## Search found 61 matches

Thu Mar 14, 2019 11:25 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: H+ in Cell Diagram
Replies: 1
Views: 77

### H+ in Cell Diagram

Can someone give in an example of an equation in which you would include the Hydrogen ion in the cell diagram? How would you include it, because you most likely will not use a porous disk to separate the ions since H+ will be in the same phase as one of the ions. But how do you know when to include ...
Thu Mar 14, 2019 11:03 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Molecularity
Replies: 5
Views: 199

### Re: Molecularity

No, molecularity only depends on the molecules which react so we are only looking at the reactants. When considering molecularity we are evaluating how many molecules are colliding which again would only be considering the reactants.
Thu Mar 14, 2019 11:00 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Catalysts
Replies: 6
Views: 187

### Re: Catalysts

It is important to differentiate between a catalyst and an intermediate. A catalyst is present from the beginning of the reaction and is not consumed. However, an intermediate is produced by the reaction and is used up in the reaction.
Thu Mar 14, 2019 10:58 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Arrhenius Equation
Replies: 4
Views: 142

### Re: Arrhenius Equation

I dont recall prof Lavelle explaining in class but I remember him saying in this class we will generally be using A=1.
Fri Mar 08, 2019 8:00 pm
Forum: Zero Order Reactions
Topic: how do we tell if a reaction is zero order?
Replies: 5
Views: 204

### Re: how do we tell if a reaction is zero order?

If the graph of [A] vs time is linear, then the reaction is zero order because the reaction rate is independent from the concentration of reactants.
Fri Mar 08, 2019 7:58 pm
Forum: Zero Order Reactions
Topic: Determining Rate Orders
Replies: 3
Views: 143

### Re: Determining Rate Orders

You look at when the concentration of one reactant changes and the amount their corresponding reaction rates change. You then raise the concentration to the power "n" and set it equal to the change in reaction rates to find the exponents of the reactants in the rate law. Once you find the ...
Fri Mar 08, 2019 7:46 pm
Forum: General Rate Laws
Topic: Graph of ln[A] against time
Replies: 4
Views: 149

### Re: Graph of ln[A] against time

If the graph of [A] vs time is linear then it's a Zero Order reaction.
If the graph of ln[A] vs time is linear then it's a First Order reaction.
If the graph of 1/[A] vs time is linear then it's a Second Order reaction.
Sun Feb 24, 2019 7:13 pm
Forum: Balancing Redox Reactions
Topic: 1/2 Rxns: Elements vs. Compounds
Replies: 3
Views: 115

### 1/2 Rxns: Elements vs. Compounds

When balancing half reactions, should we be just writing down the element that is involved or should we be including the entire compound that that element is apart of? Does it depend on the reaction and if the compound includes oxygen/hydrogen?
Sun Feb 24, 2019 7:10 pm
Forum: Balancing Redox Reactions
Topic: Balancing Half Reactions
Replies: 3
Views: 66

### Re: Balancing Half Reactions

As said above, this is because the standard cell potential is an intensive property so it is not affected by a change in coefficients. However, if it was an extensive property, like Enthalpy, you would multiply its value by a change in the coefficients.
Sat Feb 23, 2019 1:37 pm
Forum: Balancing Redox Reactions
Topic: Reactant as Reducing and Oxidizing Agent
Replies: 1
Views: 77

### Reactant as Reducing and Oxidizing Agent

I’m confused on how to balance a redox reaction when there is one reactant that acts as both the reducing and oxidizing agent. For example, in #6K3 in the 7th edition textbook, it gives the equation: Cl2(g) —> HClO(aq) + Cl2(g) Cl2 is the only reactant and acts as both the reducing and oxidizing age...
Thu Feb 21, 2019 9:35 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Anode v. Cathode
Replies: 9
Views: 318

### Re: Anode v. Cathode

One way to remember which (anode or cathode) is redox or oxidation is by using:
A RED CAT (redox--cathode)
AN OX (anode--oxidation)
Thu Feb 21, 2019 9:33 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Salt Bridge/Porous Disk
Replies: 5
Views: 185

