Search found 54 matches

Sun Mar 18, 2018 9:12 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Midterm Q5
Replies: 1
Views: 295

Midterm Q5

I was looking at the midterm and I realized I’m still confused by question 5. I can do the first step and get w= -158J. What do I do from there?
Sat Mar 17, 2018 6:45 pm
Forum: Reaction Mechanisms, Reaction Profiles
Replies: 1
Views: 133

For the final, we don't have to know how to use steady-state approximations do we? Only the pre-equilibrium approach?
Sat Mar 17, 2018 1:03 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Arrhenius Equation 15.61
Replies: 3
Views: 334

Re: Arrhenius Equation 15.61

Thanks!
Sat Mar 17, 2018 12:26 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Arrhenius Equation 15.61
Replies: 3
Views: 334

Arrhenius Equation 15.61

Could someone explain how we derived this form of the Arrhenius equation in problem 15.61? Usually it is in the form lnk = -Ea/RT + lnA but for this problem we used ln(k'/k) = Ea/R (1/T - 1/T').
Sun Mar 11, 2018 8:24 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Kinetics Test Scores [ENDORSED]
Replies: 3
Views: 431

Re: Kinetics Test Scores[ENDORSED]

I don't think so
Sun Mar 11, 2018 8:22 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Intermediates
Replies: 3
Views: 246

Re: Intermediates

Wed Mar 07, 2018 1:27 pm
Forum: First Order Reactions
Topic: 15.27 C & D
Replies: 1
Views: 179

15.27 C & D

Could someone explain question 15.27 parts c and d? I understand for parts a and b we can multiply the half-lives by 3 and 2 respectively but I don't think that method will work for c and d. A substance A decomposes in a first-order reaction and its half life is 355 s. How much time must elapse for ...
Sun Mar 04, 2018 7:37 pm
Forum: General Rate Laws
Topic: Naming Clarification
Replies: 3
Views: 216

Re: Naming Clarification

Yes it is!
Sun Mar 04, 2018 7:35 pm
Forum: Administrative Questions and Class Announcements
Topic: Kinetics Test (#3)
Replies: 2
Views: 198

Re: Kinetics Test (#3)

Awesome, thanks.
Fri Mar 02, 2018 9:37 am
Forum: Administrative Questions and Class Announcements
Topic: Kinetics Test (#3)
Replies: 2
Views: 198

Kinetics Test (#3)

On the kinetics lecture outline: https://lavelle.chem.ucla.edu/wp-conten ... netics.pdf

Up to which bullet point should we study for test 3?
Sun Feb 25, 2018 10:59 pm
Forum: General Rate Laws
Topic: 15.29
Replies: 1
Views: 130

Re: 15.29

Sun Feb 25, 2018 10:51 pm
Forum: Calculating Work of Expansion
Topic: Midterm 4A
Replies: 3
Views: 225

Re: Midterm 4A

w = -PdeltaV = -(.5atm)(4.48L-2.24L) = -1.12atm*L * 101.325J/(L*atm) = -113.484J
Sun Feb 25, 2018 10:48 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Midterm Q3A
Replies: 2
Views: 321

Re: Midterm Q3A

q(iron pot) = 14000g * 0.4495 J/(g*degreesC) * (100-22degC) = 6293 J/degC * 78degC = 490854J = 4.90*10^2 kJ
q(water) = (12000g/18.02g/mol) * 75.3J/(K*mol) * (373.15K-295.15K) = 50144.3J/K * 78K = 3.91*10^3 kJ
%heat = q(water)/q(total) = 0.8905 = 89%
Sun Feb 18, 2018 10:46 pm
Forum: Balancing Redox Reactions
Topic: Exercise 14.17
Replies: 6
Views: 333

Re: Exercise 14.17

The half-rxns are given in the back of the book. Potassium and chloride are not part of the half-rxns because they're part of the solutions. Basically for this type of problem you just balance and add the half-reactions.
Sun Feb 18, 2018 10:36 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Eº in 14.11, 13, 15
Replies: 2
Views: 215

