## Search found 25 matches

Fri Mar 17, 2017 12:17 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: entropy question
Replies: 1
Views: 355

### Re: entropy question

You know the entropy of the system because the reactants have 3 moles of gas while the products have 2 moles of gas. Since the moles of gas decreases from reactants to products, you know that the entropy of the system must be decreasing, so the change in entropy of the system must be negative and th...
Sun Mar 12, 2017 11:55 pm
Forum: *Alkanes and Substituted Alkanes (Staggered, Eclipsed, Gauche, Anti, Newman Projections)
Topic: Newman Projection
Replies: 1
Views: 412

### Re: Newman Projection

Yes, the structure with the lowest potential energy is the most stable because stable molecules experience more attractive forces and less repulsive forces. Attractive forces lower the potential energy of a molecule while repulsive forces increase the potential energy of a molecule, so the structure...
Mon Mar 06, 2017 10:59 pm
Forum: Administrative Questions and Class Announcements
Topic: Quiz 3 Winter 2017
Replies: 183
Views: 19741

### Re: Quiz 3 Winter 2017

For #4 Why isn't it 1-butyl-3,4 dimethylcyclohexane? For cycloalkanes with more than two substituents, you must compare each individual number for each substituent: 1-butyl-3,4-dimethylcyclohexane (incorrect) 4-butyl-1,2-dimethylcyclohexane (correct) Since your proposed answer has 1,3,4 while the c...
Sun Mar 05, 2017 12:18 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Intermediates in Reaction Profiles
Replies: 4
Views: 674

### Re: Intermediates in Reaction Profiles

The intermediates are represented by the minimum of the curve between two peaks. The two peaks represent transition states, but not intermediates. In general, the number of intermediates formed is one less than the number of peaks or "humps" because when the graph returns to a minimum at t...
Sun Mar 05, 2017 12:14 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: rate determining and rate limiting step [ENDORSED]
Replies: 1
Views: 416

### Re: rate determining and rate limiting step[ENDORSED]

Yes the rate determining step and rate limiting step mean the same thing. It is always the slow step because it "determines" or "limits" the speed of the reaction.
Sun Feb 19, 2017 6:19 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Drawing a Cell Diagram
Replies: 3
Views: 574

### Re: Drawing a Cell Diagram

You don't write the salt bridge in the diagram. You include Pt(s) when the anode or cathode or both do not have a solid in their half reaction. This is because a solid electrode must be present for the system to function. Pt(s) is used because it is an inert conductor that allows electron flow witho...
Sun Feb 12, 2017 1:03 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: What is Q again?
Replies: 1
Views: 305

### Re: What is Q again?

Q is the reaction quotient. Mathematically, it is represented by the fraction: [products]/[reactants]. At equilibrium Q is equal to K, the equilibrium constant of the reaction. Partial pressures for gases can be used in the formula instead of concentrations if this is given in the problem. Recall fr...
Sun Feb 12, 2017 12:58 am
Forum: Administrative Questions and Class Announcements
Topic: W '17 midterm
Replies: 2
Views: 471

### Re: W '17 midterm

The midterm is mainly thermochemistry and electrochemistry I believe. Nothing after electrochemistry should be on it. The practice exams in the back of the course reader really helped me study for 14A with Lavelle, and I have been doing the same thing to prepare for this midterm. It also is helpful ...
Sun Feb 05, 2017 3:01 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8039
Views: 1411069

### Re: Post All Chemistry Jokes Here

A photon checks into a hotel and is asked if he needs any help with his luggage. He replies, "no, I'm travelling light."
Mon Jan 30, 2017 8:20 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Finding Gibbs Free Energy - 9.55 and 9.57
Replies: 1
Views: 360

### Re: Finding Gibbs Free Energy - 9.55 and 9.57

The two methods are interchangeable under standard conditions using the values given in Appendix 2A. Neither method is really preferable, but rather it depends on what information you are given in the problem or how the problem is asked. In instances under non-standard conditions, I think the second...
Wed Jan 25, 2017 10:10 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Molar Heat Capacity for Phase Change of Water
Replies: 1
Views: 297

### Re: Molar Heat Capacity for Phase Change of Water

It takes more heat to raise 1.00 g of ice by 1.00 degree Celsius than it does to raise the temperature of 1.00 g liquid water by 1.00 degree Celsius. It also takes more heat to raise the temperature of liquid water than to raise the temperature of water vapor. The equation q=cm(change in temperature...
Sun Jan 22, 2017 2:08 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Molar Heat Capacity
Replies: 4
Views: 736

