## Search found 62 matches

Wed Mar 13, 2019 11:28 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Does reaction rate mean average reaction rate?
Replies: 3
Views: 188

### Re: Does reaction rate mean average reaction rate?

Unless the problem specifies that it is average rate, in general, rate is instantaneous.
Wed Mar 13, 2019 11:27 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: rate of disappearance
Replies: 3
Views: 126

### Re: rate of disappearance

It would be in terms of the compound that is being consumed. For example,

A —> B + C
R = k[A]
Wed Mar 13, 2019 11:26 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: cell diagram
Replies: 1
Views: 79

### Re: cell diagram

Ions for both oxidation and reduction are placed closest to the salt bridge
generally in the order reactants, products
Wed Mar 06, 2019 11:45 am
Forum: Zero Order Reactions
Topic: General “order” question
Replies: 6
Views: 452

### Re: General “order” question

Order is essential to calculate kr, half life, change in concentration, or time needed to get to a particular concentration. There are different equations for each order. You’ll either be given order of reaction, or if you are given elementary reactions (and need to determine order of overall reacti...
Wed Mar 06, 2019 11:41 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: fast and slow elementary reactions
Replies: 3
Views: 152

### Re: fast and slow elementary reactions

Both reactions are important in determining overall reaction. However, pertaining to rate law, the slow step (AKA the rate determining step) is the one that is used.
Wed Mar 06, 2019 11:40 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Solubility and redox reactions
Replies: 1
Views: 94

### Re: Solubility and redox reactions

For precipitates in general the form is: REDUCTION: Precipitate + e — ions OXIDATION: Ions — Precipitate One ion will not change charge, (for AgCl) Cl- retains an oxidation number of -1, so the other ion is the one that is undergoing oxidation or reduction (the one that is going from solid to +1) Th...
Tue Feb 26, 2019 6:35 pm
Forum: Balancing Redox Reactions
Topic: Basic redox reactions
Replies: 3
Views: 157

### Re: Basic redox reactions

First balance O with H2O.
Then balance H — add h2o equal to the number of hydrogens and for every h2o, add an oh- on opposite side

So if you have 4 extra hydrogens on one side, add four h2o on opposite side to balance, and add 4 oh- on the original side
Tue Feb 26, 2019 6:32 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Gibbs free energy J/mol
Replies: 1
Views: 90

### Re: Gibbs free energy J/mol

Unless the reaction specifically states for 1 mole of formation/combustion,
to my understanding, G is either in J or kJ
Tue Feb 26, 2019 9:20 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram and Ecell [ENDORSED]
Replies: 10
Views: 39460

### Cell Diagram and Ecell[ENDORSED]

1) With gaseous and nonconducting solid compounds, is the order Inert|Gas/solid|Chg || Chg|Gas/solid|Inert? Or does it follow the order of reactants to products? Inert|Ox Reactant|Ox Product || Red Reactant|Red Product|Inert 2) With a positive Ecell, reduction is always on the right. Is this order r...
Fri Feb 22, 2019 1:04 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic Cells
Replies: 2
Views: 88

### Re: Galvanic Cells

Reduction occurs at the cathode. For reduction to occur, electrons must be present at the cathode for the reaction to “pick up” electrons.

Oxidation occurs at the anode. Oxidation thus releases electrons at the anode, which are then transported to cathode.
Fri Feb 22, 2019 1:02 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Salt Bridge
Replies: 5
Views: 178

### Re: Salt Bridge

At the anode, oxidation occurs, which leads to the buildup of positively charged ions. At the cathode, reduction occurs, which leads to the buildup of negatively charged ions. As Lorena said, the buildup of these charges will eventually stop e- flow from anode to cathode. To maintain this flow, the ...
Fri Feb 22, 2019 12:18 pm
Forum: Balancing Redox Reactions
Topic: oxidation state of MnO4-
Replies: 3
Views: 142

### Re: oxidation state of MnO4-

Mn is determined by the oxidation state of oxygen as well as the overall charge of the compound.
Oxygen = -2
Because there are 4 Oxygens and overall charge is -1, we need a +7 to balance it out.
Thus, Mn is +7
Fri Feb 15, 2019 11:50 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Isobaric
Replies: 11
Views: 692

