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ScienceNet - Physical Sciences - Physical/ Theoretical Chemistry

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ScienceNet is a World Wide Web resource database in Science. It is a community service project by Science Centre Singapore, supported by Nanyang Technological University and National University of Singapore.

We offer free electronic access to various topics in Science and Technology. Feel free to browse through our database and see if we have the answers to your questions.

Physical Sciences - Physical/ Theoretical Chemistry
Q20087 :	Do you know why is it that equilibrium constant, K_eq, only changes when temperature is changed but remains constant even when pressure and concentration of reactants and products are changed? Why is there such a difference when all these conditions are basically obeying the Le Chatelier's principle?
Q20023 :	Why is an acid electrolyte preferred over an alkaline one in the fuel cell?
Q19894 :	The absorbance spectra of oxy- and deoxyhaemoglobin seem different. Why is that so? What causes the difference in the spectra? Is it the changes in the conformation of the haemoglobin that causes the slight differences in the spectra?
Q19706 :	Why does the solubility of oxygen decrease when the salinity of the water increases?
Q19656 :	Diamond will turn into graphite over the time extremely slowly, as it is thermodynamically unstable. Why is this so?
Q19594 :	Why, and how are the particles moving in matter?
Q19580 :	Will evaporation of water occur if the surrounding temperature is lower than the temperature of water and why?
Q19512 :	If a balloon is stuff inside a bottle and the opening of the bottle is completely covered (which means that no air is allowed to escape), if we pump the balloon with air, will the whole inflated balloon stick onto the inner surface of the bottle or will there be some space left in between the balloon and the bottle? Thanks!
Q19463 :	Why do hydrophobic solutes dissolve in a hydrophobic solvent if both are non-polar as well as uncharged?
Q19404 :	Why does impure substance always have a lower melting point than pure substance?
Q19394 :	Impurities make ice's freezing point lower but I was just wondering what properties of citric acid makes ice melt faster?
Q19192 :	How much water is loss through evaporation in a typical 50m x 25m swimming pool in Singapore?
Q19098 :	What is the meaning of "net movement" in osmosis? Thank you.
Q19058 :	What is fractional distillation? In fractional distillation does the mixture of liquids evaporate together or the components evaporate individually? For example: does a mixture of alcohol and water start evaporating together at the temperature of alcohol or do they start to form distillate at their individual temperatures?
Q18843 :	Will water boil in a container at a higher temperature with lid on than with the lid off? Why is that so? Thanks.
Q18842 :	When a heated moth ball is left to cool in a room, will its temperature go below room temperature?
Q18839 :	Is it true that water molecule loses electrons during condensation?
Q18755 :	What is Donnan equilibrium?
Q18005 :	What happens in the space above the soft drink in a closed bottle or can as the soft drink warms to room temperature?
Q15216 :	What is "entropy"?
Q15208 :	What are the properties of permanent molecular dipoles, van der Waals' forces, and hydrogen bonds?
Q14902 :	I understand that the components in air such as nitrogen and oxygen are separated using the method of fractional distillation of liquid air. How is this achieved? How exactly is gaseous air converted into liquid air for this method of fractional distillation?
Q14596 :	When you get higher in the altitude does the point at which water boils change?
Q12732 :	When plane-polarised light of different wavelengths is individuially passed through an optically active solution, the angle through which the light is rotated changes with wavelength. Why is this so? Does it have something to do with the phase difference of the photons?
Q12601 :	Assuming a complete mix model, how long on average does a drop of water spend in the ocean?
Q11548 :	I understand that if light is passed through a sugar solution it becomes polarised. Why does this happen and can other materials have this effect?
Q11033 :	What is chemical kinetics and where is it used for?
Q10733 :	I am searching for portable seawater desalination systems that could be used on small boats or for other outdoor activities. Almost all I can find are huge desalination plants, mostly working with reverse osmose systems. Please tell me if there exists anything like a small portable desalination system or if not, do you think it would be useful and possible (technically) to create one?
Q10201 :	What are fuel cells? How do they work?
Q10126 :	How does temperature affect rate of reaction? Please tell me the detailed theory about it.
Q9965 :	How does corrosion occur? What is cathodic inhibition?
Q9694 :	How do osmosis and diffusion differ?
Q9468 :	Why would adding salt to cold water cool it even further?
Q9277 :	How would the rate of fermentation of different sugars differ? Would it depend on how easily the sugar is broken down?
