Search found 25 matches
- Tue Mar 14, 2017 1:08 am
- Forum: Calculating Work of Expansion
- Topic: Midterm 2013 Q4A
- Replies: 3
- Views: 759
Re: Midterm 2013 Q4A
Yes, I believe you can use either one. w=-nRTln(p1/p2) is basically found from the original w=-nRTln(v2/v1). This goes back to boyle's law p1v1=p2v2. In other words, v2/v1=p1/p2 (pressure and volume are inversely related to each other) and you plug this into the original equation.
- Thu Mar 09, 2017 11:55 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Relationship between activation energy and pseudo delta g
- Replies: 2
- Views: 2300
Relationship between activation energy and pseudo delta g
I used to think that pseudo delta g (as the gibbs free energy of activation) was related to the activation energy (Ea), but it was pointed out that in a reaction profile, pseudo delta g would depend on the difference between reactants' deltaG and transition state's deltaG and Ea would would depend o...
- Fri Mar 03, 2017 12:11 am
- Forum: *Alkanes
- Topic: Line structures
- Replies: 1
- Views: 406
Re: Line structures
I think if they vary in length they have to do with the number of bonds (ie: single, double, triple bonds). Triple bonds would be the shortest because the molecules bonded together are more firmly held together, therefore closer to each other, resulting in shorter bond length. However, I think in th...
- Fri Feb 24, 2017 11:33 pm
- Forum: General Rate Laws
- Topic: 15.5 Positive vs Negative
- Replies: 2
- Views: 608
Re: 15.5 Positive vs Negative
I'm not completely sure but I think the negative in the rate of decomposition for O2 (-d[O2]/dt) is in terms of the general reaction rate and merely indicates that the concentration of O2 is being used up. Since "reacts" already implies the negative (O2 concentration decreasing), I think a...
- Fri Feb 17, 2017 1:27 pm
- Forum: General Rate Laws
- Topic: Homework Help 15.1
- Replies: 4
- Views: 2581
Re: Homework Help 15.1
I'm not entirely sure but I used the method of initial rates: -1/a*(d[A]/dt)=1/b*(d[B]/dt)=1/c*(d[C]/dt) for aA ------> bB+cC. In this case, I did: -1/1*(d[N2]/dt)=-1/3(d[H2]/dt) Cancel out the dt's and the -1's. Then you are left with d[N2] (which is the rate of the concentration on N2) = 1/3*d[H2]...
- Sat Feb 11, 2017 8:21 pm
- Forum: Student Social/Study Group
- Topic: Study Group for Midterm Winter 2017
- Replies: 2
- Views: 669
Re: Study Group for Midterm Winter 2017
I'd love to!! How does Monday night sound to you? :)
- Sat Feb 11, 2017 10:20 am
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: 14.27
- Replies: 3
- Views: 550
Re: 14.27
I think you just have the E potentials mixed up. U+3+3e-->U is E=-1.79, U+4+e-->U+3 is E=-.61
- Fri Feb 10, 2017 1:45 am
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: 14.27
- Replies: 3
- Views: 550
Re: 14.27
I think that, in this case, we cannot add the E*'s together because the number of moles of electrons are not the same in the half-reactions (1e- vs. 3e-). According to the solutions manual, we have to use the deltaG*=-nFE* equation, to find the deltaG* of each individual half-reaction. Then we add t...
- Mon Jan 30, 2017 1:30 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Homework 8.41
- Replies: 1
- Views: 466
Re: Homework 8.41
I think it might be just because of rounding. Some of the problems I've been doing were off by about 0.2 when i used 8.314 J/(K*mol) instead of 8.32 J/(K*mol) from the solution guide, considering that there's also multiplication of huge numbers involved in this question too. I actually got 31 celsiu...
- Thu Jan 26, 2017 7:25 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Reversible Reaction
- Replies: 1
- Views: 406
Re: Reversible Reaction
A reversible reaction is a process in which the direction can be "reversed" by infinitesimal changes in some property of the system via its surroundings, without actually increasing entropy.
- Tue Jan 24, 2017 9:58 am
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Molar Heat Capacity
- Replies: 2
- Views: 576
Re: Molar Heat Capacity
I'm not sure if this is what you meant, but the ideal gas law is PV=nRT. In other words n=PV/(RT). If we plug in PV/(RT) into the molar heat = moles * molar heat capacity* change in temperature, molar heat capacity=molar heat / ((PV/(RT))*change in temperature)=molar heat*RT/(PV*change in temperatur...
- Fri Jan 20, 2017 2:00 am
- Forum: Phase Changes & Related Calculations
- Topic: Chapter 8 Question 11 Part B [ENDORSED]
- Replies: 1
- Views: 487
Re: Chapter 8 Question 11 Part B [ENDORSED]
I think that "isothermal" (constant temperature) "reversible" expansion was meant to emphasize a certain work equation we have to use: w = -nRTln(Vfinal/Vinitial)? "Isothermal" in that as a gas expands (increase in volume), the gas's pressure decreases, as stated by Boy...
