## Search found 65 matches

Fri Mar 15, 2019 9:29 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: vertical line in cell diagram
Replies: 4
Views: 195

### vertical line in cell diagram

In class we talked about that when two solid are in the same half cell, we use a vertical line to separate them in the cell diagram. Do we do the same thing if they are two pure liquid species?
Thu Mar 14, 2019 9:20 pm
Forum: General Rate Laws
Topic: Rate of Formation vs Unique Rate
Replies: 4
Views: 156

### Re: Rate of Formation vs Unique Rate

I believe they are not the same. Rate of formation depends on the coefficient of the products, but unique rate does not.
Wed Mar 13, 2019 4:28 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Log vs ln
Replies: 2
Views: 125

### Re: Log vs ln

log is log base 10, and Ln is log base e. You can use this for conversion though I do not think there will be a problem asking for converting between these two.
Wed Mar 13, 2019 4:27 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: ion-selective electrodes
Replies: 1
Views: 95

### ion-selective electrodes

For the final, how much do we need to know about ion-selective electrodes such as pH meter?
Wed Mar 13, 2019 4:25 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Concentration cell product
Replies: 1
Views: 121

### Re: Concentration cell product

In a concentration cell, the half cell with higher concentration initially will be the cathode side and the one with lower initial concentration will be the anode side. As the reaction proceed, electrons transfer from the anode side to the cathode side, lowering the substance concentration in the ca...
Sat Mar 09, 2019 3:58 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 7th edition 6O.3
Replies: 1
Views: 113

### Re: 7th edition 6O.3

Under the title "Topic 6O Exercises", it says that for the following questions use E=-0.42 for the reduction of water. I just compared the reduction potential of the ions with that of the water, and the species with higher reduction potential will be reduced.
Sat Mar 09, 2019 3:50 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Determining the order of the reaction
Replies: 2
Views: 178

### Re: Determining the order of the reaction

Another ways will involve a table listing initial reactant concentration and reaction rate. Order of a reaction can also be determined when knowing the mechanism of the reaction and the slowest step in the reaction.
Sat Mar 09, 2019 3:48 pm
Forum: First Order Reactions
Topic: Formula 15.23
Replies: 2
Views: 134

### Re: Formula 15.23

I believe it is not come from a formula. I do not have the sixth edition, but it looks like that the question is asking the concentration A at the time when B is 0.034M. The part after the minus sign is to find how much A has been used to give rise to 0.034M B, and subtract that from 0.153M A(which ...
Wed Mar 06, 2019 9:46 pm
Forum: Zero Order Reactions
Topic: zero order rate?
Replies: 14
Views: 872

### Re: zero order rate?

It is correct. Zero order reaction usually involves a catalyst or enzyme that works at its maximum potential. Increasing concentration cannot increase the rate the catalyst or enzyme works, and therefore zero order reactions do not depend on the concentration.
Wed Mar 06, 2019 9:43 pm
Forum: Zero Order Reactions
Topic: Slope = -k
Replies: 3
Views: 187

### Re: Slope = -k

I believe it is because of the integrated rate laws derived (specific sign because of the math).
Wed Mar 06, 2019 7:58 pm
Forum: Second Order Reactions
Topic: deriving the integrated rate laws
Replies: 2
Views: 149

### deriving the integrated rate laws

Are we expected to know how to derive the integrated rate laws for the final? Or are we just need to know how to use them?
Sun Feb 24, 2019 9:52 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: inert conductor besides Pt
Replies: 3
Views: 150

### inert conductor besides Pt

Can someone remind me what is the other inert conductor Dr. Lavelle mentioned in class besides Pt?
Sat Feb 23, 2019 9:29 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Line versus Comma
Replies: 2
Views: 77

### Re: Line versus Comma

A line indicates that the substance are in different phases (e.g. Cu(s)|Cu2+(aq)), and comma representing two substances in same phase (e.g. Fe3+(aq)|Fe2+(aq)).
Sat Feb 23, 2019 9:27 pm
Forum: Balancing Redox Reactions
Topic: 7th Edit 6L5 c
Replies: 1
Views: 81

