Search found 60 matches

Wed Mar 13, 2019 3:57 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: question 6.51
Replies: 1
Views: 97

Re: question 6.51

Yes that is one way to interpret electrophysiology. But the default is that electrons always go towards the anode which usually is the right side. Electrons is the more important observation but this distinction of positive ions moving towards the negatively charged cathode is correct.
Wed Mar 13, 2019 12:47 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Catalyst vs. Intermediate
Replies: 8
Views: 261

Re: Catalyst vs. Intermediate

A catalyst is a reactant first in the mechanism and then a product:

C + D ==> E (fast)

E ==> F + D (fast)

D is a catalyst

An intermediate is the opposite; it is a product first and then a reactant afterwards:

A + B ==> C (slow)

C + D ==> E (fast)

C is an intermediate
Wed Mar 13, 2019 12:43 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Units of k
Replies: 5
Views: 409

Re: Units of k

A Khan Academy video best explains how to derive K without memorization:

Wed Mar 13, 2019 12:39 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell diagram
Replies: 1
Views: 111

Re: Cell diagram

An OH is needed to balance the missing OH ions on each substance. It would be on the Cathode side since after doing the balanced half reactions, OH on the reduction half would be canceled off since the oxidizing half has 2 OH. The reason it has to be KOH instead of OH since OH by itself is highly io...
Tue Mar 12, 2019 10:42 pm
Forum: General Rate Laws
Topic: Unique rate law
Replies: 1
Views: 102

Re: Unique rate law

When looking for averages and instantaneous rates then you should be using rate of formation. This is useful when relating rates of reactants. A rate law would be used to directly observe the relationship with the reactants concentration to the reactions rate.
Tue Mar 12, 2019 10:32 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: exercise 11.77 6th edition
Replies: 2
Views: 127

Re: exercise 11.77 6th edition

A breaking of bonds is usually an endothermic process since energy is required to break bonds (which may also release some energy). The net is a positive intake of energy thus being endothermic.
Tue Mar 12, 2019 10:28 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 Equation
Replies: 3
Views: 370

Re: Boltzmann Equation

Use the Boltzmann equation whenever microstates is mentioned to calculate the changes in Entropy.
Mon Mar 11, 2019 4:38 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Activated complex
Replies: 4
Views: 382

Re: Activated complex

Since we are not focusing on chemical structures, we do not need to draw any transition states. What Dr. Lavelle did in lecture is a rough sketch of a transition state for the purpose of visualizing what bonds will be broken after reaching Activation energy threshold. For the final just understand t...
Wed Mar 06, 2019 11:50 pm
Forum: Balancing Redox Reactions
Topic: 14.119
Replies: 1
Views: 111

Re: 14.119

Au (gold) has either a +1 charge or a +3 charge. We choose the +1 charge in this situation since it has a higher positive charge potential making it more likely to be oxidized losing only one electron over 3 electrons.
Wed Mar 06, 2019 11:45 pm
Forum: General Rate Laws
Topic: 15.3
Replies: 2
Views: 128

Re: 15.3

Reaction rate depends on the duration of the NO2 not the coefficient of the substance. It would be the change in concentration over the time duration of a reaction thus it would be divided by 20s instead of 2.
Thu Feb 28, 2019 7:28 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Cell Potential Spontaneity
Replies: 7
Views: 272

Cell Potential Spontaneity

What is the relationship of Cell potential and spontaneity?

Can looking at the Gibbs Free energy equation show the relationship since it has Cell potential, and knowing that spontaneity is correlated with Gibbs Free energy.
Thu Feb 28, 2019 7:25 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: cathode vs anode
Replies: 4
Views: 190

Re: cathode vs anode

Note if Ecell is negative that means it is the opposite notation. So either flip the sign of Ecell and flip the notation as well if given a negative Ecell.
Thu Feb 28, 2019 7:24 pm
Forum: Balancing Redox Reactions
Topic: Problem K3 D
Replies: 2
Views: 114

Re: Problem K3 D

Cl2 on the right side currently has a charge of zero. Since it is reduced to Cl- on the right side, the electrons must be on the left to balance the charge. It is 2 electrons since there must be 2 Cl - on the right side to balance the equation.
Wed Feb 20, 2019 11:41 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Derivation of Gibb's Free Energy
Replies: 1
Views: 133

