/nF)lnQ. Q is equal to [Cu^2+]/[Ag^+]^2 which is (0.20)/(0.10)^2. E = 0.460V - ((8.314*298)/(2*96485))ln(20).

Kylie Lim 4G

To write the overall reaction, cancel out any species that appears in both the reactants and products side, and then add the steps together. Cancelling out NOBr2 and then adding both reactions together gives you 2NO + Br2 ---> 2NOBr.

Kylie Lim 4G

In a concentration cell, the reaction is driven by a difference in concentration, with electrons flowing from the anode (which should be at a lower concentration) to the cathode (which should be at a higher concentration). The voltage is created as the two concentrations move towards equilibrium.

Kylie Lim 4G

In the email that Professor Lavelle sent out on March 10th, he said that all of the 60 hours of review and help have been cancelled and didn't mention anything about sessions being moved online. He has posted a week 10 review on his website that we can use for practice, but since most of the UA's ar...

Kylie Lim 4G

The slow step should be the one whose specific rate law that matches the rate law for the overall reaction

Kylie Lim 4G

If deltaH is a positive value, the reaction is endothermic so heat is consumed in the reaction. In order for it to be consumed it would have to be in the reactants side but you wouldn't normally write it into the equation as a reactant, you just think of it as a reactant so that you can use Le Chatl...

Kylie Lim 4G

I doubt that he would ask us to derive the zero, first, second, and half life equations since they are given on the equation sheet. It probably wouldn't hurt to be able to go from the given rate laws to the integrated rate laws though.

Kylie Lim 4G

A, because the reaction has the smallest deltaS values, meaning in the equation deltaG = deltaH - TdeltaS, change in gibbs and change in enthalpy will be the closest to each other

Kylie Lim 4G

A rate law is instantaneous because you are getting a value for a specific time t. I think that it would be considered an average rate if you're determining the rate based off of the slope of a graph for concentration v time.

Kylie Lim 4G

For kinetics, n is the exponent that a concentration is raised to in a rate law, the sum of these exponents is the overall order of the reaction. In the homework problems you can find n based off of given experimental data that shows the variation of rates with concentrations of reactants.

Kylie Lim 4G

The rate law is a differential equation that gives change in concentration of reactants with respect to time. When you integrate it, you get an equation that shows how reactants change as a direct result of changing the value of t.

Kylie Lim 4G

From the equation deltaG = -nFE, you can tell that a reaction is spontaneous and does work if the value of Ecell > 0. Since to find E you would subtract the potential of the cathode by the potential of the anode, you will always get Ecell > 0 if the cathode value is larger.

Kylie Lim 4G

The 0.19V should be divided by (RT/NF) which I got to be 0.012839. The result is 14.798 which is approximately 15.

Kylie Lim 4G

Since we're not given the cell diagram, I assume that you would determine the anode and cathode by looking up the reduction potentials for the half reactions. The more positive value is more likely to be the cathode because it is a better oxidizing agent and the less positive value will be the anode...

Kylie Lim 4G

Because it is a concentration cell, both of the half reactions involve nickel. The anode reaction is Ni-->Ni^2+ + 2e^- and the cathode is just that reaction in reverse.

Kylie Lim 4G

to find the order of the reaction, just add the exponents for all of the concentration terms of a rate

Kylie Lim 4G

The electrochemical series is a list of reduction half reactions, with the most positive standard electrochemical potentials at the top, and the least positive electrochemical potentials at the bottom. The most positive values of E are the strongest oxidizing agents going forming reducing agents.

Kylie Lim 4G

I think you should be able to use all of the methods for finding gibbs free energy, just make to differentiate between gibbs free energy and standard gibbs free energy

Kylie Lim 4G

n is the number of moles of electrons transferred in the reaction, and I find it easiest to use the coefficient from the balanced half reaction

Kylie Lim 4G

The test contians material from the last page of thermodynamics, and all of electrochem but material from the kinetics lectures

Kylie Lim 4G

I don't know if this is right but using the equation deltaG = deltaH - TdeltaS, I assumed that G and H would be most similar at the smallest possible values of S. This means that the correct answer is A because solids -> solids have the lowest entropy.

Kylie Lim 4G

Since the reaction is exothermic, an increase in temperature will favor reactants because you can think of heat as a product. Increasing the amount of a product will shift the reaction towards reactants to maintain equilibrium.

