CHEMISTRY COMMUNITY

Sahil Jog 1F

The pre equilibrium approach basically accounts for the rate-limiting reaction to be the rate law for the overall reaction. Furthermore, Dr. Lavelle says not to worry about the steady state approach, since it would not be covered on the syllabus.

Sahil Jog 1F

Since 50 mL of 2M HCl and 50 mL of 2M NaOH is the most concentrated solution and makes the least amount of water as a product, it would be the right answer. We would need to make sure that the least amount of water is produced, since water has a very high specific heat capacity, which would hinder a...

Sahil Jog 1F

You're definitely correct. You would need to first calculate the temperature change of the copper as it absorbs 65 J of energy, and once you get that temperature, you would then calculate the change in entropy by plugging it into the entropy equation that deals with changes in temperature. Hope this...

Sahil Jog 1F

It is absolutely necessary to concert your answer to mols before doing many of the calculations, since a lot of them involve exponents and logarithms, which would lead to a different answer if not converted beforehand.

Sahil Jog 1F

If there are stoichiometric coefficients, then the overall rate of the reaction would change. For the chemical reaction aA ----> bB, the rate would equal (-1/a)*d[A]/dt = (1/b)*d[B]/dt, where a and b would be the stoichiometric coefficients of the reaction. Setting these equal to the experimentally ...

Sahil Jog 1F

We would only use a reverse reaction rate if the book specified to do so, or if the chemical reaction is an equilibria chemical reaction. Remember that once the system is in equilibrium, the forward reaction rate equals the reverse reaction rate.

Sahil Jog 1F

I would suggest looking at Dr. Lavelle's outlines on his website and make sure that you truly understand everything listed on them. Other than that, it is always useful to know all of their biological significances since it might help you connect numerous chemistry concepts together on the final!

Sahil Jog 1F

This would all depend on which order the reactants are at. For example, for a first order reaction, the rate of the reaction will be proportional 1:1 with the reactant, while in a second order reaction, the rate of the reaction would be exponential to the factor of two as compared with the reactant.

Sahil Jog 1F

Usually, to determine the order of a certain reaction, you would need to do it through experimental results that Lavelle will provide for you on the exam. Remember not to just use the coefficients from the chemical reaction! That is only for the equilibrium constant.

Sahil Jog 1F

You would need to use the Arrhenius equation whenever you would calculate the activation energy, or the reaction constant from a change in temperature.

Sahil Jog 1F

An oxidizing agent is a substance that gets reduced, while a reducing agent is a substance that gets oxidized. For example, let's say we have substance A (reducing agent) and substance B (oxidizing agent). An easier way of conceptualizing this would be to think that substance A needs to give away it...

Sahil Jog 1F

The first one would represent the reduction of water, since we are reducing water by giving it electrons. While the bottom equation represents the formation of water because of the reduction of oxygen.

Sahil Jog 1F

A shorter way of determining how many mols of electrons are being transferred would be to just look at the oxidizing or reducing agent in the equation and determine how many mols of electrons it is losing or gaining. Assuming the equation is balanced, that would be the n in your equation. Hope this ...

Sahil Jog 1F

In general, you are going to have to use the Nernst equation when we are dealing with a concentration cell, since concentrations not at equilibrium of the cell can affect the EMF of the cell. Other than that, you could use it for cells that are not at their respective equilibrium concentrations of p...

Sahil Jog 1F

Since pH = -log[H+], we can easily calculate the concentration of the H+ ions, and thus we would have a concentration cell based off of "pH". We would then use these concentrations to get a range of the minimum and maximum concentration difference and thus the min/max Ecell. This would the...

Sahil Jog 1F

Outline 5, since it covers all of electrochemistry, but you can still get started on outline 6 as long as you understand the material beforehand.

Sahil Jog 1F

As far as I know, as the electrons on the solar panel grid get excited, they move onto a different surface above this grid. This would create one grid with electrons and one panel without. Paired with conductors and a wire, we would then have the electrons flow back into its original grid and genera...

Sahil Jog 1F

Since you know that oxygen in an acidic solution would reduce the oxygen to H2O, because of the abundance of protons in the acidic solution. Thus, the cathode would be oxygen in the acidic solution and the anode would be oxygen in the basic solution.

Sahil Jog 1F

For the large part of this course, if the hydrogen is bonded to an anion, then we would assume that the oxidation number for the hydrogen is +1. However, in the case of metal and salt hydrides, like LiH or CaH2, since it is bonded to a cation, hydrogen would have an oxidation number of -1.

