Search found 102 matches
- Sun Mar 14, 2021 7:12 am
- Forum: Second Order Reactions
- Topic: Sapling #12
- Replies: 3
- Views: 379
Re: Sapling #12
Hi! So initially, we can cancel out the reaction being first order because the half-life of first order reactions is not dependent on concentration (t1/2=0.698/k). For a zero-order reaction, the equation is t(1/2)=[A]0/2k, but it indicates that as [A]0 increases, half-life also increases, which cont...
- Sun Mar 14, 2021 7:01 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: How do we tell if K changes when a stress is applied?
- Replies: 3
- Views: 239
Re: How do we tell if K changes when a stress is applied?
Hi! For changes in pressure/volume and concentration, K doesn't change because these changes disrupt the system and it will eventually return to equilibrium. K only changes with changes in temperature, where if it's endothermic and the temperature is increased, K will increase, and if it's exothermi...
- Fri Mar 12, 2021 12:07 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Sapling #13 Weeks 9/10
- Replies: 7
- Views: 425
Re: Sapling #13 Weeks 9/10
Hi! So we know that the slowest step determine the rate of the overall reaction = k[I-][HClO], but because that rate includes HClO, which is an intermediate step, you have to make an alternate expression for HClO from the first elementary step given. The forward rate for the first elementary step i...
- Fri Mar 12, 2021 11:54 am
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Sapling #14
- Replies: 2
- Views: 147
Re: Sapling #14
Hi! The Arrhenius equation that is on our equation sheet is k=Ae^(-Ea/RT) and the equation in sapling, ln(k2/k1) = (Ea/R)[(1/T1) - (1/T2)], can be derived from this original Arrhenius equation by taking the ratio of the Arrhenius equations of k2/k1 which can be simplified to the aforementioned equat...
- Tue Mar 09, 2021 7:15 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Sapling #13 Weeks 9/10
- Replies: 7
- Views: 425
Re: Sapling #13 Weeks 9/10
Hi! So we know that the slowest step determine the rate of the overall reaction = k[I-][HClO], but because that rate includes HClO, which is an intermediate step, you have to make an alternate expression for HClO from the first elementary step given. The forward rate for the first elementary step is...
- Tue Mar 09, 2021 4:29 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Homework #7
- Replies: 2
- Views: 215
Re: Homework #7
Hi! To set up this problem, you start with the general rate law, rate = k[A]^a[B]^b[C]^c and then you compare two experiments in which the concentration of one reactant changes while the others remain constant. For example, to find the order of reactant C, you would use the initial concentrations an...
- Tue Mar 09, 2021 4:20 pm
- Forum: General Rate Laws
- Topic: Outline 6 Review
- Replies: 3
- Views: 228
Re: Outline 6 Review
Hi! For the determining the order of the reaction and its rate law, from my understanding, you can only determine the order of a reaction with experimental results, like #7 on the week 9/10 sapling homework. You use the generic rate law, rate=k[A]^a[B]^b[C]^c... and compare the rates in which the in...
- Fri Mar 05, 2021 8:06 pm
- Forum: General Rate Laws
- Topic: Half-life Reactions
- Replies: 3
- Views: 225
Re: Half-life Reactions
The Sapling questions are also a good reference for figuring out how certain topics are going to be asked about. For half-life questions, they are usually related to an ordered reaction, for example, #11 in the Sapling homework gives the rate of a first-order reaction and asks you to calculate the h...
- Fri Mar 05, 2021 7:56 pm
- Forum: General Rate Laws
- Topic: why is the rate of a reaction positive?
- Replies: 5
- Views: 399
Re: why is the rate of a reaction positive?
Hi! In lecture #21, Dr. Lavelle says that in order to accurately describe how the rate at which one concentration is decreasing is equal to the rate at which another concentration is increasing, we prefer to describe rates in positive numbers. For example, he gives the equation of the instantaneous ...
- Fri Mar 05, 2021 7:35 pm
- Forum: Balancing Redox Reactions
- Topic: states of matter
- Replies: 58
- Views: 2121
Re: states of matter
Outside of Sapling and more generally, can someone please explain how to determine states of matter when balancing redox reactions? I finished the Sapling homework and all but I did not completely understand it. The states of the main components of the reaction are usually given in the equation we'...
- Fri Mar 05, 2021 7:28 pm
- Forum: Balancing Redox Reactions
- Topic: states of matter
- Replies: 58
- Views: 2121
Re: states of matter
Hi! It's in liquid form when added to balance a redox reaction.SamayaJoshi1A wrote:Does anyone know whether H20 is in liquid or gas form when you add it when balancing redox equations?
- Fri Mar 05, 2021 12:39 pm
- Forum: First Order Reactions
- Topic: How to determine the Order of reactions
- Replies: 8
- Views: 397
Re: How to determine the Order of reactions
Hi! From my understanding, the order of the reaction is determined by looking at experimental data and adding up all the individual order values using rate = k[reactant 1]^n[reactant 2]^m in order to calculate the overall reaction order. I believe you can also input given data into each of the integ...
