CHEMISTRY COMMUNITY

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when adding an inert gas, all the important aspects that we look at for chemical reactions (moles of P and R, concentrations of P and R, partial pressure, etc) don't change. If those don't change, then the reaction will not be perturbed and it will not have to shift.

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Amphoteric = can act as an acid or base amphiprotic = can accept or donate a proton all amphoteric molecules are amphiprotic because if it can be an acid or base, by the bronsted definition we know it can accept or donate a proton. But not all amphiprotic molecules are amphoteric because there are o...

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hi! for this concept, I think Lavelle introduced it so that when we have an aqueous solution we can find the concentrations of both hydronium and hydroxide even if we're only given one of them. To do this just set up Kw = 10^-14 = [H3O+][OH-], from here you can plug in whichever concentration was gi...

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use + for your products aka what is being formed and - for your reactants or what is being initially used. you should also multiply the x's by their stochiometric coefficients which can be found by balancing the chemical equation

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for this problem, it states that the reaction begins with placing PCl5 in a sealed container. The provided chemical equation is Cl2 + PCl3 --><--- PCl5. Since the reaction is starting with the right side, I thought that PCl5 should be considered the reactant in this case which would make K = [Cl2][P...

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the sapling homework says that the reaction quotient, Q, is not affected by a change in temperature but it does change K. Could someone explain this to me? I thought that by changing the temperature and perturbing the system, we suddenly would have a different Q value which would need to return to K...

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if there is a change in pressure and both sides have the same moles of gas, there is no effect on the shifting on the reaction

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i think they're the same idea but saying shifts is more accurate to the nature of the system!

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hi! just try to memorize delta H (-) = exothermic and delta H (+) = endothermic
you can think of H final - H inital to help you remember!

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In the fourth part to the chemical equilibrium audiovisual module, I keep getting stumped by this question in the post-assessment. 15. The photosynthesis reaction, 6 CO2(g) + 6 H2O(l) ⇌ C6H12O6(aq) + 6 O2(g), is endothermic. What effect will the following changes have on the equilibrium composition....

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the question: Calculate the reaction quotient, QC, from the following equilibrium data collected in a 3.00 L sealed reaction vessel for the reaction: AsH3 (g) ⇌ As (s) + H2 (g) AsH3 = 5.55 x 10-4 mol, As = 3.31 x 10-3 mol, H2 = 1.23 x 10-3 mol. my answer: i first balanced the chemical equation: 2AsH...

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why is it that chemical reactions always reach equilibrium?

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are there any experiments other than slit screen, photoelectric, bohr/atomic spectra experiment, and electron diffraction that we need to know for the exam?

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are there any experiments other than slit screen, photoelectric, bohr/atomic spectra experiment, and electron diffraction that we need to know for the exam?

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is cisplatin bidentate? do we even need to know its denticity?

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Could someone please explain the effective nuclear charge trend? I'm just confused on why the trend is that way. And how does it relate to shielding?

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I was working on this question: "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 thought that atoms only emit light when they're moving down quantum levels by emitting a photo...

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it asks which is the acid and which is the base for a reaction between H2O2 and SO3. I said SO3 is the acid because it can accept electrons from H2O2 to form a coordinate covalent bond and, therefore, H2O2 is the base (bc donating electrons). Is this reasoning correct? Did anyone think of it differe...

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Hi everyone. So, I understand what polyprotic acids are and I understand that with each round of deprotonation, the polyprotic acid can only give up one H+ at a time, but I'm confused why they bring up the example of sulfuric acid. they say that sulfuric acid is one of the few common polyprotic acid...

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Question: Decide whether an aqueous solution of each of the following salts has a pH equal to, greater than, or less than 7. If pH > 7 or pH < 7, write a chemical equation to justify your answer. (a) NH4Br; (b) Na2CO3; (c) KF; (d) KBr; (e) AlCl3; (f) Cu(NO3)2 I'm not sure how to approach this, and I...

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I know that when determining the relative acidity of a compound we use bond length and electronegativity and I understand why, but does one take precedent over the other? In the textbook (9C.19 part c) it asks if HBrO2 or HClO2 was more acidic, and I thought it was HBrO2 since Br is larger than Cl a...