Kylie Lim 4G

Usually you can infer the charges of elements from looking at the periodic table and determining whether the element is likely to gain or lose electrons. However, some exceptions are peroxides that have a charge of -1, hydrogen that can have a charge of -1 or +1 depending on if it is bonded to a met...

Kylie Lim 4G

If you get that the change in standard gibbs free energy or products is greater than reactants, the overall value of delta G will be positive which means the reaction is unvaforable

Kylie Lim 4G

Changes in temperature are fine since they will be the same for kelvin and celsius. The only time when you have to worry about converting between celsius and kelvin is if the problem specifically asks for the answer in terms of one, or if you are using a constant like R in PV = NRT when R is specifi...

Kylie Lim 4G

Oxidation is a loss of electrons, reduction is a gain of electrons (not protons). I usually remember this with the acronym OIL RIG. The only way to tell if something is reduced or oxidized is by looking at the initial and final oxidation numbers of elements in a reaction.

Kylie Lim 4G

For isobaric reactions, pressure is constant. This means that both equations for w can be used, as well as the relationship where delta H = q

Kylie Lim 4G

Usually temperature will be given to you, and qrev just means q of a reversible reaction so you use the normal q=(heat capacity)(change in T).

Kylie Lim 4G

I remember oxidation and reduction with OIL RIG (oxidation is loss, reduction is gain). Write out the net equation and it becomes easier to see which elements gained or lost electrons.

Kylie Lim 4G

The overall charge of a compound is zero unless it is specifically written with a charge. The oxidation numbers for individual elements can be inferred just by looking at the periodic table and deciding which elements are likely to lose or gain electrons. An exception is oxygen which normally has a ...

Kylie Lim 4G

In irreversible expansion, there is a sudden significant change in external pressure that allows the contents of the system to expand. In a reversible expansion, external pressure is reduced gradually and in small increments so that Pexternal = Psystem. Usually in problems it will state whether it i...

Kylie Lim 4G

The example that was used in class was that in a reversible expansion, pressure is gradually decreased in amounts that are so small it remains in equilibrium with the surroundings. In an irreversible expansion the pressure is decreased suddenly and in large amount so that it can't be reversed.

Kylie Lim 4G

Are we required to know how to predict how changes in temperature will affect the enthalpy value and Kirchhoff's law for the midterm?

Kylie Lim 4G

volume and pressure are inversely related (P1V1T2= P2V2T1), which allows us to derive alternative equations to find the entropy of a system.

Kylie Lim 4G

W, degeneracy is used in the equation S = kB*ln(W) to find the residual or positional entropy of a system

Kylie Lim 4G

Enthalpy is made up of the change of the internal energy of the system as well as the pressure and volume which means that it is related to work but comprised of the total energy not just the work energy

Kylie Lim 4G

In a closed system, matter cannot be transferred but heat energy can. In an isolated system the transfer of both heat energy and matter are contained in the system.

Kylie Lim 4G

Lavelle's website says that the midterm includes equilibrium, acid and base, thermodynamics, and thermochemistry so i assume it is cumulative

Kylie Lim 4G

In an open system, both heat and matter can be exchanged with the system's surroundings. In a closed system, energy but not matter can be exchanged, and in an isolated system neither can be exchanged with the surroundings. If the insulated water bottle has a lid and prevents heat from escaping or en...

Kylie Lim 4G

you only need to go back and use the quadratic formula if you check X and it is more than 5% of the initial value

Kylie Lim 4G

Volume and pressure are inversely related. If the volume of a system decreases, the pressure will increase due to more frequent collisions.

Kylie Lim 4G

I think that the midterm is on thermochem and thermodynamics

Kylie Lim 4G

In class we determined the number of microstates by using the equation 2^N, where N is the number of atoms and 2 represents a 2-state system

Kylie Lim 4G

You can approximate that x is 0 when K<10^-3. You can always check to see if an approximation is valid if x is less than 5% of the initial concentration.

Kylie Lim 4G

For a reaction that is entirely gasses, Kp can be used if the pressure is given. Kc can be used for gasses as well if the pressure is converted to concentration, or concentration is given initially.