- Fri Jan 13, 2017 1:32 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Calorimeters
- Replies: 3
- Views: 661
Calorimeters
I just wanted to be certain about the type of system that calorimeters are? So, all calorimeters act as isolated systems because they have to be thermally insulated, right? I was confused because calorimeters measure the transfer of energy as heat, so couldn't it be a closed system? Thank you!
- Fri Dec 02, 2016 12:26 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: 2nd Final 2007 Q4C
- Replies: 1
- Views: 482
2nd Final 2007 Q4C
The equil. constant Kc equals 0.045 at 250C for the decomposition reaction PCl5 <--> PCl3 + Cl2 Calculate the percentage of PCl5 that disassociates if 0.05 mole of PCl5 is placed in a closed vessel (constant volume) at 250C abd 2.00atm pressure.. what i tried to do was find molar concentration by fi...
- Tue Nov 29, 2016 11:11 pm
- Forum: General Science Questions
- Topic: Sig Figs
- Replies: 3
- Views: 1020
Re: Sig Figs
The way I learned it was not to round until the final value because otherwise the rounded value at each step can become very different from the actual value?
- Fri Nov 25, 2016 8:32 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: 11.13
- Replies: 2
- Views: 744
Re: 11.13
I think that since parts a and c involved gases only, it used partial pressures (P)? Since part b involved only aqueous solutions, it used molar concentrations instead ([])?
- Mon Nov 14, 2016 4:49 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Equil. Constants and Temperature
- Replies: 1
- Views: 466
Equil. Constants and Temperature
So, if K changes with temperature, then how is that shown with the equilibrium constant expression? Is it based on the P=MRT equation and the molar concentration changes, so the equil. constant also changes, or is there another equation that relates equil. constants and temperature?
- Sun Nov 13, 2016 3:40 pm
- Forum: Bond Lengths & Energies
- Topic: Question 5B Midterm
- Replies: 1
- Views: 764
Re: Question 5B Midterm
I think this is because n = 3 refers to the 3rd orbital. l = 2 refers to the d-orbital. So, the subshell notation becomes 3d orbital, and the d-orbital contains 5 orbitals. :)
- Wed Nov 02, 2016 10:09 am
- Forum: Dipole Moments
- Topic: Polar and Non-polar bond
- Replies: 8
- Views: 2081
Re: Polar and Non-polar bond
I don't think we have to know the exact values... just the general trend to find out which is more electronegative than the other. Also, the electronegativities given in the book are a bit different from the ones from my ap chem teacher and online so i dont think they'll be that specific as to findi...
- Sun Oct 30, 2016 1:05 pm
- Forum: Dipole Moments
- Topic: Polar and Non-polar bond
- Replies: 8
- Views: 2081
Re: Polar and Non-polar bond
I believe you can find whether a bond is polar or not by determining the difference in the electronegativities of the atoms being bonded. For example, Na-F is polar because Fluorine's electronegativity of 4.0 - Sodium's electronegativity of 0.93 = a huge polarity of 3.07. To determine whether the po...
- Thu Oct 27, 2016 8:59 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: VSPER Model [ENDORSED]
- Replies: 2
- Views: 678
Re: VSPER Model [ENDORSED]
Yes, I believe they mean the same thing :)
- Wed Oct 19, 2016 4:33 pm
- Forum: Lewis Structures
- Topic: Formal Charge vs. Octet [ENDORSED]
- Replies: 1
- Views: 650
Formal Charge vs. Octet [ENDORSED]
Which is more stable for BF3, as it is with FC all equaling 0 or as a coordinate covalent bond (because boron's formal charge would no longer be 0 then?)?
If the former, why would BF3 react in the first place if it's already stable?
Thank you!!
If the former, why would BF3 react in the first place if it's already stable?
Thank you!!
- Fri Oct 14, 2016 1:47 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Electron configuration representation
- Replies: 1
- Views: 460
Electron configuration representation
Hi,
Does it matter whether we have to use the previous noble gas in brackets to shorten the e- configuration representation of an element X or if we could use any element prior to that element X? Thanks :)
Does it matter whether we have to use the previous noble gas in brackets to shorten the e- configuration representation of an element X or if we could use any element prior to that element X? Thanks :)
- Fri Oct 07, 2016 1:19 pm
- Forum: Properties of Electrons
- Topic: Chapter 1 HW Question 15 [ENDORSED]
- Replies: 1
- Views: 542
Re: Chapter 1 HW Question 15 [ENDORSED]
Oh that's because n2^2 is in the denominator and ~0.112=1/9. So basically 1/n2^2=1/9 basically means n2^2=9 and n2=sqrt(9)=3 :)
- Fri Sep 30, 2016 2:25 pm
- Forum: Photoelectric Effect
- Topic: About photons.... [ENDORSED]
- Replies: 3
- Views: 1888
About photons.... [ENDORSED]
Can increasing the amount of photons emit an electron or must the photons themselves need more energy to eject an electron? Thank you :)