### Re: Isobaric

That also means that you must use the Cv value for ideal gases

MONOATOMIC: 3/2*R
LINEAR: 5/2*R
NONLINEAR: 7/2*R
Fri Feb 15, 2019 11:45 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Cv vs. Cp
Replies: 6
Views: 487

### Re: Cv vs. Cp

When calculating change in entropy for systems that have a change in both volume and temperature: S = nRln(V2/V1) + nCvln(T2/T1) Because entropy is a state function: you can add change in volume to change in temperature. For change in temperature, you use Cv. Cv and Cp can also be found for linear a...
Fri Feb 15, 2019 11:39 am
Forum: Calculating Work of Expansion
Topic: Reversible vs Irreversible
Replies: 4
Views: 171

### Re: Reversible vs Irreversible

^^ Adding onto Faith’s answer:

For reversible, the question will also state that system is isothermal.

Also, Ssys is the same for irreversible and reversible work.
The only difference is Ssurr.
Fri Feb 08, 2019 12:43 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Knowing which one to use
Replies: 3
Views: 212

### Re: Knowing which one to use

Heat capacity (neither specific nor molar) is used if no mass/moles are given.

An example is using a calorimeter calibration.
q = Ccal * delta T
Then plug in Ccal to determine q for a different reaction.
Fri Feb 08, 2019 12:39 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Delta H
Replies: 7
Views: 682

### Re: Delta H

You can also use bond enthalpies to determine delta H:
Delta H = H bonds broken (reactants - H bonds formed (products)

But this is not always accurate, as it uses average enthalpy values for the bonds.
Fri Feb 08, 2019 12:36 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: How to know which gas constant to use
Replies: 2
Views: 106

### Re: How to know which gas constant to use

8.314 J/K*mol

.082 L*atm/K*mol

^^ Like Josephine said, it depends on the units in the question.
Thu Jan 31, 2019 7:36 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Comparing SHC
Replies: 3
Views: 183

### Re: Comparing SHC

Not necessarily: Water SHC = 4.184 Benzene SHC = 1.74 Benzene has more atoms than water, yet its SHC is less than water. SHC depends on the types of bonds, not necessarily the amount of atoms. Molar heat capacity is dependant on amount of each substance, but again, the types of bonds mostly determin...
Thu Jan 31, 2019 7:29 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Phase changes
Replies: 2
Views: 118

### Re: Phase changes

^^ Like Gwyn said, heat is not only needed to raise the temperature of the substance, but it is needed to convert it from solid to liquid and liquid to gas. Heat is applied in order to break the intermolecular forces between molecules. Since more heat is required to completely sever bonds (liquid to...
Thu Jan 31, 2019 7:23 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Perfect system
Replies: 3
Views: 237

### Re: Perfect system

A perfect system would involve no loss of energy to surroundings. This by definition is an isolated system, which though exists in theory, there is no completely isolated system in reality.
Wed Jan 23, 2019 11:20 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: All products are solids
Replies: 3
Views: 159

### Re: All products are solids

Equilibrium constant would be equal to
1/[r] — if concentrations are given or reactants are aqeous
1/(Pr) — if reactants are gases
Wed Jan 23, 2019 11:16 am
Forum: Ideal Gases
Topic: atm vs. bar?
Replies: 23
Views: 778

### Re: atm vs. bar?

Different units of measurement
Thus entails use of different value for R constant.
Wed Jan 23, 2019 11:14 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5% Rule
Replies: 5
Views: 237

### Re: 5% Rule

The 5% approximation technique can be used for any K calculation, provided

K < 10-3 — Very little product formed, R-x = R
K > 103 — Very little reactant remaining, P+x = P
Wed Jan 16, 2019 2:32 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Pka and Acidty
Replies: 2
Views: 323

### Re: Pka and Acidty

Small Ka = high pKa = weak acid
Big Ka = low pKa = strong acid
Wed Jan 16, 2019 2:30 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Leveled
Replies: 2
Views: 96

### Re: Leveled

I believe a substance can be leveled by a solvent.

So in the case of a strong acid, if it is dissolved with a solvent that is a strong base, it is “leveled off.”

Both solute and solvent become more neutral
Wed Jan 16, 2019 1:49 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: 5% approximation for weak acids/bases
Replies: 2
Views: 125

### Re: 5% approximation for weak acids/bases

The 5% approximation can be used for values of K that are very large or very small.

