CHEMISTRY COMMUNITY

Andrew Bennecke

You can have catalysts present in the Rate Law, but you can't have intermediates because they only exist for an instant and therefore don't affect the rate, but must instead be substituted using the steady state approximation (Not for the final) or the pre-equilibrium approach.

Andrew Bennecke

The profile is lnk vs. 1/T when referring to the graph of the Arrhenius Equation, with slope =-Ea/R. the graph for lnk vs. T would not be linear, so we would view that as incorrect, but the graph ln[A] vs. T would be linear with slope -k.

Andrew Bennecke

Not really, the k' in the pseudo rate laws act as the original k, but under different conditions, generally the changing of the order of the reaction by having an excess of one reactant.

Andrew Bennecke

Using the equation ln[A]=-kt+ln[A]o, we see how it has the same format as y=mx + b, the skeleton equation for a linear equation. In this case, y=ln[A], m=-k, x=t, and b=ln[A]o. Therefore, we can graph ln[A] in terms of t, where ln[A]o is the initial concentration of [A] at t=o. ln[A] does not take t...

Andrew Bennecke

This type of problem where we are given information about both A and B, A being a reactant and B being a product occurs several times in the 7B exercises of the 7th edition of the textbook. I also don't know which equations to use that involve information about both A and B, I assume it is setting 2...

Andrew Bennecke

The half-life of A in a second-order reaction is 50.5 s when [A]not=0.9=84 mol*L^-1. Calculate the time needed for the concentration of of A to decrease to (a) one-sixteenth; (b)one-fourth; (c) one-fifth of its original value. Plugging-in the calculated k value and the given initial concentration in...

Andrew Bennecke

For certain cell diagrams that contain electrodes without solids, i.e, only aqueous solutions, require metal conductors and platnium works best.

Andrew Bennecke

The correct reduction half reaction is actually Ag+(aq) + 1e- -> Ag(s) in the book.

Andrew Bennecke

Write the half reactions and devise a galvanic cell (write a cell diagram) to study the following reaction: AgBr(s) -> Ag+(aq) + Br-(aq) Could someone please explain to me why, in the answer key, they have the oxidation half reaction as Ag(s) + Br-(aq) -> AgBr (s) + 1e- and the reduction half reacti...

Andrew Bennecke

You have to split up the product, HCl, into its ions, H+ and Cl-. When you do this, the reduction half reaction is Cl2(g) + 2e- ->2Cl- and the oxidation half reaction is H2(g) -> 2H+(aq) + 2e-.

Andrew Bennecke

This is the value of moles of electrons that cancel in each of the half reactions before writing the whole net ionic equation.

Andrew Bennecke

Within the equation for Gibbs Free Energy, delta G=nFEcell, n is the number of moles of electrons transferred in a reaction. This would be the quantities in the half reactions that must cancel out before writing the complete net reaction. Therefore, I don't think that that the concentration of react...

Andrew Bennecke

I believe the skeletal equations are the ones first given, where the species are unbalanced completely. So, if it's asking for the skeletal equation, we wouldn't show any water or electron exchange, just the given reactants and products.

Andrew Bennecke

If the single reactant has two products in the given equation, we look at the oxidation numbers of each element within each compound. For example, in Br2 (l) -> BrO3- (aq) + Br- (aq), the Br on the reactant side has an Oxidation number of 0, because it is a diatomic molecule. The Br within BrO3- has...

Andrew Bennecke

We use Boltzmann's equation to calculate residual or statistical entropy within a system. This differs from the majority of calculations that we do, finding the CHANGE in entropy.

Andrew Bennecke

Also, we may use other thermodynamics concepts from before the midterm to calculate Gibb's on Test 2.

Andrew Bennecke

An example of a state function Lavelle gave in class was going up in altitude level. To go from Altitude A to Altitude B, we could just take any combination of pathways to get from A to B. This is the same as calculating entropies, we can use a wide range of methods to obtain the total change of ent...

Andrew Bennecke

The X represents the number of possible orientations in which a molecule could exist. If we were to draw every resonance structure of a molecule (Ignoring changes in bond order), they would each represent a different orientation of the molecule.

Andrew Bennecke

They aren't directly proportional; however, when vibrational, translational, and rotational energies are stored within a molecule as the internal energy, U, this could indicate the amount of enthalpy or entropy within that molecule or system.

Andrew Bennecke

Usually, we would use Gibbs Free Energy to find the spontaneity of a reaction; however, since we won't be using Gibb's on the midterm, the 7th edition indicates another way in table 4I.1. If delta S total > 0, then the reaction is spontaneous.

