## Search found 61 matches

Mon Mar 11, 2019 9:11 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium Constants and Solubility
Replies: 2
Views: 132

### Re: Equilibrium Constants and Solubility

Higher equilibrium constants indicate higher rates of solubility because for a solubility reaction, the products are the dissolved ions and the reactants are the undissolved solute.
Mon Mar 11, 2019 8:49 pm
Forum: Administrative Questions and Class Announcements
Topic: Final Exam Topics
Replies: 8
Views: 347

### Re: Final Exam Topics

There is no lecture on Friday (it is a review day) and there are only two slides on Wednesday, but all that is covered up to and including the information given on Wednesday IS fair game for the final generally.
Mon Mar 11, 2019 8:48 pm
Forum: General Rate Laws
Topic: Rate definition
Replies: 3
Views: 152

### Re: Rate definition

The rate constant is represented by a lowercase k. Being a constant, it does not change if the concentrations of the reactants change; it is constant for the reaction at that temperature. On the other hand, the rate of the reaction is what k times concentrations of reactants equals. In other words, ...
Mon Mar 04, 2019 6:49 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: electrolytic cell
Replies: 4
Views: 476

### Re: electrolytic cell

This notation is just a technicality because in an electrolytic cell, the electrons in the anode are being drawn towards the positive external charge of what is supplying energy to the chemical reaction. Meanwhile, electrons are being pushed towards the cathode on the other side, so they write it as...
Mon Mar 04, 2019 6:40 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Different k values
Replies: 3
Views: 178

### Different k values

Why can the value of k be different for two versions of the same reaction with the same concentration and temperature?
Mon Mar 04, 2019 6:32 pm
Forum: General Rate Laws
Topic: Differential vs. Integrated Rate Law
Replies: 2
Views: 106

### Re: Differential vs. Integrated Rate Law

Differential rate law is where the rate is a function of [R]. Integrated rate law is where rate is a function of time.
Mon Feb 25, 2019 8:53 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Question 14.25 (Sixth Edition)
Replies: 3
Views: 167

### Re: Question 14.25 (Sixth Edition)

Remember that a metal having a more negative (or less positive) reduction potential means it is a stronger reducing agent (which means it is the species that is doing the reducing). For the first part of the problem, all the metals except Cu have negative reduction potentials, so compare those value...
Mon Feb 25, 2019 8:45 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Order of redox reaction in a galvanic cell
Replies: 1
Views: 100

### Re: Order of redox reaction in a galvanic cell

When writing the cell diagram for a galvanic cell, the convention is to put the cathode on the right and the anode on the left, if that’s what you’re referring to. That would influence which half reaction goes where.
Mon Feb 25, 2019 8:44 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Standard reaction Gibbs free energy
Replies: 1
Views: 128

### Re: Standard reaction Gibbs free energy

Standard Gibbs Free Energy is the value of Gibbs Free Energy at standard conditions. It does not change as the reaction proceeds, which is nice because Gibbs Free Energy does. When calculating standard Gibbs Free Energy, use standard cell potential.
Sat Feb 23, 2019 12:42 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 4J7
Replies: 1
Views: 119

### Re: 4J7

∆G, ∆S, and ∆H are all expressed in terms of one mole of reaction. You already account for the number of moles involved when you used the S°m, ∆H°f, and ∆G°f for each reactant/product, so the result you calculate is in terms of the reaction as a whole.
Sat Feb 23, 2019 12:36 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Daniell cell
Replies: 1
Views: 110

### Re: Daniell cell

I think it’s essentially the same thing as a Galvanic/electrochemical cell, just another name for it.
Sat Feb 23, 2019 12:34 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: electrochemical vs. electrolytic
Replies: 2
Views: 123

### Re: electrochemical vs. electrolytic

An electrochemical cell, also known as a Galvanic cell, converts chemical energy into electrical energy. An electrolytic cell does the opposite, converting electrical energy into chemical energy.
Tue Feb 12, 2019 8:54 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 7th ed. 4I9
Replies: 2
Views: 166

