CHEMISTRY COMMUNITY

605168557

How do you know the oxidation number for a species? For example in the reaction MnO4- (aq) + H2C2O4 (aq) --> Mn2+ (aq)+ CO2 (g) the oxidation number for Mn decreases from +7 to +2 and the oxidation number for C increases from +3 to +4 but how do you get these values other than the +2 that is shown o...

605168557

Can someone explain the significance of microscopic reversibility and an example of how we might need to apply it?

605168557

I think the main thing to remember for pseudo-first order rate law is just that N=1 because [B] and [C] are in large excess they remain essentially constant.

605168557

Since it's asking for the change in the internal energy of the reaction mixture resulting from the neutralization reaction, you use the relation of q(reaction) = -q(calorimeter) like the answer book shows. I think we are supposed to assume deltaU = q for this problem because there is a constant volu...

605168557

If at equilibrium G=0 and Ecell=0, and if a positive value for E means reduction is spontaneous, would the value for deltaG also be positive? Is this the same type of direct relation?

605168557

For the final can we assume that there will be a sheet with the Ecell values for reactions like we had with Test 2?

605168557

If we can't measure the electron transfer of one cell in a half reaction what can we compare it to when calculating the e redox ? I remember having to compare it to a standard hydrogen electrode but is there an example for this?

605168557

Also is there another method for finding max potential before any current flow besides using the Nernst equation?

605168557

How is max cell potential related to the Gibbs free energy difference between reactions and products in a redox reaction? Can someone give an example to show the relation?

605168557

When calculating the deltaG of a reaction with standard conditions can we always assume n = 1.00 mol in -nFE?

605168557

Is the work done by a system the same thing as Wmax?

605168557

In general what is the significance of the dependence on cell potential on concentration? Do we just use Le Chatelier's Principle or is there some other explanation for the relation between increasing/decreasing concentrations and the Ecell?

605168557

When finding the rate law (rate function concentration) or the integrated rate law (rate function time), why do we only consider the reactants?

605168557

I have the notes for the problem in class if you need that!

605168557

An electrolyte refers to a chemical compound that can conduct electricity by changing into ions when mixed in a solution. In a cell diagram there is an electrolyte and two electrodes (anode and cathode). The electrolyte is usually some solution of water or other solvents in which the ions are dissol...

605168557

Can someone explain the steps for the method of initial rates to determine k & n ? I couldn't find an example of it in my notes

605168557

In general for all reactions: aA --> bB + cC

The unique rate is -1/a * d[A]/dt = 1/b * d[B]/dt = 1/c * d[C]/dt

The unique rate is the same for all R & P in that 'unique' reaction

605168557

Was the reasoning of snow/ice melting on a sunny day being spontaneous the same reason for part c of this problem where the cooling of a hot cup of coffee after it was just brewed was also supposed to be ΔG < 0 ? I was confused because I thought the phase change causing an increase in entropy wouldn...

605168557

What are the patterns/relations for ordering species in increasing reducing power going from their neutral to second oxidation state given the E value? And also what are the patterns/relations for ordering species in increasing oxidation power going the opposite way from their second oxidation state...

605168557

Can someone explain the steps for this problem please? The ionic dissociation of water is given by the following reaction: The standard enthalpy for the reaction is 58 kJ. mol-1. The Kw for the reaction at 25 degrees Celsius is 10^-14. Is a pH of 7 acidic or basic at 10 degrees Celsius? The reaction...

605168557

I remember during lecture Lavelle went over problems of catalysts in the same phase as R and catalysts in different phases. He also emphasized that catalysts speed up a reaction (k increases) by lowering Ea.

605168557

homework problems! also reviewing lavelle's class notes because he always mentions that any type of problem he goes over during lecture should be known / can show up on exams.

605168557

First make sure your equations are balanced. The second equation is reversed and added to the first, plus 2x the third equation. When you do this the total change in enthalpy equation should look like this: -1300kJ.mol^-1 + 1560 kJ.mol^-1 + 2(-286 kJ.mol^-1) and when you calculate this you should ge...

605168557

You should assume ideal behavior and 1 mol N2 gas so the n value when calculating the change in entropy will be (1.00 mol)

605168557

Did you make sure to convert the 17.4 mg to 0.0174 g CO2? Also when finding the Kc you should be dividing the concentrations of [NH3]^2 and [CO2} by 0.250 not the 25.0 g amount given in the question.

605168557

Did you make sure to convert the 17.4 mg to 0.0174 g CO2? Also when finding the Kc you should be dividing the concentrations of [NH3]^2 and [CO2} by 0.250 not the 25.0 g amount given in the question.

605168557

When we use the equation deltaG= -nFE what are the standard conditions it is pertaining to? Does this mean the conditions before current flow or is that only related to the Nernst equation?

605168557

When calculating the change in Gibbs free energy, if the change in enthalpy is given in kilojoules and the change in entropy is given in joules is there a preference in the units used when converting?

605168557

How is the max cell potential related to the Gibbs free energy difference between reactants & products in redox reactions?

605168557

Why is the ratio (P1/P2) in the equation deltaS=nRln(P1/P2) instead of (P2/P1) like with the case of changing volume and changing temperature?

605168557

Is there a general structure to follow when writing an equilibrium expression when only given the one reactant for example HClO2(aq)? I understand that the H3O+(aq) ion in addition to the acid's conjugate base(ClO2-(aq)) goes on the right side (product side) of the expression but is H2O(l) always in...