Andrew Bennecke

Within the 7th Edition, we have covered almost all the topics up to 4E and he mentioned entropy at the end of lecture on Friday, so I'm assuming we will begin covering "The Second & Third Laws of Thermodynamics" section of the syllabus now, beginning with section 4F.

Andrew Bennecke

In an open system, the pressure of the system=the pressure of the exterior because there is nothing preventing the exterior pressure from maintaining its pressure within the system. However, in closed and isolated systems (where no matter can be exchanged), the exterior pressure cannot interact with...

Andrew Bennecke

I think I am missing a step somewhere for 4A.7 (part a) in the 7th edition because I'm plugging in the given values to the equation, but can't obtain the correct answer. q=m*C*(Delta T) q=(400g)(0.38 J*C^-1*g^-1)(80 C-1) q=12.2 kJ The textbook says that the answer is 112 kJ, but I can't figure out w...

Andrew Bennecke

Enthalpy is the overall change of energy within a system, while heat is the exchange of thermal energy that causes a temperature difference. Internal Energy (U) is the sum of all bonds and inter molecular relations within a system (Generally unable to be calculated), so we calculate the change in U ...

Andrew Bennecke

We've been doing Bronsted Acids and Bases for the most part because of the [H3O+] and [OH-] on the products sides mostly because we've been dealing with pH and pOH levels within solutions.

Andrew Bennecke

The Reaction Quotient (Q) is similar to the Equilibrium Constant (K) in that they are calculated the same way. However, Q only equals K when at equilibrium, it is somewhat like a "temporary" K value. You would need to calculate Q whenever the system is not in equilibrium, or you are unsure...

Andrew Bennecke

According to Le Chatelier's Principle, a system will always attempt to minimize the effects of a perturbation. Because of this, when the temperature is increased, it will favor the side without heat (reactants in an exothermic reaction and products in an endothermic reaction) in order to generate le...

Andrew Bennecke

The pH is defined as the concentration of H+ ions within a solution by using the equation pH=-log[H+], so the higher the concentration of H+ ions within a solution indicates that the pH of the acid is lower and therefore stronger.

Andrew Bennecke

If a substance can donate or accept H+ atoms or lone e- pairs, it is most likely a weak acid or base. The only exceptions would be the strong acids (HCl, HF,HBr, etc.) and the strong bases (Group 1 or 2 elements + OH- ion).

Andrew Bennecke

We would use the amphoteric compound, Ammonia/NH3, that acts as a weak base in this reaction In order to create Ammonium, NH4+, by mixing it with water. This would give us the equation NH3 (aq) + H2O (l) <-> NH4+ (aq) + OH- (aq).

Andrew Bennecke

In the reaction, we lose 2 moles of NO for every 1 mole of N2 and 1 mole of H2 produced. In the ICE box, the Change in Partial Pressure row would be -2x,+x,and +x. The Equilibrium of Partial Pressure row will be (1.0-2x), x, and x.

Andrew Bennecke

If a problem like that appears on a test, we would assume that the constants in the factored expression are much greater than the x value of change. So we would ignore the X's in the 3rd degree polynomial and proceed to calculate with the constants instead.

Andrew Bennecke

Q and K are calculated the same way. They are essentially the same value, except K is the equilibrium constant while Q's relation to K indicates whether the forard or reverse reaction will be favored until Q=K. Also, I believe that we will either be given the K value, or the means to calculate it.

Andrew Bennecke

Aside from memorizing the several strong acids and patterns for strong bases, learning the different trends of the acids with a halogen and strength of a H atom in a H-bond can also help decide which molecule is more acidic or more basic when given two to compare.

Andrew Bennecke

HOCl is a stronger acid than HOI because the Cl is far more electronegative than the I in their respective acids. The more electronegative a molecule is, the less electron density around the H, making it easier for the H to be donated to another molecule. The easier a H atom is donated from an acid,...

Andrew Bennecke

We just write the chemical equations with equilibrium arrows, which shows how either the two compounds on either side are an acid and base.

Andrew Bennecke

I believe that it is because Oxygen only has 2 unpaired electrons in its valence shell, so it is the most stable when those two unpaired electrons are in 2 bonded pairs, but introducing a third bonding pair would imply that one of Oxygen's already bonded pairs has formed a covalent bond with the Hyd...

Andrew Bennecke

I believe we will only be required to know of the exceptions mentioned in the book - H2O (aqua), NH3 (ammine), CO (carbonyl), NO (nitrosyl) - along with the general rule of dropping the -e at the end of -ide, -ite, and -ate and adding an -o.