### Re: 7th Edit 6L5 c

Consider HCl to be H+ and Cl-. The anode side will be H2 and H+, and the cathode side will be CL2 and CL-.
Sat Feb 23, 2019 3:30 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: inert conductor in cell diagrams
Replies: 3
Views: 128

### inert conductor in cell diagrams

When writing the cell diagram for a reaction, when do we need to add inert conductor (such as Pt)?
Mon Feb 18, 2019 4:31 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 7th edition 4I. 5
Replies: 3
Views: 193

### Re: 7th edition 4I. 5

The delta S refers specifically to the hot water and the cold water, and delta S total is the sum of delta S for the cold water and the hot.
Mon Feb 18, 2019 4:29 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Delta G vs. Delta G (degree sign)
Replies: 4
Views: 401

### Re: Delta G vs. Delta G (degree sign)

I think you are right. Delta G depends on specific conditions the reaction is in, but standard delta G is just under standard conditions, which means that standatd delta G will be constant for a reaction.
Mon Feb 18, 2019 4:26 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Replies: 35
Views: 1289

Last semester with chem 14A the midterm was given back one week after it was taken.
Sun Feb 10, 2019 8:05 pm
Forum: Calculating Work of Expansion
Topic: Work sign convention
Replies: 3
Views: 175

### Work sign convention

Can someone explain if work is done on a system, do we use the positive or negative sign? What about for work done by a system?
Sat Feb 09, 2019 3:19 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: How to Calculate Degeneracy
Replies: 5
Views: 176

### Re: How to Calculate Degeneracy

I do not think there is a formula that always works for degeneracy. But it can be calculated using simple math. For example, if there are three particles and each can be in one of the two directions, then the degeneracy is 2^3=8.
Sat Feb 09, 2019 3:17 pm
Forum: Calculating Work of Expansion
Topic: Reversible vs Irreversible
Replies: 10
Views: 428

### Re: Reversible vs Irreversible

It depends on the conditions that the problem gives. For example, if the question states that there is infinitesimal changes, use the reversible equation. When the change is too large(cannot by reversed by an infinitesimal change), then use the irreversible equation.
Sat Feb 09, 2019 3:13 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: delta H
Replies: 3
Views: 177

### Re: delta H

I believe that means the delta H is measured in standard conditions.
Sat Feb 02, 2019 2:08 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Forms of U Equations
Replies: 3
Views: 163

### Re: Forms of U Equations

Athena L 1B wrote:If we have the equations U = q + w, q = H, and w = PV, why does U = H - PV, instead of U = H + PV?

Actually w=-PdeltaV(the negative charge refers to the direction that energy acts on), and this is why we get U = H - PV.
Sat Feb 02, 2019 1:45 pm
Forum: Calculating Work of Expansion
Topic: SI unit for P
Replies: 6
Views: 265

### SI unit for P

Can anyone tell me what is the SI unit we use for pressure? Is it atm or pa?
Sat Feb 02, 2019 10:15 am
Forum: Phase Changes & Related Calculations
Topic: PΔV for solids and liquids
Replies: 5
Views: 189

### Re: PΔV for solids and liquids

I think what Dr. Lavelle meant is that the equation can also be applied to liquids and solids, but the change is too small that we typically do not consider them.
Sat Jan 26, 2019 7:05 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: energy production
Replies: 4
Views: 243

### Re: energy production

Cellular respiration breaks down the energy contained by glucose and stores the energy in the form of ATP. The heart uses ATP but not the energy from breaking glucose bond directly.
Sat Jan 26, 2019 4:28 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bonds being broken in reaction
Replies: 4
Views: 139

### Re: Bonds being broken in reaction

During a chemical reaction, if a bond is broken, it must be broken completely so that new bonds can form. Also, different bonds have different strength and thus nees different amount of energy to break.
Mon Jan 21, 2019 4:07 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 7th edition 6D.15(b)
Replies: 1
Views: 107

### 7th edition 6D.15(b)

This question ask for the pH of 0.055M AlCl3(aq). Could anyone explain how we calculate the pH of a solution with highly charged metals?
Wed Jan 16, 2019 9:42 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: pH
Replies: 5
Views: 176