### Re: Molar Heat Capacity

Since the molar heat capacity is concerned with a temperature change, it can be expressed in terms of degrees Celsius or degrees Kelvin. Zero degrees Celsius is equal to 273.15 Kelvin, and this difference can be used to calculate degrees Celsius from Kelvin by subtracting this number, and to calcula...
Mon Jan 16, 2017 4:13 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Problem 8.19
Replies: 2
Views: 377

### Problem 8.19

On problem 8.19 of the homework exercises, there are two terms for the total heat supplied, one to eat the copper kettle and one to heat the water. In both cases the temperature change used is 100-22 degrees Celsius. For these types of problems, is the temperature change of the container always the ...
Wed Nov 30, 2016 4:58 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Problem 11.43
Replies: 2
Views: 472

### Re: Problem 11.43

Since volume is not clearly defined in this problem, I think that it is acceptable to assume that at whatever volume the reaction is taking place, the pressure of NO2=1.00 bar while the concentration of the products is the same as their partial pressures. There should exist some volume where this ho...
Wed Nov 30, 2016 4:36 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8039
Views: 1411069

### Re: Post All Chemistry Jokes Here

What is Cesium and Iodine's favorite TV show?
CSI
Wed Nov 30, 2016 4:30 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Calculating pH
Replies: 1
Views: 342

### Re: Calculating pH

If the concentration of H3O+ is 10^-7, then pH= -log(10^-7). Using the log rule dealing with exponents, pH= 7 log(10), and pH=7, which proves that the solution would be neutral. Autoprotolysis refers to the transfer of a proton between two identical molecules. In this case two molecules of H2O yield...
Sun Nov 20, 2016 3:21 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8039
Views: 1411069

### Re: Post All Chemistry Jokes Here

Got mole problems? Call Avogrado at 602-1023.
Sun Nov 20, 2016 3:15 pm
Forum: Lewis Acids & Bases
Topic: Lewis vs Bronsted
Replies: 3
Views: 595

### Re: Lewis vs Bronsted

That is correct. Both Lewis and Bronsted explanations can describe the same acid or base. Notice that for acids, the net change in charge is -1, while for bases, the net change in charge is +1. When an acid donates a proton its charge becomes more negative, and when it accepts an electron its charge...
Sun Nov 13, 2016 1:28 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Valence electron configuration
Replies: 1
Views: 393

### Re: Valence electron configuration

You write (π2p)^4 because in molecular orbital diagrams you can't determine which p orbitals are x, y, and z due to the different ways molecular orbitals interact during bonding. The expanded version is used for valence electron configurations of a single atom. When writing the valence electron conf...
Wed Nov 02, 2016 4:14 pm
Forum: Ionic & Covalent Bonds
Topic: Ionic character
Replies: 2
Views: 565

### Re: Ionic character

LiH is more ionic than HCl because it has a greater difference in electronegativity between the two atoms. Even though hydrogen is at the left of the periodic table, it is actually more electronegative than one might expect. If you look in the chart in the course reader, you can see that hydrogen ha...
Sat Oct 29, 2016 4:19 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 8039
Views: 1411069

### Re: Post All Chemistry Jokes Here

What did the chemist say when he wrote down nitrogen dioxide incorrectly? ONO!!!
Sat Oct 22, 2016 7:10 pm
Forum: Trends in The Periodic Table
Topic: Ch2 Q.71 Diagonal Relationship
Replies: 1
Views: 359

### Re: Ch2 Q.71 Diagonal Relationship

A diagonal relationship is when diagonal elements in the Periodic Table show similar chemical properties. For example, elements that have similar atomic radius and ionization energies will likely exhibit similar chemical properties. The diagonal strip of metalloids demonstrates this characteristic s...
Fri Oct 14, 2016 3:03 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Definition of Orbitals
Replies: 1
Views: 416

### Re: Definition of Orbitals

S, P, D, and F are subshells of an electron shell (n). Each subshell is further divided into orbitals. Each orbital can contain up to two electrons. S subshells (1s, 2s, 3s...) have one orbital. P subshells (2p, 3p, 4p...) have three orbitals. D subshells have 5 orbitals, and F subshells have 7 orbi...
Fri Oct 14, 2016 2:49 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Electron configuration representation
Replies: 1
Views: 292

### Re: Electron configuration representation

For the purposes of this class, it is best to use the previous noble gas in brackets for shorthand electron configurations. Using other elements is not as practical because you would most likely confuse yourself by using an element in the middle of the period because it would become more difficult t...
Tue Sep 27, 2016 11:07 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Charges [ENDORSED]
Replies: 2
Views: 589

### Re: Charges[ENDORSED]

For the purposes of molar mass calculations such as those in section E, charges are pretty much irrelevant to what we are doing. The charge on Cu^2+ in E23a is there to show that CuBr2 is an ionic compound in which electrons are shared between the atoms that compose it. Since the single copper atom ...