### Re: 7th ed. 4I9

No work is done in free expansion because there is no pressure against which the gas expands and does work. But you don’t need to figure out IF it’s free expansion because the problem will always indicate this, as this one has.
Tue Feb 12, 2019 8:48 pm
Forum: Calculating Work of Expansion
Topic: 4.7
Replies: 2
Views: 153

### Re: 4.7

In this case, I think because the reaction occurs at 25°C, H2O is a liquid because it condenses after it is formed.
Tue Feb 12, 2019 8:44 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Irreversible Entropy Changes
Replies: 1
Views: 113

### Re: Irreversible Entropy Changes

Because ∆S = qrev/T, if you’re looking for change in entropy due to temperature change, you can substitute out q for nC∆T, then simplify to get ∆S = nCln(T2/T1).
Sat Feb 09, 2019 12:42 pm
Forum: Calculating Work of Expansion
Topic: Derivatives and Integrals
Replies: 5
Views: 241

### Re: Derivatives and Integrals

They might give you the basic equation, ∆S = q/T and expect you to evaluate for the changing value specified in the problem, but as long as you have the formulas or the relationships between variables (like q = nC∆T) memorized, you should be able to work backwards to show the integration/get the for...
Sat Feb 09, 2019 12:33 pm
Forum: Calculating Work of Expansion
Topic: Units
Replies: 7
Views: 255

### Re: Units

It is important to know that there’s a slight difference between bars and atm (1.013 bar = 1 atm) but from the homework problems it seems rare that they give something in terms of bars and you need to convert to atm. Atm is also helpful because of the useful conversion 101.325 J/L*atm.
Sat Feb 09, 2019 12:27 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Systems
Replies: 6
Views: 483

### Re: Systems

Open systems can exchange both matter and energy with the surroudings. I think of it like an open, uninsulated container. Closed systems can exchange just energy. So no matter can be added to change the system, but energy can be exchanged with the surroundings, so basically any closed container. Iso...
Thu Jan 31, 2019 12:40 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Piston Problem in class
Replies: 2
Views: 184

### Re: Piston Problem in class

The system has internal energy, ∆U, which is q + w. Therefore, the system has the capacity to do work. In the particular problem I believe you are referring to, we are letting the system do work on surroundings, meaning it is pushing the piston out. Were the piston to be compressed, the volume would...
Thu Jan 31, 2019 12:04 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 2
Views: 139

### Re: Bond Enthalpies

Yes, they are both given in terms of mol, so you have to multiply by the stoichiometric coefficients if you want to find the enthalpy of the reaction based off of bond enthalpies or standard enthalpies of formation.
Thu Jan 31, 2019 12:00 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Heat Capacity
Replies: 1
Views: 100

### Re: Heat Capacity

For the slopes I believe. At the slopes, increasing heat will actually cause the substance to change temperature, whereas at phase changes (the flat portions), increasing heat does not change the temperature, which would make it difficult to determine heat capacity because it is based on temperature...
Mon Jan 21, 2019 10:44 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 6th edition 12.69 Ka
Replies: 3
Views: 171

### Re: 6th edition 12.69 Ka

The value of Ka will probably be given to you on the test. Also you will probably need to know how to write a reaction similar to this. Basically, whenever a salt with a highly charged small cation is dissolved, the cation surrounds itself with the maximum number of water molecules, 6, which is what...
Mon Jan 21, 2019 10:34 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Salt
Replies: 4
Views: 184

### Re: Salt

Salt is a product in a neutralization reaction. However, the same salt formed from a neutralization reaction, or another other acidic/basic salt for that matter, can be dissolved in water and may affect pH.
Mon Jan 21, 2019 10:28 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: pKa
Replies: 2
Views: 135

### Re: pKa

pKa is the negative log of the Ka, which is just the K value but for a weak acid.
Mon Jan 14, 2019 7:36 pm
Forum: Ideal Gases
Topic: Kc and Kp
Replies: 6
Views: 147

### Re: Kc and Kp

According to the textbook, technically if you are asked for K and everything is in gas phase, you’re supposed to write it with partial pressures. However, the problem will likely specify which they are looking for, or will give values in concentration or partial pressure. In the event they give you ...
Mon Jan 14, 2019 7:28 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: the value of equilibrium constant
Replies: 3
Views: 146