- Thu Feb 25, 2021 8:22 pm
- Forum: Balancing Redox Reactions
- Topic: sapling 7/8 number 3
- Replies: 4
- Views: 273
Re: sapling 7/8 number 3
Hi! So to account for the reaction occurring in a basic solution, you first balance it as if its occurring in an acidic solution with H+ and H2O, then you add OH- ions to both sides of the reaction to neutralize the H+ and create H2O. You also cancel out the H2O on both sides of the reaction so that...
- Thu Feb 25, 2021 7:54 pm
- Forum: Balancing Redox Reactions
- Topic: Sapling Week 7/8 #5
- Replies: 1
- Views: 123
Sapling Week 7/8 #5
Screenshot 2021-02-25 193054.png Hi everyone! I balanced the first reaction for #5 correctly and I did the same process for the second reaction, but I'm having trouble getting the correct answer. I'm not sure if it's just a mistake in combining the two half reactions or if I just completely messed ...
- Thu Feb 25, 2021 4:22 pm
- Forum: Balancing Redox Reactions
- Topic: Sapling Question 3
- Replies: 4
- Views: 177
Re: Sapling Question 3
Hi! You multiply the Fe half reaction by 4 to balance out the 4 electrons lost in the oxidation half reaction. For the H+ ions, you first conduct it like an acidic solution by adding H2O to the balance out the oxygen in the reaction and then adding the H+ to balance out the hydrogen from the H2O. Th...
- Thu Feb 25, 2021 3:30 pm
- Forum: Balancing Redox Reactions
- Topic: oxidation states
- Replies: 2
- Views: 157
Re: oxidation states
Hi! I'm not totally sure if this answers your question, but for this problem, we know from the general rules for oxidation states that oxygen tends to have an oxidation state of -2 and that monoatomic ions have oxidation states equal to their ionic charges. So by this second rule, we know that K has...
- Thu Feb 25, 2021 1:03 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Salt Bridge
- Replies: 30
- Views: 1294
Re: Salt Bridge
Hi, is there case in which you do NOT include a salt bridge? or is the salt bridge always included? I think that a salt bridge is always included, unless the cell uses a porous disk, which also allows ion transfer to keep the solutions neutral. Without either a salt bridge or a porous disk, the gal...
- Thu Feb 18, 2021 4:03 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Van't Hoff Equation
- Replies: 1
- Views: 104
Re: Van't Hoff Equation
Hi! I think we would be given one of the K values since that's the only way we can solve the equation. An example of this is example 5J.5 in section 5J.3 of the textbook, where the first K value and the temperature values are given. Hope this helps!
- Thu Feb 18, 2021 3:06 pm
- Forum: Van't Hoff Equation
- Topic: Van't Hoff equation
- Replies: 13
- Views: 1448
Re: Van't Hoff equation
Hi! The Van't Hoff Equation is just derived from the ΔG°=-RTlnK equation where the standard Gibbs Free Energy equation, ΔG°=ΔH°-TΔS°, is substituted for ΔG°to get ΔH°-TΔS°=-RTlnK and then manipulated to arrive at the Van't Hoff equation. So they both should arrive at the same solution, but I think t...
- Thu Feb 18, 2021 2:57 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Textbook 4G.1
- Replies: 3
- Views: 261
Re: Textbook 4G.1
Hi! So the way you approach this problem is by first calculating the degeneracy which is W = (the number of state)^(number of molecules). For a), if all the molecules are oriented in the same direction, there is only one state, which means W = (1)^64, since there are 64 molecules. From there you can...
- Thu Feb 18, 2021 1:58 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: delta U=0
- Replies: 17
- Views: 2514
Re: delta U=0
Hi! In lecture #13, Dr. Lavelle discusses how for isothermal, reversible reactions of ideal gases, any energy lost by the system during expansion (the work value) is replaced in the form of heat absorbed by the system (the q value). Thus, q=-w and by the equation ΔU = q+w , the net change in the int...
- Thu Feb 18, 2021 1:20 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Relationship between Work and Entropy
- Replies: 4
- Views: 297
Re: Relationship between Work and Entropy
Hi! This doesn't really pertain to a specific relationship between work and entropy, but in response to the second part of your question, the change in entropy equation we have for the isothermal expansion of a gas is ΔS = nRln(V2/V1) and because there is a change in volume indicated, I think that w...
- Sat Feb 13, 2021 3:36 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Sapling Week 5/6 #20
- Replies: 4
- Views: 223
Re: Sapling Week 5/6 #20
Hi! The top left and top right are referring to the spontaneity of the reaction and because the reaction is moving toward the minimum free energy value in both the forward and reverse directions, they're both spontaneous. For the bottom left and right options, the left one refers to the forward reac...
- Fri Feb 12, 2021 3:16 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Lecture 2/12 Question about equation ∆G = ∆G° + RT ln Q
- Replies: 2
- Views: 152
Re: Lecture 2/12 Question about equation ∆G = ∆G° + RT ln Q
Hi! ΔG°refers to the standard free energy change, where a reaction occurs under standard conditions that I believe are 1 atm and 298 K, while ΔG refers to a reaction under any other conditions. So, they are not equal values which is why the equation is ∆G = ∆G° + RT ln Q and not just ∆G = RT ln Q. H...