Re: Eº in 14.11, 13, 15

Adding on to this, we can use the Eº values for the half-rxns to determine which element is oxidized and which is reduced by seeing which way the half-rxns can be manipulated to result in the highest total Eº value. By this I mean we see which half-rxn has to be reversed in order for the total Eº to...
Sun Feb 18, 2018 10:27 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: About the standard cell potentials for aqueous solutions
Replies: 2
Views: 154

Re: About the standard cell potentials for aqueous solutions

Which question is this about specifically? It might be easier to work through an example.
Mon Feb 12, 2018 10:21 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Using Nernst Equation
Replies: 2
Views: 205

Re: Using Nernst Equation

It describes how cell potential (the direction of electron transfer) depends on concentration under non-standard conditions. So, we could use the Nernst equation to solve that example about gold dissolving in nitric acid if we were given non-standard conditions (not 1M).
Mon Feb 12, 2018 10:13 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: delta u
Replies: 2
Views: 172

Re: delta u

If pressure increases, internal energy can increase even if temperature is constant. This happens when we are NOT dealing with ideal gases because at high pressure, molecules in non-ideal gases repel each other.
Mon Feb 12, 2018 10:00 am
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: 9.23 Determining what has higher entropy state
Replies: 4
Views: 323

Re: 9.23 Determining what has higher entropy state

I have a follow up question to this... are we saying the three F atoms in BF3 can only be in one set position/they are not interchangeable? It seems like they would still be able to move into different positions.
Mon Feb 12, 2018 12:37 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: higher molar entropy
Replies: 2
Views: 206

Re: higher molar entropy

Yes
Sun Feb 04, 2018 10:05 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Equations
Replies: 4
Views: 261

Re: Equations

I don't think that will be on the test
Sun Feb 04, 2018 10:04 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Favorability
Replies: 4
Views: 280

Re: Favorability

So if delta S for the "universe" is positive, then there is a spontaneous process (favorable). In the Gibbs free energy equation, the favorability depends on both delta S and delta H in the following way: delta S: positive, delta H: negative, is it favorable: yes delta S: positive, delta H...
Wed Jan 31, 2018 5:21 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.13
Replies: 5
Views: 335

Re: 9.13

There was a correction made to the solution manual for this problem on the class website. In the correct solution Cv=5/2 R is used.
Sun Jan 28, 2018 7:54 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Cp for an ideal gas
Replies: 2
Views: 186

Re: Cp for an ideal gas

This is explained in depth in section 8.10 of the textbook
Sun Jan 28, 2018 7:52 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Definition of Entropy
Replies: 10
Views: 561

Re: Definition of Entropy

We could define entropy as a property of a particular system that describes the likelihood/probability that the system will be in a particular state.
Sun Jan 21, 2018 8:06 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Question 8.41
Replies: 1
Views: 159

Question 8.41

Why do we have to find both the enthalpy of fusion of the ice and the heat (q=gCs deltaT) of the ice and then add them?
Sun Jan 21, 2018 8:02 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Heat of Combustion & Heat of Formation
Replies: 3
Views: 220

Re: Heat of Combustion & Heat of Formation

Heat of combustion is the enthalpy of a combustion reaction. This will be a negative number because heat is given off.

The heat of formation, or standard enthalpy of formation, is the heat given off when a substance is formed from its pure elements under standard conditions.
Wed Jan 17, 2018 7:28 pm
Forum: Phase Changes & Related Calculations
Topic: Compression (Question 8.3)
Replies: 4
Views: 177

Compression (Question 8.3)

Question 8.3 is about compressing a bike pump. Part B asks if the work is positive or negative with respect to the air in the pump. The answer is positive, but why? To me it seems like it would be negative.
Sun Jan 14, 2018 9:12 pm
Forum: Phase Changes & Related Calculations
Topic: Question 8.39
Replies: 2
Views: 296

Question 8.39

Could someone explain how to solve this problem please
"How much heat is needed to convert 80.0 g of ice at 0.0 degrees C into liquid water at 20.0 degrees C?"
This question probably isn't hard but I don't really know how to do it.
Sun Jan 14, 2018 8:54 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard Enthalpy Formation
Replies: 2
Views: 105

