## Search found 55 matches

Sat Mar 17, 2018 1:13 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Closed systems
Replies: 2
Views: 280

### Re: Closed systems

I think that delta U = q + w applies to all systems. It is the equation that explains the first law of thermodynamics
Fri Mar 16, 2018 4:40 pm
Forum: General Rate Laws
Topic: Writing out states for rate laws
Replies: 4
Views: 418

### Writing out states for rate laws

Do we have to rate out the states of the reactants in rate laws? In the book, the states of the reactants (gas, solid, liquid) are not included in the rate laws.
Wed Mar 14, 2018 10:42 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Electrolysis Anode and Cathode
Replies: 2
Views: 217

### Electrolysis Anode and Cathode

Hi! I'm a little confused about electrolysis. Do we put the higher reduction potential at the anode? and the lower reduction potential at the cathode? (even though the cathode will be reduced and the anode will be oxidized?) Also, if we were presented with two substances that might take place at the...
Sat Mar 10, 2018 11:16 am
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.69
Replies: 2
Views: 150

### 15.69

Hi! For problem 15.69, I was wondering if the rate coefficient was indicative of the rate? because I notice that in the solutions manual, even though the reaction rate increase by a factor of 1000., it uses the Arrhenius Equation and comparison of rate constants instead of reaction rates to get the ...
Sat Mar 10, 2018 11:14 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Changes with Temperature [ENDORSED]
Replies: 2
Views: 94

### Re: Changes with Temperature[ENDORSED]

I think that the Arrhenius equation illustrates the change in k with the change in temperature because k=Ae^(Activation energy)/RT. Also I would reference equation 14 in the textbook on page 642, which compares the rate constants at different temperatures.
Mon Mar 05, 2018 9:21 pm
Forum: General Rate Laws
Topic: 15.3 Rate Laws Depending on concentrations of products
Replies: 3
Views: 154

### 15.3 Rate Laws Depending on concentrations of products

Hi! For Chapter 15 Section 3, on page 621, there is an example for the rate law for the decomposition of ozone. In the rate law, both the concentration of products and reactants matter. How do you know when the rate law depends on both the concentration of products and reactants, and not just the re...
Sat Mar 03, 2018 10:48 pm
Forum: First Order Reactions
Topic: k
Replies: 16
Views: 662

### Re: k

I think it depends on the units in the rest of the problem. If it is stated that the rate is mol/L- min, then the k will probably by 1/min. However, if nothing is given in terms on units in the rest of the problem, I think it would be best to use time units as seconds.
Thu Mar 01, 2018 6:07 pm
Forum: General Rate Laws
Topic: Rate Law dependent on Reactants [ENDORSED]
Replies: 4
Views: 245

### Rate Law dependent on Reactants[ENDORSED]

Why is the rate law only include the concentration of reactants along with k? For example, all of the rate laws in table 15.1

Thanks!
Wed Feb 28, 2018 3:17 pm
Forum: General Rate Laws
Topic: Rate constant = k
Replies: 1
Views: 103

### Rate constant = k

I was wondering when we were calculating k, would we calculate k based on the initial concentrations and reaction rates because I remember taking notes about the importance of initial reaction rates?
Thu Feb 22, 2018 3:36 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: When writing cell diagrams, how do you know when to include an additional element at the electrode?
Replies: 5
Views: 217

### Re: When writing cell diagrams, how do you know when to include an additional element at the electrode?

I think I2 is not a metal, there it does not conduct electricity. I think must conducting solids are metals or metallic.
Thu Feb 22, 2018 3:32 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Standard E values and inverse values
Replies: 2
Views: 151

### Re: Standard E values and inverse values

E is an intensive property so I think that E (red) will stay the same regardless. However, when approaching problems to solve for E(cell), I found this earlier post that explains it quite well, because I know Dr. Lavelle went over calculating E (cell) in two ways. https://lavelle.chem.ucla.edu/forum...
Wed Feb 21, 2018 2:17 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.107 Determining K
Replies: 1
Views: 98

