Thought experiment

List similarities and differences in the design of selective supramolecular hosts for anions and cations. What are the key considerations in each case Build on these ideas by suggesting reasons why the supramolecular chemistry of anions has developed more slowly than that of cations. 

The values for H3PO4 are 2.1,6.2 and 12.4. From your reading of this chapter, or otherwise, suggest possible hosts types that may be selective for the anions H2P04, HP04 and P04. What might be key considerations in the host design process  

Simmons, H. E., Macrobicyclic amines. 3. Encapsulation of halide ions by in,in-l,(K+2)-diazabicyclo K.L.M alkane-ammonium ions. J. Am. Chem. Soc. 1968, 90, 2431-2432. 

Schmidtchen, F. R, Berger, M., Artificial organic host molecules for anions. Chem. Rev. 1997, 97, 1609—1646. 

Shannon, R. D., Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides. 

---

Simulations act as a bridge in another sense between theory and experiment (see figure B3.3.2. We can test a theory using idealized models, conduct thought experiments , and clarify what we measure in the laboratory. We may also carry out simulations on the computer tliat are difficult or impossible in the laboratory (for example, working at extremes of temperature or pressure). 

From the previous thought experiment it is natural to suppose that if reaction temperature increases, the heat transfer rate should increase more than the heat generation rate. This is expressed mathematically as ... 

An even deeper dilemma confronts an honest physicist when trying to understand what really happens during a quantum measurement. Despite using (macroscopically) intuitive descriptions of the quantum-entangled objects, what really happens remains a deep mystery. Or, consider the following simple thought experiment using CA. 

An Educational Thought Experiment on Working Memory and Chemical Symbolism... 

What is the relatiorrship between the way stndents nse the three levels of representation and their capability to test their models As testing models (from thought experiments and/or empirical ways) is an essential stage of the modelling process, their expertise in dealing with the three levels of representation seems to be vital for their learning in modelling-based corrtexts. 

The Flory distribution gives a polydispersity of 2 in the limit of high conversion. Yet, a thought experiment suggests that a small batch of self-condensing molecules would eventually condense to form a single, cyclic molecule. Reconcile this apparent inconsistency. 

Experimentally undefined parameters, which have a real physical meaning that is, they reflect an actual physical phenomenon but cannot be determined from the experimental data (even a thought experiment to measure them cannot be conceived) or by a thermodynamic calculation. In isolated cases such parameters can be calculated on the basis of nonthermodynamic models. The equations used for calculations generally contain sums, differences, or other combinations of such parameters that are measurable. The Galvani potential at the interface between two dissimilar conducting phases is an example. 

Nurse Let s do a thought experiment. Let s give them so much nutrition and energy source that it is coming out of their ears, what is then limiting growth ... 

In friability tests the material s susceptibility to attrition is evaluated. But it is not as simple as it may seem at first to select the suitable test procedure. In this context Pell (1990) gave a simple thought experiment to illustrate the difficulties If we took a batch of rubber stoppers and a batch of diamonds, and rubbed them on abrasive paper, we would conclude that the diamonds were more attrition resistant. If we instead struck the particles with a hammer we would conclude that the rubber were more attrition resistant. So, different test methods can rank materials differently with respect to their attritability. This effect was for example observed by Knight and Bridgwater (1985). They subjected spray-dried powders to a compression test, a shear test and a test in a spiral classifier. They found that each test gave a different ranking of the materials. Obviously, there is no... 

That is certainly one solution. To measure for many short time intervals and average together the readings certainly is, in principle, another solution, but one that we cannot find a justification for. Perhaps some of our readers knows of, or can do a thought experiment to come up with a scenario that would require many separate short data collection sessions that would provide data that could be averaged as we describe, but does not allow for a single protracted measurement. 

Considering this thought-experiment from the point of view of thermodynamics, the additional particles add enthalpy,... 

Before we start, we perform a thought experiment and, for convenience, we will consider making 1 mol of sodium chloride at 25 °C. There are two possible ways to generate 1 mol of gaseous Na+ and Cl- ions we could start with 1 mol of solid NaCl and vaporize it the energy needed is A//. j ul cci. Alternatively, we could start with 1 mol of sodium chloride and convert it back to the elements (1 mol of metallic sodium and 0.5 mol of elemental chlorine gas (for which the energy is — A H ) and, then vaporize the elements one at a time, and ionize each in the gas phase. The energies needed to effect ionization are I for the sodium and (ea) for the chlorine. 

The two atoms of X are brought yet closer in our thought experiment, causing the energy to decrease until a minimum is reached. 

But why do we heat the mixture to effect reaction We will perform a thought experiment imagine immersing iron into nitrogen at different temperatures. We will see the effects of the relative differences between physisorption and chemisorption. 

In our thought experiment we can force fluid to flow through this die at a certain volume per unit time or volumetric flow rate Q and allow no drag with the walls. This is a total slip condition so no shear will be applied to the fluid. The fluid will travel faster as the geometry contracts so the velocity V(l) in a plane across the geometry simply depends upon the area at any length / ... 

The drab outlook of Hume s thought experiment is obviously contradicted by the many instances of cooperation found in human and animal societies. In fact, we stopped too soon with our quote of Hume. It is not true, he argues, that I shou d in vain depend upon your gratitude . In fact, I can depend on it because I can depend on your needing my services for the next harvest, or, in Hume s words, because I foresee that you will return my service, in expectation of another of the same kind . But foresight is not actually needed and neither is the teaching of moralists or politicians which Hume seems to believe essential. All that is needed is the next harvest. 

Einstein refused to accept the idea of such randomness in nature. Gott wurfelt nichf ( God doesn t play dice ), he insisted more than once. So he invented a series of thought experiments in an attempt to show that quantum mechanics was an inconsistent theory. (A thought experiment is an experiment that cannot actually be performed, but which nevertheless can be used to elucidate some fundamental principle.)... 

In this thought experiment we inject a perfectly sharp pulse 5(0) whose total amount is unity. This pulse is a Dirac delta function defined as a rectangle centered about time zero with a height 1/s and a width f in the limit e 00 so that the area of the function remains unity as the height goes to infinity. 

There are technical challenges still to be overcome before every thought experiment in this brave new realm of molecular science can be realized in practice, but there is good reason for optimism. While simple gas-phase reactions of comparatively small molecules will continue to attract serious attention, the forefronts of femtochemistry today encompass far wider perspectives. 

We have now done enough thought experiments to determine the Stokes parameters I, Q,U,V ... 

It is common practice, in VSEPR thought experiments in which electrons are unpaired and/or excited to higher energy orbitals, to reverse electron spins. Spin reversal is a forbidden transition in spectroscopy, but is of no consequence in electron pair construction in valence shells. 

Q Use the description of the operation of VSEPR theory given above for NOz to draw the thought experiment box diagram which outlines the logic necessary for deciding its structure. 

Q Draw the box diagrams associated with the thought experiment which describes the VSEPR approach to the determination of the methane structure. 

---