- Fri Feb 12, 2021 3:06 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Textbook 4C.11 solution
- Replies: 3
- Views: 160
Re: Textbook 4C.11 solution
Hi! I think that there's a typo in the solutions manual for 4C.11 where it says "this process is composed of two steps: melting the ice at 0° and then raising the temperature of the liquid water from 0°C to 25°C" but the calculation and resulting solutions that are shown are calculated wit...
- Fri Feb 12, 2021 2:04 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Using 5/2 and 3/2
- Replies: 6
- Views: 300
Re: Using 5/2 and 3/2
what is the difference between monatomic and diatomic? Hi! Monoatomic means that the molecules in an element are made up of one atom, which diatomic means that the molecules in an element have two atoms bonded together. Noble gases are some examples of monatomic elements, while H2, N2, and F2 are s...
- Fri Feb 12, 2021 1:43 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: lecture 16
- Replies: 4
- Views: 115
Re: lecture 16
Hi! You're correct that we just use ΔG° = 0 in order to find the unknown temperature. So basically using, ΔG° = 0 is just an analysis of the equation ΔG° = ΔH° - TΔS°equation in the context of the given values of the problem. We know that if ΔG° is negative then a reaction is spontaneous and the val...
- Fri Feb 05, 2021 10:09 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: sapling #10
- Replies: 2
- Views: 144
Re: sapling #10
Hi! So for this problem, the equation you would use is (the heat needed to melt the ice) + (heat needed to bring ice to final temperature) = (heat released to cool water to the final temperature). So the initial temperature for the water is 45°C, but the initial temperature for the ice is 0°C becaus...
- Thu Feb 04, 2021 7:22 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Sapling using ΔH and ΔU
- Replies: 4
- Views: 199
Re: Sapling using ΔH and ΔU
Can someone explain why q equaled the change in U in the last few questions. I am confused on why they are the same answer but use different notations. Hi! In the last few sapling questions, it is specified that there is a constant volume, which means that there is no work being done on the system ...
- Thu Feb 04, 2021 2:04 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Textbook 4A.3
- Replies: 1
- Views: 88
Re: Textbook 4A.3
Hi! I think that in this particular problem ΔU=w because there is no energy transferred to the pump as heat, so q=0. Heat isn't absorbed by the system and only work is being done to it, so you would only use the work value to calculate the change in internal energy. Hope this helps!
- Thu Feb 04, 2021 1:58 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: w= -nRTln(Vfinal/ Vinital Question
- Replies: 2
- Views: 121
Re: w= -nRTln(Vfinal/ Vinital Question
Hi! Someone correct me if I'm wrong, but I don't think that a reaction is reversible once the temperature has been changed, meaning it is no longer isothermal. So to answer your question, I think that the equation w= -nRTln(Vfinal/Vinital) only applies when the reaction is isothermal (meaning the te...
- Thu Feb 04, 2021 1:39 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Examples for types of systems
- Replies: 8
- Views: 286
Re: Examples for types of systems
Hi! Some examples of an open system would be an open beaker (the example Dr. Lavelle gave in lecture), a living plant, or gasoline burning in a car engine because matter and energy can exchange with its surroundings. For example, the plant can take in nutrients from its environment or release water ...
- Fri Jan 29, 2021 12:16 am
- Forum: Student Social/Study Group
- Topic: Pnemonic device for remembering strong bases?
- Replies: 3
- Views: 279
Re: Pnemonic device for remembering strong bases?
Hi! Adding onto what Benjamin said, I just want to add that a good general rule for identifying strong bases is that strong bases tend to have a metal cation and OH, while weak bases tend to contain nitrogen.
- Fri Jan 29, 2021 12:01 am
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Problem 5J.5
- Replies: 2
- Views: 110
Re: Problem 5J.5
Hi! I was confused on this one too, but it's just an error in the textbook. The actual equation is supposed to be 2HD(g) ⇌ H2(g) + D2(g), which makes the number of moles of gas equal on both sides and thus, there would be no change when the pressure increases. You can find the correction in the solu...
- Wed Jan 27, 2021 10:58 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: textbook 4D.15
- Replies: 2
- Views: 108
Re: textbook 4D.15
Hi! So I think that with this problem, you can't just subtract the sum of the values given of reactants from the values given of the products because we are only given ΔH°c and the referenced equation is only applicable to calculating the standard reaction enthalpy with the standard enthalpy formati...
- Wed Jan 27, 2021 10:15 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: #26 Chemical Eq Post Assessment
- Replies: 2
- Views: 139
Re: #26 Chemical Eq Post Assessment
Hi! I think were you made the error that messed up your calculations in the NH3 column of you ICE table. There are two moles of NH3 in the balanced chemical equation, which means that the change in concentration should be +2x. The problem states that the equilibrium concentration of NH2 is 0.15M, wh...
- Wed Jan 27, 2021 10:07 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Q19 Chemical Eq 2 Post-Assessment
- Replies: 2
- Views: 132
Re: Q19 Chemical Eq 2 Post-Assessment
Hi! I think your problem is just a minor calculation error, where you forgot to calculate the concentrations of AsH3 and H2 to use in the equation for the reaction quotient and you instead used the values of the number of moles given in the prompt. You just need to divide the number of moles by the ...
