Search found 51 matches

by Justin Lau 1D
Tue Mar 13, 2018 11:01 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: UV catalyst
Replies: 3
Views: 139

Re: UV catalyst

UV light isn't a catalyst but something that provides energy to activate the reaction. NO is the catalyst in this reaction.
by Justin Lau 1D
Tue Mar 13, 2018 11:00 pm
Forum: Balancing Redox Reactions
Topic: Water, oxygen, etc.
Replies: 1
Views: 83

Re: Water, oxygen, etc.

Water, H+ and OH- are only included in the half reactions when the half reactions occur in an acidic or basic solution, or if the reaction itself such as the electrolysis of water involves these factors.
by Justin Lau 1D
Tue Mar 13, 2018 10:58 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Arrhenius when Temperature Changes
Replies: 3
Views: 137

Re: Arrhenius when Temperature Changes

No, it shouldn't matter which temperature/rate constant pair you use for k1/T1 and k2/T2 as long as you make sure you use the right one in the equation.
by Justin Lau 1D
Mon Mar 12, 2018 11:15 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.67
Replies: 3
Views: 224

Re: 8.67

The enthalpy off vaporization must be subtracted because you're looking for the liquid state. We know that all bond enthalpies are given in the gas state. So we need to account for the extra enthalpy gained during phase change.
by Justin Lau 1D
Mon Mar 12, 2018 11:11 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: What is A?
Replies: 4
Views: 144

Re: What is A?

So is there some way to observe the value of A? Like could we measuremit without measuring anything else?
by Justin Lau 1D
Mon Mar 12, 2018 11:08 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Slow reaction
Replies: 2
Views: 148

Re: Slow reaction

I think it's because there's an equilibrium for the first step due to the bottleneck effect, the two rates are equal. Also, O is an intermediate in this reaction so I think they're comparing that to eliminate the intermediate.
by Justin Lau 1D
Sat Mar 03, 2018 8:13 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: different ways of calculating K
Replies: 2
Views: 105

Re: different ways of calculating K

K is normally found by experimentally adjusting the concentrations of the reactants and finding the rate. Once these values are determined, k can be found by rearranging the appropriate equation (based on reactant order).
by Justin Lau 1D
Sat Mar 03, 2018 8:08 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: different ways of calculating K
Replies: 2
Views: 105

Re: different ways of calculating K

K is equal to the concentration of the products over the concentrations of reactants.
by Justin Lau 1D
Wed Feb 28, 2018 10:46 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: Homework Problem 15.99
Replies: 1
Views: 103

Re: Homework Problem 15.99

The rate constant k can be found by the Arrhenius equation k=Ae^(EA/RT). Thus, we see that it shouldn't be a linear graph but exponential.
by Justin Lau 1D
Wed Feb 28, 2018 10:41 am
Forum: First Order Reactions
Topic: After Integration [ENDORSED]
Replies: 3
Views: 142

Re: After Integration [ENDORSED]

The k is negative here because it is left over from the unique average rate law equation, which says Rate=-(1/a) x d[A]/dt. Therefore, when you rearrange the equation to integrate, you get -kt on the right. Because the negative denotes a -1 basically, it is a constant and remains. For the second ord...
by Justin Lau 1D
Wed Feb 21, 2018 10:37 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.15 A cell diagram set-up [ENDORSED]
Replies: 2
Views: 126

Re: 14.15 A cell diagram set-up [ENDORSED]

Solid Ag is acting as the electrode for the anode so it must be on the outside.
by Justin Lau 1D
Wed Feb 21, 2018 10:34 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: homework question
Replies: 1
Views: 120

Re: homework question

The sign of Gibbs free energy changes to negative because the reverse reaction is happening. The values of the given Gibbs for Tl 3+ is Tl becoming Tl 3+. The question is asking for the standard potential of Tl 3+ to Tl, so it needs to be flipped.
by Justin Lau 1D
Wed Feb 21, 2018 10:25 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.37 C
Replies: 2
Views: 111

Re: 14.37 C

Basically, the question has an unfavorable cell diagram. The answer is a negative voltage, which tells you that the Cl2 "anode" is actually the cathode; that is, the electrons would flow from right to left in this cell.
by Justin Lau 1D
Fri Feb 16, 2018 11:11 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.15 KOH
Replies: 2
Views: 116

14.15 KOH

In 14.15c, why is it specifically KOH that must be used in the cell diagram? What's wrong with NaOH or any other strong base?
by Justin Lau 1D
Fri Feb 16, 2018 11:09 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Water in cell diagram
Replies: 3
Views: 121