### Re: Salt Bridge/Porous Disk

It is most important to know they allow ion transfer which helps maintain neutral solutions.
Tue Feb 19, 2019 9:24 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Negative Delta G
Replies: 7
Views: 618

### Re: Negative Delta G

Also it is important to remember when Delta G is negative the reaction is spontaneous!
When it is positive it is non spontaneous.
Sun Feb 10, 2019 3:31 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Predict entropy change
Replies: 3
Views: 124

### Re: Predict entropy change

Gases have greater entropy, because gas molecules expand to fill their whole container and can move around freely so there is more disorder... So since this reaction goes from having one mole of gas to having zero, its entropy decreases.
Sun Feb 10, 2019 3:27 pm
Forum: Calculating Work of Expansion
Topic: Work equations
Replies: 2
Views: 106

### Re: Work equations

hi miriam! They both represent different things.. the lowercase w is to calculate work done on the system which is used for reversible and irreversible reactions. While, the capital W represents degeneracy, so it used to calculate residual entropy.
Sun Feb 10, 2019 3:24 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Quick Conceptual question
Replies: 7
Views: 296

### Re: Quick Conceptual question

In addition to what was said above, entropy can determine if a reaction is spontaneous (favorable) or not but Enthalpy cannot determine this.

Total entropy >>0 - Spontaneous
Total entropy <<0 - Non spontaneous
Mon Feb 04, 2019 5:27 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess's Law
Replies: 2
Views: 113

### Re: Hess's Law

I saw a problem like this too, and was wondering if we can just use the enthalpies of formations for each of the compounds and use the equation:
Enthalpy of formation (products) - Enthalpy of formation (reactants)
Mon Feb 04, 2019 5:21 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Important Thermochemistry Equations
Replies: 3
Views: 161

### Important Thermochemistry Equations

Does someone mind listing all the important equations we need to know for the thermochemistry unit? I get confused when reading the book, which equations are necessary to know and which are just examples...
Thank you!!
Sun Feb 03, 2019 1:02 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess's Law vs. Rxn Enthalpies
Replies: 2
Views: 248

### Hess's Law vs. Rxn Enthalpies

How do you know when to you use Hess's Law to calculate the overall reaction Enthalpy versus when to use the equation: Enthalpy of formation for products - the enthalpy of formation for the reactants For example #4D15 in the 7th edition, I used the equation above but the solutions manual used Hess's...
Thu Jan 31, 2019 4:07 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Work Calculation
Replies: 3
Views: 136

### Work Calculation

I remember Lavelle going over this but couldn't remember his explanation... why must the constant pressure have a negative sign in front for the calculation of work done on a system?
Thu Jan 31, 2019 4:05 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Reversible Processes
Replies: 2
Views: 125

### Reversible Processes

Why is the greatest work done for processes that take place reversibly when the definition of a reversible process is one that can be reversed by a very small change?
Thu Jan 31, 2019 4:02 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Different Kinds of Symptoms
Replies: 6
Views: 213

### Different Kinds of Symptoms

Can someone please give examples for open, closed, and isolated systems? I'm still kind of confused by the definitions of them all so I think examples would help me understand the concepts better. Thanks!
Wed Jan 23, 2019 11:46 am
Forum: Ideal Gases
Topic: Pressure in terms of mols
Replies: 3
Views: 157

### Re: Pressure in terms of mols

Consider pressure in terms of volume as well. When the number of moles stays the same and the volume decreases, the pressure will increase because now there is a more concentrated system. Same vice versa, when the volume increases, the solution is less concentrated so the pressure decreases.
Wed Jan 23, 2019 11:44 am
Forum: Ideal Gases
Topic: The Difference between Q and Kc [ENDORSED]
Replies: 18
Views: 1794

### Re: The Difference between Q and Kc[ENDORSED]

We use Q to determine which way the reaction must proceed to reach equilibrium which can also help us in settling up our ICE boxes.
Wed Jan 23, 2019 11:42 am
Forum: Ideal Gases
Topic: Units for concentration
Replies: 5
Views: 184