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question: Which is a stronger base: BrO- or C17H19O3N aka morphine? I said BrO- which is correct, but my reasoning was just that it has a negative charge so that it wants to be protonated and morphine contains carbon which is indicative of a weak base. The answer manual's reasoning though was BrO- h...

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Question: The molar concentration of HCl in hydrochloric acid is reduced to 12 percent of its initial value by dilution. What is the difference in pH values of the two solutions? I wasn't sure how to do this and the answer manual's solution didn't make much sense to me, if someone could explain, I w...

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I made a mistake above!!! i meant C2O4 for oxalate not C2H4

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the name given is sodium bisoxalate (diaqua) ferrate (III) and you're supposed to write the chemical formula. I got Na[Fe (C2H4)2 (H20)2], but the answer has the oxalate and water flipped. So I guess my question is more of clarification: when naming and in writing the formula we use the alphabetical...

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so with these different definitions of acids and bases, I feel like I sometimes get confused and feel like the definitions contradict each other. Could someone please explain how the two definitions of acids and bases support each other?

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for [AsO4]^3-, the shape is tetrahedral which means that no bonds are directly across from each other, so I thought this would mean that the molecule is polar, but the solution says that the dipoles all cancel, how is this possible if the molecule is not symmetrical?

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Hi everyone! For determining whether the H atoms lie in the same plane for H2CCH2, H2CCCH2, and H2CCCCH2, I don't understand why the hydrogen atoms for H2CCCH2 are arranged differently than the other molecules. I think it's related to the fact that it has a distinct central atom, but I don't underst...

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when a molecule has three attached atoms and two lone pairs, is the shape always t-shaped? and why don't the lone pairs go on opposite sides of the central atom? wouldn't that minimize repulsion?

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hey everyone!
I was wondering, with N2, for example, each N has three P orbitals with only one electron each. Does it matter what P orbital (x, y, z) we assign the sigma bond to?

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hey guys! one of the learning goals for chemical bonds is "explain how covalent bond dissociation energy is related to covalent bond multiplicity, atomic radius, and the presence of unpaired electrons" is this just about - single covalent bonds are the weakest, triple covalent bonds are th...

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so then why do these molecules not have dipole-dipole?

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hi! so for this problem, you have to determine id CHI3 or CHF3 would have a higher melting point. I said it would be CHF3 because they both show dipole-dipole, but F is more electronegative than I, so F would pull C's electrons more and have a greater partial charge, thus making it have stronger dip...

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for this question, we're supposed to determine which of BBr3, BaBr2, or BeBr2 has the most ionic character. I approached this by looking for the greatest difference in electronegativity and got BeBr2 since Be and Br are physically the farthest away from each other on the periodic table, but BaBr2 wa...

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and NaBr vs NaI?

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does KBr or NaBr have greater ionic character? why?

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hey! for part a, how do you determine that the Cl would have the unpaired electron instead of O?

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hi! for this question you have to draw the lewis structure for (HPO4)^2-
what I don't get is how we're supposed to know that the H is bonded to an O? since P can have an expanded octet i assumed it would bond to P
[img]a[/img]

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Chem_Mod wrote:This is the most stable structure. If Cl were to have two bonds and then two lone pairs, its formal charge would be 7-(4+4/2) which equals +1.

so when drawing structures, we should always just go with what gives us the most stable configuration regardless of the atom's electronegativity?

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also for part c you have to draw ONF and its O=N-F but why is the double bond with O if F is more electronegative?

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hi guys! for this question, you have to draw the lewis structure for COCl2. I was able to get the correct structure of carbon in the middle with single bonds to the two Cls and a double bond to oxygen. the Cls both have 3 lone pairs and the O has 2. I was wondering why we don't have resonance here. ...

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hey guys! does anyone know if Matthew has answer keys for his workshop problems? if so, does anyone know if they're posted here, or if I should email him? if I do need to email him, if someone could let me know what his email is, I would really appreciate it.
thanks!

