1. ### Engineering Deriving the Wassiljewa mixture model equation

Hello, I'm in the process of deriving the Wassiljewa mixture model equation for a binary solution. I have to find an expression gE which represents the excess g term which is added to gIS, the ideal solution, to predict the g for a real solution. I have gotten up to a point but now I'm stuck...
2. ### Thermodynamic meaning of molar Gibbs free energy

I know that when it is ΔG>0 , it means there is no spontaneity, when ΔG=0 there is equilibrium, and when ΔG<0, there is spontaneity. But what happens when this is in the context of partial molar properties, when G is molar? I suppose molar ΔG is referred to a solution. Right? In that case, is...
3. ### Solvation of Ionic compound in water

When you dissolve, for example, NaCl in water, then you get "NaCl in water" solution. Will the "NaCl in water " solution have different chemical properties from its constituents(NaCl and H2O)? i.e. is a "NaCl in water" solution a new compound with respect to NaCl or H2O ? And is the ion...
4. ### Chemistry What precipitates form by mixing 2 saturated solutions?

At first I thought it was C. A few sources agree with me. The book says D is correct. Here was my reasoning for C: With both salts having a formula of MX3, their [OH-]'s can be compared according to their Ksp values. Tl(OH)3 has a smaller Ksp, so it has a smaller [OH-] at saturation than...
5. ### I Is my solution to Buffon's needle OK?

Buffon's needle was presented as a problem in David Griffiths' "Introduction to Quantum Mechanics". In the book, a needle is of length l is dropped randomly on a sheet of ruled paper with the lines of the paper also a distance l apart. It is required to find the probability of the needle...
6. ### A way to separate the components of a solution?

Hi all, A solution contains ions, positive and negative ones (i.e k+ cl-). Is there a simple but passive way (without adding any kind of energy) to separate by exemple the potassium ions from the solution? (IMHO, I do not think so)
7. ### Understanding solutions of Dirac equation

some notes: There was actually no proof given why ##u^s(p)## or ##v^s(p)## should solve the Dirac equation, only a statement that one could prove it using the identity $$(\sigma\cdot p)(\bar\sigma\cdot p)=p^2=m^2.$$ We were using the Wely-representation of the ##\gamma##-matrices, if this should...
8. ### Calculating field transformation

Homework Statement Let ##\psi(x)=u(p)e^{-ipx}##, where $$u((m,0)) = \sqrt{m}\begin{pmatrix} \xi\\\xi \end{pmatrix}\quad\text{where}\quad \xi = \sum_{s\in \{+,-\}}c_s\xi^s\quad \text{and}\quad \xi^+\equiv\begin{pmatrix} 1\\ 0 \end{pmatrix}\quad \xi^-\equiv\begin{pmatrix} 0\\ 1 \end{pmatrix},$$...
9. ### A Confusing eigensolutions of a wave function

Consider a potential cavity $$V(r)=\begin{cases}\infty, &x\in(-\infty,0]\\\frac{\hslash^2}{m}\Omega\delta(x-a), &x\in(0,\infty)\end{cases}$$ The eigenfunction of the wave function in this field suffices $$-\frac{\hslash^2}{2m}\frac{d^2\psi}{dx^2}+\frac{\hslash^2}{m}\Omega\delta(x-a)\psi=E\psi$$...
10. ### Determining if the pH changes when a chemical is added

Homework Statement The question asks, how many of the following statements is/ are correct. I want to know which ones are right (I don't know the answer, but I will give a guess). BaCl2 added to an HCL solution does not change the pH NaBr added to an HBr solution will raise the pH. NaC2H3O2...
11. ### A Solution?: Quintic Equation from Physical System

First time in this forum, so greetings to everyone! I am currently working with some physical models in the field of natural ventilation and I came across the following 5th order polynomial equation (quintic function): $X^{5}+ C X - C =0$ This is the steady state solution of a physical system...
12. ### Timoshenko, Strength of materials example solution

Hi everyone, I am new here, so please be kind if I make mistakes on this forum, I will try to learn fast. I need help in explaining the solution of one of the examples from Timoshenko's Strength of Materials book. The solution is provided in the book, but I did not get it, no matter at which...
13. ### How does a pH probe work

Homework Statement How does a pH probe work? Homework Equations The Attempt at a Solution A combined pH probe is comprised of 2 electrodes a measuring and reference electrode. The measuring electrode is composed of glass with a silver alloy electrical wire submerged into a neutral KCl...
14. ### Which of the following combinations would act as buffered solutions

Homework Statement Which of the following combinations would act as buffered solutions? a. HCl and NaCl b. CH_3COOH and KCH_3COO c. H_2S and NaHS d. H_2S and Na_2S Homework Equations none really... The acid needs to be weak and the base strong though. The Attempt at a Solution HCl is one...
15. ### I How to identify admissible functions in QM by simple math?