### Re: Units for concentration

Yes it is equivalent... it is just suggested to use mol/L when doing calculations so you are more aware of what units are being used and canceled and which remain.
Tue Jan 15, 2019 6:46 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Same/different @ equilibrium
Replies: 2
Views: 54

### Same/different @ equilibrium

Is the only thing that remains the same at equilibrium between two different size samples of the same reactants and products, the equilibrium expression (kc)? How come the ratio without the exponents changes but the ratio with the exponents doesn't change?
Tue Jan 15, 2019 6:43 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Le Chatelier - Volume
Replies: 2
Views: 75

### Le Chatelier - Volume

I'm confused on how to explain your observation for the change in volume in relation to the Le Chatelier principle. Lavelle said not to discuss the increase or decrease in moles when the volume is changed, but rather to discuss the reaction quotient. How would you do this? Can someone provide an exa...
Tue Jan 15, 2019 6:35 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Reaction Quotient
Replies: 10
Views: 335

### Re: Reaction Quotient

The reaction quotient can be calculated the same way as K. The concentration values used for the calculation of Q are the values before the reaction reaches equilibrium, and the values used to calculate K are the values when the reaction is at equilibrium.
Wed Jan 09, 2019 9:04 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE Table
Replies: 4
Views: 74

### Re: ICE Table

We assume the concentrations are very low and close to zero, so to make the calculations easier we just use 0.
Wed Jan 09, 2019 9:01 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Spectator Ions and Equilibrium Constants
Replies: 2
Views: 324

### Re: Spectator Ions and Equilibrium Constants

A spectator ion is unchanged on both sides of the reaction and does not affect equilibrium so it is therefore not included in the equilibrium expression.
Wed Jan 09, 2019 8:57 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: finding K Value
Replies: 3
Views: 61

### Re: finding K Value

In the expression, you must put the concentrations of the reactants and products to the power of their stoichiometric coefficients!
Mon Dec 03, 2018 7:04 pm
Forum: Conjugate Acids & Bases
Topic: basicity strength
Replies: 3
Views: 359

### Re: basicity strength

It may also be helpful to memorize the main strong bases... group 1 and 2 hydroxides! It will be easier/faster to identify the strong base if you know the general strong bases.
Mon Dec 03, 2018 7:01 pm
Forum: Bronsted Acids & Bases
Topic: Water with Acids and Bases
Replies: 3
Views: 178

### Re: Water with Acids and Bases

You will know if water acts as an base or an acid based off of what compound it is reacting with. If it is reacting with a base, it will act as an acid and donate protons; however, if it is reacting with an acid, it will act as a base and accept protons. And I believe the strength of an acid/base do...
Mon Dec 03, 2018 6:56 pm
Forum: Amphoteric Compounds
Topic: Definition
Replies: 5
Views: 192

### Re: Definition

Amphoteric refers to a compound that can act as either a base or an acid. The most well known example of an amphoteric compound is water, because it can act as both a base and acid.
Wed Nov 28, 2018 11:13 am
Forum: Dipole Moments
Topic: Polarizability vs Polarizing power
Replies: 8
Views: 292

### Re: Polarizability vs Polarizing power

Polarizability is related to anions and how readily able they are to have their electron cloud distorted by the cation. Polarizability increases as atomic radius increases because more electron shielding. Polarizing power is related to cations and their ability to distort the electron cloud of anion...
Wed Nov 28, 2018 11:10 am
Forum: Dipole Moments
Topic: Size and IM interactions
Replies: 2
Views: 74

### Re: Size and IM interactions

This is referring to polarizability. The London Dispersion Forces are stronger when the anion is more polarizable and the anion has higher polarizing power. And the anion is more polarizable when it is larger because there is more electron shielding.
Wed Nov 28, 2018 11:08 am
Forum: Dipole Moments
Topic: Interaction Potential Energy
Replies: 4
Views: 430

### Re: Interaction Potential Energy

No I don't think we have to know the formula since we never really did any math with it, I think you just have to know the general concept of how potential energy relates to the behavior of IM forces.
Mon Nov 19, 2018 9:11 pm
Forum: Hybridization
Topic: D-orbital
Replies: 5
Views: 188