### 14.107 Determining K

Hi I am confused with how we are supposed to calculate K at pH= 1 and pH= 14. In the solutions manual, it states that the K at pH=14 is (1.0 x 10^-14) / (1.0). Where did we get the 1.0 M from? Also for the pH=1 the K is (0.1/ 1.0 x 10^-14). Where did the 1.0 x 10^-14 come from?
Sun Feb 18, 2018 1:26 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.21 cell notation
Replies: 1
Views: 76

### 14.21 cell notation

How come the I- (aq) is written in the innermost to the salt bridge, when it is the reactants part of the reaction with Ag(s) to make AgI (s) + e- ?
Sun Feb 18, 2018 11:49 am
Forum: Balancing Redox Reactions
Topic: Half reaction
Replies: 1
Views: 110

### Re: Half reaction

I would think of it as one being less negative than the other. Since the -3 is more negative than the -1, the -1 needs to have two electrons added to it for it get the charge of -3. In order words the I- is reduced to I3-.
Sat Feb 17, 2018 8:34 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.13 b
Replies: 1
Views: 77

### 14.13 b

Hi!

Why do we use platinum for the iodide solid because i thought we if we were dealing with solids there would be no use for an inert electrode?
Tue Feb 13, 2018 9:23 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.13 moles of gas
Replies: 1
Views: 117

### 9.13 moles of gas

Hi! I know that in the solutions manual to assume 1.00 moles of nitrogen gas for this problem, but could we have hypothetically calculated the moles of nitrogen gas given that it is an ideal gas with PV = nRT?

Thanks
Mon Feb 12, 2018 2:00 pm
Forum: Calculating Work of Expansion
Topic: Free Expansion internal energy?
Replies: 1
Views: 83

### Free Expansion internal energy?

For a free expansion process, is the change in internal energy 0? Also it if it is, can you explain why? and how free expansion is supposed to have positive entropy?
Sat Feb 10, 2018 7:59 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Multiplying Cathode Equation
Replies: 2
Views: 116

### Re: Multiplying Cathode Equation

I think it is because E is an intensive property, meaning that does not depend on the system size or the amount of material in the system
Sat Feb 10, 2018 7:50 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Oxidation
Replies: 4
Views: 123

### Re: Oxidation

Also since oxidation means loss of electrons, oxidation occurs in the anode side of the cell because it is the supplier of electrons (e-) to the other side of the cell.
Sat Feb 10, 2018 2:16 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Equilibrium Constant when calculating gibbs free energy
Replies: 1
Views: 96

### Equilibrium Constant when calculating gibbs free energy

For the equilibrium constant when calculating gibbs free energy of change in G=-RTlnK, can K only be calculated in terms of pressure for moles of gas or can it also be calculated with the concentrations of the the moles of gas? I remember distinctly that K can only apply to partial pressures and tha...
Fri Feb 02, 2018 10:01 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Reversible Processes
Replies: 1
Views: 109

### Reversible Processes

Hi I am still a bit confused on reversible processes and what they mean. I know that they are slow in process, but while measuring entropy in reversible processes if one factor was not constant, like when we calculate change in entropy of temperature, pressure, or volume, does that mean the remainin...
Fri Feb 02, 2018 9:54 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.47 [ENDORSED]
Replies: 2
Views: 125

### Re: 9.47[ENDORSED]

I think that change in internal energy is 0 because it says that the reaction is isothermal. I remember that internal energy is dependent on the temperature of the system for an ideal gas so if the temperature is constant, then no heat is moving in or out of the system, and the change in internal en...
Fri Feb 02, 2018 9:49 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Residual Molar Entropy?
Replies: 3
Views: 191

