## Search found 52 matches

Fri Mar 16, 2018 4:40 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Rate Determining
Replies: 7
Views: 419

### Re: Rate Determining

According to my TA, information on whether the steps in a mechanism are slow or fast will be given.
Fri Mar 16, 2018 4:37 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: What has greater residual entropy at 0K?
Replies: 5
Views: 523

### Re: What has greater residual entropy at 0K?

Normally, if there are more elements or number of elements in a molecule, that has greater residual entropy, but generally, bigger molecules have greater residual entropy in which case you calculate the molar masses of each molecule to find which one is bigger.
Fri Mar 16, 2018 4:34 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Calculate standard potential, Gibbs free
Replies: 2
Views: 178

### Re: Calculate standard potential, Gibbs free

I may have had a different test from you nurmerically, but I'm pretty sure in 6D you're able to add the standard potentials because they're from the half reactions. So, based of the equation E(anode)+E(cathode) = E cell, you get the overall standard cell potential. On #7, you can't do the same thing...
Fri Mar 16, 2018 11:26 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.17-how to write equation
Replies: 1
Views: 160

### Re: 14.17-how to write equation

I had trouble identiying the elements in the half reactions as well, but as a quick solution, I think it's best to refer to the table of half reactions since this is a more complicated reaction. The half reactions will most likely be given on the final since they were also given on the tests. Hope t...
Sat Mar 10, 2018 11:22 pm
Forum: Balancing Redox Reactions
Topic: Homework 14.13b
Replies: 2
Views: 166

### Homework 14.13b

Reaction: Ce4+(aq) + I-(aq) -> I2(s) + Ce3+(aq) I separated into half reactions, identified the reduction and oxidation reaction, and write the cell diagram to be: I2(s) | I-(aq) || Ce3+(aq), Ce4+(aq) | Pt(s) But, the correct cell diagram is Pt(s) | I2(s) | I-(aq) || Ce3+(aq), Ce4+(aq) | Pt(s) Why i...
Tue Mar 06, 2018 11:07 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 15.19 (a)
Replies: 3
Views: 375

### Re: 15.19 (a)

I got that answer too. I believe it is fine to round the number to 9.
Mon Mar 05, 2018 12:29 am
Forum: General Rate Laws
Topic: Homework Problem 15.19C
Replies: 5
Views: 314

### Homework Problem 15.19C

I'm not sure how to get the answer in the solutions. The correct answer is supposed to be 2.85x10^(12). I keep getting k=2.85 by inputting the values of experiment 1 into the rate law.
Rate law: rate = k[A][B]^(2)[C]^)2)
8.7 = k (1.25)(1.25)^(2)(1.25)^(2) -> k = 2.85
Mon Mar 05, 2018 12:24 am
Forum: General Rate Laws
Topic: Rate laws and integrated rate laws
Replies: 3
Views: 304

### Re: Rate laws and integrated rate laws

There are two types of rate laws. One of them is the differntial rate law, and the other is the integrated rate law. The differential rate law depends on the concentration and describes the reactions rate in terms of (delta) [R] / (delta) t. The integrated rate law is the integration of the differen...
Thu Feb 22, 2018 12:47 pm
Forum: Balancing Redox Reactions
Topic: Balancing H+
Replies: 4
Views: 266

### Re: Balancing H+

You can use H+ to balance the number of H's. I think using the H3O+ is the correct way to balance corresponding to the reaction, but my TA brought up in section that you can use H+ and then replace it with H3O+ at the end since it makes more sense to use H+ when balancing.
Tue Feb 20, 2018 11:16 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.23a
Replies: 2
Views: 144

### 14.23a

Why does the left side of the cell diagram not have a Pt(s), and the right side does?

This is the reaction: 2(NO3)-(aq) + 8H+(aq) + 6Hg(l) -> 3(Hg2)2+(aq) + 2NO(g) + 4H2O(l)
Tue Feb 20, 2018 10:21 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.15a
Replies: 4
Views: 243

### Re: 14.15a

I'm also confused. Why can you assume that you there is a Ag cathode and Br anode?
Tue Feb 20, 2018 1:11 pm
Forum: Balancing Redox Reactions
Topic: Anode vs Cathode and their Equations
Replies: 1
Views: 140

