CHEMISTRY COMMUNITY

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adibiatic is when there's no heat transfer, and isothermal is when the temperature is constant/no change in T

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The reaction profile shows an endothermic reaction, so the reverse reaction has a lower activation barrier than the forward reaction. From this, we know that the rate constant of the reaction with the higher activation barrier will increase when temperature is raised. Since the reaction is endotherm...

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Can someone who went to the review session post pictures of it? Thanks

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Can anyone explain this, it's from the Kinetics outline:

Explain how the collision model and activated complex model account for the temperature
dependence of reactions.

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So on the Thermodynamics outline on the class website, one of the bullet points says: "Show how ∆S is related to ∆H for a change at constant temperature and pressure and explain the relationship"

Can someone explain this concept and how to show it?

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A is false because catalysts never change the equilibrium constant. It changes both the rate of the forward and reverse reactions B is true because a catalyst is a substance that increases the rate of reaction, but is not consumed in it. C is false because a catalyst provides a new pathway for the r...

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The reaction will not shift either way because solids are not included in the equilibrium constant. Thus, adding a solid will not affect the Q value nor the reaction.

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The anode and the cathode are the same in this cell diagram, so the E°cell = 0. You dont need the specific value for HCl because it's the same on both sides. Now just use the Nernst equation to find Ecell from the difference in concentrations.

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First, write out the balanced reaction: C7H5O2 + water --> C7H6O2 + OH-. This reaction is basic, so you need to convert pKa into pKb to use for this reaction. 14-pKa=pKb, so pKb = 9.596. Next, convert pKb into Kb in order to use it in an ice table. 10^-pKb = Kb = 2.535x10^10. Now, from an ice table,...

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The rate constants themselves are not the same for forward and reverse reactions at equilibrium. The rates are equal, but not their K values.

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So to find the reaction of B, you divide reaction 2 by reaction 4. This cancels out K, A, and C, leaving just the rate in relation to B. (8.7/50.8)=(1.25)^y/(3.02)^y. By solving this equation, you get (1/5.8)=(1/2.4)^y. This simplifies to (2.4)^2=(2.4)^y. Therefore, y, which is the exponent on [B] a...

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I believe that since they give one part in pressure and one in concentration, you can just use those values to find E=E°-(.025693V/n)ln(P/[M]). This still gives a usable relationship between the products and reactants. One half as 1 torr pressure with different concentrations while the other half ha...

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THANKS!!!

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Can someone help me with 14.11 in the 6th edition? I'm studying for the test and practicing problems but the solutions manual seems to be backwards from what I'm expecting every time...

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I was sick on Friday of week 6 (2/15) and was wondering if anyone could post a picture of their notes? Thanks!

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Enthalpy and entropy are somewhat related to each other. If energy is added to or released from the system, it has to be partitioned into new states. Therefore an enthalpy change can also have an effect on entropy.

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Will someone explain how to balance d in chapter 14 problem 5 in the 6th edition. I don't understand why the OH is on the right side instead of the left when you would add H2O on the left and therefore OH- on the right First, you want to balance the oxygen by adding 8 H2O molecules on the left. Now...

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For this reaction, I think that the Cl2 is being oxidized and also being reduced. It's oxidation number goes up from O to +1 in HClO and it goes down from 0 to -1 in Cl-.

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Depending on what the units are in the problem, you can give your answer in terms of J or KJ as they are essentially interchangeable. Normally, it will be in terms of KJ/mol I presume.

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Yes. Here, K is the equilibrium constant, which is [products]/[reactants] at equilibrium

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Hi Katherine! dS = q/t when you're dealing with a reversible process. dS = nRln(Vf/Vi) when the process is isothermal. dS = nCln(Tf/Ti) when there's a change in temperature associated with the change in entropy. Your C value will change based on whether your volume (Cv) or pressure (Cp) are constan...

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Because heat is lost by one and absorbed by the other. Negative for one and positive for the other.

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They don't need to convert it because Celsius is Just kelvin—273. Therefore an increase of 80°C is also an increase of 80°K.
∆T(°C) = ∆T(K)

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If he said he isn't gonna post the answers, could someone post them so I can check my answers?

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For part A, you want to find the enthalpy of the reaction H2g + (.5)O2g ——> H2O(l) Now use bond enthalpies to find the enthalpy change: 1mol(436KJ/mol) to break the H-H bonds in H2 and 1mol(496KJ/mol) for the O-O bonds in O2. This is the breaking of the reactant bonds 2mol(463KJ/mol) to form the 2mo...

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I believe that it might be because part a is given exactly one mole of the substance, so that's standard conditions? While part b gives a mass in grams of the substance which then must be converted to moles. This is the only difference that I can think of, other than maybe that in part a it's at 0°C...