### Re: pH

The pH of a number is the negative log of that number. For example, pH(10^-1)=-log(10^-1)=1
Wed Jan 16, 2019 9:40 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Acid & Bases
Replies: 1
Views: 60

### Re: Acid & Bases

The bronsted definition of acid is any species that can donate a proton, and a base is any species that can receive a proton. The conjugate acid of a base is a base gaining a proton(for example, the conjugate acid of NH3 is NH4+), and the conjugate base of an acid is an acid losing a proton (for exa...
Wed Jan 16, 2019 9:34 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Le Chatelier's Principle- example from class
Replies: 3
Views: 173

### Re: Le Chatelier's Principle- example from class

Le Chatelier's principle is that after a change occurs, the reaction shifts to minimize the change. In the above equation, increasing [N2] would cause the reaction to shift right(forming more products), increasing [NH3] and decreasing [H2] will both cause the reaction to shift left (more reactants w...
Sat Jan 12, 2019 6:04 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kc and Kp
Replies: 12
Views: 437

### Re: Kc and Kp

Ana Pedreros wrote:If asked for the K expression, can Kc and Kp be used interchangeably?

I think the question will state clearly whether Kc or Kp is asked. If not, it will depend on the states of the substance involved in the reaction or the condition in the question.
Sat Jan 12, 2019 5:57 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE Table
Replies: 6
Views: 327

### Re: ICE Table

Basically, yes; whenever you set up the ICE table, you start by assuming that the reaction hasn't taken place yet. Therefore, there won't be any products formed yet, so their initial concentrations are 0. So if we assume that the reaction hasn't happened yet, is that why for anything that has an in...
Sat Jan 12, 2019 5:52 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: "Shifting"
Replies: 15
Views: 1105

### Re: "Shifting"

Consider "sitting" as describing which side (reactants or products) the reaction favors, and "shifting" only when referring to a change.
Thu Dec 06, 2018 7:04 pm
Forum: Naming
Topic: naming the ligands
Replies: 1
Views: 111

### naming the ligands

When asked to name the ligands of a coordination compound, do we name them as charged or uncharged?
Thu Dec 06, 2018 1:48 pm
Forum: Amphoteric Compounds
Topic: Amphoteric vs Amphiprotic
Replies: 4
Views: 300

### Re: Amphoteric vs Amphiprotic

An amphoteric substance is one that can act both as a base and as an acid. An amphiprotic substance is one that can both accept H+ and donate H+. Amphiprotic substance is a part of amphoteric substance. For example, if a molecule act as both lewis acid and lewis base but do not donate or accept prot...
Thu Dec 06, 2018 1:42 pm
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Problem 6C.17
Replies: 1
Views: 89

### Re: Problem 6C.17

There are two rules to decide the relative strength of two acids: 1. strong acids can lose proton(s) easily: if a acid has a long and weak A-H bond, then it can lose the proton more easily, and therefore making it a stronger acid. 2. strong acids has anions that are stable: 1) typically, if the anio...
Wed Dec 05, 2018 3:49 pm
Forum: Bronsted Acids & Bases
Topic: acetic acid vs formic acid
Replies: 2
Views: 182

### acetic acid vs formic acid

Can someone explain why formic acid(CH2O2) is considered stronger than acetic acid(CH3COOH)?
Fri Nov 30, 2018 9:36 pm
Forum: Naming
Topic: Ligand names on Final
Replies: 2
Views: 141

### Ligand names on Final

For our final exam, will we be given a ligand name chart like the one on the class website or are we expected to memorize all of them?
Fri Nov 30, 2018 9:45 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Polydentates
Replies: 3
Views: 259

### Re: Polydentates

Oxalate is a bidentate because the arrangement of its atoms only allows two oxygen to bind to a given metal at a given time.
Fri Nov 30, 2018 9:38 am
Forum: Naming
Topic: Naming complexes and coordination compounds
Replies: 4
Views: 190

### Re: Naming complexes and coordination compounds

We use bis, tris, tetakis, or pentakis as prefix if the ligand's name starts with di, tri, tetra, or penta.
Sun Nov 25, 2018 12:08 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Shapes Not covered in Lecture
Replies: 10
Views: 493

