CHEMISTRY COMMUNITY

Christopher Tran 1J

The equation ln(k 2 /k 1 )= Ea/R(1-T 1 -(1-T 2 ) is derived from the Arrhenius equation for two temperatures. ln k 2 = -Ea/RT 2 + ln A ln k 1 = -Ea/RT 1 + ln A By subtracting the two equations, you get ln k 2 - ln k 1 = -Ea/RT 2 + Ea/RT 1 Then you can factor out -Ea/R to get ln k 2 - ln k 1 = -Ea/R ...

Christopher Tran 1J

The species with the greatest reducing power has the most negative value, so the answer is:

Pb < Cd < Mn

Christopher Tran 1J

Could someone let me know what they got for 6 a, b, and c for Test 3, and how they reasoned out the answers? a. In order of increasing reducing power going from their neutral to second oxidation state: Pb, Cd, Mn b. In order of increasing oxidation power going from their third oxidation state to neu...

Christopher Tran 1J

What would be the purpose of finding the average or instantaneous rate of a reaction?

Christopher Tran 1J

A reaction involving [A][B] is not necessarily a second order reaction since the rate of the reaction might not be dependent on the concentration of one of the reactants (such as when they're already in excess compared to the other reactant). The sum of the powers of the reactant concentrations have...

Christopher Tran 1J

In a zero-order reaction, concentration decreases over time (linear with slope -k). In a first-order reaction, ln/concentration decreases over time (linear with slope -k). In a second-order reaction, 1/concentration decreases over time (linear with slope k). https://chem.libretexts.org/@api/deki/fil...

Christopher Tran 1J

I also was unsure about why they rounded to one sig fig. I tried it with the log equation instead of ln, and got 10^6 that way.

Christopher Tran 1J

To find n, you can write out the two half-reactions for the cell reaction: Reduction: 6 Fe 3+ (aq) + 6 e- -> 6 Fe 2+ (aq) To balance the charges on both sides, 6 e- is added to the left side. Oxidation: 2 Cr 3+ (aq) + 7 H 2 O (l) -> Cr 2 O 7 2- (aq) + 14 H + The left side has a total charge of 6+ an...

Christopher Tran 1J

n is the number of electrons transferred in the cell reaction, and you can calculate it by finding the half reactions and determining the number of electrons exchanged.

Christopher Tran 1J

The standard Gibbs free energy of a cell reaction is calculated with the formula:

delta G = -nFE, where n is the number of electrons transferred.

For the first reaction, determine the half reactions for the oxidation and reduction parts and balance them to find the number of electrons transferred.

Christopher Tran 1J

Could someone explain the purpose and importance of having a salt bridge between the galvanic cells?

Christopher Tran 1J

Acids and bases tend to be expressed as aqueous in solutions with water as a liquid. However, when they dissociate with water, the conjugate acid/base and the water that donates or accepts a proton are all considered aqueous in the solution.

Christopher Tran 1J

The question basically asks you what the value of the equilibrium constant (K) means. If it is significantly large (>10^3), then that means the reaction favors the right side of the equation, meaning that products are more stable than reactants. If it's significantly small, then the reactants are mo...

Christopher Tran 1J

Work is being done on the system when w is positive, since the internal energy (U) of the system increases.

Christopher Tran 1J

oops didn't know there were different forms. The question asks for the pH of a .030M solution of sodium sorbate(C6H7O2), given that the pKa of sorbic acid(C6H8O2) is 4.74. The reaction is: C6H7O2+H2O<=>C6H8O2+OH Ka = 1.82*10^-5 Kb = 5.50*10^-10 x = [OH-] = 4.06*10^-6 pOH = 5.39 Therefore, pH = 14-5...

Christopher Tran 1J

If your question had a pKa value of 4.17 for 0.040M sodium ascorbate, the pH of the solution is 8.39.

Christopher Tran 1J

The delta H of the system is equal to the negative delta H of the surroundings; the answer key basically just puts a negative sign before delta H of the system in the equations where you can also use delta H of the surroundings.

Christopher Tran 1J

During a phase change, the energy is used to either form or break bonds, rather than increase the temperature of the substance by increasing its kinetic energy.

Christopher Tran 1J

I'm pretty sure your first equation should be ln(V2/V1).

