## Search found 57 matches

Sat Mar 17, 2018 8:16 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Catalysts
Replies: 3
Views: 319

### Re: Catalysts

if it is seen in the overall reactant and also in the products therefore "cancelling out" and not being consumed
Fri Mar 16, 2018 2:16 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.103
Replies: 3
Views: 310

### 8.103

Are we supposed to know that average kinetic energy is equal to (3/2)RT? Overall, how does the solution manual obtain these answers and are we expected to know this formula even though it's not given on the sheet?
Thu Mar 15, 2018 4:13 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Max work and delta G
Replies: 1
Views: 162

### Max work and delta G

Conceptually, how does delta G = work max = -nFE ?
Wed Mar 14, 2018 12:42 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Slow steps and intermediates
Replies: 2
Views: 152

### Re: Slow steps and intermediates

No, that did not indicate that the second step was the slow step. You have to test it. I think he did that just to have us go through a little more work because if the first step was the slow step, it would have been an easier, shorter problem.
Wed Mar 07, 2018 8:39 pm
Forum: First Order Reactions
Topic: UA worksheet [ENDORSED]
Replies: 2
Views: 202

### Re: UA worksheet[ENDORSED]

If your half life is 6 days, in 30 days you will go through 5 half lives.

If you start with 100% you divide it by 2 (or multiply by 1/2) five times to get 3.1%
100/2=50% 1 half life
50/2=25% 2 half lives
25/2=12% 3 half lives
12/2=6.25% 4 half lives
6.25/2=3.125% 5 half lives
Wed Mar 07, 2018 8:19 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Finding the intermediate(s)
Replies: 5
Views: 270

### Re: Finding the intermediate(s)

If it is produced in a step and a product in another, therefore being cancelled out of the overall reaction, then it is an intermediate
Wed Mar 07, 2018 10:21 am
Forum: General Rate Laws
Topic: Stoichiometric Coefficients
Replies: 2
Views: 164

### Stoichiometric Coefficients

Why does unique rate use stoichiometric coefficients and the other equations do not need coefficients?
Sun Mar 04, 2018 4:35 pm
Forum: First Order Reactions
Topic: Second Order Half Life Equation
Replies: 2
Views: 180

### Re: Second Order Half Life Equation

.693 and my response is actually for a first order half life equation. t(1/2)= (ln2)/k

second order half life is t(1/2)=1/(k[A]0)
Sun Mar 04, 2018 4:07 pm
Forum: First Order Reactions
Topic: Second Order Half Life Equation
Replies: 2
Views: 180

### Re: Second Order Half Life Equation

second order half life numerator is always ln 2 because it is not dependent on initial concentration so .693 is just ln 2
Sun Mar 04, 2018 3:52 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Stopped Flow Technique
Replies: 3
Views: 263

### Re: Stopped Flow Technique

Reactions that are initiated by mixing the reagents can be studied by the stopped-flow technique, in which solutions of the reactants are forced into a mixing chamber very rapidly and, within a few milliseconds, the formation of products is observed spectroscopically. This procedure is commonly use...
Sun Mar 04, 2018 3:39 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Stopped Flow Technique
Replies: 3
Views: 263

### Stopped Flow Technique

What is the stopped flow technique and what is it's relation to kinetics?
Sun Feb 25, 2018 1:04 pm
Forum: First Order Reactions
Topic: Pseudo Order
Replies: 1
Views: 143

### Pseudo Order

What exactly is a pseudo order reaction? Do we need to know this?
Wed Feb 21, 2018 9:37 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 14.83 [ENDORSED]
Replies: 2
Views: 209

### 14.83[ENDORSED]

Why is it that in part b, the solution manual says that E cell not and E cell are both temperature dependent? Shouldn't E cell not only be at 25 degrees Celsius? How is it temperature dependent then?
Wed Feb 21, 2018 9:23 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Replies: 3
Views: 380

it is thermally insulated. heat does not enter or leave the system
Tue Feb 13, 2018 7:46 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: ΔG° vs ΔG
Replies: 5
Views: 1048

### Re: ΔG° vs ΔG

ΔG° is Gibbs free energy at standard conditions. You use ΔG° to find ΔG by ΔG=ΔG°+ RTlnQ
Tue Feb 13, 2018 7:44 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: PV = nRT
Replies: 6
Views: 403

### Re: PV = nRT

When dealing with an ideal gas and if you are looking for one of the variables and given the others. You're not really directed to use it, but you use it to find a missing variable that you might need. For example, if you need to use volume but you're given moles, temperature, and pressure. Also, wo...
Tue Feb 13, 2018 7:40 pm
Forum: Calculating Work of Expansion
Topic: -w vs +w
Replies: 2
Views: 207

