CHEMISTRY COMMUNITY

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Is the change in cell potential E-E(standard) or E(standard)-E

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Today in review session, the cathode/reduction reactions was Br2(g) -> 2Br-(aq), but in the cell diagram, Br-(aq) comes before Br2(g). So in what cases do we abandon the reactant to product convention in the cell diagram, and put the product first? Is this always the case that the aqueous has to be ...

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If the given Ecell is positive, can we assume its a galvanic cell and the standard Ecell will also be positive? If so, would the same be the case if the given Ecell is negative can I assume that the standard Ecell is negative and the cell is electrolytic?

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Yeah I have the same question

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If there are three steps in a reaction, two of which are fast, how do we know for which of the two to find K and substitute?

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When given delta H of a reaction, I'm confused as to when you multiply and when you divide delta H by the amount of moles of a reactant

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I feel like even after doing the homework, I have yet to use the pre-equilibrium approach to solve any problem. Or I may just be using it unconsciously. Does anyone have an example in section 7C (7th edition) that implements concepts from the pre-equilibrium approach? Thanks!

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Why is it that the species with the greater reduction potential is preferentially reduced?

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What is microscopic reversibility?

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We ignore the faster, because it is negligible when considering the overall rate.

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I was confused on this question. It asks to write the two species that would give the largest Ecell. Does anyone know how to solve this?

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Isn't the formula for entropy of temperature using C, not R? Is this a mistake in the book?

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How is a second order reaction different than a first order reaction?

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Assuming that there are no other reactants, it is simply k.

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What is kinetic control and how does It relate to kinetics?

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If a question asks for the balanced half reactions, is the final answer with or without multiplying the half reaction through by a number (in the case that you need to match the electrons transferred in both half reactions)?

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I'm pretty sure H+ and OH- are included, but you don't include H20 because saying H+ and OH- are aqueous assumes that they're in water

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For #6 on the Gibbs free energy worksheet, how do we know that delta G is zero? Also, if delta G is zero and delta S of system is zero, why isn't delta S of surroundings also 0?

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For #4 on the Gibbs worksheet, I keep getting -42.2 kj/mol and I can't figure out what I'm doing wrong

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in part d, the reduction equation is: O3(g)+H20(l)+2e- --> O2(g)+2OH-

Why does OH-(aq) come before O3(g),O2(g) in the cell diagram, when it is a product of the half reaction?

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I have the same question

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When do we use OH versus H2O to balance the hydrogens on both sides. Are they interchangeable?

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Can we assume that an ion in either the cathode or anode half reaction is always aqueous (if the phase is not given)? If so, why?

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If given a cell diagram such as this:

Ag(s) I AgI(S) I I-(aq) II....

How would I know if Ag + I make up the reactants or the products for the anode half reaction of the cell?

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I understand that in a cell diagram, the left side are where the anode half reaction and the right side is cathode half reactions. However, I am confused about the order to list each individual element/ion in each half reaction. Is it: Anode reactant I Anode product II Cathode reactant I cathode pro...

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Does anyone know where that goes up to in the 7th edition textbook?

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Will test 2 cover "The Definition of Standard Potential" and "The Electrochemical Series" (6.M.1-2 in 7th edition)?

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Write the half-reactions, the balanced equation, and the cell diagram for: Cl2(g) +H2(g) --> HCl (aq) So the cathode reaction is: Cl2 + 2e- --> 2Cl- And the anode reaction (after reversal) is: H2 --> 2H+ + 2e- In the answer, Cl-(aq) comes before Cl2 (g), and I am wondering why that is the case.

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I have the same question

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Gibbs free energy refers specifically to the energy that can be used as work

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If we have the value when the system is in equilibrium and delta G =0, then we can find the behavior (in terms of spontaneity) for any temperatures above or below that value.

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Why is it that if a reaction is spontaneous it will favor the forward reaction?

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For #10, should both heat capacities (of ice and of water be the same), or should we use the heat capacity of ice on the left side of the equation. I remember at the review he used 4.184 for both, but shouldn't we take into account C of ice as well?

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Does anyone know how to solve #9?

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for #6, how do we know that change in entropy is zero?

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Kenan Kherallah 2C wrote:For question 4, Im just wondering if the condition is temperature at zero or if the change (delta T) of temperature is zero so an isothermal condition?

I was wondering the same thing.

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When solving for the change of enthalpy of a reaction either using bond enthalpies or enthalpy of formation, should our answer be in kj/mol or just kj?

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Always look at the units and how they cancel. That should indicate which to use.

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When you are given all the components besides for one in the ideal gas law, or if the question states to assume the gas is ideal, it's an indicator that you may need to use the ideal gas law. Also, if you feel you aren't given enough information to solve the question using formulas you've learned in...

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Yes. It's helpful to look at it before to get familiar with where things are.

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for #6, shouldn't the work be -12.4kJ?

w=-PxdV = (-122atm/L)(101.33J/atmL) = -12.4kJ

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For the first law worksheet, how do you do #2? First you have to do stoichiometry to find how many moles of Pb is made from 49.7 g PbO. You multiply the number of moles of product times the enthalpy value given, which gives you the q to plug into your regular q=mC s (Tf-Ti). Once you solve for mass...

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For the first law worksheet, how do you do #2?

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Are closed systems either at constant volume nor at constant pressure?

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Does an isolated system always imply constant volume?

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A state function only depends on the initial and final states - the path from getting form one to the other does not affect its value. Heat is an example of something that is not a state function.

