CHEMISTRY COMMUNITY

Timothy_Yueh_4L

Transitions states are the hills, or local maxims, of a reaction profile diagram, and these states are where the bonds of the chemicals are being broken and reformed, having high energy.

Timothy_Yueh_4L

When concentration goes up on one side it means that that particular side if being made therefore the reaction is proceeding in that direction. The reverse is true when a side's concentration is decreasing meaning that the reaction is proceeding to the opposite side. At the same time the reaction co...

Timothy_Yueh_4L

I believe the question is asking for the work done by irreversible expansion in which case is found using the equation W = P*delta(V). We multiply delta(V), 2.23L, with the constant external pressure, 1 atm, and get 2.23 L*atm which being a unit of energy is not in its standard form joules. To conve...

Timothy_Yueh_4L

Intermediates are created and used up therefore it doesn't show up in the overall reaction whereas catalysts appear in the beginning and the end of a reaction. In this example, the intermediate is C and there are no catalysts.

Timothy_Yueh_4L

When k < 10^-3, we assume the change in reactant is negligible therefore the value of the reactants is the same. Ex) A + B --> C: std defn of k = [C]/([A][B]). After equilibrium k = [C+x]/([A-x][B-x]), with x denoting the change in concentration, however the change is negligible therefore the equati...

Timothy_Yueh_4L

You could also determine if a reactant is zero order by looking at a table of reactant concentration and rate. If the concentration changes but the rate doesn't, the reactant has a zero order reaction.

Timothy_Yueh_4L

You would rank them according to decreasing standard reduction potential (+ --> -). This is because the lower the reduction potential, the stronger the oxidation potential therefore when finding the element with the strongest reducing power we want the element with the highest reduction potential wh...

Timothy_Yueh_4L

The integrated rate law of a first order reaction is ln[A] = -kt + ln[A]o. In order to determine the half life of a first order reaction, we set ln[A] = ln[0.5A]o and solve for t. Overall we get the unsimplified version: (ln[0.5A]o - ln[A]o)/-k = t. According to log rules when you subtract 2 logs, y...

Timothy_Yueh_4L

When looking at a graph, equilibrium is reached when the reactants and products in question stabilize to a horizontal line. It essentially means that the the rate between the reactants and products are equal.

Timothy_Yueh_4L

So if there is a solid in the reaction then you don't include Pt at the end? If the elements undergoing redox reactions are present in solid form (electrodes composed of those elements), then a conducting solid such as platinum is not needed however if if they are not in solid form, rather in a gas...

Timothy_Yueh_4L

To break this down, an element that has a strong reducing ability is essentially the same as the reducing reagent, the element responsible for reducing another element in a redox reaction, and to determine between a group of elements in order of increasing reducing ability, we must determine which e...

Timothy_Yueh_4L

You are correct, we use this convention because all bond enthalpies given are positive and when bonds are broken, energy is required into the system therefore the H is positive and when bonds are formed, energy is released therefore H is negative so a negative sign is placed in front of the sum of b...

Timothy_Yueh_4L

Gibbs free energy refers to the amount of energy from a chemical reaction that can be used to do work.

Timothy_Yueh_4L

A state function is a property whose value does not depend on the path taken to reach a specific value. For the sake of this class, pressure, density, temperature, volume, enthalpy, internal energy, Gibb's free energy, and entropy are state functions.

Timothy_Yueh_4L

Best bet is to use atm for pressure but I'm sure the equation sheet will give us conversions between different pressure values.

Timothy_Yueh_4L

To add on, you use the equation, w = -nRT ln V2/V1, to calculate the total amount of work as the pressure equalizes at infinitesimally small intervals (it sums up the maximum amount of work that is able to be done). On the other hand, we use w = - P ∆V when dealing with irreversible/sudden expansion...

Timothy_Yueh_4L

So which one does more work? I think it would be reversible bc of the curve, but I'm not entirely sure why Reversible isothermal expansion would do more work because it calculates the amount of work done over the courses of the entire expansion, summing the work done at infinitesimally small interv...

Timothy_Yueh_4L

Is this why delta U = delta H in biological systems since reactions in biological systems take place in liquids? The reason why delta U = delta H in biological systems is because these reactions usually occur in aqueous solutions, which unlike gas is unable to expand or compress to perform work. Th...

