Search found 64 matches

Sun Mar 01, 2020 7:01 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Concentration Cell Examples
Replies: 3
Views: 37

Re: Concentration Cell Examples

The example we had in class was with Ag+ and Ag. In the cell, you would have Ag metal on both sides with a porous disk in the middle. On one side, there would be a 1.0 M concentration of Ag+ and the other would have a 0.10 M concentration of Ag+. The one with the lower concentration would be a produ...
Sun Mar 01, 2020 6:59 pm
Forum: Balancing Redox Reactions
Topic: OH and H
Replies: 8
Views: 89

Re: OH and H

For OH and H, you would add them on whichever side is needed so that all the elements are balanced on both sides of the equation.
Sun Mar 01, 2020 6:58 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6M.1
Replies: 1
Views: 45

Re: 6M.1

I was a bit confused by this too, and I think they made Cu the anode so that it would be oxidation and the other reaction would be reduction because the problem is asking for the standard reduction potential of M2+/M. You could still do the problem with Cu as the cathode but then you would just have...
Sat Feb 29, 2020 6:16 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6l7
Replies: 1
Views: 26

Re: 6l7

The nickel is being reduced, so the Ni(OH)3 already has OH that is given off, and there is no additional OH added. The cadmium is oxidized and you have to add OH to the solid Cd in order to get Cd(OH)2.
Sat Feb 29, 2020 6:12 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Homework question
Replies: 1
Views: 37

Re: Homework question

The value of "n" is the number/moles of electrons that are transferred. For this problem, you need to write out the half-reactions and balance them in order to find the total number of electrons that are transferred in the full reaction.
Sat Feb 22, 2020 5:58 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 6N.3
Replies: 6
Views: 99

Re: 6N.3

I think they got Q from the concentrations given in the problem. Also, I was confused about why the book didn't use Faraday's constant either, so I checked and apparently RT/F is equal to 0.025693V at 298K, so that's what they used instead. The solutions manual can be a little confusing sometimes.
Sat Feb 22, 2020 5:55 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Using an inert electrode
Replies: 2
Views: 16

Re: Using an inert electrode

Iodine is a nonmetal, so it cannot conduct electricity. Pt is used on both sides so that the electrical current will flow.
Sat Feb 22, 2020 5:53 pm
Forum: Balancing Redox Reactions
Topic: Elements with only 1 ionization state
Replies: 1
Views: 29

Re: Elements with only 1 ionization state

The ionization state or oxidation number of an element depends on what else it is combined with. Oxygen is usually 2- but it can change depending on what molecule it is in. For example, in H2O2, oxygen is 1-. Hydrogen is usually +1 or 0.
Sat Feb 22, 2020 5:47 pm
Forum: Administrative Questions and Class Announcements
Topic: Curve?
Replies: 5
Views: 54

Re: Curve?

I don't believe Lavelle curves tests. I think he uses them to calculate the final grades and then curves the final grades a little bit. I could be wrong though.
Sat Feb 22, 2020 5:45 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Standard Cell Potentials
Replies: 2
Views: 28

Re: Standard Cell Potentials

My solutions manual has the copper anode and its potential is 0.34 V. The cell potential is given as -0.689 V. You would set up an equation for -0.689 V= E not of the cathode - 0.34 V. Then, solve for E not of the cathode and you should get -0.349 V.
Sun Feb 16, 2020 2:51 pm
Forum: Balancing Redox Reactions
Topic: Number of electrons
Replies: 5
Views: 48

Re: Number of electrons

No, you only have to write the electrons in the half-reactions because, in the total equation, the electrons would cancel out as they exchange between the other elements in the reaction.
Sun Feb 16, 2020 2:48 pm
Forum: Balancing Redox Reactions
Topic: oxidation states (6K.1)
Replies: 2
Views: 14

Re: oxidation states (6K.1)

Also, the oxidation states should add up to the total charge of the molecule. In the equation you have, both molecules have a total charge of zero so all the oxidation states of each element should add up to zero. If the molecule has a negative or positive charge, then it should add up to that number.
Sun Feb 16, 2020 2:29 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 5.55
Replies: 4
Views: 76

