CHEMISTRY COMMUNITY

Labiba Sardar 2A

For Q4. a), how do you know that 5.00 x 10^-3 mol H2C2O4 = 1.00 x 10^-2 mol H+?

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If you increase the concentration of the reactants, I understand that this increases the rate of the reaction, but why doesn't this have an effect on the rate constant?

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Why doesn't the fast step have an effect on the overall reaction?

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When deriving the half life equation for a first order reaction, why do you set [A] equal to .5[A]0 when t = t(1/2)?

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If a reaction is in second order, when can you assume that it will be a pseudo-first-order reaction?

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The combustion reaction C2H4 (g) + 3O2 (g) --> 2CO2 (g) + 2H2O (g) has a unique rate of .44 mol.L^-1.s^-1 When finding the rate at which oxygen reacts and the rate at which water forms, why do both of these rates have positive values? Shouldn't they be opposite values since one is used up in the rea...

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k is unit-less because it is a ration of concentrations of products and reactants thanks for all the answers everyone but i forgot to clarify in my original question that i'm referring to the k that is in rate laws. i thought that k in the context of kinetics had units? In terms of kinetics, the un...

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Is a "strongly reducing metal" the same thing as a reducing agent?

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If the anode in a concentration cell is diluted, why does this increase the cell potential?

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Why does E cell decrease as the cell reaction progresses but Eºcell does not decrease?

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How come when you flip the reaction at the anode to make it an oxidation reaction, you don't have to flip the sign of the electrode potential at the anode? For example, for Zn (s) -->Zn^2+ (aq) + 2e-, the solution manual says that the electrode potential in this for is -.76 V. Why wouldn't it be +.7...

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When you have to find which metal is the stronger reducing agent, how do you know which reduction potential to use? For example, if the question just asks about Fe, how would you know whether to use the reduction potential using Fe2+ or Fe3+?

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For the reaction AgBr (s) <--> Ag+ (aq) + Br- (aq), how are you supposed to know which half reaction will be the anode/cathode once you have the balanced half reactions? The oxidation numbers also stay the same, so I'm also confused on how to balance these half reactions.

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For the given reaction, Cl2 (g) + H2 (g) --> HCl (aq), when writing the half reactions, why is the product 2Cl- for the reduction of Cl2 and the product for the oxidation of H2 is 2H+? Why aren't the products HCl like how it's given in the question?

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Why is the solution with lower concentration the product in a concentration cell?

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When deriving the Nernst equation at 25ºC, why is lnQ changed to logQ in the ending equation?

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In the case when there's no salt bridge (and there's a build up of charges in the anode and cathode), why does the left side (anode) build up in positive charge while the right side (cathode) build up in negative charge?

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Sydney Pell 2E wrote:When comparing temperatures, deltaS and deltaH are assumed to stay constant for both temperatures which could be why deltaS/R seems to be ignored.

Why can you assume that delta S is constant when you're using the van't Hoff equation to compare temperatures?

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When you're given the cell diagram of a galvanic cell, how do you know which side will be the anode and which will be the cathode? Is the left side always the anode and the right side always the cathode?

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Section 6K has a useful table that explains how to balance reactions in acidic and basic solutions. When it comes to balancing a reaction in a basic solution, you balance oxygen first with water on either side and then to balance hydrogens, you add water to the side that needs more hydrogens and ad...

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I need help trying the balance the half reaction Br-(aq) --> BrO3-(aq) in a basic solution. I've balanced the reaction so then the O's are balanced on both sides: Br-(aq) + 3H2O (l) --> BrO3- But I don't understand what to do after this part, especially where you're supposed to put more H2O molecule...

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Would there ever be a case where a question doesn't specify whether the redox reaction is in an acidic/basic solution? If so, how would you know if it's in an acidic/basic solution?

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What's the difference between the equations ΔGr = ΔG° + RTlnQ and ΔGr = -RTlnK? To elaborate, when are you supposed to use one over the other?

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I'm confused on what value of K you're supposed to use for delta G = -RTlnK. The problem gives you the partial pressures, so are you supposed to find Kp? But at the same time, it says that K = 6.8, so which one are you supposed to use?