Timothy_Yueh_4L

When dealing with the singular unit kJ, we typically refer to the amount of energy that is involved in the system, whether it be the formation of products, reactants, or the total amount of energy that was released or absorbed based on the amount of substance in the reaction. On the other hand, kJ/m...

Timothy_Yueh_4L

You use Hess's law when adding the enthalpy of reactions for two or more reactions are given, with certain compounds able to be replaced in between the two reactions. A + B --> C plus C + D --> E: the compound C is used and created in both situations. On the other hand enthalpy of formation is used ...

Timothy_Yueh_4L

In general you disregard any ions from the 1st group, 2nd group, and the halogens which act as spectator ions. Others such as compounds in the form of solids and liquids are also ignored.

Timothy_Yueh_4L

In this case you'll need the values for volume (V) and moles (n) of the particular gas you are examining.

Timothy_Yueh_4L

Any salt compounds that disassociate into an ion from the 1st, 2nd, and halogen groups, do not impact the pH of the system because their charges are not strong enough to break the bonds of water (its charge localizes the electrons away or towards the ions thus releasing OH- or H+). These ions act as...

Timothy_Yueh_4L

The pKa/pKb have no direct relation to the actual pH of a solution, however you use the values pKa and pKb to determine the hydronium and hydroxide ions of their respective reaction and use those values to determine the pH.

Timothy_Yueh_4L

By the brosted-lowry model, a molecule is an acid if it denotes a proton and produces hydronium ions after reacting with water, and a molecule is a base if it takes a proton to produce a hydroxide ion after reacting with water. Generally if a molecule has a nitrogen atom, it's lone pair can attract ...

Timothy_Yueh_4L

The reason inert gases don't affect the equilibrium of a reaction is because it has no affect on the pressure due to the law of gases regarding the volume of gas particles are negligible.

Timothy_Yueh_4L

When removing chemicals from either side of a reaction, the the equilibrium quotient will change however not the equilibrium constant. The products and reactants would reach the equilibrium level after sometime but the final concentrations from each side will be different than when you started. Addi...

Timothy_Yueh_4L

When calculating the reaction quotient you are evaluating the reaction at some time that is not at equilibrium and you use the value to determine its relativity to reaching equilibrium. In the case where Q < K, there are more reactants compared to the reaction at equilibrium, therefore more products...

Timothy_Yueh_4L

You would use the ideal gas law if the question gave you a both concentration and pressure values which you would use to convert all the values to either concentration or pressure to solve for the equilibrium constant.

Timothy_Yueh_4L

By adding more NH3 to the chemical reaction, you increase the concentration of the that particular chemical on the reactants side which gives an Q constant that is lower than the equilibrium constant, Kc. This will result with the forward reaction being favored as more product will be formed until t...

Timothy_Yueh_4L

I'm not sure if this is what you mean but hybridization formulas (sp, sp2, sp3, etc.) denote regions of electron density and depending on how many electrons are in the hybridized orbitals (paired or unpaired) it would inform you whether or not the atom can have a certain amount of bonds.

Timothy_Yueh_4L

Polar molecules that can form strong intermolecular bonds, i.e. dipole-dipole/hydrogen bonds, or dipole-induced dipole bonds, tend to have higher boiling points and depending on the polar end of the molecule, it would determine the relative strength between the two molecules. On the other hand, nonp...

Timothy_Yueh_4L

A bronsted acid is a proton donor and a lewis acid is an electron acceptor. A bronsted base a proton acceptor and a lewis base is an electron donor.

Timothy_Yueh_4L

What Dr. Lavelle was referring to in class were that pi bonds are formed by the overlap of electron densities that are perpendicular to the sigma bond. Because of their orientation, they are extremely limited in their movement unable to rotate like a single sigma bond. Due to this it results in diff...

Timothy_Yueh_4L

The isolobal principle states that an element or group of elements with similar shape, symmetry and radial extent; with approximately the same energy; and with the same number of electrons available for cluster bonding is able to replace another. In the case of benzene, the C-H can be replaced by N ...

Timothy_Yueh_4L

The number of hybrid orbitals equals the number of electron densities that result from bonded and lone pair electrons.

Timothy_Yueh_4L

I believe we need to know more or less the bond angles for most shapes, but not the actual values of particular molecules. Here is a image of the ideal bond angles of different shapes:

Timothy_Yueh_4L

As a common trend, the strength of repulsion follows: one lone pair > lone bonding pair > bonding bonding pair, with the strongest repulsion resulting in greater bond angles.