### Re: -w vs +w

If work is done by the system, -w, it means expansion. If work is done onto the system, +w, it means compression.
Fri Feb 09, 2018 10:15 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Cv,m vs Cp,m vs R
Replies: 4
Views: 4258

### Re: Cv,m vs Cp,m vs R

Also, if there are two changes in a combination of temperature, pressure, and volume, you would add the two steps together to get combined entropy change. In a review session, an example was entropy change of 2.00 mol of Argon gas volume from 10L to 5L and Temperature from 300K to 100K with Cv= 12.4...
Fri Feb 09, 2018 10:12 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Cv,m vs Cp,m vs R
Replies: 4
Views: 4258

### Re: Cv,m vs Cp,m vs R

Cv is specific heat in constant volume and Cp is specific heat in constant pressure. So when you are calculating entropy change with a change in temperature and constant volume, you would use the equation delta s = nCvln(T2/T1). If you are calculating entropy change with a change in temperature and ...
Mon Feb 05, 2018 9:21 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 9.63
Replies: 4
Views: 263

### 9.63

Why is it that the compounds with a positive free energy of formation are unstable with respect to the elements?
Sat Feb 03, 2018 3:01 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Extensive/Intensive Property [ENDORSED]
Replies: 4
Views: 276

### Re: Extensive/Intensive Property[ENDORSED]

You can change an extensive property to intensive by dividing it by something like mass so that it is not "dependent" anymore
Thu Feb 01, 2018 11:44 pm
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: Third Law
Replies: 3
Views: 259

### Re: Third Law

Yes the third law states that the limit of t approaching 0K of S will be equal to 0 for perfect monatomic crystals
Wed Jan 31, 2018 2:28 pm
Forum: Administrative Questions and Class Announcements
Topic: Chem Community Posts
Replies: 5
Views: 520

### Re: Chem Community Posts

End of Sunday
Tue Jan 23, 2018 11:25 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 4
Views: 228

### Re: Bond Enthalpies

You use bond enthalpies to find the enthalpy of formation by subtracting the sum of the bond enthalpies of formed bonds from the sum of the bond enthalpies of the broken bonds.

H=sum of broken - sum of formed
Tue Jan 23, 2018 11:23 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.73 and Units for Reaction Enthalpy
Replies: 1
Views: 121

### Re: 8.73 and Units for Reaction Enthalpy

I think the book tends to denote enthalpy as kJ/mole of the reaction given, which does not mean necessarily per mole of the molecule. I believe my TA said that Dr. Lavelle usually doesn't write it this way in lecture as it can be confusing, but I believe the book just means kJ per mole of the reacti...
Tue Jan 23, 2018 11:14 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Calorimeters Isolated
Replies: 2
Views: 330

### Re: Calorimeters Isolated

The bomb calorimeter is isolated because it does not allow exchange of heat or matter, but the coffee cup calorimeter has to be open to have constant pressure.
Fri Jan 19, 2018 4:09 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Concept Clarification
Replies: 3
Views: 171

### Re: Concept Clarification

I would consider the ideal gas law PV=nRT because you are changing the number of moles which may change another variable, which would affect the energy of the system.
Fri Jan 19, 2018 4:05 pm
Forum: Calculating Work of Expansion
Topic: 8.11
Replies: 1
Views: 86

### 8.11

How did the solutions manual go from -(1.00atm)(1.20L) to -122J?
Fri Jan 19, 2018 3:10 pm
Forum: Phase Changes & Related Calculations
Topic: 8.47
Replies: 3
Views: 151

### Re: 8.47

The work is positive because the work was done onto the system instead of by the system.
Thu Jan 11, 2018 10:36 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.67
Replies: 1
Views: 370

### 8.67

Can someone walk me through how to do this problem? (Use tables 8.3, 8.6, 8.7) Estimate the enthalpy of formation of each of the following compounds in the LIQUID state. (standard enthalpy of carbon sublimation is 717 kj/mol) a) H2O b) methanol, CH3OH c) benzene, C6H6 (without resonance) d) benzene,...
Thu Jan 11, 2018 10:20 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Ch 8 Problem 49
Replies: 1
Views: 215

### Re: Ch 8 Problem 49

For most equations we assume the temp is 25 degrees celsius, which is equivalent to 298K, so I think it was just assumed the equation took place at standard temperature since a temperature wasn't given.
Thu Jan 11, 2018 10:16 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.61
Replies: 4
Views: 206