### Shapes Not covered in Lecture

For test 3 and the final, do we need to know the VSEPR shapes that are not covered in lectures(like T-shaped)?
Sun Nov 25, 2018 9:47 am
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Pi Bonds
Replies: 1
Views: 161

### Re: Pi Bonds

Imagine 2 p orbitals side by side to each other, there are two regions of overlapping for each pi bond. If you hold one of the orbitals unmoved and try to rotate the other, at least one of the overlapping regions will no longer exist. Therefore, when you try to rotate a pi bond, it breaks.
Sun Nov 25, 2018 9:43 am
Forum: Hybridization
Topic: d orbital
Replies: 2
Views: 164

### Re: d orbital

You include d when the regions of electron density is higher than or equal to five.
2 regions of electron density=sp
3 regions of electron density=sp2
4 regions of electron density=sp3
5 regions of electron density=sp3d
6 regions of electron density=sp3d2
...
Sun Nov 18, 2018 2:28 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: Homework Question: 3F.13
Replies: 1
Views: 138

### Re: Homework Question: 3F.13

Cl and H have a large electronegativity difference; therefore, when Cl is positioned facing H, there will be an attractive force between them. If there are more Cl on one atom and H on another atom facing closely to each other, the intermolecular force will be stronger.
Sun Nov 18, 2018 2:20 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 4 regions of electron density
Replies: 3
Views: 173

### Re: 4 regions of electron density

When there are four regions of electron density, the regions are tetrahedrally arranged. Just think about the model Dr. Lavelle used in class, when replacing a bonded atom with a lone pair, we are basically "taking off a yellow ball". There are no two balls that are arranged exactly opposi...
Sun Nov 18, 2018 2:12 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Shape and Polarity? [ENDORSED]
Replies: 4
Views: 227

### Re: Shape and Polarity?[ENDORSED]

If a molecule has no dipole moments, it is nonpolar; if it has dipole moments but the dipole moments that cancel out, it is also nonpolar(for example, the two C-O bonds in CO2 are polar, but they are arrange exactly opposite to each other, so the dipole moments cancel out); if the molecule has dipol...
Fri Nov 09, 2018 12:34 pm
Forum: Ionic & Covalent Bonds
Topic: Polarizability
Replies: 9
Views: 415

### Re: Polarizability

Polarizing power is the ability of a cation to distort an anion(like to which extent an atom can affect another atom), while polarizability is the ability to form instantaneous dipoles(How much the atom itself can be affected).
Fri Nov 09, 2018 12:19 pm
Forum: Dipole Moments
Topic: Classification of Van der Waals
Replies: 2
Views: 119

### Re: Classification of Van der Waals

It means all molecules have Van der Waals forces and the forces are always attractive.
Fri Nov 09, 2018 12:14 pm
Forum: Electronegativity
Topic: Trend Exceptions
Replies: 5
Views: 294

### Re: Trend Exceptions

I believe for atomic radius, the element going up and down matters more because when you go down a group, there are additional shells added. For ionization energy and electron affinity, there are less obvious trends.
Fri Nov 02, 2018 10:20 am
Forum: Resonance Structures
Replies: 5
Views: 257

I believe usually it is the intake of energy that breaks a more stable molecule into parts and cause radicals to form. For example, Dr. Lavelle talked about the energy of photon can cause H2O to separate into H and OH in upper atomsphere while OH is a radical.
Fri Nov 02, 2018 10:13 am
Forum: Resonance Structures
Topic: Tricks for Resonance Structures
Replies: 5
Views: 406

### Re: Tricks for Resonance Structures

I think you need to draw the Lewis structures out to see how many resonance there are for a compound. And for your second question, usually we only choose the best representation(the one with most atoms having formal charge 0 and with the most electronegative atoms having the negative formal charges...
Fri Nov 02, 2018 10:01 am
Forum: Ionic & Covalent Bonds
Topic: Covalent Bonds
Replies: 16
Views: 633

### Re: Covalent Bonds

Usually two non-metals bond to form a covalent bond, while a metal and a non-metal bond to form an ionic bond.
Sat Oct 27, 2018 12:31 pm
Forum: Quantum Numbers and The H-Atom
Topic: Orbitals
Replies: 4
Views: 215

