## Search found 51 matches

Mon Mar 12, 2018 1:06 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: 15.89 reaction profile
Replies: 1
Views: 106

### Re: 15.89 reaction profile

We aren't given info on whether the activation energy for step 1 or step 3 is higher, so as long as both are different to each other and less than the activation energy for step 2, it should be ok.
Mon Mar 12, 2018 12:54 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Reaction Profiles
Replies: 2
Views: 160

### Re: Reaction Profiles

The x axis is reaction progression and y axis is potential energy (organic chemists use ∆G). It's probably good to know how to find ∆G using the reaction profile in addition to the activation energy and to be able to compare a catalyzed reaction profile vs. a non-catalyzed one.
Mon Mar 12, 2018 11:47 am
Forum: *Alcohols
Topic: functional groups [ENDORSED]
Replies: 4
Views: 552

### Re: functional groups[ENDORSED]

It's probably a good idea to be familiar with the functional groups and how to draw line structures.
Wed Mar 07, 2018 11:12 am
Forum: General Rate Laws
Topic: Rate of a Reaction
Replies: 2
Views: 168

### Re: Rate of a Reaction

You use stoichiometry (3 mmol H2 consumed for every 2 mmol NH3 produced), so (1.15 mmol NH3/Lh)(3 mmol H2/2 mmol NH3) = 1.72 mmol H2/Lh
Wed Mar 07, 2018 11:04 am
Forum: First Order Reactions
Topic: 15.37(B) homework
Replies: 3
Views: 170

### Re: 15.37(B) homework

Since final concentration is 10% of the initial, dividing initial by final would result in 10. Therefore, you get ln(10)/k.
Wed Mar 07, 2018 11:02 am
Forum: General Rate Laws
Topic: Problem 15.37
Replies: 3
Views: 170

### Re: Problem 15.37

Since final concentration is 10% of the initial, dividing initial by final would result in 10. Therefore, you get ln(10)/k.
Fri Mar 02, 2018 11:09 am
Forum: General Rate Laws
Topic: Calculating Rate vs. Unique Average Rate
Replies: 2
Views: 114

### Calculating Rate vs. Unique Average Rate

When will we know whether we need to calculate the rate vs. the unique average rate? What would the problem say to indicate that it is looking for one vs. the other?
Fri Mar 02, 2018 11:05 am
Forum: First Order Reactions
Topic: Pseudo-First-Order Reactions [ENDORSED]
Replies: 3
Views: 175

### Re: Pseudo-First-Order Reactions[ENDORSED]

We won't need to know how to do calculations, but we need to be familiar with what they are.
Wed Feb 28, 2018 10:44 am
Forum: First Order Reactions
Topic: 15.105
Replies: 1
Views: 126

### Re: 15.105

You can use 150 mg as the "concentration" since volume is constant and the conversion from mass to moles is constant.
Wed Feb 21, 2018 10:35 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.15 Part C
Replies: 1
Views: 105

### Re: 14.15 Part C

KOH is used as an arbitrary strong base that contains OH- (could be NaOH, OH-, etc).
Wed Feb 21, 2018 10:29 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.47 Mistake in Notation?
Replies: 1
Views: 114

### Re: 14.47 Mistake in Notation?

It should be Sn^4+, Sn^2+ because the one that gets reduced should be on the left and the one that gets oxidized should be on the right (higher positive charge on the left).
Wed Feb 21, 2018 10:20 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: #14.11
Replies: 2
Views: 186

### Re: #14.11

There shouldn't be three reactions (and I don't believe there are in 14.11).
Thu Feb 15, 2018 12:48 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Pt(s) vs. C(graphite) [ENDORSED]
Replies: 1
Views: 172

### Pt(s) vs. C(graphite)[ENDORSED]

In what situations (cost aside) would it be better to use graphite instead of platinum?
Thu Feb 15, 2018 12:12 am
Forum: Balancing Redox Reactions
Topic: Balancing Redox Reactions
Replies: 2
Views: 93

### Re: Balancing Redox Reactions

Typically for balancing redox reactions, O will be the element you need to balance using water, OH-, and H+ (depending on whether the environment is acidic or basic).
Thu Feb 15, 2018 12:10 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Change in Entropy for the Surroundings vs. System
Replies: 2
Views: 253