605168557

How can you tell when a molecule is more stable given the equilibrium constant? The textbook uses the reasoning that a larger equilibrium constant (for example F2 in comparison to Cl2) to explain that Cl2 is more stable relative to its atoms @ 1000K and I was wondering if someone could explain that ...

605168557

How do you calculate the percentage of decomposition at equilibrium in general? For example, problem 5G.5 from the 7th edition textbook asks what percentage of some diatomic molecule, X2 has decomposed at equilibrium and the answer is (6/11)*100=54.5% but I was confused on where to get those numbers...

605168557

The textbook mentions the formation constant Kf and refers back to a table with formation constants for other coordination complexes in aqueous solutions in a different section. Do we need to know these?

605168557

Does anyone have a list of intramolecular vs. intermolecular forces? (specifically for the problems that ask to name which forces are involved)

605168557

Conjugate acids gains an H+ while the conjugate bases donate an H+

605168557

Ligands are Lewis bases attached to the central atom or ion in a d-metal complex. They typically have 1 lone pair of electrons with which it bonds to the central atom or ion through a coordinate covalent bond. Ligands make up the coordination sphere of the central atom/ion and the number of points a...

605168557

based on the amount of bonding sites to the single central atom

605168557

Chelation involves the formation or presence of 2 or more separate coordination bonds between a multiple bonded ligand and central atom. The 'chelate' just refers to that specific type of ligand. You can identify based on its polydentate structure.

605168557

Is this referring to the cyanide ligand? If so it has a monoanionic charge

605168557

Is it necessary to have the common ligands from table 9C.1 in the textbook memorized? (Not just the neutral ones but the anionic ligands)

605168557

It is possible for rain to be acidic because as it falls from the atmosphere, it collects impurities which change the pH of the rain water to be acidic or alkaline.

605168557

When Ka(cation)=Kb(anion) it is neutral

605168557

Basic salts form from the neutralization of a strong base and a weak acid. For example, the reaction of sodium hydroxide (strong base) with acetic acid (weak acid) will yield water and sodium acetate which is a basic salt. Similarly, acid salts form from the neutralization reaction between a strong ...

605168557

Cl is more electronegative than I. The O-H bond in HOI is stronger than the O-H bond in HOCl. As a result, HOI is a weaker acid.

605168557

Porphyrin ligands have 4 linked pyrrole rings that coordinate the metal ion

605168557

How does the resonance affect the molecule's polarity?

605168557

The strength of the dipole moment isn't really necessary because as long as the structure of the molecule is not symmetric, it will be polar. The number of dipole moments however is necessary, because if the dipole moments cancel each other out, it will be non-polar.

605168557

Melting and boiling points result from the intermolecular forces present. Hydrogen bonding as an intermolecular force will increase both melting and boiling points because greater energy is needed to separate the molecules.

605168557

I think the only way would be to draw the Lewis structure and see if it is attached to the central atom by 2 or more bonds. Knowing the number of donor atoms with electron pairs can also help identify if it would be a polydentate.

605168557

If the value of the quantum number l=0,1,2,3 then the orbital will be s,p,d,f respectively

605168557

ENC refers to the net positive charge of the protons in the nucleus acting on the valence electrons. It is always less than the number of protons present in the nucleus because of the shielding effect (decrease in attraction) where the more electron shells there are, the greater the shielding effect...

605168557

Since salts consist of a positive ion of a base and the negative ion of an acid, it will neutralize in the reaction.

605168557

Transition metals have the highest number of unpaired valence electrons which are unstable and will want to form bonds, allowing for several different oxidation states.

605168557

When they said more than one 'tie' were they referring to ligands bonding through multiple sites and is that the same as bonding through more than one atom?

605168557

I was confused on that too because I drew them next to each other but I wasn't sure if there was overlap or not

605168557

I think you can use the bonds around the lone pair to determine the hybridization. If you know the hybrid orbitals used to build the sigma bonds (for example, an sp^2 hybridized nitrogen atom has 3 sp^2 orbitals and 1 p orbital), then you can determine the lone pair of electron is in a p orbital.

605168557

Polyprotic means there are multiple acidic protons that dissociate. Polyprotic acids can lose 2 or more of these protons, which become less acidic as they are lost in sequential steps.

605168557

amphoteric = can act as both an acid and a base

I sometimes confuse it with amphiprotic so just a reminder amphiprotic means it can both donate or accept hydrogen!

605168557

if both possible structures have similar values for FC, then when the central atom has a formal charge = 0 that should be the most stable resonance structure.

605168557

I think if you know the equilibrium constant you can calculate these values similar to pH and pOH.
pKa=-log(Ka)
pKb=-log(Kb)

And then you know a large Kb value indicates the high level of dissociation of a strong base, so a lower pKb value will indicate a stronger base.

605168557

These are the abbreviations for ethylenediamine and ethylenediaminetetraacetic acid when the respective complex compounds are ligands (when attached to a central metal atom through coordinate bonding)

605168557

Is homework still being collected by TAs at the end of lecture on Friday or are they collecting it during discussion sections now?

605168557

Depending on the metal's properties, it is easier to remove electrons from some metals than others. The variations in threshold energies are dependent on the metal's work function. The smaller the work function (minimum amount of energy required), the lower the frequency.

605168557

The textbook also uses v to represent frequency, for example in the relation lambda (wavelength) * v ( frequency) = c (speed of light)

Search found 65 matches