Water in cell diagram

Why is water not included in the cell diagrams even when it are involved in the half reactions?
by Justin Lau 1D
Fri Feb 16, 2018 11:08 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell diagram acidic/basic
Replies: 3
Views: 107

Cell diagram acidic/basic

Is it necessary to write H+ or OH- for the cell diagram if the solution is acidic/basic and they are in the half reactions?
by Justin Lau 1D
Sat Feb 10, 2018 9:34 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.49 STP vs. SATP
Replies: 2
Views: 131

Re: 8.49 STP vs. SATP

Basically all problems in this section are assumed to be 298 K unless stated otherwise. I know that STP is 273 K but I guess that only applies for gas laws and the like.
by Justin Lau 1D
Thu Feb 08, 2018 3:38 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Clausius inequality
Replies: 1
Views: 77

Re: Clausius inequality

I wouldn't worry about this as Dr. Lavelle never covered this in class, so it won't be on the midterm.
by Justin Lau 1D
Thu Feb 08, 2018 3:33 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: Boltzmann's Equation
Replies: 1
Views: 95

Re: Boltzmann's Equation

This approach is usually used for a specific molecule or number of molecules. The Boltzmann equation only works for molecules at or near 0 kelvins. Usually if a problem like this shows up they will either give you the number of possible states the molecule can have or give you a way to figure it out...
by Justin Lau 1D
Wed Jan 31, 2018 9:22 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Change in S with changes in P, V, and T
Replies: 3
Views: 139

Change in S with changes in P, V, and T

What specific heat capacity is to be used for an ideal gas when there are changes in P, V, and T as pressure and volume are both not constant? Is it even possible for all three to be changed together?
by Justin Lau 1D
Mon Jan 29, 2018 7:32 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Pressure and Volume on Spontaneity
Replies: 2
Views: 123

Pressure and Volume on Spontaneity

Does pressure and/or volume affect the spontaneity of a reaction? Is it because entropy is changing when these factors change?
by Justin Lau 1D
Mon Jan 29, 2018 7:21 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Thermodynamics 1st 2nd 3rd Law
Replies: 2
Views: 182

Re: Thermodynamics 1st 2nd 3rd Law

The first law just says that the internal energy of an isolated system doesn't change i.e. energy is conserved. The second law states that the entropy increases in an isolated system for any spontaneous process. Finally, the third law says that as the temperature approaches 0 Kelvins, the entropy of...
by Justin Lau 1D
Thu Jan 25, 2018 10:17 pm
Forum: Calculating Work of Expansion
Topic: Expanding VS Compressing
Replies: 2
Views: 106

Re: Expanding VS Compressing

Well if it's not expanding against a vacuum it would be doing work. Whether delta U is positive or negative also depends on the heat, however. But if you are solely analyzing work, i.e. isothermal expansion where temperature is constant, it would be negative as it is doing work on another system.
by Justin Lau 1D
Wed Jan 24, 2018 9:57 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Significant Figures of ∆H
Replies: 3
Views: 151

Re: Significant Figures of ∆H

Yeah, they probably do because they are confirmed experimental values.
by Justin Lau 1D
Wed Jan 24, 2018 9:56 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Boltzmann's Equation in relation to temperature
Replies: 4
Views: 138

Boltzmann's Equation in relation to temperature

Does Boltzmann's equation account for entropy increase/decrease due to temperature? The only factor it has is microstates, so does that mean a molecule has the same entropy value a two different temperatures?
by Justin Lau 1D
Wed Jan 17, 2018 1:19 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Density of Aqueous Solutions [ENDORSED]
Replies: 2
Views: 106

Re: Density of Aqueous Solutions [ENDORSED]

I think the textbook says "dilute solutions" can basically have values equated with pure water but for the most part I believe most of the solutions they give us are going to be along those lines anyway.
by Justin Lau 1D
Wed Jan 17, 2018 1:01 am
Forum: Calculating Work of Expansion
Topic: 8.93 [ENDORSED]
Replies: 1
Views: 92

8.93 [ENDORSED]

In problem 8.93, why is the water produced from the combustion in part a in liquid form and not gaseous form? Is it because the reaction is occurring at 25 degrees Celsius?
by Justin Lau 1D
Wed Jan 17, 2018 12:57 am
Forum: Calculating Work of Expansion
Topic: 8.27
Replies: 1
Views: 82