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Why is heat capacity considered to be an extensive property whereas specific heat capacity and molar heat capacities are intensive properties?

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When you're doing the 5 percent rule, are you checking to see if the x value that you solved for is 5% of the initial concentration of your reactant? What if there's multiple reactants with initial concentrations?

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What's the effect of adding an inert gas to a reaction at equilibrium? I know it has something to do with the pressure and volume, but I don't remember which of these are affected.

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What causes there to still be some energy, allowing it to have some disorder? I thought that at 0 Kelvin, all particles stop moving, therefore there wouldn't be any disorder. At 0 K, there is no contribution to entropy from rotational/thermal motion. However, there is, for most molecules, residual ...

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Also, in what conditions are you supposed to use this equation? Is it only if the problem states what the degeneracy value is or if it says what the number of microstates and particles are?

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Conceptually, is this equation just saying that if you have a higher W, the W value means that you have more microstates/particles, which causes there to be more disorder (S, or entropy)?

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I believe residual entropy is the energy that remains even when a sample is brought to 0 Kelvin caused by disorder in the sample. What causes there to still be some energy, allowing it to have some disorder? I thought that at 0 Kelvin, all particles stop moving, therefore there wouldn't be any diso...

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How is residual entropy different from the regular entropy that we've been using for any other problem (for example, like delta S)?

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(a) Calculate the heat that must be supplied to a copper kettle of mass 500.0 g containing 400.0 g of water to raise its temperature from 22.0°C to the boiling point of water, 100.0°C.

For part a, why does the q value of the metal have to be added to the q value of the water?

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In an adiabatic process, no energy is transferred as heat. Indicate whether each of the following statements about an adiabatic process in a closed system is always true, always false, or true in certain conditions (specify the conditions): (a) delta U = 0; (b) q = 0; (c) q < 0; delta U = q; (e) del...

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When you're trying to find the value of work, when would pressure be negative when calculating -P*deltaV, making the work positive?

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Can someone explain what the difference is between enthalpy and heat? I'm a little confused between the two.

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What's the difference between q and delta H? To elaborate, how do you know if a problem is talking about q vs a problem talking about delta H?

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What's the difference between between bond enthalpies and standard enthalpies of formation? Bond enthalpies are the amount of energy in a bond, but how is that different from standard enthalpies of formation?

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When trying to find the change in enthalpy of the reaction by using bond enthalpies, do you always have to manipulate the given bond enthalpies? For example, if that bond enthalpy is given as positive, do you have to make it negative if this bond is broken?

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When converting from L.atm to joules, I saw both the constants (101.325 J / L.atm) and (8.314 J.K.mol^-1 / .08206 L.atm.K^-1.mol^-1). Is either fine to use when you're trying to convert to joules?

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After you calculate the value for work, does this value represent the work done by the system or the work done on the system? I'm confused on what it means when work is positive as opposed to when work is negative.

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What's the difference between a closed and an isolated system?

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A student added solid Na2O to a volumetric flask 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 pH of the diluted solution is 13.25." For the seco...

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505316964 wrote:I also got a negative number.

Can ph be negative?

It's definitely possible to calculate a negative value for pH. It's just a little hard to accurately verify it when working in a lab.

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CO (g) + H2O (g) <--> CO2 (g) + H2
Question: If the partial pressure of CO2 is increased, what happens to the partial pressure of H2?

I understand that when the partial pressure of CO2 is increased, the reaction will make more reactants. But why does this decrease the partial pressure of H2?

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So for example, if Q > K instead, would the K equation be [SO2][NO2] / [NO][SO3]?

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When Q < K, is saying "the reaction proceeds to the right" the same thing as saying "the reaction proceeds to form products"?

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For the reaction SO2 (g) + NO2 (g) <--> NO (g) + SO3, you're given the initial amount of moles for both the products and reactants. For this problem, why is it necessary to find Q first, and then find K?

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When you're comparing two different K values, what does it mean by which reaction would be "thermodynamically more stable"?

