Search found 47 matches
- Fri Feb 15, 2019 5:05 pm
- Forum: Calculating Work of Expansion
- Topic: Free Expansion
- Replies: 3
- Views: 26
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: 21
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: 30
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: 12
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: 12
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: 32
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: 55
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: 33
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: 26
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: 29
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: 75
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: 24
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: 11
- Views: 53
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: 33
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: 26
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: 33
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
- Topic: Adding a liquid
- Replies: 7
- Views: 37
Re: Adding a liquid
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: 30
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 8:31 am
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Drawing Tetrahedral Structures
- Replies: 4
- Views: 70
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 8:21 am
- Forum: Octet Exceptions
- Topic: expanded octet
- Replies: 12
- Views: 285
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 12:44 pm
- Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
- Topic: Double bond
- Replies: 5
- Views: 202
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 12:22 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Naming shape
- Replies: 7
- Views: 135
Re: Naming shape
You have to account for lone pairs, as they count as areas of electron density.
- Sat Jun 02, 2018 12:03 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Bond Angles
- Replies: 7
- Views: 150
Re: Bond Angles
We should know the main bond angles for each structure.
- Sat May 26, 2018 6:18 pm
- Forum: Polarisability of Anions, The Polarizing Power of Cations
- Topic: Polarizing power
- Replies: 10
- Views: 359
Re: Polarizing power
Cations have polarizing power while anions have polarizability.
- Sat May 26, 2018 6:05 pm
- Forum: Formal Charge and Oxidation Numbers
- Topic: Formal charge with ions
- Replies: 4
- Views: 143
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 7:06 pm
- Forum: Ionic & Covalent Bonds
- Topic: Formal charge?
- Replies: 12
- Views: 290
Re: Formal charge?
Yes! The equation [valence electrons - non-bonding valence electrons - (bonding electrons/2) ] would also work
- Fri May 18, 2018 6:19 pm
- Forum: Lewis Structures
- Topic: Exceptions to the Octet
- Replies: 5
- Views: 108
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 6:14 pm
- Forum: Dipole Moments
- Topic: polarization power
- Replies: 3
- Views: 85
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 6:08 pm
- Forum: Bond Lengths & Energies
- Topic: calculating bond length
- Replies: 3
- Views: 90
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 11:19 am
- Forum: Lewis Structures
- Topic: SO2
- Replies: 5
- Views: 240
Re: SO2
Two double bonds, because of the formal charges, but the actual structure is a hybrid of all three.
- Sat May 12, 2018 11:16 am
- Forum: Octet Exceptions
- Topic: Exceptions [ENDORSED]
- Replies: 7
- Views: 305
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 9:17 pm
- Forum: Heisenberg Indeterminacy (Uncertainty) Equation
- Topic: Delta X
- Replies: 4
- Views: 179
Re: Delta X
Someone asked about this in class and the answer was to plug in the diameter.
- Thu May 03, 2018 5:12 pm
- Forum: *Shrodinger Equation
- Topic: Midterm [ENDORSED]
- Replies: 2
- Views: 151
Re: Midterm [ENDORSED]
I believe Dr. Lavelle said that we should just know the concepts behind it.
- Thu May 03, 2018 5:01 pm
- Forum: Trends in The Periodic Table
- Topic: Electron affinity
- Replies: 4
- Views: 105
Re: Electron affinity
I believe that atoms with a full octet are an exception though.
- Thu May 03, 2018 4:56 pm
- Forum: Trends in The Periodic Table
- Topic: Electron affinity
- Replies: 4
- Views: 105
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 1:03 pm
- Forum: Photoelectric Effect
- Topic: Test 2 final question [ENDORSED]
- Replies: 15
- Views: 373
Re: Test 2 final question [ENDORSED]
It is a one to one ratio so 1000 electrons.
- Sat Apr 28, 2018 1:00 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Lobes [ENDORSED]
- Replies: 4
- Views: 147
Re: Lobes [ENDORSED]
I think we also need to know which axis each lobe lays on.
- Sat Apr 28, 2018 12:51 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Why does the 4s orbital come before the 3d?
- Replies: 7
- Views: 163
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 5:08 pm
- Forum: DeBroglie Equation
- Topic: HW 1.39 [ENDORSED]
- Replies: 8
- Views: 263
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 5:00 pm
- Forum: Photoelectric Effect
- Topic: 1.9
- Replies: 6
- Views: 119
Re: 1.9
1 MHz is equal to 10^6 Hz, so you would multiply by 10^6.
- Thu Apr 19, 2018 4:06 pm
- Forum: DeBroglie Equation
- Topic: HW 1.33
- Replies: 12
- Views: 328
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 3:02 pm
- Forum: SI Units, Unit Conversions
- Topic: Length Units
- Replies: 15
- Views: 377
Re: Length Units
Yes, but the question should specify the units you need.
- Fri Apr 13, 2018 3:00 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Textbook Version Confirmation
- Replies: 1
- Views: 77
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 2:58 pm
- Forum: Limiting Reactant Calculations
- Topic: Two limiting reactants?
- Replies: 10
- Views: 483
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 5:34 pm
- Forum: SI Units, Unit Conversions
- Topic: L35, What is t? (Conversion)
- Replies: 3
- Views: 105
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 5:28 pm
- Forum: Limiting Reactant Calculations
- Topic: Mass of Products VS. Mass of Reactants- Class Assessment
- Replies: 5
- Views: 147
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 5:15 pm
- Forum: General Science Questions
- Topic: Rusty on High School Chem [ENDORSED]
- Replies: 113
- Views: 33156
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.