### Re: 8.61

So you know the first equation is multiplied by 2 to get 2HBr, the second equation is reversed, and the third is left alone. If you write these out, it's easy to see which parts cancel. 2NH3, 2NH4Br, and N2 cancel leaving you with the desired H2+B2+2HBr. Remember to respectively change the delta H t...
Fri Dec 08, 2017 10:36 am
Forum: Conjugate Acids & Bases
Topic: 12.3a
Replies: 4
Views: 419

### Re: 12.3a

It would but in a two-step process. The first equation would yield HSO4- and the second would have HSO4- as the acid and yield SO4(2-)
Fri Dec 08, 2017 10:34 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: 12.21
Replies: 2
Views: 166

### Re: 12.21

It's an equilibrium constant at specifically 25 degrees celsius. Since it's a constant it's always the same number at this temperature.
Sun Dec 03, 2017 12:23 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: 12.35
Replies: 1
Views: 152

### 12.35

Give the Ka value for the acids
part d, HSeO4- pKa2=1.92
would you just solve for Ka2? Can you solve for Ka1? In the solution manual it has the answer for Ka2 but it is labeled Ka1? Or am I seeing it wrong?
Sun Dec 03, 2017 12:09 pm
Forum: Lewis Acids & Bases
Topic: Lewis Acid & Base vs. Bronsted Acid & Base [ENDORSED]
Replies: 2
Views: 212

### Re: Lewis Acid & Base vs. Bronsted Acid & Base[ENDORSED]

Lewis acid: electron pair acceptor
Lewis base: electron pair donor
Bronsted acid: proton donor
Bronsted base: proton acceptor

(focus is just different!)
Thu Nov 23, 2017 11:49 am
Forum: Naming
Topic: H2O in coordination compounds
Replies: 2
Views: 189

### H2O in coordination compounds

Does it matter if you write H2O or OH2 when writing the coordination compound if it has "aqua" in the name?
Tue Nov 21, 2017 2:55 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: 11.41
Replies: 1
Views: 170

### 11.41

A 25.0-g sample of ammonium carbamate, NH4(NH2CO2) was placed in an evacuated 0.250-L flask and kept at 25 degrees C. At equilibrium, 17.4 mg of CO2 was present. What is the value of Kc for the decomposition of ammonium carbamate into ammonia and carbon dioxide? The rxn is NH4(NH2CO2) (s) <--> 2NH3 ...
Mon Nov 13, 2017 11:46 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: "more or less than 109.5 degrees"?
Replies: 4
Views: 622

### Re: "more or less than 109.5 degrees"?

You are just supposed to understand that if you have molecules with lone pairs, it will "push" the other atoms to create an angle slightly less than what would usually be expected
Mon Nov 13, 2017 11:42 pm
Forum: Limiting Reactant Calculations
Topic: Limiting Reactant vs Theoretical Yield
Replies: 3
Views: 1085

### Re: Limiting Reactant vs Theoretical Yield

A limiting reactant is the reactant in an equation that determines how much product will be produced. This is found by determining how many moles of each reactant you have and comparing it to the ratio of reactants found when balancing the chemical equation. Theoretical yield is the maximum potentia...
Tue Nov 07, 2017 5:29 pm
Forum: Lewis Structures
Topic: 3.97
Replies: 2
Views: 190

### 3.97

No one responded to me so I'm posting this question again

Is the solution manual indicating the shape of the molecule? Why is it drawn this way?
Mon Nov 06, 2017 4:42 pm
Forum: Dipole Moments
Topic: Dipole Moment of CO
Replies: 3
Views: 1436

### Re: Dipole Moment of CO

CO can be linear and have a dipole moment because it is not cancelling out. The oxygen will "pull" on the carbon creating a dipole moment. In comparison, CO2 does not have a dipole moment because it is linear and the bond dipoles cancel each other out.
Mon Nov 06, 2017 4:38 pm
Forum: Lewis Structures
Topic: 3.97
Replies: 2
Views: 150

### Re: 3.97

Chem_Mod wrote:Hi Kaylin,

Would you mind including a photo of said question and corresponding answer?