Q7528 :	What are the actual physics behind optical isomers? I would like to know more than the fact they have an asymmetric centre. Why/how do they rotate polarised light? I have search a fair bit on the Net and not found a sufficient answer. Please feel free to get detailed or provide technical links, assume second year chemistry/physics knowledge or higher. Thanks.
Q7525 :	Does osmosis refer to only water molecules moving from a region of high concentration to a region of lower concentration thru a semi-permeable membrane?
Q7081 :	Why does ice melt faster in water than it does in air?
Q6687 :	What purpose does vinegar serve in dyeing Easter eggs?
Q6398 :	Do oxygen dissolve better in hot or cold water?
Q6346 :	My son's teacher told him that certain fruits (and veggies) conduct electricity. We did an experiment with a 6-volt battery, a 6-volt light bulb. At first we connected the positive and negative wires to a graphic rod to make sure that the light bulb would come on. But when we connect to any fruit, the light bulb does not come on. His teacher says that certain fruits should make the light bulb come on. Any idea?
Q6337 :	What are the definitions and examples of a solution, a suspension and a colloid?
Q6306 :	What would happen to the saturated solution of sugar (sucrose) and water if its temperature were to drop? Specifically, what would happen to sugar in this solution?
Q6173 :	Is there pH = -1 or pH = 15?
Q5894 :	Are all liquids wet? What are the examples for liquids that are not wet?
Q5855 :	What valuable crystal is form when carbon is subjected to great heat and pressure?
Q5742 :	How does melting point relate to pressure?
Q5497 :	What is the effect of soap on surface tension?
Q5469 :	When a drop of water is introduced to hot oil, why does it cause a small explosion?
Q5202 :	One of my chemistry teachers mentioned some very unusual properties of helium when it is a liquid, like with magnetic fields you can make it flow out of a beaker. Is this true, and how is this possible? Does liquid helium have any other strange properties?
Q5160 :	Is the anode an electron provider or an electron acceptor? When taking about batteries, sites refer to the anode as the source, whereas many of my textbooks state the anode as positive. Also, is an anode positive or negative? As it seems to be named oppositely to the terminals.
Q5136 :	How does a car battery work?
Q5084 :	What is hydrolysis and how exactly does it work? Any experiment?
Q4807 :	What makes one type of battery (e.g. alkaline) last longer than another type?
Q4727 :	Is it possible to increase the surface tension of water with an additive?
Q4599 :	Can the life span of a soap bubble be extended in different temperatures and atmospheric conditions?
Q4590 :	Why are the air bubbles in the water spherical?
Q4269 :	What is actually happening when an electron gets excited and jumps to a different energy level? How does this relate to making a molecule?
Q3952 :	How do rechargeable batteries work?
Q3902 :	What exactly is the relationship between Avogadro's constant (6.02 x 10²³) and Avogadro's Law?
Q3890 :	What is a wet cell exactly? What could be a possible house-hold item that would be an electrolyte?
Q3830 :	Why do impurities decrease the melting point and freezing point and increase the boiling point?
Q3091 :	How do fuel cells work? Is it possible to make a simple hydrogen-oxygen fuel cell?
Q3019 :	What is distillation and fractional distillation?
Q3001 :	Why is it that the melting point of ice and the freezing point of water are the same?
Q2736 :	Can you describe how the process of water desalination works?
Q2545 :	Is a car battery considered a wet-cell?
Q2487 :	Is it true that diamond has a high melting point? However, it is said that diamond is thermodynamically unstable. Please elaborate.
Q2480 :	How many types of chemical bonds are there? How are they classified?
Q2345 :	How does a chemical cell produce a voltage difference between its terminals?
Q2140 :	I heard that in the process of metal plating, a god electrolyte is extremely important. Why is it so? In addition, what are some examples of a good electrolyte?
Q2090 :	Why do all solutions (the ones which I have tested) not flow faster than water? And if there are any aqueous solutions which flow faster than water, what are they.
Q2087 :	Why is oil able to mix with water when a little liquid soap is added?
Q1393 :	I'm a Sec.3 pure science student. I would like to know why is it that when we exert some pressure on ice it will melt. And why is it that when there's no more pressure, the ice freeze back again. Another question is that, why is it the melting point of water will decrease when impurities is added to the water?
Q967 :	Is nichrome a solution? If yes, what are the solvent and solute?
Q814 :	What is the ratio of spaces between molecules of solids, liquids and gases?
Q696 :	What is reverse osmosis?
Q689 :	Why do alkyl halides exhibit optical isomerism? How did van't Hoff and Le Bel explain optical activity?
Q578 :	Our chemistry teachers would like to know how Avogadro's number was experimentally determined. They would like to know also how the volume of 22.4 litres for the molar volume of gases at standard temperature and pressure (STP) was experimentally determined.
Q36 :	How do scientists count the atoms or molecules in an object since they are so small and so many?
Q35 :	How are atoms formed? What is the record of the first person who found out atoms? How are electrons, protons formed? Where do they come from?

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