## Search found 50 matches

Mon Mar 12, 2018 4:03 pm
Forum: Reaction Mechanisms, Reaction Profiles
Replies: 2
Views: 168

I believe Lavelle said that we will only work with the Pre-Equilibrium Approach as it is less complex than the Steady-State Approach but still gives us the same result!
Mon Mar 12, 2018 3:54 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Oxidation State
Replies: 2
Views: 200

### Re: Oxidation State

The oxidation state is zero for elements in their free (uncombined) state (ex: Zn(s), Al(s)), including those found in nature as diatomic elements (ex: O2, N2, H2).
Mon Mar 12, 2018 3:33 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: rate constant k
Replies: 1
Views: 194

### Re: rate constant k

For 15.61, the ln(k'/k) simply comes from the equation, ln(k'/k) = Ea/R * (1/T1 - 1/T2). This equation is no longer on Lavelle's online equations sheet, however it was on one of his older equation sheets! Here is the derivation: lnk = -Ea/R (1/T1) + lnA lnk' = -Ea/R (1/T2) + lnA lnk' - lnk = [-Ea/R ...
Tue Mar 06, 2018 9:06 pm
Forum: First Order Reactions
Topic: Key Words for First Order Reactions Half Life Problems
Replies: 2
Views: 213

### Re: Key Words for First Order Reactions Half Life Problems

I also believe the problems should always tell you the order of the reaction as 23, 25, 27, and many others also do. But in the case they don't, you can always check the units of k! For your reference: - zero-order: k is in units of mol * L^-1 * s^-1 - first-order: k is in units of s^-1 - second-ord...
Tue Mar 06, 2018 8:50 pm
Forum: Administrative Questions and Class Announcements
Topic: review session schedule?
Replies: 2
Views: 204

### Re: review session schedule?

Yep! You can find the link titled "Important Final Exam Information" under Exam Information on his website!
Tue Mar 06, 2018 8:48 pm
Forum: Administrative Questions and Class Announcements
Topic: Chapters on test?
Replies: 3
Views: 292

### Re: Chapters on test?

In lecture last Friday, Lavelle also said that it would cover all of Kinetics up to (not including) his Reaction Mechanisms slide!
Thu Mar 01, 2018 9:04 pm
Forum: General Rate Laws
Topic: nth order reactions [ENDORSED]
Replies: 2
Views: 206

### Re: nth order reactions[ENDORSED]

In my discussion, my TA said that we'll only be working with zeroth, first, and second order reactants, however the overall reactions themselves may end up being a higher order (after all the individual orders are added up!). Hope this helps!
Thu Mar 01, 2018 5:45 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.19
Replies: 4
Views: 310

### Re: 15.19

I agree. It took me a while to get the correct answer because I kept incorrectly converting from mmol to mol. I'd recommend converting all of the mmols to mols in the beginning and also paying attention to the order with respect to each reactant!
Thu Mar 01, 2018 5:41 pm
Forum: First Order Reactions
Topic: 15.29 b
Replies: 1
Views: 131

### Re: 15.29 b

So for part b) of this problem, we need to reuse the first-order integrated rate law again to solve for t. We need to convert from mols of B to mols of A and subtract this value from the initial A concentration to take into account how much A was used up to produce the 0.030 M concentration of B. Th...
Thu Feb 22, 2018 10:10 pm
Forum: Balancing Redox Reactions
Topic: Cell Diagram [ENDORSED]
Replies: 7
Views: 441

### Re: Cell Diagram[ENDORSED]

I believe you're referring to the single lines in between the I- ions and I2(s) - if so, cell diagram notation involves separating elements/compounds that are in different states (solid/liquid/gas/aq) on both sides!
Thu Feb 22, 2018 10:01 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: double lines between anode and cathode
Replies: 3
Views: 295

### Re: double lines between anode and cathode

The double lines represent the salt bridge in galvanic cells. The elements to the left of the double lines represent the anode/oxidation reaction, while the elements to the right of the double lines represent the cathode/reduction reaction.
Thu Feb 22, 2018 5:22 pm
Forum: Balancing Redox Reactions
Topic: Oxidation
Replies: 3
Views: 277

### Re: Oxidation

Here are a few things that are helpful to remember about oxidation numbers
- Oxygen has a oxidation number of -2 in compounds
- Elements in their natural/most stable/free state have oxidation numbers of 0
- Monoatomic ions have oxidation numbers equal to their charge
Thu Feb 15, 2018 10:02 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta G
Replies: 3
Views: 235