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the sapling homework keeps using the phrase "bond character" but i dont know what that means, could someone please explain?

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I am a little confused on the difference between orbitals vs subshells, so if you understand the difference, please let me know how you keep them straight
thanks!

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for part d we have to determine if element Ga would be more likely to lose or gain electrons if it had to. Since Ga is in group 13 and pretty far to the right of the periodic table, I thought its relatively high electron affinity would make it want to gain electrons to become an anion, but the sapli...

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Q: Give the notation for the valence-shell configuration (including the outermost d-electrons) of (a) the alkali metals; (b) Group 15 elements; (c) Group 5 transition metals; (d) the “coinage” metals (Cu, Ag, Au). I honestly just don't know how to do this, so if someone could please walk me through ...

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hi! could someone walk me through how to write the electron configuration for silver(Ag)? i thought it would be [Kr]5s^2 5d^9 but the asnwer is [Kr]4d^10 5s^1. i understand how its better to have a full 4d shell because its lower energy, but i'm just not sure how to do this correctly

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Hey guys! In today's lecture (monday 11/9), all of the interactions that gave rise to attractive forces that Lavelle discussed had negative energies. I'm not sure I fully understand why that is, so if someone could explain, I would really appreciate it!
Thanks

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4s has a lower energy than 3d, it's a sort of exception, so you write 4s first. check out the textbook it had a great explanation for this

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this was just having you write it as a noble gas configuration which is a sort of shorthand, so you don't need to do this but it just helps to write the configuration with just its valence electrons since the noble gas it gives has the same electron configuration as the atom's core

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cations are smaller because now that they've lost a valence electron which exposes the ions core which is smaller than the parent atom. there is also less electron repulsion which allows the ion to be smaller than its parent atom. the textbook covers this really well so i recommend checking that out!

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4s is a lower energy orbital than 3d and you want to have the lowest energy configuration possible, so you want to fill up the 4s shell before the 3d. There are two (i think) exceptions which the textbook covers, so i'd check that out!

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Z = atomic number = number of electrons for that element

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you have the right thinking and math just remember that SI units use kg and not grams!

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p is momentum which is p = mv (mass times velocity). you want to use debroglie's for the wavelength of anything with rest mass since it is taken into account in the equation

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just divide the difference of the wavelengths by the wavelength of the neutron and multiply that by 100% !

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for uncertainty you want to keep it in kg because planck's constant's units are J*s which is a simplification of (kg*m^2*s^-2)(s)
*** 1 J = kg*m^2*s^-2

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for uncertainty you want to keep it in kg because planck's constant's units are J*s which is a simplification of (kg*m^2*s^-2)(s)
*** 1 J = kg*m^2*s^-2

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if the problem gives an uncertainty of position in nm should I convert to m, or vice versa? thanks!

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Q: A metal M forms an oxide with the formula M2O, for which the mass percentage of the metal is 88.8%. (a) What is the molar mass of the metal? (b) Write the name of the compound. when i looked at the textbook solution, I get why they got their answer but i dont really understand the thought process...

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Hi! So first, I would write the combustion reaction out: CxHyOz + O2 --> CO2 + H2O Once you have this, you're given the mass of CO2 and H2O produced, so the first thing you should always do is convert to moles. For CO2, it will be 1.2073g divided by its molar mass (44.01g/mol), which will give you ...

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question: you have a compound that has only Carbon, oxygen, and hydrogen. 0.66666 g of this compound undergoes combustion and produces 1.2073 g CO2 and 0.2115 g H2O. what is the empirical formula for this compound? im totally blanking on this, so if someone could let me know how they solved it, that...

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Question: 1A.3 Which of the following happens when the frequency of electromagnetic radiation decreases? Explain your reasoning. (a) The speed of the radiation decreases. (b) The wavelength of the radiation decreases. (c) The extent of the change in the electrical field at a given point decreases. (...

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Q: A mixture of NaNO3 and Na2SO4 of mass 5.37 g contains 1.61 g of sodium. What is the percentage by mass of NaNO3 in the mixture?
I'm totally blanking on this, does anyone know how to do it?

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does anyone know where i can find the textbook solutions?