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Can someone explain the relationship of why when Q<K, it means that more products are formed?

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It's because the concentration of solids and liquids don't change since they are pure substances, so they don't affect the value of K.

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When a question asks you to find K for a reaction that involves gases and it doesn't specify whether to find Kc or Kp, should you just find Kp? Or should you put down both Kc and Kp?

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Why is K written in terms of the partial pressures of the reactants and products rather than the concentrations of the reactants and products for both parts 5G.3 a) and b)?

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For 20, why is the expected geometry tetrahedral and square planar?

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Can someone please explain conceptually why decreasing [OH-] makes the pOH increase?

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When do you know that a molecule with London dispersion forces will have stronger intermolecular forces than a molecule with dipole-dipole interactions? More specifically, why aren't the dipole-dipole interactions stronger than the London dispersion forces? An example can be H2S (LDF's) vs. H2Se (di...

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When you have a reaction of a strong acid and a strong base, after finding how many moles H+ the strong acid makes and how many moles OH- the strong base makes, why do you have to subtract the moles of H+ from the moles of OH- to get the resulting concentration of H+?

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Are all polydentates considered to be chelating ligands?

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Can someone please explain the concept behind hybridized orbitals and how orbitals are mixed together to create these hybridized orbitals?

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When H2O is a reactant in an acid-base reaction, how do you know whether it will act as an acid or base? Do you first look at the other reactant and determine whether that other reactant will be an acid/base?

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For example, in 17b) under Fundamentals J, it asks to write the chemical reaction for when KClO reacts with H2O. The reaction looks like...
ClO- + H2O --> HClO + OH-
In this example, why are H2O and HClO not written as ions?

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When writing net ionic equations, how do you know which molecules will be written as ions and which molecule(s) will be written together (not as ions)?

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When you're writing out the equations for acid-base reactions, how do you know whether the molecules (for both products and reactants) will be an aqueous solution or a liquid if the question doesn't specify?

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When you're writing out the formula for compounds, does the order of the ligands matter? For example, for 9C. #3d), would it be wrong to write Na[Fe(C2O4)2 (OH2)2] instead of Na[Fe(OH2)2 (C2O4)2 ]?

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Why does a bigger atomic size have stronger London dispersion forces?

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Except for a molecule that has the VSEPR formula AX2E3 (linear shape), would all molecules with lone pairs be polar?

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When drawing the Lewis structure for XeF2, Xe has three lone pairs around it, but why is its molecular shape linear with a bond angle of 180 degrees instead of the lone pairs pushing down on the bonded atoms? Why isn't this shape similar to a bent molecule, like H2O, where it has two lone pairs arou...

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I know that the bigger the size of an atom/molecule is, the more polarizable it is, but how do atoms/molecules with higher polarizability have stronger attractions?

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When do dipole-induced dipole interactions occur? Is it when a molecule with dipole-dipole gets close to/interacts with a molecule that doesn't have dipole-dipole interactions? What would be an indicator of dipole-induced dipole interactions ?

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When drawing the Lewis structure for ICl3, how do you know that iodine will have 2 lone pairs around it? Why can't you add multiple bonds, making the atoms have an expanded octet?

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If that's the case, when would you look at London dispersion forces rather than dipole-dipole interactions to determine which molecule is stronger? Would you only do this when both of molecules have dipole-dipole interactions?

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The question has a ball-and-stick model of a linear molecule (bond angle of 180 degrees) and asks whether there must, may be, or can't be one or more lone pairs on the central atom. Why may this specific molecule have lone pairs on the central atom? I thought if it was linear, it wouldn't have any l...

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The solutions manual says that between CHI3 and CHF3, CHI3 has a higher normal melting point because it has stronger London dispersion forces, but don't they both have dipole-dipole interactions and then determine which has stronger attractions from there?

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Can someone please explain the process of drawing Lewis structures for atoms with an expanded octet? I really don't understand how to draw the structures for these molecules. Do you just put all the single bonds in and lone pairs on the outside atoms, and then draw double bonds until you've used up ...

