## Search found 59 matches

Mon Mar 11, 2019 6:19 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Delta U
Replies: 5
Views: 340

### Re: Delta U

Isothermal reactions have a constant temperature and since internal energy is a state function dependent on temperature, the internal energy change is zero.
Mon Mar 11, 2019 2:57 pm
Forum: Zero Order Reactions
Topic: Half-life
Replies: 4
Views: 698

### Re: Half-life

These are the equations I found for Half Lives: For a zero order reaction A products , rate = k: t½ = [Ao] / 2k For a first order reaction A products , rate = k[A]: t½ = 0.693 / k For a second order reaction 2A products or A + B products (when [A] = [B]), rate = k[A]2: t½ = 1 / k [Ao]
Mon Mar 11, 2019 2:52 pm
Forum: First Order Reactions
Topic: Half-life Clarification
Replies: 5
Views: 191

### Re: Half-life Clarification

Yes, and these are the equations I found: For a zero order reaction A products , rate = k: t½ = [Ao] / 2k For a first order reaction A products , rate = k[A]: t½ = 0.693 / k For a second order reaction 2A products or A + B products (when [A] = [B]), rate = k[A]2: t½ = 1 / k [Ao]
Fri Mar 08, 2019 3:43 pm
Forum: Zero Order Reactions
Topic: initial concentration
Replies: 6
Views: 272

### Re: initial concentration

I found this answer online, "Zero-order reactions are typically found when a material that is required for the reaction to proceed, such as a surface or a catalyst, is saturated by the reactants".
Fri Mar 08, 2019 1:57 pm
Forum: General Rate Laws
Topic: Mechanism
Replies: 2
Views: 112

### Re: Mechanism

If you mean the rate law, kinetics predicts that rates of chemical reactions will be affected by factors that increase the kinetic energy of the reactants, which makes it more likely that the reactants will interact with each other. Examples of this would be temperature changes or the presence of a ...
Fri Mar 08, 2019 1:49 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Final
Replies: 3
Views: 168

### Re: Final

Yes, the website says the final covers all material and questions will come from the Homework and Online Assessments.
Sat Mar 02, 2019 5:21 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: E˚ vs E
Replies: 13
Views: 1673

### Re: E˚ vs E

E˚ is the standard electrode potential under standard conditions while E is the cell potential under other conditions
Thu Feb 28, 2019 9:52 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Reaction Order
Replies: 3
Views: 151

### Re: Cell Reaction Order

The anode is on the left side while the cathode is on the right side.
Thu Feb 28, 2019 9:37 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: H+, OH-, water
Replies: 9
Views: 290

### Re: H+, OH-, water

A previous chem community post stated, "it seems that the elements/molecules are included that contribute to an oxidation number change or the overall charge on a side of a reaction. H+ and the other ions contribute to charge difference and therefore, electron balance. The neutral NO2(g) molecu...
Sat Feb 23, 2019 11:11 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Favor ability of Cell portential
Replies: 5
Views: 277

### Re: Favor ability of Cell portential

If the cell potential is negative, does that also mean that the reverse reaction is spontaneous?
Sat Feb 23, 2019 11:04 am
Forum: Balancing Redox Reactions
Topic: Test 2 Material
Replies: 11
Views: 277

### Re: Test 2 Material

Yes, the class website states that the test will cover Gibbs Free energy and electrochemistry
Thu Feb 21, 2019 4:44 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy and Spontaneity
Replies: 2
Views: 155

### Re: Gibbs Free Energy and Spontaneity

delta G is negative for any reaction where delta H is negative and delta S is positive. Any reaction for which delta G is negative should be spontaneous.
Fri Feb 15, 2019 5:05 pm
Forum: Calculating Work of Expansion
Topic: Free Expansion
Replies: 3
Views: 198

### Re: Free Expansion

free expansion is the unrestrained expansion of a gas into a volume
Fri Feb 15, 2019 4:57 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: work
Replies: 5
Views: 158

