## Search found 61 matches

Fri Mar 15, 2019 10:35 am
Forum: General Rate Laws
Topic: Rate laws
Replies: 1
Views: 73

### Rate laws

For all rate laws do we only look at one reactant at a time to simplify the math? For example, for the integrated and differential rate laws there is only one variable A that represents the concentration of reactant. When there is a chemical reaction with two reactants how do we know which one to fo...
Fri Mar 15, 2019 10:29 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: ion-selective electrodes
Replies: 1
Views: 91

### Re: ion-selective electrodes

I think we should just have a general understanding of how they work (how they measure the concentration of H+).
Fri Mar 15, 2019 10:21 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Kinetics v. Thermodynamics
Replies: 1
Views: 256

### Re: Kinetics v. Thermodynamics

I believe kinetic stability has to do with having a large activation energy, meaning the reactant is not as likely to overcome the energy barrier and form the product. Thermodynamic stability has to do with whether or not the change in Gibbs free energy is positive or negative, and whether the react...
Fri Mar 08, 2019 10:03 am
Forum: Second Order Reactions
Topic: graph
Replies: 2
Views: 155

### Re: graph

Also for second order reactions, the straight line graph will have a positive slope, while first order will have a negative slope.
Fri Mar 08, 2019 10:00 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: k & K
Replies: 18
Views: 811

### Re: k & K

To add to the previous answer, K in thermodynamics is the equilibrium constant, which describes the concentrations of reactants and products at equilibrium, and doesn’t have anything to do with the speed of the reaction.
Fri Mar 08, 2019 9:57 am
Forum: Zero Order Reactions
Topic: Differentiating Zero and One Order Reactions
Replies: 2
Views: 140

### Re: Differentiating Zero and One Order Reactions

You would look at the labels for the axes. For zero order, the straight line graph will be concentration vs time, but for first order it will be ln(concentration) vs time.
Sat Mar 02, 2019 2:49 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Activation Energy
Replies: 2
Views: 137

### Re: Activation Energy

I think with the example of diamond to graphite, since we know from experience that diamonds don't spontaneously convert to graphite, we can assume that the activation energy is too high for it to be kinetically spontaneous. However, unless it is another example that we would easily know, I don't th...
Sat Mar 02, 2019 2:46 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: liquid and gaseous states in a cell diagram
Replies: 3
Views: 156

### liquid and gaseous states in a cell diagram

If we have different states on one side of the redox reaction, do we list them with a comma in the cell diagram or a line separating them? Also, is there a specific order we have to follow when listing things in cell diagrams (besides the electrodes being on the outsides)?
Sat Mar 02, 2019 2:44 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Order of a Reaction
Replies: 2
Views: 118

### Re: Order of a Reaction

Dr. Lavelle said we would talk about this more next week, but you need the order of a reaction to determine the reaction mechanism.
Fri Feb 22, 2019 7:32 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: electromotive force vs cell potential vs voltage
Replies: 1
Views: 82

### electromotive force vs cell potential vs voltage

Can someone explain the difference between electromotive force, cell potential, and voltage? I'm a bit confused about the theory behind the Galvanic cell.
Fri Feb 22, 2019 7:30 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: delta G at equilibrium
Replies: 1
Views: 80

### delta G at equilibrium

Why is delta G always 0 at equilibrium? I think I vaguely understand this but I would appreciate if someone explained it.
Fri Feb 22, 2019 7:21 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Homework Questions on Test 2
Replies: 1
Views: 83

### Re: Homework Questions on Test 2

The test is on all topics on Gibbs free energy and electrochemistry up to but not including the Nernst equation, so that includes the end of chapter 9, the beginning of 11, and 14.
Wed Feb 13, 2019 12:02 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Constant pressure
Replies: 1
Views: 277

### Re: Constant pressure

if pressure is constant, we know that w=-PdeltaV and we know that q=deltaH
Wed Feb 13, 2019 11:58 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Midterm
Replies: 4
Views: 206

### Re: Midterm

I think we should be familiar with them since acid/base equilibria is on the midterm
Wed Feb 13, 2019 11:57 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Residual vs positional entropy
Replies: 2
Views: 141

### Re: Residual vs positional entropy

I think for the purpose of the class, they are the same thing
Sat Feb 09, 2019 10:07 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: ΔS = nRln(v2/v1)
Replies: 1
Views: 142

### Re: ΔS = nRln(v2/v1)

I'm not sure, but I think it's because R is equal to k b multiplied by N A . Since the N A is actually the exponent within the natural log, you can take it out of the natural log and multiply it with K b , which is equal to R. The n comes from the fact that since we used Avagadro's number we are cal...
Sat Feb 09, 2019 9:58 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Predict entropy change
Replies: 3
Views: 126