- Fri Jan 22, 2021 7:04 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: 5% rule [ENDORSED]
- Replies: 1
- Views: 169
Re: 5% rule [ENDORSED]
Hi! The 5% rule means that if the x, the equilibrium concentration of the product, is 5% of the initial concentration of the reactant, then using the approximation of x is okay rather than going through the process of using the quadratic formula. The calculation for this is the same as if you were c...
- Fri Jan 22, 2021 5:27 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Textbook problem 4D.23
- Replies: 1
- Views: 102
Re: Textbook problem 4D.23
Hi! from what I understand of your explanation, you are correct. You have to take into account the number of moles in the chemical equation 2 NO + 3/2 O2 -> N2O5 and input that into the equation for the standard reaction enthalpy, ΔH°(reaction) = sum of ΔHf°(products) - sum of ΔHf°(reactants) using ...
- Fri Jan 22, 2021 4:19 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: reaction enthalpy of O2
- Replies: 4
- Views: 657
Re: reaction enthalpy of O2
Hi! I believe that Dr. Lavelle stated the standard enthalpy of formation for O2 is zero, not the bond enthalpy. I think that the bond enthalpy of O2 is 498 kJ/mol, but if you meant to ask about the standard enthalpy of formation instead of the bond enthalpy, then Jay explains it well above. Hope thi...
- Fri Jan 22, 2021 3:27 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Selecting a Method + Using the Tables
- Replies: 1
- Views: 38
Re: Selecting a Method + Using the Tables
Hi! As far as I know, the only pages we're allowed to have during the exam is the periodic table and equations sheets, so I don't think we will be allowed to print out the bond enthalpies table. I assume that we will be given the necessary values to be able to solve enthalpy problems and related to ...
- Fri Jan 22, 2021 3:21 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: 6D.15 part b)
- Replies: 3
- Views: 184
Re: 6D.15 part b)
Hi! for part b, I used the Ka of Al^3+=1.4 x 10^-5 and I couldn't find it in the book, so I just looked it up. I don't think there's any other way to solve it if the Ka value isn't on the tables in the textbook. Hope this helps!
- Sat Jan 16, 2021 10:35 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Sapling #1 (Week 2)
- Replies: 4
- Views: 128
Re: Sapling #1 (Week 2)
Hi! So the way I solved it was that I used the example chemical equation [acid]+[H2O]-><-[H3O+]+product and created an ICE box with 0.45 as the initial concentration for the unknown weak acid, and (0.45-x) for the acid, x for H3O+, and x for the unknown product for the equilibrium concentrations. Th...
- Sat Jan 16, 2021 10:36 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Textbook Problem 5I.21
- Replies: 1
- Views: 118
Re: Textbook Problem 5I.21
Hi! You may have accidentally misread your solutions manual because mine says that the correct concentration for O2 is 4.6x10^-4 mol/L, which lines up with your answer. According to the ICE table, the equation for the equilibrium concentration of O2 should be (5x10^-4)-X and if X is equal to (4.3x10...
- Fri Jan 15, 2021 11:32 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: today's lecture
- Replies: 8
- Views: 187
Re: today's lecture
so i understand that if the equilibrium constant is less than 10^-4, approximation is okay. i am a bit confused/curious though as to why 10^-4 is the baseline or value that allows for approximation. is that just something memorize or is there reasoning behind it? Hi! I think the 10^-4 is just a gen...
- Thu Jan 14, 2021 9:09 pm
- Forum: Phase Changes & Related Calculations
- Topic: equilibrium when taking away product
- Replies: 3
- Views: 236
Re: equilibrium when taking away product
Hi! Jenny explained it really well above, but I just wanted to add that once product is taken away from a system in equilibrium, that system is no longer in equilibrium, so Kc is no longer applicable to or calculated from the new system. As covered in lecture, under Le Chatlier's Principle, the syst...
- Thu Jan 14, 2021 9:00 pm
- Forum: General Science Questions
- Topic: pH to PKa
- Replies: 3
- Views: 295
Re: pH to PKa
Hi! A balanced chemical equation would be a good piece of additional information to be able to solve for pKa given the pH. An example of this is question 6D.3 in the textbook: "When the pH of 0.10 M HClO2 was measured, it was found to be 1.2. What are the values of Ka and pKa of chlorous acid?&...
- Fri Jan 08, 2021 2:42 pm
- Forum: Ideal Gases
- Topic: Change in pressure and inert gas
- Replies: 6
- Views: 266
Re: Change in pressure and inert gas
Hi! An inert gas is just a gas that, when added to the equilibrium system, won't cause a chemical reaction. When an inert gas is added to the sealed reaction vessel, it does increase the pressure but because the volume of the reaction vessel itself doesn't change, the volume of the gases contained d...
- Fri Jan 08, 2021 2:30 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Change in pressure = same volume
- Replies: 3
- Views: 139
Re: Change in pressure = same volume
Hi! Similar to what Sydney said above, the volume of the sealed vessel that the gases are contained in is not affected once the inert gas is added. When the gas is added, the vessel's size isn't increased or decreased, so the pressure increases, but the volume and the concentration of the gases cont...
- Fri Jan 08, 2021 2:03 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Difference between Kp and Kc in lecture 3
- Replies: 5
- Views: 222
Re: Difference between Kp and Kc in lecture 3
Hi! Kp and Kc can both be used for gases, but Kp can only be used for gases and not other states of matter. The question should (hopefully) indicate which K that it's asking for and if you are given molar concentrations but asked for Kp or partial pressures, then you can use PV=nRT to calculate the ...