Kylie Lim 4G

Ka and Kb are calculated the same way as K but for weak acids and bases, with the concentration of products on the top and the concentration of reactants on the bottom. PKa and Pkb are the -log(Ka) and -log(Kb)

Kylie Lim 4G

k<10^-3 is a weak acid because to have a small number, there has to be a high concentration of reactants. If there are a lot of reactants, the acid is weak because it does not completely dissociate.

Kylie Lim 4G

Enthalpy is the heat lost or gained by a system in a reaction. Once that heat energy is lost it is available to do work.

Kylie Lim 4G

I memorized a chart of the most common strong acids, for bases though it is any of the oxides or hydroxides of group 1 and 2 elements.

Kylie Lim 4G

If pressure is increased due to a decrease in volume, the reaction will favor the side with fewer moles. If pressure is increased due to the addition of an inert gas there is no change in equilibrium.

Kylie Lim 4G

Kw is always 1.0x10^-14 at 25 degrees celsius

Kylie Lim 4G

when you form a bond, the process is exothermic because you are going from a state of higher to lower energy. when you break a bond the process is endothermic.

Kylie Lim 4G

Superacids can have negative pH if the concentration of H3O+ is greater than 1, because if you take the negative log of a value greater than 1 you get a negative value

Kylie Lim 4G

When Q>K, the numerator or [P] is larger for Q than K which means there are more products at the time Q is being calculated than there are at equilibrium. In order to compensate for the larger concentration of products, the reaction will produce more reactants and the reverse reaction is favored. Wh...

Kylie Lim 4G

Kp is used when you have the partial pressures of a gas, and Kc is used for concentration which can be found using PV=nRT

Kylie Lim 4G

Equilibrium constant for a single reaction is affected by temperature changes, not pressure

Kylie Lim 4G

R is a gas constant that is on the constants and formulas sheet that we get on tests (also on Lavelle's website)
R= 8.314 J·K-1·mol-1 = 8.206 x 10-2 L·atm·K-1·mol-1 = 8.314 x 10-2 L·bar·K-1·mol-1= 62.364 L·Torr·K-1·mol-1

Kylie Lim 4G

As long as the temperature is constant, K will have the same value for a reaction even if more reactants are added. This is because K is a [P]/[R], so adding more reactant will eventually lead to more product which will reduce to the same value of K.

Kylie Lim 4G

If it has multiple bonding sites/if it is polydentate

Kylie Lim 4G

I think that sp2 is fine for hybridization, but if it asks which orbitals are overlapping like in the Marshmallow review question 17 it might be safer to just write 2sp2

Kylie Lim 4G

Linear comes from the parent electron geometries of trigonal bipyramidal and octahedral, whereas bent comes from trigonal planar and tetrahedral

Kylie Lim 4G

A hydrogen bond can occur between and H bonded to a N,O,F or any N,O,F with a lone pair

Kylie Lim 4G

I memorized the most common strong acids and I'm going to hope that all the rest are weak.

Kylie Lim 4G

Yes, a lewis acid is an electron acceptor and a Bronsted acid is a proton donor. A Bronsted acid or base is always either a lewis acid or base but some Lewis acids and bases are not Bronsted.

Kylie Lim 4G

During one of the review sessions they said that sig figs for pH count after the decimal so 12.22 has 2 sig figs.

Kylie Lim 4G

HF is a weaker acid because the strength of an acid is determined by how completely that acid will dissociate. Since the bond between HF is stronger than the bond between HCl, HCl will more completely dissociate which makes it a stronger acid.

Kylie Lim 4G

A single bond has a sigma bond, a double is one sigma and one pi, and a triple is one sigma and two pi. I think this is something that is best to just memorize.

Kylie Lim 4G

A single electron is still considered a region of electron density, so the molecule that you mentioned would have 4 regions.

Kylie Lim 4G

I think it's more important to know the biological functions of molecules like cisplatin and hemoglobin than it is to memorize what they look like. He said in class that we wouldn't be asked to draw the compound from memory on the test I think.

Kylie Lim 4G

A bent molecule will have a lone pair that forces the other two bonded atoms into a bent bond angle, and the linear molecules either have no lone pairs, or the lone pairs are evenly distributed so that the molecule is still linear (in molecules with 5 or 6 electron density regions)

Kylie Lim 4G

Unless the dipole-dipole IMF is hydrogen bonding, LDF can have a significant effect on the boiling/melting point of a molecule.