### Re: Residual Molar Entropy?

Residual molar entropy is the entropy that still exists due to positional disorder at T=0, because at T=0, there should hypothetically be no entropy if the molecule is a crystal, as seen by the third law of thermodynamics. I drew the different orientations of SO2F2, with S being the central atom bec...
Thu Jan 25, 2018 12:34 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Combustion Equations [ENDORSED]
Replies: 4
Views: 227

### Combustion Equations[ENDORSED]

For when we write out combustion equations and calculate enthalpy of combustion, do we treat the water in the products as a water or gas? (because I think the enthalpy of formation of water as a gas and water as a liquid is different)
Thu Jan 25, 2018 12:30 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: 8.65
Replies: 3
Views: 193

### Re: 8.65

I think that they did not include it because the enthalpy of formation for N2 gas is 0 and it does not contribute to the enthalpy formation.
Tue Jan 23, 2018 10:26 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: relation between internal energy and enthalpy
Replies: 1
Views: 81

### relation between internal energy and enthalpy

I know that the equation is change in enthalpy = change in internal energy - work, but can someone conceptually explain why when work is done by the system (therefore, volume expands) why enthalpy is greater than internal energy? and vice versa for when work is done on the system?

Thanks!
Sun Jan 21, 2018 9:46 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.67 gas to liquid
Replies: 2
Views: 110

### 8.67 gas to liquid

For the problems, you have to convert the reactants from gas to liquid phase. When you convert from gas to liquid phase, is enthalpy positive or negative and why?
Fri Jan 19, 2018 11:30 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Heat capacity vs Specific Heat capacity
Replies: 5
Views: 215

### Re: Heat capacity vs Specific Heat capacity

Heat Capacity is more generalized and it doesn't matter about the mass of the substance. It is equal to heat supplied/ temperature rise produced. For example, it takes 12 Joules to raise the temperature of water by 2 K. Therefore, the heat capacity of this water is 6 Joules/K. Specific Heat capacity...
Fri Jan 19, 2018 11:22 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: PV=nRT
Replies: 4
Views: 228

### Re: PV=nRT

Hi. I think we use PV=nRT in this chapter to calculate enthalpy. In the example in class today, it says that change in enthalpy = change in internal energy + P (change in V). If we do not know the change in volume of the system and it is not given, we can use the change in moles of gas to calculate ...
Fri Jan 19, 2018 11:16 pm
Forum: Phase Changes & Related Calculations
Topic: Change in enthalpy and change in internal energy
Replies: 2
Views: 115

### Re: Change in enthalpy and change in internal energy

If there is no change in the moles of gas, there will be relatively little expansion work done and little heat lost as work, which would result in change in enthalpy to equal change in internal energy. If there is a net change in the moles of gas, there will be expansion work done and the system wil...
Sun Jan 14, 2018 8:30 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Type of Systems
Replies: 2
Views: 161

### Re: Type of Systems

Hi! An open system is where both matter and energy can be exchanged with the surroundings. A closed system is where only energy can exchanged with its surroundings (i.e. heat) because the closed system cannot get any more matter (number of moles does not change). An example would be a cold pack (I'm...
Sat Jan 13, 2018 5:28 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Calorimeters
Replies: 1
Views: 80

### Re: Calorimeters

I don't think we will have to because those are the only ones I see in the book, but if Dr. Lavelle mentions any other types of calorimeters, I think we will be expected to know them
Sat Jan 13, 2018 5:23 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Question 8.41
Replies: 2
Views: 88

### Re: Question 8.41

While the ice cube is gaining heat from the water, the water is simultaneously losing the same amount of heat. The negative sign indicates the loss of heat
Thu Dec 07, 2017 9:32 am
Forum: Ionic & Covalent Bonds
Topic: Strength of ionic v covalent bonds
Replies: 2
Views: 174

### Strength of ionic v covalent bonds

Do ionic bonds (with larger electronegativity difference) tend to have a lower or higher disassociation energy compared to covalent bonds?
Wed Dec 06, 2017 11:00 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 11.45
Replies: 1
Views: 172