- Fri Jan 08, 2021 1:46 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Increasing Volume in Change of Pressure
- Replies: 7
- Views: 139
Re: Increasing Volume in Change of Pressure
Hi! Increasing the volume will decrease the concentration of the gases in the system, which will cause the reaction to favor the side of the reaction with more moles of gas. So if the volume is increased and there are more moles of gas on the left, then the reaction will favor the reactants and if t...
- Fri Jan 08, 2021 1:34 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: lecture 3 question
- Replies: 4
- Views: 91
Re: lecture 3 question
Yep, you use the quadratic equation when you are given the initial molar concentrations of the reactants and Kc/Kp and you are trying to calculate the unknown values for the equilibrium molar concentrations of the reactants and products.Heather Costa 2C wrote:ok so it's just for when there are unknown concentrations?
- Sat Dec 12, 2020 5:07 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Orbitals and Their Nodal Planes
- Replies: 7
- Views: 594
Re: Orbitals and Their Nodal Planes
Hi! In a review session this week, one of the TA's mentioned that the calculation for the number of nodal planes is [n(principal quantum #)-1]. They also said that they expected that we would only need to know about nodes for the s and p, so for s its 0 and for p its 1. Hope this helps!
- Thu Dec 10, 2020 1:52 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Uncertainty of Position in an Atom
- Replies: 2
- Views: 210
Re: Uncertainty of Position in an Atom
Hi! Yes, you double the atomic radius to use the atomic diameter because it's the max distance that the electron can travel within the atom. Hope this helps!
- Thu Dec 10, 2020 1:14 pm
- Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
- Topic: Inter vs Intramolecular Forces
- Replies: 2
- Views: 471
Re: Inter vs Intramolecular Forces
Hi! I'm not sure if this is the answer you were looking for, but intermolecular forces occur between different molecules while intramolecular forces occur between the atoms within a molecule. So intramolecular forces refer to bonds within a molecule and those that have stronger, shorter bonds would ...
- Thu Dec 10, 2020 12:57 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: VSEPR Shapes on Exam
- Replies: 3
- Views: 304
Re: VSEPR Shapes on Exam
Hi! I don't think there are necessarily only "a few" out of the list of molecular shapes that we should know -- it's probably safer to know all of the ones we have gone over. Here's a good table to reference https://courses.lumenlearning.com/introchem/chapter/table-of-geometries/. But over...
- Wed Dec 09, 2020 9:33 pm
- Forum: Naming
- Topic: Steps for Naming Coordination Compounds
- Replies: 9
- Views: 1511
Re: Steps for Naming Coordination Compounds
Hi! Lecture #25 from 11/30 addresses coordination compound namingEmily_Stenzler_3H wrote:Does anyone know which lecture addresses naming?
Re: en
en is ethylenediamine (H2NCH2CH2NH2) Do you know if there are any other shorthand versions of compounds that we should know? Hi! Other shorthand names for compounds are edta (ethylenediaminetetraacetato), ox (oxolato), and dien (diethylenetriamine, NH2CH2CH2NHCH2CH2NH2). The guide on naming coordin...
- Sat Dec 05, 2020 10:02 am
- Forum: Lewis Structures
- Topic: Most Stable Structure
- Replies: 23
- Views: 3470
Re: Most Stable Structure
Hi! Adding onto the comments above, if you end up with two structures that have the same amount of charges on the atoms, then the structure with the negative charge on the most electronegative atom is the more stable one. For example, if you have the structures HCNO, the structures with the lowest c...
- Fri Dec 04, 2020 3:09 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Molecular Geometry vs. Electron Geometry
- Replies: 6
- Views: 305
Re: Molecular Geometry vs. Electron Geometry
Hi! In addition to the above answer, I think that if a sapling or textbook question asks for "the shape," it's referring to molecular geometry since that's what we focused on more in lecture, but I'm sure that the question will specify if it's asking for electron geometry. Hope this helps!
- Fri Dec 04, 2020 12:21 pm
- Forum: Hybridization
- Topic: Sigma/pi bonds
- Replies: 6
- Views: 146
Re: Sigma/pi bonds
Hi! I think Dr. Lavelle's depiction of a triple bond in that way was just to visually demonstrate that the bond was made up of two pi bonds and one sigma bond. I don't think they need to be in that order, but I also believe that we would be asked to identify the number of pi and sigma bonds present ...
- Fri Dec 04, 2020 12:15 pm
- Forum: Amphoteric Compounds
- Topic: Amphoteric - how to tell if it is an acid or base
- Replies: 4
- Views: 276
Re: Amphoteric - how to tell if it is an acid or base
Hi! Like the previous response said, Dr. Lavelle stated in today's lecture that you can tell when an amphoteric compound is acting like an acid or a base depending on what else is present in the reaction. You are correct in that in the presence of a base, it acts as an acid and in the presence of an...
- Sun Nov 29, 2020 11:37 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Seesaw Shape
- Replies: 5
- Views: 354
Re: Seesaw Shape
Hi! like other people have said above, in a seesaw shape, there is 5 regions of electron density with 4 bonding pairs and 1 lone pair. 5 regions of electron density would normally be a trigonal bipyramidal shape, but because lone pairs are not used to name the shape, we replace one of the atoms in t...