Re: Standard Enthalpy Formation

Standard enthalpy of formation is the change in enthalpy when one mole of any substance forms from its pure elements (at 1 atm of pressure and 25 degrees Celsius). Stable elements, like O2, H2, F2, etc, have zero change in enthalpy because there is actually no change that occurs; they aren't "f...
Sun Jan 14, 2018 8:44 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Molar Heat Capacity
Replies: 4
Views: 115

Re: Molar Heat Capacity

Yes, I am pretty sure that molar heat capacity increases as mass increases.
Sat Dec 09, 2017 5:12 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Question From Test 4
Replies: 1
Views: 211

Question From Test 4

How do you draw the Lewis structure of [NiBr3(CO)2] ? I know its hard to type Lewis structures but any help would be appreciated!
Sat Dec 09, 2017 4:54 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Dentates
Replies: 4
Views: 345

Re: Dentates

Yes, I think you also look for O that has a lone pair.
Fri Dec 08, 2017 10:04 am
Forum: Hybridization
Topic: Review Worksheet Ch.3&4
Replies: 2
Views: 244

Re: Review Worksheet Ch.3&4

It does, thanks!
Thu Dec 07, 2017 6:57 pm
Forum: Hybridization
Topic: Review Worksheet Ch.3&4
Replies: 2
Views: 244

Review Worksheet Ch.3&4

Hi, I got confused by question 7 of the Ch. 3 and 4 review worksheet that was posted today. It is: What are the hybrid orbitals present in each of the atoms with arrows pointed at them? Write your answer below the arrows. How many sigma and pi bonds are present in this molecule? CH3CHCHCN The arrows...
Mon Nov 27, 2017 5:59 pm
Forum: Student Social/Study Group
Topic: Is it me?
Replies: 3
Views: 426

Re: Is it me?

Some of the stuff we're doing now is review from high school for me so I'm not too lost. But i see how you could be confused if this is all new to you
Mon Nov 27, 2017 10:42 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: HW Question 11.53
Replies: 1
Views: 131

Re: HW Question 11.53

I noticed you typed 0.04 instead of 0.4.
0.4/3 =0.133333
0.1333 * 0.6 = 0.08
Were you just having trouble with this part?
Mon Nov 27, 2017 10:36 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond angles (help please) [ENDORSED]
Replies: 3
Views: 409

In addition, the textbook on pages 114 to 115 talks about the repulsion of axial vs equatorial lone pairs. In the example given the axial bond takes more energy and the bond length is shorter than an equatorial bond, which the book says is 120 degrees. So i think it is always 120.
Mon Nov 27, 2017 10:32 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond angles (help please) [ENDORSED]
Replies: 3
Views: 409

I believe the angle between the two equatorial ligands is exactly 120 degrees. The lone pairs repel the electrons just enough to keep them this position.
Sun Nov 19, 2017 8:19 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Question 4.45
Replies: 2
Views: 254

Question 4.45

Hi, can someone please explain how to get the answer to this question? "Describe the structure of the formaldehyde molecule CH2O in terms of hybrid orbitals, bond angles, and sigma and pi bonds." C is the central atom.
Sun Nov 19, 2017 8:03 pm
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Ligands
Replies: 2
Views: 248

Re: Ligands

Basically a coordination compound involves a metal atom surrounded by nonmetal atoms. The nonmetal atoms connected to the metal atom are called ligands.
Sun Nov 12, 2017 11:20 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Question 4.29 [ENDORSED]
Replies: 3
Views: 554

Question 4.29[ENDORSED]

I am not sure how to answer this type of problem in the textbook. It says, "There are three isomers of dichlorobenzene, C6H4Cl2, which differ in the relative positions of the chlorine atoms on the benzene ring. (a) Which of the three forms are polar? (b) Which has the largest dipole moment?&quo...
Sun Nov 12, 2017 11:09 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone pairs versus bonding pairs
Replies: 3
Views: 448