### Re: Anode vs Cathode and their Equations

The cathode is usually identified as an oxidation reaction, and the anode is identified as a reduction reaction. I believe the signs for the values of the cell potential of the cathode/anode are flipped if you filpped the equation, and vice versa.
Tue Feb 20, 2018 1:05 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic cells
Replies: 2
Views: 116

### Re: Galvanic cells

You would reverse it if you were using the equation Ecell = E(anode) + E(cathode). There's another equation Ecell = E(cathode) - E(anode), where you don't need to flip the sign.
Tue Feb 20, 2018 12:56 pm
Forum: Balancing Redox Reactions
Topic: oxidation states
Replies: 4
Views: 241

### Re: oxidation states

Additoinally, there are a few rules you can follow when determining oxidation states. H will always have the oxidation state of +1. O will have the oxidation state of -2, except in H2O2, when oxygen's oxidation state is -1. The charges of elements are the oxidation state numbers. For example, Cr 3+ ...
Tue Feb 20, 2018 1:21 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.13b
Replies: 2
Views: 156

### 14.13b

How do you know when to use Pt as an anode/cathode?
Tue Feb 20, 2018 1:18 am
Forum: Balancing Redox Reactions
Topic: 14.13C
Replies: 1
Views: 151

### 14.13C

Write the half-reaction, the balanced equation for the cell reaction, and the cell diagram for the following skeletal equations: c) Cl2(g) + H2(g) -> HCl(aq) I don't understand why it doesn't split into the two half reactions: 1) Cl2 -> HCl 2) H2 -> HCl Also, an explanation would help. Thanks!
Tue Feb 13, 2018 11:50 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Review Session Question
Replies: 2
Views: 188

### Review Session Question

True or false: Removing heat from a system is exothermic, so temperature must decrease. If energy is being removed from a system, isn't it similar to an exothermic process, which means the temperature of the system should decrease? Why is the answer false?
Sat Feb 10, 2018 3:12 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.47 delta S = 0
Replies: 2
Views: 198

### 9.47 delta S = 0

Does delta S of the total reaction = 0 when a process if reversible? Why?
Wed Feb 07, 2018 9:35 pm
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: Molar Entropy
Replies: 2
Views: 154

### Molar Entropy

The bigger the molecule, the higher the molar entropy. When determining the greater molar entropy, does disorder in the number of different orientations matter more than the size of the molecule?
Wed Feb 07, 2018 9:31 pm
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: 9.25
Replies: 1
Views: 136

### 9.25

Why does W = 6 raised to avogadro's number? I don't get avogadro's number part. Can't it be 6 (# of orientations) raised to 6 (# of different molecules)?
Sat Feb 03, 2018 11:57 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Replies: 4
Views: 251

For an adiabatic system, q=0, but that does not mean necessarily mean that temperature = 0.
Wed Jan 31, 2018 1:40 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.13 [ENDORSED]
Replies: 1
Views: 154

### 9.13[ENDORSED]

Why can you assume that n=1.00mol? Is it because of the ideal gas laws? Can it be further explained if it is?
Wed Jan 31, 2018 12:34 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.13 [ENDORSED]
Replies: 6
Views: 536

### Re: 9.13[ENDORSED]

I believe this is an error in the solutions manual. The correct solutions uses Cv. Here's the link: https://lavelle.chem.ucla.edu/wp-conten ... rs_6Ed.pdf
Fri Jan 26, 2018 12:35 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Bomb calorimeter
Replies: 7
Views: 397

### Re: Bomb calorimeter

In addition to the above responses, it is important to note that a bomb calorimeter is at constant volume, which means work = 0.
Wed Jan 24, 2018 9:31 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Changing the energy of a system
Replies: 6
Views: 374

### Changing the energy of a system

When you add more of an amount of a substance in a system, does it increase or descreae the energy of a system?
Sun Jan 21, 2018 5:36 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Calorimetry Questions
Replies: 2
Views: 174

### Calorimetry Questions

Do we have to add the heat of the calorimeter with the heat of the reaction to calculate the amount of heat released/absorbed from the reaction? Or is the heat absorbed by the calorimeter negligible?
Sun Jan 21, 2018 2:03 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Textbook Example 8.13
Replies: 1
Views: 181

### Textbook Example 8.13

Estimate the enthalpy of the reaction between bromine and propene (propylene) to form 1,2-dibromopropane. The enthalpy of vaporization of Br2 is 29.96 kJ/mol, and taht of CH3CHBrCH2Br is 35.61 kJ/mol. The reaction is Br2(l) + CH3CHCH2 -> CH3CHBrCH2Br(l). In order to solve the problem, I tried a diff...
Sun Jan 21, 2018 1:57 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard enthalpies on test 1 [ENDORSED]
Replies: 7
Views: 389