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The pH difference according to molecular structure stems from the electron-withdrawing ability of the group attached to the acid. In other words, as electronegativity of the function group attached to the acid increases, the acidity of the acid will increase. Acidity therefore increases, let's say, ...

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Yes because if the system gives off heat, they are losing internal energy and there is a decrease in entropy (negative delta S). Vice versa for the surroundings.

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Work is found in Joules, so I got -1.50x10^2 J for my work, which is essentially the same as your 148 value. However, I think you may be misinterpreting your 148 J value for 148 KJ. The answer I got was -1.50x10^2 J or -.150 KJ. Hope this helps! If not, I can run you through the steps of the problem.

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Start out by balancing the equation: 2HCl + Zn --> H2 + ZnCl2 Find the limiting reactant (Zinc). Now use Hess's law to find the Heat of the reaction (ΔHrxn), which is just the sum of the heats of formation of products minus the sum of the heats of formation of the reactants. This should give you the...

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Yes. At this point, I feel like anything we've done so far should suffice for HW, since it's all preparation for the midterm anyways.

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Yes, work can still be done on an adiabatic system (no transfer of heat (q=0)). Delta U in this system will then just equal W since the value for q is 0. Hope this helps!

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Entropy has the units energy over temperature, or joules per kelvin. You are correct that you need to add them together. However, you need to find the individual entropies by dividing the joules by their temperature in kelvin. Then add those values like the book to find entropy. hope this helps.

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In general, I believe that the reversed reaction can do more work because less of the energy is lost as heat.

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Yes. Steam has more energy so it causes more severe burns.

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They are not considered state properties because their value depends on the path taken from the initial to final values. State properties do not depend on the path taken, such as pressure or temperature.

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When using an ICE table to determine equilibrium concentrations, when are we allowed to assume x is negligible for the reactant concentration so that we don't have to deal with the quadratic? Thanks

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The H3O+ concentration will be .15 M in the E column because the .15 M of H2SO4 dissociates completely into H3O+. The initial concentration of H3O+ will be 0 M. Hope this helps.

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Strong acids and bases disassociate/ionize completely while weak acids and bases do not completely. this is the main difference.

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Since there is excess water its concentration changes slightly and isn't taken into account since it's the solvent.

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a catalyst only speeds up a reaction but doesn't actually change the k value. the only thing that can change the value of k/equilibrium constant is a change in temperature.

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This is talking about whether the equilibrium sits more toward the product or the reactant side of the reaction. Sitting to the left refers to having a higher reactant concentration at equilibrium and K value that's less than 1. On the other hand, sitting to the right refers to having a higher produ...

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This is talking about whether the equilibrium sits more toward the product or the reactant side of the reaction. Sitting to the left refers to having a higher reactant concentration at equilibrium and K value that's less than 1. On the other hand, sitting to the right refers to having a higher produ...

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Yes, hydrogen bonds are a dipole-dipole interaction, and happen with a hydrogen and either O,N, or F. They are stronger than basic dipole-dipole interactions.

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The third "hidden" reactant is oxygen. It is in excess so its original mass is not given. Therefore, this excess oxygen can account for the discrepancy in mass between the products and reactants.

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Concentration should be in Molarity M, which is moles per liter (moles L^-1)

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In the equations, the acids are the compounds that donate/lose a hydrogen H+. Therefore, the acids are:
a)H3O+
b) CH3COOH
c) HI

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Conjugate acids and bases are molecules that differ by one proton. The conjugate acid is the molecule in the reaction that is formed by the acceptance of an H+ that is donated by the base. Example: Conjugate acid = H2O; Base = OH-. In the same way, conjugate bases and acids are similar in that they ...

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I believe that strong bases ionize completely in water because they are better proton donors. This means that they completely donate a proton while a weaker base does donate, but not as completely.

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trigonal planar is sp2 since it has 3 electron densities, while tetrahedral would be sp3 since it has 4 electron densities.

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The d orbital is needed because it has an extra 10 electron capacity. s and p are filled up first and can only hold 8 (full octet), so the extra 10 from d orbital are used to exceed the octet.

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Pi bonds are fixed because there is an electron overlap below and on top of the atoms' plane. On the other hand, sigma bonds can be rotated because there is just an overlap of two orbitals.

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Polarity of a molecule depends on whether or not the molecule is symmetrical in regards to its partial charges and sharing of electrons. If the molecule is symmetrical and has no dipole moments, or the dipole moments on opposite sides cancel out (like in water) the molecule is non-polar. However, if...