Re: Lone pairs versus bonding pairs

Lone pairs have more repulsion than bonding pairs, meaning they push other electrons away more than a bonding pair would. This bends the shape of the molecule away from the lone pair.
Sun Nov 05, 2017 6:38 pm
Forum: Ionic & Covalent Bonds
Topic: Ionic vs Covalent Bonds
Replies: 4
Views: 327

Re: Ionic vs Covalent Bonds

Ionic is stronger in general but there are cases in which covalent is stronger.
Thu Nov 02, 2017 11:14 am
Forum: Photoelectric Effect
Topic: Emission Spectrum
Replies: 1
Views: 137

Re: Emission Spectrum

Yes it would change the emission spectrum because the energy levels would change as the electron moved orbitals. So as the electron lowered its energy level, energy would be released as light.
Sun Oct 29, 2017 11:46 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Spin of electron [ENDORSED]
Replies: 2
Views: 207

Re: Spin of electron[ENDORSED]

No it doesn't matter but by convention it is drawn upwards first.
Wed Oct 25, 2017 9:36 pm
Forum: Lewis Structures
Topic: Lewis Dot Structure
Replies: 2
Views: 166

Re: Lewis Dot Structure

No, just fill up each side of the symbol (top, left, bottom, and/or right) with up to 2 dots, and if there needs to be a bond draw the lines to connect them.
Sun Oct 22, 2017 6:36 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Quantum Numbers [ENDORSED]
Replies: 2
Views: 180

Re: Quantum Numbers[ENDORSED]

You would have to know the value of l. ml ranges from -l to +l, so for example if l=2, ml can equal -2, -1, 0, 1, or 2.
Thu Oct 19, 2017 11:33 am
Forum: *Shrodinger Equation
Topic: Electron Spin
Replies: 6
Views: 621

Re: Electron Spin

Just to add on to what the others were saying, it may be helpful to know about an experiment that led to the discovery of electron spin. In class Professor Lavelle mentioned the Stern-Gerlach experiment which involved a beam of silver atoms going through a magnetic field and splitting into two beams...
Sun Oct 15, 2017 8:20 pm
Forum: Properties of Light
Topic: Question 1.15
Replies: 2
Views: 329

Question 1.15

Hi, I can't figure out problem 1.15 from the textbook. The problem says "In the ultraviolet spectrum of atomic hydrogen, a line is observed at 102.6 nm. Determine the values of n for the initial and final energy levels of the electron during the emission of energy that leads to this spectral li...
Sun Oct 15, 2017 8:14 pm
Forum: DeBroglie Equation
Topic: When to use DeBroglie equation? [ENDORSED]
Replies: 4
Views: 374

Re: When to use DeBroglie equation?[ENDORSED]

De Broglie said that all matter behaves like waves. The De Broglie equation is used to relate Einstein's equation E = mc^2 (which says the energy of an object is equal to its mass times the speed of light squared) to the equation E = hv (which says the energy of photons of light is equal to Planck's...
Sun Oct 08, 2017 8:09 pm
Forum: Balancing Chemical Reactions
Topic: Combustion [ENDORSED]
Replies: 3
Views: 351

Combustion[ENDORSED]

If we are given the chemical formula for a product of a reaction, such as butane, how do we find the chemical equation for its combustion?
Fri Oct 06, 2017 12:03 pm
Forum: Balancing Chemical Reactions
Topic: Diatomic Molecules
Replies: 3
Views: 963

Re: Diatomic Molecules

Hi! There's a few naturally occurring diatomic elements. They are H2, O2, F2, N2, Br2, I2, Cl2. All of them are gases (bromine and iodine are liquid at room temp. but gases at higher temps.) Of course there are many diatomic molecules where the two molecules are different elements such as CO and HCl.
Fri Oct 06, 2017 10:20 am
Forum: Limiting Reactant Calculations
Topic: M9
Replies: 3
Views: 258

Re: M9

Hey! You're right, we haven't covered net ionic equations in class. The reaction that occurs is Cu(NO3)2(aq) + 2NaOH(aq) -> Cu(OH)2(s) + 2NaNO3(aq). In other words copper nitrate combines with sodium hydroxide to form copper hydroxide and sodium nitrate. But thats not the correct ionic equation beca...