Re: 5.55

Since C(s) is in solid form, it is not included in the equation for the equilibrium constant. There is no concentration for C(s) at equilibrium because it does not change much from the initial concentration and is not related to equilibrium.
Sun Feb 16, 2020 2:17 pm
Forum: Balancing Redox Reactions
Topic: 6K.1
Replies: 1
Views: 15

Re: 6K.1

Yes, basically it is similar to how we added equations in the enthalpy reactions. If any of the elements/substances are the same on either side of the equations, they would cancel out. Then everything else would be added up and you should get an equation that is similar to the original one you were ...
Sun Feb 16, 2020 2:13 pm
Forum: Van't Hoff Equation
Topic: Delta H and S naught
Replies: 2
Views: 45

Re: Delta H and S naught

I think we are also meant to assume that since delta H and S naught are the differences between the final and initial states of the reaction, the difference itself is not changing. We assume both the final and initial numbers are increasing by the same amount so the difference between them should st...
Sat Feb 08, 2020 6:03 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Reason for decrease in entropy
Replies: 5
Views: 65

Re: Reason for decrease in entropy

Entropy decreases when a system goes from more disordered to less disordered, such as from a gas to liquid.
Sat Feb 08, 2020 6:01 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 4J.3 part b
Replies: 1
Views: 19

Re: 4J.3 part b

For 4J.3 part b, I have the temperature as being -45 degrees C.
Sat Feb 08, 2020 5:49 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: Temperature and entropy change
Replies: 1
Views: 22

Re: Temperature and entropy change

The Boltzmann formula is for just S not delta S. The entropy does increase with temperature, but the change in entropy is how much the entropy changes in relation to the temperature.
Sat Feb 08, 2020 5:44 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: internal energy
Replies: 3
Views: 37

Re: internal energy

If a system is a constant pressure and volume then w would equal zero. Since, deltaU=q+w and q=deltaH I think it would just be deltaU=deltaH if both pressure and volume is constant.
Sat Feb 08, 2020 5:40 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: units
Replies: 3
Views: 32

Re: units

H and G are usually in kJ/mol. S can J/K or J/K/mol. U can be either kJ or J depending on q and w.
Sat Feb 01, 2020 4:55 pm
Forum: Calculating Work of Expansion
Topic: Changing external pressure
Replies: 1
Views: 30

Re: Changing external pressure

I think it was referring to how reversible reactions can go in either direction depending on temperature, pressure, or amount of substance. If you change any variable slightly, a reaction could go out of equilibrium and go in the reverse direction.
Sat Feb 01, 2020 4:45 pm
Forum: Calculating Work of Expansion
Topic: Reversible vs Irreversible process
Replies: 2
Views: 31

Re: Reversible vs Irreversible process

A reversible process is not at constant pressure and uses the equation w=-nRTln(V2/V1). A irreversible process is at constant pressure and uses w=PdeltaV.
Sat Feb 01, 2020 4:40 pm
Forum: Calculating Work of Expansion
Topic: When to Use the Integral
Replies: 2
Views: 16

When to Use the Integral

In my notes I have that w = the negative integral from V1 to V2 of PdV = -PdeltaV. Does this mean we can just use the -PdeltaV equation and don't actually need the integral. How do we know if we have to actually use the integral or not?
Sat Feb 01, 2020 4:35 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Water and Equilibrium
Replies: 2
Views: 28

Re: Water and Equilibrium

Gaseous H2O is usually a product and not used as a solvent, so its concentration would affect the equilibrium constant as it is formed. H2O as a liquid is not included in equilibrium constants because its concentration is so big and does not change much in the reaction so it would not affect the rate.
Sat Feb 01, 2020 4:29 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Problem 4D.7
Replies: 1
Views: 9

Re: Problem 4D.7

The equation for deltaU is q + w. q is equal to deltaH, so you would have to calculate w by using the PV=nRT equation. Then add to calculate deltaU.
Sat Jan 25, 2020 6:56 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Dimensional Analysis for Molar Heat Capacity
Replies: 3
Views: 29

