Search found 21 matches
- Sun Feb 25, 2018 11:24 pm
- Forum: First Order Reactions
- Topic: 15.27
- Replies: 7
- Views: 1390
15.27
15.27 A substance A decomposes in a first-order reaction and its half life is 355 s. How much time must elapse for the concentration of A to decrease to (a) 1/8 [A] ; (b) one-fourth of its 80 initial concentration; (c) 15% of its initial concentration; (d) one-ninth of its initial concentration? How...
- Sun Feb 25, 2018 11:10 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: 15.67
- Replies: 1
- Views: 282
Re: 15.67
viewtopic.php?f=151&t=12747
This one helped me a lot!
This one helped me a lot!
- Sun Feb 25, 2018 10:57 pm
- Forum: Student Social/Study Group
- Topic: Post All Chemistry Jokes Here
- Replies: 9651
- Views: 3739170
Re: Post All Chemistry Jokes Here
I'm planning to go into a freezing chamber at -273.15 degrees C. My friends were worried but I told them I'd be 0K
- Sun Feb 18, 2018 10:54 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Electrochemical Series Definition
- Replies: 4
- Views: 798
Electrochemical Series Definition
Can someone define what an "Electrochemical series" is? The textbook uses this term in 14.7. Thanks!
- Sun Feb 18, 2018 10:50 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: galvanic vs electrolytic
- Replies: 4
- Views: 499
Re: galvanic vs electrolytic
Oops sorry didn't see someone else commented.
- Sun Feb 18, 2018 10:49 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: galvanic vs electrolytic
- Replies: 4
- Views: 499
Re: galvanic vs electrolytic
An electrolytic cell is a cell where an electric current drives a nonspontaneous reaction. A galvanic cell is an electrochemical cell where a spontaneous reaction is used to create an electric current.
- Sun Feb 18, 2018 10:45 pm
- Forum: Balancing Redox Reactions
- Topic: Exercise 14.17
- Replies: 6
- Views: 771
Re: Exercise 14.17
14.17 (a) Write balanced half-reactions for the redox reaction of an acidified solution of potassium permanganate and iron(II) chloride. (b) Write the balanced equation for the cell reaction and devise a galvanic cell to study the reaction (write its cell diagram) I would look up the redox reactions...
- Sun Feb 11, 2018 10:28 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Cell potential
- Replies: 2
- Views: 1802
Re: Cell potential
∆G° = - n F E°
At standard conditions, the gibbs free energy is equal to the negative mols of electrons moving from the anode to the cathode x Faraday's constant x the standard cell potential.
At standard conditions, the gibbs free energy is equal to the negative mols of electrons moving from the anode to the cathode x Faraday's constant x the standard cell potential.
- Sun Feb 11, 2018 10:25 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: 8.93
- Replies: 1
- Views: 337
8.93
Calculate the work that must be done against the atmosphere for the expansion of the gaseous products in the combustion of 1.00 mol C6H6(l) at 25 degrees C and 1.00 bar.
How would you start to do this problem?
How would you start to do this problem?
- Fri Feb 02, 2018 5:38 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Entropy [ENDORSED]
- Replies: 5
- Views: 2060
Re: Entropy [ENDORSED]
When the system goes from solid to liquid, or liquid to gas, entropy also increases. If a reaction creates more mols of gas than were previously present then entropy increases as well.
- Fri Feb 02, 2018 4:21 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Change in vol and temp
- Replies: 2
- Views: 392
Re: Change in vol and temp
If there's a change in volume and temperature, you use two different equations, which you can do because Entropy is a state function, so there's the same change whether both volume and temperature change at the same time, or whether volume changes, then temperature. First you can calculate the entro...
- Wed Jan 31, 2018 10:29 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: The value of Cp
- Replies: 8
- Views: 1543
Re: The value of Cp
kaushalrao2H wrote:Cp for ideal gases is 4R. Cv for ideal gases is 3R. When in doubt, remember that Cp = Cv + R
I thought for an ideal gas Cp is (5/2)R and Cv is (3/2)R?
- Fri Jan 26, 2018 11:18 pm
- Forum: Phase Changes & Related Calculations
- Topic: When to use Kelvin or Celsius
- Replies: 10
- Views: 6877
Re: When to use Kelvin or Celsius
In addition, for entropy you have to use Kelvin, because in the equation you aren't using delta T, you are using T, so multiplying the other terms by 25 (degrees celsius) will get a much different result than multiplying the other terms by 298 (degrees kelvin). In contrast, for a problem asking for ...
- Fri Jan 26, 2018 11:05 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: Box 9.1 Absolute Zero
- Replies: 2
- Views: 329
Box 9.1 Absolute Zero
Do we need to know the methods of reaching absolute zero in box 9.1 (page 336-337)?
- Fri Jan 26, 2018 10:51 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: reversible and irreversible reactions
- Replies: 4
- Views: 607
Re: reversible and irreversible reactions
I think it will indicate in the question. If it doesn't specify reversible or irreversible, it's probably irreversible. If "Work is done at a constant pressure" it must be reversible since the internal and external pressures won't be incredibly close together for most of the expansion.
- Fri Jan 19, 2018 11:26 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: 723
Re: Heat capacity vs Specific Heat capacity
Heat capacity is the amount of energy required to raise the temperature of the system/something by one degree celsius. Specific heat capacity is the amount of energy required to raise the temperature of one gram of a substance by one degree celsius. Heat capacity is mostly useful for calorimeters, b...
- Fri Jan 19, 2018 11:03 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Difference between a lattice enthalpy and lattice energy
- Replies: 1
- Views: 8004
Difference between a lattice enthalpy and lattice energy
I know that for this chapter we're using enthalpy not energy, but I don't understand what the difference between the lattice enthalpy and the lattice energy even is. If anyone could explain this to me please do thank you!
- Fri Jan 19, 2018 10:50 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Enthalpies [ENDORSED]
- Replies: 3
- Views: 354
Re: Enthalpies [ENDORSED]
I've been working based on the following and it seems to be working! If they give you multiple other reactions and their enthalpies, then you probably need to use Hess's law. If they refer you to Appendix 2A, you should use the enthalpies of formation. If they tell you to use bond enthalpies, then u...
- Sat Jan 13, 2018 8:11 pm
- Forum: Phase Changes & Related Calculations
- Topic: Phase Changes
- Replies: 13
- Views: 1557
Re: Phase Changes
Ishita Monga 1B wrote:Sue Xu 2K wrote:Condensation, solidification and deposition are all exothermic phase change that release heat during the process.
follow up- what is deposition?
Deposition is the process of a vapor going straight from vapor to solid. It's the reverse of sublimation.
- Sat Jan 13, 2018 8:06 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: enthalpy vs heat
- Replies: 2
- Views: 435
Re: enthalpy vs heat
Yes, because enthalpy is a state function and heat is a path function. The enthalpy value will be determined by the current state of the substance, whereas heat is defined by the textbook as "the energy that is transferred as a result of a temperature difference between a system and its surroun...
- Fri Jan 12, 2018 11:57 pm
- Forum: Phase Changes & Related Calculations
- Topic: Heat and work not state functions
- Replies: 7
- Views: 928
Re: Heat and work not state functions
Yet another way to think about it: The difference between a state function and a path discussion is the difference between the distance between point a and b and the distance walked. If you start at Pauley and walk to Hedrick and then to CS50, the distance between your start and endpoint will only b...