Re: 8.27

Yeah you need the ln to get the correct answer. It's a typo in the answer key cuz the later part with real numbers has ln in it. Also yeah V2 is final answer V1 is initial.
by Justin Lau 1D
Wed Jan 10, 2018 2:59 pm
Forum: Phase Changes & Related Calculations
Topic: Energy and Phase Changes
Replies: 5
Views: 234

Re: Energy and Phase Changes

The hydrogen bonds that in water are probably what requires such a large enthalpy of vaporization. Going from ice to liquid water only requires a breaking of the lattice structure. However, liquid To gas needs energy to break the hydrogen bonds entirely and separate the molecules, as the liquid form...
by Justin Lau 1D
Wed Jan 10, 2018 2:52 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat capacity of calorimeters
Replies: 1
Views: 113

Heat capacity of calorimeters

Does the heat capacity of the calorimeter always include the water that is inside (if applicable) or do we have to account for this separately?
by Justin Lau 1D
Mon Jan 08, 2018 2:24 pm
Forum: Phase Changes & Related Calculations
Topic: Light vs. Heat [ENDORSED]
Replies: 2
Views: 155

Re: Light vs. Heat [ENDORSED]

Usually there is heat involved when light is a product of the reaction, so for most purposes I think you can assume this.
by Justin Lau 1D
Thu Dec 07, 2017 2:13 pm
Forum: Bronsted Acids & Bases
Topic: Protons/ H+
Replies: 1
Views: 88

Re: Protons/ H+

You can't have a proton that isn't H+. H+ is usually a single proton; you're not really going to see deuterium or tritium in a normal reaction.
by Justin Lau 1D
Thu Dec 07, 2017 2:11 pm
Forum: Bronsted Acids & Bases
Topic: Electronegativity vs Bond length
Replies: 1
Views: 123

Re: Electronegativity vs Bond length

When you are looking at elements in the same period, electronegativity is the primary factor in determining acid strength. However, when you're looking at elements in a group, it's the bond length.
by Justin Lau 1D
Wed Nov 29, 2017 11:36 am
Forum: Dipole Moments
Topic: Dipole moments and Formal Charges
Replies: 2
Views: 211

Re: Dipole moments and Formal Charges

No, I think looking at the structure is enough to determine polarity. I don't believe formal charge is used to find partial charges; formal charge is to determine stability of the Lewis structure.
by Justin Lau 1D
Wed Nov 29, 2017 11:31 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Unit conversions
Replies: 1
Views: 108

Unit conversions

For the units in chemical equilibrium calculation: if we are given the molecule in mmol is it ok to keep it as that or should we convert it to mol? Also, if we are given pressure in bars or atm, does it matter which pressure unit we use?
by Justin Lau 1D
Sat Nov 25, 2017 9:51 pm
Forum: Hybridization
Topic: 4.43 - "s-character"
Replies: 1
Views: 115

Re: 4.43 - "s-character"

What I took it to mean was that there were less p orbitals hybridized with the s orbital, so the s orbital "retains more character" in the hybridization. Basically, I guess there's more of the fractional s orbital per hybridized orbital. The reason that the bond angles increase as there's ...
by Justin Lau 1D
Sat Nov 25, 2017 9:46 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Confused about bond angles
Replies: 1
Views: 115

Re: Confused about bond angles

Seems correct to me, except I don't think there's a need to put <120 for the T shape VSEPR because it's basically missing most of the equatorial atoms.
by Justin Lau 1D
Thu Nov 16, 2017 3:30 pm
Forum: Hybridization
Topic: Pi bonds
Replies: 4
Views: 211

Re: Pi bonds

Actually overlapping bonds usually refers to sigma bonds. Pi bonds are really orbitals that are side by side.
by Justin Lau 1D
Wed Nov 15, 2017 4:27 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Maximum number of ligands
Replies: 3
Views: 185

Maximum number of ligands

Are six ligands the maximum amount of ligands that can be attached to any cation for coordination compounds? Could this number possibly be exceeded if, say, there was a stronger cation charge or more d orbital electrons?
by Justin Lau 1D
Mon Nov 13, 2017 11:50 am
Forum: Hybridization
Topic: Electron spin in hybridization [ENDORSED]
Replies: 1
Views: 148

Electron spin in hybridization [ENDORSED]

In hybridization, is it possible for the electron to change spin? For example, when the carbon orbitals are hybridized to sp3, the electrons are all drawn with parallel spin. However, based on the Pauli exclusion principle, one electron must have had an opposite spin in the 2s orbital to fill it. Ho...
by Justin Lau 1D
Wed Nov 08, 2017 11:42 am
Forum: Electronegativity
Topic: Ionic vs Covalent Based on Electronegativity Difference for LiI
Replies: 2
Views: 205

Re: Ionic vs Covalent Based on Electronegativity Difference for LiI

Yeah it would be very polar covalent, not ionic. However, LiI should still dissociate into ions in solution.
by Justin Lau 1D
Sun Nov 05, 2017 1:17 am
Forum: Ionic & Covalent Bonds
Topic: Is the ionic/covalent electronegativity value guideline absolute?
Replies: 2
Views: 197

Is the ionic/covalent electronegativity value guideline absolute?