Re: Dimensional Analysis for Molar Heat Capacity

If the units have K in it, then I would convert from Celsius to Kelvin so that it cancels out. The units need to be the same in order for it to cancel, so it would be easier to convert the temperature.
Sat Jan 25, 2020 6:54 pm
Forum: Phase Changes & Related Calculations
Topic: Entropy vs Enthalpy
Replies: 9
Views: 64

Re: Entropy vs Enthalpy

In high school chem, we also used the word "chaotic" to describe entropy. Usually, we used it for different phases, because gases would be more disordered/chaotic than liquids and solids.
Sat Jan 25, 2020 6:50 pm
Forum: Phase Changes & Related Calculations
Replies: 5
Views: 64

I usually base the readings and homework on what we have been learning in class, so I just read over the parts concerning enthalpy, which I believe would be sections 4C-4E. We've just begun learning about bond enthalpies and standard enthalpies.
Sat Jan 25, 2020 6:46 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Excluding H2O from Ka and Kb
Replies: 5
Views: 47

Re: Excluding H2O from Ka and Kb

H2O is typically used as a solvent in its liquid form, so the concentration does not change much before and after the reaction occurs. Since it mostly stays the same, it would not have an affect on the rate of the reaction.
Sat Jan 25, 2020 6:41 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: enthalpy reaction
Replies: 4
Views: 29

Re: enthalpy reaction

We do reactants minus the products for bond enthalpies because it is broken minus made. The bonds broken require energy, while forming bonds releases energy.
Sun Jan 19, 2020 5:17 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 6A.23
Replies: 1
Views: 19

Re: 6A.23

Ba(OH)2 is a strong base so it completely dissociates into Ba2+ and OH-. You then calculate the concentrations and use the Kw to find the H3O+ concentration.
Sun Jan 19, 2020 5:11 pm
Forum: Ideal Gases
Topic: concentration
Replies: 5
Views: 42

Re: concentration

I think you could be able to use the PV=nRT to find the concentration because concentration is equal to n/V so if you have the pressure, temperature, and the gas constant you could possibly find the concentration.
Sun Jan 19, 2020 5:06 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: pKa
Replies: 13
Views: 87

Re: pKa

An acid is stronger if it has a lower pKa. It's similar to how a lower pH means an acid is stronger.
Sun Jan 19, 2020 5:04 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Identifying endothermic vs exothermic
Replies: 7
Views: 66

Re: Identifying endothermic vs exothermic

A reaction is exothermic if the products have more energy than the reactants, and it is endothermic if the reactants have more energy than the products. Usually, the reaction would give you a deltaH value if it is asking about temperature. DeltaH would be negative if the reaction is exothermic and p...
Sun Jan 19, 2020 4:59 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: pH vs. pOH
Replies: 13
Views: 131

Re: pH vs. pOH

The pOH is used when you have the concentration of OH- and is calculated the same way you would calculate pH. You can tell if you are calculating for an acid if it is giving off a proton and you are getting the H3O+ concentration. If it is a base, it would accept a proton and give you the OH- concen...
Sat Jan 11, 2020 7:06 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Simplifying cubic equations
Replies: 3
Views: 38

Re: Simplifying cubic equations

In one of the module videos, Professor Lavelle said that a cubic would result in very small values of x, so you just leave the initial concentrations the same for the reactants and plug those numbers into the equilibrium equation to find the concentration of the product.
Sat Jan 11, 2020 7:03 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Effect of pressure on Chemical Equilibrium
Replies: 3
Views: 25

Re: Effect of pressure on Chemical Equilibrium

Pressure affects the volume of a container the reaction takes place in. Higher pressure means less volume and a greater concentration. The concentration is equal to moles/volume, so if the volume is smaller and moles do not change, the concentration will be higher. This causes the reaction to shift ...
Sat Jan 11, 2020 6:59 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Difference between K and Q
Replies: 6
Views: 65

Re: Difference between K and Q

K is the ratio of products to reactants only when the reaction is at equilibrium. Q is the ratio of products to reactants when the reaction is NOT at equilibrium.
Sat Jan 11, 2020 6:55 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: States of matter [ENDORSED]
Replies: 4
Views: 31