### Re: Predict entropy change

From what I know, the difference in entropy between a gas and a liquid is greater than the difference in entropy between a liquid and a solid. Since gas molecules have many more possible positions than molecules in the liquid state, it's safe to say that gases take precedence.
Sat Feb 09, 2019 9:56 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Examples
Replies: 1
Views: 85

### Re: Examples

An example of an open system: an open beaker, since matter and energy can exchange with the surroundings. A closed system: a closed beaker, since only energy (in the form of heat) can exchange with the surroundings. It's hard to find an example of a perfectly isolated system, but like you said, a cl...
Fri Feb 01, 2019 3:11 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: 1st law of thermodynamics
Replies: 7
Views: 249

### 1st law of thermodynamics

How does the universe being an isolated system prove the first law of thermodynamics?
Fri Feb 01, 2019 3:08 pm
Forum: Calculating Work of Expansion
Topic: formula for work with integral
Replies: 3
Views: 125

### formula for work with integral

Hi guys, can someone explain to me what Lavelle showed us in lecture with the work formula as a definite integral? Was that just to derive the work formula or will we be using that expression to solve questions?
Fri Feb 01, 2019 7:33 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Enthalpy vs Internal energy
Replies: 5
Views: 174

### Re: Enthalpy vs Internal energy

http://chemed.chem.purdue.edu/genchem/t ... emical.php
this page has a section that explains the difference between the two
Wed Jan 23, 2019 9:15 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kw - applies to solutions other than 100% water?
Replies: 3
Views: 119

### Re: Kw - applies to solutions other than 100% water?

I think we are supposed to assume the solvent is water. Also, I think you can always use Kw to relate [H3O+] and [OH-].
Wed Jan 23, 2019 9:10 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Volume and Le Chatelier's Principle
Replies: 5
Views: 199

### Re: Volume and Le Chatelier's Principle

Just to add on, it's because the concentrations of all the reactants and products increase proportionally when you change the volume if there is an equal number of moles on both side, so the equilibrium stays the same.
Wed Jan 23, 2019 9:06 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Adding a Liquid or Solid to an Equation
Replies: 2
Views: 189

### Re: Adding a Liquid or Solid to an Equation

I think in this case, we treat water as a reactant, and not just a solvent. In the photosynthesis reaction, the water is split to provide electrons for the electron transport chain, so increasing the amount of water will affect the equilibrium.
Thu Jan 17, 2019 8:43 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Hydronium Concentration
Replies: 3
Views: 138

### Re: Hydronium Concentration

Just to add on, there is already an [h3O+] of 10^-7 present in the water, and the total [h30+] even with the weak acid ends up being about the same as neutral water.
Thu Jan 17, 2019 8:38 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Autoprotolysis
Replies: 2
Views: 228

### Re: Autoprotolysis

According to wikipedia, "Any solvent that contains both acidic hydrogen and lone pairs of electrons to accept H+ can undergo autoprotolysis." But I think we only focus on the autoprotolysis of water in class.
Thu Jan 17, 2019 8:31 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Weak acids
Replies: 2
Views: 106

### Re: Weak acids

I was also wondering this. I think we don't have to, since the change from the acid is substantially larger than the original [H3O+] of water, but I'm not sure.
Thu Jan 10, 2019 7:07 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 6th edition 11.23
Replies: 1
Views: 67

### 6th edition 11.23

Can someone share how they solved 11.23? I think I have the concept down but I can't seem to get the right answer.
Thu Jan 10, 2019 6:55 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: degree symbol over some variables [ENDORSED]
Replies: 1
Views: 73

### Re: degree symbol over some variables[ENDORSED]

I believe it means standard lab conditions (solutes at 1M, gases at 1 atm)
Thu Jan 10, 2019 6:52 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K vs Kp [ENDORSED]
Replies: 4
Views: 356

### K vs Kp[ENDORSED]

If an equation involves gases only and we are given the equilibrium constant K, can we assume that they mean Kp?
Sat Dec 08, 2018 10:04 pm
Forum: Lewis Acids & Bases
Topic: Lewis acids and pH
Replies: 2
Views: 618

### Lewis acids and pH

How do Lewis bases/acids affect the pH of a solution? If they are bases, they should cause the OH- concentration to increase or the H+ concentration to decrease. If they are acids, the opposite. However, I don't see how they can do that if they are simply electron acceptors/donors. Can someone expla...
Tue Dec 04, 2018 8:23 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: strong or weak base
Replies: 3
Views: 275

### Re: strong or weak base

Also Dr. Lavelle mentioned in lecture that when you see nitrogen in a compound, it's usually a weak base.
Tue Dec 04, 2018 8:21 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: K
Replies: 3
Views: 143

### Re: K

It is a constant used to show the equilibrium of a reaction. Ka refers to acid dissociation, while Kb refers to bases.
Tue Dec 04, 2018 8:16 pm
Forum: General Science Questions
Topic: Can We Take The Final In Pencil?
Replies: 14
Views: 773