### Re: Standard enthalpies on test 1[ENDORSED]

Diatomic molecules are made of two elements. The seven diatomic elements from the periodic table are nitrogen, oxygen, bromine, iodine, chlorine, hydrogen, and fluorine. Because they are the same elements, they have a standard enthalpy change of 0.
Wed Jan 17, 2018 10:19 pm
Forum: Phase Changes & Related Calculations
Topic: Conditions of Different Systems [ENDORSED]
Replies: 1
Views: 136

### Conditions of Different Systems[ENDORSED]

What's the difference between an isothermal system, an isothermal system with an ideal gas, and an adiabatic system?
Wed Jan 17, 2018 10:15 pm
Forum: Phase Changes & Related Calculations
Topic: 8.15 b
Replies: 3
Views: 188

### Re: 8.15 b

An adiabatic system only allows the transfer between one energy: work. In this case, q = 0, but this does not necessarily mean the change in temperature (or delta T) is equal to 0 since the internal energy may also change when work occurs within the system.
Wed Jan 17, 2018 10:05 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat Capacity of Gases
Replies: 2
Views: 127

### Re: Heat Capacity of Gases

Cv, m = 3/2R is the equation used to calculate a heat capacity for atoms or monotomic atoms at a constant volume. Cp, m = 5/2R is the equation used to calculate a heat capacity for atoms at a constant pressure. The R represents the gas constant, R = 8.314 J/K*mol.
Wed Jan 17, 2018 9:59 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Specific Heat Capacity
Replies: 5
Views: 1753

### Specific Heat Capacity

The book states that the heat capacity of a dilute solution is taken to be the same as the pure solvent. Why?
Fri Dec 08, 2017 10:04 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Dipole Moment
Replies: 2
Views: 214

### Dipole Moment

How do you know when the dipole moments of some molecules can cancel out?
Fri Dec 08, 2017 4:18 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Strong Acids/Bases
Replies: 3
Views: 277

### Re: Strong Acids/Bases

Strong acids and bases do not have Ka and Kb values because they completely dissociate in water. Ka and Ka are used to describe only weak acids, but pH values can be used to describe both strong and weak acids.
Mon Nov 27, 2017 12:24 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone pairs and naming shape
Replies: 2
Views: 139

### Re: Lone pairs and naming shape

Lone pairs are taken into consideration when naming the shape of the molecule because the electron repulsion from the lone pairs affects the bond angles and therefore the shape of the molecule.
Mon Nov 27, 2017 12:21 pm
Forum: Naming
Topic: Ligand order in coordination sphere
Replies: 3
Views: 207

### Re: Ligand order in coordination sphere

I believe that if you wanted to write the ligands in alphabetical order, you'd refer to the name (amino) rather than the molecule (NH3). In addition, it's helpful to note that prefixes are not taken into consideration when alphabetizing.
Sun Nov 26, 2017 9:56 pm
Forum: Naming
Topic: Roman numeral placement
Replies: 4
Views: 292

### Re: Roman numeral placement

Normally, the Roman numerals are written after the name of the compounds between the brackets so that you can specify the charge of the transition metal.
Fri Nov 24, 2017 1:30 pm
Forum: Hybridization
Topic: How to tell the hybridization [ENDORSED]
Replies: 4
Views: 335

### Re: How to tell the hybridization[ENDORSED]

To tell the hybridization, I usually look at the number of electron dense areas. The total number will help you identify the hybridization by looking at the exponents of each letter. For example, an atom with four electron dene areas will have a hybridzation of sp^3.
Sun Nov 19, 2017 10:12 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Angular
Replies: 2
Views: 160

### Re: Angular

Angular is synonymous to bent. You can use either angular or bent to describe a certain molecular structure.
Sun Nov 19, 2017 10:09 pm
Forum: Lewis Structures
Topic: Best way to start Lewis Structures
Replies: 12
Views: 732

### Re: Best way to start Lewis Structures

Normally, I'd draw the bonds to connect the atoms together first and then figure out how many electrons are left to distribute amongst the structure. It's helpful to know how the formal charge equation plays a role in each atom when assigning bonds. For example, oxygen has six valence electrons, so ...
Fri Nov 10, 2017 5:57 pm
Forum: Lewis Structures
Topic: Lewis structure
Replies: 4
Views: 322