### Re: the value of equilibrium constant

No. Therefore, if it tells you to calculate the reaction quotient, Q, and compare it to a given K for example, make sure you use partial pressure or concentration depending on if you’re given Kp or Kc.
Mon Jan 14, 2019 6:49 pm
Forum: General Science Questions
Topic: molarity question
Replies: 2
Views: 183

### Re: molarity question

In pure water, the H3O+ and OH- concentrations are equal. Therefore, because they gave you Kw, you can find each of the concentrations by square rooting the given value.
Mon Jan 07, 2019 10:37 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Aqueous in K expression
Replies: 4
Views: 178

### Re: Aqueous in K expression

Just make sure the units are the same if you are given a gas and an aqueous solution.
Mon Jan 07, 2019 10:33 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Heterogeneous equilibrium
Replies: 3
Views: 162

### Re: Heterogeneous equilibrium

You would have to convert one of the given values to match the units of the other. Because an aqueous solution does not have a partial pressure, you should convert the partial pressure of the gas to a concentration.
Mon Jan 07, 2019 8:19 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Concentrations of products/reactants
Replies: 6
Views: 251

### Re: Concentrations of products/reactants

It is a ratio of the equilibrium concentrations.
Thu Dec 06, 2018 2:38 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: How can H2O bond with a metal?
Replies: 1
Views: 114

### Re: How can H2O bond with a metal?

H20 is polar because O has a delta negative partial charge. This causes it to have attraction to delta positive atoms, such as the metal atom it binds to.
Thu Dec 06, 2018 2:34 pm
Forum: Polyprotic Acids & Bases
Topic: Identifying polyprotic acids and bases
Replies: 2
Views: 332

### Re: Identifying polyprotic acids and bases

Some common examples of polyprotic acids are: H2SO4, H2CO3 and H3PO4. These can donate more than one proton.
Thu Dec 06, 2018 2:27 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: H2O Denticity
Replies: 1
Views: 107

### Re: H2O Denticity

Dentate refers to the number of places the ligand can attach to the central atom. Water has two lone pairs, but because they are both on oxygen, it cannot bind in two places, only on one atom.
Mon Nov 26, 2018 10:31 pm
Forum: Hybridization
Topic: Question from textbook
Replies: 4
Views: 208

### Re: Question from textbook

When you draw the Lewis structure, the molecule is shown to have two lone pairs on Br in addition to the three bonds Br forms with the three F. Because each lone pair represents another region of electron density, five hybridized orbitals are needed and there are five sp3d orbitals.
Mon Nov 26, 2018 10:16 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Polarizability
Replies: 3
Views: 226

### Re: Polarizability

Polarizability refers to how easily an atom’s electrons can be distorted by polarizing atoms. The lower the electronegativity, the higher the polarizability, because the atom’s electrons are not held as tightly. Likewise, the larger the atom, the higher the polarizability.
Mon Nov 26, 2018 10:11 pm
Forum: Hybridization
Topic: bond angles and increasing s-character
Replies: 2
Views: 277

### Re: bond angles and increasing s-character

S-character basically refers to what fraction of the hybridized orbital is made up from the s-orbital. For example, sp has greater s-character than sp^2. Because there are fewer sp hybridized orbitals than there are sp^2 hybridized orbitals, 2 versus 3, as the s-character increases and the number of...
Sun Nov 25, 2018 10:19 pm
Forum: Hybridization
Topic: pi bond breaking
Replies: 1
Views: 72

### Re: pi bond breaking

I remember either hearing or reading that the breaking of pi bonds is important in vision, but that’s the only specific example I can recall. The presence of pi bonds is important in determine the shape of a molecule because it is stiffer than a sigma bond, which is likely important for proteins, as...
Sun Nov 25, 2018 10:14 pm
Forum: Hybridization
Topic: Question 4.31 (Sixth Edition)
Replies: 1
Views: 77

### Re: Question 4.31 (Sixth Edition)

This question is asking for how the hybrid orbitals would likely be arranged three dimensionally around the nucleus. You can determine this by looking at the number of regions of electron density and then determining what shape a molecule in which all the regions had bonds would be. For example, the...
Sun Nov 25, 2018 10:06 pm
Forum: Hybridization
Topic: hybridization
Replies: 2
Views: 156