Derivation of Gibb's Free Energy

Can anyone explain the derivation of Gibb's Free energy to get G = nFE when work from previous chapters was charge over T.
Wed Feb 20, 2019 11:34 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Standard Cell Potential
Replies: 2
Views: 148

Standard Cell Potential

What is standard in Standard Cell Potential? Is it just temperature and pressure? What does it mean when it above 0?
Wed Feb 20, 2019 11:27 pm
Forum: Balancing Redox Reactions
Topic: Oxidation Numbers
Replies: 2
Views: 100

Re: Oxidation Numbers

Yes, it is the charge after the transfer of electrons.
Fri Feb 08, 2019 10:19 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: 9.25, Calculation
Replies: 1
Views: 93

Re: 9.25, Calculation

Yes, since the Boltzmann Formula relates entropy and how the molecules arrange in said micro-states:

Thus 6 ^ avogadro's number would be W.
Fri Feb 08, 2019 10:05 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond
Replies: 2
Views: 117

Re: Bond

Bond angles can influence the way the atoms are arranged. Electron densities such as an atom itself or even lone pairs of electrons can greatly alter the shape. The order of the strength of repulsion goes as follows: Lone pair e - Lone pair e > Atom - lone pair e > atom - atom Lone pair electrons ta...
Fri Feb 08, 2019 11:47 am
Forum: Calculating Work of Expansion
Topic: Reversible Expansion
Replies: 3
Views: 138

Re: Reversible Expansion

A reversible expansion has a pressure that is constantly changing therefore the derivation of volume (the area under the curve) is needed to show a changing pressure. That is why the integral goes from one volume to another and why work for a reversible expansion is w=-nRTln(V2/V1) while a irreversi...
Fri Feb 08, 2019 11:26 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Delta H
Replies: 7
Views: 684

Re: Delta H

Delta H is enthalpy of the system. When pressure is constant, Delta H can tell you if the system is absorbing or losing energy in the form of heat. A negative H is the loss of heat while a positive H is the absorption of heat. The equation of the enthalpy of the system is the summation of H of the p...
Fri Feb 08, 2019 11:13 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Entropy, Enthalpy, Free Energy.
Replies: 2
Views: 143

Entropy, Enthalpy, Free Energy.

How is entropy, enthalpy, and free energy related?

I know that you can combine entropy and enthalpy to equal free energy ( the total energy). When solving thermodynamic problems and equations, I am still unsure what the relationships are. When do you use one equation over the other?
Fri Feb 01, 2019 4:13 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: 1st law of thermodynamics
Replies: 7
Views: 249

Re: 1st law of thermodynamics

An isolated system is where energy exchange and transfers are bounded by the system. The universe is the closed system and cannot exchange energy with its surroundings for there may not be one. Therefore it is considered that the universe contains everything. Every energy transformation is within th...
Thu Jan 31, 2019 5:35 pm
Forum: Calculating Work of Expansion
Topic: Homework Problem 8.3 Question
Replies: 1
Views: 100

Re: Homework Problem 8.3 Question

The values given in the problem does not include the change in Volume. The pipe is a circular surface and to calculate its volume it would be pi * radius^2 * height. In this case the height would be how much the pipe decompressed. Thus to get change in volume you have to find radius which would be h...
Fri Jan 25, 2019 11:43 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Increasing Pressure
Replies: 3
Views: 156

Re: Increasing Pressure

Reactants are only favored when pressure increases equilibrium shifts to the side where there is less moles. This is Le Chatelier's Principle. When pressure decreases it would do the opposite: equilibrium would shift to the side where there is more moles.
Fri Jan 18, 2019 5:19 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Knowing Acids or Bases
Replies: 3
Views: 145

Re: Knowing Acids or Bases

There is 7 strong acids: Best to remember them by is the middle elements in group 17. Nitric acid, Sulfuric acid and chloric acids ( with at least 3 oxygen atoms). HCl, HBr, HI, HNO3, HClO3, HClO4, H2SO4 There is 8 strong bases: Best to remember them is the group 1 elements and the middle elements i...
Fri Jan 18, 2019 4:40 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Endothermic
Replies: 2
Views: 83

Re: Endothermic

The process is endothermic since it requires energy therefore essentially absorbing energy. It may use energy to break a bond which may release some energy but the whole process has a net gain of energy. When you look at a free energy graph of reactants and products of an endergonic reaction, you ma...
Mon Jan 14, 2019 2:30 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: HW Q 6th ed. 11.53
Replies: 3
Views: 114