### Re: Change in Entropy for the Surroundings vs. System

∆S(system) = ∆H(system)/T since (assuming constant pressure) ∆H(system)=q(system), and if heat were added to the system, then entropy would increase. (+q(system) --> +∆S(system)). ∆S(surroundings) = -∆H(system)/T since if heat from the surroundings were added to the system, then the entropy of the s...
Tue Feb 06, 2018 11:26 pm
Forum: Balancing Redox Reactions
Topic: Water in Redox reaction
Replies: 1
Views: 84

### Re: Water in Redox reaction

Was "Reduction: 8H^+ + MnO4^- + 5e- --> Mn^2+ + 4H2O" the equation? If so, water (and H+) are needed since MnO4^-, which is being reduced, has O in it, so to balance the equation in terms of substances, H2O must be included in the reaction to account for the oxygens in MnO4^-. Also, I beli...
Tue Feb 06, 2018 11:19 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 4 cases for change in entropy
Replies: 1
Views: 82

### Re: 4 cases for change in entropy

∆G = ∆H - T∆S ∆S ∆H Reaction/Physical Change + - Spontaneous at all T + + Spontaneous at high T - - Spontaneous at low T - + Not spontaneous at any T When ∆G < 0, the reaction is spontaneous (and when ∆G > 0, the reaction is nonspontaneous). Given a positive ∆S, if the ∆H is negative, then ∆G will b...
Mon Feb 05, 2018 5:24 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Salt Bridges
Replies: 2
Views: 117

### Salt Bridges

What types of salts are typically used for a salt bridge? Are there any salts that are more effective?
Mon Jan 29, 2018 11:20 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy Definition [ENDORSED]
Replies: 2
Views: 170

### Re: Entropy Definition[ENDORSED]

You can think of entropy as energy dispersion or degeneracy.
Mon Jan 29, 2018 11:11 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Relationship between Enthalpy and Entropy [ENDORSED]
Replies: 1
Views: 120

### Re: Relationship between Enthalpy and Entropy[ENDORSED]

The negative sign in ∆S = -∆H/T is there because the ∆S is of the surroundings, while ∆H is of the system. Heat lost by the system is gained by the surroundings (and vice versa), so there needs to be a negative sign to account for that difference.
Mon Jan 29, 2018 11:02 am
Forum: Calculating Work of Expansion
Topic: Deriving Equations for Work [ENDORSED]
Replies: 2
Views: 150

### Deriving Equations for Work[ENDORSED]

Do we need to be familiar with the exact steps to derive the equations (using integrals) for work of irreversible and reversible processes as well as entropy?
Wed Jan 24, 2018 10:53 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: C(deltaT) vs mC(deltaT)
Replies: 4
Views: 395

### Re: C(deltaT) vs mC(deltaT)

C in C∆T is heat capacity, while C in mC∆T is specific heat (Cs). C = mass x Cs, so those two equations are essentially equivalent.
Wed Jan 24, 2018 10:02 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Replies: 3
Views: 209

Is the difference between adiabatic and isolated systems that adiabatic systems can have energy transferred as work while isolated systems can have no energy transfer at all?
Wed Jan 24, 2018 9:52 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Significant Figures of ∆H
Replies: 3
Views: 183

### Significant Figures of ∆H

If we are provided with ∆H values, do we assume they have an infinite amount of significant figures (i.e. are exact values)?
Wed Jan 17, 2018 1:16 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Density of Aqueous Solutions [ENDORSED]
Replies: 2
Views: 121

### Density of Aqueous Solutions[ENDORSED]

Up to what concentration can we assume that the density of aqueous solutions is the same as that of pure water? Do we assume a density of 1 g/mL for all aqueous solutions?
Wed Jan 17, 2018 1:06 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Calculating Reaction Enthalpies with Bond Enthalpies
Replies: 2
Views: 132

### Calculating Reaction Enthalpies with Bond Enthalpies

Since Dr. Lavelle said that bond enthalpies are the least accurate form of calculating reaction enthalpies, should we avoid using bond enthalpies to do our calculations on exams, or is there usually not a significant enough discrepancy in accuracy?
Wed Jan 17, 2018 1:02 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: R value in equation
Replies: 4
Views: 165