### Re: 11.45

Once you determine the K of both dissociations by using the ICE table, you figure out that the K of chlorine is smaller than the K of fluorine. As a result, you know that in dissociation equilibrium, chlorine favors its reactants more (since K = concentration of products/concentration of reactants) ...
Wed Dec 06, 2017 10:55 pm
Forum: Bronsted Acids & Bases
Topic: J5 Net Ionic Equations
Replies: 1
Views: 108

### Re: J5 Net Ionic Equations

What I think the book was trying to do was hydronium ion H30+ and hydroxide ion OH- and that would equal 2H20 I think I remember in class that Dr. Lavelle sometimes said that hydronium was abbreviated to H+.
Tue Nov 28, 2017 9:35 pm
Forum: Naming
Topic: 17.29d
Replies: 1
Views: 139

### 17.29d

For 17.29d, why did the book place the sulfate ligand (S04)2- before the anime (NH3) ligand? I thought that the ligands were supposed to be placed in alphabetical order in the molecular formula as well.
Mon Nov 27, 2017 5:20 pm
Forum: Naming
Topic: Naming -ate
Replies: 2
Views: 178

### Re: Naming -ate

The complex, which doesn't include the potassium is still negative. The 6 F's create a -6 charge and the Co creates a +3 charge, resulting in an overall -3 charge for the complex. The entire coordination compound, which includes the potassium, is of neutral charge.
Mon Nov 27, 2017 5:15 pm
Forum: Naming
Topic: Problem 17.31 d [ENDORSED]
Replies: 3
Views: 238

### Problem 17.31 d[ENDORSED]

I thought we named ligands in alphabetical order, so why did the book list bisoxalato before the diaqua in problem 17.31d? I know we are also supposed to disregard the prefixes when putting the ligands in alphabetical order as well.
Tue Nov 21, 2017 11:21 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: 4.75 Molecular Shape
Replies: 1
Views: 117

### Re: 4.75 Molecular Shape

It would be bent around the O atom because there are four regions of electron density, but two of the regions are occupied with lone pairs. This shape can also be seen in the common example of the O atom in water, which is also bent and has four regions of electron density: two are lone pairs and tw...
Mon Nov 20, 2017 2:58 pm
Forum: Hybridization
Topic: Pi orbital structure
Replies: 2
Views: 115

### Pi orbital structure

I know that in class Dr.Lavelle said that one pi bond means that the atoms are forced in place and any rotation would result in a breaking of the pi bonds. What would happen with two bi ponds? Someone mentioned that they could rotate but I don't understand how.
Thu Nov 16, 2017 4:04 pm
Forum: Dipole Moments
Topic: 4.29b
Replies: 2
Views: 150

### Re: 4.29b

I think that you can treat the the C-Cl dipole bonds are vectors. That way in 3, the dipole moments cancel each other out, because they have the same magnitude but are pointing in different directions. The C-Cl dipole bonds in 2 (120 degrees) have less overlap than those in 1 (60 degrees). I think t...
Thu Nov 16, 2017 3:55 pm
Forum: Dipole Moments
Topic: Dipole Moments
Replies: 2
Views: 181

### Re: Dipole Moments

I also think that the closer together similar charges are, the more of a dipole moment there is. And for 1 on 4.29, I think it has the biggest dipole moment also because of the smaller angle between the two C-Cl bonds
Mon Nov 13, 2017 12:07 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: VSEPR for four electron densities
Replies: 2
Views: 136

### VSEPR for four electron densities

Hi I was wondering how to distinguish between a tetrahedral and a trigonal pyramid. I know both have four electron densities. Also how would hybridization would work differently for the two structures?
Mon Nov 13, 2017 12:03 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Homework week 7
Replies: 1
Views: 128

### Re: Homework week 7

It is from chapter 4
Sun Nov 05, 2017 9:40 pm
Forum: Resonance Structures
Topic: Delocalized electrons
Replies: 4
Views: 260