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Review all your notes to make sure you've grasped the material conceptually. If there's anything you don't understand you can check the textbook to clear things up. Then after you've done that do the assigned homework - it's really good practice.

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Why does an open beaker imply constant pressure? What does a closed beaker imply?

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If I ever attempt a homework problem and don't fully understand it, I read the corresponding section in the textbook and it's very helpful.

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Can our homework for week 4 be anything from sections 4A-4D (7TH EDITION)?

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What are the implications of something being a state property?

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For #5 on worksheet 1, don't we need the value of R to calculate the volume?

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What is the formula for percent ionization for acids and for bases?

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If Ka or Kb is given, can we assume that what we're dealing with is a weak acid or base

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Just a note: it is helpful to remember that nitrogen with a lone pair means it's a weak base

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What's the difference between percent ionization, percent protonated, and percent deprotonated?

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For this question, why can't we use [H30+][OH-]=10^-14 for the concentration of H30+ in (ii)?
When I try to use it, I get [H30+]=6.67x10^-15 so I know it's wrong.

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When can we assume that [OH-]=[H30+]? Is it when Kw is less than 10^3?

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I know Dr. Lavelle mentioned this in class, but what are the sigfig rules for pH/pOH? Also, is there any situation where we disregard this rule?

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Does anyone know if test 1 covers only everything up to and including Le Chatelier's principle, or if it also includes acids and bases?

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Increasing temperature increases pressure, and we know this because of the ideal gas law.

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Is it true that when delta H is positive it's endothermic and if delta H is negative it's exothermic? If so, why is that?

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Do we treat a change in partial pressure the same way we would a change in molar concentrations?

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I'm still confused as to the conceptual reason behind not including units for K. Can anyone explain?

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We use Kelvin because as Dr. Lavelle mentioned in the beginning of 14A, Kelvin is an absolute scale (0 K is absolute zero).

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I don't know how to do the following question. Does anyone know how and can explain it conceptually? Question: A mixture initially consisting of 0.250 N2 (g) and 0.500 M H2 (g) reacts to form NH3 (g) which is 0.15 M NH3 (g) at equilibrium. Calculate the concentration of N2 (g) at equilibrium for the...

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What is the acid rain equation that includes nitrogen?

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Are we expected to know the formula for acetic acid, phosphoric acid, bromous acid, etc.?

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Are bronsted and Lewis acids the same? When is using one more correct than using the other?

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So bidentate isn't considered polydentate? Only tridentate+?

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Why isn't H20 polydentate, even though the oxygen has two lone pairs?

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How can you determine if a molecule is polydentate?

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Wait, I read it wrong, sorry.

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I looked at a periodic table with electronegativity

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If a molecule is polar, does that mean it must be possible for the molecule to experience a dipole-dipole interaction?

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CO2 is father apart, but CS2 is more electronegative

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If I'm not given a chart of electronegativity, how would I determine which has more ionic character: CO2 or CS2

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In regards to London dispersion, what is the significance of this formula:
Ep prop to a1a2/r^6

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If length and strength are inversely proportional to one another, why is it that sigma bonds are both larger and stronger than pi bonds?

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What's the difference between a dipole and an induced-dipole?

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What really is hydrogen bonding and why is it important? Also, how attractive is the force of hydrogen bonding?

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The textbook says that the greater distortion of the electron cloud on the anion, the greater the covalent character. Why is that the case?

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In what way does hybridization explain bond strength?

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Why doesn't it take a lot of energy to promote Carbon? Are there any atoms for which there are very high promotion energies?

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When two atoms bond head on they create a sigma bond. When there's a double bond, the first bond is a sigma bond, but the second bond of the double bond can't face the other atom head on. Instead, it overlaps side by side as a result of repulsion from the first bond. This is the reason that a single...

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What are the conceptual reasons behind the trends of polarizability and polarizing power? Specifically, why are both affected by size, effective nuclear charge, and electronegativity?

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I'm confused as to what distortion of electron clouds actually means in the context of polarizability and polarizing power. Can someone explain the concept of smaller/larger distortions?

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High polarizing power means it's smaller, has a higher effective nuclear charge, and higher electronegativity.

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The rule does not apply for those cases.

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Polarizability is directly related to size, while polarizing power is inversely related to size.

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It helps to remember that polarizability is larger and inversely related to electronegativity and positive charge, and that polarizing power is smaller and directly related to electronegativity and positive charge.

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Higher ionization energy means more energy is required to remove an electron, so the atom is less likely to form a cation, which requires the removal of an electron.

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Electrons in an atom with d orbital can fit 10 in the d orbital, which allows for an expanded octet.

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What are the exceptions to the octet rule? Is Br one of them?

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I really appreciate the response and understand how you came to your answer. What's bothering me, however, is that I end up with n^2 being 10.3. This is my work: change of e = hv = 7.56 x 10^-20 = Rh/(n1)^2 - Rh/(n2)^2 When I plug n2=4 into the equation and add that to hv that leaves me with the fol...

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An excited hydrogen atom emits light with a frequency of 1.14 x 10^14 Hz to reach the energy level n = 4. In what principle quantum level did the electron begin? I keep solving and getting the incorrect answer. Can someone please solve this (not using Rydberg equation) and actually compute the numbe...

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I read that it was derived by integrating wave functions over the bell curve.

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You need to understand the conceptual implications of the equation, specifically regarding wave functions and orbitals. You don't need to know calculations.

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There were one or two questions on the homework that required you to know specific wavelengths, so it may be helpful to know.

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It's a fancy way of saying wavelength increases, and we know that because c = wavelength x frequency

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