Re: States of matter[ENDORSED]

Solids and liquids do not change in concentration much during the reaction, so their concentrations do not affect the reaction much. For example, water is typically used as a solvent and has a larger concentration that does not change much as products are produced.
Sat Jan 11, 2020 6:51 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: When to do ice tables [ENDORSED]
Replies: 4
Views: 46

Re: When to do ice tables[ENDORSED]

You should also make sure you have the equilibrium constant in order to solve the ice table. You then use the K=[Products]/[Reactants] equation to solve for x and find the equilibrium concentrations.
Sun Nov 17, 2019 8:26 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: VSEPR
Replies: 7
Views: 75

Re: VSEPR

I'm pretty sure Lavelle said to just know how to draw the Lewis Structure and then what shape it is and maybe the bond angle.
Sun Nov 17, 2019 8:25 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond angle
Replies: 3
Views: 25

Re: Bond angle

I think we may just need to know the usual angle, such as linear is 180 or tetrahedral is usually 109.5, and then remember that the size can make the angle slightly smaller/bigger.
Sun Nov 17, 2019 8:23 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: np force?
Replies: 2
Views: 21

Re: np force?

Nonpolar molecules usually have London dispersion forces, which are also called Van Der Waals or induced dipole-induced dipole. Some may also have other forces, such as hydrogen bonding or small dipoles, depending on the atoms in the molecule.
Sun Nov 17, 2019 8:19 pm
Forum: Electronegativity
Topic: More electronegative?
Replies: 3
Views: 129

Re: More electronegative?

Electronegativity decreases as you go down the groups. Oxygen is higher on the periodic table than chlorine, so its electronegativity is higher.
Sun Nov 17, 2019 8:18 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles
Replies: 3
Views: 39

Re: Bond Angles

The bond angle should always be smaller because because lone pairs have a stronger repulsion strength than bonding pairs, so the lone pairs should always push the bonded angles closer together.
Mon Nov 11, 2019 4:45 pm
Forum: Ionic & Covalent Bonds
Topic: Water molecules and ionic substances
Replies: 5
Views: 93

Re: Water molecules and ionic substances

Something I learned from my high school chem teacher is that water is polar and is better at dissolving other polar substances and less good at dissolving non-polar substances. Ionic substances tend to be more non-polar because electrons are more unevenly distributed so they break apart more easily ...
Mon Nov 11, 2019 4:34 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: types of intermolecular forces
Replies: 5
Views: 41

Re: types of intermolecular forces

For problems like these, I like to draw out the Lewis structure in order to visualize how the electrons are distributed across the molecule. This helps to figure out what type of interaction the molecule has.
Mon Nov 11, 2019 4:31 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: polar bonds and molecular shape
Replies: 2
Views: 26

Re: polar bonds and molecular shape

In high school, my class learned that molecules with an uneven electron distribution, like water, are polar, while molecules with a more even electron distribution, such as methane, are considered to be non-polar.
Mon Nov 11, 2019 4:25 pm
Forum: Ionic & Covalent Bonds
Topic: Solid v. Liquid v. Gas
Replies: 8
Views: 102

Re: Solid v. Liquid v. Gas

I think Dr. Lavelle was also talking about elements at room temperature. Usually I think they would tell you but if not Mercury and Bromine are the only elements that are liquids at room temperature. The metals and some nonmetals would be solid, and the Noble Gases, Nitrogen, Oxygen, Fluorine, and C...
Sun Oct 27, 2019 5:49 pm
Forum: Trends in The Periodic Table
Topic: 1F.19
Replies: 2
Views: 37

Re: 1F.19

The s-block metals have lower ionizations energies and can more easily lose electrons than the p-block metals. This makes it easier for the s-block metals to react and form bonds.
Sun Oct 27, 2019 5:43 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Effective Nuclear Charge
Replies: 4
Views: 55

Re: Effective Nuclear Charge

Effective nuclear charge affects ionization energy because more protons and pull the electrons closer to the nucleus and make it harder to remove electrons.
Sun Oct 27, 2019 5:37 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Exceptions to Electron Configuration
Replies: 7
Views: 88