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VSEPR does not take in account what type of bond a bond is. In this sense, a single bond affects VSEPR in the same way as a double bond and triple bond and so on. For VSEPR, a bond is a bond.

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Double bonds are more stable than single bonds. This is because double bonds also have a π (Pi) bond, while single bonds only have σ (sigma) bonds. Pi bonds prevent rotation thus making double bonds more stable.

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After completing the Lewis Dot structure, GeF4 has 4 single bonds and no lone pairs around the central atom. Therefore, from VSEPR, the shape is tetrahedral.

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Yes, Hydrogen Bonds are dipole-dipoles with N,O, and F. Not all dipole-dipoles are hydrogen bonds though, while all hydrogen bonds are dipole dipoles.

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In general, the more electronegative atom should have the negative formal charge since the electrons are more strongly attracted/pulled to them.

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Bond length decreases as the number of bonds increases since the two atoms are more strongly attracted to one another. For example, triple bonds are shorter than double bonds which are shorter than single bonds. When determining bond length, take the average of all the bond lengths in the resonance ...

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Can anyone help me with 9b? It asks for the electron configuration of Chromium. I got an answer of [Ar]4s2 3d4 but I looked it up online and it says that its' actually [Ar]4s1 3d5. Why is one of the 4s electrons actually in the 3d orbital? I looked it up and it mentioned something about stability? S...

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This question is asking what metal ion with a positive 3 charge (3+) will have the following electron configurations. This confused me at first too, but M is not a symbol for an element, but rather a placeholder/variable for any metallic element. After realizing that, I began writing out the electro...

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Formal charge is used to determine the stability of a molecule. However, resonance structures, since they are different arrangements of the same bonds, are equally stable as one another.

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De Broglie's wavelength equation is used for particles and objects, such as electrons or a baseball, while the speed of light/Einstein equation is used only when calculating the wavelength or frequency of light. C=λv can't be used with particles because it describes a relationship with light. This i...

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Nitrogen has 5 valence electrons, so it needs three more electrons to fulfill its octet. This doesn't necessarily mean that it's going to make 3 bonds, but rather it starts with 5 electrons when determining the lewis structure. It will make its bonds to fill its octet.

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I found that completing the online modules on the class website is helpful in reviewing lecture material and building a strong conceptual foundation. Then, I simply do many hw problems to master the different types of problems. I also plan on going to some review sessions this week.

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Double Bonds are shorter because they share more electrons between the two atoms, meaning that those two atoms are more tightly bonded are therefore closer together. The attraction between the two is greater than if it were just a single bond. Similarly, a triple bond would then have a shorter bond ...

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You would just use [Xe] since it has the same electron configuration as that noble gas. No need to go backwards to [Kr].

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The roman numeral signifies what the charge on that atom is. For example, depending on what Iron or another element is bonded to, it could be Iron II or Iron III to balance the charges. Hope this helps! #sickomode

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To my knowledge, this is simply an exception to the octet rule.

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No such thing as a dumb question, David!! And, to answer your question, nonmetals (right side of periodic table) do not form cations because they only gain a few electrons to fill their octet, meaning they become anions. Metals, on the other hand, lose electrons to fill their octet. Hope this helps!...

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You are correct, Fluorine has a higher ionization energy than Chlorine. However, I'm pretty sure that Helium has the highest first ionization energy because it's outermost electron is closest to the nucleus.

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So I'm taking the first test tomorrow and I am slightly confused on one of the post-module assessment questions in the Molarity and Dilution section. I was wondering if anyone could just run me through as to how to go about solving this problem? I know to start by finding the initial concentration o...

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By process of elimination, you know that the hydrogen, carbon, and nitrogen must come from the caffeine molecule, since they couldn't have come from O2. After this, solve for the empirical formula using the mass of the products formed, and those masses are the same as the masses in the original caff...

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This is just a guess, but maybe use the mass for the neutron as the mass from the isotope? That way, the two masses are slightly different and will have different wavelengths. For example, carbon has an atomic mass of 12.011. The proton weight would be 6, and the neutron weight would be 6.011. Maybe...

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Yes, the first is essentially derived from the latter. Sometimes you will need to use just the M1V1=M2V2, depending on what is given, but sometimes you will need both to complete the problem.

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I doubt that specifics are needed as to why the actual yield is less than the theoretical yield, especially since this is a "relatively" introductory chemistry class. However, it is good to know some possibilities or why in general this disparity occurs. For example, since the theoretical ...

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Normally, yes. Both masses should be given to then determine which reactant is limiting and which is in excess. If only one is given, I would assume that that reactant is the limiting reactant since no other information is given. However, based on the context of the question, you may want to always ...

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