### Re: Delta G

Delta G is not pathway dependent, so it is only necessary to examine the initial and final states! On the other hand, q, w, and E are not state functions so their pathways are significant in calculations.
Thu Feb 15, 2018 9:36 pm
Forum: Balancing Redox Reactions
Topic: Half-Reactions on Test 2
Replies: 5
Views: 378

### Re: Half-Reactions on Test 2

I believe that for all tests, we'll be given all the information the homework problems ask us to look for in the appendixes. Hope this helps!
Thu Feb 15, 2018 9:30 pm
Forum: Student Social/Study Group
Topic: Sections on Test 2
Replies: 3
Views: 355

### Re: Sections on Test 2

I agree! Lavelle just posted an announcement confirming this :)
Tue Feb 06, 2018 1:38 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: hw9.59 standard reaction entropy
Replies: 3
Views: 259

### Re: hw9.59 standard reaction entropy

I believe that you should work with the balanced equations! For both 9.57 and 9.59, the equations they gave are already balanced so you can go ahead and work with those. For these problems just remember that the ΔHf and ΔGf of O2 are 0. Hope this helps!
Tue Feb 06, 2018 1:28 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: constant pressure and constant volume
Replies: 3
Views: 201

### Re: constant pressure and constant volume

For monatomic ideal gasses, at constant volume Cv = (3/2)R and at constant pressure Cp = (5/2)R.
Tue Feb 06, 2018 1:21 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.45
Replies: 1
Views: 280

### Re: 9.45

For this problem, you will mainly be using the formulas, ΔS(surr) = - ΔH(system)/T and ΔS(system) = ΔH(system)/T. Note that the negative sign in the ΔS(surr) equation assumes that for exothermic reactions (ΔH of system is negative), the entropy of the surroundings is increased as it accepts heat rel...
Tue Jan 30, 2018 12:20 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Homework 9.5 [ENDORSED]
Replies: 11
Views: 678

### Re: Homework 9.5[ENDORSED]

When it comes to these problems, it helps to look at the direction of heat transfer from each of the objects/systems involved! When heat is being released by an object, q is negative with respect to that object, whereas when heat is being absorbed by another object, q is positive.
Tue Jan 30, 2018 12:14 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.11 P is inverse of V
Replies: 2
Views: 184

### Re: 9.11 P is inverse of V

I believe this is referring to the relationship between P and I in the ideal gas law: PV = nRT. If the equations are rearranged as P = nRT/V or V = nRT/P, and n and T are kept constant, you can see that P and V share an inverse relationship. When either P or V goes up, the other one goes up to maint...
Tue Jan 30, 2018 12:08 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: unit of entropy
Replies: 11
Views: 660

### Re: unit of entropy

The units end up being J/K as kB = 1.381 x 10^-23 J.K^-1 and also ΔS = nRln(V2/V1) cancels out into J.K^-1.
Wed Jan 24, 2018 4:27 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Positive and Negative Signs 8.21
Replies: 3
Views: 254

### Re: Positive and Negative Signs 8.21

I think it would also help to look at it in terms of the objects themselves. q is positive when heat has been absorbed by the system, whereas q is negative when heat has flowed from the system. Hope this helps!
Wed Jan 24, 2018 4:19 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess's Law [ENDORSED]
Replies: 7
Views: 447

### Re: Hess's Law[ENDORSED]

I agree, while the questions may differ on what they ask for using the final reaction, the problems should give the additional reactions and enthalpies we'll need to complete the final reaction.
Wed Jan 24, 2018 4:14 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: qp=deltaH
Replies: 2
Views: 4084

### Re: qp=deltaH

This can also be proven with equations. Because ΔH = ΔU + PΔV and ΔU = q + w, you can plug ΔU into the ΔH equation as follows: ΔH = q + w + PΔV. Because w = -PΔV, the last two terms cancel each other out: ΔH = q - PΔV + PΔV, leaving us with ΔH = q at constant pressure. Hope this helps!
Fri Jan 19, 2018 3:17 pm
Forum: Phase Changes & Related Calculations
Topic: 8.47
Replies: 3
Views: 151

### Re: 8.47

I think that because w = -P∆V for expansion problems, the 22 kJ in expansion work becomes equal to w = -P∆V = -(22 kJ). Therefore, when plugging it back into the equation, ∆U = ∆H - P∆V = -15 kJ - (-22 kJ) = - 15 kJ + 22 kJ = +7 kJ. Hope this helps!
Fri Jan 19, 2018 3:05 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: q and delta H interchangeable in calculations?
Replies: 4
Views: 696