- Tue Nov 24, 2020 1:39 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Angular Molecular Shape
- Replies: 3
- Views: 108
Re: Angular Molecular Shape
Hi! Angular and bent refer to the same molecular structure.
- Tue Nov 24, 2020 12:28 pm
- Forum: Sigma & Pi Bonds
- Topic: Figuring out Carbon hybridization
- Replies: 2
- Views: 111
Re: Figuring out Carbon hybridization
Hi! The px and py just signify the specific orbitals within the p subshell. So, because the p-shell has three orbitals, electron location within the shell can be denoted more specifically in the electron configuration by using px, py, and pz rather than just p^6. Dr. Lavelle said that we can write i...
- Tue Nov 24, 2020 11:25 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Textbook Section 2E Exercise glitch
- Replies: 3
- Views: 304
Re: Textbook Section 2E Exercise glitch
Hi! I was just having that problem too, but once I exited out of the page and reloaded the book from the Sapling website, I could see the full problem. So, maybe try reloading your book if you're viewing on a computer browser and if the problem persists, email Sapling customer service? Hope this hel...
- Tue Nov 24, 2020 11:16 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: VSEPR formula
- Replies: 4
- Views: 174
Re: VSEPR formula
So just for clarification, both a single non-bonded electron and a non-bonded electron pair count as one region of electron density? Yes, I believe they would both be counted as one region of electron density, although I don't think we'll be asked to determine the molecular shape of molecules with ...
- Fri Nov 20, 2020 1:35 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Linear VSEPR issues
- Replies: 3
- Views: 138
Re: Linear VSEPR issues
Can I3- can be bent as well? I was thinking that since lone pairs have a stronger force in repulsion that it will cause the structure to have a bent shape. Can someone explain more as to why it is linear? I'm not completely certain, but I think I3- would be linear instead of bent because it matters...
- Fri Nov 20, 2020 1:02 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Linear VSEPR issues
- Replies: 3
- Views: 138
Re: Linear VSEPR issues
Hi! I believe that the shape of I3- is linear because it has 5 regions of electron density, which means it has trigonal bipyramidal geometry. But, because only atom positions are used to name the shape of a molecule and there are three lone pairs, if you consider the model of a trigonal bipyramidal ...
- Fri Nov 20, 2020 12:35 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Homework Question
- Replies: 2
- Views: 151
Re: Homework Question
Hi! The molecular shape of a sulfite ion is trigonal pyramidal because it has 4 regions of electron density (3 bonding pairs and 1 lone pair) and follows the AX3E VSEPR notation. The four pairs are arranged tetrahedrally, but because only atom positions are used to name the shape of a molecule, the ...
- Tue Nov 17, 2020 12:20 pm
- Forum: Formal Charge and Oxidation Numbers
- Topic: Number of Resonance Structures
- Replies: 7
- Views: 1513
Re: Number of Resonance Structures
Thank you so much!! For the formal charge can't you also determine which is the most stable by the structure that has the least amount of charges within the molecule? Yep! The most stable structure is the one with the least amount of charges on each atom within the molecule (I might have mistyped t...
- Tue Nov 17, 2020 12:13 pm
- Forum: Ionic & Covalent Bonds
- Topic: 2A.9
- Replies: 2
- Views: 63
Re: 2A.9
Hi! So for this question, we know that for each positive charge in a cation, we remove one electron from the electron configuration. Because both of the cations in (a) and (b) are in the d-block and have a 2+ charge, the electrons that are removed from their electron configurations are the 4s^2 elec...
- Sat Nov 14, 2020 12:11 pm
- Forum: Formal Charge and Oxidation Numbers
- Topic: Number of Resonance Structures
- Replies: 7
- Views: 1513
Re: Number of Resonance Structures
Hi! From my understanding, there's no easy way to know or calculate how many resonance structures there are for a molecule, you just have to practice knowing how to identify them when drawing the Lewis structure. Hopefully, we will be given relatively simple ones if asked on the midterm, like C4H4, ...
- Fri Nov 13, 2020 11:33 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Electron Configuration Exceptions?
- Replies: 5
- Views: 276
Re: Electron Configuration Exceptions?
Hi! I believe Dr. Lavelle said in the lecture on electron configurations that after the 4s subshell is fully occupied and you enter the 3d subshell, then the 3d state becomes lower energy than 4s, resulting in an electron configuration of [Ar] 3d^5 4s^2. The same rule also applies to 5d and 4s. Hope...
- Fri Nov 13, 2020 2:23 pm
- Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
- Topic: Identifying intermolecular forces
- Replies: 2
- Views: 96
Identifying intermolecular forces
Hi! So I understand the difference between the different interionic and intermolecular forces, but I need a bit of help to make sure I can assign the correct force when given a molecular formula. Hydrogen bonding is rather straightforward where the H has to be bonded to N, O, or F, but how do you id...
