## Search found 33 matches

Sat Mar 16, 2019 8:35 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Review Session-Thermo-files- Wednesday-Q11-clarification [ENDORSED]
Replies: 10
Views: 837

### Re: Review Session-Thermo-files- Wednesday-Q11-clarification[ENDORSED]

For #11, I read your explanation but am confused still. dStotal = dSpressurechange + dStemperaturechange For dSpressurechange, we use S=nRln(P1/P2), to see how entropy changes as a result of pressure changing along with something (either V or T). I assumed that V would be changing in this part 1 of ...
Sat Mar 16, 2019 10:49 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: HW 4F.11
Replies: 1
Views: 299

### HW 4F.11

During the test of an internal combustion engine, 3.00 L of nitrogen gas at 18.5 C was compressed suddenly and irreversibly to 0.500 L by driving in a piston. In the process, the tempeerature of the gas increased to 28.1 C. Assume ideal behavior. What is the change in entropy of the gas? My understa...
Sat Mar 16, 2019 10:44 am
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: dS = nC ln(T2/T1) [ENDORSED]
Replies: 1
Views: 258

### dS = nC ln(T2/T1)[ENDORSED]

The textbook version has dS = C ln (T2/T1) without the n. Could someone explain why there's a difference in the 2 formulas?
Fri Mar 15, 2019 5:55 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Activation energy units
Replies: 2
Views: 129

### Activation energy units

The units for Ea are J/mol or kJ/mol etc. What is the /mol referring to? Is it per mole of product? What if 2 products are made? Does that mean per .5 mole of each product? (and energy per .333 mole if there were 3 products etc.)
Fri Mar 15, 2019 5:08 pm
Forum: Polyprotic Acids & Bases
Topic: Ka and Ka2
Replies: 1
Views: 407

### Ka and Ka2

Will be asked to find pH given Ka and Ka2 of a diprotic acid? How would we set up an ice tablee in that case?
Fri Mar 15, 2019 5:07 pm
Forum: Bronsted Acids & Bases
Topic: pH and pOH
Replies: 1
Views: 363

### pH and pOH

Because bronsted acids and bases don't directly affect H+ and OH- concentration, how do they affecrt pH?
Thu Mar 14, 2019 2:48 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: isothermal irreversible free expansion
Replies: 2
Views: 298

### Re: isothermal irreversible free expansion

Why does irreversible free expansion mean delta S = 0?
Thu Mar 14, 2019 2:44 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy change: V, P, T
Replies: 4
Views: 434

### Re: Entropy change: V, P, T

Why does higher pressure mean less entropy? Couldn't there still be an equal volume of gas but at higher pressure?
Thu Mar 14, 2019 2:39 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: units
Replies: 7
Views: 460

### Re: units

Any combination of units work AS LONG AS they are related by the correct units in gas constant R. Conversely, to use R you either have to convert given values' units so they work for R or convert R into a different form of itself with the right units.
Thu Mar 14, 2019 2:37 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Enthalpy of phase change
Replies: 5
Views: 393

### Re: Enthalpy of phase change

Breaking Br2 into 2Br doesn't automatically make the 2Br a gas.
Thu Mar 14, 2019 2:35 pm
Forum: Phase Changes & Related Calculations
Topic: ΔH vs ΔU?
Replies: 8
Views: 603

### Re: ΔH vs ΔU?

Can't there be expansion with constant pressure? Wouldn't that still be work done?
Thu Mar 14, 2019 2:33 pm
Forum: Phase Changes & Related Calculations
Topic: steam at 100ºC burn worse
Replies: 7
Views: 377

### Re: steam at 100ºC burn worse

This also assumes that the number of water and steam particles are equal. Don't intuit that steam burns less because typically when you put your hadn in 100C water your hand is in contact with a lot more molecules than if you had your hand above the steam from boiling water.
Thu Mar 14, 2019 2:32 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Is there a significance with 298 degrees Kelvin?
Replies: 5
Views: 1805

### Re: Is there a significance with 298 degrees Kelvin?

Standard conditions temp in kelvin! Because 25 C + 273
Thu Mar 14, 2019 2:31 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Internal energy
Replies: 2
Views: 284

### Re: Internal energy

"The energy lost as work is replaced by heat"; but you say these reactions normally happen in a heat bath? What if there isn't a heat bath? Would it simply not be isothermal reversible?
Thu Mar 14, 2019 2:29 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Delta U
Replies: 5
Views: 340

