CHEMISTRY COMMUNITY

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When do we use the pre-equilibrium approach?

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Intermediates are produced and then consumed, so they will be on the products side for one step and then on the reactants side for a second step. Catalysts are present in the beginning of the reaction (on the reactants for the first step) and present in the end of the reaction (on the products for t...

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What does it mean for a reaction to be kinetically/thermodynamically controlled? How does temperature affect a reaction that is kinetically controlled?

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I think when are there are multiple reactants, we treat the reaction as a pseudo-reaction. It's difficult to study a reaction when the concentrations of multiple reactants are changing, so we let one reactant change and keep the others constant.

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Other than the unique rates have coefficients in the equation, what is the difference between instantaneous and unique rate? What does it mean that the unique rate is the same for all reactants and products in that unique reaction?

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What does it mean for a reaction to have zero order?

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Are stoichiometric coefficients included in cell diagrams?

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Are H2O and H+ included in a cell diagram? In 6M.5 part c, the solutions manual contains H+ in the cell diagram.

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Hello, I'm having trouble with this problem. It says: A student was given a standard Cu(s)|Cu2+(aq) half-cell and another half-cell containing an unknown metal M in 1.00 M M(NO3)2 (aq) and formed the cell M(s)|M+(aq)||Cu2+(aq)|Cu(s). The cell potential was found to be -0.689 V. What is the value of ...

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Dr. Lavelle discussed that a salt bridge or porous disk must be added to reaction beakers to remain neutral. What is the purpose of that?

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Why is the maximum potential difference calculated when there is very little current flow?

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Hello, Today in lecture Dr. Lavelle discussed the chem reaction 8H+ + MnO4- + 5Fe2+ --> Mn2+ +5Fe3+ + 4H2O How did we determine that iron was oxidized and lost 5 electrons? I know that manganese was reduced because its oxidation number went from +7 to +2, and iron was oxidized because it went from 2...

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Why are heat capacities extensive, but specific and molar heat capacities intensive properties?

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Hello,

When substituting -nrT for -PΔV, how do you know what changing (moles or temperature)?

Layal Suboh 1I

Hello,

Is it possible to have 0 entropy? Also, what is the difference between residual, translational, vibrational, and transitional entropy?

Thanks

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Hello,

When is the equation U= 3/2 nrT used? Is it only applicable when the system is isothermal? Also, for this question, is the volume constant and pressure changing?

Thanks!

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Hello,

Why do we need to know both enthalpy and entropy to determine if the reaction will occur spontaneously? If the reaction is exothermic, won't the products be favored?

Thanks

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Hello, Dr. Lavelle went over a question in class last week that said "an exothermic reaction occurs an open beaker producing a net 8 moles of gas at 25 C. What is the change in internal energy?" How do we know that this reaction is occurring under conditions of constant pressure? Thanks!

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Hello,

When will we know when do use the different methods for calculating reaction enthalpies?

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Hello,

I'm confused about the difference between an extensive property and an intensive property.What is the significance of each?

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Hello,

What is the difference between the enthalpy of reaction and the enthalpy of formation? Are they calculated the same way?

Thanks

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Hello,

I'm still confused about why steam causes more severe burns at 100 degrees celsius compared to liquid at 100 degrees celsius. Is it because more energy is required for liquid to become gas, so it releases more energy when it touches skin (which is significantly cooler than steam)?

Thanks!

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Usually, if you are given a Kb value, then you know it's a weak base. Also, there are 6 strong bases: LiOH, NaOH, KOH, Ca(OH)2, Sr(OH)2, Ba(OH)2.

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Hello,

Is the 5% rule calculated the same way as percent deprotonation/protonation?

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In class today, Dr. Lavelle said that if the concentration of hydronium ion is less than 10^-7, then the solution is considered neutral. I understand that it is because the pH would be greater than 7, which is considered basic, but why exactly would the concentration of hydronium ion in a solution r...