HW Q 6th ed. 11.53

A reaction mixture that consisted of 0.400 mol H2 and 1.60 mol I2 was introduced into a 3.00-L flask and heated. At equilibrium, 60.0% of the hydrogen gas had reacted. What is the equilibrium constant K for the reaction H2(g) + I2(g) <-> 2 HI(g) at this temperature? I have already calculated the con...
Mon Jan 14, 2019 2:25 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 7th Edition 5H 3
Replies: 2
Views: 87

Re: 7th Edition 5H 3

K should still be the quotient of concentration of products over the concentration of reactants. In this case there will be two concentrations of products on top and 2 concentrations of reactants on the bottom:

[Br2] [HCL] / [BrCl]^2 [H2]
Wed Jan 09, 2019 11:38 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Help with question 11.7
Replies: 2
Views: 72

Re: Help with question 11.7

The fractions of the molecules is equivalent to to partial pressures of each molecule; just multiply those fractions by .10 to convert to partial pressures. Then use the equilibrium expression of partial pressures to get the equilibrium constant. Hope this helps.
Mon Jan 07, 2019 4:02 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kc Value
Replies: 4
Views: 289

Re: Kc Value

In terms of kinetics, having a large equilibrium constant indicates that the reaction is favored to move forward leading to an increase of products formed. The difference in the amount indicates what reaction will create more of a product at a larger rate.
Wed Dec 05, 2018 12:00 pm
Forum: Bronsted Acids & Bases
Topic: Sixth Edition 12.51
Replies: 1
Views: 131

Re: Sixth Edition 12.51

Typically the more likely it would lose an H+ ion, the stronger the acid. Therefore, the bigger the atom radius is a much stronger acid. In your example, HCl would be a stronger acid than HF since Cl is such a larger atom. You can also determine through electronegativity; F is the most electronegati...
Mon Dec 03, 2018 12:27 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Calculating pH
Replies: 3
Views: 127

Re: Calculating pH

You can easily solve for each other when you have one concentration or the other.

14 = pH + pOH

Unless, you have a weak acid therefore you have to use the Ka concentration.
Mon Dec 03, 2018 11:34 am
Forum: Photoelectric Effect
Topic: Work Function
Replies: 2
Views: 386

Re: Work Function

If the frequency is considered to be the amount of which where an electron is taken off the surface of the metal, the work function is the same as the energy of a photon that is needed to remove the electron. Thus the equation is also E(work) = hv.

Note that photon to electron ratio is 1:1.
Mon Dec 03, 2018 11:31 am
Forum: Balancing Chemical Reactions
Topic: Aqueous compounds
Replies: 5
Views: 395

Re: Aqueous compounds

If the compound is a solvent in water then it is considered to be aqueous.

E.g.
NaOH(aq) + HCl(aq) <==> Na(aq) + Cl(aq) + H2O(l)

When a compound is hydrophilic, the compound is then aqueous. Otherwise it is hydrophobic and may form a precipitate.
Mon Dec 03, 2018 9:56 am
Forum: Naming
Topic: Anions
Replies: 3
Views: 126

Re: Anions

Anions should have negative charge; when it doesn't have a charge it may be bonded to a cation. You may still have to end with -ate unless it is at a lower oxidation state then -ite should be used. Anions of only a single atom should end in -ide. Some monoatomic ions also have -ide such as cyanide (...
Tue Nov 27, 2018 12:55 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: Dipole Moments
Replies: 1
Views: 129

Re: Dipole Moments

Not all molecules have a dipole moment. They can only occur if there is a significant difference in electronegativity between two atoms. For a non-polar molecule the dipoles cancel each other out thus not inducing any particular electrical attraction towards one end or the other. While polar molecul...
Tue Nov 27, 2018 12:49 am
Forum: Dipole Moments
Topic: Problem 6.1
Replies: 1
Views: 156

Re: Problem 6.1

You are correct. SO2 is a polar molecule with two doubles bonds between the Sulfur and the two Oxygens. Thus, lone pairs contributes to the partial charges. Each oxygen has two lone pairs while the sulfur only has one. Therefore the sulfur is a delta positive while the two oxygens are the delta nega...
Mon Nov 26, 2018 12:20 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Coordination Compounds and Ligands
Replies: 1
Views: 112