### Re: Delta U

Why does no temperature change = no change in U?
Thu Mar 14, 2019 2:28 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Determine if molecule is in most stable form
Replies: 5
Views: 360

### Re: Determine if molecule is in most stable form

I think you can also consider whether or not the molecule is in its most oxidised state. If it is then it's in a lowest energy configuration (I think).
Thu Mar 14, 2019 2:25 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Assuming ideal gas
Replies: 3
Views: 349

### Re: Assuming ideal gas

I think a lot of questions just require you to think the gas is ideal to apply formulas. IRL lot of energy is lost to heat or sound etc. so even if it's not stated explicitly you basically assume gas is ideal all the time.
Wed Mar 13, 2019 9:34 pm
Forum: General Rate Laws
Topic: Molarity and rates
Replies: 1
Views: 84

### Molarity and rates

In lecture, professor said that most elementary reactions are 1, 2, or 3 (but even rarely 3) order because the more orders means the more physical molecules have to bump into each other at the same time with enough energy for the reaction to occur. My question is, in that case, what about 1 M or 1 m...
Wed Mar 13, 2019 9:24 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Isothermal
Replies: 5
Views: 202

### Isothermal

Why is isothermal deltaU = 0? A formula explanation would be nice if there is one!
Wed Mar 13, 2019 9:24 pm
Forum: Administrative Questions and Class Announcements
Replies: 179
Views: 12562

Thank you :)
Wed Mar 13, 2019 9:20 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Elementary Step
Replies: 1
Views: 72

### Elementary Step

Is the reaction mechanisms individual steps the only elementary steps? What else can elementary reactions be?
Tue Mar 12, 2019 7:42 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Converting
Replies: 2
Views: 123

### Converting

When is it valid to substitute rate constant k? What formulas relate k to k' for a pseudo rate law?
Tue Mar 12, 2019 7:41 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst
Replies: 14
Views: 357

### Nernst

Is n the total number of e- moved after balancing the half reactions?
Sun Mar 10, 2019 2:40 pm
Forum: General Rate Laws
Topic: Rate Constant
Replies: 1
Views: 64

### Rate Constant

Is the rate law constant's (k) units different when in a pseudo rate equation since there is only one concentration that contributes to its units? (assume other reactants' concentration changes don't affect pseudo rate)
Sun Mar 10, 2019 2:39 pm
Forum: General Rate Laws
Topic: Units pseudo rate law
Replies: 2
Views: 98

### Units pseudo rate law

What are the units of for pseudo rate law constant (k')?
Sun Mar 10, 2019 2:37 pm
Forum: First Order Reactions
Topic: Units for lnconc
Replies: 1
Views: 70

### Units for lnconc

What are the appropriate units when plotting ln[conc] for a first order reaction?
Thu Feb 28, 2019 6:29 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Electrolytic cell
Replies: 1
Views: 76

### Electrolytic cell

Why is the electrolytical cell +/- on the electrodes different? Isn't current going the same way?
Tue Feb 26, 2019 3:21 pm
Forum: Balancing Redox Reactions
Topic: Knowing oxidation states
Replies: 2
Views: 70

### Knowing oxidation states

In HW, 6L 1.9, it says the balance the reaction between potassium permanganate and iron2 chloride. How do we know the change in manganese's oxidation state (from +7 to +2)? Should we just know? +7 is deducible but not +2 (I think).
Thu Feb 21, 2019 7:44 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Gibbs
Replies: 3
Views: 158

### Gibbs

Could someone explain to me in words (to help me conceptualise) what Gibbs Free energy is?
Sun Feb 17, 2019 1:49 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Entropy using statefunctions
Replies: 2
Views: 324

### Entropy using statefunctions

If a gas changes volume and temperature during a compression, for the entropy formulas that involve a constant T or V to find deltaS using changes in T or V, how do you know what value to use?
Wed Feb 13, 2019 10:41 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Ideal Gas C
Replies: 5
Views: 419

### Ideal Gas C

For ideal gases, why is Cp 5/2R and Cv 3/2R
Sat Feb 09, 2019 1:32 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Spontaneity
Replies: 1
Views: 68

### Spontaneity

Are phase changes spontaneous (based on entropy or Gibbs energy)? and how does that fit into the formulas?
Tue Feb 05, 2019 9:15 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Cv vs Cp
Replies: 3
Views: 147

### Cv vs Cp

To clarify, Cp is larger than Cv because Cp = heat supplied to heat the system + work down to expand the gas above. Is this correct? Does this also mean Cv=Cp if the system proceeds in a vacuum?