Search found 21 matches

by Naomi Jennings 2H
Sun Feb 25, 2018 11:24 pm
Forum: First Order Reactions
Topic: 15.27
Replies: 6
Views: 357

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...
by Naomi Jennings 2H
Sun Feb 25, 2018 11:10 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.67
Replies: 1
Views: 74

Re: 15.67

viewtopic.php?f=151&t=12747
This one helped me a lot!
by Naomi Jennings 2H
Sun Feb 25, 2018 10:57 pm
Forum: Student Social/Study Group
Topic: Post All Chemistry Jokes Here
Replies: 7726
Views: 1046744

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
by Naomi Jennings 2H
Sun Feb 18, 2018 10:54 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Electrochemical Series Definition
Replies: 4
Views: 186

Electrochemical Series Definition

Can someone define what an "Electrochemical series" is? The textbook uses this term in 14.7. Thanks!
by Naomi Jennings 2H
Sun Feb 18, 2018 10:50 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: galvanic vs electrolytic
Replies: 4
Views: 113

Re: galvanic vs electrolytic

Oops sorry didn't see someone else commented.
by Naomi Jennings 2H
Sun Feb 18, 2018 10:49 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: galvanic vs electrolytic
Replies: 4
Views: 113

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.
by Naomi Jennings 2H
Sun Feb 18, 2018 10:45 pm
Forum: Balancing Redox Reactions
Topic: Exercise 14.17
Replies: 6
Views: 228

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...
by Naomi Jennings 2H
Sun Feb 11, 2018 10:28 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Cell potential
Replies: 2
Views: 127

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.
by Naomi Jennings 2H
Sun Feb 11, 2018 10:25 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 8.93
Replies: 1
Views: 119

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?
by Naomi Jennings 2H
Fri Feb 02, 2018 5:38 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Entropy [ENDORSED]
Replies: 5
Views: 316

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.
by Naomi Jennings 2H
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: 105

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...
by Naomi Jennings 2H
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: 379

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?
by Naomi Jennings 2H
Fri Jan 26, 2018 11:18 pm
Forum: Phase Changes & Related Calculations
Topic: When to use Kelvin or Celsius
Replies: 10
Views: 697

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 ...
by Naomi Jennings 2H
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: 121

Box 9.1 Absolute Zero

Do we need to know the methods of reaching absolute zero in box 9.1 (page 336-337)?
by Naomi Jennings 2H
Fri Jan 26, 2018 10:51 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: reversible and irreversible reactions
Replies: 4
Views: 152

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.
by Naomi Jennings 2H
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: 203

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...
by Naomi Jennings 2H
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: 1257

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!
by Naomi Jennings 2H
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: 128

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...
by Naomi Jennings 2H
Sat Jan 13, 2018 8:11 pm
Forum: Phase Changes & Related Calculations
Topic: Phase Changes
Replies: 13
Views: 579

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.
by Naomi Jennings 2H
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: 149

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...
by Naomi Jennings 2H
Fri Jan 12, 2018 11:57 pm
Forum: Phase Changes & Related Calculations
Topic: Heat and work not state functions
Replies: 7
Views: 372

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...

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