### Re: Can We Take The Final In Pencil?

Since the midterm was pen only, I think the final will also be the same way.
Tue Nov 27, 2018 4:37 pm
Forum: Sigma & Pi Bonds
Topic: Pi bond concepts
Replies: 4
Views: 194

### Re: Pi bond concepts

Each p orbital has two "lobes" that extend in opposite directions. So the parts of the bond that extend up and down are actually between 1 set of p orbitals.
Tue Nov 27, 2018 3:51 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Determining Central Atom
Replies: 2
Views: 228

### Re: Determining Central Atom

I thought carbon was the central atom in HCN?
Tue Nov 27, 2018 3:48 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: how to determine coordination number
Replies: 1
Views: 38

### how to determine coordination number

I don't know if Lavelle went over this in lecture, but can someone explain why the transition metal cations we talked about in class form 6 coordinate covalent bonds? Does it have to do with the number of valence electrons the metal has?
Tue Nov 27, 2018 3:46 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: mechanisms behind hydrates
Replies: 1
Views: 63

### mechanisms behind hydrates

Can someone explain why hydrates form around coordination complexes?
Tue Nov 27, 2018 3:44 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Determining Bond Angle
Replies: 3
Views: 70

### Re: Determining Bond Angle

You first should consider the electron arrangement (tetrahedral) to get an estimate of the angle being 109.5. However, you should take into consideration that since the shape is actually trigonal pyramidal and there are lone pairs, the angle will be slightly less than 109.5, since lone pairs have mo...
Tue Nov 27, 2018 3:41 pm
Forum: Coordinate Covalent Bonds
Topic: Difference between coordinate covalent and covalent bond
Replies: 6
Views: 3547

### Re: Difference between coordinate covalent and covalent bond

In a coordinate covalent bond, one electron rich species donates both electrons to the bond. In a normal covalent bond, one electron comes from each species. However, they are both covalent bonds because they are sharing electrons.
Thu Nov 15, 2018 4:39 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: VSEPR model
Replies: 3
Views: 139

### VSEPR model

Does anyone know why double bonds and triple bonds are treated the same way as single bonds in the VSEPR model? And even though the VSEPR model doesn't distinguish between types of bonds, do double/triple bonds actually affect the shape of the molecule?
Thu Nov 15, 2018 4:25 pm
Forum: Dipole Moments
Topic: Dipoles
Replies: 2
Views: 66

### Re: Dipoles

A molecule has a dipole when it has an area of partial positive and partial negative charge. Polar covalent bonds have dipoles, since one atom pulls on the electrons more and becomes partially negative as a result. Other nonpolar molecules can have induced dipoles, which are very temporary and weak,...
Tue Nov 13, 2018 5:16 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles [ENDORSED]
Replies: 2
Views: 92

### Re: Bond Angles[ENDORSED]

That depends on the molecular geometry of the molecule. The shape of a molecule can be octahedral, but instead of all 6 of the groups bonded to the central atom being atoms, they can also be lone pairs. This changes the molecular geometry from octahedral, to square pyramid, to square planar, to t-sh...
Thu Nov 08, 2018 5:01 pm
Forum: Bond Lengths & Energies
Topic: Affect of direction of a bond relative to other bonds on bond length
Replies: 1
Views: 120

### Re: Affect of direction of a bond relative to other bonds on bond length

I know that the shape influences the bond angle but I don't think it influences the bond length. I think only things like the identity of the atoms being bonded and the number of electrons being shared would affect the bond length.
Thu Nov 08, 2018 4:55 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: Induced dipoles
Replies: 2
Views: 92

### Induced dipoles

Can someone explain to me exactly how a molecule with a temporary dipole induces dipoles in other molecules it interacts with?
Thu Nov 08, 2018 4:51 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: Interaction Potential Energy and Distance
Replies: 1
Views: 52

### Re: Interaction Potential Energy and Distance

If distance is inversely proportional to the interaction potential energy, that means as distance decreases (molecules get closer) they do have higher potential energy.
Wed Oct 31, 2018 7:52 pm
Forum: Ionic & Covalent Bonds
Topic: Removing the second electron
Replies: 8
Views: 275

### Re: Removing the second electron

Once the first electron is removed, the atom becomes a positive ion. It has an overall positive charge, so removing another electron from it would be much harder than removing an electron from a neutral atom due to the electrostatic attraction between the nucleus and electrons.
Wed Oct 31, 2018 7:48 pm
Forum: Ionic & Covalent Bonds
Topic: Valence electrons
Replies: 2
Views: 151