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Solids and liquids are not included because they do not affect the reaction amount at equilibrium. Solids remain as solids, so their concentration will not change. Also, we assume that there is a large excess of solvent in the reaction, so liquids will remain at the end of the reaction (cancel out i...

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Hello, I'm having difficulty with this problem It says: A student added solid Na2O to a volumetric flaks of volume 200.0 mL, which was then filled with water, resulting in 200.0 mL of NaOH solution. Then 5.00 mL of the solution was transferred to another volumetric flask and diluted to 500.0 mL. The...

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Hello, I'm a bit confused about how changing temperature changes K. I understand that if the reaction requires heat to form products, then heating will favor products and if the reaction releases heat to form products, then heating will favor reactions, but how does this affect K? Wouldn't the react...

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If Q<K, more reactants are present in the reaction (Dr. Lavelle said that there may be some other source adding reactant) than products being removed, so in order to decrease the amount of reactant to reach equilibrium, the forward reaction is favored to produce more product. If Q>K, there is a high...

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When K > 1, the equilibrium favors the formation of products. When k < 1, the equilibrium favors the decomposition back to reactants. When k=1, there is the same concentration of reactants and products.

Hope this helps!

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Hybridization gives the correct number of bonds. For example, using atomic orbitals, CH4 could only form two bonds, but we know that carbon forms 4 bonds. When you use hybrid orbitals, there are four hybrid orbitals (sp^3), which allows carbon to form 4 bonds. Also, the bond angles are incorrect for...

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What makes certain elements have acid or basic quality in certain compounds? Also, is there a way to know whether something is amphoteric or not, or do we just have to memorize them?

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HCL is already in units of concentration (mol/L), so in order to find the number of moles, you would have to multiply by 200 mL (.2 L). In order to find the pH of the desired solution, you take the -log[.025 M]. In order to find the actual pH, you would need to divide the number of moles by .25 L an...

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Why is acetic acid stronger than formic acid? The only difference between the two structures is the extra two hydrogens on acetic acid, so I'm confused to as to why it's stronger. Does it have something to do with being an oxoacid?

Thanks!

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Amines are bases. For example, in ammonia, NH3, the nitrogen has a lone pair, making it a base. Amines are considered weaker bases because they are not completely ionized in water.

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2s specifics the energy level and the orbital of the atom. S just refers to what type of orbital.

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AsF3 is polar because it has a lone pair, so the dipoles do not completely cancel. All the dipoles in AsF5 cancel, that's why it is non polar. Because AsF3 is polar, it has dipole-dipole intermolecular forces, so its boiling point would be higher.

Hope this helps!

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When are tetrahedrals polar and non polar? For example, a molecule like CCl4 is non polar because the atoms around Carbon are the same, but wouldn't there still be a dipole moment because of the 109.5 angle? I'm a little confused about when you know a molecule (in two planes) is polar or nonpolar.

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I think P is in the middle because it is the least electronegative. When drawing lewis structures, the least electronegative atoms goes in the middle, which in this case, would be phosphorus because it is lower on the periodic table.

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Hello, I'm having a little difficulty understanding this question: Noting that the bond angle of an sp3 hybridized atom is 109.5 and that of an sp2 hybridized atom is 120, do you expect the bond angle between two hybrid orbitals to increase or decrease as the s-character of the hybrids is increased?...

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In class, we talked about the different intermolecular forces, and Dr. Lavelle mentioned that London Dispersion Forces are the weakest. What exactly are London Dispersion Forces, and why are they much weaker?

Thanks

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Hello, I'm a little confused by the difference between polarizability and polarizing power. I know the polarizability refers to the large size of anions, and polarizing power refers to small size cations, but what exactly is the reason for how strongly a cation can polarize an anion and how easily a...

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Hi! You can determine if some molecules are polar based on the difference in electronegativity of the bond (ie if the difference in electronegativity is between 0 and 0.4, the bond is non polar. If the difference is between 0.5 and 1.4, the bond is polar) . For example, N2 is non-polar because the d...