If K is large — P+x = P
If K is small — R-x = R

But the verification must be computed after calculating equilibrium values.
Fri Jan 11, 2019 12:28 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: liquids in equilibrium
Replies: 2
Views: 108

### Re: liquids in equilibrium

The change in concentration of pure liquids and solids are insufficient — they essentially remain constant.
Thus, they are not included in equilibrium calculations.
Fri Jan 11, 2019 12:24 pm
Forum: Ideal Gases
Topic: Pressure and volume
Replies: 4
Views: 174

### Re: Pressure and volume

Pressure and volume are inversely related, according to Boyle’s law.

Thus increasing pressure implies a decrease in volume.
Decreasing volume causes reaction to move to side with fewer moles of gas.
So increasing pressure causes reaction to move to side with fewer moles of gas.
Thu Jan 10, 2019 9:27 am
Forum: Ideal Gases
Topic: Algebra
Replies: 5
Views: 178

### Re: Algebra

Concentration is n (mol) / V (L)

Given the ideal gas law: PV = nRT
We write P = (n/V)RT
Thus P = (Conc)RT

Then to determine concentration, we divide P by RT
And get P/RT = Conc
Wed Dec 05, 2018 1:33 pm
Forum: Bronsted Acids & Bases
Topic: J.9
Replies: 2
Views: 182

### Re: J.9

KOH + HC2H3O2 >> KC2H3O2 + H2O

Net ionic: OH- + HC2H3O2 >> H2O + C2H3O2-

Acetic acid donates a proton, which makes the conjugate base C2H3O2-
KOH is a base, which means it accepts a proton to form water,

Because KOH is a strong base and acetic acid is a weak acid: the salt is basic.
Wed Dec 05, 2018 1:26 pm
Forum: Electronegativity
Topic: Electronegativity
Replies: 2
Views: 309

### Re: Electronegativity

Electronegativity follows a diagonal trend: increasing towards the upper right: however, period is more important than group. This is because a lower period is associated with fewer energy shells, and thus a higher Zeff. Higher Zeff implies greater electronegativity: because the stronger the nuclear...
Wed Dec 05, 2018 1:22 pm
Forum: Lewis Acids & Bases
Topic: Difference between Bronsted and Lewis Acids
Replies: 2
Views: 5725

### Re: Difference between Bronsted and Lewis Acids

Bronsted acids are more specific than Lewis acids. Bronsted acids are compounds that can donate a proton, where Lewis acids are electron pair acceptors. So all Bronsted acids are Lewis acids, but not all Lewis acids are Bronsted acids.
Sat Dec 01, 2018 11:05 am
Forum: Naming
Topic: Neutral ligand
Replies: 2
Views: 153

### Re: Neutral ligand

One way of determining charge of complex is through the presence of anions or cations outside []. Basically, the overall charge of the complex equals the charge on the anion or cation present.
Sat Dec 01, 2018 11:01 am
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Equilibrium Constants
Replies: 2
Views: 141

### Re: Equilibrium Constants

From my understanding, we do not need to do calculations involving weak acids or bases. In general, however, the value of the constant remains the same: the concentrations of the conjugate acids and bases will decrease. This is because for weak acids and bases, there is incomplete disassociation, he...
Sat Dec 01, 2018 10:56 am
Forum: Sigma & Pi Bonds
Topic: Number of Sigma and Pi Bonds
Replies: 6
Views: 498

### Re: Number of Sigma and Pi Bonds

Sigma bonds refer to overlap of s orbitals: since there is only one s orbital, there can only be one sigma bond. Pi bonds, on the other hand, refer to overlap of p orbitals. Since there are multiple p orbitals, multiple pi bonds can form.
Thu Nov 22, 2018 7:18 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 7th Edition Question 2E. 29
Replies: 2
Views: 48

### Re: 7th Edition Question 2E. 29

Because the two chlorines are closer together on the first molecule, they create a strong negative pull. In the second molecule, they are a bit farther apart, and because of this the negative pull created by the individual chlorines partially cancel each other, creating a weaker overall pull.
Thu Nov 22, 2018 7:10 pm
Forum: Hybridization
Topic: Hybridization and drawing
Replies: 3
Views: 163

### Re: Hybridization and drawing

Hybridization depends on regions of electron density. While VSEPR does help visualize these regions, it is not necessary to determine hybridization.
Thu Nov 22, 2018 7:08 pm
Forum: Octet Exceptions
Topic: Expanded Octets
Replies: 1
Views: 326