### Re: R value in equation

Usually when solving for something involving joules/work/energy, you would use 8.314 J/mol•K. If it involves pressure (or if you need to use PV=nRT), you would use the other R constants with pressure units.
Wed Jan 10, 2018 2:53 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Vibrational Energy [ENDORSED]
Replies: 1
Views: 161

### Vibrational Energy[ENDORSED]

At what temperature does vibrational energy contribute significantly?
Wed Jan 10, 2018 2:51 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Cp,m --> Cv,m
Replies: 2
Views: 385

### Cp,m --> Cv,m

Why does Cp,m = Cv,m + R?
Mon Jan 08, 2018 2:22 pm
Forum: Phase Changes & Related Calculations
Topic: Light vs. Heat [ENDORSED]
Replies: 2
Views: 163

### Light vs. Heat[ENDORSED]

If light (or some other form of energy) is released/absorbed rather than heat, would the reaction still be considered exothermic/endothermic?
Wed Dec 06, 2017 10:37 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Molecular Structure and Acid Strength
Replies: 2
Views: 133

### Re: Molecular Structure and Acid Strength

Acids tend to be stronger with higher bond polarity (when comparing acids with central atom elements in the same period) and with weaker bond strength (when comparing acids with central atom elements in the same group). Oxoacids are stronger if the central atom element is more electronegative and if...
Wed Dec 06, 2017 10:32 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: ClF3 Lewis acid/ base?
Replies: 2
Views: 544

### Re: ClF3 Lewis acid/ base?

ClF3 could act as a Lewis base because it has lone electron pairs that can be donated (definition of a Lewis base).
Wed Nov 29, 2017 11:32 am
Forum: Determining Molecular Shape (VSEPR)
Topic: T Shape or Trigonal Pyramidal
Replies: 3
Views: 203

### Re: T Shape or Trigonal Pyramidal

Trigonal pyramidal occurs when tetrahedral electronic geometry has a lone e- pair as one of its four regions of e- density. T shape occurs when a trigonal bipyramidal electronic geometry has lone e- pairs as two of its five regions of e- density or when an octahedral electronic geometry has lone e- ...
Wed Nov 29, 2017 11:25 am
Forum: Naming
Topic: 17.31 (d) (diaqua)
Replies: 1
Views: 117

### Re: 17.31 (d) (diaqua)

There isn't a particular reason that it's in parentheses (and diaqua should be before bisoxalato even though the book says otherwise).
Wed Nov 22, 2017 9:22 am
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.19 b)
Replies: 2
Views: 129

### Re: 4.19 b)

I believe it's because the formal charges are better (closer to 0) if the Sn in SnCl2 has only one lone pair and two single bonds to each Cl2. The formal charges would all be 0, vs. having 2 lone pairs of electrons and the Sn having a -2 formal charge.
Wed Nov 22, 2017 9:16 am
Forum: Photoelectric Effect
Topic: Higher Frequency and Kinetic Energy [ENDORSED]
Replies: 5
Views: 348

### Re: Higher Frequency and Kinetic Energy[ENDORSED]

Assuming that the frequency is already high enough for an electron to be ejected, higher frequency light would emit electrons with higher kinetic energy. However, for the midterm question, you can't make this assumption (and therefore the statement is not true).
Thu Nov 16, 2017 9:57 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Chapter 4 19b
Replies: 1
Views: 120

### Re: Chapter 4 19b

Beryllium actually has just 2 regions of electron density (its two bonds with the two carbons), but relative to the carbon atoms (with carbon as the central atom), the molecular shape is tetrahedral since it has 4 regions of electron density (its three bonds with the three hydrogens and one bond wit...
Wed Nov 15, 2017 10:23 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Specifying molecular geometry
Replies: 3
Views: 275

### Specifying molecular geometry

For molecular geometries that are both called the same thing but have different origins in terms of electronic geometry (e.g. bent molecular geometry can be from 3 or 4 regions of electron density, trigonal planar and tetrahedral electronic geometries respectively), do we need to specify which elect...
Wed Nov 08, 2017 11:41 am
Forum: Electronegativity
Topic: Ionic vs Covalent Based on Electronegativity Difference for LiI
Replies: 2
Views: 235