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In class today, Dr. Lavelle discussed how electron distortion and polarizability can predict states of matter for certain molecules (like methane and pentane). I'm having a little trouble understanding how the size or molar mass can predict if a molecule is a solid, liquid, or gas. If someone could ...

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Hello,

I'm having difficulty understanding polarity. I know that it causes a separation of charge (for example, O becoming slightly negative and H becoming slight positive), but what does it mean that polarity is how easily electrons are distorted?

Thanks

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Hello,

Does the octet rule have to be fulfilled for resonance hybrids? Is it possible to draw resonance for a molecule that's central atom does not have a complete octet?

Thanks

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Hello,

I'm having troubling knowing when to add double bonds to a lewis structure. When do you know when to change a lone pair to a double bond? Also, when do you know when to stop adding doubling bonds?

Thanks

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Hi, I'm having difficulty with this problem from the homework: Which M3+ ions (where M is a metal) are predicted have the following ground-state electron configurations: (a) [Ar] 3d6; (b) [Ar] 3d5; (c) [Kr] 4d5; (d) 4d3. I thought you would add 3 electrons to each electron configuration, but the ans...

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Hi, I'm having difficulty with solving this question from the homework: On the basis of the expected charges of the monatomic ions, give the chemical formula of each of the following compounds: a) manganese arsenide; b) indium (III) sulfide; c) aluminum hydride; (d) hydrogen telluride; e) bismuth (I...

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Hello,

In one of the workshops, we discussed that the wave function is the solution to Schrodinger's equation. What exactly does that mean?

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Why does sulfur have a higher ionization energy than oxygen?

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Hi,

I know that the p subshell has 2px, 2py, and 2pz orbitals, what specific orbitals would the f subshell have?

Thanks!

Layal Suboh 1I

Hello,

I'm having trouble understanding the significance of Schrodinger's equation. What exactly did it prove? Is there any equation related to it?

Thanks!

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Hi!

You compare the wavelength you calculated to the speed of light (3.00*10^8 m/s). If the wavelength you calculated is greater than the speed of light, then it is unrealistic.

Hope this helps!

Layal Suboh 1I

Hello, I'm having a little difficulty understanding orbitals, specifically nodal planes. I know that the S-orbital does not have any nodal planes because it has one orbital, the P-orbital has one nodal plane, and the D-orbital has two nodal planes, but what are the exact functions and significance o...

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Hello,

I'm a little confused about the process of the photoelectric experiment. I know that through this experiment, light was shown to be a particle, but how exactly was this experiment conducted so that the quantum mechanic description of light was proven?

Thank you!

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Hello,

I'm confused about the applications of the Balmer and Lyman series. I understand that they deal with identifying spectral lines, but what exactly are they used to calculate, when do you use each of them, and how can you use both of the equations in the same problem?

Thanks!

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Hello, I'm having trouble with 1.A.11. The question is: In the spectrum of atomic hydrogen, several lines are generally classified together as belonging to a series (for example, Balmer series or Lyman series, as shown in Fig.1A.1). What is common to the lines within a series that makes grouping the...

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Hello! First, in order to know how many atoms of Astatine you will need, you must calculate the mass of Gallium. You use the 9 atoms from the picture and avogadro's number to convert to moles, then the molar mass of Gallium to convert from moles to grams: Mass Gallium= (9 atoms) *(1 mol Ga/6.02*10^2...

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I'm having difficulty understanding question G. 25. I know that after doubling the volume the first time, the concentration will decrease to 0.5 mol.L^-1, but I don't know how to double the concentration 90 times without fully writing it out. Practitioners of the branch of a alternative medicine kno...

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First, you would need to convert grams of KMnO4 to moles: 5g KMnO4/158.04 g/mol= 0.0316 mol Then, you would need to calculate the initial molarity of this solution by dividing by the initial volume: 0.0316 mol KMn04/ 0.15 L= 0.2109 M KMnO4 Now, you use the MinitialVinitial=MfinalVfinal equation to f...

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