Use delta S = n*R*ln(V2/V1) for an isothermal process, and delta S = n*Cv (or Cp)*ln(T2/T1) when there is a temperature change.

Christopher Tran 1J

Residual entropy just means the randomness of the system based on the position of the elements/molecules inside of it, when there is no movement (temperature is K=0).

Christopher Tran 1J

Gas molecules tend to occupy a larger space and move freely at higher speeds than liquids and solids, meaning that there is a greater number of possible states (position) that they can occupy compared to liquids and solids. This ultimately means that gases tend to have greater entropy than liquids, ...

Christopher Tran 1J

Normal entropy refers to the randomness exhibited by the elements of a system due to their constant movement (like molecules in liquid). Residual entropy is entropy at absolute zero, meaning that the elements are no longer moving. Even though there is no movement, there is still residual entropy due...

Christopher Tran 1J

Cp refers to the heat required to raise the temperature of one mole gas by 1 degree C at constant pressure, and Csp refers to the heat required to raise the temperature of one gram gas by 1 degree C at constant pressure.

Christopher Tran 1J

To find out the final temperature, you should start out by writing the chemical equation and figuring out which is the limiting reactant (that's what the molarity values are for). After finding out the limiting reactant, you can then find the enthalpy of reaction (delta H) and multiply that by the n...

Christopher Tran 1J

Metal cations in water will form tetra- or hexa- aqua complexes in water. The Al cation in water will form Al(H 2 O) 6 3+ , which will act as a weak acid with Ka = 1.4 x 10^-5. (This is all in 12.13 in the textbook). So the equation is: Al(H 2 O) 6 3+ (aq) + H 2 O (l) -><- H 3 O + (aq) + Al(H 2 O) 5...

Christopher Tran 1J

Yes, if the percent deprotonation is less than 5%, then you are safe to approximate by assuming that a change of 0.1-x, for example, is 0.1.

Christopher Tran 1J

When pressure is increased, equilibrium will favor the side with less moles of gas. Since the reaction has two moles of reactant gas and two moles of reactant product, there is no change in equilibra.

Christopher Tran 1J

Percent ionization is the concentration of {H3O+] or [OH]- divided by the initial concentration of the acid or base, multiplied by 100%.

Christopher Tran 1J

HF is a weak acid due to the high electronegativity difference between hydrogen and fluorine, making it harder for HF to give up an H+ and dissociate.

Christopher Tran 1J

I have the 6th edition textbook and solution manual for it. As I was working on 12.29 part d, i noticed that I got pOH=0.15 & pH=13.85 but the solutions manual has pOH=3.15 and pH=10.85 . The way i solved was ((2.00 mL/.500mL)*(.175))= .7 then i did -log(.7) which gave me the pOH=.15 what the b...

Christopher Tran 1J

Instead of explaining that, as volume decreases, the reaction shifts towards the side with less moles of gas, Dr. Lavelle is saying that it is better to discuss the effect of the volume change in terms of concentration. He used the reaction N2(g) + 3 H2(g) => 2 NH3 (g) to explain the concept: For ex...

Christopher Tran 1J

Increasing the pressure for gases will not affect the equilibrium constant, but changing the temperature of the system will.

Christopher Tran 1J

The equilibrium value K is constant, so if you were to increase the concentration of reactants, that would mean the concentration of the products would also need to increase in order to maintain the constant value of K.

Christopher Tran 1J

It's basically the textbook, but with just the pages not bound together. It comes with an access code so that you can get the online version of the textbook as well.

Christopher Tran 1J

Order these anions in order from least to most polarizable: I-, Cl-, S2-, P3- Order these cations in order from least to most polarizing power: Li+, Ca2+, Cs+, Ba2+ How would I go about determining the relative sizes of ions? I know that a small cation has high polarizing power, and a large anion is...

Christopher Tran 1J

H3O+ and H+ in an aqueous solution basically mean the same thing, as H+ in water is the hydronium ion. Both are used interchangeably, H+ is just the shorter way.

Christopher Tran 1J

I just remember it as, since Lewis structures involve electron pairs, a Lewis acid accepts (A in acid -> accept) electron pairs and a Lewis base therefore donates electron pairs.

For Bronsted, I have to just remember that an acid donates a proton/H+ and a base accepts a proton/H+.