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When you have to draw double bonds by using taking away the lone pairs on certain atoms, how do you know which atoms' lone pairs you should take away to form these double bonds?

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In 2B 19 a), when drawing the Lewis structure for NO+, why is it drawn so then the formal charge on O is +1? I thought you had to draw structures so then the most electronegative atoms have a negative charge.

The same goes for c) for CO, where C has a -1 charge and O has a +1 charge.

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Are all resonance structures considered to be resonance hybrids? If so, when we draw resonance structures, can we just draw all the resonance structures and just say it's a hybrid?

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Why are all three molecules (ammonium chloride, potassium phosphide, and sodium hypochlorite) in #5 under 2B drawn as ions for their Lewis structures rather than the traditional connected Lewis structures that we've typically been doing?

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Why is the effective nuclear charge (Z_eff_e) less than the nuclear charge (Ze)?

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What's the difference between electronegativity and electron affinity? Also, why does electron affinity increase across and up the periodic table?

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After drawing the Lewis structure with single bonds and the lone pairs each atom but you have left over valence electrons you need to fit into the Lewis structure, how do you know whether these left over electrons will be made into a double bond or lone pairs?

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How do you know which electrons are delocalized in resonance structures?

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When referring to the shapes of atomic orbitals, what are nodal planes and electron density?

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Are there other elements that are also exceptions to the octet rule, or is there a trend we need to remember that helps us know which atoms are exceptions of the octet rule?

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Why are P, Cl, and S exceptions to the octet rule?

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What's the correlation between effective nuclear charge and ionization energy? Is it that the higher the effective nuclear charge is, the higher the ionization energy will be since it will be harder to remove the electron?

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Tungsten's ground-electron configuration is [Xe] 4f^14 5d^4 6s^2. Why doesn't this follow the exception rule like chromium and copper? As in, why wouldn't the electron configuration be [Xe] 4f^14 5d^5 6s^1?

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What's the trend for effective nuclear charge on the periodic table, and can someone explain it conceptually in terms of the other electrons in the atom?

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How do you find the values of ml, and what do those values specifically signify?

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What does it mean if l has multiple possible values? Specifically, what does each number represent? For example, if l = 2, then its possible values are -1, 0, 1, or if l =3, then its possible values are -2, -1, 0, 1, 2.

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Also, how do you translate it to each other (like finding how many subshells are in a given n or how many orbitals are in subshells with l equal to a certain number)?

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Can someone please explain the differences between n, l, and m conceptually?

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In the book, it gives an example where if n = 3, l can have any three values (0,1, and 2), but what do these three numbers indicate?

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The velocity of an electron that is emitted from a metallic surface by a photon is 3.6 x 10^km s^-1. (a) What is the wavelength of the ejected electron? ... (c) What is the wavelength of the radiation that caused photoejection of the electron? What's the difference between the wavelengths in parts (...

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For part b, since you want to find the energy and it gives you the frequency (2.50 x 10^16 Hz or 2.50 x 10^16 s^-1), use Planck's constant to evaluate E from E=hv.

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Is the unit for E always implied as being J/atoms or J/photons?

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Sodium vapor lamps emit yellow light of wavelength 589 nm. How much energy is emitted by b) 5.00mg of Na atoms emitting light at this wavelength? From a) I found that the energy emitted by an excited sodium atom is 3.37 x 10^-19 J. Then for part b, I found that 5.00mg of Na atoms = 1.31 x 10^20 Na a...

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When you're trying to find the limiting reactant and see which reactant makes the least amount of product, do you have to convert the moles of product to grams or can you just leave it as moles?

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When finding the percent yield, how do you know whether or not you have to find the limiting reactant (because there were questions like M.3 where you don't need to find the limiting reactant)? Do you find the limiting reactant only if the both/all the masses of the limiting reactants are given as o...

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In question M.5 b), the reaction 6ClO2 (g) + 2BrF3 (l) --> 6ClO2 (s) + Br2 (l) is carried out with 12 mol ClO2 and 5 mol BrF3. It asks to estimate how many moles of each product will be made and how many moles of the excess reactant will remain. From a) I understand that the excess reactant will be ...

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