### Re: Orbitals

I believe usually "shell" is referred to n, "subshell" to l, and "orbital" to ml.
Sat Oct 27, 2018 12:28 pm
Forum: Quantum Numbers and The H-Atom
Topic: Quantum Numbers
Replies: 5
Views: 230

### Re: Quantum Numbers

If you mean the magnetic spin quantum number, +1/2 is for the anti-clockwise rotation and -1/2 is for the clockwise rotation.
Sat Oct 27, 2018 12:14 pm
Forum: Trends in The Periodic Table
Topic: Electron Affinity
Replies: 8
Views: 234

### Re: Electron Affinity

I believe in the case of lithium and beryllium, lithium has only one electron in its 2s orbital but beryllium has two, which means the 2s orbital of beryllium is already full. Therefore, beryllium is like the noble gases in some way, when you add additional electron to its already full shell, it req...
Fri Oct 19, 2018 10:28 am
Forum: DeBroglie Equation
Topic: De Broglie equation
Replies: 3
Views: 211

### De Broglie equation

Can someone explain how De Broglie equation is derived? I have on my notebook that energy is equal to momentum times velocity but I really do not understand this and could not go on.
Fri Oct 19, 2018 10:12 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: H bar
Replies: 5
Views: 230

### Re: H bar

I do not think h bar will be given as a constant during the test, but the equation of delta x * delta p >=h/4pi will probably on the equation sheet. So don't worry about h bar(unless you really like to use it and if so just remember h bar equals to h/2pi).
Fri Oct 19, 2018 10:02 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: 7th Edition, 1B.27
Replies: 3
Views: 124

### Re: 7th Edition, 1B.27

I believe it applies to the uncertainty in position. My TA said if we are given a question about an atom or a sphere, we need to pay attention to whether the given value is radius or diameter, and we need to use the diameter value for delta X.
Fri Oct 12, 2018 9:38 am
Forum: Photoelectric Effect
Topic: electron with no KE in reality
Replies: 2
Views: 159

### electron with no KE in reality

I understand how electrons behave in experiments when energy of the incoming light equals to its threshold energy, but can someone explain what it is like in reality when the ejected electron has no kinetic energy?
Fri Oct 12, 2018 9:29 am
Forum: Einstein Equation
Topic: 7th 1B.15 When do you use E = hv or Ek = 1/2m v^2?
Replies: 4
Views: 421

### Re: 7th 1B.15 When do you use E = hv or Ek = 1/2m v^2?

In other words, use E=hv when finding the energy of a photon(the inputing energy), and Ek=1/2mv^2 as the energy of the ejected electron(energy left), which is the energy of the photon minus the threshold energy of the electron.
Fri Oct 12, 2018 9:04 am
Forum: Properties of Light
Topic: How light behaves
Replies: 8
Views: 337

### Re: How light behaves

"I cannot conceptualize light being both photon (PACKETS) of energy and wavelengths. I find it difficult to exercise this into equations when I do not understand how it can be both and have one number. Please explain and possibly use equations in your explanation if possible. If not that is ok...
Thu Oct 04, 2018 8:56 am
Forum: Balancing Chemical Reactions
Topic: Why didn't we take into account charges
Replies: 4
Views: 271

### Re: Why didn't we take into account charges

Don't worry about charges so much for now because we are not balancing ions but mostly molecules. Pay more attention to the charges and electrons when doing problems with redox reactions later.
Thu Oct 04, 2018 8:38 am
Forum: Empirical & Molecular Formulas
Topic: Definition of Empirical Formula
Replies: 8
Views: 312

### Re: Definition of Empirical Formula

I believe empirical formula does not directly refer to the mass percent composition of a molecule because mass percent composition is based on the mass of each type of atom over the total mass(and different atoms have different masses) while the empirical formula is more about the relative ratio of ...
Thu Oct 04, 2018 8:30 am
Forum: Significant Figures
Topic: M11 Sig Figs
Replies: 4
Views: 230

### Re: M11 Sig Figs

I believe it's better to use 3 sig figs for your answer in part C even though the answer in the book only gives 2 sig figs because all numbers given in the question have 3 sig figs.