Christopher Tran 1J

I think that we will mostly focus on calculating pH, but I would know how to find pOH from pH, [H3O+], and [OH-] just in case.

Christopher Tran 1J

Couldn't there be double bonds connecting the two oxygen atoms with two lone pairs to the central atom, along with one lone pair on the central oxygen? That would lead to 18 total electrons and a formal charge of zero for all three oxygen atoms. Or does the central oxygen also have to obtain a full ...

Christopher Tran 1J

London dispersion forces increase as the size of the molecule increases, particularly surface area by which the interactions can take place.
Pentane is linear and not as compact, and therefore should have stronger London forces.

Christopher Tran 1J

Polarizability is the ease by which an electron cloud can be distorted, while polarizing power describes the ability to distort an electron cloud. Polarizability describes an anion, and increases as its size increases (since a larger electron cloud is easier to distort) and negative charge decreases...

Christopher Tran 1J

I am pretty sure we are not expected to know how to calculate the actual dipole moment/charge difference, just be able to identify if a molecule has a dipole moment or not.

Christopher Tran 1J

HCl forms a covalent polar bond between H and Cl, since both are nonmetals and have a electronegativity difference of less than 2. Therefore, since it is covalent and polar, a dipole moment exists in HCl where the negative end of F and the positive end of H in another HCl molecule attracts each other.

Christopher Tran 1J

In CH2O, carbon forms a double bond with oxygen. Double bonds consist of one sigma bond and one pi bond. Therefore, there are 3 sigma and 1 pi bonds.

Christopher Tran 1J

Forming double bonds with oxygen allows the oxygen atoms to have a formal charge of zero, rather than -1 with single bonds.

Christopher Tran 1J

The topics discussed in lecture on Monday (ligands and coordinating compounds) will not be covered on Test 3, right?

Christopher Tran 1J

Oxygen has a greater electronegativity value compared to chlorine. Both compounds are ionic, but since the electronegativity difference between oxygen and phosphorous is greater, compound A, P4O10, has greater ionic character.

Christopher Tran 1J

Typically nonmetals located in period 3 and below are able to have expanded octets, but metals are unlikely to have expanded octets as they tend to lose electrons instead of gaining in order to fill a valence shell.

Christopher Tran 1J

Balancing chemical equations makes sure that the number of moles of reactants and products are the same, and therefore agree with the law of conservation of mass.

Christopher Tran 1J

Week 8 homework should be turned in with week 9 homework if your discussion is on Thursday or Friday. I would ask your TA if your discussion section is on Tuesday or Wednesday, though.

Christopher Tran 1J

Electron geometry describes the arrangement of electrons in an atom, including lone pairs, while molecular geometry describes the arrangement of atoms without lone pairs. A molecule with two atoms bonded to a central atom and one lone pair, such as H2O, will have a trigonal planar electron geometry....

Christopher Tran 1J

From Dr. Lavelle's website:

Test 3 covers: End of Bonding from 3.12 (6 Ed.) and from 2D (7 Ed.); and all of Molecular Shape and Structure

Christopher Tran 1J

I learned in high school that, with each additional lone pair, the bond angles are typically reduced by 2.5 degrees from what is suggested by the model. However, as long as you note that the angles are less than the model, that should be fine.

Christopher Tran 1J

Typically, when a lone pair is present in the molecule, bond angles will slightly differ since lone pairs repel other electrons more strongly than bonded pairs.

Christopher Tran 1J

Does anyone know where/if there's a VSEPR chart in the 6th edition of the textbook?

Christopher Tran 1J

You can determine which atoms have ionic bonds by looking at their electronegativity differences. A difference of over approximately 2 typically means that there is an ionic bond. The Ba - Br bond has a larger difference in electronegativity values compared to Be + Br and B + Br. Br = 2.96, Ba = 0.8...

Christopher Tran 1J

Why is there a decrease in electronegativity for one of the elements between atomic numbers 20 and 30, and between 40 and 50?

Christopher Tran 1J

Alpha represents the polarizability, which depends on the number of electrons and the size of the atom or molecule. r is the distance between the two atoms or molecules. The potential energy equation shows that an increase in size or molar mass,, or a decrease in distance, leads to a stronger attrac...

Christopher Tran 1J

Should our Week 6 Homework include topics that were already covered on the midterm, or only the new material from Friday's lecture?