### Re: D-orbital

Yes, Lavelle says he prefers to put the d-orbital after the s-orbital but either is correct notation!
Mon Nov 19, 2018 9:02 pm
Forum: Hybridization
Topic: electron density in regards to # of hybrid orbitals
Replies: 4
Views: 193

### Re: electron density in regards to # of hybrid orbitals

In class today, Professor Lavelle said the number of hybrid orbitals = the number of electron density regions around the central atom.
Mon Nov 19, 2018 8:59 pm
Forum: Hybridization
Topic: Unhybridized orbitals
Replies: 10
Views: 559

### Re: Unhybridized orbitals

I am also still confused on if all lewis structures obtain hybridized orbitals? Or how do you determine if they do or don't?
Thu Nov 15, 2018 12:19 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: AX and AXE
Replies: 2
Views: 134

### AX and AXE

I'm not sure if we have to know this, but I remember in high school chem, we had to derive AX2 or AX2E2 or whatever based off of the number of bonding pairs and lone pairs on the central atom and from that, you could derive the shape of the molecule. I remember knowing this helped me a lot but I can...
Thu Nov 15, 2018 12:10 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: What to memorize in VSEPR?
Replies: 8
Views: 369

### Re: What to memorize in VSEPR?

I'm assuming we have to memorize the angles too because we are supposed to understand the concept of how lone pairs affect the bond angles, so therefore you should be able to derive the angles based on the shape of the molecule.
Thu Nov 15, 2018 12:07 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Will we have to calculate bond angles?
Replies: 8
Views: 261

### Re: Will we have to calculate bond angles?

I think we have to know the bond angles of each shape and basically how those angles are derived. For instance, you have to know that by adding lone pairs, the angles will be affected and will generally become smaller.
Fri Nov 09, 2018 7:41 am
Forum: Octet Exceptions
Topic: The center atom
Replies: 20
Views: 1001

### Re: The center atom

Oxygen is the center atom because you also have to consider the bond formation. Oxygen forms more bonds than Chlorine, so it should be the center atom, since there are two other atoms to form bonds with.
Fri Nov 09, 2018 7:37 am
Forum: Electronegativity
Topic: Electron Affinity vs. Ionization Energy
Replies: 8
Views: 381

### Re: Electron Affinity vs. Ionization Energy

Electron affinity is the energy given off when electrons are added to the atom. So basically, the electron affinity of an atom can determine if the atom wants electrons or not. On the other hand, ionization energy is the energy needed to remove an electron from an atom. They both increase across the...
Fri Nov 09, 2018 7:35 am
Forum: Electronegativity
Topic: What are the trends useful for?
Replies: 12
Views: 376

### Re: What are the trends useful for?

All of these trends feed off of each other so it is important to understand all of them. For instance, ionization energy feeds off of atomic radius, as the smaller the radius, the higher the ionization energy, because the pull from the nucleus is greater. Another significant reason to know these tre...
Wed Oct 31, 2018 2:48 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Stable Condition
Replies: 8
Views: 1967

### Re: Stable Condition

I believe molecules are always the most stable when the formal charge is equal to zero because that shows that the molecule is neutral.
Wed Oct 31, 2018 2:46 pm
Forum: Resonance Structures
Topic: How does a resonance structure work?
Replies: 10
Views: 502

### Re: How does a resonance structure work?

Resonance basically means that the lewis structure of a molecule can be written in different forms, but the one that is the most appropriate to use would be the one that has a formal charge of 0, because it means it is most stable. The general lewis structure of molecules with resonance would be the...
Wed Oct 31, 2018 2:44 pm
Forum: Ionic & Covalent Bonds
Topic: Interactions between ions
Replies: 3
Views: 190

### Re: Interactions between ions

If it is not included in one of the sections listed in his outline or if he didn't go over it in lecture (which I think he only briefly addressed it), I don't think we will have to know it for the midterm! I don't think this topic will be focused on in the midterm, I would focus on the other ones li...
Thu Oct 25, 2018 9:07 am
Forum: Quantum Numbers and The H-Atom
Topic: spin
Replies: 4
Views: 170