Re: Coordination Compounds and Ligands

Ligands are molecules attached to a central metal atom. It is just like what we have been doing so far in terms of VSEPR and Lewis Structures that mostly consist of covalent bonds. You can imagine that ligands are their own electron density clouds. The bonds form coordination compounds or complexes.
Fri Nov 23, 2018 2:07 pm
Forum: Lewis Structures
Topic: Boron
Replies: 1
Views: 66

Re: Boron

Since Boron has only 5 electrons in total with 3 valence electrons, it can be an exception to the octet rule. To complete the octet, Boron can gain 5 valence electrons or lose its 3 valence electrons to complete the octet. Boron could never have a maximum 5 bonds for it is a small atom. Therefore, i...
Mon Nov 19, 2018 12:12 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Regions of electric density in VSEPR Model
Replies: 2
Views: 68

Re: Regions of electric density in VSEPR Model

Considering that lone pairs can freely move around their region while bonded electrons are stuck in between atoms explains why lone pair - lone pair interactions repulse electrons farther. Like you said, that bonded electrons are clustered into one region, but lone pair regions take up more space si...
Thu Nov 15, 2018 10:19 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Double/Triple Bonds
Replies: 5
Views: 277

Re: Double/Triple Bonds

No they do not; they are treated as single electron density therefore can repulse only as much. Angles change from the influence of lone pairs which has a larger repulsion since they take up more space than bonded atoms. Knowing that atoms are bonded with either double or triple bonds only help form...
Wed Nov 14, 2018 10:38 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Molecular Shape
Replies: 4
Views: 157

Re: Molecular Shape

There are 8 angles between 6 bonds thus named an octahedral.
Wed Nov 14, 2018 12:01 pm
Forum: Student Social/Study Group
Topic: Test 3
Replies: 6
Views: 579

Re: Test 3

The next test is most likely on Outline 4 on all about VSEPR and hybridization.
Wed Nov 14, 2018 11:40 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Determining VSEPR bond angles
Replies: 5
Views: 532

Re: Determining VSEPR bond angles

Thanks for the help.

In lecture, Dr. Lavelle did confirm that we do not need to calculate bond angles but we should know how lone pairs influence bonding angles between other atoms therefore a difference in angles between different atoms.
Tue Nov 13, 2018 1:04 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Determining VSEPR bond angles
Replies: 5
Views: 532

Determining VSEPR bond angles

How do you calculate the VSEPR bond angles between several atoms in a molecule? An example: For 4.7 (a) What is the shape of the thionyl chloride molecule, SOCl2? Sulfur is the central atom. (b) How many different OSCl bond angles are there in this molecule? (c) What values are expected for the OSCl...
Wed Nov 07, 2018 6:21 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: Effect of Size of Atom/Molecule on Distortion
Replies: 2
Views: 138

Re: Effect of Size of Atom/Molecule on Distortion

All of these properties effect size of an atom. Specifically for distortion, the amount of electrons and where its distributed around the nucleus directly contributes to dispersion forces. The larger the atom, the farther the electrons are from the nucleus which means they are held together weakly a...
Fri Nov 02, 2018 11:14 pm
Forum: Photoelectric Effect
Topic: Test #2 Question #2b
Replies: 4
Views: 500

Re: Test #2 Question #2b

Since the electron can be already ejected surpassing threshold energy, increasing the intensity of the light increases the amount of ejected electrons and the speed of which electrons are ejected. This is because light intensity is directly proportional to frequency as a mechanical view of light (ki...
Fri Nov 02, 2018 12:25 pm
Forum: Quantum Numbers and The H-Atom
Topic: Degeneracy Formula
Replies: 1
Views: 90

Re: Degeneracy Formula

Degeneracy is the amount of orbitals with the same energy. Simply, it is how many orbitals in a sub-shell. For example, p has 3 orbitals in one sub-shell: px, py, and pz.
Fri Nov 02, 2018 12:18 pm
Forum: Bond Lengths & Energies
Topic: Midterm
Replies: 1
Views: 102

Re: Midterm

Up to 3.11 in the 6th ed. From Outlines 1 to 3.
Fri Nov 02, 2018 12:03 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Replies: 1
Views: 131