Kylie Lim 4G

Guanine in the n7 position has an exposed nitrogen. The Cl in cisplatin will displace the nitrogen, and bond to the guanine.

Kylie Lim 4G

Larger molecules have more polarizable electrons which means they will be more distorted. This makes dispersion stronger and the melting/boiling point of the compound higher

Kylie Lim 4G

bent and angular are the same thing

Kylie Lim 4G

I think that doing the homework problems assigned and going to the review sessions before midterms and tests are the most helpful

Kylie Lim 4G

It might be helpful to know the order of strength for intermolecular forces so that you can determine which molecules will have higher or lower melting points based on their bonds. I don't think we are expected to have memorized melting points of specific molecules.

Kylie Lim 4G

I think that you should probably just memorize them since we haven't learned a way to calculate them. Trigonal planar is 120 though not 107.

Kylie Lim 4G

The seesaw shape occurs when there are 4 bonding pairs and 1 lone pair

Kylie Lim 4G

Everything since the midterm, so intermolecular forces, dipoles, VSEPR/molecular shape

Kylie Lim 4G

yes, it would still alter the bond angles and create repulsion

Kylie Lim 4G

I think that for intramolecular bonds, the shorter it is the stronger it is. This might not be the case for IMF's between molecules though.

Kylie Lim 4G

there is the greatest difference in electronegativity between Ba and Br, which means it is the most ionic

Kylie Lim 4G

I don't think that orbital shape will likely be tested on the midterm, but you should probably know how the quantum numbers n,l,ml relate to the location of an electron

Kylie Lim 4G

E=hv can be used for the energy of a photon, so if you think of light as acting like a particle rather than a wave you can use that equation.

Kylie Lim 4G

First convert the mass of GarBreadium from g/mol to one kg/atom using avogadro's number. Then you should be able to just use de broglie's equation plugging in the mass of one atom, and the velocity that is given to you.

Kylie Lim 4G

I think since you're likely to be using it with planck's constant, it's safest for units to be in joules

Kylie Lim 4G

I would use formal charge to find the most likely structure, and then for resonance check to see if any of the double or single bonds can have different orientations/locations

Kylie Lim 4G

The chlorine atom in the middle would not have a complete octet, so normally they would give you ClO2 as an ion (-1) which gives it 20 electrons

Kylie Lim 4G

The atomic weight is the weight of just one atom, and you don't have to calculate it because it's given to you on the periodic table. The molecular mass is the mass of multiple atoms in a molecule and it can be calculated by adding atomic masses together.

Kylie Lim 4G

For finding the wavelength of anything that is not light, or in the photoelectric effect if you need to find velocity of an electron

Kylie Lim 4G

I don't think we have gone over this yet, but in addition to H, He, Li, Be, some elements can have an expanded octet by using the d/f orbitals.

Kylie Lim 4G

I think that subshells are s,p,d,f, and the orbitals are the different possible orientations of the subshells.

Kylie Lim 4G

3d is at a lower energy state than than 4s so it is written first, even though the d block comes after the s block in the periodic table.

Kylie Lim 4G

The + and 3+ charges tell you that you have a cation that lost electrons. To write the electron configuration just write the expected ground state, and remove the necessary amount of electrons. For example for Bi3+ the electron configuration for Bi is [Xe]5d106s26p3 and after removing 3 electrons be...

Kylie Lim 4G

I did the problems from the Quantum World section because the syllabus says that the section covers electron configuration which we went over this week.

Kylie Lim 4G

I think that the wave function squared is the same as the s,p,d,f orbitals because they both represent the electron density or probability of finding an electron.

Kylie Lim 4G

The rydberg constant only works for the hydrogen atom because it only has one electron. It doesn't take into account electron-electron repulsion.

Kylie Lim 4G

The wave function is just a way to describe the position of an electron, since electrons have wavelike properties. The wave function squared is the probability of finding an electron (electron density) which is what the s,p,d,f orbitals represent.

Kylie Lim 4G

I think ψ2,0,0 is a valid combination if you're talking about quantum numbers (n, l, ml) to describe position of an electron.

Kylie Lim 4G

Zeff is also helpful in comparing sizes of elements by looking at how strongly the positive charge of the nucleus is holding electrons.

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