Sahil Jog 1F

Standard Condition is always going to be 1M when dealing with concentrations, 1 atm when dealing with pressures at 273.15K.

Sahil Jog 1F

For the most part, yes. Since most of the problems require you to either find the concentration of reactants, products, the voltage of the cell, etc. , you should assume that there will be a positive voltage unless specified.

Sahil Jog 1F

When emf is negative, the cell does not "absorb energy". All this means is that the reaction would be unfavorable and thus non-spontaneous. Hope this helps.

Sahil Jog 1F

There are numerous examples of autoprotolysis other than H20, since autoprotolysis is the proton transfer between two of the same molecules. An example would be acetic acid: CH3COOH <------> CH3COO- + CH3COOH2+. In addition, the Keq would likely be very very small, favoring the reactants, since they...

Sahil Jog 1F

Don't forget that the temperature is changing in the Van't Hoff Equation, since it relates the Keq with a change in temperature. Thus, this makes the change in Gibbs Free Energy not constant.

Sahil Jog 1F

We should always keep track of the electron transfer between the molecules that are getting reduced and oxidized, since we are assuming that throughout this reaction, the mass of all the molecules is conserved, thus the electrons as well.

Sahil Jog 1F

To understand why pressure does not change during an isobaric process, we need to first understand what "pressure" is. Pressure is directly proportional to the frequency at which the gas molecules collide with the piston and their speed. In order to conserve the pressure throughout this pr...

Sahil Jog 1F

Honestly, I do feel the same way about this midterm, since it did involve high level problem solving skills which you cannot really prepare for except for just practicing problems. However, I think that the best way to prepare for a midterm like this would still be more and more practice problems un...

Sahil Jog 1F

We would use this equation when we are given the degeneracy, but Lavelle might make us calculate W first. Remember that W=(# of positions the molecules could be at)^(# of atoms or molecules).

Sahil Jog 1F

Could someone please summarize this chart please? What is R and why would it be the way it is on the chart?

Sahil Jog 1F

Yes, that equation and also the fact that G is also a state function. This would mean that the standard free energy formation of a reaction would equal the standard free energy formation of the products minus the standard free energy formation of the reactants. This could come in handy on the midterm.

Sahil Jog 1F

There is no difference between these equations. q=CAT happens when m=1 g.

Sahil Jog 1F

When n=1 mol, the molar heat capacity (q=nCAT) would equal CAT. Similarly, when m=1 g, the specific heat capacity (q=mCAT) would equal CAT.

Sahil Jog 1F

Having a concentration of 3.1M would definitely result in a negative pH. There are certain acids called superacids that do result in a negative pH, since they are so strong. Thus, remember that if you get a negative pH with a high molar concentration of H30+ ions, the formula is still -log(concentra...

Sahil Jog 1F

To determine how this reaction is affected by temperature, you would need to look if the reaction is exothermic or endothermic. If the reaction is endothermic (which I assume it is), then increasing temperature would favor product formation and vice versa for if the reaction is exothermic.

Sahil Jog 1F

It is just a difference in notation. I do not really know why he makes it this confusing.

Sahil Jog 1F

Under conditions of constant pressure, the piston has to be freely movable, thus accommodating for the constant pressure when heated. This would mean that under constant pressure the q would be the enthalpy change or equivalent to the amount of heat added. However, under conditions of constant volum...

Sahil Jog 1F

Yes they are referring to constant external pressure, since a dynamic external pressure would do unnecessary work on a system, and thus be unreasonable problem to solve.

Sahil Jog 1F

Yes, since Lavelle just finished Thermochemistry and just started Thermodynamics.

Sahil Jog 1F

I assume that he might give us a brief overview on this material very soon. The general idea is that most of the energy in a molecule would be stored in the vibrations of their respective bonds, rotations of single bonds, and translations.

Sahil Jog 1F

We utilize the integral when both the pressure and volume of a system are changing. This is because if we have a system with constant pressure and a change in volume, the integral would basically be the area of the rectangle which is P*(delta)V and no need to use calculus. If the pressure in changin...

Sahil Jog 1F

When the total entropy of a system is negative, this would indicate that the final entropy state of the system is less than its initial, or in simple terms, the system has become more ordered while increasing the disorder of its surroundings. The reverse reaction then, might be spontaneous, as it wo...

Sahil Jog 1F

They are essentially the same thing, but with one small difference. Standard reaction enthalpy would be the difference between the enthalpies of the reactants and products, but standard enthalpy of formation would be the difference between the enthalpies of the reactants and products in their standa...