### Re: hybridization

In some cases, you can look at the number of electrons an atom has and where those electrons are located to determine how many regions of electron density there can be.
Wed Nov 14, 2018 9:54 pm
Forum: Ionic & Covalent Bonds
Topic: Hydrogen Bond
Replies: 7
Views: 475

### Re: Hydrogen Bond

As a side note, there are both intermolecular and intramolecular hydrogen bonds, in that there are interactions involving hydrogen between separate molecules and within molecules. Intramolecular hydrogen bonds are just covalent bonds involving hydrogen.
Mon Nov 12, 2018 10:33 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 2E5 HW Problem on 7th Edition
Replies: 2
Views: 93

### Re: 2E5 HW Problem on 7th Edition

This seemed like a good explanation!
viewtopic.php?t=1250
Mon Nov 12, 2018 9:30 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Molecules with Lone Pairs
Replies: 1
Views: 110

### Re: Molecules with Lone Pairs

Due to electron repulsion, the presence of lone pairs alters the shape of the model. They push the atoms away from them, which causes the angles between the atoms to be different. You can tell whether or not the central atom has any lone pairs from the resulting angle between the atoms, so it’s more...
Thu Nov 08, 2018 2:05 pm
Forum: Resonance Structures
Topic: Resonance Structures
Replies: 3
Views: 288

### Re: Resonance Structures

The actual structure of the molecules tends to be a hybrid of multiple resonance structures because it is the most stable.
Thu Nov 08, 2018 2:00 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: Difference between the bonds
Replies: 4
Views: 292

### Re: Difference between the bonds

Dipole-dipole occurs between two molecules that are polar on their own. Dipole-induced dipole occurs between a polar and non-polar molecule in which the polar molecule causes the non-polar molecule to exhibit polar character.
Thu Nov 08, 2018 11:55 am
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Electron Configuration for Ions
Replies: 2
Views: 307

### Re: Electron Configuration for Ions

The 3d orbital is closer to the nucleus than the 4s orbital, making the electrons harder to remove once they have been put in there. This is why the 3d is written before the 4s in the atoms that have a 3d shell and why electrons in 3d do not move to the 4s orbital when it is vacant. Therefore, in th...
Mon Oct 29, 2018 11:13 pm
Forum: Trends in The Periodic Table
Topic: 2.67 Ed 6, electron afinity
Replies: 2
Views: 159

### Re: 2.67 Ed 6, electron afinity

This has to do with the orbitals. All three of N’s p orbitals already have one e- each in them. C has one open p orbital, so it has a higher electron affinity because it has space to put another e-. N does not have the space unless it pairs electrons, which would cause it to have higher energy due t...
Mon Oct 29, 2018 11:08 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Stable Condition
Replies: 8
Views: 2004

### Re: Stable Condition

I’m not sure if this is what you’re asking, but for the second part of your question, a molecule is negative when it has more electrons than it does positive charge from protons to even it out and positive when it has fewer electrons than it does protons as a whole.
Mon Oct 29, 2018 10:12 pm
Forum: Ionic & Covalent Bonds
Topic: 2A.11 7th Edition
Replies: 1
Views: 99

### Re: 2A.11 7th Edition

The problem is asking you to find the metal 3+ ion with the given electron configuration. In the case of the first problem, [Ar]3d^6, you can see that the ion has lost both electrons from the 4s orbital, as the 4s orbital fills before the 3d but has not been written on the ground state configuration...
Wed Oct 24, 2018 12:01 am
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Uncertainty of an Electron's Velocity & Speed of Light
Replies: 4
Views: 290

### Re: Uncertainty of an Electron's Velocity & Speed of Light

Nothing with rest mass can have a higher velocity than the speed of light. Because an electron’s mass can be determined, as it exists when it is at rest, it is said to have rest mass. Light, on the other hand, ceases to exist when it is not moving and can therefore not be weighed, therefore having n...
Tue Oct 23, 2018 11:57 pm
Forum: Properties of Light
Topic: Electromagnetic Spectrum
Replies: 5
Views: 333