Hi, in QM literature the inadmissible solutions to the Schrödinger eqn are often , if not always, quoted in the text as "inadmissible", because they are discontinuous, not-single valued, not square integrable and not infinitely differentiable. However in a discussion with Dr Du yesterday...
16. ### A Non-selfadjointness and solutions

Hi, I have the two operators: $$Q = i\hbar \frac{d}{dx} - \gamma$$ $$Q' = -i\hbar \frac{d}{dx} - \gamma$$ where ##\gamma## is a constant. Both of these are not self-adjoint, as they do not follow the condition: ...
17. ### Why is one a buffer solution but not the other?

Homework Statement A student prepares two solutions: Solution A is prepared by mixing 50cm3 of 0.100mol dm-3 CH3COOH(aq) with 25cm3 of 0.100mol dm-3 NaOH(aq) Solution B is prepared by mixing 25cm3 of 0.200mol dm-3 CH3COOH(aq) with 50cm3 of 0.100mol dm-3 NaOH(aq) Explain why solution A is a...
18. ### Chemical Polymer Separation (PLA, ABS, HIPS, and PETG)

Good day all! I've got a granular mixture of PLA, ABS, HIPS, and PETG with a particle size of about a quarter inch, and I'm trying to isolate each polymer from the mix. PLA and PETG have densities of about 1.27g/ml, and ABS and HIPS have densities of around 1.06g/ml. I think a weighted solution...
19. ### Does anyone know of a thermally-stable endothermic reaction?

Hello all, I've used physicsforums a few times over the years, but I believe this is my first post. I'm working on an engineering project in which I need to find a highly-endothermic reaction where the reactants and products will be stable at very high temperatures (well over 800C), or at least...
20. ### Green's functions: Logic behind this step

Homework Statement Hi all, I came across these steps in my notes, relating to a step whereby, $$\hat{G} (k, t - t') = \int_{-\infty}^{\infty} e^{-ik(x - x')}G(x-x' , t-t')dx$$ and performing the following operation on ##\hat{G}## gives the following expression, [\frac{\partial}{\partial t}...
21. ### Precipitation of colloidal solutions

Hello, I read about the colloidal solutions in my chemistry book, and came across this sentence: "Emulsoids (a type of colloidal solutions) are difficult to be precipitated, e.g. by concentrated solution of NaCl (removes H2O film by its osmotic power then it neutralize the charges)." I don't...
22. T

### Trouble finding where I went wrong calculating concentration

In our laboratory class we were required to calculate the stock (mM) and final (µM) concentrations for Glycerol. The tutor said my final calculations were incorrect and that I had made an error. He didn't have enough time show me where I went wrong. I have compared my results with another...
23. ### B Peeking at the answer of an unsolved problem.

Should peeking at the answer of an unsolved problem be avoided at any cost? I'm self studying at the moment and have a document with the solutions. It doesn't happen frequently, but I have had to peek at answers a couple of times. I really hate doing it though. Thoughts?
24. ### Need an explanation -- Consider pure water separated from...

Consider pure water separated from an aqueous starch solution by a semipermeable membrane, which allows water to pass freely but not starch. After some time has elapsed, the concentration of starch solution a. will have increased b. will have decreased c. will not have changed d. might have...
25. ### Vectors Homework

Homework Statement You go to an amusement park with your friend Betty, who wants to ride the 90-m-diameter Ferris wheel. She starts the ride at the lowest point of a wheel that, as you face it, rotates counterclockwise. What is the magnitude of her displacement vector when the wheel has...
26. ### Question on showing general formula of solution

Homework Statement show that the general solution of the differential equation d^2/dt^2 + 2 *alpha * dr/dt + omega^2 * r = 0, where alpha and w are constant and R is a function of time "t" is R = e^(-alpha * t) * [ C1*sin( sqrt(omega^2 - alpha^2) * t) + C2*cos( sqrt(omega^2 - alpha^2) * t)...
27. ### Ansys Solution as Input Geometry

So I have a rectangular section as my geometry that needs to be formed in three stages. So after 1st operation I want to take that deformed shape and perform another operation (all analysis use Explicit Dynamics). Is this possible in ANSYS? Thanks in advance
28. ### Fourier transform of the Helmholtz equation

Hi guys, I have been trying to solve the Helmholtz equation with no luck at all; I'm following the procedure found in "Engineering Optics with MATLAB" by Poon and Kim, it goes something like this: Homework Statement Homework Equations Let's start with Helmholtz eq. for the complex amplitude ##...
29. ### Mechanics of materials torsion doubt

Good evening. I've got stuck in this question from my book of Mechanics of Materials by Beer and Johnston about torsion. The allowable shearing stress is 15 ksi in the 1.5-in.-diameter steel rod AB and 8 ksi in the 1.8-in.-diameter brass rod BC. Neglecting the effect of stress concentrations...
30. ### Discover the form of real solution set

Homework Statement ##|4^{3x}-2^{4x+2}*3^{x+1}+20*12^x*3^x| > 8*6^x(8^{x-1}+6^x)## For some numbers ##a, b, c, d## such that ##-\infty < a <b < c <d < +\infty ## the real solution set to the given inequality is of the form ##(-\infty, a] \cup [b, c] \cup [d, +\infty)## Prove it by arriving at...