Thanks!
Mon Nov 06, 2017 2:23 pm
Forum: Lewis Structures
Topic: 3.97
Replies: 2
Views: 150

### 3.97

Is the solution manual indicating the shape of the molecule? Why is it drawn this way?
Fri Nov 03, 2017 11:01 pm
Forum: Lewis Structures
Topic: 3.67(b)
Replies: 2
Views: 226

### 3.67(b)

Why wouldn't ClO2 have double bonds instead of single bonds? (The solution manual shows the answer with single bonds)
Fri Nov 03, 2017 10:50 pm
Forum: Lewis Structures
Topic: Extra electrons
Replies: 1
Views: 159

### Extra electrons

In 3.61 for example, how do you know where to put the extra electrons? Iodine gets more lone pairs added instead of bonding more. Do you just try different structures and test for the lowest formal charge?
Sat Oct 28, 2017 11:37 pm
Forum: Lewis Structures
Topic: Placement [ENDORSED]
Replies: 6
Views: 382

### Re: Placement[ENDORSED]

The central atom tends to be the one with lower ionization energy or the least electronegativity, so you would have to know the trends of the periodic table.
Sat Oct 28, 2017 11:03 pm
Forum: Lewis Structures
Topic: Central Atom [ENDORSED]
Replies: 3
Views: 209

### Re: Central Atom[ENDORSED]

The atom with the least electronegativity or the lowest ionization energy tends to be the central atom.
Sun Oct 22, 2017 4:47 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: unpaired electrons [ENDORSED]
Replies: 4
Views: 678

### unpaired electrons[ENDORSED]

How do you determine how many unpaired electrons an atom has? I understand the Aufbau principle and Hund's rule, so I'm wondering if you have to write out the electron configuration to figure this out or if there's an easier way?
Sun Oct 22, 2017 3:03 pm
Forum: Trends in The Periodic Table
Topic: Atomic Size Trend [ENDORSED]
Replies: 4
Views: 299

### Re: Atomic Size Trend[ENDORSED]

Very simply, as the number of protons increase, the added valence electrons will be pulled toward the nucleus more, which makes the radius smaller. So as you move right on the periodic table, more protons and electrons = greater attraction and smaller radius
Sun Oct 15, 2017 8:15 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Heisenberg's Uncertainty Principle - test
Replies: 1
Views: 156

### Re: Heisenberg's Uncertainty Principle - test

Uncertainty is not on this test. It will cover up to de Broglie but you can read ahead to prepare for what's coming up since it is in the chapter.
Sun Oct 15, 2017 8:13 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Why don't we use the Rydberg equation from the book?
Replies: 8
Views: 516

### Re: Why don't we use the Rydberg equation from the book?

It does the same exact thing. Dr. Lavelle said he doesn't prefer the equation in the book because students were getting confused on which place to put the final and initial energy levels whereas the delta E equation is more clear and straight forward AND tells you which direction the energy is going...
Sun Oct 15, 2017 8:08 pm
Forum: DeBroglie Equation
Topic: When to use DeBroglie equation? [ENDORSED]
Replies: 4
Views: 372

### Re: When to use DeBroglie equation?[ENDORSED]

It describes how light has wavelike properties. In problems it is used when given momentum, mass, velocity, wavelength since those are the variables. You would not cross over this equation with the others though because that's about light as particles or photons.
Sun Oct 08, 2017 5:01 pm
Forum: SI Units, Unit Conversions
Topic: Problem E7
Replies: 3
Views: 671

### Re: Problem E7

moles of Carbon = (2.1x10^9 atoms)/(6.0221415 × 10^23 mol^-1) = 3.5x10^-15 mol C

divide by Avogadro's number because it refers to how many atoms are in one mole
Sun Oct 08, 2017 4:55 pm
Forum: Limiting Reactant Calculations
Topic: Calculating how much of the excess remains [ENDORSED]
Replies: 4
Views: 383

### Re: Calculating how much of the excess remains[ENDORSED]

You would first find the limiting reactant and then use the ratio from the balanced chemical equation to find how much of the excess will be used. Then subtract how much will be used by the total excess... So if you have two moles of each reactant and the ratio is 1:2, the amount of excess used is 1...
Sun Oct 08, 2017 4:48 pm
Forum: Empirical & Molecular Formulas
Topic: Friday Oct 6 Test
Replies: 7
Views: 691

### Re: Friday Oct 6 Test

^I believe that was the molecular and empirical formula since we were also given the molar mass
Mon Oct 02, 2017 8:48 pm
Forum: Molarity, Solutions, Dilutions
Topic: G25 homework problem
Replies: 7
Views: 573

### G25 homework problem

The question: Practitioners of the branch of alternative medicine known as homeopathy claim that very dilute solutions of substances can have an effect. Is the claim plausible? To explore this question, suppose that you prepare a solution of a supposedly active substance, X, with a molarity of 0.10 ...