Sahil Jog 1F

Amphoteric molecules are molecules that are both acidic and basic in character, while amphiprotic molecules are molecules that can both donate and receive H+ ions. Usually an amphoteric molecule is also amphiprotic due to the commonality of being both an acid/base and donating/receiving H+ ions. For...

Sahil Jog 1F

Since no chemical reaction takes place, no bonds or broken nor formed. Thus, the standard reaction enthalpy change would be 0. This is the only element to consider when looking at a reaction that does not occur under standard conditions.

Sahil Jog 1F

Since a single water molecule consists of H2O, when it ionizes into H30+ then we would have a remainder of one hydroxide molecule (OH-). Thus a concentration of 10^-7 mol/L H3O+ would mean that the solution also has 10^-7 mol/L OH-, and thus the solution would be neutral or a pH of 7.

Sahil Jog 1F

When you're given the bond enthalpies on a table, you would make the enthalpies negative when bonds are formed (the products). This is because the net enthalpy of a reaction is the enthalpies of bonds broken minus the bonds formed.

Sahil Jog 1F

An increase in temperature in endothermic reactions would favor product formation, since it requires energy or heat for the products to form. Furthermore, in an endothermic reaction an increase in temperature would cause an increase in K, and thus more product formation. This effect is the opposite ...

Sahil Jog 1F

Yes, acid and base reactions are just like other reactions and most of the time are at equilibrium, unless the problem states otherwise.

Sahil Jog 1F

K is very energy dependent, because adding or taking away heat from a chemical reaction would change the overall kinetics of the reaction itself, and thus affect K. Changing the concentrations would not change K, as increasing the concentration of products would result in an increase in concentratio...

Sahil Jog 1F

Decreasing the pressure would mean that it would increase the volume of the reactants/products. This would indicate that the concentration of the reactants/products would decrease. This would mean that the reaction would shift towards the side with the least amount of moles, since it would have a lo...

Sahil Jog 1F

Yes, the K value would only include the partial pressure of gases or their concentrations. Furthermore, solids and liquids would not be present in the equation.

Sahil Jog 1F

I am fairly sure that Dr. Lavelle will go over acid/base titrations between tomorrow's lecture or Friday's. Anything he taught from week 1 is fair game for the first test.

Sahil Jog 1F

If the reaction is exothermic, then adding heat to the reaction would make the reverse reaction more favorable, and thus more reactants would form. Vice versa for removing heat. If the reaction is endothermic, then adding heat would make the forward reaction more favorable. Vice versa for removing h...

Sahil Jog 1F

During Dr.Lavelle's last lecture he mentioned that changes in pressure does not necessarily cause a forward or reverse reaction to be favored. Instead, he said that it all relies on changes in concentration not change in pressure. Can someone please explain this?

Sahil Jog 1F

Usually, you would use Kp for gases and Kc for other compounds with given concentration. However, whichever you use, you would get the same equilibrium ratio, so it does not really matter.

Sahil Jog 1F

Typically, you would use Kc when you are given the concentration of the compounds, while Kp when you are working with gases. But in this case, it would not really matter which ones you use to calculate, since the equilibrium ratio would be the same.

Sahil Jog 1F

You would need to know the quadratic equation only when you do not know the change in initial partial pressure and the final partial pressure. In order to compensate for this, we would say that the change would be x and thus the final partial pressure for the products would be x, while the final par...

Sahil Jog 1F

If pH<PKa, then the solution will be more acidic. This is due to the shift in chemical equilibrium, as the weak acid will deprotonate in order to shift the solution's acidity so that pH=PKa.

Sahil Jog 1F

Since Flourine is such a small molecule, the bond between fluorine and the hydrogen is the shortest when comparing the other halogen-based acids. This would mean that it is much more difficult to break this bond and thus less H+ exist in an aqueous solution of HF.

Sahil Jog 1F

I think this means to make sure that you understand that the atomic orbitals are electron density probability regions (areas in which the electrons exist, not the individual electrons themselves). This is because of the Heisenberg's uncertainty principle, since we cannot know the momentum and the po...

Sahil Jog 1F

A general guidline to figure out conjugate acids and bases would be to draw the formula out and first identify the acids and bases involved in the reaction. Then, looking at the products, the product of the acid would be its conjugate base and the product of the base would be its conjugate acid. For...

Sahil Jog 1F

I really doubt that you would have to memorize the hydrocarbon structures, since that is basically organic chemistry. It would however be helpful to know some common hydrocarbons, such as benzene, methane, and ethane.

Sahil Jog 1F

An oxoacid is any acid containing an oxygen group. The presence of the oxygen group helps withdraw the electrons and stabilize the structure, which would then result in a stronger acid.