### Delocalized electrons

Hello,

I am confused about resonance structures and delocalized electrons. What is a delocalized electron and could you provide an example with the specific delocalized electrons marked or highlighted in some way?
Sun Nov 05, 2017 9:37 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: 3.5 Give the ground state configuration expected for each of the following ions:
Replies: 3
Views: 562

### Re: 3.5 Give the ground state configuration expected for each of the following ions:

Hi

For Ga+3, the neutral state configuration is [Ar]3d10 4s2 4p1. I think the issue was that you forgot that once the 3d orbitals start filling up with electrons, it becomes lower in energy than the 4s orbital. Therefore, you take the 4s2 and 4p1 out.
Sat Oct 28, 2017 10:44 pm
Forum: Trends in The Periodic Table
Topic: Effective Nuclear Charge [ENDORSED]
Replies: 4
Views: 423

### Effective Nuclear Charge[ENDORSED]

Hi!

I'm a bit confused about effective nuclear charge and the trends in the periodic table regarding the effective nuclear charge, and shielding. How does the effective nuclear charge relate to (if it relates to) shielding?
Sat Oct 28, 2017 10:36 pm
Forum: Resonance Structures
Topic: Resonance vs. Isomers [ENDORSED]
Replies: 3
Views: 390

### Re: Resonance vs. Isomers[ENDORSED]

Hi!

Resonance structures only differ in structure of electrons. However, isomers differ in structure of electrons and atoms. They are essentially different compounds with the same number of atoms. Examples of isomers include butane and isobutane that you can look up on google if you want
Fri Oct 20, 2017 11:19 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: s-, p-, d-, f- Orbitals [ENDORSED]
Replies: 3
Views: 260

### Re: s-, p-, d-, f- Orbitals[ENDORSED]

Regarding the carbon question, an uncharged carbon atom will have 6 electrons. 2 go in the 1s orbital (paired), 2 go in the 2s orbital (paired), and the other 2 will go in the 2 p orbital. One will be in the p sub x and one will be in the p sub y. They are unpaired because they first need to fill th...
Fri Oct 20, 2017 11:11 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Replies: 6
Views: 411

### Re: Understadning Heisenberg Indeterminacy Equation

I think the Heisenberg indeterminacy equation is used to show that the exact momentum ( and thus velocity) and the position of an electron in an atom cannot be known. The indeterminacy of momentum x the indeterminacy of position has to be greater than h/4pi. If there is a greater indeterminacy in mo...
Thu Oct 12, 2017 9:25 pm
Forum: Einstein Equation
Topic: Lyman and Blamer series [ENDORSED]
Replies: 7
Views: 708

### Re: Lyman and Blamer series[ENDORSED]

Both the Balmer and Lyman series work only for hydrogen. In the Balmer series, the electron transitions from higher energy levels to n=2 and for the Lyman series, the electron transitions from higher energy level to n=1
Thu Oct 12, 2017 9:22 pm
Forum: Properties of Light
Topic: Homework 1.23
Replies: 2
Views: 124

### Re: Homework 1.23

I don't think we need to know the exact conversion, because all of the conversions will probably be given to us on the equations sheet. However, it would be helpful to know how to convert from kEV to Joules as general practice.
Thu Oct 05, 2017 8:55 pm
Forum: Limiting Reactant Calculations
Topic: M.15 (b)
Replies: 2
Views: 221

### Re: M.15 (b)

I think it would be sufficient enough to just find the limiting reactant and then follow by finding the theoretical yield. I think the book just went an extra step.
Thu Oct 05, 2017 8:48 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: E7 [ENDORSED]
Replies: 9
Views: 546

### Re: E7[ENDORSED]

I agree. I don't start rounding off my sig figs until the very end when I receive the answer, to which I then correctly round the sig figs to. However, I am sure that even if you round your sig figs after every step, points will not be taken off for not having the most accurate answer.