Andrew Bennecke

Or Toolbox 9C.1 on page 723 in the 7th Edition

Andrew Bennecke

I believe the prefix bis- has something to do with it, perhaps it indicates that both ligands already have a Greek prefix. Also, the book says to ignore Greek prefixes when alphabetizing ligands, but the bis-, tris-, and tetrakis- prefixes aren't explicitly said to be Greek, so maybe we include them...

Andrew Bennecke

I am confused as to what exactly polydentate means. I understand that it involves the number ligands attached to the central metal ion or atom, but I couldn't understand the exercises associated with them.

Andrew Bennecke

In a nonpolar Lewis Structure with a tetrahedral shape (CH4), we draw just as we have been drawing it since the dipoles cancel and each of the terminal atoms provide equal repulsion unto the central atom. However, in a Polar Lewis structure with a tetrahedral shape (CClH3), we should draw the struct...

Andrew Bennecke

We always remove the termianl atom from the equatorial plane because this maximizes the bond angles. The two atoms on the axial plane will become just slightly less than 90 apart from those on the equatorial plane, but if we were to remove a terminal atom from the axial plane, the 3 remaining atoms ...

Andrew Bennecke

I can't think of any examples with the AXE VSEPR, but I believe it would be of a linear geometry if it were to exist because the single loan pair of electrons would want to maximize the distance between itself and the terminal atom.

Andrew Bennecke

I can't think of any examples with the AXE VSEPR, but I believe it would be of a linear geometry if it were to exist because the single loan pair of electrons would want to maximize the distance between itself and the terminal atom.

Andrew Bennecke

Since Kinetic Energy = Initial Energy - Work Function, one could find the frequency of the incoming light by using the De Broglie Equation (Wavelength=Planck's Constant/momentum), you can find the velocity of the ejected electron. Using this velocity in the equation for kinetic energy (E=(1/2)mv^2),...

Andrew Bennecke

Also, the idea of Diagonal Relationships is relevant to the metalloids and other atoms with similar physical properties.

Andrew Bennecke

Since 1 eV=1.602*10^19 J, 1keV=1.602*10^22 J.

Andrew Bennecke

To tell whether a molecule is polar or nonpolar, one could look at whether or not the dipoles cancel, the electronegativity, and whether or not the electron pull of each atom is symmetrical. For example, in F2, the electrons of each F atom have the same pull, so it is a nonpolar molecule. However, i...

Andrew Bennecke

Test 3 will likely contain everything we've covered so far after the midterm, which includes intermolecular bonding and molecular structure.

Andrew Bennecke

We only need to add the charges if it is asking for the most likely resonance structure or strongest contributor to the resonance hybrid.

Andrew Bennecke

Generally, a molecule has resonance structures if a double bond exists with an atom that appears twice in the structure. One example would be in NO3-, the Nitrogen has single bonds with 2 oxygen and one double bond with the third oxygen. In the Lewis structure, the double bond could be on any single...

Andrew Bennecke

I was attempting to do Self-test 2C.2B in the 7th edition of the textbook (Write the Lewis Structure of I3 -). I wondered if it were possible for the terminal atoms to have an expanded valence shell too?

Andrew Bennecke

Thank you, I was genuinely confused about this topic as well!

Andrew Bennecke

I don't know if this is correct, but I believe that the first electron spins up, while the second spins down. I am basing this off of when we draw our electron configurations, we draw the first electron as an arrow pointing up in each orbital.

Andrew Bennecke

No if two atoms have the same n value, then they share degeneracy. The l value is the subshell that the electron is located.

Andrew Bennecke

Since we are unable to use the Ek formula, which formula must we use in order to solve the problem?

Andrew Bennecke

The work function itself, or the values needed to calculate the kinetic energy and initial energy will be given. We are not expected to calculate the work function using the "complicated math".

Andrew Bennecke

I can't seem to figure our which equation to use in part a to calculate the wavelength of the electron. Does anyone know which equation is used?

Andrew Bennecke

Because the problem was given to us with picometers as the primary source of measurement, I believe that the answer should remain in picometers.

Andrew Bennecke

I am confused as to how we know when to switch between different units in the Reaction Stoichiometry section. For example, on number 5a, we are given an amount in kilograms, but the answer in the back of the textbook is in grams. Is this just a subjective preference, or would it affect the amount of...

Andrew Bennecke

Usually if the amount of moles is a decimal, which doesn't appear to multiply easily with the ithers in the compound, you may still have to divide each of the mole values by the smallest mole value.

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