### Re: work

The work done on the system will be positive if a system is compressed and delta-V is negative
Fri Feb 15, 2019 4:22 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Cv vs. Cp
Replies: 6
Views: 486

### Re: Cv vs. Cp

The professor also stated on a previous chem community post that " a monatomic ideal has 3 degrees of freedom and each contributes (1/2)nRT towards the internal energy. So the total internal energy would be (3/2)nR. And since equating both we get Cv = 3/2R. And you know Cp-Cv = R so Cp = Cv + R...
Sat Feb 09, 2019 4:59 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Closed, Open, and Isolated Systems
Replies: 5
Views: 200

### Re: Closed, Open, and Isolated Systems

An example of an insulated system would be hot liquid inside of a thermos.
Sat Feb 09, 2019 4:51 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Closed, Open, and Isolated Systems
Replies: 5
Views: 200

### Re: Closed, Open, and Isolated Systems

A closed system has a fixed amount of matter but can exchange energy with its surroundings. An open system can exchange both matter and energy with its surroundings. An isolated system has no contact with its surroundings.
Sat Feb 09, 2019 4:48 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 3/2R and 5/2R
Replies: 5
Views: 264

### Re: 3/2R and 5/2R

Yes, this varies because diatomic gases have a greater number of degrees of freedom compared to monoatomic gases.
Sat Feb 02, 2019 8:30 pm
Forum: Phase Changes & Related Calculations
Topic: Negative work
Replies: 11
Views: 376

### Re: Negative work

Yes, negative work is when work leaves the system.
Sat Feb 02, 2019 8:20 pm
Forum: Phase Changes & Related Calculations
Topic: U and its relations to work
Replies: 8
Views: 254

### Re: U and its relations to work

Delta H is enthalpy while q is heat flow.
Sat Feb 02, 2019 7:34 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: bond enthalpy equations
Replies: 6
Views: 196

### Re: bond enthalpy equations

I believe Dr.Lavelle drew out the structure of each reactant and product in order to help us visualize which bonds were being broken.
Sun Jan 27, 2019 1:58 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 3 Methods
Replies: 3
Views: 135

### Re: 3 Methods

Yes, Dr.Lavelle mentioned that method 2, the bond enthalpy method, is the least accurate because it uses averages from many different molecules.
Sun Jan 27, 2019 1:51 pm
Forum: Phase Changes & Related Calculations
Topic: Modules
Replies: 17
Views: 431

### Re: Modules

The modules are an extremely helpful review for subjects you might be a little rusty on, and I recommend doing the assessments to complement the lectures and homework.
Sat Jan 26, 2019 4:59 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: method 1
Replies: 4
Views: 128

### Re: method 1

Yes, if there is the same chemical on both the reactant side and product side, then it cancels out when you add the equations.
Sat Jan 19, 2019 9:50 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Ka vs. Kb
Replies: 12
Views: 657

### Re: Ka vs. Kb

Yes Kp is the equilibrium constant expressed in terms of partial pressures of gases
Sat Jan 19, 2019 9:34 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Concentrations Effect on K
Replies: 8
Views: 201

### Re: Concentrations Effect on K

K doesn't change when concentrations change. However, a change of temperature can change an equilibrium constant.
Sat Jan 19, 2019 9:31 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Pressure
Replies: 4
Views: 219

### Re: Pressure

Since the number of moles is equal on both sides, there is no net change in order to restore equilibrium.
Sat Jan 12, 2019 5:47 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Why no units for K?
Replies: 3
Views: 165

### Re: Why no units for K?

Equilibrium constants are calculated using activity, and activity is unitless, so K is also unitless.
Sat Jan 12, 2019 4:18 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Replies: 7
Views: 242

Only the position of equilibrium is changed if you add a liquid. The reaction shifts to ensure that the expression for K remains the same.
Sat Jan 12, 2019 3:58 pm
Forum: Ideal Gases
Topic: Notation [ENDORSED]
Replies: 5
Views: 228