### Ionic vs Covalent Based on Electronegativity Difference for LiI

For LiI, the difference in electronegativity between Li and I is less than 2, so would it be considered polar covalent instead of ionic?
Wed Nov 08, 2017 11:35 am
Forum: Lewis Structures
Topic: H2SO2 Lewis Structure [ENDORSED]
Replies: 1
Views: 830

### H2SO2 Lewis Structure[ENDORSED]

In the Lewis Structure for hyposulfurous acid (H2SO2), why are the H atoms attached to the O atoms instead of the S atom? (both attaching the H atoms to the O atoms or the S atom can result in a formal charge of 0 for all the atoms). Hypophosphorous acid (H3PO2) has an H atom attached to the P in it...
Sun Nov 05, 2017 1:23 am
Forum: Ionic & Covalent Bonds
Topic: Is the ionic/covalent electronegativity value guideline absolute?
Replies: 2
Views: 234

### Re: Is the ionic/covalent electronegativity value guideline absolute?

The general guideline should be rough and not absolute
Thu Nov 02, 2017 12:31 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron configurations of noble gases
Replies: 1
Views: 111

### Electron configurations of noble gases

For writing out the electron configuration of noble gases (and ions that have the same electron configurations as noble gases), can we just put the shorthand (e.g. for neon, [Ne]) or do we need to write out the electron configuration from the previous noble gas (e.g. for neon [He]2s2 2p6), or are bo...
Wed Oct 25, 2017 11:18 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Helium block
Replies: 2
Views: 250

### Helium block

Would helium be considered part of the s-block since its electron configuration is 1s2 even though it's attached to the p-block elements?
Mon Oct 23, 2017 11:47 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electronic Configuration for d-block elements [ENDORSED]
Replies: 9
Views: 624

### Re: Electronic Configuration for d-block elements[ENDORSED]

Also, why are most of the 4d elements exceptions, and why is platinum an exception?
Mon Oct 23, 2017 11:16 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electronic Configuration for d-block elements [ENDORSED]
Replies: 9
Views: 624

### Re: Electronic Configuration for d-block elements[ENDORSED]

For the electron configuration exceptions in the d-block, why is tungsten not an exception (it is [Xe]4f14 5d4 6s2 instead of [Xe]4f14 5d5 6s1) while elements in the same group (chromium and molybdenum) are?
Wed Oct 18, 2017 1:06 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Heisenberg Uncertainty Equation
Replies: 7
Views: 414

### Re: Heisenberg Uncertainty Equation

Where does the 4π come from? (Why is it 4π and not some other number?)
Wed Oct 18, 2017 11:45 am
Forum: Quantum Numbers and The H-Atom
Topic: Quantum Numbers
Replies: 4
Views: 456

### Re: Quantum Numbers

Why is the ms quantum number ±1/2? (How did people decide on the number 1/2 and not some other number?)
Sun Oct 15, 2017 12:53 pm
Forum: Properties of Light
Topic: Photons
Replies: 7
Views: 358

### Re: Photons

Does a photon have a mass?
Thu Oct 12, 2017 8:39 pm
Forum: Properties of Light
Topic: Wavelengths and Frequency of Electromagnetic Radiation [ENDORSED]
Replies: 7
Views: 486

### Re: Wavelengths and Frequency of Electromagnetic Radiation[ENDORSED]

When the textbook shows the range of wavelengths that fall into each type of EMR, which category do the ones in between belong to (e.g. x-ray is 10 nm - 1 pm, gamma ray is 1 pm - 0.1 pm, is radiation of wavelength 1 pm considered an x-ray or gamma ray)?
Wed Oct 04, 2017 11:34 am
Forum: Significant Figures
Topic: Significant Figures of Conversion Factors [ENDORSED]
Replies: 3
Views: 705

### Significant Figures of Conversion Factors[ENDORSED]

For conversion factors (including molar masses provided by the periodic table e.g. 12.01 g/mol C), should we assume that they have infinite significant figures and base the number of significant figures in the answer on those of the measured values (e.g. 17.3 m)?
Wed Oct 04, 2017 11:00 am
Forum: Balancing Chemical Reactions
Topic: Combustion Reaction Water Phase
Replies: 2
Views: 305

### Combustion Reaction Water Phase

During a combustion reaction of an organic compound, is water vapor usually produced, or are there situations in which liquid water is produced instead?