### Re: Lewis structure

For Lewis structures, the atom with the lowest ionization energy will be used as the central atom. Additionally, carbon, when present, is usually the central atom.
Fri Nov 10, 2017 5:51 pm
Forum: Trends in The Periodic Table
Topic: Electron Affinity Exception
Replies: 3
Views: 1083

### Electron Affinity Exception

As an exception for the electron affinity periodic trend, why does nitrogen have a lower electron affinity than oxygen?
Fri Nov 03, 2017 3:13 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Ionization energy vs. electron affinity [ENDORSED]
Replies: 5
Views: 574

### Re: Ionization energy vs. electron affinity[ENDORSED]

According to the book, the ionization energy is the minimum amount of energy needed to remove an electron from a gas-phase atom, and electron affinity is the energy released when an electron is added to a gas-phase atom.
Mon Oct 30, 2017 12:54 pm
Forum: Lewis Structures
Topic: Homework Question 2.37B [ENDORSED]
Replies: 2
Views: 158

### Homework Question 2.37B[ENDORSED]

True or false? Electrons in an s-orbital are more effective than those in other orbitals at shielding other electrons from the nuclear charge because an electron in an s-orbital can penetrate to the nucleus of the atom. Will someone please explain why the answer is true in terms of the "shieldi...
Thu Oct 26, 2017 10:55 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Heisenberg Module #23?
Replies: 4
Views: 393

### Re: Heisenberg Module #23?

Hi, the correct answer for this delta V is 2 x 10^-39 m/s, so yes, it does have a negative exponent, but there may be an error in the set up of your equation or calculation.
Thu Oct 26, 2017 10:45 pm
Forum: Heisenberg Indeterminacy (Uncertainty) Equation
Topic: Post-Module Question #14
Replies: 2
Views: 299

### Post-Module Question #14

Which one of the following statements is correct in describing Heisenberg's uncertainty (indeterminacy) equation? A. The less precisely the position is determined, the less precisely the momentum is known in this instant, and vice versa. B. The more precisely the position is determined, the more pre...
Thu Oct 19, 2017 5:01 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Copper Ion Electron Configuration
Replies: 3
Views: 434

### Re: Copper Ion Electron Configuration

Why is copper different in that it doesn't follow the normal order (or pattern on the periodic table) of an electron configuration?
Thu Oct 19, 2017 4:53 pm
Forum: Quantum Numbers and The H-Atom
Topic: The magnetic quantum number
Replies: 2
Views: 381

### Re: The magnetic quantum number

No, the magnetic quantum number does not only have three values. I believe the maximum number of values is seven (-3, -2, -1, 0, 1, 2, 3) because the f-orbital contains 14 electrons, giving it 7 subshells in the electron configuration.
Sat Oct 14, 2017 3:33 pm
Forum: Photoelectric Effect
Topic: Post-Module Question #29 [ENDORSED]
Replies: 1
Views: 183

### Post-Module Question #29[ENDORSED]

"Light hits a sodium metal surface and the velocity of the ejected electron is 6.61 x 10^5 m.s-1. The work function for sodium is 150.6 kJ.mol-1. 29) How much energy is required to remove an electron from one sodium atom?" I believe the question asks for the work function, but I'm confused...
Sat Oct 14, 2017 1:43 pm
Forum: Properties of Light
Topic: Exited state
Replies: 5
Views: 462

### Re: Exited state

Because the higher energy state is not as stable, the electron has a tendency to move to the ground state, where it is in closer proximity to the protons, positively charged sub-particles.
Fri Oct 06, 2017 9:36 am
Forum: Limiting Reactant Calculations
Topic: Limiting Reactants - Neither?
Replies: 2
Views: 243

### Limiting Reactants - Neither?

I'm confused about when neither of the reactants is limiting in the chemical reaction. Could someone give an example/explanation?
Fri Oct 06, 2017 9:30 am
Forum: Empirical & Molecular Formulas
Topic: F1
Replies: 3
Views: 412

### Re: F1

We divide the mass of C, H, and O by 152.228g/mol in order to find the mass percent composition of each element. If there are 10 carbons in the formula, you would multiply 12.01*10 in order to find the total mass of carbon, which is 120.1g. Then divide by the total mass of the molecule to find the a...