### Re: spin

Since this number is determined off of the electron configuration, how do you know when to draw an arrow faced down or faced up so you can determine if it is +1/2 or -1/2?
Thu Oct 25, 2018 9:03 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Electron Configurations
Replies: 3
Views: 115

### Re: Electron Configurations

4s would logically come next because it is the shell that is after Argon, however, in this case as we move onto the 3d level, we have to remember that the 3d level is less in energy than the 4s level. Electron configurations are always written in lowest energy to highest energy, so this electron con...
Thu Oct 25, 2018 9:00 am
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Spins
Replies: 4
Views: 174

### Re: Spins

In addition to the all the previous replies, spin up and spin down is referenced when an atom has unpaired electrons (it subshells aren't filled).
Thu Oct 18, 2018 1:36 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: ground state electron configuration
Replies: 3
Views: 1109

### Re: ground state electron configuration

I am also confused on this... For when you are asked to write the electron configuration, when do you not fill up the first orbital and move onto the next one? Like if you were to write 1s2,2s2,2p6,3s1,3p3,3d... How do you determine which orbitals you don't fill?
Thu Oct 18, 2018 1:30 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: l and ml
Replies: 1
Views: 49

### l and ml

I am still confused on the variables l and ml that mean the orbital angular momentum quantum number and the magnetic quantum number. How do you determine both of these values when they give you a specific orbital?
Mon Oct 15, 2018 2:58 pm
Forum: Student Social/Study Group
Topic: Note Taking
Replies: 32
Views: 2501

### Re: Note Taking

I agree that sharing this info will be very beneficial for all of us! Personally, what I find to be quite helpful is handwriting my notes in class, so I can include equations and diagrams, but when I get back from class I type up my notes that I had just wrote down in class. I do this so that I am r...
Wed Oct 10, 2018 11:25 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: What does ground state mean? [ENDORSED]
Replies: 4
Views: 382

### Re: What does ground state mean?[ENDORSED]

Ground state means that the atom is not ready to bond with another atom, as it would be if it were in the excited state. Therefore, for the electron configuration for atom in the ground state, if possible, all of the electrons would be paired. On the other hand, for the excited state, there would be...
Wed Oct 10, 2018 11:20 pm
Forum: Properties of Light
Topic: Do I need to memorize the Light Spectrum? [ENDORSED]
Replies: 13
Views: 349

### Re: Do I need to memorize the Light Spectrum?[ENDORSED]

I was curious about this too, because I noticed in lecture today, Lavelle was asking the class what region a certain wavelength range was, so I am wondering if we have to know the general wavelength of each region or if we just have to know the relative strength.
Wed Oct 10, 2018 11:16 pm
Forum: Properties of Light
Topic: Problem 1.23
Replies: 2
Views: 66

### Re: Problem 1.23

As Melody said, I believe the book used the more exact number to match the number of sig figs in the data provided, and also it is helpful to use the more exact number instead of rounding to get a more precise calculation. However, since Lavelle noted 6.626 and most resources note Planck's constant ...
Wed Oct 03, 2018 9:20 pm
Forum: SI Units, Unit Conversions
Topic: Formula Units??
Replies: 3
Views: 216

### Formula Units??

I am still confused what formula units are... In fundamentals E. 25 it says determine the number of KNO3 formula units in 0.750 mol KNO3.. Is that the same as saying the number of molecules/atoms? Where I am guessing you would use the conversion of moles to avogadros number.
Wed Oct 03, 2018 7:32 pm
Forum: SI Units, Unit Conversions
Topic: Week 2 homework
Replies: 2
Views: 127

### Week 2 homework

For week 2 homework that is due during our discussion session, should we be doing 7 problems that are still from the high school review section or should we be moving onto the next topics? I was wondering because some discussions are after only one of the lectures so we haven't reviewed much of the ...
Mon Oct 01, 2018 12:16 pm
Forum: SI Units, Unit Conversions
Topic: Office Hours [ENDORSED]
Replies: 2
Views: 106

### Office Hours[ENDORSED]

Do office hours begin this week? Also, when do the peer learning sessions start and what do those entail?