# Tag Info

21

Long story short, no, they don't. Charging a vessel to 1 MV is not a big deal, if you look at it from the inside. To put things into perspective, imagine a vessel of about 10 cm across, which is kinda OK for a flask. Imagine it spherical to make the calculations easier. Now, the capacitance of a sphere is $C=4\pi\varepsilon_0R$, which evaluates to 5.56 pF (...

12

The top of my list for exhibiting piezo activity and can be easily purchased and is also transparent.. Quartz That's about it. It's used everywhere - as an oscillator for quartz crystal watches, quartz crystal microbalances, etc. Most of the other piezoelectric options: Lead Zirconium Titanate (PZT) Barium Titanate ($\ce{BaTiO3}$) Zinc Oxide ($\ce{ZnO}$) ...

11

No: trying to catch up with 100+ years of technological optimizations in your kitchen won't be an economical enterprise. Store-brought batteries are standardized and relatively inexpensive. Power from an outlet is even less expensive (by one or two orders of magnitude). On the other hand, in many places you can save on electricity by going solar. Even if ...

10

The answer to this question hinges on two key questions: What kind of dust are we dealing with? How is the dust arranged (i.e. what is your experimental setup)? Which Dust? Firstly, I'm going to assume you meant domestic dust (since there are more kinds of dust than you'd imagine). I quote Wikipedia: Dust in homes, offices, and other human ...

8

The $\pu{3.6-3.8 V}$ range is a good general choice, but it may be battery-specific. The particular voltage for 40% charge may differ for different cell technologies, e.g. various deviations of electrode materials and due to cell aging. The optimal storage conditions, as you mentioned, are more often expressed as charge/capacity % ratio. Usually, the optimal ...

7

Batteries are constructed with an internal barrier between the two electrolytes that does not conduct electricity (i.e., electrons can't pass), but that does allow ions to pass through. See the figure below (taken from Wikimedia, open source), of a simple alkaline dry cell (e.g., an AA battery), in particular the part labeled "ION CONDUCTING SEPARATOR." ...

7

Historically, this sort of process has been done with the Fischer–Tropsch process. The core of this process is to use "syngas" (a mixture of $\ce{CO}$ and $\ce{H2}$) in the presence of a catalyst to make higher molecular weight hydrocarbons: $$\ce{(2n + 1) H2 + n CO → C_{n}H_{2+2n} + n H2O}$$ Under normal conditions, this will actually make mostly ...