- Fri Nov 13, 2020 12:58 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Rules for Assigning Shape
- Replies: 6
- Views: 261
Re: Rules for Assigning Shape
Hi! like others have said above, you can still assign a shape to a molecule even if the bond angles aren't all the same, as demonstrated by the examples given in lecture. Dr. Lavelle stated in lecture that the reason he didn't assign a shape to NH3 was because the lone pair makes naming the shape mo...
- Fri Nov 13, 2020 11:19 am
- Forum: Dipole Moments
- Topic: Boiling point of molecules
- Replies: 5
- Views: 295
Re: Boiling point of molecules
Hi! I believe it's because tetrachloromethane has more electrons and thus, has stronger dispersion forces than methane, so it takes more energy to break the bond and it boils at a higher temperature.
- Sat Nov 07, 2020 7:09 pm
- Forum: Electronegativity
- Topic: Electronegativity Table/Chart in Lecture
- Replies: 14
- Views: 454
Re: Electronegativity Table/Chart in Lecture
I don't think we'll need to know specific values, but we will have to remember the periodic trends in electronegativity and be able to organize elements in order of electronegativity according to the general trend. Hope this helps!
- Sat Nov 07, 2020 7:01 pm
- Forum: Bond Lengths & Energies
- Topic: Bond Lengths
- Replies: 10
- Views: 779
Re: Bond Lengths
To add on to this question, will bond lengths always be given to us in a problem or will we sometimes have to calculate it? If so, what would the process to do that look like? I believe Dr. Lavelle mentioned in lecture that the example bond lengths he used in examples were found through experimenta...
- Fri Nov 06, 2020 4:36 pm
- Forum: Ionic & Covalent Bonds
- Topic: Homework due date
- Replies: 49
- Views: 2051
Re: Homework due date
which sections of hw will be on the midterm? I do not recall if it is cumulative or not... I'm pretty sure I remember my TA say in discussion that the midterms are not cumulative, so the next midterm should be based on the end of the week 2/3/4 homework on the quantum realm and the week 5/6 homework.
- Fri Nov 06, 2020 3:44 pm
- Forum: Electronegativity
- Topic: Electron Affinity
- Replies: 6
- Views: 127
Re: Electron Affinity
While there may be exceptions, because noble gases already have a full valence shell, they are unlikely to form any chemical bonds and gain an electron. I think it is possible because Dr. Lavelle mentioned in lecture that, while adding an electron to a noble gas is unfavorable, it would take a lot o...
- Fri Nov 06, 2020 2:29 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Midterm Curve?
- Replies: 12
- Views: 510
Re: Midterm Curve?
Like Alexandra said above, because of the point system, the class and the tests, aren't curved. However, there were partial points given on the midterm on certain questions based on potential miscalculations.
- Thu Oct 29, 2020 1:45 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Sapling Energy Level and Wavelength
- Replies: 3
- Views: 117
Re: Sapling Energy Level and Wavelength
Hi! I think you're talking about question 11 on the sapling hw (you might not be, but it's a similar question so I'll explain how I worked through it). I didn't use the Rydberg equation solving this one, I just used ΔE = E2-E1 and En = -(hR)/(n)^2. So because the wavelength of the emission is 434 nm...
- Wed Oct 28, 2020 8:44 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Spectral lines/hydrogen emission spectrum
- Replies: 4
- Views: 180
Re: Spectral lines/hydrogen emission spectrum
Hi, I was wondering about the term ground state with regards to the Hydrogen emission spectrum. Would the ground state be n=2 for the Balmer series, or would it be n=1? Hi! For the Balmer series, the visible region, the ground state is n=2 and for the Lyman series, the UV region, the ground state i...
- Wed Oct 28, 2020 8:39 pm
- Forum: Properties of Light
- Topic: Midterm
- Replies: 42
- Views: 1390
Re: Midterm
Does anyone know when we will get our exam results? And will the scores be curved? I believe we get our scores after all discussion sections have taken it and the exams closes, which is Friday - so, we should get our results by the end of the day on Friday. The course isn't curved, so I don't think...
- Wed Oct 28, 2020 8:34 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: 3d and 4s orbitals
- Replies: 9
- Views: 297
Re: 3d and 4s orbitals
Hi! In Monday's lecture on electron configuration, Dr. Lavelle said that the 3d state is actually lower energy than the 4s state, which is why 3d is written first. Hope this helps!
- Wed Oct 28, 2020 8:31 pm
- Forum: General Science Questions
- Topic: polyatomic ions
- Replies: 6
- Views: 358
Re: polyatomic ions
Hi! For Midterm 1, we do not need to know memorize polyatomic ions as we have not covered them yet and it is not part of the syllabus that the midterm covers. We may have to for future exams, but I believe I remember Dr. Lavelle say in a lecture that we won't be required to memorize and recall more ...
- Fri Oct 23, 2020 3:57 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Rydberg Equation
- Replies: 2
- Views: 146
Re: Rydberg Equation
The order does matter and it also depends on what the question is asking in relation to the Rydberg Equation. When asked to calculate how much energy is emitted by the electron, n1 is the final state, but when asked how much energy is absorbed by the electron, n1 is the initial state. n1 must always...
- Fri Oct 23, 2020 2:15 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Orbitals
- Replies: 3
- Views: 112
Re: Orbitals
Hi! Schrodinger's equation uses a wave function to describe the location of an electron in an atom at x, y, and z in a 3D space. Those wave functions are the S, P, D, and F-orbitals, which show the region an electron is likely to be in within the atom. Hope this helps!