### Re: Valence electrons

In the outermost shell, n=4, manganese has 7 valence electrons because it has 2 electrons in the s subshell, and 5 in the d subshell. Usually when we talk about bonding and the octet rule, we look at only the s and p orbitals, but since manganese is a transition metal, we also look at the d subshell.
Wed Oct 31, 2018 7:42 pm
Forum: Lewis Structures
Topic: Most stable lewis
Replies: 1
Views: 82

### Re: Most stable lewis

All resonance structures by definition are equally likely to occur, so they're all equally stable. To decide what Lewis structure in general is the most stable for a molecule, use the formal charges. The Lewis structure with the most formal charges of 0 is the most stable.
Wed Oct 24, 2018 6:53 pm
Forum: *Shrodinger Equation
Topic: Shrodinger Equation on Outline
Replies: 2
Views: 408

### Re: Shrodinger Equation on Outline

So the Schrodinger equation is a model to describe electrons in an atom based on their wavelike properties and the Heisenberg uncertainty principle. I don't think we are supposed to be able to completely understand the mechanics behind it, since it would probably involve a lot of complicated math. T...
Wed Oct 24, 2018 6:44 pm
Forum: Trends in The Periodic Table
Topic: Periodic Table 2.85
Replies: 1
Views: 73

### Re: Periodic Table 2.85

Because as energy levels increase, the energy difference between one and the next decreases. This means there is less of a clear distinction between which subshell has a lower energy and therefore should be filled first.
Wed Oct 24, 2018 6:41 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 2.33 6th Edition: Electron Transitions
Replies: 1
Views: 73

### Re: 2.33 6th Edition: Electron Transitions

I'm not sure, but I think it's because orbitals aren't rigid structures, but rather probability distributions of where the electron could be. When the electron gets excited, it moves away from the nucleus to a higher orbital, meaning that two of the three electrons are farther from the nucleus, incr...
Thu Oct 18, 2018 3:08 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Orbital Interaction
Replies: 2
Views: 91

### Re: Orbital Interaction

To add on to what was said before, so when two atoms bond, they interact with each others' electrons. So atoms can't interact if there are nodal planes, where there are no electrons, in specific areas.
Thu Oct 18, 2018 3:02 pm
Forum: Properties of Light
Topic: Tip for frequency equation
Replies: 4
Views: 161

### Re: Tip for frequency equation

Thu Oct 18, 2018 2:46 pm
Forum: *Shrodinger Equation
Topic: dz orbital
Replies: 2
Views: 79

### Re: dz orbital

I think he meant that the area within the cone up to the boundary of the cone is an area of reactivity, but the cone itself is a nodal plane.
Wed Oct 10, 2018 4:22 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: 6th edition 1.13 part A
Replies: 1
Views: 74

### 6th edition 1.13 part A

Can someone show me how they worked through question 13 in the 6th edition chapter 1? Specifically part A, since the others build off of it. I tried plugging the numbers into the Rydberg equation and I ended up with the wrong wavelength.
Wed Oct 10, 2018 4:11 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg formula
Replies: 1
Views: 62

### Rydberg formula

I'm confused about the Rydberg formula for calculating the wavelength/frequency of light emitted as a hydrogen electron changes energy levels. In the textbook, it is defined as v (frequency) = R(1/n 1 2 - 1/n 2 2 ). However, when I looked online for more information, almost every online source repla...
Wed Oct 10, 2018 3:45 pm
Forum: Properties of Light
Topic: Photoelectric Effect PostMod #34
Replies: 1
Views: 91

### Re: Photoelectric Effect PostMod #34

Use the wavelength of 194 nm to find the energy of the photons being shined at the metal, which I found to be 1.02x10^-18 J. When the question is asking for the maximum kinetic energy of an emitted electron, I believe it's just asking for the E k that we have calculated before in class. We know that...
Thu Oct 04, 2018 3:23 pm
Forum: SI Units, Unit Conversions
Topic: SI Units
Replies: 7
Views: 245

### Re: SI Units

I'm not 100% sure, but I think if the question asks for grams, we should keep our answer in grams. When we are doing calculations that require inputting the mass of something into a formula, that's when we convert from grams to kilograms.
Thu Oct 04, 2018 3:19 pm
Forum: Limiting Reactant Calculations
Topic: alternate method to calculating limiting reactant
Replies: 3
Views: 108

### alternate method to calculating limiting reactant

In high school, my chemistry teacher taught us a way to find which reactant was the limiting one by: -finding the number of moles of each reactant -using the stoichiometric ratios to convert to the number of moles of a product formed by each reactant (we would pick any of the products) -the reactant...
Mon Oct 01, 2018 7:56 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Exercise E9
Replies: 3
Views: 172

### Re: Exercise E9

I think the tricky part about this problem is the formula for Epsom salt, which is MgS04.7H20 (the "." is supposed to represent the notation for hydrates, but I couldn't figure out how to type it out). The problem states that epsom salt is magnesium sulfate heptahydrate, which means that i...