7

In the lead battery it is very important that the electrodes transform into insoluble lead sulfate when discharged, especially at the cathode where lead(IV) oxide is turning into lead(II) sulfate. Consider the two half reactions of the lead-acid battery: $$\ce{Pb(s) + HSO4−(aq) → \color{red}{PbSO4(s)} + H+ (aq) + 2e−}$$ $$\ce{\color{red}{PbO2(s)} + HSO4−(aq)... 7 Yes. Another example is VO2. Over 67 °C its crystal structure changes to rutile with a band gap of ~0.1 eV. Dopants of other substances can reduce the temperature at which it becomes a conductor. 7 The short answer is: The ending stage uses much smaller charging current, so it lasts longer. TCharging of any cell in the contant voltage mode, not limited to lithium cells, leads to asymptotically decreasing of the charging current and progressively slowing down charging proces. The reason behind is the charging voltage must not cross the maximal allowed ... 6 It depends on what you are prepared to consider a gas and what you are prepared to consider room conditions. The gas inside all discharge lamps (fluorescent lamps and neon lamps in shop signs, for example) conducts electricity and the lamps work under normal room conditions. However, the gases are often at low pressure and are, strictly speaking, plasmas ... 6 I won't do any rib poking, but there is some flawed thinking here. Certainly not off topic though. Nomenclature: First, when you pass a current through water, you are not breaking the hydrogen bonds, which are intermolecular forces, but (a) breaking the bond between hydrogen and oxygen and (b) forming molecular oxygen and molecular hydrogen, \ce{2H2O ->... 6 ... are homemade batteries ... a practical alternative for powering your appliances ...? No, those type of batteries don't have enough energy to power more than a small light bulb or a transistor radio. If fact the light bulb probably won't stay lit for more than 10 minutes. An LED would be much better. You need at least 30 car batteries to power your home ... 6 Air at STP does conduct a tiny bit due to ionization by cosmic rays; this might even provide a path for lightning leaders. "Alex V. Gurevich of the Lebedev Physical Institute [et al] suggest that... cosmic ray... might provide a conductive path that initiates lightning." In addition, ionization-type smoke detectors use a little radioactive material (e.g. \... 6 The key here is the concept of metallic bonding. or, the sharing of electrons between metal atoms like those in a copper wire (a typical conductor). In this type of atomic bond, electrons no longer belong to one atom or another; they're shared equally amongst all atoms. As such, one electron truly does go bouncing around between the atoms in the direction ... 6 When a current is passed through an electrolyte, a chemical reaction takes place. This alters the composition of the solution over time and you won't actually be measuring the conductivity(or conductance) of the initial solution. Since in AC current, equal current flows in both directions over a given amount of time(larger enough than time period), reaction ... 5 The charge doesn't "move back through the battery" because in order to do that, it would have to pass directly through the chemical reactions that put it there in the first place. It moves through the external circuit, because that's the only path available to it. To take it to the next level of detail, the half-reactions that occur at the two plates inside ... 5 As the comment indicated, it is probably equilibrating. When you are discharging the battery, you are causing the materials in the electrodes and the electrolyte to rearrange. The surface of the electrodes are where the reactions are happening, so the products of the discharge reactions tend to accumulate at or near the surfaces of electrodes. This causes ... 5 You would've probably heard of the commonly given example, rubbing a glass rod with silk. The glass rod becomes positively charged, and the silk becomes negatively charged. But why? That's your question I believe, and for that we need to zoom in a little further, until we can see the molecular structure. Glass, is a polymer mainly composed of silicates. It ... 5 Yes, there are. Ionic conductivity greatly varies between compounds. For some of them is much higher then for others. They are called fast ion conductors, or superionic conductors. Well known example is silver iodide. While it may be called a "salt", it's probably more covalent then ionic, that is, before it's heated to 146 °C, when its structure changes ... 4 The pH should be around 8.4 and the conductivity in the range of 2.5 - 3 mS/cm. The lower value is appropriate for freshly prepared water. The conductivity is used for the determination of TDS (total dissolved particles). 4 In part, there is no abrupt cutoff because the gradient of the field is not spread evenly across the electrolyte: the gradient is steep at the interface between electrodes and the electrolyte, where gas evolution actually takes place, not in the body of the electrolyte. Note where bubbles arise in this video. However, if the conductivity of the electrolyte ... 4 The gas inside discharge neon lamp is not really hot. Also, think of St. Elmo's fires - these definitely do appear at ambient pressure and are "cold", i.e., normally they would not burn anything. But there is a catch: here we are looking at strongly non-equilibrium situations, caused by strong electric fields. As for the gases which would behave like that ... 4 By not removing every last trace of copper from the sanded-side of the pennies, I created a kind of short-circuit that discouraged the charges from moving through the stack of pennies. This is the main problem. Until all of the copper is gone from the zinc side of each penny, there is little reason for the two halves of the electrochemical reaction ... 4 doesn't explain why electrons in the conduction band are able to conduct electricity while electrons in the valence band can't Electrons in the valence band can conduct electricity, as long as the valence band is not completely filled. This occurs in semiconductors, when you thermally promote electrons from the valence to the conduction band, you are ... 4 The cathode ray tube doesn't conduct electricity per se. It liberates free electrons that are simply moving through a vacuum from one end to the other. In practice, you can't create a real vacuum, so a low pressure gas (as low as possible) is used instead. Air has a high enough dielectric strength that it will dampen the effect of the applied voltage. That ... 4 According to this Wikipedia article: Dielectric-barrier discharge (DBD) is the electrical discharge between two electrodes separated by an insulating dielectric barrier. Originally called silent (inaudible) discharge and also known as ozone production discharge or partial discharge, it was first reported by Ernst Werner von Siemens in 1857. On right, ... 4 My book has a few metals/alloys listed in a Seebeck Thermoelectric Series: Antimony, Nichrome, Iron, Zinc, Copper, Gold, Silver, Lead, Aluminum, Mercury, Platinum-Rhodium, Platinum, Nickel, Constantan, Bismuth There's also the Seebeck formula for emf of a thermocouple:$$E_{\text{AB}} = a_{\text{AB}}\theta + \frac{1}{2}b_{\text{AB}}{\theta}^2 Here, \$...

4

The ions in the salt bridge never leave the salt bridge. That's not true. The ions literally have to move to balance the charge of the gain / loss of the electrons at the electrodes. (You even allude to this in your question.) One of the ways that a battery can run out is that the bridge is used up. You could views this by using a deeply colored ions (e....

4

The acceleration of the freshly generated ions is stepwise (similar to a linear particle accelerator), i.e. the beam of ions is guided an array of electrodes with a small opening in their centre, as schematically depicted below: (image source) Hence when ions approach the first accelerator electrode from the left hand side, their interaction with the ...

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