### Re: q and delta H interchangeable in calculations?

In addition, because the amount of heat absorbed or released at a constant pressure is defined as the enthalpy, we can write that q = ∆H.
Fri Jan 19, 2018 2:38 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: open system
Replies: 6
Views: 398

### Re: open system

In all systems, the matter/substance involved in the system contributes to its energy. Because matter can be exchanged with the surroundings of an open system, the addition or removal of substance from the system can change its energy.
Fri Jan 12, 2018 4:28 pm
Forum: Phase Changes & Related Calculations
Topic: Heat Enthalpies We Need to Know
Replies: 3
Views: 196

### Re: Heat Enthalpies We Need to Know

Nope! Lavelle will provide these values on the tests. I believe he just includes the table under the reading because we'll need to reference it for some homework problems and it allows us to compare the heat capacities for different elements/substances. Hope this helps!
Fri Jan 12, 2018 4:08 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: tables in chapter 8
Replies: 5
Views: 269

### Re: tables in chapter 8

I agree. I'm pretty sure we'll be given the values, and all we'll need to do is know how to use them or manipulate them if we need to (i.e. divide reaction enthalpy by the number of moles to find enthalpy for formation of one mole of a substance). Hope this helps!
Fri Jan 12, 2018 12:48 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Heat and state function
Replies: 2
Views: 177

### Re: Heat and state function

Heat is path dependent and therefore cannot be determined simply by its current state. When calculating the values of both heat and work, it matters how the end condition is achieved. Therefore, you cannot simply subtract the final condition from the initial condition as you would for a state functi...
Wed Dec 06, 2017 2:50 pm
Forum: Hybridization
Topic: sp2 hybridization
Replies: 5
Views: 417

### Re: sp2 hybridization

I agree with the others. I prefer to think of hybridization as the number of attachments to the central atom, with bonds and lone pairs each acting as one attachment. Boron has three Fluorides attached to it, so it is sp2 hybridized. Hope this helps!
Wed Dec 06, 2017 1:44 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: dipole moment chapter 4 test [ENDORSED]
Replies: 3
Views: 577

### Re: dipole moment chapter 4 test[ENDORSED]

PO43- and PCl^5 do not have dipole moments because they have a symmetrical molecular shape (PO43- is a tetrahedral and PCl^5 is trigonal bipyramidal), which cancels out the dipole moments. Hope this helps.
Tue Nov 28, 2017 12:59 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.19 b
Replies: 3
Views: 267

### Re: 4.19 b

The shape of (CH3)2Be is only tetrahedral about the carbon atoms as they both have 4 regions of electron density (3 hydrogens about them and are both bonded to Be). However, Be only has two regions of electron density, so the C-Be-C bond is linear with a bond angle of 180 degrees. Hope this helps!
Tue Nov 28, 2017 12:50 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Q and K
Replies: 2
Views: 215

### Re: Q and K

This means that at that time, the ratio of the concentrations of product to reactants is larger than the ratio at equilibrium. This means that at that time, the concentration of the product is higher than it should be at equilibrium, causing the reaction to shift to the left/reactants to reach equil...
Fri Nov 24, 2017 3:00 pm
Forum: Naming
Topic: Naming coordination cmpd
Replies: 2
Views: 178

### Re: Naming coordination cmpd

In discussion, my TA stated that for the purposes of the test, two of the more important Latin root elements to remember are Copper and Iron. In a coordination compound with a negative charge, Copper is written as Cuprate and Iron is written as Ferrate.
Fri Nov 24, 2017 12:04 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Calculating K from manipulations of Equation
Replies: 1
Views: 182

### Re: Calculating K from manipulations of Equation

We square our K value when we double the chemical equation because of how doubling the coefficients also doubles the exponents in the formula K = [product]^(product coefficient) / [reactant]^(reactant coefficient). For example, if you had 2A -> B, K = [B]^(1) / [A]^(2). When you double the equation,...
Wed Nov 15, 2017 9:32 pm
Forum: Photoelectric Effect
Topic: Midterm question [ENDORSED]
Replies: 6
Views: 500

### Re: Midterm question[ENDORSED]

This statement is incorrect in its use of the word always. Higher frequency light only emits electrons with higher kinetic energies if the energy has already surpassed that of the work function; if the light's energy has not yet reached that of the work function, no electrons would be emitted.
Wed Nov 15, 2017 12:47 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Regions of electron density
Replies: 4
Views: 323

### Re: Regions of electron density

Yes, lone pairs count as regions of electron density! An unpaired electron also counts as a single region of electron density.
Sun Nov 12, 2017 12:54 am
Forum: DeBroglie Equation
Topic: When to use DeBroglie Equation
Replies: 4
Views: 322