### Re: Notation[ENDORSED]

Brackets represent concentration, so I've seen them used in Kc problems, while I've seen both parentheses and nothing used with equilibrium problems concerning partial pressure
Sun Jun 10, 2018 9:31 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Drawing Tetrahedral Structures
Replies: 4
Views: 234

### Re: Drawing Tetrahedral Structures

I believe you can just draw the lines, and that the triangles and dashes were just used to help us fully understand the structure.
Sun Jun 10, 2018 9:21 am
Forum: Octet Exceptions
Topic: expanded octet
Replies: 12
Views: 1063

### Re: expanded octet

Any elements with an atomic number larger than 10 have access to the d orbital and can have an expanded octet.
Sat Jun 02, 2018 1:44 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Double bond
Replies: 5
Views: 397

### Re: Double bond

If there are resonance structures for one of the molecules, then the double bond for that molecule will be longer than the double bond for the other.
Sat Jun 02, 2018 1:22 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Naming shape
Replies: 7
Views: 389

### Re: Naming shape

You have to account for lone pairs, as they count as areas of electron density.
Sat Jun 02, 2018 1:03 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angles
Replies: 7
Views: 363

### Re: Bond Angles

We should know the main bond angles for each structure.
Sat May 26, 2018 7:18 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Polarizing power
Replies: 10
Views: 2905

### Re: Polarizing power

Cations have polarizing power while anions have polarizability.
Sat May 26, 2018 7:05 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal charge with ions
Replies: 4
Views: 350

### Re: Formal charge with ions

You would use the normal equation to calculate the formal charge but when you add up all of the formal charge, it should equal the charge of the ion.
Thu May 24, 2018 8:06 pm
Forum: Ionic & Covalent Bonds
Topic: Formal charge?
Replies: 12
Views: 710

### Re: Formal charge?

Yes! The equation [valence electrons - non-bonding valence electrons - (bonding electrons/2) ] would also work
Fri May 18, 2018 7:19 pm
Forum: Lewis Structures
Topic: Exceptions to the Octet
Replies: 5
Views: 295

### Re: Exceptions to the Octet

Yes, it would be 10 electrons because the d subshell has 5 orbitals with two electrons each.
Fri May 18, 2018 7:14 pm
Forum: Dipole Moments
Topic: polarization power
Replies: 3
Views: 215

### Re: polarization power

Polarizing power refers to cations because the electrons around the nucleus of the anion are drawn to the cation.
Fri May 18, 2018 7:08 pm
Forum: Bond Lengths & Energies
Topic: calculating bond length
Replies: 3
Views: 237

### Re: calculating bond length

I believe we just need to know that single bonds would have a longer bond length compared to double and triple bonds. The bond length also corresponds to bond strength.
Sat May 12, 2018 12:19 pm
Forum: Lewis Structures
Topic: SO2
Replies: 5
Views: 447

### Re: SO2

Two double bonds, because of the formal charges, but the actual structure is a hybrid of all three.
Sat May 12, 2018 12:16 pm
Forum: Octet Exceptions
Topic: Exceptions [ENDORSED]
Replies: 7
Views: 635

### Re: Exceptions[ENDORSED]

The expanded octet applies to atoms where n is greater than or equal to 3 because they have access to the d orbital.
Wed May 09, 2018 10:17 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Delta X
Replies: 4
Views: 341

### Re: Delta X

Thu May 03, 2018 6:12 pm
Forum: *Shrodinger Equation
Topic: Midterm [ENDORSED]
Replies: 2
Views: 273

### Re: Midterm[ENDORSED]

I believe Dr. Lavelle said that we should just know the concepts behind it.
Thu May 03, 2018 6:01 pm
Forum: Trends in The Periodic Table
Topic: Electron affinity
Replies: 4
Views: 244

### Re: Electron affinity

I believe that atoms with a full octet are an exception though.
Thu May 03, 2018 5:56 pm
Forum: Trends in The Periodic Table
Topic: Electron affinity
Replies: 4
Views: 244