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for the molecular formula I got C48 H78 N6 O12 but when i googled it, it was C49 not C48, did anyone else get that?

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c is the speed of light ina vacuum

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increasing intensity of light means increasing the number of photons which does make the light brighter. the important point here is that the energy of the indivudal photons doesn't change just the number of them

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the work function tells you how much energy is needed to remove ONE electron, so the units should reflect that. I wouldn't be surprised though if the midterm asked for the answer in joules/mole or something, but you would just do the calculations as normal unitl the end when youd make the conversion...

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to find kinetic energy from velocity use the Ek = 1/2mv^2 equation!

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in today's lecture, Lavelle's explanation of the standing wave model kind of flew over my head. How does this model explain how electrons have quantized energy states in atoms?

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14. For large everyday objects does Heisenberg's uncertainty (indeterminacy) principle play any measurable role? A. Yes, the uncertainties in position, speed, and momentum of a stationary object are noticeable or measurable. B. Yes, the uncertainties in position, speed, and momentum of a moving obje...

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in lecture 5 (todays lecture), lavelle explains the properties of electrons and how they have wave-like behavior in the photoelectric experiment. the module on the chem 14a website titled "wave properties and the debrogile equation" is very helpful for understanding when and how objects an...

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make sure youre converting the given velocity from km/hr to m/s using fence posting, this will help you get the right units for the correct answer!

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the kinetic energy of the ejected electron is the excess energy that is produced when the energy of the incoming photon is greater than the energy needed to remove the electron from its metal surface. the kinetic energy is 0 when the energy of the photon is equal to the energy needed to remove the e...

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your equations are right in regards to which uses velocity and which uses frequency. it is super easy to mix them up since their symbols both look like v! try to start writing your frequency variable as the greek letter nu which is like v but slightly different (id recommend looking up a picture of ...

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the intensity of a light ray is proportional to the number of photons which then confers brightness. what we care about with the photoelectric effect is the individual energy of each photon, not how many photons there are. to increase the energy of the individual photons, we increase the frequency o...

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Could someone please explain the reasoning to their answer please

Question:
Can molecular spectroscopy be used to identify molecules? If so why is it possible?

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I actually figured it out while waiting for a response lol. for anyone wondering, I just took the 11 J/ 1 second from the question and multiplied it by 1 photon/1.0751x10^-19 J = 1x10^20 photons per second

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Hi, I just have no idea where to start with this question, so if you know please help me out Question: The meter was defined in 1963 as 1,650,763.73 wavelengths of radiation emitted by krypton-86 (it has since been redefined). What is the wavelength of this krypton-86 radiation? To what region of th...

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Hi! I got the first part of the question, but how do you calculate the number of photos? Question: In 1.0 s, a 60 W bulb emits 11 J of energy in the form of infrared radiation (heat) of wavelength 1850 nm. What is the energy per photon of light emitted? How many photons of infrared radiation does th...

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105482502 wrote:Would this type of question involving these kinds of compounds be something we should look out for on the midterm/final?

i would assume anything we see in this class is fair game!

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105482502 wrote:Would this type of question involving these kinds of compounds be something we should look out for on the midterm/final?

i would assume anything we see in this class is fair game!

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i would say it's always best to use whole numbers for stoichiometric coefficients! just remember that if you do have a fraction for a coefficient and you want to eliminate it by multiplication, make sure you multiply both sides by the same number (all coefficients will change then)!

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I would say that use the exact molar mass if it is given in the question. I think for exams we'll all use the same periodic tables and we should also then just use the exact molar mass given without rounding. I think a general rule of thumb is always save rounding for the end!

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if the decimal is present start with from the left side of the number and counts the figures starting with the first nonzero figure. Everything to the right of that is also significant. If the decimal is absent start from the right and start counting sig figs once you hit your first nonzero. everyth...

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Hi! I recommend you start by finding the grams of carbon and hydrogen in the products by using percent mass composition. You need to do this before finding the mass of oxygen in the CxHyOz compound since O2 is a reactant and contributes to the oxygen in both products. Since chemical reactions follow...

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