- Fri Oct 23, 2020 2:02 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: 1B.27
- Replies: 5
- Views: 198
Re: 1B.27
The "+/- 5.0 m/s" part of the question that describes the velocity indicates the spread of the possible velocities around 5 m/s. This spread of velocity means that the velocity is "uncertain" because it can be anywhere from 0 to 10 m/s and therefore, the uncertainty in velocity i...
- Thu Oct 22, 2020 9:12 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Indeterminacy Problem
- Replies: 3
- Views: 153
Re: Indeterminacy Problem
Hi! I agree with Carolina's answer about that you have to manipulate Heisenberg's Indeterminacy Equation to find ∆x and you get ∆x ≥ h/(4π∆p), which is also ∆x ≥ h/(4π x m∆v) where ∆p=m∆v. I would also like to clarify that the reason that ∆v=10 m/s is because of the "+/- 5.0 ms-1" part of ...
- Thu Oct 22, 2020 8:55 pm
- Forum: *Black Body Radiation
- Topic: Midterm 1
- Replies: 15
- Views: 818
Re: Midterm 1
arisawaters3D wrote:Do we need to know how to use Wien's Law for the midterm?
I don't think we do because we didn't go over it in lecture and it's not mentioned in the parts of the syllabus that the midterm will cover.
- Fri Oct 16, 2020 2:51 pm
- Forum: Properties of Electrons
- Topic: calculating the frequency of Light
- Replies: 4
- Views: 81
Re: calculating the frequency of Light
Hi! In the equation En=(-hR)/(n)^2, the negative sign refers to the decrease in the electron's energy after it returns to the ground state and emits electromagnetic radiation, thus losing energy. So if the question had asked how much energy the electron lost, the answer would be the -4.09x10^-19 J. ...
- Fri Oct 16, 2020 2:06 pm
- Forum: Properties of Electrons
- Topic: Using empirical equation for h-atom
- Replies: 4
- Views: 113
Re: Using empirical equation for h-atom
Hi! Like Carolina and Alexandra mentioned above, the coefficients are derived from the denominator n^2 of the equation En = (-hR)/(n)^2. So because the denominators are (n=2)^2 -> 4 and (n=4)^2 -> 16, he just moved the denominators of 4 and 16 to the front of the calculations to form -(1/4)(nR) and ...
- Fri Oct 16, 2020 1:59 pm
- Forum: Properties of Light
- Topic: rydberg equation
- Replies: 7
- Views: 315
Re: rydberg equation
Hi! From what was explained in the lecture, he would prefer us to use the method used in the lecture but you can use the rydberg equation as long as you understand what the equation means and how to correctly use it in calculations. Also, if we do have to use it in the future it can be easily derive...
- Fri Oct 16, 2020 1:50 pm
- Forum: Photoelectric Effect
- Topic: Sapling HW #4 Part 2 Photoelectric
- Replies: 3
- Views: 99
Re: Sapling HW #4 Part 2 Photoelectric
Hi! In the lecture on the photoelectric effect, it is mentioned that one photon interacts with one electron. Therefore, if each proton has sufficient energy to remove each electron, the maximum number of electrons ejected would be equal to the number of photons. So, you would divide the total energy...
- Fri Oct 16, 2020 1:35 pm
- Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
- Topic: Atomic Spectra Video Module Question
- Replies: 2
- Views: 102
Re: Atomic Spectra Video Module Question
Hi! Once the excited electron returns to its ground state and releases energy in the form of electromagnetic radiation, the energy of the electron decreases. Thus the difference in energy, as described by the equation, is denoted by a negative sign because the electron's energy has decreased. Hope t...
- Fri Oct 09, 2020 9:53 pm
- Forum: Molarity, Solutions, Dilutions
- Topic: Fundamentals G.7
- Replies: 2
- Views: 54
Re: Fundamentals G.7
Hi! I believe the question is just asking for the masses of H2O and KNO3 in grams that you need to prepare the aqueous solution. So because you are given a sample of 510 g grams and it is stated that 5.45% of that sample is KNO3 by mass, you need to figure out how much KNO3 you need. You would find ...
- Thu Oct 08, 2020 4:10 pm
- Forum: Molarity, Solutions, Dilutions
- Topic: Post Assessment Survey Question Help
- Replies: 3
- Views: 102
Re: Post Assessment Survey Question Help
Jenny's response above is correct! You are given the unbalanced reaction of 2C6H6 + __O2 --> __CO2 + __H2O and you need to balance this equation to find the number of moles of oxygen necessary to complete the reaction. If you balance the equation to 2C6H6 + 15O2 --> 12CO2 + 6H2O, you find that 15 mo...
- Thu Oct 08, 2020 3:26 pm
- Forum: Limiting Reactant Calculations
- Topic: Self test M.3B
- Replies: 1
- Views: 218
Re: Self test M.3B
Hi! I calculated this and I got the same answers as you: I found for the reactants that there are 0.6086 moles of NO2 and 0.9991 moles of H20, and with a ratio of 3:1, NO2 is the limiting reagent. Using the chemical equation and the moles of NO2, I calculated that the theoretical yield is 0.4057 mol...