Timothy_Yueh_4L

As mentioned previously, bond length will have no effect on bond angle rather it's the types of bond present that affect shape and angle. As a rule of thumb, repulsion strength follows as Lone lone pair > lone bonding pair > bonding bonding pair, with the greater the repulsion strength giving the gr...

Timothy_Yueh_4L

Polarization is the measure of how easily an electron cloud is distorted by an electric field with an electric field being an external source such as an electrode or a charged particle (cation and anion) or a partially charged particle (polar molecules). I don't think we need to know how to measure ...

Timothy_Yueh_4L

In order to determine the exact bond length between atoms, additional information must be given however it is possible to determine the relative lengths by comparing types of bonds. By convention the lesser amount of bonds (single bonds) equates to a longer bond length and the greater amount of bond...

Timothy_Yueh_4L

Dispersion forces are synonymous with the term dipole-induced dipole-induced interactions, which as the name suggests deals with the polarzability of an atom. In the case of Cl2 and F2, both molecules have a significantly smaller atomic radius and have less electrons compared to Br2 which indicates ...

Timothy_Yueh_4L

I believe so. I went to Amir's review session on friday and he said that organic molecules may be on the test. I don't believe molecules as complex as glycine will be tested though.

Timothy_Yueh_4L

Phosphorus can form an expanded octet with 5 bonds due to the fact that it exists in the 3rd period, giving it access to the d-orbitals associated in the 3rd shell (3d).

Timothy_Yueh_4L

Ionization energy is the energy required to eject an electron from an element, which increases across a period because the distance and force between proton and electron become greater. Electron affinity is the energy given off when a neutral atom in the gas phase gains an extra electron to form a n...

Timothy_Yueh_4L

Here's an image of the f-orbitals. As previously mentioned I don't think you'll need to know what they are, just know that they have 7.

Timothy_Yueh_4L

(a) As shell level increases, the energy level of electrons also increase (linear relationship) (b) The value of n directly correlates to the shell level therefore an increase from 1 to 2 would increases the value of n from 1 to 2. (c) The value of l would increase because the electron moves from th...

Timothy_Yueh_4L

You use the previous noble gas as the short hand and follow the standard rules for electron configuration. Ex) Electron Configuration for Argon = [Ne] 3s^2 3p^6

Timothy_Yueh_4L

How many electrons can occupy the (a) 4p-orbitals;
(b) 3d-orbitals; (c) 1s-orbital; (d) 4f-orbitals of an atom?

Timothy_Yueh_4L

How do you derive E = Rh (1/nf^2 – 1/ni^2) from v = R (1/nf^2 – 1/ni^2)?

Timothy_Yueh_4L

Since it is 1/nf^2 – 1/ni^2, the resulting energy value is positive if nf is the smaller value. Since delta E represents the change of energy, which tends to be a positive value, nf needs to be the smaller primary quantum number in order to satisfy that condition.

Timothy_Yueh_4L

Just wanted to add that the speed of light is constant throughout the entire electromagnetic spectrum (~3.00 * 10^8 m/s)

Timothy_Yueh_4L

You should generally convert your answers to scientific notation when 1) dealing with large numbers, 2) dealing with small numbers, or 3) to indicate significant figures with zeros (i.e. 5600 with 4 sig figs: 5.600 * 10^3)

Timothy_Yueh_4L

The photoelectric effect also shows a difference between the quantum and mechanical models of waves. In the macro world, an increase in energy would result in an increase in amplitude whereas in the quantum world an increase in energy would result in an increase in frequency.

Timothy_Yueh_4L

I typically balance equations starting off with elements that has the least amount of atoms, and then begin balancing the rest in order of least to most. When dealing with combustion, I again begin with the element with the smallest amount (C, N, etc.) and work my way to H and then O. I keep an eye ...

Timothy_Yueh_4L

@isarose00 When Na2CO3 dissociates in water the balanced equation is: Na2CO3 --> 2Na^+ + CO3^2-, thus showing that it takes 2 moles of sodium ions to produce one mole of sodium carbonate, hence the division by 2.

Timothy_Yueh_4L

When rounding with sig figs, there are generally two rules two follow: one dealing with multiplication and subtraction and the other with multiplication and division. In the first scenario, when you multiply or divide any two values, the final answer in sig figs will equal the least accurate amount ...

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