Is it possible for an ionic bond to be within the covalent range for the difference in electronegativities and vice versa? For example, MgI2 has an electronegativity difference of 1.35, so does that mean this is a covalent bond because a difference <1.5 is supposed to be covalent? Magnesium generall...
by Justin Lau 1D
Sun Nov 05, 2017 1:07 am
Forum: Lewis Structures
Topic: Bonds
Replies: 1
Views: 103

Re: Bonds

There's actually a report published that shows the possibility of quadruple bonds in molecules like C2, but I don't think it's important to know for this class because it seems kind of rare. Apparently it's also possible in transition metals around the lanthanoid/actinoid series. http://metallome.bl...
by Justin Lau 1D
Wed Oct 25, 2017 10:59 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: P-orbital electrons [ENDORSED]
Replies: 1
Views: 1798

P-orbital electrons [ENDORSED]

Do p-orbital electrons move between lobes? Say that if there is one unpaired electron in the px orbital, does it have the ability to move between the two lobes of the px orbital freely? If so, how does it get past the nodal plane of the nucleus?
by Justin Lau 1D
Mon Oct 23, 2017 11:14 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron orbital filling order [ENDORSED]
Replies: 1
Views: 144

Electron orbital filling order [ENDORSED]

When an electron fills a p orbital, does it always fill the px orbital first? Since the p orbitals are all at the same energy, could the electrons fill any of the other two orbitals (py and pz) first? Does this also apply to d and f orbitals if this is true?
by Justin Lau 1D
Sun Oct 22, 2017 6:32 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: post-module question #22
Replies: 2
Views: 175

Re: post-module question #22

Basically the kinetic energy value is per electron; in fact, all calculations for this chapter are all specifically for one molecule i.e. per electron, per photon, etc. Because the value is for a single electron in this case, the answer is technically J/electron. To get the value for an entire mole ...
by Justin Lau 1D
Fri Oct 20, 2017 11:43 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Configuration Notation [ENDORSED]
Replies: 5
Views: 233

Configuration Notation [ENDORSED]

For electron configurations of atoms with p and d orbitals, is it necessary to specify the orbital type in the configuration e.g. 2px1 2py1 or is it acceptable to put them all together e.g. 2p2?
by Justin Lau 1D
Sun Oct 15, 2017 4:18 pm
Forum: Properties of Light
Topic: Formulas [ENDORSED]
Replies: 5
Views: 256

Re: Formulas [ENDORSED]

Basically the Rydberg Formula, v=R(1/n1^2 - 1/n2^2) is derived from the previous energy formula, E=-hR/n^2. As we know, E=hv. Thus, when we subtract the formulas of energy using the energy level, E=-hR/n1^2 - (-hR/n2^2), we can plug hv to substitute for E. Then, because Planck's constant cancels out...
by Justin Lau 1D
Fri Oct 13, 2017 11:18 am
Forum: Photoelectric Effect
Topic: What is the extent of elements for the photoelectric effect?
Replies: 2
Views: 153

What is the extent of elements for the photoelectric effect?

It seems like generally the photoelectric effect is described to apply to metals, and mostly transition metals like copper to be precise. However, does it also occur with more volatile metals like sodium or magnesium? How about metalloids and solid nonmetals?
by Justin Lau 1D
Sun Oct 08, 2017 3:39 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Atomic Spectra Post-Module Assessment Q. 42
Replies: 1
Views: 157

Re: Atomic Spectra Post-Module Assessment Q. 42

Use Rydberg's equation, which is v=R(1/n1^2 - 1/n2^2). n1 (also known as n final) is 4,so the answer should come out to be B, 6.
by Justin Lau 1D
Sun Oct 08, 2017 3:05 pm
Forum: Molarity, Solutions, Dilutions
Topic: Is density necessary?
Replies: 1
Views: 174

Is density necessary?

I realized that in some problems they give a few different solutes with masses and it specifically says a specific volume of water (e.g. 30 g NaCl and 50 g NaBr in 800 mL water to make a solution). However, the final solution volume isn't given. Therefore, as there is no density given for the solute...

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