### Re: When to use DeBroglie Equation

The DeBroglie Equation is used to find the wavelength of any particle with momentum! Hope this helps.
Sun Nov 12, 2017 12:53 am
Forum: Empirical & Molecular Formulas
Topic: Practice Midterm Question
Replies: 4
Views: 373

### Re: Practice Midterm Question

I agree with Karan! If the molar mass of the compound is given (which I think it was!), you can just multiply it by the percentages to find out how many grams each element would contribute to the total mass of one mole of the compound. You can then directly divide the mass of each element by their r...
Sat Nov 04, 2017 11:10 pm
Forum: Lewis Structures
Topic: Bases and Acids
Replies: 3
Views: 241

### Re: Bases and Acids

I hope these examples of Lewis Acids and Bases also help!
Examples of Lewis Bases: NH3, F-, and OH-
Examples of Lewis Acids: BF3 and H+.
Sat Nov 04, 2017 10:44 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Aufbau principle
Replies: 4
Views: 408

### Re: Aufbau principle

I agree with Ayona. Also,in the powerpoint, it was written that "we apply Pauli Exclusion Principle and Hund's Rule to determine e- configuration," which is what is accomplished through the Aufbau Principle. Hope this helps!
Tue Oct 24, 2017 1:21 pm
Forum: Trends in The Periodic Table
Topic: 2.67 part B
Replies: 4
Views: 345

### Re: 2.67 part B

In Nitrogen, all three orbitals in the p subshell are half-filled with one electron each which makes it more stable than Carbon, which has two half-filled and one empty p-orbital. Thus, Carbon has a higher electron affinity than Nitrogen. Hope this helps!
Tue Oct 24, 2017 12:59 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 2.55
Replies: 2
Views: 158

### Re: 2.55

I agree with Kaushal. Also, on his powerpoint, Lavelle wrote that we only need to know the s-block, the p-block, and just the first d-block row, so I don't think we will have to worry much about the other elements!
Sat Oct 21, 2017 1:17 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: N Quantum Number [ENDORSED]
Replies: 3
Views: 299

### Re: N Quantum Number[ENDORSED]

Yes, the principle quantum number n determines the energy and size, and is also called a shell. The angular momentum quantum number l corresponds to the s/p/d/f-orbitals and describes the shape.
Sat Oct 21, 2017 1:00 pm
Forum: Properties of Light
Topic: test 2 topic
Replies: 9
Views: 766

### Re: test 2 topic

For the most part, I feel that Lavelle will only test us on the topics he covers in lecture. In addition to reviewing the assigned homework and lecture notes, I also like looking at the lecture outlines to see exactly which topics we are expected to understand.
Sat Oct 14, 2017 4:48 pm
Forum: Properties of Electrons
Topic: Threshold level and Work Function [ENDORSED]
Replies: 6
Views: 622

### Re: Threshold level and Work Function[ENDORSED]

Yes they are! They are just names that are used interchangeably and are both denoted by the symbol Φ.
Sat Oct 14, 2017 4:36 pm
Forum: Photoelectric Effect
Topic: Conversions for units in work function [ENDORSED]
Replies: 2
Views: 234

### Re: Conversions for units in work function[ENDORSED]

I also remember Lavelle saying he will give us the conversion factors when the values are in units we do not use as often! But to be safe, it always helps to remember the conversion factors. Here they are for eV and keV: 1 eV = 1.602 x 10^-19 J and 1 keV = 1.602 x 10^-16 J.
Thu Oct 05, 2017 8:58 pm
Forum: Limiting Reactant Calculations
Topic: After determining the limiting reactant, how do you find the mass of a product?
Replies: 2
Views: 274

### Re: After determining the limiting reactant, how do you find the mass of a product?

After you determine the limiting reactant, which in this case is C6H9Cl3, you would multiply the moles of C6H9Cl3 by its molar ratio with AgCl, which is 1 mol C6H9Cl3 : 3 mol AgCl (from the balanced equation). This gives you the moles of AgCl produced, which you can then multiply with the molar mass...
Thu Oct 05, 2017 8:31 pm
Forum: Limiting Reactant Calculations
Topic: M.15 (b)
Replies: 2
Views: 254

### M.15 (b)

The problem: Aluminum metal reacts with chlorine gas to produce aluminum chloride. In one preparation, 255g of aluminum is placed in a container holding 535 g of chlorine gas. After reaction ceases, it is found that 300g of aluminum chloride has been produced. (a) Write the balanced equation for the...