### Re: Electron affinity

Electron affinity going from left to right of the periodic table increases because the amount of protons an element has also increases. There is an attractive charge between the positively charged protons in the nucleus and the negatively charged electrons. So, the outer electrons are more attracted...
Sat Apr 28, 2018 2:03 pm
Forum: Photoelectric Effect
Topic: Test 2 final question [ENDORSED]
Replies: 15
Views: 850

### Re: Test 2 final question[ENDORSED]

It is a one to one ratio so 1000 electrons.
Sat Apr 28, 2018 2:00 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Lobes [ENDORSED]
Replies: 4
Views: 322

### Re: Lobes[ENDORSED]

I think we also need to know which axis each lobe lays on.
Sat Apr 28, 2018 1:51 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Why does the 4s orbital come before the 3d?
Replies: 7
Views: 497

### Re: Why does the 4s orbital come before the 3d?

I think 4s might fill up first because of electron repulsion. I was looking online and it said that was related to the fact that 4s fills up before 3d.
Thu Apr 19, 2018 6:08 pm
Forum: DeBroglie Equation
Topic: HW 1.39 [ENDORSED]
Replies: 8
Views: 575

### Re: HW 1.39[ENDORSED]

Yes, you would use the equation lambda=h/mv, and make sure to convert the given values into SI units.
Thu Apr 19, 2018 6:00 pm
Forum: Photoelectric Effect
Topic: 1.9
Replies: 6
Views: 266

### Re: 1.9

1 MHz is equal to 10^6 Hz, so you would multiply by 10^6.
Thu Apr 19, 2018 5:06 pm
Forum: DeBroglie Equation
Topic: HW 1.33
Replies: 12
Views: 600

### Re: HW 1.33

For part A, you can use the equation lambda=hc/Energy of the electron or (1/2mv^2. Then, you plug in Planck's constant and the speed of light on the top and the mass of an electron and the given velocity(3.6x10^6 when converted from km/s to m/s) on the bottom. The answer would be 33.7 nm, so the wav...
Fri Apr 13, 2018 4:02 pm
Forum: SI Units, Unit Conversions
Topic: Length Units
Replies: 15
Views: 764

### Re: Length Units

Yes, but the question should specify the units you need.
Fri Apr 13, 2018 4:00 pm
Forum: Administrative Questions and Class Announcements
Topic: Textbook Version Confirmation
Replies: 1
Views: 123

### Re: Textbook Version Confirmation

I have the sixth edition and I haven't had a problem. I'm pretty sure the sixth edition is the one we're supposed to have.
Fri Apr 13, 2018 3:58 pm
Forum: Limiting Reactant Calculations
Topic: Two limiting reactants?
Replies: 10
Views: 1216

### Re: Two limiting reactants?

No, but two reactants can be used up in equal amounts. Neither of them limits the other.
Tue Apr 10, 2018 6:34 pm
Forum: SI Units, Unit Conversions
Topic: L35, What is t? (Conversion)
Replies: 3
Views: 244

### Re: L35, What is t? (Conversion)

I think I remember Dr. Lavelle saying that we would be given unit conversions if it was a unit we wouldn't normally know.
Tue Apr 10, 2018 6:28 pm
Forum: Limiting Reactant Calculations
Topic: Mass of Products VS. Mass of Reactants- Class Assessment
Replies: 5
Views: 681

### Re: Mass of Products VS. Mass of Reactants- Class Assessment

I remember that question from the module assessment and the answer is no.
Tue Apr 10, 2018 6:15 pm
Forum: General Science Questions
Topic: Rusty on High School Chem [ENDORSED]
Replies: 197
Views: 139016

### Re: Rusty on High School Chem[ENDORSED]

Yeah I was also a little rusty but the video modules really helped and I reviewed my old AP chem notes so I'm feeling more confident for the first test. The solutions manual is also extremely helpful.