### Re: Expanded Octets

A bond is only formed if it is energetically favorable, meaning that electrons in a bond have a lower energy then free electrons. Thus, it is more energetically favorable to fill 1 d orbital and have all electrons in a bond, as opposed to having electrons in a free orbital.
Sat Nov 17, 2018 11:43 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Sigma bond and Pi bonds
Replies: 2
Views: 268

### Re: Sigma bond and Pi bonds

Sigma bonds = overlap of two s orbitals, overlap of s and one lobe of p, overlap of 2 p orbitals (one lobe only)
Pi bonds = both lobes of p orbitals overlap — atoms cannot rotate

Single bonds = sigma bond
Double bond = sigma and pi bond
Triple bond = sigma and 2 pi bonds
Sat Nov 17, 2018 11:40 am
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Instantaneous dipole equation
Replies: 1
Views: 132

### Re: Instantaneous dipole equation

By instantaneous interactions, I assume you are referring to induced dipole interactions. Polarazability (the amount an electron field can be distorted) is directly proportional to atomic radius: the larger the radius, the more distortion, Greater polarizability allows for stronger induced dipole in...
Sat Nov 17, 2018 11:34 am
Forum: Hybridization
Topic: Electron promotion
Replies: 2
Views: 204

### Re: Electron promotion

Electron promotion allows for bond formation. In most cases, forming bonds equates a lower energy state. Lower energy states are most favorable: Pauli Exclusion Principle is less favorable.
Thu Nov 08, 2018 12:42 pm
Forum: Resonance Structures
Topic: Resonance Structures
Replies: 3
Views: 177

### Re: Resonance Structures

If there is an equivalent Lewis structure that can be formed (overall formal charge value remains the same)
simply by exchanging positions of atoms — then a molecule has resonance.
Thu Nov 08, 2018 12:30 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: Potential Energy of London interactions
Replies: 2
Views: 165

### Re: Potential Energy of London interactions

In terms of bond strength: type of bond is more important than size of molecule A larger radius, as you said, implies greater electron distortion Greater distortion of electrons means that the atom is more easily polarizable: will more easily form a dipole Since LDF forces are based on the formation...
Thu Nov 08, 2018 12:12 pm
Forum: Dipole Moments
Topic: Van Der Waal vs Hydrogen Bons
Replies: 2
Views: 152

### Re: Van Der Waal vs Hydrogen Bons

Hydrogen bonding and Van der Waal forces are both intermolecular forces. VDW forces are present in all molecules H-bonding is typically characterized by H-NOF bonds From my understanding, because VDW forces is a bond between induced dipoles (which arise from a “temporary” dipole formation), hydrogen...
Thu Nov 01, 2018 5:06 pm
Forum: Resonance Structures
Topic: Radicals and "damaging"
Replies: 5
Views: 250

### Re: Radicals and "damaging"

Taking antioxidants (vitamins) can help offset some of the damage.
Thu Nov 01, 2018 4:56 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 1E.25
Replies: 1
Views: 96

### Re: 1E.25

Alkali — (no d electrons) s1
Grp 15 — if period 3+: (n-1)d10ns2np3
Grp 5 — (n-1)d3ns2
Coinage metals — acheive greater stability with a partially or completely filled d subshell
(n-1)d5ns1 OR (n-1)d10ns1

n = principal quantum number
Thu Nov 01, 2018 4:51 pm
Forum: Resonance Structures
Topic: Delocalized electrons
Replies: 2
Views: 143

### Re: Delocalized electrons

Delocalized electrons are electrons spread over multiple atoms: they do not belong to a single atom. This usually occurs in double bonds or triple bonds.
Thu Oct 25, 2018 7:42 pm
Forum: Photoelectric Effect
Topic: Work Function
Replies: 14
Views: 949

### Re: Work Function

It depends on information given. If given kinetic energy and energy/wavelength/frequency of incoming light, you can just subtract the energy of the incoming light from the value of kinetic energy to obtain the work function. Another way is if you are given the value of energy of photon at 0KE (maxim...
Thu Oct 25, 2018 7:39 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Quantum Numbers n, l, and m
Replies: 5
Views: 175