Christopher Tran 1J

Nitrogen should be in the center of the Lewis structure since it is the least electronegative atom of the two.

Christopher Tran 1J

The central element for the Lewis structure of ONF should be the atom with the lowest electronegativity, which in this case is nitrogen.

Christopher Tran 1J

Oxygen is more electronegative compared to chlorine, and therefore should be the atom with the negative formal charge in the molecule.

Christopher Tran 1J

Finding out the formal charge of the central atom should tell you whether or not the element will follow the octet guideline, given that the element is in Periods 3+. For example, in ClO4-, three O are double bonded with the Cl so that the Cl has a formal charge of zero. If the three O were single b...

Christopher Tran 1J

Metals tend to lose electrons in order to acquire a noble gas configuration, and for Ga, it is easier to lose three electrons than to gain five electrons.

Christopher Tran 1J

HClO3 has 1+7+(3*6) = 26 valence electrons Start by putting Cl in the center (since it's the least electronegative), then draw the three oxygen around the Cl. For one of the oxygen, add the hydrogen next to it. Connect each of them with a single bond, and then fill the rest of the lone pairs. Howeve...

Christopher Tran 1J

The question notes that v/c is used to represent energy with unit cm-1 (reciprocal centimeters) in infrared spectroscopy, rather than absolute wavelength.

Christopher Tran 1J

Electron density represents the probability of an electron being present in a given space around the atom's nucleus, and is responsible for the shapes of the orbitals (which are mathematical functions that represent this probability).

Christopher Tran 1J

Essentially chromium has five 3d orbitals, four of which have a valence electron. Another electron is taken from the 4s energy level in order to occupy the fifth 3d orbital (so that all five 3d orbitals have one electron each) since symmetry is favored. The same happens for copper, where all but the...

Christopher Tran 1J

The delta speed is multiplied by 2 since ±1.0 mm/s means a range of uncertainty of 2.0 mm/s.

For example, if the speed were 5.0mm/s ±1.0 mm/s, then that would mean the speed would be anywhere between 4.0 mm/s and 6.0 mm/s.

6.0 - 4.0 = 2.0 mm/s, which is the uncertainty in the speed (∆v).

Christopher Tran 1J

Since both the proton and the neutron have the same mass, their wavelengths are the same as well. The difference is 0, so the percentage should be 0%.

Christopher Tran 1J

Essentially we are trying to use the Heisenberg Uncertainty Model to disprove the atomic model that an electron is located inside the nucleus of an atom with diameter 1.7*10^-15 m (electrons are located in the space around the nucleus). We used the uncertainty model to determine the delta velocity (...

Christopher Tran 1J

705160853 wrote:Also, is the quiz only testing topics in Outline 1? In other words, is the quantum stuff going to be on the test too

My TA said that the quiz will only cover the Fundamentals topic, and will not include stuff on The Quantum World.

Christopher Tran 1J

First, you need to find the amount of energy that is released by one atom of sodium using E=hv and c=(lambda)v You're given the wavelength as 589 nm (which is lambda), and the speed of light (c) is given as 3.00x10^8 m/s Plug those values into c=(lambda)v to find v (remember to convert units first),...

Christopher Tran 1J

You can do problems from either the Quantum World or Fundamentals for Week 2

Christopher Tran 1J

Usually, I don't round off my answers to each step until the very end when I write the final calculation in the proper number of significant figures. I find that rounding off steps tends to give me an answer that's off by a few digits, so I would recommend storing each step's answer on the calculator.

Christopher Tran 1J

For Part B and C, you need the number of moles of CuCl 2 * 4H 2 O calculated in Part A, which is 0.0417 mol CuCl 2 *4H 2 O . Part B: For each mole of CuCl 2 *4H 2 O, there are two moles of Cl- because of the subscript number 2 in CuCl 2 . Therefore, multiply 0.0417 by 2 to get 0.0834 mol Cl- ions . ...

Christopher Tran 1J

The question first wants you to determine the metal "M" in M(OH)2 with molar mass 74.10 g/mol, which we can find by finding the molar mass of "M." (OH)2 has molar mass: (16.00+1.01)*2 = 34.02 g/mol Molar mass of "M" in M(OH)2 = 74.10 g/mol - 34.02 g/mol = 40.08 g/mol Lo...

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