Sahil Jog 1F

HOCl and HOI are both oxoacids and act quite differently, because of the oxygen involved in their structure. Since the electrons are withdrawn (or pulled due to the high electronegativity of oxygen and chlorine), they are delocalized and are more prone to get rid of the H+ proton than HOI. But when ...

Sahil Jog 1F

Drawing the Lewis structure and calculating the charges definitely would give you the net charge of the molecule. However, it would be much easier and more efficient if you just memorized the charges of common polyatomics and ligands.

Sahil Jog 1F

In chemistry, a conjugated system generally refers to a molecule, in which the electrons are delocalized and are much more stable. this usually occurs in the hybridization of the p-orbitals involved in the respective atoms. Since the electrons are delocalized, the molecule is much more stable. I don...

Sahil Jog 1F

I think it would be helpful to understand the chemical properties of EDTA and their purposes when they act as ligands. Other than that, I would not expect him to ask us its molecular structure.

Sahil Jog 1F

The product of Cl- + SO2 would essentially be SO2Cl. This could be very easily figured out by drawing their respective Lewis structures and checking for any lone pairs which the atoms can either donate or receive, Since SO2 has one lone electron, and chlorine has 7 valence electrons, they can form a...

Sahil Jog 1F

Since you know that nitrate has a negative charge, it would most likely be bonded to a hydrogen and act as an acid. Vice versa for zinc, because of its positive charge. Thus, this reaction takes into consideration that zinc hydroxide (a base) reacts with nitric acid (an acid) and forms a salt (zinc ...

Sahil Jog 1F

Since the other halogen based acids are much stronger than HF (due to weaker bonds between hydrogen and the halogen), they would not be strong conjugate bases. HF would be the only halogen based acid that is a strong conjugate base for a weaker acid.

Sahil Jog 1F

I really doubt that the exam will be on topics that we haven't yet tested on. It will most likely be an equal distribution of topics from before the midterm and after the midterm. I'm assuming that the exam will be hard, not because of the content, but the combination of different concepts. Or bette...

Sahil Jog 1F

I would assume that resonance structures would not rotate, since their electrons are still delocalized throughout the molecule, which expresses a similar 3 dimensional structure as a double bond (1 sigma and 1 pi bond), and thus not allowing for rotation.

Sahil Jog 1F

Firstly, a molecule is ionic based off the electronegativity difference between its bonded atoms. If it's great enough, then it displays ionic character. Next, a polyprotic acid is an acid that could donate multiple protons (H+) instead of one. An example of a polyprotic acid is H2SO4, where 2 H+ ca...

Sahil Jog 1F

The EDTA ligand would form an octahedral complex once it's bonded to the metal ion and it would wrap around it. The molecule itself does not look like it can wrap around the central transition metal ion, but because of VSPER theory, its shape is very complicated due to numerous trigonal planar and t...

Sahil Jog 1F

To do 9C3, you would need to understand how they write the coordination complex and translate it to the chemical formula. Once you understand that, the easiest way to do the problem would just be to break it down bit by bit. potassium hexacyanidochromate(III) becomes potassium (K), hexacyanido (6 cy...

Sahil Jog 1F

For a molecule to be a polydentate, it must must donate more than one pair of electrons to the central transition metal. Also, because of the shape of certain molecules, they are only able to donate one pair of electrons to the central atom, even if they have more lone pairs. Taking all this into ac...

Sahil Jog 1F

A chelate is a compound where the central atom is essentially "wrapped" inside a ring created by more molecules. These molecules need to be bonded to each other in a ring shape, essentially allowing for greater stability of the entire molecule. You can tell whether a compound is a chelate ...

Sahil Jog 1F

To form a chelating complex, you would need the molecules that form a ring relatively close to each other, so they can bond with each other. This essentially "wraps" the central atom in a ring, and thus makes it a chelating complex. Since isomers a and c do not have the amine group close e...

Sahil Jog 1F

From all the problems that I have done, I think iron is the only exception where we use the Latin name for the transition metal. But all the other times we should use the English name.

Sahil Jog 1F

Chelates are able to bind to cations tightly because of their stable ring structure, allowing for more rigidity. In simpler terms, the cation is essentially "tucked in" the chelating complex, and the rings around it allow for a much more stable and strong shape.

Sahil Jog 1F

Resonance should not affect the way we name chemical compounds in this course.

Sahil Jog 1F

In molecules, such as CH2F2 the bond angles would of course not be exactly 109.5 degrees, because of the different size of the atoms attached to the carbon. However, for the sake of simplification, we can assume that they are roughly 109.5 degrees. This would indicate that the F-C-F bond angle would...