To calculate total nodes just subtract quantum number n by 1: n - 1 = total nodes. To get radial and angular nodes look at l. If l = 1 there is one radial node and one angular node. If l= 2 there is 2 angular nodes and 2 radial nodes having a total n = 4. And so on.
Thu Nov 01, 2018 12:12 am
Forum: Lewis Structures
Topic: HW Problem 2B.9 Part B
Replies: 1
Views: 91

Re: HW Problem 2B.9 Part B

This is an ionic bond therefore there are no electrons shared. That is why it is spaced out with no lines that indicate covalent bonds. Phosphorus P has brackets (at the center) with the charge 3- since it gains 3 electrons from each Potassium K. This is signified by the + sign by each K ion which t...
Wed Oct 31, 2018 11:54 pm
Forum: General Science Questions
Topic: Calculator for midterm
Replies: 4
Views: 252

Re: Calculator for midterm

Scientific Calculators are rather cheap and can be found in lots of retailers such as Target. I personally have Texas Instruments TI30XIIS. At Target it can be bought for \$12.99 or buy from Amazon if you have Amazon Prime for students.
Tue Oct 30, 2018 9:40 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 2.45 6th Edition
Replies: 1
Views: 101

Re: 2.45 6th Edition

Even though it has electrons in the d - subshell, there are only 4 valence electrons therefore Thorium is the right answer. It would be 7s25f2 but for the first 4 elements in the Actinoid family can interchange between the f or d orbitals due to little difference in energy between orbitals.
Wed Oct 24, 2018 1:43 pm
Forum: Trends in The Periodic Table
Topic: Electron Affinity
Replies: 2
Views: 60

Electron Affinity

Just making sure: Is electron affinity the same as electronegativity? I know in Biology calls an ability to attract electrons with electronegativity. If they are different I do no want to mix them up.
Thu Oct 18, 2018 7:16 pm
Forum: DeBroglie Equation
Topic: post assessment #29
Replies: 2
Views: 150

Re: post assessment #29

Instead of speed, the particles would have the same momentum. Since the particles' mass are not equivalent, the electron will still move faster than the proton due to its extremely small weight.
Mon Oct 15, 2018 5:28 pm
Forum: Properties of Light
Topic: Problem 1.21 6th Ed.
Replies: 1
Views: 68

Problem 1.21 6th Ed.

From the following list of observations, select the one that best supports the idea that electromagnetic radiation has the properties of particles. Explain your reasoning. (a) Black-body radiation. (b) Electron diffraction. (c) Atomic spectra. (d) The photoelectric effect. I chose d) which is the co...
Wed Oct 10, 2018 9:24 pm
Forum: Properties of Electrons
Topic: Problem 1.15 6th ed.
Replies: 1
Views: 63

Problem 1.15 6th ed.

Question : In the ultraviolet spectrum of atomic hydrogen, a line is observed at 102.6 nm. Determine the values of n for the initial and final energy levels of the electron during the emission of energy that leads to this spectral line. I am unsure how to begin this question. I tried to use the Rydb...
Wed Oct 10, 2018 9:08 pm
Forum: Properties of Light
Topic: Question 1.25 (Sixth Edition)
Replies: 1
Views: 66

Re: Question 1.25 (Sixth Edition)

For part a) you should solve for frequency (v) from the wavelength given. Therefore use the equation which relates wavelength and frequency: c = λν. Using that wavelength use the Energy of the photon equation to solve for energy: E = hv. For part b) use number of photons per mole constant in substit...
Wed Oct 10, 2018 9:20 am
Forum: Properties of Light
Topic: Problem 1.3 6th ed.
Replies: 3
Views: 120

Problem 1.3 6th ed.

Which of the following happens when the frequency of electromagnetic radiation decreases? Explain your reasoning. (a) The speed of the radiation decreases. (b) The wavelength of the radiation decreases. (c) The extent of the change in the electrical field at a given point decreases. (d) The energy o...
Wed Oct 03, 2018 9:23 am
Forum: Significant Figures
Topic: Calculating Sig Figs
Replies: 3
Views: 167

Re: Calculating Sig Figs

Generally, just look at the amount of sig figs of each value and then round to the nearest number according to the lowest number of sig figs (to be less precise). For example, when dividing 3.04 mol by 1.2 L to get a molarity of 2.5M instead of 2.53M. Since 1.2L is two sig figs the answer must be al...