### Re: Electromagnetic Spectrum

It’s probably helpful to know some of the electromagnetic spectrum, specifically around the visible light and UV range. The order of the spectrum is expressed in terms of the wavelengths of each type of light. So from the longer wavelength (and lower energy) to shorter (and higher energy) would be: ...
Tue Oct 23, 2018 11:47 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Nodal Planes
Replies: 6
Views: 253

### Re: Nodal Planes

S-orbitals fully encompass the area around the nucleus. There is no area surrounding the nucleus in an s-orbital where the probability of finding an electron is 0, which is what a nodal plane defines, so there is no nodal plane for the s-orbital.
Tue Oct 16, 2018 1:21 pm
Forum: Properties of Light
Topic: Mass of Light
Replies: 5
Views: 275

### Re: Mass of Light

Additionally, light does not exist when it is not moving. Unlike an object like an electron, which is said to have a “rest mass”, light has no mass when it is not moving because it doesn’t exist when it is resting. Something must be in existence when it is not moving for its mass to be measured. Obj...
Tue Oct 16, 2018 11:38 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Heisenberg's Indeterminacy Equation
Replies: 3
Views: 132

### Re: Heisenberg's Indeterminacy Equation

Delta p is the uncertainty in the momentum of the electron or whatever is being studied, with units kg*m*s^-1. Delta v is the uncertainty of the velocity of the object being studied, with units m*s^-1. Delta v is related to delta p by the equation delta p=mass times delta v. Also the values of delta...
Tue Oct 16, 2018 11:30 am
Forum: Properties of Light
Topic: Vocab
Replies: 5
Views: 251

### Re: Vocab

Additionally, in the case of the energy levels of electrons being quantized, it means that they have to have the energy at a distinct level, ie. n=1 or n=2, and cannot have levels of energy between those distinct levels.
Tue Oct 09, 2018 9:47 pm
Forum: Properties of Light
Topic: Planck's constant
Replies: 5
Views: 278

### Re: Planck's constant

I believe Lavelle said that Planck’s constant is the proportionality constant derived from experimental data on the relationship between energy and frequency, since energy and frequency are proportional. If you were to graph them both on a regular coordinate plane, the data points would be in a stra...
Tue Oct 09, 2018 9:12 pm
Forum: Molarity, Solutions, Dilutions
Topic: Molarity
Replies: 4
Views: 407

### Re: Molarity

V1 should not be 0.150L because the problem says that only 20.00mL of the 0.211M solution is used in the dilution. Therefore, V1 should be 0.020L.
Tue Oct 09, 2018 9:03 pm
Forum: Einstein Equation
Topic: 7th 1B.15 When do you use E = hv or Ek = 1/2m v^2?
Replies: 4
Views: 411

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

It looks like the problem gave the electron volts for the (b) section of the Example 1B.3. They went from Joules from electron volts using a conversion factor. The Ek function is used specifically to find the kinetic energy of an ejected electron, otherwise known as the excess energy the photon tran...
Wed Oct 03, 2018 9:44 pm
Forum: Empirical & Molecular Formulas
Topic: Molar Mass: E21
Replies: 3
Views: 189

### Re: Molar Mass: E21

Start by calculating the molar mass of the compound. The molar mass will be in grams/mol.
Tue Oct 02, 2018 10:25 pm
Forum: Molarity, Solutions, Dilutions
Topic: Question G23
Replies: 3
Views: 154

### Re: Question G23

Find the moles of Cl- in each compound by using stochiometry and then add the two and divide by the total volume.
Mon Oct 01, 2018 11:33 pm
Forum: SI Units, Unit Conversions
Topic: Conversion Factors
Replies: 3
Views: 140

### Re: Conversion Factors

What about when you are calculating molar mass and the problem gives you a rounded mass for an element, such as 16 g for oxygen or 1 g for hydrogen? Are those also considered conversion factors or do you use them when determining sig figs?
Mon Oct 01, 2018 11:26 pm
Forum: SI Units, Unit Conversions
Topic: Conversion Factors
Replies: 3
Views: 140

### Conversion Factors

If a conversion factor is necessary in solving a problem, do the significant figures in that conversion factor matter?