Sahil Jog 1F

The best way to tell the bonds apart would be to look at the electronegativity difference between the two atoms. The greater the electronegativity difference, the greater the ionic character behind that bond and vice versa. Furthermore, you can analyze the polarizability of the two atoms to figure o...

Sahil Jog 1F

To start this problem, you would first need to sketch the Lewis structures of each molecule, since you need the Lewis structure to correctly identify the VSEPR model for each molecule. Then, according to the VSEPR model, you can calculate the electron density clouds around each central molecule (Pho...

Sahil Jog 1F

The hybridization on all the carbons would be sp2, since each carbon has 3 electron density clouds. The hybridization on the oxygen attached would be sp3, since the oxygen has 4 electron density clouds.

Sahil Jog 1F

Part D of this question asks for which molecule has a more covalent character, not the one with the greatest lattice energy. Since Tl2O would have a charge of +3, it would be more polarizing, and thus a greater covalent character.

Sahil Jog 1F

It is particularly difficult to deduce dipole moments by looking at a chemical formula. It would be much more helpful if you drew out the Lewis structure of the molecule and utilizing electronegativity to figure out where the electrons or negative dipole are pulled towards. This would help you under...

Sahil Jog 1F

I would assume that you would need to know T-shaped geometry, since it is the structure of many molecules, such as ClF3, where the Chlorine would have 3 bonded pairs with Fluorine, but 2 lone electron pairs, creating a T-shape.

Sahil Jog 1F

Even if a molecule with a trigonal pyramidal shape looks to be arranged tetrahedrally (bond angles=109.5), the lone electron pair has a greater electron repulsion strength than a bonded one, forcing the 3 bonded atoms closer to each other, and thus making their bond angles slightly less than 109.5.

Sahil Jog 1F

The molecular shape would be the 3 dimensional shape of the molecule, emerging from their respective electron arrangement. A specific electron arrangement between atoms would determine the shape of the molecule, as the electron-electron repulsion would be the force holding its shape.

Sahil Jog 1F

The seesaw shape is more favorable, since the most stable structure would be the one with the least electron repulsions. The only way to accomplish this on a structure with 4 bonding pairs and 1 non bonding pair would be to position the electrons in such manner.

Sahil Jog 1F

Atomic spectroscopy deals with electron transitions within in one atom, while molecular spectroscopy deals with electron transitions in two or more bonded atoms. Since the bonding of atoms alters their orbitals and where the valence electrons are truly located, they would have very similar, but diff...

Sahil Jog 1F

A coordinate covalent bond is different from a covalent bond, because instead of both atoms each sharing one electron to form a bond, there is only one atom that donates two of its electrons to form a bond. Coordinate covalent bonds do not just occur in Lewis acids and bases, and could also be found...

Sahil Jog 1F

We use brackets when the overall compound has a net charge, or when using ionic molecules, since in ionic molecules, the anions simply strip away the electron from the cation. Thus, leaving the cation with a new positive charge and the anion with the net negative charge.

Sahil Jog 1F

Correction on the last part of my response: N2O would be most stable when triple bonded to a nitrogen and double bonded to the oxygen*

Sahil Jog 1F

The reason why you may put the extra electron on one atom and not the other does not depend on electronegativity, but depends on the formal charge. Since it is a universal rule that most things in the universe love to attain maximum stability, the most stable Lewis Structure of a molecule would be t...

Sahil Jog 1F

I highly doubt that we need to know any polyatomics, since they most likely will be listed on any one of the questions that have them. But, it is helpful to know these ones: C2H3O2- Acetate CN- Cyanide ClO- Hypochlorite ClO2- Chlorite ClO3- Chlorate ClO4- Perchlorate CO3- Carbonate SO4- Sulfate MnO4...

Sahil Jog 1F

This is a very complicated question, but most of the time the ionic radius has the opposite periodic table trend than the atomic radius, since the atomic radius is the general radius of the atom, while the ionic radius would be the general radius of the ion. Since certain atoms lose or gain electron...

Sahil Jog 1F

If you take NO3- (Nitrate) for example, Nitrogen would need to form a single double bond with Oxygen in order for it to be stable. Since we have 3 Oxygens that it can form a double bond to, we can write out three different Lewis Structures of Nitrate, indicating that it is a resonance structure. Fur...

Sahil Jog 1F

You were really close, but the formula goes like this. Frequency = R ((1/nf^2) - (1/ni^2)), where nf means n (final) indicating that this is where the electron will be at the end and ni meaning n (initial) indicating where it started. I think you switched your initial and final values, resulting in ...

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