### Re: Quantum Numbers n, l, and m

n = principle energy level (shell), l is angular momentum (subshell), and ml = magnetic quantum (orbital).
The highest value of l is equal n-1
Values of l correspond to subshells: 0-s, 1-p, 2-d, 3-f
Thu Oct 25, 2018 7:36 pm
Forum: *Shrodinger Equation
Topic: Help on how to find l, ml, and ms
Replies: 6
Views: 10245

### Re: Help on how to find l, ml, and ms

l is angular momentum quantum number.
It is the number of subshells per principal energy level
l = n-1

ml is magnetic quantum number, and refers to the number of orbitals per subshell
ml = 2l + 1

ms is spin quantum number, and refers to spin of electron. It is either positive or negative one half
Sun Oct 21, 2018 1:31 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Electron Configuration [ENDORSED]
Replies: 1
Views: 76

### Re: Electron Configuration[ENDORSED]

Atoms prefer to be in the lowest energy state possible. A half-filled or fully-filled d-subshell has a lower energy, which is why electron configurations that should be written as 3d4-4s2 or 3d9-4s2 are instead written 3d54s1 and 3d104s1
Sun Oct 21, 2018 1:27 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Effective Nuclear Charge
Replies: 3
Views: 161

### Re: Effective Nuclear Charge

Nuclear charge refers to the strength of nuclear pull on electrons of an atom. However, the presence of more electrons creates shielding, which lowers the nuclear pull. Z-eff refers to the value of nuclear charge - shielding.
Sun Oct 21, 2018 1:25 pm
Forum: Properties of Electrons
Topic: Atomic Spectra: absorption vs emission
Replies: 3
Views: 101

### Re: Atomic Spectra: absorption vs emission

I believe frequencies in absorption and emission spectra would be different. For example, if red light is absorbed, green light would be given off, and red and green have different frequencies.
Sat Oct 13, 2018 10:02 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: H-Atom Emperical Equation
Replies: 2
Views: 97

### Re: H-Atom Emperical Equation

Since other atoms have more than one electron, determining energy would depend on both distance from nucleus and electron-electron repulsion.
Sat Oct 13, 2018 9:56 pm
Forum: Photoelectric Effect
Topic: Intensity — Photoelectric Effect
Replies: 1
Views: 121

### Intensity — Photoelectric Effect

Is there a way of mathematically calculating intensity/amplitude via the photoelectric effect equation:
KE electron = Energy of photon - Threshold energy?
Sat Oct 13, 2018 9:25 pm
Forum: Photoelectric Effect
Topic: Work Function
Replies: 4
Views: 114

### Re: Work Function

More information would need to be provided, unless the problem specifies kinetic energy is 0 (i.e. longest wavelength). In this case, set threshold energy equal to energy of photon (velocity does not need to be calculated).
Sat Oct 13, 2018 8:42 pm
Forum: Photoelectric Effect
Topic: Work Function
Replies: 4
Views: 114

### Re: Work Function

More information would need to be provided, unless the problem specifies kinetic energy is 0 (i.e. longest wavelength). In this case, set threshold energy equal to energy of photon (velocity does not need to be calculated).
Wed Oct 10, 2018 4:53 pm
Forum: Significant Figures
Topic: Repeating Decimal
Replies: 3
Views: 777

### Repeating Decimal

When we have a repeating decimal number, such as 1/3, do we simply follow “normal” (lowest decimal point value for addition/subtraction and lowest number of sig figs for multiplication/division)? Or are there special rules? Also, how does rounding work?
Thu Oct 04, 2018 8:35 am
Forum: Empirical & Molecular Formulas
Topic: Molar mass and molecular weight
Replies: 3
Views: 264

### Molar mass and molecular weight

Technically, don’t molar mass and molecular weight refer to the same concept: the total weight (in grams) of the molecular formula?
Wed Oct 03, 2018 11:33 pm
Forum: Empirical & Molecular Formulas
Topic: Definition of Empirical Formula
Replies: 8
Views: 292

### Re: Definition of Empirical Formula

Theoretically, doesn’t it also refer to mass percent composition of the molecule?
Wed Oct 03, 2018 10:41 pm
Forum: Empirical & Molecular Formulas
Topic: Definition of Empirical Formula
Replies: 8
Views: 292

### Definition of Empirical Formula

Does the empirical formula represent the relative number of atoms of a compound or the relative mass ratio of the atoms in a compound?

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