Re: Exceptions to Electron Configuration

I know we only use the first row of the d-block for Chem 14A, but I thought that atoms in the same column as Copper and Chromium, like Silver, also filled up the d-shell before the s-shell?
Sun Oct 27, 2019 5:32 pm
Forum: Octet Exceptions
Topic: Exceeding the Octet Rule
Replies: 5
Views: 79

Re: Exceeding the Octet Rule

I think it was meant that in that one particular example it had 10 valence electrons. I'm not sure if it necessarily meant if had to have 10. I was also a little confused as to where he got the 10 though.
Sun Oct 27, 2019 5:28 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge
Replies: 5
Views: 80

Re: Formal Charge

In formal charge, a bond counts as two electrons.
Sun Oct 20, 2019 9:03 pm
Forum: Trends in The Periodic Table
Topic: Study Buddies?
Replies: 8
Views: 105

Re: Study Buddies?

Hi! Thanks for posting this! My email is elenabell2019@gmail.com
Sun Oct 20, 2019 9:00 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Memorizing Wavelengths and Frequencies?
Replies: 2
Views: 35

Memorizing Wavelengths and Frequencies?

So I was curious as to whether we had to know the Lyman and Balmer series or the different frequencies, energies, and wavelengths? There were some questions in the text book asking about the types of radiation and their frequencies and wavelengths. Is there an easy way to memorize it if we have to?
Sun Oct 20, 2019 8:47 pm
Forum: Properties of Electrons
Topic: Energy of Electron
Replies: 3
Views: 75

Re: Energy of Electron

Yes, when the electrons absorb energy when they jump up to a higher energy level and emit energy when they jump down. Also for s-orbitals l=0 and for p-orbitals l=1. The n value is which shell an electron is in such as 1s, 2s, 2p, 3d, etc.
Sun Oct 20, 2019 8:42 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Atomic spectra module question
Replies: 1
Views: 49

Re: Atomic spectra module question

I believe in atomic spectra you can use the E=hv and c=(lambda)(v) equations. Another equation we had for atomic spectra was E=-hR/n^2. I know that isn't a lot of information but I hope it helps a bit.
Sun Oct 20, 2019 8:34 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Exceptions to Orbital Rules
Replies: 8
Views: 116

Re: Exceptions to Orbital Rules

The exceptions we learned is class was the d5 and d10. We learned that these energy states are more stable than their previous states of d4 and d9. Normally, the energy level would increase in numeric order but because atoms like to be stable, the electrons go to the d5 or d10 level instead of the d...
Sun Oct 13, 2019 7:56 pm
Forum: Photoelectric Effect
Topic: Photoelectric Effect
Replies: 2
Views: 34

Re: Photoelectric Effect

Thank you!
Sun Oct 13, 2019 7:53 pm
Forum: Properties of Light
Topic: electron ejection
Replies: 1
Views: 27

Re: electron ejection

Light with long wavelengths cannot eject electrons because longer wavelengths=lower frequency and less energy. Light with short wavelengths can eject electrons because shorter wavelengths=higher frequency and more energy. The electrons need higher energy in order to be ejected.
Sun Oct 13, 2019 7:49 pm
Forum: DeBroglie Equation
Topic: De Broglie's Equation
Replies: 17
Views: 262

Re: De Broglie's Equation

De Broglie's equation requires an object to have a mass, therefore, the equation cannot be used for light because light does not have a mass.
Sun Oct 13, 2019 7:45 pm
Forum: Photoelectric Effect
Topic: Photoelectric Effect
Replies: 2
Views: 34

Photoelectric Effect

Can the photoelectric effect only be used for when an electron jumps down an energy level, or can it also be used when an electron jumps up an energy level?
Sun Oct 13, 2019 7:39 pm
Forum: Properties of Light
Topic: De Broglie's Equation
Replies: 4
Views: 40

Re: De Broglie's Equation

De Broglie's equation is used to calculate the wavelength of a of a moving object. The idea is that all matter has wavelike properties, however, it is only noticeable for small moving objects.